Entropy generation due to combustion destroys as much as a third of the theoretical maximum work that could have been extracted from the fuel supplied to an engine. In this paper, an optimal control problem is set up to minimize the entropy generation in an adiabatic internal combustion engine, with the piston velocity profile serving as the control input function. The compression ratio of the engine is fixed, thereby imposing a constraint on the piston motion. The switching conditions for the optimal bang-off-bang control is determined based on Pontryagin's maximum principle. In thermodynamic terms, the optimal solution reduces to a strategy of equilibrium entropy minimization. This result is independent of the underlying combustion mechanism.

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