Numerical study of lubricant oil drop induced pre-ignition in engines

Pre-ignition in engines has been the subject of current research with the advent of boosted engines for reduced fuel consumption and emissions. Lube-oil-drop-induced pre-ignition was observed in large natural gas engines which find application in the marine industry. In order to understand the mechanism of pre-ignition in the present study, a computational simulation of pre-ignition by lube-oil drops was performed for a production natural gas marine engine. The engine grid was generated using ICEM tool. For CFD simulations, an in-house version of KIVA4 code was employed. Oil throw-off into the combustion chamber was modeled by a lube oil stripping model, which sets the criteria for oil drops to be stripped from the piston rings/crevice regions and enter the combustion chamber. To capture the ignition caused by the stripped oil drops precisely, single particle ignition cell (SPIC) model was used that utilizes computations of thermal and chemical changes in refined grid cells for the lube oil containing computational cells. For modeling chemical kinetics, a reduced lube oil reaction mechanism previously developed was used. Factors affecting the lube oil stripping process such as thickness, velocity, and temperature of the lube film and its subsequent pre-ignition behavior were studied and discussed. Higher initial thickness, higher film temperature and higher initial film velocity all lead to earlier stripping of lube-oil film into the combustion chamber. Once the film is stripped, keeping the local lube vapor equivalence ratio low is the key to prevent pre-ignition.