Effects of the engine oil on the ignition of iso-octane premixed gas have been investigated using a rapid compression machine. The ignition delay times of the iso-octane premixed gas at an equivalence ratio of 1.0 with or without engine oil in temperature and pressure ranges of 680 - 730 K and 3.0 - 3.8 MPa were measured. The pressure profiles of the iso-octane with the engine oil show a single stage pressure rise over the entire temperature and pressure range, while those of iso-octane show a two-stage pressure rise. We found that there was a line determining the limits of temperature and pressure conditions where the ignition delay times of the iso-octane with engine oil were shorter than those of iso-octane. These results indicate that there are some temperature and pressure conditions in engine cylinder, where the engine oil promote the ignition of the iso-octane premixed gas.
