A nonequilibrium approach for the instantaneous calculation of the composition of 29 chemical species is used in this work to simulate the evolution of the gas composition in a Diesel engine cylinder from the start of combustion to the exhaust opening. A discretization of the heat release law is used as a sequential source of combustion products, which are then subjected the evolution of pressure directly measured from the cylinder engine, and to the evolution of a burnt-zone temperature obtained from the same pressure signal through a diagnosis thermodynamic model. For each burning fuel package, the equilibrium composition and the corresponding adiabatic flame temperature are considered as initial conditions for the kinetic calculation of the gas composition evolution.A reasonably good agreement was found between the model results and the measured NOx and CO emissions in a 0.6 litre single-cylinder DI Diesel engine, when some engine parameters, such as the injection timing, were modified. The modification of other engine parameters such as the injection pressure required changes on the dilution rate of burnt products in order to adjust the predicted emissions to the measured ones. The instantaneous concentration in the cylinder of some pollutant species for varying dilution rates was revealed as a useful information to understand the effect of some engine design parameters on the pollutant kinetics.