Diesel combustion is a complex process, including autoignition, premixed combustion and diffusion combustion. A novel TI(Time-scale Interaction) combustion model has been developed for simulating combsution phenomena with high accuracy from premixed charged combustion to diffusion combustion. This model is based on a reasonable combustion mode, taking into accout the characteristic time scale of chemical reactions and turbulence eddy break-up. Comparisons of measured and calculated heat release patterns and pressure histories showed good agreement for various operating conditions. The diesel combustion mechanism was analyzed under several fuel injection timings and engine loads using TI combustion model.