Effect of asymmetric fuel injection on combustion characteristics and NO_x emissions of a hydrogen opposed rotary piston engine

Opposed rotary piston engines have the characteristics of high-power density and simple mechanisms. The applications of hydrogen fuel to internal combustion engines significantly are without carbon dioxide emission, alleviating the global warming. In this paper, hydrogen fuel was asymmetrically injected into combustion chambers to increase hydrogen penetration distance via; in the meantime, the engine performance and nitrogen monoxide (NO) emission with different ignition timing are explored by numerical simulation method. The symmetrical fuel injection scenario was provided as a baseline. In the scenarios of asymmetrical fuel injection, the engine had the best hydrogen injector position and ignition timing. Peak in-cylinder pressure P_max reached 56.0 bar under ignition timing t_i of −14.2° CA before top dead centre (bTDC) and hydrogen injector position (θ₂) of 60.5°; in the meantime, heat loss rate H_L and heat release rate Q_r reached maximum values. Compared with the symmetric fuel injection engine, the peak NO emission of the asymmetric fuel injection engine was reduced by 15%. The proportions of energy loss by cylinder walls of asymmetric fuel injection engine were low and showed low dependency on ignition timing and hydrogen injector layout. Additionally, the asymmetric hydrogen injection structure makes hydrogen distribute evenly in the combustion chamber.