Distribution of volumes and their change in the diesel engine cylinder is an essential parameter of each numerical model. Quasidimensional numerical model divide space inside the engine cylinder into two main areas: fuel spray packages and a large surrounding area without combustion, which is used for air distribution into the fuel spray packages. This paper analyzes the four-stroke diesel engine for thelight truck drive in several operating modes. Numerical model is validated by using laboratory measurements. In a selected engine operating mode are presented the results of a numerical model for the observed volumes inside the engine cylinder. The observed volume change provides insight into the details of the air-fuel mixing process and fuel evaporation. Described changes are the basis for the calculation of heat-release and pressure changes in the cylinder. The developed numerical model provides insight into the details of the process inside the engine cylinder which cannot be measured with standard measuring equipment.