Today, homogenous charge compression ignition (HCCI) engines are becoming very popular because of their potential to reduce soot and nitric oxides (NOx) emissions simultaneously. But, their performance and emission characteristics are very much dependent upon fuel injection strategy and parameters. However, they also have many challenges viz., improper combustion phasing, high rate of pressure rise and narrow operating range. Therefore, addressing them is very essential before making them a commercial success.
This study focuses on evaluating the effect of fuel injection strategy and parameters on the performance and emission characteristics of a HCCI engine by computational fluid dynamics (CFD) analysis. In this study, a four-stroke engine operating in the HCCI mode is considered and the CFD analysis is carried out by using the CONVERGE. All the CFD simulations are carried out from the inlet valve opening (IVO) to the exhaust valve opening (EVO) period, at the engine speed of 1500 rev/min., with the compression ratio of 16:1. Here, homogeneous mixture is achieved by the injection of fuel into the engine cylinder directly during the early compression stroke, with the fuel injection pressure of 800 bar. The analysis is carried out to study the effect of multiple fuel injection strategy, fuel mass split ratio, injection timing and pressure on the performance and emission characteristics of the engine. In addition, the results of the HCCI mode are compared with that of the conventional CI engine operating at the same load conditions.
From the results, it is found that, the HCCI mode with three-stage fuel injection having fuel mass split ratios of 40-50-10%, fuel injection timings of 260, 300 and 360 CAD, and fuel injection pressure of 1200 bar shows higher indicated thermal efficiency by about 1.2% and lower NOx emissions by about 81.9% compared to that of conventional CI engine mode.