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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]

Highlights • A CFD model of H 2 -gasoline fueled rotary engine was established and validated. • The CFD model was modified by installing the compound intake ports. • The mean in-cylinder pressure and indicated thermal efficiency were increased. • Combining compound intake with HDI obtained a better engine performance. • CO emission was decreased, but NOx emissions were increased. Abstract The compound intake possesses large port area. Applying it in Wankel rotary engine (WRE) could increase volumetric efficiency and reduce pumping loss. To investigate the effect of the compound intake on the mixture formation and combustion process in gasoline WREs with hydrogen port and direct injected (HPI and HDI) enrichment, a three-dimensional computational fluid dynamics (CFD) model was established and validated. Investigation results showed that the peripheral-ported intake flow plays a leading role in the compound-ported WRE. Because the peripheral-ported intake flow has the same direction with the rotor movement, the formation time of mainstream flow field is shortened and the mean flow speed is increased, the flame propagation in the same direction with mainstream flow field is accelerated. Meanwhile, the improvements in volumetric efficiency and quality of in-charged mixtures result in the rise of temperature and pressure at spark timing, which could also improve the initial thermal conditions. Therefore, the compound intake effectively accelerates the combustion process in WRE. In HPI conditions, compared with the side-ported WRE, the peak in-cylinder pressure and indicated thermal efficiency in compound-ported WRE are respectively increased by 4.5% and 3.9%. In HDI conditions, the flame could propagate to the rear combustion chamber and eliminate the unburned zone, the maximum in-cylinder pressure and indicated thermal efficiency in side-ported WRE with HDI are 84.7% and 6.6% higher than those of in side-ported WRE with HPI. At the same time, the compound intake could further increase the in-cylinder pressure and indicated thermal efficiency by 6.8% and 2.5%, respectively. However, the improved combustion performance increases the in-cylinder temperature, which provides a suitable thermal-atmosphere for nitrogen oxide (NO x) formation. The compound intake increases mass fractions of NO x emissions from 0.111% to 0.141% in HPI conditions and those from 0.268% to 0.284% in HDI conditions. Considering the compound intake promotes the combustion characteristics and effectively decreases carbon monoxide (CO) emission from 0.043% to 0.033% in HPI conditions, and from 0.008% to 0.003% in HDI conditions, it is a feasible way to improve the performance of WREs. Especially, combining it with HDI could obtain a better engine performance under low engine speed and part load conditions. [ABSTRACT FROM AUTHOR]

Abstract The comparative study on performance of the hydrogen/gasoline and hydrogen/n-butanol rotary engines was conducted in the present paper. Considering the stable operation of the engine, for both hydrogen/gasoline case and hydrogen/n-butanol case, the operating conditions were set at: 4000 rpm (engine speed), 35 kPa (intake pressure) and 30 °CA BTDC (spark timing). The total excess air ratio of mixture was maintained at 1.0 through all the tests. The testing results displayed that hydrogen enrichment improved performance of both gasoline and n-butanol rotary engines. To be more specific, brake thermal efficiency was increased, flame development and propagation periods were shortened, the coefficient of variation in flame propagation period was decreased, and the emissions of HC and CO were decreased. NOx emissions were mildly increased after hydrogen addition. Besides, hydrogen/n-butanol rotary engine possessed the similar performance to hydrogen/gasoline rotary engine. Highlights • Performance of HGRE and HBRE was studied. • BTE and Tmax was increased after H 2 blending. • CA0-10, CA10-90 and engine instability were shortened by H 2 addition. • H 2 addition resulted in the reduced HC and CO emissions. • HBRE shares highly similar performance with HGRE. [ABSTRACT FROM AUTHOR]

Highlights • A CFD model of H 2 -gasoline fueled rotary engine was established and validated. • H 2 was direct injected in the combustion chamber under different strategies. • In-cylinder pressure increased with retarded HIT and extended HID. • The lowest CO emission was achieved in HIT of 110 °CA BTDC, HID of 40 °CA. • Higher NO x emissions were acquired in retarded HIT and extended HID. Abstract In Wankel rotary engine (WRE), high mainstream velocity in combustion chamber blocks flame propagating to the end of combustion chamber, which causes high emissions and low combustion efficiency due to unburned mixtures. To solve this problem, a three-dimensional dynamic simulation model of a hydrogen-gasoline blends fueled WRE is built and validated. The in-cylinder mixture formation and combustion process are investigated under different hydrogen injection timing (HIT) and duration (HID) conditions. The study results show that the concentration of hydrogen distributed between the spark plug region and rear combustion chamber increases with retarded HIT and extended HID. Faster flame speeds are obtained for HIT of 110 °CA BTDC and HID of 40 °CA. At a fixed HID of 20 °CA, compared with HITs of 210 and 160 °CA BTDC, the peak in-cylinder pressures for HIT of 110 °CA BTDC are increased by 14.3% and 6.8%, respectively. At a fixed HIT of 110 °CA BTDC, the peak in-cylinder pressure in HID of 40 °CA is 52.3% and 9.21% higher than HIDs of 20 and 30 °CA. The highest in-cylinder pressure is achieved with the hydrogen injection strategy that HIT of 110 °CA BTDC, HID of 40 °CA. However, as the temperature increases with pressure, nitrogen oxide emissions are also increased with retarded HIT and extended HID obviously. Considering the lowest carbon monoxide is achieved and the unburned zone in the rear region of combustion chamber is eliminated in HIT of 110 °CA BTDC, HID of 40 °CA. The hydrogen direct injection strategy that HIT of 110 °CA BTDC, HID of 40 °CA acquires the best engine performance in this research. [ABSTRACT FROM AUTHOR]

The performance of a hydrogen-blended gasoline direct injection engine under various second gasoline direct injection timings is investigated on a modified commercial gasoline direct injection engine. All tests are carried out at a typically congested city-driving condition using lean burn and split gasoline direct injection modes. Results show that under pure gasoline fuel supply mode, brake mean effective pressure, brake thermal efficiency, flame development period, flame propagation period, and maximum in-cylinder pressure vary obviously with various second gasoline direct injection timings and the best second gasoline direct injection timing for engine performance is 130 CAD before top dead center. Blending hydrogen could weaken variations of engine performance related parameters caused by changing second gasoline direct injection timing compared to that under pure gasoline mode. Besides, blending hydrogen could also reduce flame development and propagation periods, and enhance the maximum in-cylinder pressure under the same second gasoline direct injection timing. With hydrogen addition, the coefficient of variations in indicated mean effective pressure drops to less than 1.1%, but second gasoline direct injection timing has no obvious effect on it any more. Besides, adding hydrogen could reduce hydrocarbon and carbon monoxide emissions by 33.10% and 18.28% in average, respectively. Particulate number has a reduction of order of magnitudes (∼10 8 to ∼10 6  n/cm 3 in average). With hydrogen addition, nitrogen oxides emissions increase. [ABSTRACT FROM AUTHOR]

Hydrogen (H 2 ) owns some excellent fuel specialties and can be used as enhancer to improve the performance of original engine. In the present survey, percent of performance improvement of a Wankel gasoline rotary engine by H 2 enrichment was experimentally studied. The tested engine was initially run at idling and then 3000 rpm with an intake pressure of 37.5 kPa. For the two tested operations, H 2 energy percent ( β H2 ) in the total energy was varied from 0% to 37.0% and 0% to 28.3%, respectively. Results indicated that engine performance was improved by extending β H2 . Overall, performance improvement of idling was more effective than that of 3000 rpm. Percent of performance improvement of idling was generally bigger than that of 3000 rpm. Besides, performance improvement by adding H 2 was relatively efficient at low β H2 , especially below 10%. [ABSTRACT FROM AUTHOR]

A CFD model of hydrogen-enriched gasoline Wankel rotary engine is established and validated. The mixture formation and combustion processes are investigated under both hydrogen port and direct injection enrichment conditions with different hydrogen addition levels. It was found that, under hydrogen port injection enrichment conditions, the peak in-cylinder pressure of 6% is 8.4% higher that of 3%. Meanwhile, under hydrogen direct injection enrichment conditions, the peak in-cylinder pressure of 3% hydrogen direct injection enrichment is 15.3% higher than that of 3% hydrogen port injection enrichment. It was also found that the mainstream field with same direction of rotor rotation is formed during the compression stroke and a vortex with high vorticity existed in the combustion chamber. With the effects of mainstream field and vortex, the hydrogen fills more than half volume of the entire combustion chamber under 4%, 5% and 6% HDIE conditions. At the same time, a local low velocity zone is formed around the vortex because the hydrogen direct injection flow slows down the dissipation of vortex. According to the analysis by PREMIX, the fastest flame speed is achieved at equivalence ratios around 1.4. The proper rich hydrogen region distribution is obtained under 4%, 5% and 6% hydrogen direct injection enrichment conditions. Both the enhanced flame propagation by proper equivalence ratio distribution and the reduced local mainstream flow velocity by vortex existence contribute to solving the unburned zone problem. Compared with 6% hydrogen port injection enrichment, the maximum value of in-cylinder pressure of 4%, 5% and 6% hydrogen direct injection enrichment is improved by 59.6%, 88.4% and 91.6%, respectively. However, carbon monoxide and nitrogen oxide emissions are increased obviously. As a relatively low carbon monoxide emission is obtained with 4% case under hydrogen direct injection enrichment conditions and the problem of unburned zone in the rear region of combustion chamber is solved. The hydrogen volume fraction of 4% with direct injection enrichment achieves the best engine performance in this study. [ABSTRACT FROM AUTHOR]

The combustion process within the cylinder directly influences the thermal efficiency and performance of the engines. As for the rotary engine, the long-narrow combustion chamber prevents the mixture from fully burning, which worsens the performance of the rotary engine. As a fuel with excellent properties, hydrogen can improve the combustion of the original engine. In this paper, improvements in combustion of a gasoline rotary engine by hydrogen supplement under different operating conditions were experimentally investigated. The experiment was conducted on a modified hydrogen-gasoline dual-fuel rotary engine equipped with an electronically-controlled fuel injection system. An electronic control module was specially made to command the fuel injection, excess air ratio and hydrogen volumetric fraction. Integral heat release fraction (IHRF) was employed to evaluate the combustion of the tested engine. The tested engine was first run at the idle speed of 2400 rpm and then operated at 4500 rpm to investigate the combustion of the hydrogen-blended gasoline rotary engine under different hydrogen volume fractions, excess air ratios and spark timings. The testing results demonstrated that the combustion of the gasoline rotary engine were all improved when the hydrogen was blended into the chamber under all tested conditions. [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]

The study aims to numerically investigate the combustion and emissions formation processes in a spark-ignition rotary engine fueled with hydrogen-gasoline blends. The Renormalization Group k-ε turbulence coupled with a skeletal primary reference fuel mechanism were adopted to simulate the engine working process under 0%, 2% and 4% hydrogen volume fractions in CONVERGE software. The flow field variation and detailed combustion processes were analyzed and discussed. Results showed that a mainstream flow field along with the rotor movement was formed during the compression stroke and sustained in the combustion chamber until the exhaust valve opening. The center of the burned zone would move in same direction with the mainstream flow. Meanwhile, due to the effect of the mainstream flow, the flame propagation in direction of the mainstream flow was expedited. While the flame propagation in contrary direction was retarded, consequently, the unburned mixtures at rear region of combustion chamber suffered incomplete combustion. The distributions of nitric oxide and carbon monoxide emissions were also dominantly affected by the flow field in the combustion chamber. After hydrogen addition, the increased OH, H and O radicals concentrations combined with the intense flow flied accelerated the combustion process, which resulted in the improvement and advancement of in-cylinder pressure and temperature. Compared with original gasoline case, the peak in-cylinder pressure was increased by 9.1% and 13.7% with 2% and 4% hydrogen blends, respectively. With hydrogen enrichment, the increased in-cylinder temperature promoted the formation of nitric oxide emission. Besides, Carbon monoxide emission was decreased with the increase of hydrogen addition fraction. [ABSTRACT FROM AUTHOR]

In the present paper, the cyclic variations of a hydrogen-blended gasoline rotary engine operated under various conditions were experimentally investigated. The experiments were carried out on a modified hydrogen-gasoline dual-fuel rotary engine equipped with an electronically-controlled fuel injection system. An electronic control module was specially made to command the fuel injection, excess air ratio and hydrogen volumetric fraction. The tested engine was first run at idle condition with a speed of 2400 rpm and then operated at 4500 rpm to investigate the cyclic variations of a hydrogen-enriched gasoline rotary engine under different hydrogen volumetric percentages in the total intake, excess air ratios and spark timings. The experimental results demonstrated that the coefficient of variations (in peak pressure, engine speed, flame development period and flame propagation period) of the gasoline rotary engine were distinctly decreased with the increase of hydrogen volume fraction under all the tested conditions. In particular, at idle and stoichiometric conditions, the coefficient of variation in CA0-10 and CA10-90 were reduced from 9.25% to 5.01%, 15.40% to 8.70%, respectively. [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 paper presented an experimental study about the idle performance of a rotary engine fueled with hydrogen and gasoline blends. The idle speed was reduced from original 2400 to 2300 and 2200 rpm, and hydrogen energy percentage ( β H2 ) was varied from 0% to 35.0%. Test results showed that cyclic variation was raised with the decrease of idle speed whereas reduced with the increase of β H2 . Both decreasing idle speed and increasing β H2 were effective on reducing engine fuel consumption. Total fuel energy flow rate was effectively dropped from 22.4 MJ/h under “2400 rpm and β H2 = 0%” to 20.01 MJ/h under “2200 rpm and β H2 = 35.0%”. Combustion duration was reduced through increasing β H2 . HC and CO emissions were dropped with the increase of β H2 , but increased after reducing idle speed. CO 2 emission was decreased after reducing idle speed and adding hydrogen. [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 limit of properties of gasoline and irregular design of chamber, the pure gasoline rotary engine generally encounters partial burning, increased noxious emissions or even misfire at lean conditions. This situation could be deteriorated at idle because of the high variation in the intake charge and low combustion temperature. Hydrogen addition is proved to remit the deterioration of performance of sparked-ignited (SI) engines at idle and lean conditions. This paper conducted an experiment on a modified rotary engine equipped with gasoline and hydrogen port-injection systems to explore the performance of a hydrogen–gasoline rotary engine (HGRE) at idle and lean conditions. An electronic management unit (EMU) was invented to manage spark and fuel injection. Excess air ratio ( λ ) and hydrogen volumetric fraction in the total intake ( α H 2 ) were also governed through the EMU. For this study, the HGRE was operating at idle and α H 2 was kept at 0% and 3%, respectively. For a specific α H 2 , gasoline flow rate was reduced to make the HGRE run at desired λ . Results indicated that engine fluctuation and fuel energy flow rate were both decreased after hydrogen addition. Combustion duration was cut down and central heat release point was advanced after hydrogen addition. Peak chamber temperature ( T max ), pressure and heat release were enhanced after hydrogen blending. HC, CO and CO 2 emissions were simultaneously reduced because of hydrogen enrichment. Specifically, at λ = 1.00, HC, CO and CO 2 emissions were respectively reduced from 42,411 to 26,316 ppm, 1.86 to 0.78% and 9.96 to 8.58% when 3% hydrogen was added. [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]

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]

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]

The hydrogen-enriched gasoline engine is a promising option for future spark-ignited (SI) engines. However, the lack of quasi-dimensional combustion models for hydrogen-gasoline blends restrains the efficient prediction of its performance for varying operating conditions and hydrogen enrichment strategies. In this paper, a quasi-dimensional model was developed and validated for hydrogen-enriched gasoline engines with a new laminar flame speed expression. Correspondence between the calculated and experimentally measured engine combustion parameters was observed for different hydrogen addition levels. The comparison results indicated that the proposed quasi-dimensional model is suitable for engine performance prediction of hydrogen-enriched gasoline engines. [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]

This study aims to explore the combined effect of injection angle and injection pressure in a gasoline direct injection rotary engine through numerical simulation. Simulation results show that with the increase of injection angle, the fuel impinging position changes from the rotor recess to the middle cylinder block. At the same injection angle, the fuel enrichment area turns to the front of the combustion chamber with the increase of injection pressure. The lower injection angle is helpful to obtain a more uniform fuel distribution. Especially, with increase of injection pressure, the in-cylinder inhomogeneity index presents a downward trend. Under different injection pressures, the flame propagation period of the 0° injection angle is the most stable. The stable flame development and propagation processes make it easy to obtain higher indicated thermal efficiency. The highest indicated thermal efficiency is obtained at 0° injection angle and 15 MPa injection pressure, which is up to 24.99%. Moreover, compared with the fuel intake port injection, part of direct injection strategies help to get higher in-cylinder peak pressure. The higher in-cylinder temperature promotes the formation of NOx, but the organization of the in-cylinder fuel distribution can effectively reduce CO and Soot emissions. • A rotary engine simulation model with gasoline direct injection was established and validated. • The combined effects of injection angle and injection pressure were investigated. • The lower injection angle can obtain higher in-cylinder pressure and indicated thermal efficiency. • Lower in-cylinder inhomogeneity index is helpful to reduce Soot and CO emissions. [ABSTRACT FROM AUTHOR]

Abstract: This paper numerically investigated the combustion process in a spark-ignited (SI) engine fueled with hydrogen–gasoline blends through the computational fluid dynamics (CFD) calculation. Satisfying agreement between the calculated and measured in-cylinder pressure traces was observed for all test cases. The calculation results demonstrated that, the hydrogen addition availed the increased flame propagation speed and the enhanced degree of flame wrinkling. Compared with the original engine, the peak flame propagation speed was raised by 37.18% and 60.47% at the hydrogen volume fractions of 3% and 6%, respectively. The peak average flame surface densities of the 3% and 6% hydrogen-enriched engines were 28.88% and 35.99% higher than that of the original engine, respectively. [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: In this paper, a laminar flame speed correlation was developed and validated for the computational fluid dynamics (CFD) simulation of hydrogen-enriched gasoline engines. This correlation was derived through the tabulated data which was determined by a self-developed calculation program according to the flame temperature-based mixing rule. Wide ranges of hydrogen volume fractions (0–10%), equivalence ratios (0.6–1.5), unburned gas temperatures (300–2500 K), pressures (1–50 bar) and residual gas mass fractions (0–20%) were simultaneously considered in this correlation to cover the burning conditions encountered in SI engines. The estimated values of the new correlation were found to be in satisfying agreement with the experimental data under normal burning conditions. Moreover, the new correlation was implemented in the extended coherent flame model to evaluate its suitability for CFD simulation. Satisfying agreement between the experimental and calculated results was observed under all examined hydrogen addition levels. This indicated that the new correlation was suitable for the CFD simulation of hydrogen-enriched gasoline engines. [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: This paper proposed a new combustion strategy for the spark-ignited (SI) engines. A gasoline engine was converted into a hybrid hydrogen–gasoline engine (HHGE) by adding a hydrogen injection system and a hybrid electronic control unit. Different from the conventional gasoline and hydrogen–enriched gasoline engines, the HHGE is fueled with the pure hydrogen at cold start to produce almost zero emissions, with the hydrogen–gasoline blends at idle and part loads to further improve thermal efficiency and reduce emissions, and with the pure gasoline to ensure the engine power output at high loads. Because the HHGE is fueled with the pure gasoline at high loads and speeds, experiments are only conducted at clod start, idle and part load conditions. Since lean combustion avails the further improvement of the engine performance, the HHGE was fueled with the lean mixtures in all tests. The experimental results showed that the hybrid hydrogen–gasoline engine was started successfully with the pure hydrogen, which produced 94.7% and 99.5% reductions in HC and CO emissions within 100s from the onset of the cold start, compared with the original gasoline engine. At an excess air ratio of 1.37 and idle conditions, indicated thermal efficiency of the 3% hydrogen–blended gasoline engine was 46.3% higher than that of the original engine. Moreover, the engine cyclic variation was eased, combustion duration was shortened and HC, CO and NOx emissions were effectively reduced for the hybrid hydrogen–gasoline engines. [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: 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: 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: 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: 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]

In order to improve the performance, reduce the emissions and enhance the calibration efficiency of a gasoline Wankel rotary engine (WRE), three advanced machine learning (ML) methods, including artificial neural network (ANN), support vector machine (SVM), and Gaussian process regression (GPR), were applied to develop the prediction model of the torque, fuel flow, nitrogen oxide, carbon monoxide, and hydrocarbon. The effect of feature numbers was examined using the recommended parameters of the ANN, SVM, and GPR models. It was concluded that using speed, manifold absolute pressure, and air fuel ratio as input parameters to build the prediction model performed best. The generalization ability of the three ML models was compared on the interpolative and extrapolative data sets using the extended recommendation parameters. The results showed that the GPR model performed the best generalization ability in scarce data sets and was simpler to train compared with ANN and SVM. The response surfaces constructed using the GPR model were very smooth and accurate, in which the coefficient of determination for all the predicted parameters was more than 0.99. It is strongly proposed that the GPR approach is a universal approach which will be an essential direction for WRE system control and surrogate model modeling. [Display omitted] • Gasoline Wankel rotary engine prediction models are established. • The advanced machine learning methods are tested in scarce data sets. • The input feature numbers of the machine learning model are determined. • GPR model shows the best result in performance and emissions prediction. [ABSTRACT FROM AUTHOR]

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]

• A gasoline direct injection rotary engine CFD model was established and validated. • The coupled effects of injection position and injection angle were investigated. • The mixture formation, combustion and emissions process were analyzed. • Direct injection obtains higher indicated thermal efficiency than intake port injection. • Upper injection position with 0° injection angle can reduce carbon-based emissions. A computational fluid dynamics model was established and validated to numerically investigate the effects of different injection positions and injection angles on the mixture formation and combustion process in a gasoline direct injection rotary engine. The results show that as the injection position approaches the top dead center and the increasing injection angle, the rich zone of fuel changes from the rear to the front of the combustion chamber. The local equivalence ratio near the two spark plugs shows an increasing trend with the injection position upward and the increasing injection angle. Compared with the lower and middle injection positions, the upper injection positions can make fuel more concentrated near the leading spark plug and the trailing spark plug at ignition timing. The injection strategies corresponding to the upper injection position are conducive to complete combustion, in which the mass fraction of fuel burned all beyond 99%. Besides, with the increasing injection angle, the oil film formation position changes from the rotor recess to the middle cylinder block, which further affects the mixture formation and combustion process. Especially, the highest peak pressure is obtained at 0° injection angle corresponding to the upper injection position and is 12.39% higher than the in-cylinder peak pressure of intake port injection. [ABSTRACT FROM AUTHOR]

[Display omitted] • An SVM-based prediction model is developed for cyclic variation. • The data processing, kernel function, loss function of the SVM model is discussed. • The R2 of idle and part load conditions are 0.9904 and 0.9972, respectively. • SVM coupled genetic algorithm shows the best performance and training speed. To investigate the influence of operation parameters on the cyclic variation of the Wankel rotary engine with hydrogen enrichment, an intelligent regression model based on the support vector machine (SVM) was implemented to predict the cyclic variation. For modeling the prediction model, the cyclic variation of speed ( CoV n ) and cyclic variation of the main combustion duration ( CoV C A 10 - 90 ) were used as an evaluator for idle and part load conditions, respectively. The operation conditions including main fuel type (gasoline and n-butanol), hydrogen volume percentage (β H 2 ), excess air ratio (λ), ignition timing (IT)and speed were used as independent variables. When optimizing the prediction model, the data processing method, kernel function, loss function and optimization method on the prediction performance were discussed in detail. The results indicated that an optimized model can be obtained by using genetic algorithm combined with [0, 1] data processing method, and the coefficient of determination, mean square error and mean absolute percentage error of CoV n were 0.9904, 0.0783 and 0.3845%, corresponding to CoV C A 10 - 90 were 0.9972, 0.0197 and 1.1729%, respectively. For the CoV n , gasoline as the main fuel was lower than the n-butanol at the same operating condition. The CoV n at high speed was greater than that at low speed. When operating at part load conditions, the CoV C A 10 - 90 decreased with the increasing β H 2 , and first decreased and then increased with advancing IT. [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]

• The characteristics of a rotary engine are predicted by support vector machine model. • The coefficient of determination of the optimized models is greater than 0.98. • The effects of parameters on performance, combustion and emissions are studied. • The optimal thermal efficiency and nitrogen oxides are 18.12 % and 248.58 ppm. The purpose of current research was to implement an intelligent regression model and multi-objective optimization of performance, combustion and emissions characteristics for a hydrogen-enriched gasoline rotary engine. The brake thermal efficiency (BTE), fuel energy flow rate (E f), nitrogen oxides (NO X), carbon monoxide (CO) and hydrocarbon (HC) were predicted by intelligent regression model with hydrogen volume fraction (α H 2 ), excess air ratio (λ) and ignition timing (IT) as independent variables. The intelligent regression models were based on support vector machine (SVM) and optimized by the genetic algorithm (GA) to obtain the optimal parameters of the regression model. The data for training the SVM model were derived from the experimental results of a hydrogen-enriched rotary engine, in which the speed was kept constant at 4500 r/min, the absolute manifold pressure remained at 35 KPa, the variation of α H 2 , λ and IT were 0–6%, 1–1.3 and 24–42 °CA before top dead center (bTDC), respectively. After optimized by GA, the coefficient of determination of BTE, E f , NO X , CO and HC between the SVM model and the corresponding data were greater than 0.98, and the mean absolute percentage error were <1%. The performance, combustion, and emissions characteristics including BTE, E f , NO X , CO and HC were considered for multi-objective optimization to obtain higher performance and lower emissions, and were solved using the non-dominated sorting genetic algorithm II. For this study, when the Pareto-optimal solutions were obtained, the optimal operating parameters were further obtained by limiting the performance and emissions parameters with the α H 2 of 5.06%, λ of 1.09%, and IT of 34.27 °CA bTDC. [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]

For spark-ignited gasoline engine, cold start emission of hydrocarbon (HC) and carbon monoxide (CO) is a long-term concern due to a large portion of HC and CO emitted during cold start period. Starting by hydrogen or adding a fraction of hydrogen can greatly reduce the engine cold start emissions of HC and CO due to the carbonless and excellent combustion characteristics of hydrogen. However, the higher combustion speed and temperature of hydrogen tend to cause more NO x emissions. Therefore the amount of hydrogen addition to conventional fuel should be optimized at different engine operating conditions. In this paper, a spark ignited gasoline engine was retrofitted to a hydrogen gasoline flexible fuel engine by adding a set of hydrogen injection system, and the engine can be fueled with gasoline, hydrogen or both. An electronic control system was developed and applied to control the injection timings and durations of hydrogen and gasoline. In order to reduce cold start emissions of HC and CO, the engine started with hydrogen and then changed to run on gasoline with hydrogen addition or on pure gasoline to avoid high NO x generation. The basic composition of the control system was introduced and the cold-start emission control strategy for the hydrogen gasoline flexible fuel engine was investigated. And finally the emission of the vehicle running on the hybrid hydrogen and gasoline fuel mode was tested over the New European Driving Cycle (NEDC), and compared with that of the original gasoline car. The experimental results showed that the cold start emissions of HC and CO greatly decreased when the vehicle engine operating on hybrid hydrogen gasoline mode. [ABSTRACT FROM AUTHOR]