Theoretical and simulated models for an irreversible Otto cycle

Abstract

We show in this work that a finite-time-thermodynamics model of an irreversible Otto cycle is suitable to reproduce performance results of a real spark ignition heat engine. In order to test our model we have developed a computer simulation including a two-zone combustion model and compared the evolution of the performance parameters of the simulated engine as functions of the rotational speed (ω) with those obtained from a simple theoretical scheme including chemical reactions. A theoretical Otto cycle with irreversibilities arising from friction, heat transfer through the cylinder walls, and internal losses properly reproduces simulation results by considering extreme temperatures and mass inside the cylinder as functions of ω. Furthermore we obtain realistic values for the parameters characterizing global irreversibilities, their evolution with ω, and a clearer understanding of their physical origin not always well established in theoretical models.