Abstract: To investigate the coupling effect of the turbulent flow field and injection position on mixture formation and combustion process in the spherical combustion chamber of an X-type rotary engine under a hydrogen-air premixed atmosphere, a three-dimensional simulation model is constructed based on CONVERGE software. The fuel injection characteristics and combustion process are investigated at four in-cylinder direct injection positions: top, bottom, left and right. It is demonstrated that stronger turbulence is induced during the intake stroke with left and top injection. Among them, uniform mixture distribution is achieved at the end of the compression stroke with left injection, as the spray direction is coordinated with the intake flow. For right injection, the reverse fuel spray leads to the weakest turbulence intensity, and fuel retention is observed in local regions. The shortest ignition delay period is obtained with left injection, while the longest ignition delay, the highest peak heat release rate and the fastest combustion process are presented with right injection. Compared with the other three injection positions, the highest indicated work per cycle of 73.4 J is achieved with right injection, although knock risk is introduced. Through the adoption of four typical injection positions, the coupling law between injection position, in-cylinder flow field evolution and combustion dynamics is revealed, which provides a theoretical basis and data support for the refined design of the combustion system of direct-injection X-type rotary engines.

Key words: X-type rotary engine, fuel injection position, flow inside the cylinder, combustion characteristic