The effect of ambient gas hydrocarbon content on diesel spray ignition and combustion was examined in this research project. A single-stroke rapid compression machine was used to prepare the ambient gas pressure and temperature before the diesel fuel injection process. Variations of ambient gas composition were achieved by adding different quantities of methane and propane to the intake air, the content ranged from 0.0 to 0.6 equivalence ratio. The two-color method was applied to analyze the flame temperature and KL factor was determined from the colored flame image taken by a high-speed camera. Also, compression ignition characteristics of lean methane-air and propane-air mixtures were examined.