Numerical study on the effects of spark plug position and ignition timing on the performance of hydrogen direct-injection oval rotary engine under different excess air ratio conditions

The oval rotary engine (ORE) has smooth rotation, high power density, and a more flexible combustion chamber shape than the Wankel rotary engine, with a great future in carbon-free power. This ORE numerical model works with the hydrogen direct-injection and spark ignition to study the impact of different spark plug positions, ignition timings, and excess air ratio (λ) on the engine performance. The results indicate that high turbulence occurring near the top dead center (TDC) in the combustion chamber edge accelerates flame propagation on trailing spark position in combustion chamber. The case with the spark position on the trailing side of the combustion chamber has the shortest ignition delay period of 3.9° crank angle (CA) and main combustion period of 11.7°CA. In-cylinder vortices become smaller and hydrogen-air mixing becomes poorer with delaying ignition. Mixture stratification in rich mixture results in NOx emission of the case with λ of 1.4 27 % lower than λ of 1.6. Overall, the optimal working condition is λ of 1.8 with ignition at 6° CA before TDC, which is 21 % higher on IMEP, just 0.9 % lower on ITE of 36.4 %, but 19.4 % higher on NOx emission than the case with ultra-lean mixture.