Comprehensive comparison of single-stage and novel two-stage hydrogen direct injection strategies on the combustion and thermodynamic performance of X-type rotary engine using gasoline-hydrogen fuel

In this paper, the CFD simulation model of a high-efficiency X-type rotary engine using premixed gasoline and hydrogen direct injection is established. The effect of hydrogen injection timing on combustion, pollutant emissions, and thermodynamic performances is investigated under hydrogen single-stage direct injection (HSDI). Furthermore, a novel hydrogen two-stage direct injection (HTDI) strategy using different first injection mass fractions (FIMF) and the same total injection pulse width of 3.5 °CA is proposed for improving combustion performance in the later phase under HSDI. The results show that the hydrogen injection timing of 290 °CA presents a 6.09% higher indicated thermal efficiency than that of 270 °CA under HSDI. The delay of the hydrogen injection timing leads to a decrease in soot emission. The optimal HTDI strategy is obtained at the FIMF of 60%, which shows a 6.35% higher combustion efficiency and a 0.89% higher indicated thermal efficiency than the optimal HSDI.