Growing concern regarding energy resources and the environment has increased interest in developing Diesel engines for better fuel economy and lower emissions. A three dimensional CFD simulation of a 4-stroke engine is developed for a Ruggerini RD 270 engine using internal combustion engine module in ANSYS-FLUENT. A cold flow simulation is performed first to visualize the air motion inside the cylinder and to detect the changes of air properties through the different strokes of the engine. This simulation is validated against a compression test performed on the engine at the