In-depth analysis of the key combustion parameters in the hydrogen-fueled Wankel rotary engine

Hydrogen-fueled Wankel rotary engine is considered the potential carbon-free power device. Due to the special structure and operating mode, the heat release process of the Wankel rotary engine is significantly different from the piston engine. To understand the heat release process and further optimize its combustion, the present work conducts a series of experiments, such as engine speed, excess air ratio and qualitative control experiments, to analyze the key combustion parameters under different conditions. The main results are as follows: Both engine speed and excess air ratio play important roles in flame development and propagation. In particular, the excess air ratio only affects the early stage of flame propagation due to its impact on the later stage is covered by incylinder turbulence. CA0-10 is prolonged from 15.9 to 11.2 degrees CA while CA50-90 does not show regular changes when the excess air ratio is reduced from 2.0 to 1.2. For qualitative control mode, variation of combustion parameters will become the obstacle to expanding lean flammable limits. In particular, the distribution of CA10 and CA50 or CA90 and CA50 can be fitted by linear regression, and the gradient and intercept of the fitted line can be used to represent engine speed and excess air ratio. 1000 r/min corresponds to 1.07 gradient and 2500 r/ min is 1.27. NO emission is closely related to time-based CA0-10 and CA10-90 that can be applied as the independent variable of the Support Vector Machine with radial basis function kernel function to predict NO emission, and the maximum coefficient of determination is 0.92.