2015 年 81 巻 830 号 p. 15-00154
Highly efficient natural gas engines have been widely used in wide range of sectors from industry and transportation. However, because combustion process in gas engines with a pre-chamber is very complicated, it is difficult to experimentally investigate the combustion process including flame propagation from the pre-chamber. In this study, combustion characteristics in the gas engine with a pre-chamber were numerically investigated by using three-dimensional numerical simulation with detailed chemical reactions. Torch flame combustion brings about high temperature and strong turbulence to the main chamber. Combustion processes of the natural gas engine with pre-chamber can be categorized in three stages. The first stage is high speed flame propagation induced by flame torches from the pre-chamber. The second stage is simple flame propagation in the main-chamber. This flame propagation speed is relatively lower than the first stage combustion, because turbulence kinetic energy is lower than that during the first stage. The curvature of rate of heat release relates to the surface area of flame front and excess air ratio in the flame front. The third stage is autoignition of the unburned mixture in the end gas region. Autoignition in the main-chamber occurs between the torches. The intensity of pressure oscillation and rate of heat release depend on both the mass of the unburned mixture in the end gas region and the onset positions of autoignition.
