An optimal control approach to minimizing entropy generation in an adiabatic internal combustion engine

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. The optimal bang-bang control is shown to be a function of the pressure difference between the instantaneous thermodynamic state of the system and its corresponding equilibrium thermodynamic state. At optimality, the entropy difference between these two thermodynamic states is shown to be a Lyapunov function. Therefore, the equilibrium serves as the attractor for the optimal state trajectory. The results are independent of the underlying reaction mechanism, which may be highly nonlinear.