Diesel combustion diagnosis is frequently performed through the calculation of apparent heat release rate, using single zone combustion models. This computation lies on the solution of energy balance equation and utilizes experimentally determined in-cylinder pressure data. The information obtained by means of such an approach is considerably exempt of empiric adjustment parameters and can be used for the development and testing of multizone or multidimensional simulation tools.Due to its simplicity as well as to the strong experimental character conferred to the results, the application of this sort of experimental study in the exergetic analysis of the processes occurring in diesel engines is also an interesting approach. In this work, a single zone combustion model is used in the exergy diagnosis of a high speed direct injection diesel engine and the obtained results are discussed in detail.Additionally, the transformation of the exergy supplied to the engine cylinder is analyzed taking into account the rate of exergy destruction, the rates of exergy transfer associated to heat and work interactions and the rate of exergy accumulation in the working fluid. The last term was subdivided in order to distinguish the influence of pressure and temperature variation as well as the contribution of the fuel injection and burning processes.