Hydrogen direct injection for knock suppression and combustion optimization in elliptical rotary engines for range-extender

Hydrogen direct injection technology can effectively control fuel-air mixture distribution, thereby optimizing the combustion and emission performance of elliptical rotary engines. This paper investigates the effects of combustion chamber configuration and hydrogen injection angle on the flow, combustion, and emissions. The results show that, under both types of offset combustion chamber conditions, a 0° injection angle prevents excessive fuel accumulation and achieves better fuel-air mixing. However, a central combustion chamber configuration increases the tendency toward incomplete combustion and knock. Overall, aligning the combustion chamber offset with the rotor rotation direction significantly improves in-cylinder flow characteristics. Under this condition, combining a 0° injection angle achieves optimal distribution of the hydrogen-air mixture, thereby effectively ensuring complete combustion and suppressing the tendency for knock. Meanwhile, the indicated thermal efficiency reaches 31.08%, the indicated mean effective pressure reaches 0.54 MPa, and the NOx emissions are controlled at 6.24 g/(kW∙h). This study provides theoretical guidance for the design of combustion chambers and the optimization of injection strategies, and is of great significance for reducing carbon emissions.