Comparison of combustion, emission and abnormal combustion of hydrogen-fueled Wankel rotary engine and reciprocating piston engine

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 recip-rocating 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.