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The hydrogen-fueled Wankel rotary engine with excellent power and emission characteristic is under spotlight, while the leakage is still the major problem for Wankel rotary engine, especially the leading spark plug leakage. The peak pressure is increased from 3.34 MPa to 3.52 MPa and the indicated thermal efficiency reaches maximum value of 38.29% when the moving distance of leading spark plug is −6.5 mm, and the mass of leakage fresh mixture is reduced from 0.00311 g to 0 g. When leading spark plug is moved to minor axis, the flow field structure of working chamber is enhanced. However, the peak pressure and indicated thermal efficiency decrease when the moving distance of leading spark plug exceeds −6.5 mm. The excess leakage residual gas has negative effects on combustion. The optimum moving distance of leading spark plug is −6.5 mm at 3000 rpm with λ of 1.6. • The leakage mechanisms of spark plugs are analyzed. • The influence of leading spark plug location on gas leakage is analyzed. • The influence of leading spark plug location on combustion is analyzed. • The influence of leading spark plug location on flow field is analyzed. • The optimum location of leading spark plug is given. [ABSTRACT FROM AUTHOR]

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

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

• Knock of hydrogen-fueled Wankel rotary engine is investigated in this work. • Effect of ignition timing, spark plug location and number, λ and speed are studied. • Knock intensity with distribution, knock duration and cyclic variation are analyzed. • All of aspects studied in this work have significant effects on the knock. Hydrogen-fueled Wankel rotary engine (HWER) is an excellent power device with superior power and emission performances. Besides, unlike hydrogen-fueled reciprocating piston engines, HWRE is less prone to backfire due to its structural advantages. However, limited by its long combustion chamber, knock, one of abnormal combustion in engines, still hinders the development of HWER. Hence, based on this consideration, the goal of this work is to investigate the knock of HWRE from different aspects, including ignition timing, spark plug number, spark plug location, excess air ratio and engine speed, to provide relevant information for the design of hydrogen-specific WRE. The results show that the knock intensity gradually increases as the ignition timing is advanced, the excess air ratio is decreased and the engine speed is increased, but the knock duration shows different variations. Adopting dual spark plugs tends to lead to stronger knock caused by unstable combustion of hydrogen, while only adopting leading spark plug tends to lead to the knock caused by auto-ignition. When dual spark plugs are used, the leading spark plug is more responsible for the knock caused by unstable combustion and the trailing spark plug is more responsible for the knock caused by auto-ignition. [ABSTRACT FROM AUTHOR]

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

• The model of HFRE with active pre-chamber TJI was established. • The combustion characteristic of HFRE-SC was analyzed. • The optimum HIT and HID was obtained. Hydrogen can be used as fuel to replace gasoline, with the benefit of reducing harmful emissions of rotary engine (RE). The swirl chamber (SC) coupling spark plug and nozzle will achieve diffusion combustion and higher power as compared to the conventional spark plug. In the current work, a CFD model of a hydrogen-fueled rotary engine with swirl chamber (HFRE-SC) is established to study the impacts of hydrogen injection timing (HIT) and hydrogen injection duration (HID) on combustion characteristics of HFRE-SC. Results reveal that SC combustion system may achieve more combustion efficiency and higher indicated power when compared to port injection (PI). Moreover, lean hydrogen in the rear of combustion chamber (ROCC) can result from retarding HIT and extending HID. In addition, when the rich zone in SC moves toward the spark plug, making it difficult for flames to develop and spread. The best performance can be obtained when using the HIT at 75 °CA BTDC and the HID during 35 °CA, with an 8.42 % up in indicated power compared to the PI. [ABSTRACT FROM AUTHOR]

Highlights • A CFD model of gasoline/H 2 fueled rotary engine was established and validated. • The ignition system consisted of leading-spark plug and trailing-spark plug. • H 2 was direct injected in the combustion chamber under varying DSP arrangements. • The preferable combustion was achieved when the DSP positioned symmetrically. • CO emission notably reduced and NO x emission slightly increased. Abstract A gasoline rotary engine enriched with directly injected hydrogen could be regarded as an appealing option to improve combustion efficiency while reducing emissions. In this paper, a three-dimensional dynamic simulation model coupling with the chemical kinetic mechanisms was established using CONVERGE software and validated by the experimental data. The numerical model was implemented for evaluating the influences of varying duel-spark plug locations on flow field distributions, combustion processes and major emissions formation of a gasoline rotary engine with hydrogen direct injection enrichment. Simulation results showed that, a mainstream flow field formed during the end period of the compression stoke whose direction was identical to the rotor rotating direction. The variation of trailing-spark plug location resulted in slight influence on the mean flow velocity as well as notable impact on hydrogen concentration and turbulent kinetic energy distribution. It was conducive to initial ignition when the local equivalence ratio was intensified near the duel-spark plug on the leading side of the combustion chamber. Higher hydrogen concentration near spark plugs could effectively improve the combustion intensity. The preferable combustion and emission performance were achieved when the duel-spark plug positioned symmetrically with respect to the minor axis. Compared with the scheme of the closest duel-spark plug, the peak pressure increased by 24.4% and corresponding crank position advanced by 9.2°CA. Despite nitric oxides emissions increased slightly, carbon monoxide emission notably reduced by 57.6% versus the scheme of the farthest duel-spark plug. When the leading-spark plug remained constant, the trailing-spark plug arranged on the major axis of cylinder wall and kept an appropriate offset from the minor axis was recommended in engineering applications. [ABSTRACT FROM AUTHOR]

In this study, a double spark plugs direct injection rotary engine is used to investigate the effects of synchronous and asynchronous changes of ignition timing on combustion and emission performance. The three-dimensional dynamic model was established by CONVERGE software and validated by the experimental data. The results indicate that setting the fuel injector toward the spark plug can reduce the fuel distribution at the tail of the combustion chamber, and the in-cylinder mixture inhomogeneity index gradually increases with the advance of the ignition timing. Compared with the synchronous change of ignition timing, advancing the ignition timing of the tailing spark plug can promote the combustion process. When the ignition timing of the leading spark plug is too early, the flame front will be irregular. With the advance of ignition timing, CA 0–10 corresponding to synchronous and asynchronous change all gradually increase, and the change of CA 10–90 is more stable than that of CA 0–10. Whether the ignition timing is changed synchronously or asynchronously, with the advance of the ignition time, the in-cylinder pressure shows an upward trend. The mean in-cylinder pressure corresponding to the synchronous change with the same change amplitude is slightly higher than that of asynchronous change. The peak pressure of 16.4% higher than that of the original engine can be obtained by adopting the ignition strategy of the synchronous advance of 30° CA. Under this ignition strategy, the temperature and NOx mole fraction in the combustion chamber are all the lowest. • A direct injection rotary engine CFD model was established and validated. • The combined effects of direct injection and ignition strategy were investigated. • The mixture formation, combustion, and emissions process were analyzed. • The in-cylinder inhomogeneity index increases with the advance of ignition timing. • The synchronous advance of ignition time by 30° CA can increase the pressure by 16.40%. [ABSTRACT FROM AUTHOR]

• Two calculation methods for the leakage area of spark plug cavities are given. • The leakage gas mass of three types apex seal leakage is calculated. • The effects of three types apex seal leakage on engine performance are compared. • Measures to reduce apex seal leakage are given. • The effects of the movement of leading spark plug on leakage are calculated. Under the background of carbon peaking and carbon–neutral, the hydrogen-fueled Wankel rotary engine with excellent power and emission characteristic is under the spotlight. The leakage problem, especially the apex seal leakage, is considered to be an important engineering problem restricting the development of hydrogen-fueled Wankel rotary engine. To make up for research gaps, this study was conducted to investigate the effects of three types of apex seal leakage on engine performance. Two methods for calculating the leakage area of spark plug cavities are proposed and compared, and the definition method based on leakage direction is more consistent with the experimental results. The leading spark plug leakage and corner seal leakage has the greatest impact on peak pressure and IMEP, which reduce the peak value of pressure by 0.249 MPa and 0.047 MPa, and reduce the IMEP by 8.68 % and 10.51 % respectively. In addition to reducing the leakage area, reducing the distance between leading spark plug and minor axis by 5.5 mm could increase the peak pressure by 0.2 MPa and reduce the leakage from the working chamber to the adjacent chambers from 0.055 g to 0.038 g. [ABSTRACT FROM AUTHOR]

• Hydrogen Wankel rotary engine and reciprocating piston engine are compared. • This work studies the comparison from combustion, emission and abnormal combustion. • HWRE can achieve excellent power, but with low efficiency and poor NO emission. • Backfire won't prevent the application of HWRE, but knock will. • Efficiency, thermal load and knock need to be improved in the development of HWRE. Hydrogen-fueled Wankel rotary engine (HWRE) as an excellent power device deserves more in-depth study. The goal of this work is to provide a more comprehensive understanding of the pros and cons of HWRE and what should be done when developing a hydrogen-specific WRE by comparing HWRE with hydrogen-fueled reciprocating piston engine (HRPE), as well as some gasoline-fueled conditions, in terms of combustion, emissions and abnormal combustion. The results show that HWRE can achieve higher power per displacement compared to the RPE fueled by whether gasoline or hydrogen, as well as slightly low brake thermal efficiency and extremely poor NO emission. At 2500 r/min, the maximum power per displacement of HWRE is 1.66 and 1.23 times that of hydrogen and gasoline RPE, respectively, however, accompanying absolute reductions of 4.96% and 3.06% in maximum brake thermal efficiency. In addition, the characteristics and mechanisms of abnormal combustion in HWREs are different compared to HRPEs. In particular, in HWRE, the backfire can be eliminated by the improvement of the spark plug hole, while the knock problem is more prominent. Overall, HWREs have the potential to win a place in the future of zero-carbon engines, however, some works, such as improving thermal efficiency, reducing thermal load and preventing knock, need to be done for the development of hydrogen-specific WRE. [ABSTRACT FROM AUTHOR]

• A rotary engine simulation model with gasoline port and direct injection was established and validated. • The combined effects of ignition position and injection method were investigated. • Higher in-cylinder pressure can be obtained by direct injection under the same ignition strategy. • Using double spark plugs ignition and port injection can reduce carbon-based emissions. This research aims to numerically investigate the combined effect of ignition position and injection method on the gasoline rotary engine. The three-dimensional dynamic model was established by CONVERGE software and validated by the experimental data. The results indicate that compared with port injection, the direct injection leads to obvious fuel stratification in the combustion chamber, and the local equivalence ratios around the two spark plugs are different. The index of in-cylinder fuel inhomogeneity corresponding to direct injection decreases linearly with the progress of the mixing process. Adopting the double spark plug can obtain a higher release heat rate and combustion efficiency than adopting the single spark plug ignition. Higher in-cylinder peak pressure and indicated thermal efficiency also can be obtained by using double spark plugs ignition. Only using leading spark plug ignition would cause a large in-cylinder unburned area, resulting in poor power performance of the rotary engine. In particular, the direct injection can obtain higher mean in-cylinder pressure than the port injection, but the indicated thermal efficiency of port injection is higher than that of direct injection. In the aspect of emissions, double spark plugs ignition would lead to higher in-cylinder temperature and NOx content than other ignition modes, but double spark plugs ignition can alleviate incomplete combustion and reduce HC emission. Under the same ignition strategy, the port injection can effectively reduce CO emission than direct injection. [ABSTRACT FROM AUTHOR]

• 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]