Effects of Scavenging-Port Semi-Direct Injection Strategy on Mixture Formation for a Two-Stroke Spark-Ignition Kerosene Piston Engine

Abstract The two-stroke spark-ignition (SI) kerosene piston engines (KPE) are commonly utilized in lightweight unmanned aerial vehicles. The quality of mixture formation is crucial for the engine performance. This paper investigates the mixture quality in a semi-direct injection (SDI) SI KPE. Computational models were established using a 1D simulation tool and a 3D computational platform to analyze the effects of injection pressure, injection timing, and fuel temperature on atomization and mixture formation. The results indicate that increasing injection pressure promotes a more uniform mixture distribution. Higher injection pressures also enhance the formation of fuel film. At the top dead center (TDC), the average equivalence ratio (ER) with an injection pressure of 0.7 MPa is 3.8% higher than that of 0.3 MPa and 1.9% lower than that of 0.5 MPa. Delaying the injection timing increases the pressure difference between the cylinder and scavenging port, weakening fuel penetration and improving the fuel gasification rate. When the injection timing is set to 180 °CA ATDC, the average ER at TDC is 10.4% higher than that at 140 °CA ATDC, with a 6.6% decrease in fuel capture rate. Increasing fuel temperature effectively enhances the fuel gasification rate. However, excessively higher fuel temperatures will not significantly improve mixture quality. At a fuel temperature of 380 K, the average ER at TDC is 2.9% higher than that at 340 K. Response surface analysis reveals that the control parameters affect the average ERs in the following order of influence: injection timing, fuel temperature, and injection pressure. This study provides theoretical support for optimizing control parameters in SDI SI KPEs.