Asymmetric spray characteristics of opposed-piston two-stroke gasoline direct injection engine

Abstract

The opposed-piston two-stroke (OP2S) gasoline direct injection (GDI) engine has a larger stroke-bore ratio than conventional piston-rod-crank engine, and its fuel injector and spark plug are arranged on the side wall of the cylinder liner, which puts forward new requirements for the distribution of spray and mixture formation. In this paper, an asymmetric spray method is designed on the intake and exhaust sides with the cylinder center cross-section as the reference plane. AVL-FIRE software is used to simulate the effects of injection direction, timing, and pressure on the mixture formation and equivalence ratio distribution in asymmetric spraying process. While the injection angle of the intake and exhaust side affect the spray distribution, the increase of the injection angle of the intake side is beneficial to improve the mixture uniformity, and the increase of injection angle of the exhaust side will lead to the decrease of the evaporation rate. For the injection angle of intake side (α) = 30° and the injection angle of exhaust side (β) = 15°, the fuel evaporation rate is the highest. The fuel injection timing is 220°CA at 3000 rpm and 200°CA at 6000 rpm, which can improve the fuel evaporation rate, enhance the mixture uniformity and avoid the fuel short circuit. The injection pressure of 13 MPa is set to optimize the mixture formation at the speed of 6000 rpm. At part load, the effect of two-stage injection strategy with different injection timing and injection ratio on mixture stratification is studied based on optimized results. Research indicates that mixture distribution is effected by the second injection ratio and mixture uniformity is effected by the second injection timing. The first injection timing of 220°CA and the second injection timing at 270°CA with 20% total fuel quantity can reach the ideal in-cylinder mixture distribution of 50% load at 3000 rpm.