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This work is based upon a simulation model for spark-ignition engines that considers the instantaneous heat transfer, the combustion process occurring at a finite rate as well as intake and exhaust processes. The model calculates the thermodynamic properties - including exergy - of each gas mixture composition of the working fluid. Besides the common features of thermodynamic simulation models, the determination of instantaneous irreversibilities, exergetic efficiencies of each process and an overall cycle exergetic analysis are also included. Based upon the simulation model, first and second law analysis are applied to a parametric study with emphasis in the combustion process and the valve timing effects. Exergy destructions taking place during the combustion of an ethanol fueled engine and a gasoline version of the same engine are compared.

Equations governing the flow through admission and exhaust ducts in diesel engines are presented taking into consideration the fluid compressibility, the variation of the duct cross section, and heat transfer and friction between the gases and the duct walls. The hyperbolic nature of the equations is shown and a solution is obtained using the method of the characteristics. The algorithm of this solution is included in a simulation model for a single cylinder diesel engine, based on the single zone combustion formulation. This model is used in a study to evaluate the engine performance indexes when different admission duct shapes are used.