Study of the interaction between mechanical energy and heat exchanges applied to IC engines

The concept of thermal engine insulation has been the subject of many experiments aiming at reducing heat transfer to the water cooling jackets and most of the resulting attempts lead to poor and controversial results. The increase of efficiency expected from the thermal insulation was generally not found and the experiments show that most of the heat not transferred to the walls can be found in the exhaust gas. The aim of this work-in-progress communication is to bring a contribution to the understanding of these energy transfer phenomena between the exhaust and cooling systems of a reciprocating engine with energy recovery. It is shown with a local unsteady approach that a competition occurs between the thermodynamic expansion velocity and the heat propagation velocity during the expansion stroke. There exists a characteristic time, above which the internal wall behaves temporarily like a heat store that delivers heat back to the exhaust gas at the end of the expansion stroke. Although, it appears unrealistic to apply heat insulation to a thermal engine with the objective of increasing mechanical power and efficiency, it is however justified applying a partial thermal insulation to turbocharging and energy recovery applications.