The two-dimensional unsteady vortex gas flow in a diesel engine cylinder has been simulated on the basis of Euler equations. Two mass conservation equations have been introduced with the aim of control by the contact surface. The computational region has contained the air receiver zone, the scavenging windows and the cylinder of the variable volume with valves. The gas flow rate characteristics have been calculated for the nominal regime of the diesel motor L60MC (company MAN and B and W). These characteristics have accorded well with known experimental results. The analysis of the gas flow in the form of temperature isolines and gas concentration isolines has permitted to explain some features of the gas flow in a diesel engine.