A phenomenological multizone combustion model is developed for use in the transieat condition analysis of a turbocharged direct injection (DI) diesel engine. The main processes in the cylinder, such as spray penetration, droplet evaporation, air-fuel mixing, spray wall interaction, ignition and fuel combustion, are taken into consideration. In order to predict cylinder pressure and NOx emissions in a wide range of engine speeds, loads and air-fuel ratios under transient conditions, the model has been improved in many respects, especially in the velocity distrbution of fuel spray, zonal entrainment and the calculation of gas properties and chemical equilibrium compositions of combustion products including solid earbon. With respect to the turbocharged engine with a high pressure in the cylinder, the compression factor is odded to the ideal gas equation of state in order to simulate cylinder pressure accurately. Cylinder pressure, heat release and NOx emission histories for different operating conditions are calculated for two types of engines. The agreement between calculated and measured results is good for a wide range of operating conditions. This indicates that the model has the ability to predict cylinder pressures and NOx emissions in both steady state and transient operating conditions.