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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]

Hydrogen (H 2) is a carbon-free fuel with many excellent combustion characteristics, but abnormal combustion is one of the main obstacles to the promotion and application of hydrogen-fueled engines. This experimental study aims to investigate the suppression of the heat release rate (HRR) of a hydrogen-fueled engine through the addition of ammonia (NH 3). The engine was run at 1300 rpm, with manifold absolute pressure (MAP) of 61 kPa and NH 3 addition ratio of 0% and 2.2%, under lean-burn conditions. The results showed that the addition of small amounts of ammonia reduced the combustion rate of the fuel mixture, prolonged the flame development period (CA0-10) and propagation durations (CA10-90) of the engine, and reduced the peak in-cylinder pressure and peak HRR under lean-burn conditions. The addition of ammonia increased the peak indicated mean effective pressure (IMEP) and the peak indicated thermal efficiency (ITE) of the engine. The addition of ammonia resulted in increased nitrogen oxides (NOx) emissions. • The effect of ignition timing of an H 2 /NH 3 dual-injection engine was studied. • Reduces the peak heat release rate after ammonia was added. • CA0-10 and CA10-90 were extended after ammonia was added. • The peak IMEP and ITE were increased after ammonia was added. [ABSTRACT FROM AUTHOR]

The development of alternative fuels is important in the fight against climate change. Both hydrogen and ammonia are renewable energy sources and are carbon-free combustible fuels. In a recent experimental study, the performance and emission characteristics of a spark-ignition engine burning a premixed hydrogen/ammonia/air mixture were evaluated. The manifold absolute pressure was adjusted to 61 kPa and the engine speed was stabilized at 1300 rpm. The difference between a mixture with a 2.2% volume fraction of ammonia and a pure hydrogen fuel was analyzed in comparison. Specifically, the addition of ammonia increased the ignition delay and flame development periods and reduced the rate of in-cylinder pressure rise. In conjunction with the ignition timing strategy, the addition of ammonia did not affect the engine performance. Nitrogen oxides emissions are increased due to the addition of ammonia. The experimental results suggest that ammonia can be used as a combustion inhibitor, which provides a new reference for the development of hydrogen-fuelled engines. • The effect of ammonia addition on hydrogen-fueled engines was studied. • Direct injection and port injection were used for H 2 and NH 3 respectively. • Reduces the rate of pressure rise after ammonia was added. • The addition of ammonia has little effect on peak IMEP and ITE. [ABSTRACT FROM AUTHOR]

The application of hydrogen direct-injection enrichment improves the performance of gasoline Wankel rotary engine, and the hydrogen injection strategy has a significant impact on combustion, knock, and emissions. The Z160F Wankel rotary engine was used as the investigated compact engine, and the simulation model was developed using CONVERGE software. The combustion, knock and emissions characteristics of the engine were studied with the different mass flow of hydrogen injection, i.e., the trapezoid, wedge, slope, triangle and rectangle type of gas injection rate shape. In the numerical simulations, the in-cylinder pressure oscillations were monitored using monitoring points, and the knock index (KI) was used as an evaluation indicator. The study revealed that the gas injection rate shape significantly affected the mixture of hydrogen and air, thus impacting combustion, knock and emissions. When the injection rate shape was rectangle, the flame speed was faster, the peak pressure in the cylinder was higher, and the corresponding crank angle was earlier, which led to higher pressure oscillations in the cylinder and larger KI. Based on the rectangle injection rate shape, the KI decreased by 75.81%, 33.47%, 26.46% and 76.58% for trapezoid, wedge, slope, and triangle, respectively, and the indicated mean effective pressure increased by 15.68%, 5.07%, 0.56% and 14.98%, respectively. Due to the small difference in maximum temperature, which resulted in very little variation in nitrogen oxides for each injection rate shape, the total hydrocarbon emissions of the trapezoid and triangle injection rate shape was high due to the delayed combustion phase. This paper provides a solution for direct hydrogen injection to improve the combustion, knock and emissions behavior of the rotary engine. [Display omitted] • A rotary engine model with hydrogen direct-injection enrichment was established. • Five different types of hydrogen injection rate shapes were simulated. • The behavior of the combustion, knock and emissions was analyzed. • The optimal indicated thermal efficiency can be achieved by trapezoid type. [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]

Dimethyl ether has high cetane number and low temperature reaction characteristics. These mean that blending small amount of dimethyl ether to the spark-ignited engine would be helpful for improving the performance under lean conditions. Spark timing is one of the important factors influencing the engine combustion. Thus, it is necessary to investigate performance of the dimethyl ether-blended gasoline engine under various spark timings. The engine was run at 1400 rpm, a manifolds absolute pressure of 60 kPa and a constant excess air ratio of 1.20. Test results showed that the addition of dimethyl ether resulted in the raised indicated mean effective pressure for the gasoline engine. Over increased and decreased spark timing tended to cause the dropped indicated mean effective pressure. The coefficient of variation in indicated mean effective pressure was diminished with the spark timing advances and dimethyl ether addition. NOx and HC emissions were dropped with the spark timing decrease. NOx emissions from the dimethyl ether-mixed gasoline engine are decreased with the decrease of spark angle. [ABSTRACT FROM AUTHOR]

In this paper, a rotary engine equipped with an n-butanol and hydrogen port-injection system was developed to investigate the combustion and emissions characteristics of a hydrogen-blended n-butanol rotary engine at part load and stoichiometric conditions. A self-developed hybrid electronic control unit was adopted to adjust the injection durations of n-butanol and hydrogen. The rotary engine was run under the conditions of 4000 rpm, a manifold absolute pressure of 35 kPa and a fixed spark timing of 45 °CA before the top dead center during the whole testing operation. The hydrogen volumetric fraction in the total intake was varied from 0% to 6.30%. The test results manifested that the brake thermal efficiency and chamber temperature were simultaneously increased with hydrogen addition. The hydrogen supplement obviously shortened flame development and propagation periods. Both chamber pressure integral heat release fraction versus crank angle were increased when the hydrogen fraction was enhanced. HC emissions were reduced by 54.5% when hydrogen volume fraction was raised from 0% to 6.30%, CO and CO 2 emissions were also reduced after increasing hydrogen blending fraction. NOx emissions were mildly elevated due to the improved chamber temperature. [ABSTRACT FROM AUTHOR]

This paper aimed to study the effect of spark timing on performance of a hydrogen-gasoline dual-fuel rotary engine. For this aim, a modified rotary engine equipped with a dual-fuel port injection system was developed. An electronic management module (ECM) was specially made to command the fuel injection, excess air ratio and hydrogen volumetric fraction. In this study, the engine was operated at 4500 rpm with a manifold absolute pressure (MAP) of 35 kPa. Hydrogen volumetric percentage of total intake was kept at 0%, 3% and 6%, severally. When the hydrogen volumetric percentage was changed, the gasoline fraction was also adjusted to keep the mixture at the stoichiometric. For a specified hydrogen volumetric fraction, the ignition timing was varied from 24 to 42 °CA BTDC (before top dead center) with a fixed interval of 2 °CA. Experimental results showed that for a specific hydrogen volumetric percentage, the peak combustion pressure and chamber temperature were increased, brake thermal efficiency was first increased and then decreased with the increase of spark advance. Advancing spark timing caused the increased flame development period, the decreased flame propagation period and exhaust temperature. Cyclic variation was initially weaken and then deteriorated after raising spark advance. HC and NOx emissions were reduced after retarding spark timing. Spark timing had little effect on CO emission. [ABSTRACT FROM AUTHOR]

This study investigated effects of dimethyl ether addition on the gasoline engine combustion and emissions performance under idle and stoichiometric conditions. The engine was first modified to be fueled with gasoline and dimethyl ether simultaneously. The experimental results showed that, with the increase of dimethyl ether energy fraction in the total fuel, the total fuel energy flow rate was decreased, and the flame development and propagation periods were shortened. The cycle-to-cycle variation was reduced and the degree of constant volume combustion was increased after the dimethyl ether addition. The dimethyl ether blending was beneficial for reducing hydrocarbon and nitrogen oxide emissions from 1951 and 95 ppm of the original engine to 552 and 34 ppm of pure dimethyl ether, respectively. Meanwhile, with the increase of dimethyl ether addition level, the peak cylinder pressure and carbon monoxide emission were decreased at first, whereas increased when the dimethyl ether energy fraction exceeded 49%. Furthermore, heat release rate during the low temperature reaction was enhanced with the increase of dimethyl ether addition level. The maximum heat release rate was heightened and its relevant crank angle was advanced during the high temperature reaction period after the dimethyl ether enrichment. [ABSTRACT FROM AUTHOR]

Because of the unusual structure chamber compared with traditional engines, gasoline rotary engine always encounters partial burning and increased noxious emissions at the idle. Hydrogen-addition could enhance the characteristics of combustion and emissions of sparked-ignited engines at idle. A modified gasoline rotary engine with electronic spark control and fuel (gasoline and hydrogen) port-injection system was developed to study the impact of hydrogen-addition on idle performance of a gasoline rotary engine. A hybrid electronic control unit was invented to manage the spark, fuel injection, hydrogen volume fraction of the total intake and overall excess air ratio. In this study, the engine was operating at the idle speed of 2400 rpm and stoichiometric conditions. The hydrogen volume fraction was gradually varied from 0% to 6.8%. Results showed that the coefficient of variation in speed and fuel energy flow rate were both decreased after the hydrogen-addition. Flame development and propagation periods were shortened owning to hydrogen-addition. The peak chamber temperature was enhanced after the hydrogen-addition due to the high adiabatic flame temperature of hydrogen. Cooling loss was dropped when hydrogen was added into gasoline. HC, CO and CO 2 emissions were reduced by 79.4%, 86.0% and 25.9% when hydrogen volume fraction were raised from 0% to 6.8%. [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]

Idle elimination is a feasible way for reducing the fuel consumption and emissions at idle. The challenge for adopting idle elimination on gasoline engine is the high emissions during restart because rich mixtures have to be used at starting. This paper tries to start the engine with pure hydrogen at the restart for gasoline vehicles which adopt idle elimination. The investigation was done based on models built on AVL CRUISE. In the model, the vehicle was run under the New European Driving Cycle (NEDC). The hydrogen used on the vehicle was online produced and stored by an on-board hydrogen production and storage system. The energy for producing hydrogen is taken into account in the total fuel consumption. The simulation results showed that, with the adoption of gasoline start-idle elimination strategy, the vehicle fuel consumption during NEDC was reduced by 0.69 L/100 km, and NO x emissions were decreased by 5.5% compared with the original vehicle without idle elimination. However, HC and CO emissions at the restart were respectively increased by 87.5% and 18.1% for the gasoline vehicle due to the adoption of rich mixtures. Comparatively, with the adoption of hydrogen start-idle elimination strategy, the vehicle fuel consumption during NEDC was reduced by 0.79 L/100 km, HC and CO emissions were decreased by 70.8% and 13.6%, respectively. This shows a good capability of hydrogen combustion on reducing HC and CO emissions at the restart. However, NOx emissions were slightly increased by 7.9% under the hydrogen restart mode. [ABSTRACT FROM AUTHOR]

The rotary engines may encounter high fuel consumption and emissions due to its narrow and long combustion chamber design. The low ignition energy and high flame speed of hydrogen may help improve the combustion of rotary engines. In this paper, a gasoline rotary engine equipped with gasoline and hydrogen injectors was developed to investigate the combustion and emissions of hydrogen-blended gasoline rotary engines. The engine was run at 3000 rpm and a manifolds absolute pressure of 37.5 kPa with the stoichiometric excess air ratio. The spark timing was set to be 25°CA before the top dead center. The engine was first fueled with the pure gasoline and then blended with the hydrogen. The hydrogen volume fractions in the intake were gradually increased from 0% to 5.2%. The results showed that the combustion pressure, brake mean effective pressure, cylinder temperature and thermal efficiency were simultaneously increased after the hydrogen blending. The crank angle of peak pressure was advanced with the hydrogen addition. The hydrogen enrichment was effective on reducing flame development and propagation periods. HC emissions were reduced by 44.8% when the hydrogen volume fraction in the intake was raised from 0% to 5.2%, CO and CO 2 emissions were also reduced after the hydrogen blending. [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]

CO 2 (Carbon dioxide) dilution is a feasible way for controlling NOx (Nitrogen oxides) emissions and loads of the internal combustion engines. This paper investigated the effect of CO 2 dilution on the combustion and emissions characteristics of a hydrogen-enriched gasoline engine. The experiment was conducted on a 1.6 L spark-ignition engine with electronically controlled hydrogen and gasoline injection systems. At two hydrogen volume fractions of 0 and 3%, the CO 2 volume fraction in the intake was gradually increased from 0 to 4%. The fuel-air mixtures were kept at the stoichiometric. The experimental results demonstrated that brake mean effective pressure of the gasoline engine was quickly reduced after adopting CO 2 dilution. Comparatively, Bmep (Brake mean effective pressure) of the 3% hydrogen-enriched engine was gently decreased with the increase of CO 2 dilution level. Thermal efficiency of the 3% hydrogen-enriched gasoline engine was raised under properly increased CO 2 dilution levels. However, thermal efficiency of the pure gasoline engine was generally dropped after the CO 2 dilution. The addition of hydrogen could shorten flame development and propagation durations under CO 2 diluent conditions for the gasoline engine. Increasing CO 2 fraction in the intake caused the dropped NOx and raised HC (Hydrocarbon) emissions. Increasing hydrogen fraction in the intake could effectively reduce HC emissions under CO 2 diluent conditions. [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]

The performance of a hydrogen-blended gasoline engine at lean and the wide open throttle conditions was investigated. A hydrogen port-injection system was adopted to introduce the hydrogen into each cylinder. The engine was operated at 1400 rpm and two hydrogen blending levels of 0% and 3%. The excess air ratio was raised from 1.00 to about 1.45 for a given hydrogen addition fraction. The test results demonstrated that the hydrogen blending contributed to the raised thermal efficiency and shortened flame development and propagation durations. An increased brake mean effective pressure was found after the hydrogen addition only at lean conditions. For both stoichiometric and lean conditions, the hydrogen blending was beneficial for reducing the engine cyclic variation. This provides a possibility to run a hydrogen-blended gasoline engine with the fully opened throttle position and control the engine torque only by adjusting the excess air ratio. Toxic emissions including HC, CO and particulate were reduced after the hydrogen blending. [ABSTRACT FROM AUTHOR]

This paper analyzed the combustion characteristic of a hydrogen-blended gasoline engine running at high loads and lean conditions. The cycle-to-cycle variation in indicated mean effective pressure, cylinder pressure during combustion, heat release fraction and exhaust emissions at different conditions were experimentally investigated. The results showed that the addition of hydrogen was able to improve the engine stability through reducing the cyclic variation in indicated mean effective pressure. Moreover, the fuel heat release rate and peak cylinder pressure were accelerated after the hydrogen addition. Both HC and CO emissions were reduced significantly after the hydrogen blending. NOx emissions were slightly increased after the hydrogen addition due to the high flame temperature of hydrogen. [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]

This paper experimentally investigated the effect of hydrogen addition on the cold start performance of a methanol engine. The test was conducted on a modified four-cylinder gasoline engine. An electronically controlled hydrogen injection system was applied to realize the hydrogen port injection. The engine was started at an ambient temperature of 25 °C with two hydrogen flow rates of 0 and 189 dm 3 /s, respectively. The results demonstrated that hydrogen addition availed elevating the peak engine speed and cylinder pressure during the cold start. Both flame development and propagation periods are shortened after the hydrogen addition. When the hydrogen volume flow rate was raised from 0 to 189 dm 3 /s, HC, CO and total number of particulate emissions within 19 s from the onset of cold start were reduced by 68.7%, 75.2% and 72.4%, respectively. However, because of the enhanced in-cylinder temperature, NO x emissions were increased after the addition of hydrogen. [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]

Abstract: This paper investigated the effect of hydrogen addition on enhancing the performance of a methanol engine at part load and lean conditions. The experiment was conducted on a modified spark-ignited engine equipped with an adjustable dual-fuel injection system. The engine was run at an engine speed of 1400 rpm with two hydrogen volume fractions in the intake of 0% and 3%. The test results illustrated that the engine cyclic variation was eased and the brake thermal efficiency was enhanced after the hydrogen blending. Besides, the hydrogen enrichment was effective on reducing the flame development and propagation periods. HC and CO emissions were generally reduced after the hydrogen blending. NOx emissions from the hydrogen-blended methanol engine could be dropped to a low level when the engine was run under high excess air ratios. [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: Dimethyl ether (DME) seems to be a potential approach for improving the cold start performance for spark-ignited (SI) engines. In this paper, the cold start performance of an SI engine fueled with pure DME was experimentally investigated and compared with that of the original SI gasoline engine. The engine was successfully cold started with pure DME and pure gasoline, respectively. The test results demonstrated that, the fuel energy flow rate of the SI DME engine was only 30% of that of the original SI gasoline engine whereas the imep (indicated mean effective pressures) of the SI DME engine was effectively enhanced in the first 5 cycles. The SI DME engine had a shortened flame development period compared with the original SI gasoline engine. Meanwhile, the HC emissions were averagely decreased by 80% under the pure DME mode. The instantaneous CO and NO x emissions from the SI DME engine were slightly increased in the initial seconds after the onset of cold start and then markedly reduced compared with those from the original SI gasoline engine. In view of the above, starting an SI engine with pure DME could improve the combustion and emissions performance. [Copyright &y& Elsevier]

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: The gasoline engines always encounter the deteriorated thermal efficiency and increased toxic emissions at part load conditions. This paper investigated the effect of hydrogen/oxygen blends (hydroxygen) addition on the performance of a gasoline engine at different hydrogen volume fractions in the hydroxygen. The experiment was conducted on a 1.6 L gasoline engine equipped with a hydrogen and oxygen port injection system. A hybrid electronic control unit was adopted to control the spark timing and the injection timings and durations of hydrogen, oxygen and gasoline. The test was performed at a typical city driving speed of 1400 rpm, a manifolds absolute pressure of 61.5 kPa and two excess oxygen ratios of 1.00 and 1.20. The overall volume fraction of the hydroxygen in the total intake gas was fixed at 3%. The hydrogen volume fraction in the hydroxygen was raised from 0% to 100% by changing the injection durations of hydrogen and oxygen. The test results demonstrated that the engine thermal efficiency was obviously increased with the increase of hydrogen volume fraction in the hydroxygen. The fuel energy flow rate of the 3% hydroxygen-blended gasoline engine was lower than that of the original engine when the hydrogen volume fraction in the hydroxygen exceeded 70%. Both the flame development and propagation periods were shortened after the hydroxygen addition. HC, CO and NOx emissions were decreased with the increase of hydrogen volume fraction in the hydroxygen. But NOx emissions of the hydroxygen-blended engine were higher than those of the original engine for all hydrogen volume fractions in the hydroxygen. Moreover, at an excess oxygen ratio of 1.00, CO from the 3% hydroxygen-blended gasoline engine was also higher than that from the original engine. The reduced particulate emissions can be obtained only at relatively high hydrogen volume fractions in the hydroxygen. [Copyright &y& Elsevier]

Abstract: Dimethyl ether (DME) is thought to be one of the most favorable alternative fuels or additives for internal combustion (IC) engines in the future. Because spark-ignited (SI) ethanol engines have the poor performance at cold start and low operating conditions caused by negative properties of ethanol such as the high latent heat, DME is introduced aiming at improving the engine economical and emissions performance. The experiments were carried out on a modified 4-cylinder gasoline engine under a typical city driving speed of 1400rpm and an intake manifold absolute pressure (MAP) of 61.5kPa. In this paper, the effect of DME blending on the engine performance at different excess air ratios and two DME volume fractions of 1% and 2% was experimentally investigated. The engine manifold was modified so that ethanol and DME can be injected and mixed with air simultaneously in the intake ports. A hybrid electronic control unit (HECU) was specially developed to control the injection timings and durations of ethanol and DME, accomplishing specified excess air ratios and DME volume fractions in the intake. The experimental results indicated that, DME addition benefits enhancing the indicated thermal efficiency, which is increased by about 10% at λ =1.25 compared with the original ethanol engine. And the maximum reduction of COVimep is about 50% after DME addition. Besides, the HC emissions from the DME-enriched ethanol engine at the DME volume fraction of 2% are averagely reduced by 45% compared with those from the original ethanol engine. But the NO x emissions slightly increase with the increase of DME volume fraction in the intake. Consequently, DME addition can be considered as a potentially applicable approach for improving the overall performance of SI ethanol engines. [Copyright &y& Elsevier]

Abstract: Producing the syngas by onboard ethanol steam reforming is an effective way for recovering the exhaust heat in the engine tailpipe. Besides, as hydrogen is contained in the syngas, the addition of syngas is also capable of improving engine combustion and emissions characteristics. In this paper, an experimental study was carried out on a four-cylinder 1.6 L spark-ignited engine to explore the effect of syngas addition on the engine performance. A fuel reforming reactor with the copper based catalysts was designed and mounted on the engine tailpipe, so that the ethanol solution could be decomposed to be syngas which is mainly composed of hydrogen and carbon monoxide when the catalysts were heated by the exhaust gas. The intake manifolds was also modified to permit syngas to be injected into the fourth cylinder of the engine. 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 each testing point. The syngas volume fraction in the total intake gas was gradually increased from 0% to 2.43%. Meanwhile, the gasoline injection duration governing by a hybrid electronic control unit was adjusted to keep the excess air ratio of the fuel-air mixture in the fourth cylinder at about 1.00. The experimental results demonstrated that the syngas volume flow rate was markedly enhanced from 90 to 240 L/h when the feedstock flow rate was increased from 18 to 54 mL/min. The peak ethanol conversion efficiency reached 81.16% at a feedstock flow rate of 36 mL/min. The hydrogen concentration was increased whereas carbon monoxide concentration was decreased in the syngas with the increase of the feedstock supply. The engine indicated thermal efficiency was raised to be 39.01% at the syngas volume fraction of 2.43%. The flame development and propagation durations were shortened; HC and NOx emissions were reduced whereas CO emission was increased after the syngas addition at the stoichiometric condition. [Copyright &y& Elsevier]

Abstract: Dimethyl ether (DME) and methanol are thought to be one of the most promising alternative fuels for IC engines. Meanwhile, previous investigations also have pointed out the good prospects for adopting DME and methanol in IC engines. The experiments in this paper were carried out at idle condition to investigate the effect of applying the methanol/DME blended fuel in a SI engine. The engine was modified to be fueled with the mixture of methanol and DME which were injected into the engine intake ports simultaneously. Various DME fractions were selected to investigate the effect of DME addition on engine performance. The experimental results showed that indicated thermal efficiency was increased by 25% and coefficient of cyclic variation in engine speed was decreased by 29.2% at the DME energy fraction of 85.2% in the total fuel. In addition, both flame development and propagation durations were shortened with the increase of DME enrichment level at idle condition. Meanwhile, the largest drop of HC emissions was nearly 50% compared with the original methanol engine at stoichiometric condition. However, CO and NO x emissions increase with the addition of DME. [Copyright &y& Elsevier]

Abstract: This paper compared the effects of hydrogen and hydrogen–oxygen blends (hydroxygen) additions on the performance of a gasoline engine at 1400 rpm and a manifolds absolute pressure of 61.5 kPa. The tests were carried out on a 1.6 L gasoline engine equipped with a hydrogen and oxygen injection system. A hybrid electronic control unit was applied to adjust the hydrogen and hydroxygen volume fractions in the intake increasing from 0% to about 3% and keep the hydrogen-to-oxygen mole ratio at 2:1 in hydroxygen tests. For each testing condition, the gasoline flow rate was adjusted to maintain the mixture global excess air ratio at 1.00. The test results confirmed that engine fuel energy flow rate was decreased after hydrogen addition but increased with hydroxygen blending. When hydrogen or hydroxygen volume fraction in the intake was lower than 2%, the hydroxygen-blended gasoline engine produced a higher thermal efficiency than the hydrogen-blended gasoline engine. Both the additions of hydrogen and hydroxygen help reduce flame development and propagation periods of the gasoline engine. HC emissions were reduced whereas NOx emissions were raised with the increase of hydrogen and hydroxygen addition levels. CO was slightly increased after hydrogen blending, but reduced with hydroxygen addition. [Copyright &y& Elsevier]

Abstract: The limited fossil fuel reserves and severe environmental pollution have pushed studies on improving the engine performance. This paper investigated the effect of hydrogen–oxygen blends (hydroxygen) addition on the performance of a spark-ignited (SI) gasoline engine. The test was performed on a modified SI engine equipped with a hydrogen and oxygen injection system. A hybrid electronic control unit was adopted to govern the opening and closing of hydrogen, oxygen and gasoline injectors. The standard hydroxygen with a fixed hydrogen-to-oxygen mole fraction of 2:1 was applied in the experiments. Three standard hydroxygen volume fractions in the total intake gas of 0%, 2% and 4% were adopted. For a given hydroxygen blending level, the gasoline injection duration was adjusted to enable the excess air ratio of the fuel-air mixtures to increase from 1.00 to the engine lean burn limit. Besides, to compare the effects of hydroxygen and hydrogen additions on the performance of a gasoline engine, a hydrogen-enriched gasoline engine was also run at the same testing conditions. The test results showed that the hydroxygen-blended gasoline engine produced higher thermal efficiency and brake mean effective pressure than both of the original and hydrogen-blended gasoline engines at lean conditions. The engine cyclic variation was eased and the engine lean burn limit was extended after the standard hydroxygen addition. The standard hydroxygen enrichment contributed to the decreased HC and CO emissions. CO from the standard hydroxygen-enriched gasoline engine is also lower than that from the hydrogen-enriched gasoline engine. But NOx emissions were increased after the hydroxygen addition. [Copyright &y& Elsevier]

Abstract: Because of the increased fuel-film effect and dropped combustion temperature, spark-ignited (SI) gasoline engines always expel large amounts of HC and CO emissions during the cold start period. This paper experimentally investigated the effect of hydrogen addition on improving the cold start performance of a gasoline engine. The test was carried out on a 1.6-L, four-cylinder, SI engine equipped with an electronically controlled hydrogen injection system. A hybrid electronic control unit (HECU) was applied to control the opening and closing of hydrogen and gasoline injectors. Under the same environmental condition, the engine was started with the pure gasoline and gasoline–hydrogen mixture, respectively. After the addition of hydrogen, gasoline injection duration was adjusted to ensure the engine to be started successfully. All cold start experiments were performed at the same ambient, coolant and oil temperatures of 17 °C. The test results showed that cylinder and indicated mean effective pressures in the first cycle were effectively improved with the increase of hydrogen addition fraction. Engine speed in the first 20 start cycles increased with hydrogen blending ratio. However, in later cycles, engine speed varied only a little with and without hydrogen addition due to the adoption of close loop control on engine speed. Because of the low ignition energy and high flame speed of hydrogen, both flame development and propagation durations were shortened after hydrogen addition. HC and CO emissions were dropped markedly after hydrogen addition due to the enhanced combustion process. When the hydrogen flow rate increased from 0 to 2.5 and 4.3 L/min, the instantaneous peak HC emissions were sharply reduced from 57083 to 17850 and 15738 ppm, respectively. NOx emissions were increased in the first 5 s and then reduced later after hydrogen addition. [Copyright &y& Elsevier]

Abstract: To reduce the fuel consumption and emissions of spark-ignited (SI) engines, hydrogen enrichment was used to improve the performance of a lean burn SI engine operating at low speed and load conditions. A hydrogen port-injection system was mounted on the intake manifolds to introduce hydrogen into the intake ports sequentially while keeping the original gasoline injection system unchanged. A hybrid electronic control unit (HECU) was adopted to control injection timings and durations of gasoline and hydrogen, accomplishing four excess air ratios of 1.00, 1.18, 1.43 and 1.67 and three hydrogen volume fractions in the intake of 3%, 5%, 8%. The experimental results showed that engine brake thermal efficiency and torque output were increased, combustion durations were shortened, cyclic variation and HC emissions were reduced, but NO x emissions were increased with the increase of hydrogen addition. CO emission was also reduced under lean conditions with hydrogen enrichment. [Copyright &y& Elsevier]

Abstract: Dimethyl ether (DME) has a lot of good properties and is thought to be one of the best alternative fuels for IC engines in the future. In order to improve the efficiency, combustion stability and emissions performance of a spark-ignited (SI) gasoline engine at stoichiometric condition, an experimental study aiming at improving engine performance through DME addition was carried out on a four-cylinder SI engine. The engine was modified to be fueled with the mixture of gasoline and DME which were injected into the engine intake ports simultaneously. A hybrid electronic control unit (HECU) was dedicatedly developed to control the injection timings and durations of gasoline and DME. The spark timing was adjusted to reach the maximum brake torque (MBT) without knocking. Various DME fractions were selected to investigate the effect of DME addition on engine performance, thermal efficiency, combustion characteristics, cyclic variation and emissions under stoichiometric conditions. The experimental results showed that thermal efficiency, NOx and HC emissions are improved with the increase of DME addition level. The combustion performance was improved when DME addition fraction was less than 10%. CO emission first decreased and then increased with the increase of DME enrichment level at stoichiometric condition. [Copyright &y& Elsevier]

Abstract: Because of the low combustion temperature and high throttling loss, SI (spark-ignited) engines always encounter dropped performance at low load conditions. This paper experimentally investigated the co-effect of cylinder cutoff and hydrogen addition on improving the performance of a gasoline-fueled SI engine. The experiment was conducted on a modified four-cylinder SI engine equipped with an electronically controlled hydrogen injection system and a hybrid electronic control unit. The engine was run at 1400 rpm, 34.5 Nm and two cylinder cutoff modes in which one cylinder and two cylinders were closed, respectively. For each cylinder closing strategy, the hydrogen energy fraction in the total fuel was increased from 0% to approximately 20%. The test results demonstrated that engine indicated thermal efficiency was effectively improved after cylinder cutoff and hydrogen addition, which rose from 34.6% of the original engine to 40.34% of the engine operating at two-cylinder cutoff mode and . Flame development and propagation periods were shortened with the increase of the number of closed cylinders and hydrogen blending ratio. The total cooling loss for all working cylinders, and tailpipe HC (hydrocarbons), CO (carbon monoxide) and CO2 (carbon dioxide) emissions were reduced whereas tailpipe NO x (nitrogen oxide) emissions were increased after hydrogen addition and cylinder closing. [ABSTRACT FROM AUTHOR]

Abstract: Reducing idle speed is an effective way for decreasing engine idle fuel consumption. Unfortunately, due to the increased residual dilution and dropped combustion temperature, spark-ignited (SI) gasoline engines are prone to suffer high cyclic variation and even stall at low idle speeds. This paper investigated the effect of hydrogen addition on the performance of an SI gasoline engine at reduced idle speeds of 600, 700 and 800 rpm. The test results shows that cyclic variation was raised with the decrease of idle speed but reduced obviously with the increase of hydrogen energy fraction . Decreasing idle speed and adding hydrogen were effective for reducing engine idle fuel consumption. The total fuel energy flow rate was effectively dropped from 30.8 MJ/h at 800 rpm and  = 0% to 17.6 MJ/h at 600 rpm and  = 19.9%. Because of the dropped fuel energy flow rate causing the reduced combustion temperature, both cooling and exhaust losses were markedly reduced after decreasing idle speed and adding hydrogen. HC and CO emissions were dropped with the increase of , but increased after reducing idle speed. However, NOx emissions were decreased after reducing idle speed and adding hydrogen, due to the dropped peak cylinder temperature. [ABSTRACT FROM AUTHOR]

Abstract: Regarding the limited fossil fuel reserves, the renewable ethanol has been considered as one of the substitutional fuels for spark ignition (SI) engines. But due to its high latent heat, ethanol is usually hard to be well evaporated to form the homogeneous fuel–air mixture at low temperatures, e.g., at idle condition. Compared with ethanol, hydrogen possesses many unique combustion and physicochemical properties that help improve combustion process. In this paper, the performance of a hydrogen-enriched SI ethanol engine under idle and stoichiometric conditions was investigated. The experiment was performed on a modified 1.6 L SI engine equipped with a hydrogen port-injection system. The ethanol was injected into the intake ports using the original engine gasoline injection system. A self-developed hybrid electronic control unit (HECU) was adopted to govern the opening and closing of hydrogen and ethanol injectors. The spark timing and idle bypass valve opening were governed by the engine original electronic control unit (OECU), so that the engine could operate under its original target idle speed for each testing point. The engine was first fueled with the pure ethanol and then hydrogen volume fraction in the total intake gas was gradually increased through increasing hydrogen injection duration. For a specified hydrogen addition level, ethanol flow rate was reduced to keep the hydrogen–ethanol–air mixture at stoichiometric condition. The test results showed that hydrogen addition was effective on reducing cyclic variations and improving indicated thermal efficiency of an ethanol engine at idle. The fuel energy flow rate was reduced by 20% when hydrogen volume fraction in the intake rose from 0% to 6.38%. Both flame development and propagation periods were shortened with the increase of hydrogen blending ratio. The heat transfer to the coolant was decreased and the degree of constant volume combustion was enhanced after hydrogen addition. HC and CO emissions were first reduced and then increased with the increase of hydrogen blending fraction. The acetaldehyde emission from the hydrogen-enriched ethanol engine is lower than that from the pure ethanol engine. However, the addition of hydrogen tended to increase NO x emissions from the ethanol engine at idle and stoichiometric conditions. [Copyright &y& Elsevier]

Abstract: The addition of hydrogen is an effective way for improving the gasoline engine performance at lean conditions. In this paper, an experiment aiming at studying the effect of hydrogen addition on combustion and emissions characteristics of a spark-ignited (SI) gasoline engine under various loads and lean conditions was carried out. An electronically controlled hydrogen port-injection system was added to the original engine while keeping the gasoline injection system unchanged. A hybrid electronic control unit was developed and applied to govern the spark timings, injection timings and durations of hydrogen and gasoline. The test was performed at a constant engine speed of 1400rpm, which could represent the engine speed in the typical city-driving conditions with a heavy traffic. Two hydrogen volume fractions in the total intake of 0% and 3% were achieved through adjusting the hydrogen injection duration according to the air flow rate. At a specified hydrogen addition level, gasoline flow rate was decreased to ensure that the excess air ratios were kept at 1.2 and 1.4, respectively. For a given hydrogen blending fraction and excess air ratio, the engine load, which was represented by the intake manifolds absolute pressure (MAP), was increased by increasing the opening of the throttle valve. The spark timing for maximum brake torque (MBT) was adopted for all tests. The experimental results demonstrated that the engine brake mean effective pressure (Bmep) was increased after hydrogen addition only at low load conditions. However, at high engine loads, the hybrid hydrogen–gasoline engine (HHGE) produced smaller Bmep than the original engine. The engine brake thermal efficiency was distinctly raised with the increase of MAP for both the original engine and the HHGE. The coefficient of variation in indicated mean effective pressure (COVimep) for the HHGE was reduced with the increase of engine load. The addition of hydrogen was effective on improving gasoline engine operating instability at low load and lean conditions. HC and CO emissions were decreased and NOx emissions were increased with the increase of engine load. The influence of engine load on CO2 emission was insignificant. All in all, the effect of hydrogen addition on improving engine combustion and emissions performance was more pronounced at low loads than at high loads. [Copyright &y& Elsevier]

Abstract: Hydrogen addition is an effective way for improving the performance of spark-ignited (SI) engines at stoichiometric and especially lean conditions. Spark timing also heavily influences the SI engine performance. This paper experimentally investigated the effect of spark timing on performance of a hydrogen-enriched gasoline engine at lean conditions. The experiment was carried out on a four-cylinder, port-injection gasoline engine which was modified to be an electronically controlled hybrid hydrogen–gasoline engine (HHGE) by adding a hydrogen port-injection system on the intake manifolds while keeping the original gasoline injection system unchanged. A hybrid electronic control unit (HECU) was developed to govern the injection timings and durations of hydrogen and gasoline to enforce the timely mixing of hydrogen and gasoline in the intake ports at the expected blending levels and excess air ratios. During the test, the engine speed was fixed at 1400rpm and the manifolds absolute pressure (MAP) was kept at 61.5kPa. The hydrogen volume fraction in the intake was increased from 0% to 3% through adjusting the hydrogen injection duration. For a specified hydrogen addition level, gasoline injection duration was reduced to ensure the engine operating at two excess air ratios of 1.2 and 1.4, respectively. The spark timing for a specified hydrogen addition level and excess air ratio was varied from 20 to 50 °CA BTDC with an interval of 2 °CA. The test results showed that the indicated mean effective pressure (Imep) first increased and then decreased with the increase of spark advance. The optimum spark timing for the max. Imep (OST) was retarded for the HHGE at a specified excess air ratio. The max. indicated thermal efficiency appeared at the OST. Flame development period was shortened whereas flame propagation period was prolonged with the decrease of spark advance. The coefficient of variation in indicated mean effective pressure generally gained its minimum value at the OST. HC and NOx emissions were continuously decreased with the retarding of spark timing. However, the effect of spark timing on CO emission was found insignificant. [Copyright &y& Elsevier]

Abstract: Lean combustion is an effective way for improving the spark-ignited (SI) engine performance. Unfortunately, due to the narrow flammability of gasoline, the pure gasoline-fueled engines sometimes suffer partial burning or misfire at very lean conditions. Hydrogen has many excellent combustion properties that can be used to extend the gasoline engine lean burn limit and improve the gasoline engine performance at lean conditions. In this paper, a 1.6L port fuel injection gasoline engine was modified to be a hybrid hydrogen–gasoline engine (HHGE) fueled with the hydrogen–gasoline mixture by mounting an electronically controlled hydrogen injection system on the intake manifolds while keeping the original gasoline injection system unchanged. A self-developed hybrid electronic control unit (HECU) was used to flexibly adjust injection timings and durations of gasoline and hydrogen. Engine tests were conducted at 1400rpm and a manifolds absolute pressure (MAP) of 61.5kPa to investigate the performance of an HHGE at lean burn limits. Three hydrogen volume fractions in the total intake gas of 1%, 3% and 4.5% were adopted. For a specified hydrogen volume fraction, the gasoline flow rate was gradually reduced until the engine reached the lean burn limit at which the coefficient of variation in indicated mean effective pressure (COVimep) was 10%. The test results showed that COVimep at the same excess air ratio was obviously reduced with the increase of hydrogen enrichment level. The excess air ratio at the lean burn limit was extended from 1.45 of the original engine to 2.55 of the 4.5% HHGE. The engine brake thermal efficiency, CO, HC and NO x emissions at lean burn limits were also improved for the HHGE. [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]

Abstract: With regard to the improvement of efficiency, combustion stability, and emissions in a gasoline engine at idle condition, an experimental study aimed at improving engine idle performance through hydrogen addition was carried out on a 4-cylinder gasoline-fueled spark ignited (SI) engine. The engine was modified to be fueled with the mixture of gasoline and hydrogen injected into the intake ports simultaneously. A self-developed electronic control unit (DECU) was dedicatedly used to control the injection timings and injection durations of gasoline and hydrogen. Other parameters, such as spark timing and idle valve opening, were controlled by the original engine electronic control unit (OECU). Various hydrogen enrichment levels were selected to investigate the effect of hydrogen addition on engine speed fluctuation, thermal efficiency, combustion characteristics, cyclic variation and emissions under idle and stoichiometric conditions. The experimental results showed that thermal efficiency, combustion performance, NO x emissions are improved with the increase of hydrogen addition level. The HC and CO emissions first decrease with the increasing hydrogen enrichment level, but when hydrogen energy fraction exceeds 14.44%, it begins to increase again at idle and stoichiometric conditions. [Copyright &y& Elsevier]

• SI engines fuelled with hydrogen and dimethyl ether could achieve carbon neutrality. • Performance of a hydrogen-dimethyl ether SI engine under various α DME was studied. • Low-temperature oxidation was found in HRR curve, but the peak values were lower than 1 J/°CA. • After dimethyl ether addition, Imep was improved and NOx emissions were reduced up to 49.9%. Spark-ignition combustion mode could be used to widen the operation range of homogeneous charge compression ignition combustion mode on a hydrogen-dimethyl ether (DME) engine. To improve power output and reduce nitrogen oxides emissions, this study investigated the combustion and emissions properties of a hydrogen-DME spark-ignition engine under various DME fractions (α DME). The result showed that flame development and propagation periods were extended after DME blended. The increases of both periods were 1.7 and 2.0 °CA when α DME various from 1.4% to 3.0%, respectively. However, when α DME increased to 3.4%, flame propagation period had a 1.7 °CA reduction because of the spontaneous high-temperature oxidation of a few end unburned mixtures. Blending DME could improve power output of the neat hydrogen engine. The maximum improvement of indicated mean effective pressure could achieve 18.3%, after DME addition. Because of the weakened flame kernel and flame propagation process, when α DME lower than 3.0%, blending DME increased cyclic variation yet the variations were in 0.13%. Nitrogen oxides emissions could be reduced significantly, when DME was added into the neat hydrogen engine. The maximum reduction could achieve 49.9%, based on neat hydrogen fuel-supply mode. Hydrocarbon and carbon monoxide emissions were increased after DME addition. When α DME increased from 1.4% to 3.4%, the enhancement of hydrocarbon emissions was about two-third lower than that of carbon monoxide emission. [ABSTRACT FROM AUTHOR]

Abstract: This paper investigated the emissions performance of a passenger car powered by the hybrid hydrogen–gasoline engine under the New European Driving Cycle. The hydrogen was produced from an onboard water electrolysis hydrogen generator fixed in the trunk. The test results demonstrated that, when the engine was started with pure hydrogen for the first 7s and fueled with the pure gasoline after 11s from the onset of the cold start, CO and HC emissions were reduced by 62.1% and 64.1%, respectively. The vehicle emissions performance could be improved from the Euro-II emissions standard of the original vehicle to the Euro-IV emissions standard of the hybrid hydrogen–gasoline engine-powered vehicle. [Copyright &y& Elsevier]

• A modified n-butanol-fueled rotary engine was be used to experiment. • The effects of idle speed reduction and hydrogen enrichment were studied. • Idle speed reduction is an effective way to improve the economy of the engine. • Hydrogen-enriched can improve combustion and emission performance. • High blending hydrogen level can offset the negative effect of idle speed reduction. This work aims to improve the idle performance of the n-butanol rotary engine by blending hydrogen and reducing idle speed. Hydrogen volume percentage (β H2) changes from 0 to 7.94% and the idle speed decreases from 2600 to 2400 rpm. The test results show that the engine can achieve better stability and economy due to the coupling effect of mixing hydrogen and reducing the idling. The total fuel flow rate reduces from 24.57 MJ/h at 2600 rpm when pure n-butanol is fueled to 19.35 MJ/h at 2400 rpm when β H2 equals to 7.94%. The period of flame development and propagation are observably decreased by blending hydrogen even if reducing idle speed has a few negative effects. Hydrogen enrichment is an effective way to reduce the emissions of CO and HC. Besides, the negative effects of reducing idle speed on HC and CO emissions are decreased to a negligible level when β H2 passes about 7%. Besides, NOx emission is maintained at an extremely low value in the testing range. Also, enrichment hydrogen can compensate for the negative effects on combustion and emissions of reducing idle speed. [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]