Numerical investigation of the combustion characteristics and wall impingement with dependence on split-injection strategies from a gasoline direct-injection spark ignition engine

Highly pressurized direct injection applied to automotive vehicles was developed for better power and fuel efficiency, but it causes fuel impingement, which generates more soot emissions. In the present study, analyses of the combustion characteristics and fuel impingement were conducted with a direct-injection spark ignition engine using split-injection strategies. Full three-dimensional unsteady Eulerian-Lagrangian two-phase numerical simulations were carried out to predict the flow field and the combustion characteristics as functions of the injection duration ratio and the weight of the second pulse injection. Experimental data were coupled for verification, providing the boundary and initial conditions for the benchmark case. The results showed that the weight of injection became maximally 35% less as the weight of the second pulse injection decreased. The amount of liquid fuel film, which was influenced by the injection duration ratio, had a varying range from approximately 1% to 4%. When a greater amount of the liquid fuel film impinged on the piston surface, this induced more soot formation. However, the fuel-air mixture was the most prominent factor for determining the overall combustion characteristics. A split injection can increase the thermal efficiency and the fuel consumption rate; however, without optimization, poor combustion characteristics such as knocking, incomplete combustion and soot emissions can result.