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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]

• 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]

• 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]