A Fundamental Study on Combustion Characteristics in a Pre-Chamber Type Lean Burn Natural Gas Engine

Pre-chamber spark ignition technology can stabilize combustion and improve thermal efficiency of lean burn natural gas engines. During compression stroke, a homogeneous lean mixture is introduced into pre-chamber, which separates spark plug electrodes from turbulent flow field. After the pre-chamber mixture is ignited, the burnt jet gas is discharged through multi-hole nozzles which promotes combustion of the lean mixture in the main chamber due to turbulence caused by high speed jet and multi-points ignition. However, details mechanism in the process has not been elucidated. To design the pre-chamber geometry and to achieve stable combustion under the lean condition for such engines, it is important to understand the fundamental aspects of the combustion process. In this study, a high-speed video camera with a 306 nm band-pass filer and an image intensifier is used to visualize OH∗ self-luminosity in rapid compression-expansion machine experiment. The results show that the OH∗ self-luminosity is observed in outer edge of the jet, while the luminosity in the jet temporarily weakens because the turbulent jet is exposed to low temperature surrounding in the main chamber. After that, the OH∗ luminosity is spontaneously increased near the wall due to auto-ignition when the gas temperature increases. In order capture this self-luminosity in multi-dimensional simulation, OH∗ formation and deactivation reactions are introduced into a commercial 3D-CFD code coupled with detailed chemistry to compare the measured images with the simulated ones. As a result, the OH∗ self-luminous distributions obtained by the 3D-CFD calculation have reasonable agreement with the measurement showing fundamental understanding on chemical reaction, heat release and temperature distribution of the jet.