Effect of multiple fuel injection strategies on mixture formation and combustion in a hydrogen-fueled rotary range extender for battery electric vehicles

Abstract

The hydrogen-fueled range extender based on the rotary engine is a promising solution for battery electric vehicles due to key advantages such as: high efficiency, small packaging dimensions and low weight within the framework of the near zero-emission concept. Although rotary engine has been examined over the past years, the detailed knowledge of hydrogen combustion in the rotary engine with direct injection system has not been investigated properly. In this paper, the rotary range extender was numerically studied with a focus on the influence of the direct multiple injection strategies on hydrogen distribution and combustion. The result demonstrates that due to large flame speed and diffusion length the engines fueled by pure hydrogen differ significantly from the engines with conventional fuel. The process is characterized by the weak influence of turbulence on the flame during almost the whole combustion stroke except for the late stages when 70% of the fuel is already burnt. Hence the difference in the injection strategies lead to different local hydrogen distribution that has effects on combustion rate and performance characteristics significantly. Fuel stratification leads to the formation of subregions with various hydrogen concentration. The lean mixture cannot provide enough high temperature, whereas the rich mixture is characterized by a lack of oxygen. The total NOx formation can be twice lower in comparison with premixed combustion at the same averaged equivalence ratio. The direct multiple injection strategy allows the use of a higher averaged equivalence ratio up to 0.8 which results in larger power density in combination with low NOx emission.