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Hydrogen is a renewable fuel with excellent combustion characteristics. However, the direct use of hydrogen in existing engines faces obstacles such as abnormal combustion and high NOx emissions. This study proposes a strategy for controlling the combustion and emissions performance of a port-injection (PI) hydrogen internal combustion engine using ethanol direct injection (DI). The test conditions are 1000 rpm, 1500 rpm, and 2000 rpm respectively, the excess air coefficient is 1, 1.5, and 2, and 3%, 6%, and 9% ethanol is added. The results showed that the addition of ethanol can significantly reduce the pressure rise rate of the hydrogen engine and prolong CA0-10 and CA10-90. The addition of ethanol can promote the BMEP and BTE of the hydrogen engine. The addition of ethanol can reduce NOx emissions under lean burn conditions by 18%. The disadvantage is that the addition of ethanol increases the hydrocarbon emissions of hydrogen engines by about 50%, but the total amount is less. After the addition of ethanol, the flashback phenomenon of the hydrogen engine was significantly improved. [Display omitted] • Proposed ethanol-controlled hydrogen engine backfire strategy. • Studied the effect of ethanol addition on hydrogen engines. • The addition of ethanol increases CA0-10 and CA10-90. • The addition of ethanol improves engine BMEP and ITE. • The addition of ethanol reduces NOx emissions from hydrogen engines. [ABSTRACT FROM AUTHOR]

Syngas is a fuel with a huge market and low carbon emission, which has been proven to be well applied to internal combustion engines. WRE with high power density can effectively improve the power characteristic when syngas is employed as fuel in engines, however, which has not been reported publicly. This work aims to provide insights into the performance of syngas-fueled WRE under different CO/H2 ratios and thus gives theoretical guidance for its application. The test is done at 1500 r/min and part load. It is found that with the increase of the volumetric ratio of CO in syngas (CO%), the efficiency, torque and carbon emissions are deteriorated, however, the NO emission is significantly improved and the knock level is also reduced. In addition, on the premise of constant CO%, a high brake thermal efficiency, low NO emission and knock intensity can be achieved at lean combustion. In particular, when CO% is 10%, the combustion efficiency of CO is independent of the excess air ratio, while when CO% is 20%, that is decreased with increasing excess air ratio. In summary, the syngas-fueled WRE is recommended to adopt the qualitative control and the syngas with low CO%. • Insights into the performance of syngas-fueled Wankel rotary engines. • The trade-off relationship among power, efficiency and NO emission needs to be considered. • Qualitative control and low CO% are recommended in the syngas-fueled WRE. • The combustion efficiency of CO at varied λ is closely related to CO%. [ABSTRACT FROM AUTHOR]

Ammonia and hydrogen are two carbon-free alternative fuels for engines. Considering that there are few studies on improving an ammonia-hydrogen engine's lean combustion performance, this investigation based on an engine with the Miller cycle employs hydrogen direct injection (HDI) and NH 3 port injection and then proposes an adjustment strategy to vary the start of injection (SOI) of HDI for affecting the engine combustion process. When ammonia volume share (AVS) is greater than 50%, the engine shows poor performance. Nevertheless, the stratification effect of hydrogen jets may be used to elevate the hydrogen concentration around spark plug by properly delaying SOI and then creating the locally rich mixture with a high hydrogen share, which prominently promotes the flame kernel formation, shortens CA0-90, reduces C o V P m a x , and enables the engine to reach approximately 36% BTE. It is notable that very late SOI can slightly deteriorate the heat release process and lower engine performance. • Ammonia-hydrogen engines have poor combustion process under lean conditions. • A strategy to improve the lean combustion performance of the engine is proposed. • Effects of NH 3 –H 2 premixing and H 2 stratification effect on the engine are balanced. • Properly delaying SOI enhances the ignition and combustion process of the engine. [ABSTRACT FROM AUTHOR]

The hydrogen-fueled Wanke rotary engine is a promising power system that has both high power and eco-friendly properties. This work investigated the effect of ignition timing on a dual-spark plugs synchronous-ignition hydrogen-fueled Wankel rotary engine under low speed, part load and lean combustion. The results show that with delaying the ignition timing, CA0-10 is shortened first and then lengthened and CA10-90 is consistently shortened. When the CA50 is located between 35 and 40°CA ATDC, the maximum brake torque can be realized. Besides, the selection of ignition timing needs to consider the "trade-off" relationship between the combustion phase and corresponding in-cylinder pressure. The maximum brake torque ignition timing is between 5 and 10°CA ATDC. And there is also a "trade-off" relationship between stability and thermal load when ignition timing is selected. In addition, HC and NO emissions will not become the problem limiting the power performance of hydrogen-fueled Wankel rotary engine under this operating condition. • A modified synchronous ignition hydrogen Wankel rotary engine was used. • The effect of ignition timing on performance of rotary engine was studied. • The power depends mainly on the in-cylinder pressure near 135°CA ATDC. • Selecting ignition timing needs to weigh the stability and thermal load. • Suitable ignition timing makes CA50 located between 35 and 40°CA ATDC. [ABSTRACT FROM AUTHOR]

The present work proposes the application of CH 4 and H 2 synergy to improve the performance of the Wankel rotary engine (WRE). The whole work was experimentally conducted at 1500 r/min. The results indicate that CH 4 WRE can achieve similar power and significantly higher thermal efficiency than gasoline WRE based on quantitative control, with a maximum absolute efficiency improvement of 11.4%. At the same time, it also can achieve 64% and 77% maximum reduction of CO and NO emissions, respectively. CH 4 –H 2 synergy can further improve the performance of CH 4 -fueled WRE, which can broaden the lean flammability limits and make qualitative control application possible. Compared with CH 4 WRE with quantitative control, qualitative control hybrid fuel WRE can achieve a maximum relative improvement of 6.54% in brake thermal efficiency and significantly reduced NO and CO emissions. However, the extent of qualitative control is limited by cyclic variation. Overall, CH 4 –H 2 synergy can be a potential alternative to elevate the performance of WRE, the key to which is the reasonable match of synergy level and qualitative control extent. • Comparison of performances between CH4 and gasoline Wankel rotary engines. • CH4 has significant advantages in efficiency, CO and NO emission than gasoline. • CH4–H2 synergy can further improve the performance of the CH4 Wankel rotary engine. • Blending H2 coupling qualitative control is a good load control model in CH4 WRE. [ABSTRACT FROM AUTHOR]

Amid growing environmental concerns, hydrogen (H 2) is emerging as a prospective alternative fuel for driving internal combustion engines. Employing lean combustion technology in tandem with turbulent jet ignition (TJI) has the potential to enhance combustion rates while mitigating NO x emissions. Therefore, an experiment was developed to investigate the combustion characteristics of ultra-lean premixed H 2 /air by TJI. An active pre-chamber (PC) with an additional H 2 supply was selected. Moreover, the effect of nozzle structures and equivalence ratio was discussed. The results show that with a nozzle diameter of 3 mm and an elevation of Φ PC to 1.4, the lean flammability limit is extended to an equivalence ratio of 0.13, with a consistently stabilized ignition delay within 4 ms. Increasing the nozzle number also extends the lean flammability limit, but it incurs higher energy losses. Additionally, two ignition mechanisms exist in TJI: flame ignition and combined ignition. The transition from flame ignition to combined ignition commonly occurs when the equivalence ratio of the main chamber drops below 0.3. This transition typically results in higher peak pressures and burnt fuel ratio, lower combustion duration, and longer ignition delay. • A comparison of the ignition characteristics between TJI and SI was conducted. • The hydrogen jet flame could promote early combustion of ultra-lean H 2 /air. • The effect of the nozzle and pre-chamber equivalence ratio was evaluated. • Two ignition mechanisms of TJI were found. [ABSTRACT FROM AUTHOR]

• A CFD model of spark-ignited gasoline rotary engine was established and verified. • H 2 was direct injected to chamber by varying HIPs and HNDs in the critical state. • Flame spread, combustion pressure and HRR decreased with the increased HND and HIP. • The optimal engine performance was acquired when HND of 1 mm and HIP of 0.4 MPa. • Soot, CO and HC generations tangibly reduced, though NO x generation is increased. A three-dimensional simulation on flow behavior and lean combustion in a hydrogen direct-injection gasoline rotary engine was implemented. The combined influence of hydrogen injection pressure (HIP) and nozzle diameter (HND) was numerically analyzed in the critical injection state. Results showed that with the increments of HIP and HND, further penetration and larger dispersion angle of jet-flow were presented. Increasing HIP led to larger jet-flow area and more jet-wall interaction, as well as greater deflection degree of hydrogen-flow after crashing upon the rotor surface. High-speed region expanded, while more jet-wall impingement occurred with the increment of HND. The spark ignited earlier and flame propagated faster as the HND modified smaller. As the HIP increased, the flame speed decreased slightly. The difference in the local Φ distribution and in-cylinder velocity field were the intrinsic mechanism of the HND impact, and the variation in the mixture concentration and TKE magnitude were the root causes of the HIP effect. The pressure and HRR traces were shifted to the downward clearly, while the peak positions were forming later as the HND extended larger. No perceptible difference in the peak positions of pressure and HRR were obtained with the HIP decrease, although pressure tended to increase along with heat release retard to be shortened. The combustion rate decreased with increments of HND and HIP, the timings of the initial consumption were delayed, and a proportional correspondence of reactants and intermediates was witnessed. The reduced NO x formation was obtained by increments of HND and HIP, and an inverse correlation can be seen between soot, CO, HC generations and NO x concentration. The scheme of 0.4 MPa HIP and 1 mm HND was the optimum configuration. Compared with a larger HND and higher HIP configuration, the peak pressure and maximum HRR were increased by 24.1% and 40.5%, and the productions of soot, CO, and HC were reduced by 55.7%, 61.5%, and 54.7%, respectively, though the NO x generation was increased to some extent. It was recommended in practice operations that the combination of lower HIP and smaller HND left a positive influence on improving the combustion characteristics of Wankel engines. [ABSTRACT FROM AUTHOR]

Dimethyl ether (DME), as a sustainable fuel, could be used as an ignition improver in spark ignition engines to improve the performance under lean conditions. Direct injection engines could gain higher thermal efficiency than the port fuel injection engines. To study the effects of second injection (SOI2) timing on the engine combustion characteristics, experiments were conducted on an engine with independent DME port injection and gasoline direct injection systems. Tests were performed at a constant engine speed of 1400 rpm and manifolds absolute pressure of 60 kPa under excess air ratios of 1.2 and 1.3. The start of injection during intake was kept constant at 300 oCA BTDC and the SOI2 timing was varied from 90 to 150 oCA BTDC. Split injection ratio was 1:1. Results showed that a higher brake thermal efficiency (BTE), lower cyclic variation, HC and particle emissions were obtained for DME-gasoline blends engines. Moreover, the ideal SOI2 timing could make the heat release more concentrated and ease the cyclic variation, which enhance BTE and reduce HC, NOx and particle number emissions. In addition, when more fuel was obtained, the combustion temperature was increased, improving BTE and reducing HC emissions under lean combustion conditions. • The co-effect of second injection timing and DME addition on GDI engines is studied. • Cooperating DME with proper second injection timing improves brake thermal efficiency. • Particle number emissions of the gasoline engine are reduced after DME addition. [ABSTRACT FROM AUTHOR]

• A CFD model of gasoline-H 2 blends Wankel engine was established and verified. • H 2 was direct injected in the rotor chamber under varying mass and directions. • Flame spread and combustion pressure decreased with the widened injection angle. • The optimal engine performance was acquired when α H2 of 3% and IA of 45°. • NO x generations still remained lower, though chamber pressure notably rise. To analyze the effects of hydrogen charge concentration (HCC) and injection angle (IA) on the lean combustion in a gasoline Wankel engine, the present work implemented a numerical simulation model coupling with the kinetic mechanisms and validated with the experimental data. Results found that with the increase in HCC, the penetration of hydrogen injection is enlarged and the area of the high-speed jet flow is expanded. The jet-flow area for IAs of 45° or 135° is larger than that of 90°. Changing IA could obtain the hydrogen distribution at different regions of the rotor chamber and IA of 90° acquires the smallest hydrogen-rich region. Increasing IA brings about the reduced flame speed substantially; the flame area for IAs of 45° and 90° expands with the increment of HCC whereas the contrary pattern is witnessed at the IA of 135°. Smaller IA leads to the major burning occurring untimely, which resulting in less work delivery of the engine. The hydrogen consumption for IAs of 45° and 90° increases as HCC is ascendant while that for IA of 135° is just the reverse. Variations in the mixture distribution and turbulence are the intrinsic mechanism of how the HCC and IA reflects the combustion progress. As hydrogen is injected with larger HCC and smaller IA, a relatively richer mixture and higher turbulent kinetic energy are distributed close in the spark ignition region. The peak combustion pressure reduces and its corresponding crank position delays with the widened IA at any HCC. Considering the fuel combustion and nitric oxide formation, as hydrogen volume fraction is 3% and IA is 45°, the engine could realize the optimized performance under the computational condition. An efficient combustion performance may be performed in engineering application if the hydrogen IA is in accordance with the rotor rotating direction at lower HCC. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ammonia-hydrogen fuel used in miller cycle internal combustion engine. • The stoichiometric and lean-burn conditions of the ammonia-hydrogen engine were compared. • For Miller Cycle ammonia engines, about 20% of hydrogen is required. • Expanded ammonia energy ratio can improve engine BMEP and ITE. Reducing carbon emissions in the transport sector requires technology upgrades to engines and the use of carbon–neutral fuels. Ammonia is a zero-carbon renewable fuel that complements hydrogen. This study is based on a Miller cycle spark ignition engine using ammonia-hydrogen fuel. The effects of the mixture ratio of ammonia and hydrogen under stoichiometric ratio and lean burn condition on the performance of the Miller cycle engine are focused. First, a commercial Miller-cycle ICE was modified to allow a dual fuel supply of ammonia and hydrogen. The engine was run steadily at 1500 rpm with the manifold absolute pressure (MAP) maintained at 60 kPa, and the ammonia and hydrogen supplies were adjusted to achieve different mixing ratios and excess air ratios. The test results showed that an increased ammonia percentage under stoichiometric ratio conditions significantly improved the Braking mean effective pressure (BMEP) and Braking thermal efficiency (BTE) of the ICE. Under lean burn conditions, the changes of BMEP and BTE are small with the increase of the ammonia ratio. The exhaust temperature of the ammonia-hydrogen engine is relatively low, so it is necessary to consider matching a small inertia turbocharger. Ammonia ratios above 80 % by volume resulted in erratic engine operation and even misfires. Ammonia-hydrogen fuel blends lead to higher Nitrogen oxide (NOx) emissions. [ABSTRACT FROM AUTHOR]

• The Miller cycle and variable valve timing are used in a DI hydrogen engine. • The effects of variable valve timing on the airflow exchange process are analyzed. • The engine can reach 42.22% maximum brake thermal efficiency. • Positive effects of exhaust valve timing on a DI hydrogen engine cannot be ignored. The favorable physicochemical characteristics of hydrogen make it an excellent alternative fuel for IC engines. Compared with hydrogen port injection, hydrogen direct injection provides multiple degrees of freedom for injection strategies and mixture formation, which can effectively suppress abnormal combustion and enhance engine performance. Variable valve timing (VVT) and the Miller cycle, as advanced and effective means of improving engine performance, are less investigated based on a direct-injection (DI) hydrogen engine. Hence, to optimize the performance of a DI hydrogen engine, strategies of the Miller cycle and VVT are introduced. In this work, a 1.5 L direct-injection engine with a VVT system was employed to evaluate the effects of the Miller cycle, intake valve closing (IVC) timing, and exhaust valve opening (EVO) timing on the airflow exchange process, in-cylinder charge characteristics, heat release process, dynamics and emission characteristics. The engine speed was stabilized at 1400 rpm and the strategies of lean combustion and late injection were used. The main results are as follows. As the IVC timing is delayed, the ratio of pumping mean effective pressure to indicated mean effective pressure (PMEP/IMEP) first decreases and then slightly increases, and the engine tends to achieve a high level of brake thermal efficiency (BTE) when PMEP/IMEP is lower. The optimization of intake and exhaust VVT can shorten combustion duration and reduce cyclic variation by increasing volumetric efficiency and improving mixture distribution at ignition timing. Furthermore, the engine reaches 42.22% BTE and a high level of brake mean effective pressure by the cooperative control of IVC and EVO timing. NOx emissions can be controlled below 100 ppm by employing the synergistic effect of the Miller cycle and VVT. It is worth mentioning that exhaust VVT as a way to compensate for the performance of the DI hydrogen engine with the Miller cycle should not be ignored. [ABSTRACT FROM AUTHOR]

n -Butanol is a feasible fuel candidate for spark-ignition engines. The current paper carried out an experiment to explore effects of hydrogen addition on further improving the performance of a n-butanol engine under the part load and lean conditions. Within the test, the engine intake pressure and speed were respectively kept at 61.5 kPa and 1400 rpm. The volumetric fractions of hydrogen in the total intake gas (hydrogen + air) were constrained at 0 and 3%, respectively. Under a certain hydrogen blending level, the global excess air ratio of in-cylinder charge which was changed from the stoichiometric to near the lean burn limit was adjusted by varying the n -butanol injection duration. The experimental results confirmed that the brake thermal efficiency was heightened and the lean burn limit was extended after the hydrogen addition. Besides, compared with the pure n -butanol combustion, the hydrogen enrichment enables the engine to gain dropped ignition delay and rapid combustion duration. Moreover, CO and HC from the pure n -butanol engine were reduced by the hydrogen addition. NOx were generally reduced when the excess air ratio was raised. This suggested that NOx from the hydrogen-enriched butanol engine could also be controlled by lean combustion. [ABSTRACT FROM AUTHOR]

A two-zone quasi-dimensional model is developed and validated for predicting the performance of a hydrogen-enriched methanol engine. The fractal-based turbulent entrainment model was applied to hydrogen-enriched methanol combustion simulations with a laminar flame speed correlation of hydrogen-methanol-air mixtures. The model accuracy was evaluated under different hydrogen volume fractions, equivalence ratios, loads and speeds. Satisfying agreement between numerical and experimental results was achieved. The validated model was applied to investigate the flame propagation speed, exhaust loss and brake thermal efficiency of hydrogen-enriched methanol engines. The results showed that the hydrogen enrichment could improve the flame propagation speed, reduce the exhaust loss and enhance brake thermal efficiency. Moreover, the results suggested that, for the actual vehicular engine operation, the hydrogen addition should be coupled with the lean burn strategy under low speed and part load conditions. [ABSTRACT FROM AUTHOR]

Concerning the throttling loss under part load conditions, it is feasible to further improve the engine thermal efficiency through operating the engine under the unthrottled condition and controlling its load by changing the excess air ratio. However, the narrow flammability of ethanol may lead the ethanol engine to encounter high cyclic variations under unthrottled and lean conditions. The addition of hydrogen is potentially helpful for solving this problem. In this test, the engine was run under an speed of 1400 rpm and unthrottled conditions. The hydrogen volume fractions in the intake were respectively kept at 0% and 3%. For a given hydrogen blending level, the ethanol flow rate was reduced to enable the engine to run under lean conditions. The results showed that the engine efficiency was improved with the blending of hydrogen. The highest thermal efficiency was improved by 6.07% after blending 3% hydrogen to the intake air. The addition of hydrogen could increase the engine torque output at lean conditions. Both cooling and exhaust losses were decreased after the hydrogen enrichment while adopting the lean combustion strategy. The hydrogen addition contributed to the extended lean burn limit and decreased cyclic variation under lean conditions. HC and CO emissions were decreased whereas NOx emissions were increased after the blending of hydrogen. [ABSTRACT FROM AUTHOR]

Hydrogen-fueled Wankel rotary engine (HWRE), as a high power density and eco-friendly internal combustion engine, has the potential to become an alternative for gasoline-fueled piston engines. Cooled EGR, as an effective means of improving engine performance, is less studied based on HWRE. However, due to the different operating way and structure, the flame development and propagation of WRE are significantly different from those of the piston engine, so may the effect of cooled EGR. Hence, the goal of present work is to analyze the effect of cooled EGR on the combustion characteristics of HWRE. This work is conducted under 1500 r/min and wide-open throttle conditions. The results show that when the ignition timing and excess air ratio are fixed at 5°CA ATDC and 1, the cooled EGR level has a significant influence on the combustion process and operating stability. In addition, when maximum brake torque CA50 is employed, within test range, whether stoichiometric or lean combustion, both the brake torque and brake thermal efficiency are monotonous to the cooled EGR level. And cooled EGR can achieve high brake thermal efficiency compared with lean combustion at the same brake torque. Compared with the hydrogen-fueled piston engine, HWRE allows for a higher cooled EGR level whether in terms of efficiency or power output considerations. In general, the cooled EGR can be used as an excellent load control means to achieve high efficiency of HWRE. • The effect of cooled EGR on combustion in hydrogen Wankel rotary engine is analyzed. • Cooled EGR has significant impacts on the combustion characteristic of hydrogen WRE. • Cooled EGR can be employed as an excellent means of load control of hydrogen WRE. • Cooled EGR is more suitable for hydrogen WRE than the hydrogen piston engine. [ABSTRACT FROM AUTHOR]

This paper studied the effect of spark timing on combustion and emissions characteristics of a hydrogen-enriched methanol engine. The experiment was performed on a four-cylinder gasoline engine equipped with an electronic controlled hydrogen port-injection system. The engine speed was kept at 1400 rpm and the manifolds absolute pressure was kept at 61.5 kPa with an excess air ratio of 1.20. The hydrogen volume fractions in the total intake were kept at 0, 1.5% and 3%, respectively. The spark timings for each specified hydrogen addition level were varied from 18 to 46 °CA before top dead center with steps of 2 °CA. The test results showed that the indicated thermal efficiency was first increased and then decreased with the increase of spark advance. With increase of spark advance, flame development period was prolonged whereas the flame propagation period was shortened. The coefficient of variation in indicated mean effective pressure was first decreased and then slightly increased with the advance of spark timing. HC and CO emissions were decreased after hydrogen addition. NOx from the hydrogen-blended engines could be reduced through retarding the spark timing. [ABSTRACT FROM AUTHOR]

This paper studied the idling characteristic of a hydrogen-blended methanol engine under lean conditions and three hydrogen volume fractions in the intake of 0, 1% and 2%. The test was accomplished on a spark-ignition equipped with a hydrogen port-injection system. The test results showed that the addition of hydrogen contributed to the reduced fuel energy consumption at the idle condition. Because of the reduced engine idle speed, the engine fuel energy consumption rate was further reduced after increasing the excess air ratio of hydrogen-methanol-air mixtures. Both flame development and propagation periods were shortened and HC and CO emissions were reduced after the addition of hydrogen for the methanol engine at the idle and lean conditions. [ABSTRACT FROM AUTHOR]

Methanol is a promising alternative fuel for the spark-ignition engines. This paper experimentally investigated the performance of a hydrogen-blended methanol engine at lean and various load conditions. The test was conducted on a four-cylinder commercial spark-ignition engine equipped with an electronically controlled hydrogen port injection system. The test was conducted under a typical city driving speed of 1400 rpm and a constant excess air ratio of 1.20. Two hydrogen volume fractions in the intake of 0 and 3% were adopted to investigate the effect of hydrogen addition on combustion and emissions performance of the methanol engine. The test results showed that brake thermal efficiency was improved after the hydrogen addition. When manifolds absolute pressure increased from about 38 to 83 kPa, brake thermal efficiencies after the hydrogen addition were increased by 6.5% and 4.2%. The addition of hydrogen availed shortening flame development and propagation periods. The peak cylinder temperature was raised whereas cylinder temperature at the exhaust valve opening was decreased after the hydrogen addition. The addition of hydrogen contributed to the dropped hydrocarbon and carbon monoxide. However, nitrogen oxides were slightly raised after the hydrogen enrichment. [ABSTRACT FROM AUTHOR]

Abstract: This paper proposed a way for realizing the load control of a hydrogen-blended gasoline engine running at the wide open throttle (WOT) condition through lean combustion. The engine performance of the original gasoline engine and a 3% hydrogen-blended gasoline engine running at the WOT and lean conditions under various loads at a constant engine speed of 1400 rpm was compared. The experimental results showed that because of the reduced residual gas fraction and throttling loss, brake thermal efficiency of the 3% hydrogen-blended gasoline engine running at the WOT and lean conditions was obviously higher than that of the pure gasoline engine. The 3% hydrogen-blended gasoline engine running at the WOT and lean conditions produced much lower particulate and CO emissions than the original gasoline engine. Besides, NOx emissions at part load conditions were also reduced for the 3% hydrogen-blended gasoline engine running at the WOT and lean conditions. [Copyright &y& Elsevier]

Abstract: The effect of syngas addition on the performance of a 1.6 L gasoline engine at lean condition was investigated in the paper. The syngas which produced by the onboard ethanol catalytic decomposition was mainly composed of hydrogen and carbon monoxide. A tube array reforming reactor was mounted on the engine tailpipe to produce syngas. During the test, the engine was run at 1800 rpm and a manifolds absolute pressure of 61.5 kPa. The spark timing for the maximum brake torque was adopted for all tests. The engine spark timing, injection timing and duration of the gasoline were controlled by a hybrid electronic control unit communicated with the engine original electronic control unit. The syngas volume fraction in the total intake gas was gradually increased from 0% to 1.84%. The gasoline flow rate was decreased to ensure that the global excess air ratio of the fuel–air mixture in cylinder at about 1.20. The test results confirmed that the syngas addition helped improve the indicated thermal efficiency and shorten the combustion duration. HC, NOx emissions and particle total number per cubic centimeter were reduced after the syngas addition at lean condition. [Copyright &y& Elsevier]

SUMMARY Hydrogen is the most promising alternative fuel for spark-ignited engines. This paper experimentally investigated the performance of a pure hydrogen-fueled SI engine at idle and lean conditions. The experiment was carried out on a four-cylinder gasoline-fueled SI engine equipped with an electronically controlled hydrogen port-injection system and a hybrid electronic control unit which was used to govern the hydrogen injection duration. The engine original electronic control unit was used to adjust the opening of idle bypass valve and spark timing to enable the engine to be run around its target idle speed. The test results showed that the fuel energy flow rate was reduced with the increase of excess air ratio for the pure hydrogen-fueled engine at idle and lean conditions. When excess air ratio increased from 2.08 to 3.2, the hydrogen energy flow rate was decreased from 11.79 to 9.97 MJ/h. Both the flame development and propagation periods were increased with the increase of excess air ratio. Because of the increased opening of idle bypass valve and dropped cylinder temperature, both pumping and cooling losses were reduced when the engine was leaned out. NOx and CO emissions were negligible, but HC and CO2 were still existed for the pure hydrogen-fueled SI engine due to the possible burning of the blow-by lubricant oil gas. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: The paper studied the effect of syngas addition on performance of a gasoline engine at lean conditions. The engine ran at 1800 rpm and a manifolds absolute pressure of 61.5 kPa. The spark timing for the maximum brake torque was adopted for each testing point. The syngas volume fraction in the total intake gas was fixed at 0% and 2.5%. The test results showed that peak cylinder pressure and indicated thermal efficiency were enhanced after the syngas enrichment. Flame development and propagation durations of the 2.5% syngas-blended engine were reduced by 7.2 and 5.7 °CA, compared with those of the original engine at an excess air ratio of 1.36. The coefficient of variation in the indicated mean effective pressure showed a noticeable decrease after the syngas addition. CO and NOx emissions were slightly increased with the syngas enrichment. HC emissions were first reduced and then increased after the syngas blending. [Copyright &y& Elsevier]

Abstract: Because of the increased residual gas fraction and low combustion temperature, the traditional spark-ignited (SI) gasoline engines tend to encounter the dropped thermal efficiency and increased emissions at idle. This paper experimentally investigated the effects of hydrogen addition, cylinder cutoff, lean combustion and idle speed reduction on improving the combustion and emissions performance of gasoline engine at idle. The tests were conducted on a modified 1.6 L SI engine equipped with a hydrogen port-injection system and a self-developed hybrid electronic control unit (HECU). In the experiments, cylinder cutoff was realized by stopping the hydrogen and gasoline injections to the specified cylinders. The HECU was adopted to control the opening of idle bypass valve and spark timing at the reduced idle speed of 600 rpm. The test results showed that hydrogen addition, lean burn, cylinder cutoff and idle speed reduction were all effective on decreasing the engine fuel consumption at idle. Under the given test conditions, the combination of cylinder cutoff and hydrogen addition was the most effective, which reduced the fuel consumption by 33.25% at a hydrogen volume fraction in the intake of 2.87% and two-cylinder cutoff mode, compared with that of the original engine. Moreover, engine cyclic variation, HC and CO emissions were also decreased after hydrogen addition and cylinder cutoff. Because of the dropped combustion temperature, NO x emissions were decreased at the lean combustion and decreased idle speed. However, due to the increased residual gas fraction and weakened charge flow, HC emissions from the engine operating at an idle speed of 600 rpm and a hydrogen addition fraction of 3.20% were slightly higher than those from the original gasoline engine at idle. [Copyright &y& Elsevier]

Abstract: In this paper, the cyclic variation characteristics of a hydrogen-enriched gasoline engine under various operating conditions were experimentally investigated. The test was carried out on a modified four-cylinder gasoline engine equipped with an electronically controlled hydrogen injection system. A hybrid electronic control unit was developed to govern the injection timings and durations of hydrogen and gasoline to accomplish the on-line adjusting of the hydrogen blending level and excess air ratio. The engine was first run at idle condition with an idle speed of 790 rpm and then operated at 1400 rpm to investigate the cyclic variation in a hydrogen-blended gasoline engine at different hydrogen volume fractions in the total intake, excess air ratios, spark timings and manifolds absolute pressures. The test results demonstrated that the coefficient of variation in indicated mean effective pressure was distinctly decreased with the increase of hydrogen blending ratio. At 1400 rpm and a manifolds absolute pressure of 61.5 kPa, the relevant excess air ratio for the engine lean burn limit was extended from 1.45 to 2.55 when the hydrogen volume fraction in the intake was raised from 0% to 4.5%. Besides, for a specified hydrogen addition level, the coefficient of variation in indicated mean effective pressure was continuously increased but the coefficient of variation in the peak cylinder pressure was first raised and then decreased with the increase of excess air ratio. The experimental results also showed that hydrogen addition was more effective on reducing engine cyclic variation at low loads rather than at high loads. [Copyright &y& Elsevier]

Abstract: Due to the narrow flammability of gasoline, pure gasoline-fueled spark-ignited (SI) engines always encounter partial burning or even misfire at lean conditions. Gasoline engines tend to suffer poor combustion and expel large emissions at idle conditions because of the high variation in the intake charge and low combustion temperature. Comparatively, hybrid hydrogen engines (HHE) fueled with the mixtures of hydrocarbon fuels and hydrogen seem to achieve lower emissions and gain higher thermal efficiencies than the original hydrocarbon-fueled engines due to the wide flammability and high flame speed of hydrogen. Since a HHE only requires a small amount of hydrogen, it also removes concerns about the high production and storage costs of hydrogen. This paper introduced an experiment conducted on a four-cylinder SI gasoline engine equipped with a hydrogen port-injection system to explore the performance of a hybrid hydrogen–gasoline engine (HHGE) at idle and lean conditions. The injection timings and durations of hydrogen and gasoline were governed by a hybrid electronic control unit (HECU) developed by the authors, which can be adjusted freely according to the commands from a calibration computer. During the test, hydrogen flow rate was varied to ensure that hydrogen volume fraction in the intake was constantly kept at 3%. For the specified hydrogen addition level, gasoline flow rate was reduced to make the engine operate at idle and lean conditions with various excess air ratios. The test results demonstrated that cyclic variations in engine idle speed and indicated mean effective pressure were eased with hydrogen enrichment. The indicated thermal efficiency was obviously higher for the HHGE than that for the original gasoline engine at idle and lean conditions. The indicated thermal efficiency at an excess air ratio of 1.37 was increased from 13.81% for the original gasoline engine to 20.20% for the HHGE with a 3% hydrogen blending level. Flame development and propagation periods were also evidently shortened after hydrogen blending. Moreover, HC, CO and NOx emissions were all improved after hydrogen enrichment at idle and lean conditions. Therefore, the HHE methodology is an effective and promising way for improving engine idle performance at lean conditions. [Copyright &y& Elsevier]

Abstract: Hydrogen has many excellent combustion properties that can be used for improving combustion and emissions performance of gasoline-fueled spark ignition (SI) engines. In this paper, an experimental study was carried out on a four-cylinder 1.6L engine to explore the effect of hydrogen addition on enhancing the engine lean operating performance. The engine was modified to realize hydrogen port injection by installing four hydrogen injectors in the intake manifolds. The injection timings and durations of hydrogen and gasoline were governed by a self-developed electronic control unit (DECU) according to the commands from a calibration computer. The engine was run at 1400rpm, a manifold absolute pressure (MAP) of 61.5kPa and various excess air ratios. Two hydrogen volume fractions in the total intake of 3% and 6% were applied to check the effect of hydrogen addition fraction on engine combustion. The test results showed that brake thermal efficiency was improved and kept roughly constant in a wide range of excess air ratio after hydrogen addition, the maximum brake thermal efficiency was increased from 26.37% of the original engine to 31.56% of the engine with a 6% hydrogen blending level. However, brake mean effective pressure (Bmep) was decreased by hydrogen addition at stoichiometric conditions, but when the engine was further leaned out Bmep increased with the increase of hydrogen addition fraction. The flame development and propagation durations, cyclic variation, HC and CO2 emissions were reduced with hydrogen addition. When excess air ratio was approaching stoichiometric conditions, CO emission tended to increase with the addition of hydrogen. However, when the engine was gradually leaned out, CO emission from the hydrogen-enriched engine was lower than the original one. NO x emissions increased with the increase of hydrogen addition due to the raised cylinder temperature. [Copyright &y& Elsevier]

• Experiments in a modified hydrogen-fueled rotary engine are presented. • Comparatively investigating the effect of asynchronous and synchronous ignition. • Asynchronous ignition achieves higher torque and lower tendency of knock. • Leading and trailing plugs act as primary and auxiliary spark plugs respectively. • The CA50 should be located at 35 to 40°CA ATDC to obtain the highest power. This work aims to investigate experimentally the asynchronous ignition in a hydrogen-fueled Wankel rotary engine. This work was carried out at 1500 r/min and lean combustion. The experimental results showed that a suitable asynchronous ignition may realize better power performance than synchronous ignition and earlier ignition timing of the leading plug than that of the trailing plug is more preferable. When the leading plug and the trailing plug spark at 5°CA ATDC and 20°CA ATDC, respectively, the highest torque is obtained, 36.4 N·m, higher than 35.2 N·m, the highest torque when the synchronous ignition is adopted. Besides, a declined tendency of knock also can be achieved by asynchronous ignition. Compared with synchronous ignition at 35.2 N·m, a reduction of 19.5% maximum pressure rising rate can be achieved by asynchronous ignition at 36.4 N·m. In addition, for hydrogen-fueled WRE, the CA50 should be located at 35 to 40°CA ATDC to obtain the highest output torque. [ABSTRACT FROM AUTHOR]

• Experimental and numerical study of stoichiometric and lean combustion is conducted. • High-temperature combustion and its duration have crucial effects on burning rates. • The combustion initiation and combustion duration are shortened by H2 enrichment. • H2 addition with lean operation shows higher thermal efficiency and lower emissions. • There is a close correlation between early flame growth and combustion stability. Based on a retrofitted Wankel engine, fundamental experiments and numerical simulations were conducted to investigate the role of the hydrogen addition under stoichiometric and lean combustion conditions. The test-bench recording of in-cylinder pressure, heat release, cycle-to-cycle fluctuation, and exhaust emissions were used to characterize fuel combustion. The verified CFD model clarified the inherent mechanisms behind experimental data. Results showed that the introduction of hydrogen addition caused combustion temperature to increase, the timing taken for active radical formations was significantly advanced, and the peak concentrations increased. This contributed to the increased pressure and the shortened combustion phasing in experiments. There was a proportional correspondence of the early flame growth and cyclic variation. Hydrogen addition has a minimal effect on the turbulent intensity after spark timing. However, adopting a highly diluted mixture caused the enhanced turbulent intensity, which was responsible for improving the stability of the engine. Due to the synergistic effects of the work delivery, cyclic fluctuation, and exhaust temperature, a larger hydrogen addition with stoichiometric operation showed lower higher brake thermal efficiency. Nitrogen oxide emissions increased with hydrogen enrichment and reduced with a higher degree of mixture dilution owing to a close positive correlation between the mass elevated-temperature and NO x formation. Benefits from sufficient oxygen concentration and elevated combustion temperature, the chain transfer process can be accelerated. This explained why CO emissions decreased at a larger hydrogen-enriched and leaner condition in the experimental investigation. Increasing the hydrogen content provided improvement in the desired HC emissions for all operating points. [ABSTRACT FROM AUTHOR]

To achieve more efficient and robust combustion, split direct-injected hydrogen as a new injection strategy for rotary engines was used to clarify the influences of various injection parameters, including hydrogen amount for each pulse, the dwell between pulses, and secondary injection pulse-width, on combustion performance and emissions formation by CFD modeling. The results of this investigation confirmed the benefit of split direct-injection as a useful means to govern mixture stratification which enabled the combustion more effective and rapid compared to single-injection mode. Enhanced combustion could be achieved by increasing the mass fraction of post-injection with an optimized dwell between injections. Further investigation on secondary injection pulse-width demonstrated that engine performance was substantially improved with a wider second injection pulse. From one side, as the secondary injection pulse-width was increased, the surrounding mixture distribution of the spark-plug location was richer, which was confirmed as a beneficial inhomogeneous circumstance of hydrogen to accelerate the burning rate. From another side, strong tumble level and turbulence intensity were of significant importance for facilitating the combustion process and getting optimal thermal efficiency. For emissions formation, split direct-injected hydrogen made a near-zero HC and CO emissions at the price of a comparable increase of NOx emissions. • Hydrogen split direct-injection is implemented on a gasoline SI Wankel engine. • Analyzing three factors for amelioration including first, post-injection, and dwell. • Split injection strategies can realize desirable stratified conditions of hydrogen. • Injecting proper hydrogen in each pulse with an adequate dwell is of importance. • Thermal efficiency can be notably improved benefits from the wide second injection. [ABSTRACT FROM AUTHOR]

• A thorough 3D CFD model of the H 2 -gasoline Wankel engine is built up and validated. • Burning-source connection of the twin-plug has a negative influence on flame spread. • Combustion is enhanced in the L-side of the rotor chamber by increased spark-energy. • The improvement of ignitability was gained in the H 2 -enriched ignition environment. • Maximum mass fraction of the temperature region is closely related to NO x formation. Due to the elongated shape of the combustion chamber and strong one-way flow characteristic, changing the location of enhanced combustion is an effective means to ameliorate the indicated efficiency of the Wankel engine. For this purpose, strengthening combustion can happen by allocating spark-energy in the desired location along with a favorable ignition environment. In this study, three-dimensional CFD simulations were implemented and the numerical results were compared with existing measured data, in which ignition environment variations were achieved by hydrogen enrichment within the intake manifold of a spark-ignition Wankel engine. Based on CONVERGE code with the SAGE detailed chemistry solver, the twin-plug engine model was then used to assess the location of strengthened combustion employing a spark-energy allocation from the perspective of species evolution, combustion characteristics, and emissions formation. The results indicate that enhancing spark-energy at the leading side of the rotor chamber has an overall higher burned volume rate and faster species evolution due to the later connection of two burning sources prior to quenching. Increasing the hydrogen content in the ignition environment causes richer active radicals and higher turbulence, ultimately promoting flame propagation and combustion intensity. A larger T-plug spark-energy decreases the indicated mean effective pressure, heat release rate, and thermal efficiency because of the intensified wall heat flux and the lower mass burning rate at the leading side. There is no doubt that the introduction of hydrogen enrichment presents a positive effect on both thermal efficiency and specific fuel consumption at the price of a slighter increase of nitrogen oxide formation due to higher mass fraction of high-temperature regions. It is recommended that enhancing local mass burning rate in the leading part of the rotor chamber under the hydrogen-enriched ignition environment can provide a great potential in the quest towards high-efficiency Wankel rotary engine. [ABSTRACT FROM AUTHOR]

This study focuses on a four-cylinder, four-stroke hydrogen engine equipped with a passive pre-chamber (PC). The effects of excess air ratio (λ) on the performance of the turbulent jet ignition (TJI) hydrogen engine are investigated through experimental and numerical simulations. The hydrogen engine operates at 1600 rpm with an intake manifold pressure of 70 kPa. The results show that λ values significantly influence the internal flow field, energy distribution, and flame development in the PC, affecting the combustion in the main chamber (MC). The experiment found that as λ decreases, the BMEP and BTE gradually increase. Due to the influence of jet and multi-point ignition, the heat transfer loss in lean combustion is also relatively high. The jet oscillation caused by the TJI hydrogen engine has high controllability and low destructiveness, and λ is one of the main factors controlling the jet oscillation. The influence of spark timing (ST) on engine performance is explored through experiments. The results show that as λ increases, the sensitivity of BMEP to ST gradually decreases. With the delay of ST, BTE increased first and then decreased. However, the cyclic variation is less affected by ST. For the TJI hydrogen engine, an appropriate delay in ST under the close stoichiometric ratio condition can not only ensure power output and combustion stability but also reduce emissions. [Display omitted] • Pre-chamber gas-flow movement, mixture distribution, and flame propagation are analyzed • The pre-chamber exhibits stratification of the mixture under lean combustion conditions. • The BMEP and BTE continue to decrease with the increase of lambda. • The jet oscillations in TJI engines are highly sensitive to the excess air ratio. • The spark timing has a smaller effect on lean combustion than rich mixtures. [ABSTRACT FROM AUTHOR]

Internal combustion engines fueled with mixtures of hydrogen (H 2) and ammonia (NH 3) are potential power devices for reducing carbon emissions. To improve the ignition and combustion performance of NH 3 /H 2 , turbulent jet ignition (TJI) can be used. This study aims to investigate NH 3 /H 2 /air combustion under TJI modes at low equivalence ratios. Considering that the adoption of the scavenging system is beneficial for improving the reactivity of the pre-chamber, the effect of active TJI with scavenging is also explored. The results show that injecting 1.2 times the initial mixture volume of air is optimal for scavenging, and the scavenging effect becomes significant as the NH 3 fraction increases. Using conventional active TJI and active TJI with scavenging effectively improves ignition performance and flame propagation, reducing sensitivity to the equivalence ratio compared to passive TJI mode. Although the adoption of active TJI modes improves the lean flammability limit of NH 3 /H 2 , weak flame propagation may occur in the early stage of combustion under ultra-lean conditions. Appropriately increasing the injection of auxiliary H 2 can effectively improve this phenomenon. • Scavenging in the pre-chamber is conducive to the improvement of jet generation. • H 2 -assisted pre-chamber reduces the sensitivity of combustion to equivalence ratio. • Weak flame propagation may occur in the early combustion of ultra-lean mixtures. • An appropriate increase of H 2 injection can improve the initial flame propagation. [ABSTRACT FROM AUTHOR]

• A compound intake rotary engine model was established and validated. • The effects of intake modes on mixture formation and combustion was studied. • H2/gasoline/air in peripheral port and air in side port has best performance. • The mean in-cylinder pressure and temperature of S-HGP was increased. • The CO emission of S-HGP was reduced, but NOx emissions were increased. This work aimed to realize stratified mixtures distribution in a hydrogen-enriched compound-intake gasoline Wankel engine by utilizing the difference of gas velocity from different intake ports. A three-dimension computational fluid dynamics (CFD) WRE model was established to investigate the mixture formation and combustion process under five different intake modes, i.e. the way of the binary fuel enters the combustion chamber through different intake ports (side intake port, peripheral intake port or both port). The intake mode S-HGP (the mixtures of H 2 , gasoline and air are in the peripheral intake port and pure air is in the side intake port) realized an optimal equivalence ratio distribution, in which condition, the most fuels gather near the spark plug and the minority fuel in the rear region of the combustion chamber. Since the unburned mixtures always exist in the rear region of the chamber due to the mainstream in the WRE, the stratified distribution of S-HGP could consume most of the fuel. Because the faster flame propagation release a large amount of heats near top dead center (TDC), S-HGP possesses the highest average in-cylinder pressure under five intake modes, is about 1.264 times than the worst intake mode. Moreover, S-HGP has the maximum average in-cylinder temperature, the ideal thermal condition and moderate lean combustion get the lowest CO emission, comparing with the intake mode performing the highest CO emissions, the CO emission of S-HGP is decreased by 745% near the exhaust valve opening timing (210 °CA ATDC). However, owing to the higher temperature inside cylinder, S-HGP has slightly high NO emission. In conclusion, the results mean that compound intake combined with intake modes control is an effective method for fuel distribution optimization besides the fuel direct injection. [ABSTRACT FROM AUTHOR]

• A simulation model of the hydrogen-enriched Wankel engine was built and validated. • Single-spark ignition strategies consist of split ignition, high-energy ignition. • Twin-spark ignition strategies cover asynchronous ignition and energy allocation. • The preferable arrangement of the twin spark plug was T/L = 1.5. • Optimal combustion was gained as the leading plug was ignited earlier and stronger. For the hydrogen-enriched spark-ignited Wankel engine, the optimization of ignition strategy is conducive to improve combustion performance and specifically effective to lessen the unburned region due to the elongated rotor chamber. In this paper, the role of the number of the ignition source, twin-spark plug location, asynchronous ignition, and energy allocation in improving lean combustion was investigated through the three-dimensional computational fluid dynamics model coupling with kinetic mechanisms. The model was validated by experiment, and good agreements between measured and predicted combustion pressure and the heat release rate was obtained. Results showed that the improvements of engine combustion were limited by single-spark ignition strategies, and the twin-spark ignition configuration was capable of enhancing combustion efficiency drastically. The arrangement of the twin-spark plug determined the space for flame development, and it was favorable for the trailing plug to stand a greater offset from the minor axis of the engine. An earlier leading-spark ignition enabled flame propagation faster and occurred quenching rapidly, which contributed to higher pressure-output and better heat-release. The higher energy of leading-spark ignition made the mixture consumption faster, combustion pressure higher, and combustion duration shorter. The optimum strategy on combustion was expressed as follows: the location of trailing-spark plug is offset from the minor axis by 20.7 mm; the spark timing and discharge energy of leading-spark plug is 325°EA and 0.03 J, respectively; and those of trailing-spark plug is 335°EA and 0.01 J. It was recommended that the leading-spark ignition was set earlier and stronger for practical operations. [ABSTRACT FROM AUTHOR]

• DME addition reduces HC emissions and increases CO emission. • DME addition improves BTE and combustion stability of GDI engines. • The two-stage injection mode reduces NOx emissions. • The two-stage injection mode improves BTE and combustion stability. • Co-effects of DME addition and injection ratios on GDI engines are studied. As an alternative fuel, dimethyl ether (DME) improves the combustion and reduces emissions of gasoline engines. Moreover, the control of injection strategies of direct injection (DI) gasoline engines could form the preferable stratified charge, enhancing the performance characteristics, especially under lean burning conditions. Thus, the co-effects of injection strategies and DME addition on the performance of a DI gasoline engine were investigated under the lean-burn condition. Results showed that the appropriate injection ratio (IR) during the two-stage injection strategy could exhibit a higher brake thermal efficiency (BTE), a lower cyclic variation and HC emissions compared to the single injection mode. Moreover, the cyclic variation was decreased firstly then increased, the BTE and heat release rate were raised firstly then reduced with the increase of IR. Furthermore, NOx emissions were increased firstly and then decreased, HC emissions were decreased firstly and then increased and the trend of CO emission was increased constantly. In addition, the DI gasoline engine blended with DME raised BTE, shortened the combustion phase, eased cyclic variation, increased CO emission and dropped HC emissions under tested conditions. The use of DME with optimum IR could be a practical way to improve the trade-off between BTE and NOx emissions. [ABSTRACT FROM AUTHOR]

This paper aims to reveal the effect of intake closing timing, and engine speed on the flow field, flame propagation, combustion characteristics, and emissions formations of a small-scaled side ported hydrogen-fueled Wankel rotary engine. For this reason, a three-dimensional dynamic simulation model was established using a reasonable turbulent model coupled with a kinetic reaction mechanism and validated by the experimental data. Simulation results show that an earlier intake closing timing increases the volumetric efficiency and increases intake loss. The increasing speed improves the volumetric efficiency while causing a higher intake loss. There are two peaks of the turbulence kinetic energy during the intake stroke. The first one is caused by the airflow hitting the wall, and the other is due to the backflow. During the flame development period, due to the strong unidirectional flow in the combustion chamber, which is not conducive to flame propagation backward. This phenomenon is more pronounced at higher engine speeds, resulting in a merged flame front not exceeding the trailing spark plug. The lean combustion leads to a lower in-cylinder combustion temperature, deteriorating the NOx generation environment. This paper provides a feasible method for matching the operating conditions and intake system. • The shape and area of the intake port varies with the intake closing timing. • Dual-spark plug flame propagation pattern is proposed. • The leakage of gas to adjacent cylinder is reduced at 8000 rpm. [ABSTRACT FROM AUTHOR]

[Display omitted] • Passive pre-chamber can enhance the stability of lean combustion in TJI hydrogen engines. • Passive pre-chamber internal flow characteristics, combustion, and energy conversion analysis. • Analysis of combustion and emission for TJI hydrogen engines at different injection strategies. • With the delay of SOI, the power output of the TJI hydrogen engine gradually improves. • The split-injection strategy will increase the power performance and combustion instability. Turbulent jet ignition (TJI) effectively achieves lean and stable combustion in hydrogen engines. However, research on injection strategies for TJI hydrogen engines is still lacking. In this study, experimental methods investigated the effects of single and split injection strategies on the combustion and emissions of TJI hydrogen engines under medium loads. The numerical simulation reveals the operational characteristics of fuel distribution, ignition capability, and energy conversion in the pre-chamber at different injection times in a single injection strategy. This work is conducted at 1600 rpm with a manifold absolute pressure of 70 kPa. The experimental results indicate that the delay of the start of injection (SOI) can enhance the performance of the TJI hydrogen engine. However, as SOI approaches TDC, emissions worsen, and combustion stability decreases. When SOI is 90°CA BTDC, the brake mean effective pressure (BMEP) and brake thermal efficiency (BTE) can achieve 3.1 bar and 32.9 %, with the coefficient of variation of the IMEP (COV IMEP) of 1.6 % and lower emissions. For the split injection strategy, delaying the secondary end of injection (SEOI) can increase BMEP and BTE. As SEOI gradually delays the TDC, emissions deteriorate sharply. Under the split injection strategy, COV IMEP is higher, which is unfavorable for hydrogen engine applications. [ABSTRACT FROM AUTHOR]

Turbulent jet ignition (TJI) is an advanced ignition mode that can enhance ignition and combustion performance, and it is a potential ignition strategy for ammonia/hydrogen internal combustion engines. This study aims to investigate the ignition and combustion characteristics of lean ammonia/hydrogen/air ignited by TJI, and the different ignition modes were compared. The results indicate that active TJI with auxiliary hydrogen injection in the pre-chamber improves the ignition and combustion performance of ammonia/hydrogen/air, and the appropriate shift of the pre-chamber equivalence ratio towards the rich side is considered optimal. As the ammonia fraction increases, the ignition mechanism in the main chamber changes from flame ignition to jet ignition. The advantage of TJI is mainly shown in high ammonia fraction mixtures, which is reflected in significantly lower ignition delay and combustion duration. In addition, TJI reduces the sensitivity of combustion to ammonia fraction compared to SI, due to the high ignition energy, initial flame area and turbulence provided by the hot jet. In TJI mode, the increase in jet velocity seems to be detrimental to the radial development of flames near the orifice, which may result in an increase in the duration of the final stage of combustion. • Combustion characteristics of NH 3 /H 2 /air in TJI and SI modes were compared. • Rich pre-chamber mixture promotes ignition and combustion of NH 3 /H 2 in active TJI. • The increase in H 2 fraction enhances the tolerance of ignition to turbulence. • TJI has greater potential in combustion of NH 3 /H 2 mixtures with low H 2 fractions. • The adoption of TJI reduces the sensitivity of combustion to mixture reactivity. [ABSTRACT FROM AUTHOR]

• Effect of Spark plug position on hydrogen rotary engine is investigated. • Leading spark plug can obtain higher power and low cyclic variation. • Hydrogen rotary engine's spark plug should locate the front of the minor axis. • Hydrogen rotary engine has excellent emission under lean combustion. • Best CA50 of hydrogen rotary engine locates between 35 and 40°CA ATDC. As a promising power system, hydrogen-fueled Wankel rotary engine with excellent power and emission characteristic have received attention increasingly, which makes it of great interest to investigate it. To make up for blanks, this work was conducted to experimentally investigate the effect of spark plug position on the combustion and emission characteristic of hydrogen-fueled Wankel rotary engine under 1500 r/min, 66 kPa manifold absolute pressure and 1.5 excess air ratio. The results indicate that compared to the trailing spark plug, the leading spark plug is more suitable to hydrogen-fueled Wankel rotary engines, which can realize a wider ignition range, higher maximum brake torque, lower cyclic variation and better nitric oxide emission. The maximum brake torque of adopting trailing spark plug is 31.2 N·m, which is only 87% of the maximum brake torque of 36.0 N·m with adopting leading spark plug. At the maximum brake torque ignition timing, adopting leading trailing spark plug achieves lower cyclic variation and slightly higher thermal load than adopting trailing spark plug. Besides, the optimum central heat-release point of both spark plug positions locate between 35 and 40°CA after the top dead center, and that of leading spark plug is later 2°CA than that of trailing spark plug. Moreover, both spark plug positions obtained 0 nitric oxide emission at maximum brake torque ignition timing, which means that emission will not be a problem to limit the selection of spark plug position under tested conditions. [ABSTRACT FROM AUTHOR]

• LBV of H 2 /air blends diluted by EGR with varied H 2 O ratio and air was measured. • Both EGR and air dilution can effectively control LBV of H 2 /air. • NO emission can be reduced by increasing dilution ratio and water fraction in EGR. • H 2 emission first increases and then decreases with the increasing dilution ratio. • H 2 emission increases monotonically with the increase of water fraction in EGR. Lean combustion and exhaust gas recirculation (EGR) are key strategies for controlling NO and heat release process of hydrogen engines. This paper firstly compared these two strategies on combustion behaviors of hydrogen-air mixtures within dilution ratio ranges from 0 to 50%. Then, the water vapor effects in EGR on combustion of hydrogen-air mixtures are further investigated. All tests are conducted in a constant volume combustion vessel at the initial temperature of 373 K and pressure of 1 bar. CHEMKIN PRO is adopted to predict the hydrogen-air mixtures combustion behaviors under different conditions with one-dimensional premixed adiabatic planner flame model. The unburnt hydrogen concentration and the NO mole fraction in the final products were measured. The results show that laminar burning velocity decreases more obviously with the EGR ratio than air dilution ratio. EGR dilution has much obvious influence on reducing NO mole fraction in the final products. However, both dilution strategies adversely cause the increase of incompletely combusted H 2. To balance the NO control and unburned H 2 emission, 30% EGR rate with 20% water vapor fraction is recommended based on the testing ranges of this study. [ABSTRACT FROM AUTHOR]