Effect of Split-injection on Fuel Mixing and Cylinder Flow Characteristics of GDI Engines

The mixing process and flame propagation in GDI engine are greatly influenced by the airflow velocity distribution and the level of turbulence before combustion [1–3]. Previous studies (e.g., [4,5]) have shown that optimizing the timing of two successive injection pulses at a moderate-speed moderate-load results in an increase in the cylinder pressure and a reduction in NOx and CO2 emissions. Multiple injections per cylinder increases the temperature for the converter light-off, to achieve a smooth idle and to reduce the tendency to knock [6,7]. In this work a comparison is made between split and single injection during the induction stroke on the cylinder gas velocity, turbulence and mixing process using 3D CFD simulation of CONVERGE CFD software. The simulation is carried out on a single cylinder 4-valve flat piston engine for the prediction of spray formulation, ignition timing, and flame propagation. The injection conditions and spray data used in the simulation are based on experimental data using a typical six-hole GDI injector. The results show that a split injection leads to improvement in fuel spray droplet dispersion leading to enhancing the uniformity of equivalence ratio in comparison to the single injection condition. The spatial distribution of the equivalence ratio shows richer area with a higher value of equivalence ratio when using single injection. The entrained air and turbulent intensity was relatively enhanced for the split injection case.