天然气发动机尾气排放

Equivalent combustion natural gas engines typically utilize exhaust gas recirculation (EGR) systems to tackle their high thermal burden and NOx emissions. Variable nozzle turbochargers (VNT) can increase the engine intake and EGR rate simultaneously, resulting in NOx reduction while ensuring robust power performance. Using a VNT along with engine bench testing, the impact of VNT- and EGR-coordinated control on the performance and emissions of equivalent combustion natural gas engines was investigated under different operating conditions. Subsequently, multi-objective optimization was performed using a support vector machine. The results demonstrated that the use of VNTs in equivalent combustion natural gas engines could bolster the capacity to introduce EGR under several operative conditions and extend the scope of EGR regulation, thereby decreasing the engine’s thermal burden, improving fuel efficiency, and curbing emissions. Owing to the implementation of a multi-objective optimization method based on a support vector regression model and NSGA-II genetic algorithm, VNT and EGR control parameters could be optimized to slightly improve the economy and significantly reduce NOx emissions while maintaining the original engine power performance. At 20 operating points optimized for validation, brake-specific fuel consumption (BSFC) and NOx decreased by 0.94% and 47.0%, respectively, and CH4 increased by 3.7%, on average.

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The air-fuel mixture preparation in pilot spray-ignited natural gas engines is primarily dominated by piston bowl profiles and fuel injection strategy. Piston bowl geometry is regarded as the crucial point in controlling engine pollutant emissions. In the present work, the SAGE combustion model was applied coupled with a general reaction kinetic mechanism. The engine model was validated with experimental data achieved from a Cummins ISX 400 engine, and good agreement between predicted and measured in-cylinder pressure and heat release rate was obtained. The influence of various piston bowl designs, including Mexican-hat geometry, double-lip geometry, bow geometry, and toroidal geometry, on the combustion process, engine performance, and pollutant emissions of a high-pressure direct-injection natural gas engine have been studied and analyzed numerically. The present study confirms the benefit of the piston bowl design as a beneficial tool to enhance the performance and pollutant emissions of the pilot diesel-ignited natural gas engine. Results showed that different chamber shapes slightly influence the combustion initiation, and the difference in in-cylinder pressure presents noticeable as the combustion continues. A higher turbulent kinetic energy improves the flow movement and facilitates the mixture formation in the cylinder. However, the combustion behavior is unwished caused by the improper injection angle of natural gas. Increasing the recess depth of combustion chambers reduces NOx formations at the price of sacrificing fuel economy. For the bow combustion chamber design, the NOx emission declined by 31.1%, while the indicated specific fuel consumption increased by 5.5% compared with the original engine. Although the indicated mean effective pressure and specific fuel consumption of the optimal double-lip geometry almost remain the same, NOx emissions can be reduced by 16.7% compared with the base design.

ABSTRACT The dwindling reserves of conventional fuels have spurred research into alternative options for diesel engine, particularly given diesel’s widespread use in global public transportation. Environmental concerns, notably regarding oxide of nitrogen (NOx), and smoke necessitate a shift toward alternative fuels. Diesel’s partial replacement with compressed natural gas in CI engines has shown promise in mitigating smoke and NOx emissions. The Present research utilized an RCCI engine, and employed combinations of Diesel+CNG dual-fuel to analyze how direct injection techniques affect performance, emission, and combustion features. Under full load conditions sans exhaust gas recirculation (EGR) 6 ms and 8 ms CNG yielded superior brake thermal efficiency (BTE) of 30.5% and 29.5% surpassing diesel’s 26%, although excessive CNG induction disrupted combustion, reducing efficiency, and introducing EGR, particularly at 10% enhanced BTE, with 6 ms CNG achieving a peak of 32.5%, slightly lower at 15% EGR with 30.9%. Diesel engine showcased diminishing brake-specific fuel consumption values with CNG supplementation, further mitigated by increased CNG concentrations and EGR rates. Peak combustion pressure decreased in the RCCI engine, with promising results seen at 6 ms CNG, comparable to pure diesel. EGR introduced pressure fluctuations, signifying a dilution effect on combustion, while the net heat release rate displayed increasing trends for CNG, stabilizing with EGR. NOx emissions, peaking in diesel engine, showed reductions with 6 ms CNG, further diminished with EGR implementation.

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The research objectives of pilot diesel injection (PDI) ignition natural gas technology include high efficiency, clean combustion, and low pilot diesel mass. This study is based on a single-cylinder thermodynamic engine, combined with the CONVERGE simulation model and CHEMKIN chemical reaction kinetics model. The effects and mechanisms of various PDI strategies on the mixture equivalent ratio, temperature, and characteristics of combustion and emissions were investigated. The experimental results showed that the best PDI mass was 8 mg/cycle. The thermal atmosphere and activity in the cylinder were improved with an increase in PDI mass from 2 to 8 mg/cycle, which stabilized the mixture combustion. Further, the effects of different pilot injection timing (PIT) on combustion and emissions were investigated via experiments and simulation by controlling the operating conditions and maintaining a constant PDI total mass. The results show that the diesel had a single low-temperature reaction path when the PIT was close to the top dead center, whereas the PIT at the early stage of the compression stroke (CS) changed the chemical reaction path and accelerated the transformation of CH3 to CH2O, accumulating numerous active groups and accelerating the combustion rate, which is difficult to control the ignition phase. The reaction path of the double PDI strategy was similar to that of the PIT at the early CS stage, and its combustion is closed to premixed combustion; however, the accumulation of active groups was relatively small, and the combustion rate was relatively slow because the ignition phase was controlled by the second PDI, making the combustion phase easy to control. Finally, with the double PDI strategy that had the advantages of efficient combustion and avoidance of knock, the gross indicated thermal efficiency reached 49.3% that involved a −60°crank angle (CA) after top dead center (ATDC) first injection and −4°CA ATDC second injection.

The combustion and emission characteristics as well as the economic performance of partial oxidation fuel reforming (POFR) natural gas engines were investigated by adjusting the fuel reforming ratios and the engine load. The performance of the POFR engine with a 12% fuel reforming ratio was compared with that of the original engine. The results showed that the fuel-partial-reforming was effective in reducing the cycle-to-cycle variations over the whole range of the operating conditions. The THC and NOX emissions decreased at almost all operating conditions, but showed different decreasing trends at different loads and equivalence ratios, while the CO emissions increased at all operating conditions. It was found that reducing the advancement of ignition timing of the POFR-engine can further reduce the gaseous pollutant emissions without reducing the economic performance of the engine. In conclusion, blending reforming gas improved the overall performance of the natural gas engine at low to medium load conditions.

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This study investigated engine efficiency and emissions at low load dual-fuel diesel-natural gas (NG) engine operation, which has a higher sensitivity to NG composition. 40% of the diesel fuel energy was partially substituted with gas blends containing methane, ethane, and propane. NG was delivered inside the intake manifold by low-pressure gas injectors. Results showed that blends with ethane and propane reduced the net global warming potential by ∼5% compared to pure methane, at constant fuel energy content, with the reduction primarily linked to differences in exhaust hydrocarbon composition. No statistically significant impact on the brake mean effective pressure was found. The changes in gas composition created up to a 10% increase in carbon monoxide concentrations in the exhaust, as an earlier combustion phasing increased the fraction of premixed NG trapped in the combustion chamber’s crevices. Also, a 20% reduction in specific methane, ethane, and propane emissions was achieved for mixtures with 10% propane addition. Propane addition enhanced combustion efficiency and methane oxidation compared to ethane addition. The reduction of methane, ethane, and propane mass fraction in the exhaust correlated with their auto-ignition temperatures and laminar flame speeds, with ethane and propane oxidizing significantly better than methane. Finally, the results imply the emission composition of diesel-NG dual-fuel operation was more sensitive than engine power output to the change in NG fuel composition.

A reduced chemical kinetic mechanism was coupled with computational fluid dynamics (CFD) model to explore the detailed influencing mechanism of swirl ratios and piston shapes on a micro diesel pilot...

This paper involved conducting an experimental investigation on the effects of exhaust gas recirculation (EGR) and spark timing on the combustion, performance, and emission characteristics of a China-VI heavy-duty, natural gas engine fueled with high-methane content. The results showed that increasing the EGR rate extends the spark timing range and slows the combustion. This then increases ignition delay, prolongs combustion duration, and decreases heat release rate. Peak in-cylinder pressure (PCP) and indicated thermal efficiency (ITE) initially increase because of higher boost pressure with increasing EGR rate. However, as EGR rate increases further, PCP and ITE begin to decrease because of the deviation of combustion phasing. Lower in-cylinder temperature caused by higher EGR rate may cause nitrogen oxide (NOx) emissions to reduce significantly, while total hydrocarbon (THC) and carbon monoxide (CO) emissions increase, and THC emissions could increase exponentially at high EGR rates. In-cylinder pressure, temperature, and heat release rate increase with early spark timing, but the rate of increase is reduced at higher engine speeds. Early spark timing causes THC and CO emissions to increase at part-load conditions, whereas there is little change at full-load conditions. NOx emissions also increase with early spark timing because of the higher in-cylinder temperature.

This study proposes an innovative Thermodynamic Activity Controlled Homogeneous Charge Compression Ignition (TAC-HCCI) strategy for diesel–natural gas dual-fuel engines, aiming to achieve high thermal efficiency while maintaining low emissions. By employing numerical simulation methods, the effects of the intake pressure, intake temperature, EGR rate, intake valve closing timing, diesel injection timing, diesel injection pressure, and diesel injection quantity on engine combustion, energy distribution, and emission characteristics were systematically investigated. Through a comprehensive analysis of optimized operating conditions, a high-efficiency and low-emission TAC-HCCI combustion technology for dual-fuel engines was developed. The core mechanism of TAC-HCCI combustion control was elucidated through an analysis of the equivalence ratio and temperature distribution of the in-cylinder mixture. The results indicate that under the constraints of PCP ≤ 30 ± 1 MPa and RI ≤ 5 ± 0.5 MW/m2, the TAC-HCCI technology achieves a gross indicated mean effective pressure (IMEPg) of 24.0 bar, a gross indicated thermal efficiency (ITEg) of up to 52.0%, and indicated specific NOx emissions (ISNOx) as low as 1.0 g/kW∙h. To achieve low combustion loss, reduced heat transfer loss, and high thermal efficiency, it is essential to ensure the complete combustion of the mixture while maintaining low combustion temperatures. Moreover, a reduced diesel injection quantity combined with a high injection pressure can effectively suppress NOx emissions.

Internal combustion engines (ICEs) face challenges in balancing efficiency and emissions. This study designed a non-crankshaft reciprocating engine (NCRE) using non-uniform rotational speed technology to optimize combustion and reduce emissions. The NCRE employs natural gas as the primary fuel, with gasoline ignition, to enhance combustion dynamics. A multi-disciplinary framework integrating non-uniform speed models, piston motion dynamics, and computational fluid dynamics (CFD) simulations was developed to analyze performance. The results show that compared with traditional engines, NCRE has improved by approximately 2% on the indicated thermal efficiency (ITE), and releases more energy, burns more thoroughly and more rapidly; nitrogen oxide emissions have been reduced, which is attributed to the improved turbulence and controlled piston movement. The design of NCRE introduces the method of non-uniform rotational speed into the engine, filling the gap caused by the piston movement in changing the airflow inside the cylinder, and providing a way to achieve an efficient and low-emission power system.

NOx is the main emission of lean burn natural gas engine (NGE). Water injection (WI) is an effective method to reduce NOx, which has been widely studied in conventional fuel engine. Currently, there are few researches on the application of WI in NGE. The influences of WI on NGE are not clear. In the paper, the effect mechanisms of WI on the emissions of NGE are studied. Based on the thermodynamic properties of water and the combustion mechanism of natural gas, the emissions generation mechanism of NGE with WI was analyzed. According to the experimental system, the effects of intake manifold water injection (IMWI) on the emissions of a lean burn NGE was carried out. The results show that, with WI, the in-cylinder temperature decreased greatly, which effectively inhibited the formation of thermal NO. Water generated a lot of OH groups, which effectively inhibited the formation of rapid NO. At 1800 rpm and 0.92g/s WI rate, NOx is reduced by 70.4%. OH group could effectively promote CO oxidize to CO2. At 1000 rpm and 0.92g/s WI rate, CO is decreased by 22.2%. However, since the decrease of the total activation energy of combustion reaction, the chain breaking reaction increased, resulting in a significant increase in HC. At 800rpm and 0.92g/s WI rate, HC was increased by 11.6%.

This study involved conducting an experimental and numerical investigation on the effects of the air-to-fuel ratio (AFR), engine speed, and engine load on the inlet gas component of a three-way catalyst (TWC) and on the effects of noble metal loading, noble metal ratio, and carrier pore density on the emission conversion efficiency. The results showed that AFR can significantly affect the raw emissions of NOx and THC, and better emission conversion efficiency of a TWC can be reached when AFR is controlled between 0.995 to 1. Compared with engine speed, engine load has a relatively small effect on exhaust temperature but greatly affects the flow velocity and NOx and THC emissions. Increasing the content of Pt in the catalyst can improve the THC conversion efficiency. For low Pt and Pd-Rh catalysts, the THC conversion effect is significantly deteriorated. The content of Rh affects the NOx conversion, and NOx conversion efficiency at high speeds is significantly reduced when Rh content is reduced. Higher carrier pore density can slightly improve the catalytic reaction rate and emission conversion efficiency at high engine speeds. However, high conversion efficiency can be maintained even after aging.

The approach for achieving efficient and clean combustion in a diesel–natural gas (NG) heavy-duty engine at low loads was studied by computational fluid dynamics simulation. This study proposed the concentration and temperature-stratified combustion technology and clarified its mechanism. The results revealed that different stratified combustions can be organized by controlling the pressures, timings, and durations of diesel and NG injections, and stratified combustion can be classified into moderate, lean, and rich stratified combustion modes. Efficient and clean combustion can be realized simultaneously at low engine loads: the gross indicated thermal efficiency (ITEg) of engine breakthrough was improved to 47.9%, and the indicated-specific emissions of unburned hydrocarbon (ISUHC) were greatly reduced to 1.6 g/kWh, while the indicated-specific emissions of nitrogen oxide (ISNOx) remained at 0.6 g/kWh. Moreover, the detailed analysis of three typical stratified combustion modes demonstrates that coupling control of the concentration and temperature of the charge is the key to obtaining excellent engine performance. Most of the NG-stratified mixture should burn in the react ratio range of 0.4 to 0.8 for low unburned hydrocarbon emissions, low nitrogen oxides emissions, and rapid combustion. The proper temperature stratification should ensure that a high-temperature charge is around the over-lean NG mixture. This study can provide the fundamentals of stratified combustion control and feasible solutions for commercial applications of NG engines.

The rising interest in the use of gaseous fuels, such as bio-methane and hydro-methane, in Heavy-Duty (HD) engines to reduce Greenhouse Gases pushed by the net-zero CO2 emissions roadmap, introduced the need for appropriate strategies in terms of fuel economy and emissions reduction. The present work hence aims at analysing the potential benefits derived from the application of the cylinder deactivation strategy on a six-cylinder HD Natural Gas Spark Ignition (SI) engine, typically employed in buses and trucks. The activity stems from an extensive experimental characterisation of the engine, which allowed for validating a related 1D model at several Steady-State conditions over the entire engine workplan and during dynamic phases, represented by the World Harmonized Transient Cycle (WHTC) homologation cycle. The validated model was exploited to assess the feasibility of the considered strategy, with specific attention to the engine working areas at partial load and monitoring the main performance parameters. Moreover, the introduction in the model of an additional pipeline and of valves actuated by a dedicated control logic, allowed for embedding the capability of using Exhaust Gas Recirculation (EGR). In the identified operating zones, the EGR strategy has shown significant benefits in terms of fuel consumption, with a reduction of up to 10%. Simultaneously, an appreciable increase in the exhaust gas temperature was detected, which may eventually contribute to enhance the Three-Way Catalyst (TWC) conversion efficiency. Considering that few efforts are to be found in the literature but for the application of the cylinder deactivation strategy to Light-Duty or conventionally fuelled vehicles, the present work lays the foundation for a possible application of such technology in Natural Gas Heavy-Duty engines, providing important insights to maximise the efficiency of the entire system.

As the emission regulations are getting more stringent, engine manufacturers are continuously improving engine performance and emissions along with exploring alternative fuel options. Diesel engines dominate the current on highway heavy duty engine market. Compared with diesel, natural gas engines have many advantages like near zero soot emissions, lower CO2 emissions, lower operating cost, quieter operation, and domestic natural gas availability. Natural engines can operate at stoichiometric air fuel ratio and allow for the use of cost effective three-way catalytic converter to achieve emission targets. Moreover, Renewable Natural Gas (RNG) is the only fuel in the market with carbon negative intensity. To improve the overall engine efficiency, new engine design integrates tumble combustion, dual overhead camshaft, variable valve train system, optimized fuel system, pulse Exhaust Gas Recirculation (EGR) system and optimized turbocharger. Integration and optimization of new technologies has improved the peak Brake Thermal Efficiency (BTE) by 12% above the current Cummins heavy-duty production engine. Average transient cycle BTE is improved by 16% on Ramped Mode Cycle Supplemental Emissions Test (RMCSET) and 17% on Federal Test Procedure (FTP) cycles. Optimized architecture has demonstrated system out emission capability of 0.02 g/hp-hr. on both the FTP and RMCSET cycles.

Emissions reductions are the primary driver for technological innovation in the gas compression industry with partial-fire and misfire events contributing significantly to the total output of hydrocarbons. A single misfire event in a large-bore two-stroke engine can be equivalent to over a hundred normal firing cycles. With government regulations continuing to restrict an engine’s allowable emissions, equipment manufacturers and operators are in search of solutions that can effectively and reliably reduce combustion instability, and understanding the root causes is an instrumental step towards that goal. Exploring the numerous possible contributors to combustion instability is a large endeavor, so this paper narrows the scope to studying methods of fueling and effects of spark timing on large-bore two-stroke natural gas engines. This investigation into fueling assesses both carburetion and direct injection fueling strategies at a range of spark timings. The direct injection fueling system is also tested at a series of fuel pressures. Typically, direct fuel injection has shown to lower total hydrocarbon emissions by reducing short-circuiting. However, its impact to an engine’s stability has not been thoroughly investigated for large-bore single cylinder two-stroke engines. Studying these fundamental parameters provides insight into potential contributors of engine instability and understanding how to mitigate them and ultimately reduce emissions.

ABSTRACT A direct injection (DI) CNG engine was developed and evaluated under stoichiometric and lean burn conditions, emphasising high compression ratios (CRs). A comparative analysis of PFI gasoline and PFI CNG engines was conducted to provide comprehensive insights. Results showed that the DI CNG engine exhibited a shorter combustion duration, indicating higher combustion speed, and enhanced combustion stability, particularly at low load and speed conditions, with a reduced coefficient of variation of indicated mean effective pressure (COVIMEP) below 1%. The DI CNG engine demonstrated a relative increase in net indicated thermal efficiency by 4–5% compared to the PFI CNG engine. Furthermore, CNG engines operating at a high compression ratio of 16 could run at high loads without encountering knocking issues. Lean burn operation, combined with high compression ratios, improved thermal efficiency while minimising emissions; however, challenges such as combustion instability and increased emissions under lean burn conditions were observed.

The use of natural gas as an alternative fuel in dual-fuel compression-ignition engines can lead to a substantial reduction in the majority of pollutant emissions compared to fossil fuels, while the thermal efficiency of the engine can be maintained at adequate levels. Its usage has increased widely in recent years, and significant efforts have been made to investigate the inherent physical and chemical processes that take place during this engine’s combustion, as well as the parameters that affect the operation of the engine and use natural gas as energy source. The scope of this study is to investigate the effect of EGR temperature (cold and hot) and rate (10% and 20%) on the performance characteristics and emissions of a dual-fuel compression-ignition engine operating at a specific engine operating point under dual-fuel (diesel–natural gas) conditions. For this reason, a phenomenological two-zone combustion model was developed. The results of the model were validated against the experimental data obtained from a single-cylinder direct-injection, turbocharged compression-ignition dual-fuel research engine operated under part-load conditions (IMEP = 0.52 Mpa and engine speed = 1500 rpm) and at various replacement percentages of diesel using methane (which was treated as a natural gas surrogate). The model results were in good agreement with the experimental results, revealing the ability of the model to be used in the aforementioned EGR analysis. The results of the study revealed that engine operation with 10% cold EGR does not significantly affect the engine performance characteristics, and combined with the addition of 80% gaseous fuel energy, can lead to a substantial reduction in NO and soot emissions, with a moderate increase in CO emissions. On the other hand, a significant finding of the present work is that engine operation with hot EGR under the investigated operating conditions, even though it had a beneficial effect on NO-specific emissions, led to a reduction in engine efficiency and may raise issues regarding the mechanical strength of the engine.

This paper presents an experimental and statistical study of a four-cylinder turbocharged compression ignition engine operating in dual-fuel mode with natural gas and liquid pilot fuel (diesel or hydrotreated vegetable oil). The main engine performance indicators, combustion process parameters and emissions were evaluated, as well as noise and vibration measurements were performed to determine the loading of structural elements. In order to highlight the factors affecting engine reliability and maintenance, the ANCOVA (analysis of covariance) methodology was applied, modeling the influence of load, natural gas fraction and sound pressure. The mean absolute percentage error shows that the model predicts the most important indicators quite accurately under various operating conditions. The developed ANCOVA model not only predicts engine characteristics under various load and fuel mixture conditions, but it also provides insights useful for engine maintenance planning and reliability assurance, especially in long-term or intensive operation.

This study demonstrates that hydrogen enrichment in lean-burn spark-ignition engines can simultaneously improve three key performance metrics, thermal efficiency, combustion stability, and nitrogen oxide emissions, without requiring modifications to the engine hardware or ignition timing. This finding offers a novel control approach to a well-documented trade-off in existing research, where typically only two of these factors are improved at the expense of the third. Unlike previous studies, the present work achieves simultaneous improvement of all three metrics without hardware modification or ignition timing adjustment, relying solely on the optimization of the air–fuel equivalence ratio λ. Experiments were conducted on a six-cylinder engine for combined heat and power application, fueled with hydrogen–natural gas blends containing up to 30% hydrogen by volume. By optimizing only the air–fuel equivalence ratio, it was possible to extend the lean-burn limit from λ≈1.6 to λ>1.9, reduce nitrogen oxide emissions by up to 70%, enhance thermal efficiency by up to 2.2 percentage points, and significantly improve combustion stability, reducing cycle-by-cycle variationsfrom 2.1% to 0.7%. A defined λ window was identified in which all three key performance indicators simultaneously meet or exceed the natural gas baseline. Within this window, balanced improvements in nitrogen oxide emissions, efficiency, and stability are achievable, although the individual maxima occur at different operating points. Cylinder pressure analysis confirmed that combustion dynamics can be realigned with original equipment manufacturer characteristics via mixture leaning alone, mitigating hydrogen-induced pressure increases to just 11% above the natural gas baseline. These results position hydrogen as a performance booster for natural gas engines in stationary applications, enabling cleaner, more efficient, and smoother operation without added system complexity. The key result is the identification of a λ window that enables simultaneous optimization of nitrogen oxide emissions, efficiency, and combustion stability using only mixture control.

Hydrogen is an excellent alternative fuel for spark ignition engines because of its high laminar flame velocity and no carbon intensity. However, due to challenges faced by hydrogen storage and transportation, it is desirable to blend it with a fuel such as natural gas which allows hydrogen transportation with minimal modifications to an already developed infrastructure of natural gas. Moreover, hydrogen/natural gas blends utilize the high knock resistance of natural gas fuel. The current paper investigates the impact of hydrogen/natural gas blends on a natural gas-fired, large-bore, industrial engine. In particular, the engine’s indicated thermal efficiency (ITE), combustion phasing, cyclic variability and exhaust emissions are studied at 40% load capacity and hydrogen content up to 30% by volume. The choice of 40% load was based on the engine’s significant performance decline under natural gas fuel at low loads. The results indicated that the indicated thermal efficiency improved by 3.9%. The cyclic variability was also enhanced. NOx, CH4, CO2, and VOCs emissions decreased by 95, 49, 12 and 70% respectively. The CO emissions increased by 17%. These results show promising enhancement in the performance and emissions of the natural gas-fired engines at part-load conditions. The hydrogen/natural gas blends will be tested at different equivalence ratios and spark timings to explore the impact on these industrial engines under varying operating conditions.

The power produced by the combustion of fossil fuels in internal combustion engines is transferred to the powertrain, and this generated power causes carbon dioxide (CO2) and particulate matter emissions. Systems that do not cause CO2 and other harmful emissions or cause less emissions are a strong alternative. In this context, methanol and natural gas are added to the engine to reduce emissions. In this study, engine performance and emissions were examined using three fuel mixtures. A two-cylinder gasoline engine was run using M20 fuel and natural gas was added at different rates from the engine manifold. The engine was operated at a constant 3000 rpm and using 6 different fuels (gasoline, M20, M20+50 g natural gas, M20+100 g natural gas, M20+150 g natural gas, M20+200 g natural gas), at different torque values (5, 10, 15 and 20 Nm) engine performance and emission values were compared. When fuel consumption is compared to gasoline fuel, the overall cycle average is 6% higher in M20, 3% higher in M20+50 and M20+100, 1% higher in M20+150 and 6% higher in M20+200, and emissions are reduced compared to gasoline in other fuels.

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As emissions regulations become more and more stringent and conventional fuel sources rarefaction, new alternatives are emerging to address this situation. Dual fuel engines are among the promising solutions, offering both ecological and economic advantages. However, these engines often confront constraints linked to high levels of unburnt hydrocarbons (HC) at low loads and NOx emissions at high loads. To overcome these problems and guarantee high-efficiency overall operating loads, exhaust gas recirculation (EGR) is a potential solution. In the present experimental study, appropriate modifications have been carried out to a single-cylinder diesel engine to ensure dual fuel operation with EGR. Natural gas and diesel are used as the primary and pilot fuel, respectively. At low load operations, the EGR rate is increased up to 35% until the reduction of unburnt hydrocarbons. However, at high loads, the EGR rate is carefully adjusted, as the combustion efficiency easily deteriorates due to oxygen amount lack in the combustion chamber. Also, minimizing NOx emissions is prioritized in all load conditions while keeping thermal efficiency in sight. In addition, the variation in the amount of pilot fuel is studied for improving the combination of dual fuel engine operation with the EGR technique. This made it possible to determine the influence of load, EGR rate, and pilot fuel quantity on the engine in response to the triple challenges of reducing NOx and HC and improving thermal efficiency. The results show that an adequate EGR rate of 30%, depending on the operating conditions, can reduce HC emissions by >25% while increasing thermal efficiency by around 20%. This result is accompanied by a significant reduction, over 90%, in NOx emissions.

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Due to the issues of low flame speed and high CH4 emissions for a natural gas engine, investigations into the partial oxidation fuel reforming (POFR) method used in natural gas engines to blend H2 have become increasingly valuable. In this paper, the combustion process, engine performance, and emissions of a natural gas engine with fuel-reforming gases blended together have been numerically studied. The results show that a higher fuel-reforming ratio can effectively improve the engine combustion performance, especially at lean-burn conditions. Combustion with reformed gases can increase the thermal efficiency by almost 2% at the full-load condition, whereas fuel reforming significantly affects the natural gas engine’s power performance. Furthermore, CH4 and NOX emissions decrease significantly with increasing fuel-reforming ratio. In conclusion, fuel reforming for a natural gas engine has a promising future in reducing greenhouse gas emissions and improving economic performance.

Technologies used in the transport sector have a substantial impact on air pollution and global warming. Due to the immense impact of air pollution on Earth, it is crucial to investigate novel ways to reduce emissions. One way to reduce pollution from ICE is to use alternative fuels. However, blends of alternative fuels in different proportions are known to improve some emissions’ parameters, while others remain unchanged or even worsen. It is therefore necessary to find ways of reducing all the main pollutants. For SI engines, mixtures of hydrogen and natural gas can be used as alternative fuels. The use of such fuel mixtures makes it possible to reduce CO, HC, and CO2 emissions from the engine, but the unique properties of hydrogen tend to increase NOx emissions. One way to address this challenge is to use port water injection (PWI). This paper describes studies carried out under laboratory conditions on an SI engine fuelled with CNG and CNG + H2 mixtures (H2 = 5, 10, 15% by volume) and injected with 60 and 120 mL/min of water into the engine. The tests showed that the additional water injection reduced CO and NOx emissions by about 20% and 4–5 times, respectively. But, the results also show that water injection at the rate of 120 mL/min increases fuel consumption by between 2.5% and 7% in all cases.

A computational fluid dynamics study of a large-bore, two-stroke, integral compressor engine is conducted. The engine under study operates on natural gas and uses a prechamber for ignition. The purpose of this work is to ascertain how property variations in the prechamber jet affect NOx formation in the main combustion chamber. Several testing suites were performed using a CFD model of a Cooper-Bessemer GMV four-cylinder engine. The chemical composition and temperature of the prechamber jet were manually modified for each simulation. NO emissions were found to be more sensitive to increases in the jet temperature than decreases in the jet temperature. NO2 emissions were largely insensitive to any jet temperature modification. Jet composition was modified to represent discrete prechamber fuel-air ratios. A non-monotonic relationship exists between jet composition and NOx formation. In general, the optimal balance among NOx, residual CH4, and CO was found for simulations using a prechamber equivalence ratio slightly rich of stoichiometric. NO tended to form relatively early in the cycle in areas surrounding the PCC jet. Later in the cycle, NO collected around the perimeter of the cylinder. The extended Zeldovich and N2O mechanisms were the highest contributors to NO formation. NO2 formed relatively late in the cycle in areas of high NO concentration.

There is currently a gap in the available literature on retrofitting engines with less-advanced control systems to run on hydrogen-enriched natural gas. Potential advantages of hydrogen-enriched natural gas in these engines may not be realized without altering parameters such as spark timing, exhaust gas re-circulation, or the air/fuel ratio. However, in such engines, changes in spark timing and exhaust gas recycle are often cost-prohibitive, leaving equivalence ratio adjustments as one of the few remaining viable operational strategies. In this study, a small-displacement (319 cc), naturally aspirated, single-cylinder gasoline engine without spark timing control was converted to run on a 10%vol blend of hydrogen-enriched natural gas. Stoichiometric operation improved thermal efficiency, fuel consumption, and total hydrocarbon emissions, but higher NOx emissions resulted. Despite no spark-timing control, lean-burn operation at an equivalence ratio of 0.7 was found to maintain performance improvements while also lowering emissions: fuel consumption was lowered versus the methane base case by 11%, and NOx and hydrocarbon emissions were both decreased by approximately 70% below the base case. This study concludes that in a scenario even without spark-timing control, the addition of 10%vol hydrogen can improve power, emissions, and efficiency of a spark-ignited natural gas engine, which serves as a proof-of-concept that even fairly simple, small-displacement engines can benefit from switching from gasoline to hydrogen-enriched natural gas operation.

Nowadays, due to stricter pollution standards, more attention has been focused on pollutants emitted from cars. As a very dangerous pollutant, NOx has always triggered the sensitivity of the related organizations. In the process of developing and designing the engine, estimating the amount of this pollutant is of great importance to reduce future expenses. Calculating the amount of this pollutant has usually been complicated and prone to error. In the present paper, neural networks have been used to find the coefficients of correcting NOx calculation. The Zeldovich method calculated the value of NOx with 20% error. By applying the progressive neural network and correcting the equation coefficient, this value decreased. The related model has been validated with other fuel equivalence ratios. The neural network model has fitted the experimental points with a convergence ratio of 0.99 and a squared error of 0.0019. Finally, the value of NOx anticipated by the neural network has been calculated and validated according to empirical data by applying maximum genetic algorithm. The maximum point for the fuel composed of 20% hydrogen and 80% methane occurred in the equivalence ratio of 0.9; and the maximum point for the fuel composed of 40% hydrogen occurred in equivalence ratio of 0.92. The consistency of the model findings with the empirical data shows the potential of the neural network in anticipating the amount of NOx.

This study aims to evaluate and optimize the influences of operational factors, including the engine’s rotational speed, methane mass, diesel mass, and the duration of injected diesel fuel on the methane/diesel reactivity-controlled compression ignition (RCCI) light-duty engine’s performance and emissions by executing the Nondominated Sorting Genetic Algorithm-II (NSGAII). The optimizations aimed to minimize peak firing pressure simultaneously, decrease indicated specific fuel consumption, and reduce tailpipe emissions. It is found that the excess air ratios of (2.22 to 2.37) are the range of feasible results of the RCCI engine, and the power should be less than 0.89 from the maximum design load of the diesel engine when it works without it after treatment. The methane/diesel RCCI engine achieves an indicative thermal efficiency of 51%. The Pareto results from the NSGA algorithm occur on multiple fronts, and there is a tradeoff between power and nitrogen oxide (NOx) in addition to unburned hydrocarbons (UHCs) and carbon monoxide (CO) with NOx emissions. Moreover, EURO IV emissions regulations can occur when using a start of injection (SOI) of −35 CA, a diesel mass of 1.82 mg, a methane mass of 9.74 mg, a diesel injection duration of 2.63 CA, and a rotational speed of 2540 rpm. This accomplished a reduction in indicative specific fuel consumption by 27.8%, higher indicative efficiency by 21.9%, and emissions reductions compared to a conventional diesel engine.

In reaction to the rising expense of fossil fuels and the rise in the number of pollutants in the environment, professionals are searching for alternative, renewable fuels in order to improve the efficiency of internal combustion engines and decrease the emissions that they create. This is being done in order to improve the efficiency of internal combustion engines and reduce the emissions that they produce. This study was conducted with the intention of determining whether or not alternative fuels, such as mixtures of biodiesel, methanol, and nitro-methane, could be able to effectively replace traditional diesel in an internal combustion engine (1200 r/min to 2100 r/min). Increasing the speed of the engine was helpful in achieving the desired goal of producing a more consistent combustion product. It is possible that the indicator thermal efficiency and economic performance might be improved by increasing both the number of rotations per minute and the number of nitromethane blends that are introduced into the cylinder. It has been shown that the nitro-methane approach has tremendous promise for reducing NOx emissions. However, higher rotations per minute proved beneficial for increasing the pressure and temperature within the cylinders. At a speed of 1500 r/min, this particular engine reached its optimal compression ratio of 18:1. The ratio of nitromethane impact on NOx emissions reached 10%, and the factor that had the most influence on smoke emission for NM3 (85.0% diesel, 10.0% biodiesel, 2.0% methanol, and 3.0% nitromethane) was the engine running condition.

Ammonia (NH3) has recently emerged as a promising alternative fuel for both internal and external combustion engines. The combustion of pure ammonia does not produce unwanted pollutant emissions such as oxides of carbon, total unburned hydrocarbon (THC), and particulates. Additionally, ammonia contains 17.8% by mass of hydrogen (H2), making it a potential fuel for hydrogen storage. However, its narrow flammability range, low reactivity, and low flame propagation speed have limited its engine performance. To address these issues, this study was conducted to explore the use of multiple flame generation and ammonia-methane blend approaches to enhance the flame propagation speed of ammonia and improve engine performance. The study utilized a novel metal liner to generate multiple flames inside the combustion chamber and installed four spark plugs, as well as an additional spark plug at the top of the cylinder head, similar to a spark-ignition engine. Furthermore, the study investigated the effect of adding methane to ammonia combustion, with methane fractions ranging from 30% to 60% in terms of energy fraction. The combustion process was initiated with various spark ignition cases, and a high-speed natural flame-luminosity (NFL) technique was utilized to capture various combustion cases. The results showed that multiple flames inside the chamber led to stable ammonia combustion, resulting in better engine efficiency due to a faster flame propagation rate. Additionally, the study found that increasing the methane fraction in the ammonia fuel mixture increased the in-cylinder pressure and heat release rate (HRR), improving engine performance significantly. However, higher NOx emissions were observed with increasing methane fraction in the fuel mixture, resulting from both fuel-bound and thermal NOx caused by higher in-cylinder temperatures. The study also found that higher THC and CO2 emissions were observed while increasing the methane fraction in the fuel mixture. Moreover, multiple spark ignition cases produced lower THC than the single spark plug case because it burned the air-fuel mixture rapidly.

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Compression ignition engines will still be predominant in the naval sector: their high efficiency, high torque, and heavy weight perfectly suit the demands and architecture of ships. Nevertheless, recent emission legislations impose limitations to the pollutant emissions levels in this sector as well. In addition to post-treatment systems, it is necessary to reduce some pollutant species, and, therefore, the study of combustion strategies and new fuels can represent valid paths for limiting environmental harmful emissions such as CO2. The use of methane in dual fuel mode has already been implemented on existent vessels, but the progressive decarbonization will lead to the utilization of carbon-neutral or carbon-free fuels such as, in the last case, hydrogen. Thanks to its high reactivity nature, it can be helpful in the reduction of exhaust CH4. On the contrary, together with the high temperatures achieved by its oxidation, hydrogen could cause uncontrolled ignition of the premixed charge and high emissions of NOx. As a matter of fact, a source of ignition is still necessary to have better control on the whole combustion development. To this end, an optimal and specific injection strategy can help to overcome all the before-mentioned issues. In this study, three-dimensional numerical simulations have been performed with the ANSYS Forte® software (version 19.2) in an 8.8 L dual fuel engine cylinder supplied with methane, hydrogen, or hydrogen–methane blends with reference to experimental tests from the literature. A new kinetic mechanism has been used for the description of diesel fuel surrogate oxidation with a set of reactions specifically addressed for the low temperatures together with the GRIMECH 3.0 for CH4 and H2. This kinetics scheme allowed for the adequate reproduction of the ignition timing for the various mixtures used. Preliminary calculations with a one-dimensional commercial code were performed to retrieve the initial conditions of CFD calculations in the cylinder. The used approach demonstrated to be quite a reliable tool to predict the performance of a marine engine working under dual fuel mode with hydrogen-based blends at medium load. As a result, the system modelling shows that using hydrogen as fuel in the engine can achieve the same performance as diesel/natural gas, but when hydrogen totally replaces methane, CO2 is decreased up to 54% at the expense of the increase of about 76% of NOx emissions.

LNG is a potential alternative fuel for ships. Generating H2 through exhaust reforming is an effective method to improve the performance of the LNG engine and reduce its pollutant emissions. It is necessary to study the mechanism of methane exhaust reforming to guide the design of the reformer. Based on the detailed mechanism, the characteristics of methane reforming reaction were studied for a marine LNG engine. Firstly, the reforming characteristics of exhaust were studied. The results show that methane reforming requires a lean oxygen environment, and the hydrogen production reaction will not occur when the O2 concentration is too high. Then, the effects of the O2/CH4 ratio (0.2–1) and H2O/CH4 ratio (0–2) on the reforming reaction were studied. The results show that under O2/CH4 = 0.4, the molar fraction of hydrogen at the outlet of the reactor decreases with the increase in the H2O/CH4 ratios. Finally, a mechanism analysis was conducted. The results show that an oxidation reaction occurs first and then the steam reforming reaction occurs on palladium-based catalysts.

This article explores the characteristics of biogas, its main composition (methane and carbon dioxide) and its potential to reduce greenhouse gas emissions. This study was carried out using various quantities of biogas, to analyze the main pollutants released by the engine at the end of the combustion process, according to the quantities of biogas that enter the engine. The results we obtained when carrying out the theoretical study show us that increasing the amounts of methane favors the behavior of the engine in various conditions, on the contrary, increasing methane and reducing CO2 increases the concentrations of pollutants such as CO, SO2. Biogas has been implemented as an alternative fuel, highlighting its positive impact on energy sustainability and the reduction of operating costs. Finally, we analyze that biogas has great potential to contribute to a cleaner and more sustainable energy future if current barriers are overcome.

The oil and gas industry heavily relies on lean burn spark ignited natural gas reciprocating engines. These engines produce pollutants, such as NOx and CO, but due to their premixed nature, also produce relatively large amounts of unburned methane (CH4) emissions. The primary source of methane emissions in lean burn engines are the crevices and near wall quench layers. Thus, one method to dramatically reduce methane emissions is to alter the combustion to be non-premixed, mixing-controlled combustion. In this concept the active prechamber acts as a reliable ignition source for the direct injected natural gas, which is referred to as prechamber ignited mixing-controlled combustion (PC-MCC). The PC-MCC concept enables a ~10x reduction in methane emissions, making it a promising technology for reducing the environmental impact of reciprocating engines. In this study, CFD simulations have been used to compare two modeling approaches for PC-MCC: a pure Eulerian gaseous injection approach and a gas-parcels injection method. Using the parcel method to model the gas injection enables an engineering approach to study and design the PC-MCC concept in a timely manner with coarser computational grids. This study also investigated the impact of several variables that may contribute to the performance and emissions of the PC-MCC strategy. The parameters that were examined include prechamber passageway characteristics like nozzle diameter, number of nozzles, and the orientation of nozzle orifices.

Compared to diesel, liquefied natural gas (LNG), often used as an alternative fuel for marine engines, comes with significant advantages in reducing emissions of particulate matter (PM), SOx, CO2, and other pollutants. Promoting the use of LNG is of great significance for achieving carbon peaking and neutrality worldwide, as well as improving the energy structure. However, compared to diesel engines, medium- and high-speed marine LNG engines may produce higher methane (CH4) emissions and also have nitrogen oxide (NOx) emission issues. For the removal of CH4 and NOx from the exhaust of marine LNG engines, the traditional technical route of combining a methane oxidation catalyst (MOC) and an HN3 selective catalytic reduction system (NH3-SCR) will face problems, such as low conversion efficiency and high operation cost. In view of this, the technology of non-thermal plasma (NTP) combined with CH4-SCR is proposed. However, the synergistic mechanism between NTP and catalysts is still unclear, which limits the optimization of an NTP-CH4-SCR system. This article summarizes the synergistic mechanism of NTP and catalysts in the integrated treatment process of CH4 and NOx, including experimental analysis and numerical simulation. And the relevant impact parameters (such as electrode diameter, electrode shape, electrode material, and barrier material, etc.) of NTP reactor energy optimization are discussed. The work of this paper is of great significance for guiding the high-efficiency removal of CH4 and NOx for an NTP-CH4-SCR system.

This review covers the current state, challenges, and future directions of catalytic combustion technologies for mitigating fugitive methane emissions from the fossil fuel industry. Methane, a potent greenhouse gas, is released from diverse sources, including natural gas production, oil operations, coal mining, and natural gas engines. The paper details the primary emission sources, and addresses the technical difficulties associated with dilute and variable methane streams such as ventilation air methane (VAM) from underground coal mines and low-concentration leaks from oil and gas infrastructure. Catalytic combustion is a useful abatement solution due to its ability to destruct methane in lean and challenging conditions at lower temperatures than conventional combustion, thereby minimizing secondary pollutant formation such as NOX. The review surveys the key catalyst classes, including precious metals, transition metal oxides, hexa-aluminates, and perovskites, and underscores the crucial role of reactor internals, comparing packed beds, monoliths, and open-cell foams in terms of activity, mass transfer, and pressure drop. The paper discusses advanced reactor designs, including flow-reversal and other recuperative systems, modelling approaches, and the promise of advanced manufacturing for next-generation catalytic devices. The review highlights the research needs for catalyst durability, reactor integration, and real-world deployment to enable reliable methane abatement.

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Decarbonizing long-haul goods transportation poses a substantial challenge. High-efficiency natural gas (NG) engines, which retain the efficiency of a diesel engine but reduce the carbon content of the fuel, offer substantial potential for near-term greenhouse gas (GHG) reductions. A fast-running model that can predict engine performance, GHG and air pollutant emissions is critical to assessing this approach for different applications and vehicle drivetrain configurations. This paper presents the development, validation and application of an engine system model that adapts GT-SUITE™’s phenomenological DI-Pulse predictive model to predict the performance and emissions of a 6-cylinder NG engine using a high pressure direct-injection combustion process. The model includes the engine air exchange system, enabling the prediction of the engine and in-cylinder conditions and overall performance over transient drive cycles. The engine model with a fixed set of calibration parameters captures the complex high-pressure direct injection combustion process and generates time-resolved parameters that are fed into a coupled machine learning model to predict emissions, including nitrogen oxide (NOx) and methane (CH4) emissions. While the 1-D model’s predictions for CH4 were not accurate, coupling the 1-D engine model with a machine learning model has been shown to substantially improve the estimation of CH4 emissions and allow accurate prediction of engine total GHG emissions over different duty cycles. The model has been validated using transient engine dynamometer data and is then applied to assess performance and emissions over several regulatory and real-world long-haul drive cycles. The model showed an average error of less than 5% in steady operation. Cumulative errors of NOx and CH4 emissions in studied cycles were also less than 10%. The results showed that CH4 share in total GHG emissions ranges from 0.2% to 1.4% over various drive cycles. By predicting engine performance and emissions, the developed combined model has considerable potential for use in engine evaluation studies, especially when combined with new technologies across different duty cycles.

The use of natural gas (NG) in dual-fuel heavy-duty engines has the potential to reduce pollutant and greenhouse gas (GHG) emissions from the transport sector when compared to the conventional diesel engines. However, NG composition and methane slip are of interest because both can adversely affect the benefits of NG as an alternative fuel, especially when considering GHG emissions. Therefore, this study experimentally investigated the effects of NG fuel properties on the performance and emissions of both conventional dual-fuel and reactivity-controlled compression ignition (RCCI) engine operations. Three different gas mixtures were selected to simulate typical NG compositions available in the world market, with methane numbers (MN) of 80.9, 87.6 and 94.1. These fuels were tested in a single-cylinder compression ignition engine operating at 0.6, 1.2 and 1.8 MPa net indicated mean effective pressure (IMEP). A high-pressure common rail system allowed for the use of various diesel injection strategies while a variable valve actuation system enabled the effective compression ratio to be adjusted via late intake valve closing (LIVC). The RCCI combustion was found to be more sensitive to changes in MN than the conventional NG-diesel dual-fuel operation. The gas mixture with the lowest MN reduced both total unburned hydrocarbons emissions and methane slip at the expense of higher nitrogen oxides (NOx) emissions. The effects of MN on the net indicated efficiency were more significant at 0.6 MPa IMEP, yielding differences of up to 4.9% between the RCCI operations with the lowest and highest MN fuels. Overall, this work revealed that the combination of the RCCI combustion and LIVC can achieve up to 80% lower methane slip and NOx emissions and relatively higher net indicated efficiency than the conventional dual-fuel regime, independent of the NG composition.

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Unburned methane entrained in exhaust from natural gas-fired compressor engines ("combustion slip") can account for a substantial portion of station-level methane emissions. A novel in-stack, tracer gas method was coupled with Fourier transform infrared (FTIR) species measurements to quantify combustion slip from natural gas compressor engines at 67 gathering and boosting stations owned or managed by nine "study partner" operators in 11 U.S. states. The mean methane emission rate from 63 four-stroke, lean-burn (4SLB) compressor engines was 5.62 kg/h (95% CI = 5.15-6.17 kg/h) and ranged from 0.3 to 12.6 kg/h. The mean methane emission rate from 39 four-stroke, rich-burn (4SRB) compressor engines was 0.40 kg/h (95% CI = 0.37-0.42 kg/h) and ranged from 0.01 to 4.5 kg/h. Study results for 4SLB engines were lower than both the U.S. EPA compilation of air pollutant emission factors (AP-42) and Inventory of U.S. Greenhouse Gas Emissions and Sinks (GHGI) by 8 and 9%, respectively. Study results for 4SRB engines were 43% of the AP-42 emission factor and 8% of the GHGI emission factor, the latter of which does not distinguish between engine types. Total annual combustion slip from the U.S. natural gas gathering and boosting sector was modeled using measured emission rates and compressor unit counts from the U.S. EPA Greenhouse Gas Reporting Program. Modeled results [328 Gg/y (95% CI = 235-436 Gg/y) of unburned methane] would account for 24% (95% CI = 17-31%) of the 1391 Gg of methane emissions for "Gathering and Boosting Stations", or 6% of the net emissions for "Natural Gas Systems" (5598 Gg) as reported in the 2020 U.S. EPA GHGI. Gathering and boosting combustion slip emissions reported in the 2020 GHGI (374 Gg) fall within the uncertainty of this model.

The need to decarbonize the road transport sector is driving the evaluation of alternative solutions. From a long-term perspective, biomethane and e-methane are particularly attractive as green energy carriers and a part of the solutions for the sustainable freight on-road transport, as they offer significant CO2-equivalent emissions savings in a net Well-to-Wheel assessment. However, to make methane-fuelled spark ignition (SI) heavy-duty (HD) engines competitive in the market, their efficiency must be comparable to the top-performing diesel applications that dominate the sector. To this end, dilution techniques such as exhaust gas recirculation (EGR) or lean air–fuel mixtures represent promising solutions. Within limits specific to the engine’s tolerance to the used strategy, charge dilution can improve thermal efficiency impact on the pumping and wall heat loss, and the heat capacity ratio (γ). However, their potential has never been explored in the case of methane SI HD engines characterized by a semi diesel-like combustion system architecture. This work presents an experimental study to characterize the energy and pollutant emission performance of a state-of-the-art SI HD gas single-cylinder engine (SCE) operating with EGR or with lean conditions. The engine type is representative of most HD powertrains used for long-haul purposes. The designed test plan is representative of the majority of on-road operating conditions providing an overview of the impact of the two dilution methods on the overall engine performance. The results highlight that both techniques are effective for achieving significant fuel savings, with lean combustion being more tolerable and yielding higher efficiency improvements (10% peak vs. 5% with EGR).

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Natural gas (NG) engine catalysts face unique challenges in emission control due to their distinct raw emission characteristics. This study investigates the exhaust conversion and by-product generation of a Palladium-based catalyst of an NG engine through small-sample catalyst experiments, mainly focusing on the effect of feed gas composition on the conversion efficiency and N2O/NH3 emissions. Results show that N2O is generated via NO reduction by H2 (80~275 °C) and CO (275~400 °C) in the temperature range of 80~400 °C. NH3 generation occurs at 175~550 °C, mainly via NO reduction by H2 (supplied from the water–gas shift (WGS) reaction) and CO below 425 °C and exclusively by H2 (supplied from the steam reforming (SR) reaction) above 425 °C. An increase (0.9705~1.0176) in lambda enhances CO and CH4 conversion while reducing N2O and NH3 emissions, but it inhibits NO conversion and promotes NO2 formation. A lambda of 0.9941 achieves high conversion efficiency (≥90%) for CO, CH4, and NO, with reduced N2O and zero NH3 emissions. An increase in H2O (8~16%) accelerates the WGS and SR reactions, improving pollutant conversion. However, it aggravates N2O and NH3 emissions, with peak levels rising by 54% and 31%, respectively. Increased H2 (500~1500 ppm) preferentially consumes NO and reversely shifts the equilibrium of the WGS and SR reactions, reducing CO and CH4 conversion while improving NO conversion. And it promotes N2O selectivity at high temperature and NH3 selectivity at low temperature and peak emissions, with peak concentrations increasing by 58% and 15%, respectively. These findings reveal the by-product formation mechanism in the catalyst, providing valuable insights for the emission control of NG-fueled engines.

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Stoichiometric industrial natural gas engines rely on robust design to achieve consumer driven up-time requirements. Key to this design are exhaust components that are able to withstand high combustion temperatures found in this type of natural gas engine. The issue of exhaust component durability can be addressed by making improvements to materials and coatings or decreasing combustion temperatures. Among natural gas engine technologies shown to reduce combustion temperature, dedicated exhaust gas recirculation (EGR) has limited published research. However, due to the high nominal EGR rate it may be a technology useful for decreasing combustion temperature. In previous work by the author, dedicated EGR was implemented on a Caterpillar G3304 stoichiometric natural gas engine. Examination of combustion statistics showed that, in comparison to a conventional stoichiometric natural gas engine, operating with dedicated EGR requires adjustments to the combustion recipe to achieve acceptable engine operation. This work focuses on modifications to the combustion recipe necessary to improve combustion statistics such as coefficient of variance of indicated mean effective pressure (COV of IMEP), cylinder-cylinder indicated mean effective pressure (IMEP), location of 50% mass fraction burned, and 10%–90% mass fraction burn duration. Several engine operating variables were identified to affect these combustion statistics. A response surface method (RSM) optimization was chosen to find engine operating conditions that would result in improved combustion statistics. A third order factorial RSM optimization was sufficient for finding optimized operating conditions at 3.4 bar brake mean effective pressure (BMEP). The results showed that in an engine with a low turbulence combustion chamber, such as a G3304, optimized combustion statistics resulted from a dedicated cylinder lambda of 0.936, spark timing of 45° before top dead center (°bTDC), spark duration of 365 µs, and intake manifold temperature of 62°C. These operating conditions reduced dedicated cylinder COV of IMEP by 10% (absolute) and the difference between average stoichiometric cylinder and dedicated cylinder IMEP to 0.19 bar.

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Considering the strict regulations on the transport sector emissions, predictive models for engine emissions are essential tools to optimize high-efficient low-emission internal combustion engines (ICE) for vehicles. This aspect is of major importance, especially for developing new combustion concepts (e.g. lean, pre-chamber) or using alternative fuels. Among the gaseous emissions from spark-ignition (SI) engines, unburned hydrocarbons (uHC) are the most challenging species to model due to the complexity of the formation mechanisms. Phenomenological models are successfully used in these cases to predict emissions with a reduced computational effort. In this work, uHC phenomenological model approaches by the authors are further developed to improve the model predictivity for multiple variations including engine design, engine operating parameters, as well as different fuels and ignition methods. The model accounts for uHC contributions from piston top-land crevice, wall flame quenching, oil film fuel adsorption/desorption and features a tabulated-chemistry approach to describe uHC post-oxidation. With the support of 3D-CFD simulations, multiple novel modelling assumptions are developed and verified. The model is validated against an extensive measurement database obtained with two small-bore single-cylinder engines (SCE) fuelled with gasoline-like fuel, one with SI and one with pre-chamber, as well as against data from two different ultra-lean large-bore engines fuelled with natural gas (one equipped with a pre-chamber and one dual-fuel with a diesel pilot). The model correctly predicts the trends and absolute values of uHC emissions for all the operating conditions and the engines with an accuracy on average of 11.4%. The results demonstrate the general applicability of the model to different engine designs, the correct description of the main mechanisms contributing to fuel partial oxidation, and the potential to be extended to predict unburned fuel emissions with other fuels.

Abstract Background: Maritime transportation accounts for around 80% of the world freight movements, remarkably contributing to the global environmental footprint. Dual fuel engines, running on both gaseous and liquid fuels, represent a viable way toward the reduction of emissions at the cost of additional complexity in monitoring activities. Motivation: Data-driven methods represent the frontier in research and in maritime industrial applications, and they usually require a large amount of labelled data, i.e., sensor measurements plus the associated engine status usually annotated by human operators, which are costly and seldomly available in the wild. Unlabelled samples, instead, are commonly, cheaply, and readily available. Hypothesis: The enabling technology for data-driven methods is the availability of a network of sensors and an automation system able to capture and store the associated stream of data. Methods: In this paper, we design and propose multiple alternatives toward the weakly supervised marine dual fuel engines data-driven monitoring. To this aim, we will rely on a Digital Twin of the dual fuel engine or on novelty detection algorithms and we will compare them against state-of-the-art fully supervised approaches. Results: Results on data generated from a real-data validated simulator of a marine dual fuel engine demonstrate that the proposed weakly supervised monitoring approaches lead to a negligible loss in accuracy compared to costly and often unfeasible fully supervised ones supporting the validity of the proposal for its application in the wild. Conclusion: The main outcome is a guideline for selecting the best data-driven dual fuel engine monitoring method according to the available data.

Presenting the influence of compressed natural gas (CNG) used as alternative fuel on the combustion of an automotive diesel engine represents the main objective of this paper. The paper studies brake specific energetic consumption, in-cylinder pressure and pressure rise rate, carbon dioxide, nitrogen oxides, smoke and hydrocarbons emissions at 2000 rev/min and at 40%, 55% and 70% load. Low carbon content of the alternative fuel will determine lower CO2 at all loads; NOx and smoke emissions are influenced by both energetic substitution and engine operating regime. HC emission will reach higher levels in diesel-gas mode than in conventional mode as the homogeneous percentage of the charge per cycle grows with the quantity of CNG admitted into the cylinder. In all cases in-cylinder pressure and pressure rise rate are higher in dual-fuel mode than those in conventional operating mode due to higher quantity of premixed charge developed during the ignition delay phase. The higher LHV (lower heating value) and the gaseous state of CNG will determine at all loads lower brake specific energetic consumption. Smoke emission will be negatively influenced in low to medium loads but in high loads it will drop by more than 30 percent.

Vehicular emissions deteriorate air quality in urban areas notably. The aim of this study was to conduct an in-depth characterization of gaseous and particle emissions, and their potential to form secondary aerosol emissions, of the cars meeting the most recent emission Euro 6d standards, and to investigate the impact of fuel as well as engine and aftertreatment technologies on pollutants at warm and cold ambient temperatures. Studied vehicles were a diesel car with a diesel particulate filter (DPF), two gasoline cars (with and without a gasoline particulate filter (GPF)), and a car using compressed natural gas (CNG). The impact of fuel aromatic content was examined for the diesel car and the gasoline car without the GPF. The results showed that the utilization of exhaust particulate filter was important both in diesel and gasoline cars. The gasoline car without the GPF emitted relatively high concentrations of particles compared to the other technologies but the implementation of the GPF decreased particle emissions, and the potential to form secondary aerosols in atmospheric processes. The diesel car equipped with the DPF emitted low particle number concentrations except during the DPF regeneration events. Aromatic-free gasoline and diesel fuel efficiently reduced exhaust particles. Since the renewal of vehicle fleet is a relatively slow process, changing the fuel composition can be seen as a faster way to affect traffic emissions.

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Automobile engines are the main source of harmful emissions into the atmosphere in large cities. These engines use gasoline or diesel fuel. The efforts of many scientists are aimed at developing measures to reduce the impact of gasoline engines on the environmental situation. Conversion of gasoline engines to gaseous fuel (methane) is considered in this article as an effective way to improve the environmental performance of automobile engines. An overview of research on this topic is given. The article provides a description of the technical characteristics for two gasoline engines that are converted to work on methane. The study was carried out on the basis of mathematical modeling of the engine operating cycle in the Diesel-RK program. A brief description of the mathematical model is presented. It is shown that the conversion of gasoline engines to methane leads to a decrease in power within 7.5% while simultaneously reducing the specific fuel consumption by up to 12%, and there is also a decrease in NOx emissions by 2-3 times. It has been established that the compression ratio of a methane engine has a significant impact on the technical and economic indicators. It was revealed that an increase in the compression ratio to 15 leads to an increase in the power of the gas piston engine to the level of a gasoline engine. At the same time, fuel consumption is reduced by up to 20%, and improved environmental performance is observed in comparison with a gasoline engine.

Considering the importance of alternative fuels in IC engines for environment safety, compressed natural gas has been extensively employed in SI engines. However, scarce efforts have been made to investigate the effect of compressed natural gas on engine lubricant oil for a long duration. In this regard, a comprehensive analysis has been made on the engine performance, emissions, and lubricant oil conditions using gasoline (G)92 and compressed natural gas at different operating conditions using reliable sampling methods. The key parameters of the engine performance like brake power and brake-specific energy consumption were investigated at 80% throttle opening within 1500–4500 range of r/min. For the sake of emission tests, speed was varied uniformly by varying the load at a constant throttle. Furthermore, the engine was run at high and low loads for lubricant oil comparison. Although compressed natural gas showed a decrease in brake-specific energy consumption (7.94%) and emissions content, (G)92 performed relatively better in the case of brake power (39.93% increase). Moreover, a significant improvement was observed for wear debris, lubricant oil physiochemical characteristics, and additives depletion in the case of compressed natural gas than those of (G)92. The contents of metallic particles were decreased by 23.58%, 36.25%, 42.42%, and 66.67% for iron, aluminum, copper, and lead, respectively, for compressed natural gas.

This study explores the potentiality of low/zero carbon fuels such as methanol, methane and hydrogen for motor applications to pursue the goal of energy security and environmental sustainability. An experimental investigation was performed on a spark ignition engine equipped with both a port fuel and a direct injection system. Liquid fuels were injected into the intake manifold to benefit from a homogeneous charge formation. Gaseous fuels were injected in direct mode to enhance the efficiency and prevent abnormal combustion. Tests were realized at a fixed indicated mean effective pressure and at three different engine speeds. The experimental results highlighted the reduction of CO and CO2 emissions for the alternative fuels to an extent depending on their properties. Methanol exhibited high THC and low NOx emissions compared to gasoline. Methane and, even more so, hydrogen, allowed for a reduction in THC emissions. With regard to the impact of gaseous fuels on the NOx emissions, this was strongly related to the operating conditions. A surprising result concerns the particle emissions that were affected not only by the fuel characteristics and the engine test point but also by the lubricating oil. The oil contribution was particularly evident for hydrogen fuel, which showed high particle emissions, although they did not contain carbon atoms.

Different fuels result in significant variations in physical and chemical properties, which directly affect combustion characteristics, performance efficiency, and emission levels. This study aims to conduct an experimental and numerical study on the effect of fuel‐type variation on the spark ignition (SI) engine performance represented by BP, T exh Texh , BSFC, and BTE as well as emissions of CO, CO2, and NOx. Experimentally, a single‐cylinder SI engine was tested using gasoline, a blend of 10% ethanol + 90% gasoline (E10), LPG, and biogas under full load conditions and different operating speeds (1200–3600 rpm). Numerically, Lotus Engine Simulation (v.6.01a) was used to simulate engine performance, and there was good agreement with the experimental results. The experimental results showed that gasoline fuel had the highest BP and BTE, while BSFC was lower than other fuels. For gasoline fuel, BP increased by 4.19%, 9.16%, and 25.2%, respectively, and BTE increased by 3.14%, 6%, and 10.4%, respectively, while BSFC decreased by 11%, 19.5%, and 32.5%, respectively, compared to E10, LPG, and biogas. As for emissions, it was observed that CO and CO2 emissions decreased by 12%, 25%, and 49.5%, respectively, and 3%, 5%, and 13%, respectively, for E10, LPG, and biogas compared to gasoline. Whereas the NOx emissions for gasoline decreased by 6.4% compared to LPG, while increasing by 7% and 20.2% compared to E10 and biogas, respectively. This study was characterized by previous studies by evaluating the performance and emissions of an SI engine using Iraqi fuels of different compositions.

In order to increase fuel economy and reduce pollutant emissions in the last decades light duty spark ignition (SI) engines have become smaller, supercharged and equipped with direct injection. A suitable alternative to oil derived fuel is represented by gaseous fuels, such as Natural Gas (NG) and Liquefied Petroleum Gas (LPG), whose higher knock resistance and better mixing capabilities substantially improve vehicle fuel economy and pollutant emissions. The simultaneous combustion of gasoline and gaseous fuel (Double-Fuel operation, DF) in a naturally aspirated SI engine has already been investigated in the past also by the same authors, proving remarkable results in terms of engine efficiency increment and exhaust emissions reduction. In this paper the authors present the results of a new methodical experimental study aimed to investigate engine performance, efficiency and pollutant emissions obtained on a supercharged SI engine operated in double fuel mode, with comparison to the use of “reference” pure fuels (i.e. gasoline and NG). A detailed heat release analysis is also performed with the aim to highlight the effect of fuel mixture composition (i.e. the proportion between gasoline and NG) and of charging pressure on the combustion speed.

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High exhaust temperature is an intrinsic nature of natural gas engines which underlies power de-rating and thermal aging of after-treatment system; therefore, this study integrates an organic Rankine cycle (ORC) system between engine and it's three-way catalyst (TWC) to address these challenges. ORC facilitates power output enhancement through exhaust energy recovery and alleviates thermal aging by reducing exhaust temperature. To estimate the effectiveness of this hypothesized system, a simulation-based investigation is performed. First, simulation models, including engine, TWC, and vehicle dynamic models, are built and validated by experimental data. According to the temperature characteristics of different TWCs, three scenarios, representing old, current, and prospective TWC technology, are formulated to estimate the ORC performance under Worldwide Harmonized Light Vehicles Test Cycle. Results show that ORC system can substantially alleviate the thermal damage caused by high exhaust temperature and extend TWC lifespan. It is estimated that over 98.5 % of thermal damage can be decreased by proper ORC setting, and the average TWC lifespan extension can be at least 55.4, making a reduced noble metal usage and cost of TWC. Meanwhile, with the decrease of the working temperature of TWC, ORC can recover exhaust energy under more road conditions, further improving the net power and shortening the payback period of extra ORC hardware costs. A reduction in the working temperature of TWC from 770.5 K to 618 K yields a 109 % enhancement in maximum power, coupled with a 62.30 % reduction in the payback period. These findings fully reflect the advantage of ORC-TWC coupling and indicate that ORC is supposed to be used more for the TWC with a low working temperature to maximize economic effectiveness. This study provides a novel pathway for thermal aging alleviation of TWC and a valuable reference for prospective studies on matching ORC with TWC under road conditions.

Fueling a compression-ignition engine with premixed natural gas offers the potential to combine a clean-burning, low-carbon fuel with a high compression ratio, high-efficiency engine. This work describes the development of a multi-cylinder 6.7 L diesel engine converted to run stoichiometric diesel micro-pilot/ natural gas premix combustion with a maximum diesel contribution target of 5% of the total fuel energy and a three-way catalyst aftertreatment system. Results are given by comparing the stoichiometric combustion to the diesel baseline operation, showing combustion characteristics differences, including the rapid two stage heat release. A high load output of 23 bar brake mean effective pressure was obtained with diesel-like brake thermal efficiency of 41%. This operating condition enabled a brake specific CO2 emissions reduction of up to 25% when compared to diesel. It was observed that the low load output is limited by combustion stability when operated at stoichiometric condition. The three-way catalyst is observed to run at peak efficiency with an equivalence ratio of 1.01. Injector fouling was observed through the inspection of the nozzle and its internal parts, indicating carbon build-up similar to that seen in injector coking mechanisms. A comparison of the developed engine to other engine technologies is given, showing that the diesel micro-pilot natural gas engine performance is in good standing among other diesel and gas engines in the market.

In this paper, ammonia (NH3) emissions of China-5 and three-way catalyst (TWC)-fitted China-6 heavy-duty NG vehicles and SCR-fitted China-6 diesel vehicles were characterized during real-road emission tests. The results showed that, due to side reactions within TWCs, real-world NH3 emissions of China-6 NG vehicles were significantly higher than those of their diesel counterparts and those of China-5 NG vehicles without TWCs. For China-6 NG vehicles, NH3 emissions occurred during the light-off of the TWCs and rich combustion. SCR-fitted China-6 heavy-duty diesel vehicles also had NH3 emissions mainly caused by excessive SCR reductant injection and leakage from ammonia slip catalysts (ASC). China-5 heavy-duty NG vehicles emit little NH3 for they utilized lean-combustion without SCR or TWC, where NH3 forms. Although lean combustion NG engines hardly have NH3 emissions, the extremely high engine-out NOx emissions restricted its further application.

A natural gas engine meeting the China VI emission standards was selected, and World Harmonized Transient Cycle (WHTC) tests under both cold and hot conditions were conducted using four types of fuels: low-calorific-value natural gas, high-calorific-value natural gas, liquefied petroleum gas, and commercially available natural gas. Simultaneous measurements were taken of particle number emissions with diameters above 10 nm (PN10) and above 23 nm (PN23) both before and after the three-way catalyst (TWC). The results show that PN10 under the cold WHTC cycle is 2.3 to 3.9 times, 2.0 to 3.0 times under the hot WHTC cycle and 2.1 to 3.1 times for the cold-hot weighting results compared with PN23 for this natural gas engine fueled with the four types of fuels. Compared with the hot WHTC, the raw PN10 emissions under the cold WHTC were 130% to 650% higher, and the tailpipe PN10 emissions were 228.6% to 837.5% higher. Fuels with multi-carbon components are more conducive to the formation of PN10 under hot conditions. The TWC has a limited effect on particulate number removal. Especially under cold conditions, it may even lead to an increase in PN emissions.

Due to the market presence that natural gas has and is expected to have in the future energy sector, research and development of novel natural gas combustion strategies to increase power density, lower total emissions, and increase overall efficiency is warranted. Dilution whether by excess air or by exhaust gas recirculation has historically been implemented on diesel, natural gas, and gasoline engines to mitigate various regulated emissions. In the large industrial natural gas engine industry, excess air dilution or ultra-lean-burn operation has afforded lean-burn engines increased power density and reduced NO x emissions. This advance in technology has allowed lean-burn engines to compete in markets such as electrical power generation which previously they had not been able. However, natural gas engines utilizing a non-selective catalytic reduction system or three-way catalyst must operate under stoichiometric conditions and thus are limited in power density by exhaust gas temperatures. In previous gasoline small engine research, a novel exhaust gas recirculation technique called dedicated exhaust gas recirculation was shown to have a positive impact on engine-out emissions of NO x and unburned hydrocarbons while also lowering exhaust component temperatures. This work seeks to understand the consequences of implementing a dedicated exhaust gas recirculation system on a multi-cylinder stoichiometric industrial natural gas engine. The results of this initial evaluation demonstrate reductions in engine-out NO x and CO emissions and improvements in engine-out exhaust gas temperatures with the dedicated exhaust gas recirculation technique. However, in a low-turbulence combustion chamber, dedicated exhaust gas recirculation significantly lowers the overall rate of combustion and results in significant differences in cylinder-to-cylinder combustion.

Increasingly restrictive limits on Oxides of Nitrogen - NOx levels and desire for low methane emissions from gas engines are driving the change from lean-burn to stoichiometric combustion strategies on heavy-duty on-highway natural gas engines in order to take advantage of inexpensive and effective three-way catalyst technology. The change to stoichiometric combustion has led to increased tendency for engine knock due to higher in-cylinder temperatures. To suppress engine knock, Exhaust Gas Recirculation (EGR) rates from 10 to 30% are used. While high EGR rates nominally improve Brake Thermal Efficiency (BTE) and reduce exhaust gas temperatures, they also slow down combustion. However, by deploying a controlled spark triggered homogeneous charge volumetric ignition, very short burn durations can be achieved without the destructive effects of engine knocking towards high efficiency gas engines. In the interest of achieving 45% BTE in spark ignited an on-highway class 8 truck engines fueled on natural gas and to meet EURO 6 and future California emissions standards of 0.02 gm/kw-hr NOx, Controlled Auto-Ignition (CAI) is herein demonstrated on a 15 liter truck engine. CAI is enabled by (a) having a combustion device capable of exceptionally good combustion stability in the presence of high EGR rates (COV of IMEP < 0.75 %), (b) cylinder pressure based combustion feedback, and (c) fast closed loop combustion control (using a Woodward RT-CDC control system). This system enables significant reduction in burn duration by controlling a two phase combustion event. The first phase is normal spark ignited propagating flame, which then triggers the second phase which is volumetric auto-ignition. The location and percentage of fuel that burns in the volumetric auto-ignition event is controlled relative to that which occurs via the conventional spark ignited flame propagation process by use of high speed combustion in the loop feedback control. Auto-ignition mass fraction burned (MFB) ratios of 25–50% have been achieved yielding higher heat release rates at the end of combustion than at the center of combustion with the result being a shortening of the combustion burn duration from a nominal 20–30 degrees to a near optimal 10–15 degrees even with EGR rates as high as 25%. A novel and patent pending burn duration control strategy is employed to stably maintain this knock-free combustion strategy even with compression ratio as high as 14:1. The benefits are significant increase in Brake Thermal Efficiency and substantial reduction in engine out methane emissions without sacrifice of transient responsiveness.

The urgent need to meet the stringent regulation requirements on sub-23 nm particles emissions is pushing the interest towards efficient strategies for their reduction, involving different propulsive technologies, including the Natural Gas engines. Although considered as particulate matter-free, the growing diffusion of Natural Gas Heavy-Duty engines as a key element in the low-term towards decarbonization, requires their compliance with upcoming regulations. The use of particulate filters, in combination with the Three-Way Catalyst (TWC), could represent a promising and viable solution to achieve high conversion of gas-phase criteria pollutants and high particles filtration efficiency. The present activity arose from a collaboration among research groups of CNR-STEMS, FPT Industrial and NGK Europe GmbH, two industrial companies leaders in the topics here addressed. Target of the work is the evaluation of the potentiality offered by the use of filters in the abatement of particles emitted by a Natural Gas engine. Particles number, mass and size distribution analysis have been performed over the World Harmonized Transient Cycles. The exhaust line was properly designed to foresee the installation of particulate filter downstream a conventional TWC, in a close-coupled configuration. The filtration efficiency of two filters, from hereon termed as CNG Particulate Filters (CPFs), with different wall thickness and cell structures and a filter with catalytic coating, was compared. High particle abatement efficiency was found for all the filters, with values close to 90%, without noticeable increases in backpressures. The CPF with standard porosity showed the best performance, while no further significant benefits were found with the addition of a catalytic coating. The performed analysis places in an important emphasis in view of the forthcoming EURO VII regulations on PN limits (PN10) and sets the basis and direction for further optimization in filter material properties and catalyst coating in meeting stringent PN emission targets.

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Over 50% of new refuse truck sales have been compressed natural gas (CNG). Compared to diesel, CNG is less expensive on diesel gallon equivalent (dge) basis. This study quantifies the real-world fuel use and tailpipe exhaust emissions from three front- and three side-loader refuse trucks, each with a spark ignition CNG engine, three-way catalyst, and similar gross weight. Measurements were made at 1 Hz using a portable emissions measurement system (PEMS). Inter-cycle and inter-vehicle variability is quantified. Effect of vehicle weight was analyzed and comparisons were made with MOVES predicted cycle average emission rates. In total, about 220,000 s of data covering 490 miles of operation were recorded. The average fuel economy was 1.9 miles per dge. On average the trucks spent 53% of time in idle, which includes trash collection activity. The average speeds were 10 mph and 5 mph, for front- and side-loader trucks, respectively. Overall, compared to side-loader trucks, front-loader trucks had 55% better fuel economy and 60% lower emission rates. Compared to diesel trucks, CNG truck cycle average NOx and PM emission rates, at 1.2 g/mile and 0.006 g/mile respectively, were substantially lower while CO and HC rates, at 29 g/mile and 6 g/mile respectively, were considerably higher. Fuel use and CO2 emissions rates increased by 10% due to increase in truck weight during trash collection, while CO emissions rates increased by up to 30%. Compared to measured values, MOVES estimated cycle average fuel use and CO2 emissions were 25% lower, CO emissions are 70% lower, and NOx emissions were 200% higher. Results from this study can be used to improve solid waste life cycle and tailpipe emission factor models and, when combined with previous studies on diesel refuse trucks, evaluate the effect on fuel use and emissions from adoption of CNG refuse trucks.

Although the transient NOx emissions produced from a typical range-extended hybrid vehicle can meet the requirements of the China VI emissions regulations, it is rather difficult to comply with Beijing VI emissions regulations. This is due to the fact that the sharp fluctuation in air-fuel ratio control during engine start-up period resulting in lower conversion efficiency for the three-way catalyst (TWC). In response to these issues, the potentials of different loading strategies in meeting Beijing VI were explored on a light-duty natural gas (NG) engine for range-extended hybrid application. The experiments were performed on the basis of typical Chinese City Bus Cycle (CCBC). This paper analyzed the operation characteristics of the typical range-extended hybrid NG vehicle and investigated the impacts of engine loading strategy on the vehicle’s performance and emissions during the start-up phase. Results showed that the transient NOx emissions of 30 s-averaged decreased from 786 to 504 ppm when extending the loading time from 3 to 40 s in a typical loading path (i.e. engine speed and load increased linearly). The transient NOx emissions could meet the Beijing VI NOx limit but with little margin. Research also investigated the use of a new designed engine loading strategy (i.e. engine speed and load with time-separated control manner). Results revealed that this method effectively curbed the transient NOx emissions, reducing the maximum transient NOx emissions of 30 s-averaged from 504 to 271 ppm. In comparison, this low NOx level was better to meet the Beijing VI with sufficient margin.

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Hybrid electric vehicles (HEVs) frequently cycle their internal combustion engines (ICE), potentially cooling the three-way catalyst (TWC). This challenges the use of compressed natural gas (CNG), as methane (CH4) requires high temperatures for TWC oxidation. This study experimentally investigates the performance, engine-out emissions (CO, NOx, CH4, NMHC, CO2), and catalyst temperatures of a Toyota RAV4 hybrid vehicle on gasoline (G), CNG, and dual fuel (MIX) during the WLTC. Engine-out emissions were measured upstream of the TWC. Results showed similar engine work output (~17.8 kWh/100 km), while CNG significantly reduced fuel mass consumption (−18.7%) and CO2 emissions (−27.5%) compared to gasoline, driven by both its higher LHV and higher average BTE. CO (−32.3%) and NOx (−34.0%) emissions were lower with CNG, linked to leaner operation and significantly retarded ignition timing for NOx control. However, CH4 emissions drastically increased with CNG. This study reveals a synergy between the same retarded ignition timing strategy used to successfully control engine-out NOx (−34.0%) and created a positive secondary effect, raising pre-TWC temperatures by 4.5%. Higher thermal condition is essential for the aftertreatment of chemically stable methane, highlighting a direct link between the engine’s NOx control logic and the potential to mitigate methane slip.

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Three-way catalyst (TWC) is the mainstream technology for stoichiometric natural gas vehicle gas emission purification to meet the China VI emission standard for heavy-duty vehicles. Due to the high price of Pd-Rh TWC widely used at present, it is of great significance to develop cheaper Pt-only catalysts as substitutes. However, there are few studies on Pt-only TWC, especially for natural gas vehicles. It remains a formidable challenge to develop Pt-only TWC with excellent activity and stability. In this study, we significantly improved the catalytic performance of Pt/CeO2 TWC through thermal treatment, especially steam treatment at 800 °C, and used XRD, TEM, H2-TPR, and XPS techniques to investigate how Pt/CeO2 can be activated via these treatments. Our results suggested that after these treatments, CeO2 crystallites sintered slightly, while platinum particles remained highly dispersed. Moreover, these treatments also weakened the Pt-CeO2 interaction, promoted the formation of oxygen vacancies in CeO2 support, and generated a new type of active surface oxygen in the vicinity of Ptδ+, thus improving the activity of the catalyst. After 800 °C steam treatment, the T50 of CH4 and NO decreased by 31 and 36 °C, respectively. The results obtained in this study provide implications for the synthesis of efficient Pt-based catalysts.

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To reduce air pollution worldwide, regulations on exhaust gas emissions from ships are becoming increasingly stringent. One fuel that is being considered as an alternative to replace the heavy fuel oil used in existing ship engines and thereby reduce harmful emissions, such as NOx, SOx, and greenhouse gases, is sulfur-free liquefied petroleum gas (LPG). To assess the viability of this alternative, it is necessary to understand propane reactivity, the main component of LPG, and develop after-treatment devices applicable to LPG engines. This research evaluated the performance of three prototype Pd-based three-way catalysts (TWCs) with varying Pd loadings (6.5, 4.1, and 1.4 g/L), focusing on their effectiveness concerning propane reactivity in LPG engines. For the fresh samples, catalysts with 4.1 g/L Pd demonstrated performance that was comparable to, or even surpassed, those containing 6.5 g/L Pd. Notably, the temperature of 50% conversion (T50) for NO and C3H8 in the fresh Pd-4.1 was lower by 14 °C and 10 °C, respectively, compared to the fresh Pd-6.5 sample, despite having 37% less precious-metal loading. However, after hydrothermal aging at 900 °C for 100 h, the performance of the 4.1 g/L Pd catalyst significantly deteriorated, exhibiting lower efficiency than the 6.5 g/L Pd catalyst. The study also delved into various probe reactions, including the water–gas shift and propane steam reforming. Advanced analytical techniques, such as N2 physisorption and scanning transmission electron microscopy, were employed to elucidate the texture and structural characteristics of the catalyst, providing a comprehensive understanding of its behavior and potential applications. Through this research, within the efforts of the maritime sector to address challenges posed by emission regulations and rising costs associated with precious metals, this study has the potential to contribute to the development of cost-effective emission control solutions.

In this study, a pre-matching method was developed based on measured performance parameters and theoretical calculations of turbochargers. First, the turbocharger of a natural gas engine was subjected to a comprehensive performance experiment. According to the experimental results, the maximum efficiencies of the turbine and compressor are 70% and 75%, respectively, and the efficiency of the turbine drops sharply from 70% to 56.6% as the pressure ratio increases from 1.25 to 2.4. In this thesis, a specific turbocharger pre-matching software has been developed in conjunction with a database. Three turbines and three compressors were selected from the self-developed database for matching and comparative study using this method. The simulation results showed that the maximum efficiency of turbine #1, #2 and #3 is 71.3%, 72.2% and 72.7%, respectively, and the efficiency of these three turbines is concentrated between 65% and 72.5%. Obviously, the maximum efficiency of the turbine has increased by 1.3–2.7% and the overall efficiency has improved after the pre-matching. Therefore, this developed pre-matching method can reduce time cost, improve work efficiency and engine performance, and is important for the design and development of turbochargers.

Three-Way Catalysts (TWC) undergo thermal degradation under high exhaust gas temperatures, reducing the specific surface areas of precious metals on the catalyst surface due to sintering. This also reduces the Oxygen Storage Capacity (OSC) and the TWC conversion rate. Lowering the exhaust gas temperature is a solution to minimize performance deterioration. However, low temperatures reduce the effectiveness of catalyst reactions. Perturbation (dithering or rich-lean cycle) can enhance the TWC conversion rate. In this work, synthetic gas reactor experiments are carried out to measure the purification performance data of fresh and degraded catalysts under rich-lean perturbations at 400°C. A TWC model with elementary reactions covering surface reactions and OSCs is developed. The degradation performances in the axial direction are reported. The results show that the conversion rates reach 90% within the first 30% of the catalyst length. For the catalysts with and without degradation, when the conversion rate declines, the reaction rates are slower than the mass fluxes, indicating that the reaction rates are the rate-limiting factor for each purification reaction. It is observed that the degraded catalysts have fewer active sites, and the amount of oxygen storage and consumption is small. Conversion rates of gas species, OSC, and mass flux of major species of the fresh and degraded catalysts are also compared.

This study investigates the impact of diesel pilot ignition (DPI) natural gas (NG) engine on combustion and emission characteristics across various exhaust gas recirculation (EGR) volumes. It utilizes a three-dimensional...

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To get rid of the combustion instability and knock in combustion of low-concentration coalbed methane in the large-bore engine, the combustion-supporting effect of passive pre-chamber was studied, exploring the influence of passive pre-chamber igniting position on the combustion in pre-chamber, jet characteristics and overall combustion. Three-dimensional fluid simulation was conducted to study the influence of igniting positions on the combustion performance of the engine by setting a fixed ignition time and changing the igniting position.The results show that as the igniting position lowers, the combustion rate in the pre-chamber slows down, the combustible mixture escaped from the nozzle hole during the cold jet duration decreases, and more heat is used for the hot jet to ignite the combustible mixture in the main combustion chamber. When the igniting position is 2mm away from the bottom of pre-chamber, the indicated thermal efficiency of the engine reaches its best, which is 1.6% higher than the one at original igniting position.

The oxygen storage in the Three-Way Catalyst (TWC) influences the removal efficiency of pollutants when the exhaust gas concentration deviates from the equivalence ratio. To calculate oxygen storage, a neural...

The synthesis of size-controlled ultrafine metal-based catalysts is vitally important for chemical conversion technologies. This study presents a spatial confinement strategy for the synthesis of Rh/CeO2-ZrO2 (0.5 wt % Rh) three-way catalysts with ultrafine Rh nanoparticles (1-3 nm). This strategy utilizes the self-confinement effect of Rh ions through the strong electrostatic adsorption between Rh ions and the surface of CeO2-ZrO2, as well as the spatial hindrance provided by the mesopores of the support during Rh particle growth. The nanoparticle catalyst (NPC) with a size of ∼2.19 nm exhibits high catalytic performance, surpassing the Rh single-atom catalyst (SAC) and the other NPCs with different Rh sizes in the three-way catalytic reaction under a gas mixture of carbon monoxide (CO), hydrocarbons (HCs), and nitric oxide (NO). Rh SAC displays higher CO oxidation activity and comparable C3H6 oxidation activity compared with Rh NPC in reaction atmospheres without NO gas molecules. However, the presence of NO molecules hinders the adsorption and reaction of CO and HCs on the Rh single-atom sites. The impact of NO on Rh NPC is weaker due to the multiatomic active center structure of the Rh nanoparticles, resulting in enhanced low-temperature catalytic activity in three-way reaction atmospheres. Additionally, NPC demonstrates better stability than SAC under hydrothermal aging condition.

There is an increased focus into the use of ammonia (NH3) and hydrogen (H2) as alternative fuels. Nonetheless, NOx emissions generation remains a substantial challenge for NH3/H2 operation. This study investigated the use of NH3/H2 blends at different energy substitution ratio (ESR) (i.e., the fraction of NH3 replaced by H2 in terms of energy content) and concentrations in a single-cylinder four-stroke heavy-duty compression ignition engine converted to spark ignition. The primary goal was to evaluate the effectiveness of various NH3/H2 energy substitution rates in achieving comparable combustion to methane (CH4), with minimal engine modifications. The effects of equivalence ratio (ϕ) on in-cylinder pressure, apparent heat release rate, indicated mean effective pressure and engine-out emissions were studied at medium load and constant spark timing. The results indicated that H2 addition led to an almost linear decrement in the flame inception duration and increment in flame propagation for investigated ϕ, and NOx emissions decreased for ϕ=0.7 and ϕ=0.8, while a small NOx variation was observed at ϕ=0.9. Unburned NH3 emissions reduced by 50% when ESR increased by 0.1. Similarly, nitrous oxides (N2O) emissions decreased. More, a moderate amount of H2 in the blend (ESR between 0.2 and 0.4) was enough to match CH4 combustion characteristics. There was a quasilinear correlation between equivalence ratio and energy substitution ratios to match CH4 behavior, suggesting a higher H2 fraction for stoichiometric operation. Finally, the results showed NOx emissions 5x higher than those of CH4 at ϕ=0.7 but lower at ϕ=0.9.

This numerical study explores the optimization of Prechamber Enabled Mixing-Controlled Combustion (PC-MCC) using natural gas in heavy-duty engines, aiming to enhance combustion efficiency to minimize methane slip and NOx emissions. The approach involves a prechamber ignition system, distinct from conventional spark ignition (SI) systems, to initiate combustion of direct injected natural gas. By leveraging the robust ignition characteristics of the prechamber, the PC-MCC method demonstrates significant potential in achieving efficient combustion akin to diesel engines but with lower greenhouse gas emissions. The research evaluates the effects of various geometric and operational parameters on the combustion process and emissions, including prechamber volume, nozzle diameter, direct injector (DI) geometry, and engine operating strategies. Computational Fluid Dynamics (CFD) simulations are utilized, focusing on a heavy-duty, single-cylinder engine modeled after the Caterpillar C9.3B engine. Key findings indicate that a prechamber volume of 3 cc, coupled with a nozzle diameter of 2.75 mm for two prechamber holes, strikes an optimal balance between combustion efficiency and emissions reduction. This configuration ensures robust combustion across a range of operating conditions while maintaining methane slip within targeted limits. Further investigation into DI geometry shows the significance of the injector umbrella angle and nozzle diameter in shaping the fuel-air mixing and combustion dynamics. An umbrella angle of 130° and a nozzle diameter of 300 microns are identified as optimal, promoting rapid and efficient combustion with minimized methane and NOx emissions. The study also investigates the impact of injection timing and pressure, highlighting their roles in controlling combustion timing and influencing emissions levels. Advanced injection timing is found to be crucial in achieving the desired low methane slip, whereas retarded injection timing assists to reduce NOx emissions while having a slight increase in methane emissions. Operating strategies incorporating various levels of Exhaust Gas Recirculation (EGR) are assessed for their effectiveness in further reducing emissions. The research demonstrates that a judicious combination of internal hot EGR and careful calibration of DI pressure and SOI timing can achieve significant reductions in NOx emissions while keeping methane slip under control. Specifically, an internal EGR level of 15%–25%, combined with DI pressures of 200–300 bar and injection timings at or after top dead center, is recommended. These findings contribute valuable insights into the development of advanced combustion techniques for natural gas engines, offering a viable pathway to reduce methane slip without compromising engine efficiency or performance. The PC-MCC system presents a promising solution for the future of heavy-duty natural gas engine technology to reduce methane emissions.

The tightening of environmental requirements has forced car manufacturers to look for various ways to reduce exhaust gas emissions. The existing structural solutions of internal combustion engines allow this type of pollution to be reduced by adjusting the intake valve timing. This is especially relevant when it comes to reducing spark ignition engine emissions when using natural gas as fuel. In this study, a wide range of intake valve timing adjustments from 24° to 54° every six crank angle degrees was taken at a constant engine speed (n = 2500 rpm) and different loads and fixed excess air ratios (λ = 1). The changes in oxygen (O2), carbon monoxide (CO), carbon dioxide (CO2), nitrous oxide (NOx), methane (CH4), and propane (C3H8) gas emissions were observed in the aforementioned intake valve timing range.

Liquefied natural gas (LNG) is increasingly used as a marine fuel due to its capacity to significantly reduce emissions of particulate matter, sulfur oxides (SOx), and nitrogen oxides (NOx), compared to conventional fuels. In addition, LNG combustion produces less carbon dioxide (CO2) than conventional marine fuels, and the use of non-fossil LNG offers further potential for reducing greenhouse gas emissions. However, this benefit can be partially offset by methane slip—the release of unburned methane in engine exhaust—which has a much higher global warming potential than CO2. This study presents an experimental evaluation of methane emissions from a RoPax vessel powered by low-pressure dual-fuel four-stroke engines with a direct mechanical propulsion system. Methane slip was measured directly during onboard testing and combined with a year-long analysis of engine operation using an Engine Load Monitoring (ELM) method. The yearly average methane slip coefficient (Cslip) obtained was 1.57%, slightly lower than values reported in previous studies on cruise ships (1.7%), and significantly lower than the default values specified by the FuelEU (3.1%) Maritime regulation and IMO (3.5%) LCA guidelines. This result reflects the ship’s operational profile, characterized by long crossings at high and stable engine loads. This study provides results that could support more representative emission assessments and can contribute to ongoing regulatory discussions.

Lean-burn gas engines have recently attracted attentions in the maritime industry, because they can reduce NOx, SOx and CO2 emissions. However, since methane (CH4) is the main component of natural gas, the slipped methane which is the unburned methane emitted from the lean-burn gas engines likely contributes to global warming. It is thus important to make progress on exhaust aftertreatment technologies for lean-burn gas engines. A Palladium (Pd) catalyst for CH4 oxidation is expected to provide a countermeasure for slipped methane, because it can activate at lower exhaust gas temperature. However, a deactivation in higher water (H2O) concentration should be overcome, because H2O inhibits CH4 oxidation. This study was performed investigates the effects of exhaust gas temperature or gas composition on active Pd catalyst sites to clarify CH4 oxidation performance in the exhaust gas of lean-burn gas engines. The authors developed the method of estimating effective active sites for the Pd catalyst at various exhaust gas temperature. The estimation method is based on the assumption that active sites used for CH4 oxidation process can be shared with the active sites used for Carbon mono-oxide (CO) oxidation. The molecular of chemisorbed CO on the active sites of the Pd catalyst can provide effective active sites for CH4 oxidation process. To clarify the effects of exhaust gas temperature and compositions on active Pd catalyst sites, the authors developed an experimental system for the new estimation method. This paper introduces experimental results and verifications of the new method, showing that chemisorbed CO volume on a Pd/Al2O3 catalyst is increased with increasing Pd loading in 250–450 °C, simulated as a typical exhaust gas temperature range of lean-burn gas engines. The results provide a part of the criteria for the application of Pd catalysts to the reduction of slipped methane in exhaust gas of lean-burn gas engines.

Dual fuel diesel-methane low temperature combustion (LTC) has been investigated by various research groups, showing high potential for emissions reduction (especially oxides of nitrogen (NOx) and particulate matter (PM)) without adversely affecting fuel conversion efficiency in comparison with conventional diesel combustion. However, when operated at low load conditions, dual fuel LTC typically exhibit poor combustion efficiencies. This behavior is mainly due to low bulk gas temperatures under lean conditions, resulting in unacceptably high carbon monoxide (CO) and unburned hydrocarbon (UHC) emissions. A feasible and rather innovative solution may be to split the pilot injection of liquid fuel into two injection pulses, with the second pilot injection supporting the methane combustion once the process is initiated by the first one. In this work, diesel-methane dual fuel LTC is investigated numerically in a single-cylinder heavy-duty engine operating at 5 bar brake mean effective pressure (BMEP) at 85% and 75% percentage of energy substitution (PES) by methane (taken as a natural gas surrogate). A multidimensional model is first validated in comparison with experimental data obtained on the same single-cylinder engine for early single pilot diesel injection at 310 CAD and 500 bar rail pressure. With the single pilot injection case as baseline, the effects of multiple pilot injections and different rail pressures on combustion emissions are investigated, again showing good agreement with experimental data. Apparent heat release rate and cylinder pressure histories as well as combustion efficiency trends are correctly captured by the numerical model. Results prove that higher rail pressures yield reductions of HC and CO by 90% and 75%, respectively, at the expense of NOx emissions, which increase by ∼30% from baseline. Furthermore, it is shown that post-injection during the expansion stroke does not support the stable development of the combustion front as the combustion process is confined close to the diesel spray core.

When using liquefied natural gas (LNG) as fuel for shipping, the sulphur emissions are negligible and low NOx and particle emissions can be reached together with lower CO2 emissions compared to diesel-based fuels. The drawback of LNG usage is the unburned fuel, i.e., methane can be found in the exhaust. Reliable emission detection and quantification will play a key role, as methane is also becoming regulated. In this study, different methods to measure methane are studied in the engine laboratory and on board with state-of-the-art engines. Four different measurement methods are found to give similar methane results with few exceptions. Measurements performed downstream of the methane abatement catalyst show that all instruments could detect the methane conversion efficiency to be above 95%. Comparing results from onboard studies to earlier published onboard studies with similar engines indicate that the engine (46 DF) behaved rather similarly, and the measurements carried out at different occasions on board by different devices and parties gave similar results. To measure total hydrocarbons, a flame ionization detector (FID) has generally been the accepted method (e.g., in NOx Technical Code). Based on this study, other methods as reliable as FID for methane measurement exist and these methods can also be utilized on board.

To meet stringent fuel sulfur limits, together with NOx limits, ships are increasingly utilizing dual-fuel (DF) engines operating with liquified natural gas (LNG) as the primary fuel. Compared to diesel, LNG combustion produces less CO2, which is needed in targeting the reduction of the shipping impact on the climate; however, this could be significantly interfered with by the methane emission formation. In this study, the methane emissions, together with other emission components, were studied by measurements onboard a state-of-the-art RoPax ferry equipped with two different development-stage engines. The results from the current standard state-of-the-art DF engine showed methane levels that were, in general, lower than what has been reported earlier from onboard studies with similar sized DF engines. Meanwhile, the methane emission from the DF engine piloting the new combustion concept was even lower, 50–70% less than that of the standard DF engine setup. Although the CO2 was found to slightly increase with the new combustion concept, the CO2 equivalent (including both methane and CO2) was smaller than that from the standard DF engine, indicating that the recent development in engine technology is less harmful for the climate. Additionally, lower NOx and formaldehyde levels were recorded from the new combustion concept engine, while an increase in particle emissions compared to the standard DF engine setup was observed. These need to be considered when evaluating the overall impacts on the climate and health effects.

This work experimentally examines the effect of methane (a natural gas surrogate) substitution on early injection dual fuel combustion at representative low loads of 3.3 and 5.0 bar BMEPs in a single-cylinder compression ignition engine. Gaseous methane fumigated into the intake manifold at various methane energy fractions was ignited using a high-pressure diesel pilot injection at 310 °CA. For the 3.3 bar BMEP, methane energy fraction sweeps from 50% to 90% were performed; while at 5.0 bar BMEP, methane energy fraction sweeps from 70% to 90% were performed. It is observed that minimum methane energy fraction is limited by maximum pressure rise rate leading to knock and maximum methane energy fraction is limited by a high coefficient of variation in netIMEP, which leads to high cyclic variations. For 3.3 bar BMEP, maximum pressure rise rate is 8 bar/°CA at 50% methane energy fraction while at 5 bar BMEP, it is 12 bar/°CA at 70% methane energy fraction. For 3.3 bar BMEP, engine-out NOx emissions decrease by 43 times when methane energy fraction increases from 50% to 90%, and it decreases by nearly 46 times when methane energy fraction increases from 70% to 90% at 5 bar BMEP. Engine-out unburned hydrocarbon emissions increase by nearly 9 times when methane energy fraction increases from 50% to 90% at 3.3 bar BMEP, and it increases by nearly 5 times when methane energy fraction increases from 70% to 90% at 5.0 bar BMEP. Engine-out carbon monoxide emissions increase by nearly 7 times when methane energy fraction increases from 50% to 90% at 3.3 bar BMEP and by nearly 5 times when methane energy fraction increases from 70% to 90% at 5.0 bar BMEP. In addition, cyclic combustion variations at both loads were analyzed to obtain further insights into the combustion process and identify opportunities to further improve fuel conversion efficiencies at low load operation.

Exhaust gas recirculation (EGR) in spark-ignited engines is a key technique to reduce in-cylinder NOx production by decreasing the combustion temperature. The major species of the exhaust gas in rich combustion of natural gas are hydrogen and carbon monoxide, which can subsequently be recirculated to the cylinders using EGR. In this study, the effect of hydrogen and carbon monoxide addition to methane on laminar burning velocity and flame morphological structure is investigated. Due to the broad flammability limit and high burning velocity of hydrogen compared to methane, this addition to the gaseous mixture leads to an increase in burning velocity, less emissions production, and a boost to the thermal efficiency of internal combustion engines. Premixed CH4-H2-CO-Air flames are experimentally investigated using an optically accessible constant volume combustion chamber (CVCC) accompanied with a high-speed Z-type Schlieren imaging system. Furthermore, a numerical code is applied to quantify the laminar burning velocity based on the pressure rise during flame propagation within the CVCC. According to the empirical and numerical results, the addition of hydrogen and carbon monoxide enhances laminar burning velocity while influencing the flame structure and development.

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As emissions regulations become increasingly stringent, the natural gas industry is seeking to retrofit their integral compressor engine fleet with real-time emissions control technology. The primary pollutants of concern for these engines are oxides of nitrogen (NOx) and methane. Unfortunately, there is often a tradeoff in abating these two chemical species. This paper discusses a potential control strategy for reducing both simultaneously. The strategy proposed in this work is two-tiered, consisting of slow-speed and cycle-by-cycle control of the fuel-air ratio. Its success hinges upon the ability to rapidly diagnose, learn, and predict the cycle-by-cycle thermodynamics and emissions of the engine. This work describes a zero-dimensional simulation created for this purpose. Simulated results for in-cylinder pressure and emissions are compared to experimental data for an actual engine. The simulation achieved very good agreement with the measurements and performed very well as a diagnostic tool, which bodes well for both the first and second tiers of the proposed control strategy. Future work will involve cycle-by-cycle NOx modeling and investigating how the simulation can be used to learn and rapidly predict cycle-by-cycle composition.

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Emissions of nitrogen oxides (NOx) from marine propulsion systems have gained public interest resulting in emission limits as defined by the International Maritime Organization (IMO) with IMO Tier III, especially for vessels operating in Emission Control Areas (ECA). The reduction of greenhouse gas emissions is also increasingly important for marine propulsion. Minimizing NOx while reducing climate impact calls for technologies such as the gas engine with aftertreatment systems, preferably with the ability to run on alternative fuels. A proven technology for reducing NOx in marine engines is the Selective Catalytic Reduction (SCR) aftertreatment system. It is also possible to avoid engine raw emissions by shifting the combustion process to lower temperature levels. Hydrogen is an alternative fuel with combustion properties enabling premixed operation at significantly higher air-fuel ratio than natural gas (NG) and thus, reducing raw NOx emissions. The study uses a systematic approach to compare emissions and efficiency of a lean-burn gas engine with a natural gas and a mild conversion hydrogen setup, utilizing two different strategies: combustion of NG with the assumption of an SCR catalyst and high raw NOx emissions and combustion of pure hydrogen using the NOx reduction potential of higher excess air. The scope of the study makes it possible to illustrate engine concepts for future applications in the displacement class of 4.8 L per cylinder. The highest efficiency of 45.3% was achieved with the natural gas engine and SCR. The concept with the lowest Global Warming Potential (GWP) was the hydrogen fueled engine under the prerequisite of using green hydrogen, accompanied by a reduction in efficiency of 0.6% compared to the efficiency optimum of NG with SCR. Assuming the use of gray hydrogen, the GWP was 48% and 52% higher than with NG and NG with SCR, respectively, at the efficiency-optimal operating points.

Impending and increasingly stringent emissions regulations regarding natural gas compressor engines drive the research behind blending hydrogen with natural gas to make these internal combustion engines and their combustion process more efficient. This investigation seeks to answer two fundamental questions: will blending hydrogen with natural gas reduce overall engine fuel consumption, and can greenhouse gas emissions be reduced by blending hydrogen with natural gas? A 4-cylinder Cooper–Bessemer GMV engine, housed at Colorado State University’s Powerhouse facility, was investigated for hydrogen–natural gas blending using multiple engine configurations. A lean-burn engine uses an active pre-combustion chamber as its ignition source, along with electronically activated high pressure fuel injection in the main combustion chamber. One configuration tested utilized high-pressure fuel injection and blending in hydrogen, up to 40% by volume, in both the main chamber and pre-combustion chamber fuel supplies. A second configuration, where the main combustion chamber fuel was solely natural gas and only the pre-combustion chamber received hydrogen-blended natural gas, was also tested. The final configuration to be tested used low pressure fuel injection with mechanically actuated valves in the main chamber with a traditional spark plug ignition source. All engine configurations saw reductions in methane emissions of up to 30% using blended natural gas and hydrogen. Carbon dioxide emissions were also shown to be reduced for the two configurations. A reduction in brake-specific fuel consumption of up to 2% was also seen for two configurations. These results support the hypothesis that blending hydrogen into natural gas can reduce engine total fuel consumption and reduce greenhouse gas emissions.

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Natural gas pipelines form a vital part of the energy infrastructure of the United States. In order to overcome head losses in moving the natural gas from one area of the country to another, large compressors are needed to pressurize the gas. For decades, the most efficient and cost-effective method of compressing the gas has been through the use of integral compressor engines. Pipeline companies have great financial incentive to continue using these engines, but increasingly stringent emissions regulations threaten their continued operation. In this study, the above problem was addressed by developing a zero-dimensional thermodynamic cycle simulation to predict NOx emissions for a large bore, single cylinder, naturally aspirated, 2-stroke, natural gas engine. Excellent agreement was obtained between experimental measurements and simulated predictions of the average exhaust NOx concentration. Once the simulation was validated by experimental data, a sensitivity analysis was conducted to determine the response of NOx emissions to changes in three factors: trapped equivalence ratio (TER), burned gas fraction (xb), and stuffing box temperature (SBT). This study sought to identify the fundamental thermodynamic reasons that NOx varied with each factor, and to quantify their respective effects. It was found that changes in each factor effected linear changes in the combustion temperatures, which effected linear changes in the rate constant of the first reaction in the extended Zeldovich mechanism, which effected exponential changes in the NOx emissions. TER and SBT were shown to be directly related to NOx, while xb was shown to be inversely related to NOx.

An emission prediction model was developed for a diesel/natural gas dual-fuel engine using PID-based search algorithm (PSA) optimized back propagation neural network (BPNN). The model utilized engine torque, speed, fuel injection timing and pressure, natural gas substitution rate, and excess air coefficient as inputs. Carbon monoxides (CO), nitrogen oxides (NOx), hydrocarbons (HC) and smoke emissions were the predicted outputs. The results showed that the PSA-BPNN model achieved superior performance compared to the BPNN. The mean absolute percentage error (MAPE) for CO, NOx, HC and smoke predictions were all below 6%, specifically, ranging from 4.2% to 5.8%. Additionally, all the coefficient of determination (R2) values surpassed 0.98, indicating high prediction accuracy and generalization ability. The PSA-BPNN model offers a promising new method for optimizing operating parameters and calibrating natural gas dual-fuel engines

This study investigates the effect of varying air-fuel ratios (AFR) on the performance and emission characteristics of a spark-ignition direct-injection (SI-DI) compressed natural gas (CNG) engine fuelled with enriched-carbon dioxide (CO2) natural gas mixture. The experimental work was conducted on a single-cylinder, four-stroke SI-DI engine operated at a constant speed of 3000 rpm and varying AFRs from stoichiometric (λ = 1) to lean mixtures (λ = 1.1, 1.2, and 1.3). The engine performance parameters analyzed include brake torque and brake specific fuel consumption (BSFC), while emission characteristics measured were carbon monoxide (CO), nitrogen oxides (NOx), unburned hydrocarbons (uHC), and carbon dioxide (CO2). The results indicate that the brake torque decreases progressively with increasing AFR, with a significant reduction of 50.5% at λ = 1.3 compared to the stoichiometric mixture. The BSFC initially decreases at λ = 1.1 but increases with further lean mixtures due to the reduced energy density of the enriched-CO2 fuel mixture. Emission analysis shows that NOx emissions decrease sharply with increasing AFR, reaching an 84.2% reduction at λ = 1.3. Conversely, unburned hydrocarbons increased due to incomplete combustion in leaner mixtures, peaking at 600.1 ppm/kW. CO emissions decrease by 81.8% at λ = 1.2 before a slight increase at λ = 1.3, while CO2 emissions peak at λ = 1.2 and decline thereafter. These findings demonstrate the trade-offs between engine performance and emission control with varying AFR and highlight the potential of enrihed-CO2 natural gas as an alternative fuel with optimized air-fuel ratios.

Natural gas (NG) is a potential substitute for diesel in engine applications because of its potential to reduce greenhouse gas and toxicant emissions. To maximize the benefits of NG, robust diagnostic methods are required to quantify concentration of unburned methane in the exhaust stream, without requiring frequent sensor recalibration. A wavelength modulation spectroscopy sensor has been developed to measure CH4 slip from NG engines. The sensor uses the first-harmonic-normalized, second-harmonic (2f/1f) processing method to perform long-duration, logging measurements at 20 Hz on an NG-powered marine vessel. Calibration-free 2f/1f measurements were shown to match calibrated 2f/1f measurements with an average error of 2.17% over the course of a 3 h sailing.

Compressed natural gas (CNG) in dual-fuel diesel engines offers environmental benefits but significantly increases unburned methane (CH4) emissions, especially at low engine loads. This study investigates the effectiveness of different catalytic converters in methane oxidation under transient test conditions (WHTC). Three types of catalysts (Pt-, Rh-, and Pd-based) were evaluated using a combined approach of empirical engine bench tests and mathematical modelling. The results showed that, under actual exhaust gas temperature conditions, the average methane conversion efficiencies were 3.7% for Pt, 17.7% for Rh, and 31.3% for Pd catalysts. Increasing the exhaust gas temperature by 50% improved the conversion efficiencies to 7.3%, 51.8%, and 69.2%, respectively. Despite this enhancement, none of the catalysts reached the 90% efficiency threshold required to increase the CNG content of the fuel beyond 6% without exceeding emission limits. The results highlight the need for high-activity Pd-based catalysts and optimised thermal management strategies to enable the broader adoption of dual-fuel engines, while complying with Euro VI standards.

The pursuit of achieving zero carbon emissions by 2050 has led to the implementation of green technologies in the maritime industry. One crucial aspect is the adoption of alternative fuels, with a focus on non-fossil fuels to enhance energy efficiency and minimize emissions during ship operations. This study explores the innovative dual fuel diesel – Compressed Natural Gas (CNG) technology, which offers relatively low emissions with uncomplicated modifications to the diesel engine. CNG is injected into the intake manifold, addressing the need for cleaner fuel options. However, the evolution of this technology has encountered challenges such as methane slip resulting from incomplete combustion. This research proposes an intervention using hydrogen within the combustion chamber to improve combustion quality. Oxy-hydrogen gas (HHO), a carbon-free fuel derived from water through electrolysis, is considered as a potential solution. The utilization of HHO serves as a substitute for pure H2 due to its more feasible production and application, considering the global limitations in hydrogen storage and usage in transportation. The study aims to investigate the impact of HHO on the performance and emissions of dual fuel engines. Experimental tests are conducted under low loads to simulate critical operational points of the engine. Results indicate that the dual fuel system exhibits significant fuel savings, particularly with increasing injection duration. However, the need for additional oxygen to enhance combustion perfection must be balanced. HHO injection demonstrates the potential to improve engine performance, leveraging the oxygen content in HHO and the positive characteristics of hydrogen with its high Lower Heating Value (LHV). Furthermore, the research suggests that HHO injection can mitigate methane slip issues associated with dual fuel engine operations, offering a promising avenue for emission reduction

Diesel engines are widely used due to their higher reliability and superior fuel conversion efficiency. However, they generate significant amount of carbon dioxide (CO2) and particulate matter (PM) emissions. Natural gas is a low carbon and clean fuel that generates less CO2 and PM emissions than diesel during combustion. Replacing diesel by natural gas in internal combustion engines helps reduce both CO2 and PM emissions. A practical and efficient way to replace diesel by natural gas is natural gas-diesel dual fuel combustion. One concern for natural gas-diesel dual fuel combustion engines is the methane slip which offsets the advantage of low CO2 and PM emissions of natural gas combustion. Hydrogen enrichment enhances the burning rates and extends flammability limits of hydrocarbon fuels, and therefore has potential to help address the issue of methane slip in natural gas-diesel dual fuel engines. This paper investigated the effect of hydrogen enrichment on combustion and emissions of a heavy duty natural gas-diesel dual fuel engine at low and medium load conditions. About 45% volume based hydrogen was blended with natural gas and introduced into the cylinder via engine intake manifold of a single cylinder heavy duty research engine. Overall 75% diesel was displaced by hydrogen enriched natural gas. The results revealed that hydrogen enrichment reduced methane emissions by about 44 to 58% at the investigated conditions. Meanwhile, hydrogen enrichment also improved engine efficiency at most operation conditions, especially when methane slip was significant. As a result, hydrogen enrichment helped reduce CO2 equivalent emissions by about 17 to 38% compared to natural gas only – diesel dual fuel operation, although the overall energy fraction from hydrogen in the fuel input to the cylinder was less than 15%. Hydrogen enrichment also significantly decreased carbon monoxide emissions. A side effect of hydrogen enrichment was the increase in NOx emissions.

A diesel methane dual fuel engine appears as a potential means for lowering emissions while retaining useful thermal efficiency. Ansys Forte 2023 R1 CFD software was employed to analyze the combustion parameters, performance attributes, and emissions characteristics of a methane‐diesel dual‐fuel engine at various spray angles of 100°, 105°, 110°, 115°, and 120°. Simulation is performed under 0.44 MPa load, 50% methane energy share, and −7° after TDC start of injection. Methane is injected into the intake manifold for premixing with air. Peak cylinder pressure increased as the spray angle (SA) raised to 110°. Thereafter, it slightly decreased to 120° SA. Lower combustion duration is obtained at 14.98° at 110° SA. The maximum thermal efficiency was found to be 32.04% with a low indicated specific fuel consumption of 289.43 g/kWh at 105° SA. Comparative performance is obtained from 110° SA. UHC and VOC is found to be minimum in 100° and 105° SA; thereafter, Unburned Hydrocarbons (UHC) and Volatile organic compounds (VOCs) increase rapidly. NO X emission trends first increased up to 110° SA and then decreased. Higher CO emissions were observed at 100° SA and then decreased with increasing spray angle up to 110°; however, CO emissions increased slightly. Fuel vapor mass fraction and temperature contours ensured low diffusion burning for 115° and 120° SA, resulting in unmixed remaining unburned methane and a sharp increase in UHC emissions. O and OH radical formation is hindered for converting by CO 2 from CO at 120° SA due to quenching. The optimal spray angle was determined as 110°, which provided an excellent balance of efficient burning, consistent pressure progression, and acceptable emissions.

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Shipping is a highly energy-intensive sector, and fleet decarbonization initiatives can significantly reduce greenhouse gas emissions. In the short-to-medium term, internal combustion engines will continue to be used for propulsion or as electricity generators onboard ships. Natural gas is an effective solution which can be used to mitigate greenhouse gas emissions from the marine sector. Considered to be a transitional fuel, it can provide a potential reduction in CO2 emissions of around 20–30%, compared with conventional marine fuels. This work investigated the influence of diesel-injection strategies on the performance and emissions of a single-cylinder prototype compression-ignition engine for marine applications, retrofitted to run as a Low-Pressure Dual-Fuel Engine using natural gas. Two different injection systems were used: a mass flow controller enabling continuous-mode gas feeding, and a Solenoid-Operated Gas Admission Valve for marine applications, the latter allowing phased natural-gas injection. Experimental tests were focused on partial-load conditions, which are critical for dual-fuel engines, with a natural gas/diesel mass ratio of 4:1. Phased injection resulted in reductions in fuel consumption, compared to continuous mode, of up to 11%. Further experiments demonstrated reductions in fuel consumption of up to 20.7% (in equivalent diesel); on the other hand, the unburned hydrocarbon emissions which resulted were an order of magnitude larger than the reference values for full diesel, reducing the benefits in terms of greenhouse gas emissions, with a reduction in Global Warming Potential of only 3% compared to full diesel.

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A conventional diesel engine when operated in the reactivity-controlled compression ignition (RCCI) combustion strategy faces challenges of high total hydrocarbon (THC) and carbon monoxide (CO) emissions leading to poor combustion efficiency at low engine loads. The oxides of nitrogen (NOx) versus smoke trade-off, encountered in conventional diesel combustion, is replaced by the NOx-THC trade-off in the RCCI operation. This work focuses on addressing the NOx-THC trade-off issue by systematically investigating the effects of engine control variables, such as, fuel injection timing, exhaust gas recirculation (EGR) and intake throttling, on a light duty compression ignition engine running in a methane-diesel dual fuel mode. The engine is operated at a load of 3 bar gross indicated mean effective pressure and at a speed of 1500 rev/min. Based on relationships identified between engine control variables, combustion parameters, emissions and engine performance, a bottom-up approach is used to combine the control variables synergistically to improve the NOx-THC trade-off. A combination of advanced start of injection timing of diesel (−35 degree crank angle (°CA) after top dead centre), 50% premix ratio and 55% EGR levels along with the end of port fuel injection of methane in the middle of the intake stroke (−270°CA), has resulted in a ∼34 percentage points (from 56% to 90%) improvement in combustion efficiency and a ∼9.5 percentage points improvement in thermal efficiency compared to the baseline low load dual fuel operation while maintaining good combustion stability. THC emission is reduced from 105 to ∼25 g/kWh whilst maintaining low levels of NOx (<0.3 g/kWh).

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The development of catalysts for low-temperature methane combustion is crucial in addressing the greenhouse effect. An effective industrial catalyst strategy involves optimizing noble metal utilization and boosting metal–metal interaction. Here, the PdNi-H catalyst was synthesized using the self-assembly method, achieving the high dispersion and close proximity of Pd and Ni atoms compared to the counterparts prepared by the impregnation method, as confirmed by EDS mapping. The XRD and TEM results revealed Pd2+ and Ni2+ doping within the CeO2 lattice, causing distortions and forming Pd-O-Ce or Ni-O-Ce structures. These structures promoted oxygen vacancy formation in CeO2, and this was further confirmed by the Raman and XPS results. Consequently, the PdNi-H catalyst demonstrated an excellent redox ability and catalytic activity, achieving lower ignition and complete methane burning temperatures at 282 and 387 °C, respectively. The highly dispersed PdNi species played a pivotal role in activating methane for enhanced redox ability. Additionally, the narrow size distribution range contributed to more vacancies on the surface of CeO2, as confirmed by the XPS results, thereby facilitating the activation of gas phase oxygen to form oxygen species (O2−). This collaborative catalytic approach presents a promising strategy for developing efficient and stable methane combustion catalysts at low temperatures.

Dual-fuel combustion technology allows for lower emissions of particulate matter (PM) and nitrogen oxide (NOx). However, under low load conditions, this mode of combustion has large amounts of emissions of carbon monoxide (CO) and unburned hydrocarbons (HCs) and low thermal efficiency. Several solutions have been presented to solve the issues associated with this operating mode. Optimizing the injection strategy is a potential method to enhance engine performance and reduce emissions, given that the injection parameters have significant effects on the combustion process. The present investigation optimized a methane/diesel dual-fuel engine’s emissions and performance using response surface methodology (RSM). Three parameters were investigated as input variables: dwell time (DT), diesel pre-injection timing (IT), and engine load (EL). RSM was used to optimize brake thermal efficiency (BTE), NOx emissions, and HC emissions, aiming to identify the best combination of these input factors. The RSM analysis revealed that the optimal combination of input parameters for achieving maximum BTE and minimum NOx and HC emissions is an 87% engine load, an 8° crank angle (CA) dwell time, and a 11° bTDC pre-injection timing. The RSM model demonstrated high accuracy with a prediction error less than 4%.

Natural gas (NG) injection timing of port-injection dual fuel engine has effects on its performance and emissions. The influence of the NG injection timing on the efficiency, the combustion and the emissions of the marine micro pilot ignition (MPI) dual fuel engine (substitution of 99%) is investigated by using the Computational Fluid Dynamics (CFD) method in this paper. The working processes of the different NG injection timing under different loads are simulated respectively. The results show that too early the NG injection causes the gas scavenged away from the exhaust valve during the valve overlap. Retarding NG injection timing under the high load will cause the $\mathrm{NO}_{\mathrm{x}}$ emissions increase first and then decrease, and has lower the Unburned Hydrocarbon (UHC) emission than that under the partial load. More than $90 \%$ UHC emission amount comes from the unburned methane (CH4). In order to improve the indicated efficiency and the emission, the NG injection timing under different loads has been optimized, which provides a useful reference for improving the performance of the marine medium-speed dual fuel engine.

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In this study, the characteristics of micro-pilot dual-fuel combustion with respect to the fuel mixture ratio in a single cylinder dual-fuel engine have been investigated. In order to analyze the characteristics of micro-pilot dual-fuel combustion, a metal engine and an optical single cylinder dual-fuel engine were used. The fuel mixture ratio was varied for experimental purposes; the diesel was directly injected into combustion chamber and the methane gas was supplied via intake port. The present study reports that increasing the methane mixture ratio from 0 to 97.67% changes the diesel combustion to pre-mixed combustion. As a result, the peak cylinder pressure was increased from 184 to 198 bar, and the rate of heat release was greatly advanced. In the MPDF condition, the nitrogen oxides emissions were reduced by about 90%p, and the fuel conversion efficiency increased about 5%p because of the low combustion temperature of pre-mixed combustion. However, for the same reason, the hydrocarbon emissions were increased about 95%p. The fastest combustion speed was found form the results of methane mixture ratio between 40 and 80%. In the condition of diesel combustion and micro-pilot dual-fuel combustion, the combustion periods of middle and initial were increased, respectively, resulting in the low combustion speed. The standard deviation of peak cylinder pressure, which represents the combustion variation, was correlated with initial combustion period. While the condition of methane gas mixture ratio between 40 and 80% shows the lowest combustion variation, the highest combustion variation was occurred by MPDF condition. Through the optical engine experiment, it can be found that the cycle to cycle combustion variation is ascribed to the turbulent flow and the variation of ignition position. The combustion images show that the unpredictable characteristics of the ignition position and slow flame propagation speed caused the combustion variation in micro-pilot dual-fuel combustion.

The piston bowl shape plays a crucial role in turbulence, swirl, and subsequent fuel-air mixing, which in turn affect combustion, emissions, and performance attributes. A cylinder stepped and modified re-entrant combustion chamber was investigated through Ansys Forte 2023 R1 CFD software to analyze combustion, emission, and performance characteristics in a diesel-methane dual-fuel engine. Numerical investigation is performed under 0.44 MPa load, 50% methane energy contribution, 7° start of injection bTDC, and with a 120° spray angle. Methane is injected into the inlet manifold to be premixed with air. The maximum thermal efficiency was found to be 34.11%, and a specific fuel consumption of 270.44 g/kW-h was indicated by the modified re-entrant bowl shape. The combustion duration for a modified re-entrant is 6.73% and 14.38% higher than that of a cylinder and stepped bowl. Higher combustion efficiency, combustion duration, and total apparent heat release demonstrate sustained combustion in the modified re-entrant bowl. Strong early premixed combustion in a cylinder-shaped bowl gives the highest percentage of NOx. The stepped bowl has fuel-rich zones near the center after 19° CA, with lower temperatures near the center, giving higher amounts of UHC and VOC emissions. The amount of O and OH radical formation in the modified re-entrant bowl was lower, and delayed oxidation resulted in a higher amount of CO emission. The modified re-entrant bowl offered the best combustion, performance, and emission attributes among the bowl shapes.

In this study, a novel dual-fuel combustion strategy is investigated, employing late pilot injection in diesel–methane engines to improve performance and reduce emissions. The engine was first tested with conventional diesel and methane, exploring a wide range of pilot injection timings, injection pressures, and intake boost pressures. Subsequently, experiments were repeated using a methane/hydrogen blend to assess the influence of hydrogen addition. Results show that, when using only methane, delayed pilot injections have minimal effects on engine performance. In naturally aspirated operation, unburned hydrocarbons and carbon monoxide are reduced, while in supercharged conditions, emissions increase; however, they remain within acceptable limits. Nitrogen oxides and particulate matter reach their lowest levels with delayed injection. Introducing hydrogen reduces engine performance and hydrocarbons and carbon monoxide emissions; notably, it suppresses the typical nitrogen oxides increase associated with hydrogen, while also lowering particulate matter. These findings demonstrate that combining late pilot injections with hydrogen addition and supercharging is a promising strategy for improving dual-fuel engine efficiency and emissions, offering a potential pathway toward cleaner combustion.

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Phased injection of natural gas into internal combustion marine engines is a promising solution for optimizing performance and reducing harmful emissions, particularly unburned methane, a potent greenhouse gas. This innovative practice distinguishes itself from continuous injection because it allows for more precise control of the combustion process with only a slight increase in system complexity. By synchronizing the injection of natural gas with the intake and exhaust valve opening and closing times while also considering the gas path in the manifolds, methane release into the atmosphere is significantly reduced, making a substantial contribution to efforts to address climate change. Moreover, phased injection improves the efficiency of marine engines, resulting in reduced overall fuel consumption, lower fuel costs, and increased ship autonomy. This technology was tested on a single-cylinder, large-bore, four-stroke research engine designed for marine applications, operating in dual-fuel mode with diesel and natural gas. Performance was compared with that of the conventional continuous feeding method. Evaluation of the effect on equivalent CO2 emissions indicates a potential reduction of up to approximately 20%. This reduction effectively brings greenhouse gas emissions below those of the diesel baseline case, especially when injection control is combined with supercharging control to optimize the air–fuel ratio. In this context, the boost pressure in DF was reduced from 3 to 1.5 bar compared with the FD case.

Two-wheelers emissions have been reduced by using sustainable fuels, mainly biogas, in conjunction with adsorbents made from corncob charcoal. Biogas is obtained by purifying biogas from fermented cow dung. In addition, activated charcoal adsorbents obtained from corn cobs are used in the biogas purification process. This process yields biogas with a methane concentration of 93.4%. Purified biogas is then mixed with liquid fuel. Therefore, this study employs the dual fuel combustion method, in which liquid fuel serves as the pilot fuel. The experiment was conducted by introducing biogas at a rate of 1 L/minute and without load at a constant engine speed of 900 rpm. The findings demonstrate a strong synergy between biogas and activated carbon adsorbents in significantly reducing CO and HC emissions. Notably, the adsorbent's capacity to adsorb exhaust emissions improves as the concentration of NaCl activator in activated charcoal increases. HC emissions can be reduced by up to 20%, while CO emissions can be reduced by up to 5.6%. However, CO emissions show an increase, particularly during biogas combustion. Yet, this increase is reversed when combined with activated charcoal adsorbent. The NaCl activator has been proven to widen charcoal pores effectively, enhancing absorption efficiency.

Computational fluid dynamics simulations are performed to investigate the combustion and emission characteristics of a diesel/natural gas dual-fuel engine. The computational fluid dynamics model is validated against experimental measurements of cylinder pressure, heat release rate, and exhaust emissions from a single-cylinder research engine. The model predictions of in-cylinder diesel spray distribution and location of diesel ignition sites are related to the behavior observed in measured and predicted heat release rate and emissions. Various distributions of diesel fuel inside the combustion chamber are obtained by modifying the diesel injection timing and the spray included angle. Model predictions suggest that the distribution of diesel fuel in the combustion chamber has a significant impact on the characteristics of heat release rate, explaining experimental observations. Regimes of combustion in the dual-fuel engine are identified. Turbulent flame speed calculations, premixed turbulent combustion regime diagram analysis, and high-temperature front propagation speed estimation indicated that the dual-fuel combustion in this engine was supported by successive local auto-ignition and not by turbulent flame propagation.