Numerical Analysis of the Combustion and Emission Characteristics of Multiple Injections by Using the Modified 2-D RIF Model

Fuel injection is one of the important operating parameters in internal combustion engines (ICEs) that strongly affects overall combustion phenomena, including ignition delay and emissions. Therefore, fuel injection strategy can be key to improving ICEs. The improvement of ICEs should be accompanied by a thorough investigation of combustion phenomena. CFD has advantages in replacing complex experiments and visualizing in-cylinder phenomena that experiments cannot detect; therefore, CFD has been widely used in this research field. This paper focuses on the post-injection effect on soot emission by using CFD. A modified 2-D RIF combustion model with emission models (i.e., NOx and soot) was used and validated with the experimental results. The simulation results adequately followed the experimental results in terms of pressure, heat release rate, and emissions. Based on these results, post-injection parameters such as mass or timing were varied to verify the post-injection effect on soot reduction. The results proved that the post-injection in the target engine condition was effective for soot reduction by reducing soot generation from the main injection and enhancing soot oxidation. Among the simulations with varied conditions, the optimal post-injection condition was found when it was injected at approximately 3 CA after the main injection ends.