Investigation of the gas injection rate shape on combustion,knock and emissions behavior of a rotary engine with hydrogen direct-injection enrichment

The application of hydrogen direct-injection enrichment improves the performance of gasoline Wankel rotary engine, and the hydrogen injection strategy has a significant impact on combustion, knock, and emissions. The Z160F Wankel rotary engine was used as the investigated compact engine, and the simulation model was developed using CONVERGE software. The combustion, knock and emissions characteristics of the engine were studied with the different mass flow of hydrogen injection, i.e., the trapezoid, wedge, slope, triangle and rectangle type of gas injection rate shape. In the numerical simulations, the in-cylinder pressure oscillations were monitored using monitoring points, and the knock index (KI) was used as an evaluation indicator. The study revealed that the gas injection rate shape significantly affected the mixture of hydrogen and air, thus impacting combustion, knock and emissions. When the injection rate shape was rectangle, the flame speed was faster, the peak pressure in the cylinder was higher, and the corresponding crank angle was earlier, which led to higher pressure oscillations in the cylinder and larger KI. Based on the rectangle injection rate shape, the KI decreased by 75.81%, 33.47%, 26.46% and 76.58% for trapezoid, wedge, slope, and triangle, respectively, and the indicated mean effective pressure increased by 15.68%, 5.07%, 0.56% and 14.98%, respectively. Due to the small difference in maximum temperature, which resulted in very little variation in nitrogen oxides for each injection rate shape, the total hydrocarbon emissions of the trapezoid and triangle injection rate shape was high due to the delayed combustion phase. This paper provides a solution for direct hydrogen injection to improve the combustion, knock and emissions behavior of the rotary engine.