Effects of piston bowl geometry on combustion and emissions characteristics of a natural gas/diesel RCCI engine

Reactivity controlled compression ignition (RCCI) is a novel combustion concept which uses port fuel injection (PFI) of a low reactivity fuel and direct injection (DI) of a high reactivity fuel with optimum multiple injection to provide a stratified mixture inside the combustion chamber. Piston bowl design has a considerable effect on engine’s pollutant emissions specially unburned hydrocarbons (UHC). This paper studies the influence of piston bowl design on combustion and emission characteristics of natural gas/diesel RCCI engine using CONVERGE CFD. Firstly, the obtained results are validated with the available ones in the literature. Then, three piston bowl designs including stock, bathtub and cylindrical are selected for comparison. The parametric study is conducted at three different engine speeds (i.e., 800, 1300 and 1800 rpm). Effects of piston bowl geometry showed that the optimum piston bowl design from performance and emissions point is the bathtub design.