Combustion characteristics and misfire mechanism of a passive pre-chamber direct-injection gasoline engine

Abstract

Engine combustion characteristics and misfire phenomena in a turbocharged direct-injection gasoline engine with a pre-chamber are studied through multi-dimensional modeling of the engine and jet combustion in a pre-chamber vessel. The results show that the high-speed jets generated by the pre-chamber after spark ignition result in multiple ignition spots and enhanced flow turbulence in the main combustion chamber, accelerating the subsequent turbulent flame propagation. It is also found that the momentum of the gas jets directly correlates with the main chamber combustion phasing and duration, which means that varying the design parameters of the pre-chamber to generate higher jet momentum can produce faster flame propagation and better combustion phasing, improving the engine’s thermal efficiency. On the other hand, flame quenching phenomena at the engine low-load conditions were captured in the simulation with the reaction-mechanism combustion model, whose predictivity of jet flame quenching was verified by the pre-chamber vessel experiments. It was found that, in addition to the unfavorable lower in-cylinder pressure and temperature, leaner fuel–air mixture, weaker turbulence, and wall heat losses would lead to slower flame development in the pre-chamber and the jet flame to quench in the main chamber, resulting in engine misfire or ignition instability. The simulation further verified that flame quenching could be mitigated by using a heat-insulated pre-chamber, improving air–fuel mixing in the main chamber and pre-chamber with advanced fuel injection timing, and igniting the mixture at a higher gas temperature and pressure with advanced spark timing.