Performance Limits for a Class of Irreversible Internal Combustion Engines

Abstract

The performance of a class of irreversible internal combustion engines with finite rate heat exchange with the environment and nonzero entropy generation due to combustion chemical reactions in the cylinder is studied in this paper by using finite time thermodynamics. It is assumed that the heat transfer between the working fluid in the cylinder and the environment obey linear phenomenological law [q ∝ Δ(T−1)] in the irreversible thermodynamics, and the combustion chemical reactions in the cylinder obey a general rate equation of reactions. The upper bounds of power output and efficiency of the internal combustion engines are derived by applying optimal control theory. For the special examples with one chemical reaction and some linearly independent chemical reactions, the average optimal control problems are transformed into nonlinear programming problems, and the Kuhn−Tucker conditions corresponding to the optimal solutions are found. Analytical solutions of minimum entropy generation for the two cases are provided. The results obtained herein are compared with those obtained with different rate equation of reactions and Newton’s heat transfer law ([q ∝ Δ(T)]). The methods used and the results obtained in this paper can provide some theoretical guidelines for the optimal design and operation of practical internal combustion engines.