Simulation of Instantaneous Heat Transfer in Spark Ignition Internal Combustion Engines: Unsteady Thermal Boundary Layer Modeling

Abstract

Simulation of internal combustion engine heat transfer using low-dimensional thermodynamic modeling often relies on quasisteady heat transfer correlations. However, unsteady thermal boundary layer modeling could make a useful contribution because of the inherent unsteadiness of the internal combustion engine environment. Previous formulations of the unsteady energy equations for internal combustion engine thermal boundary layer modeling appear to imply that it is necessary to adopt the restrictive assumption that isentropic processes occur in the gas external to the thermal boundary layer. Such restrictions are not required and we have investigated if unsteady modeling can improve the simulation of crank-resolved heat transfer. A modest degree of success is reported for the present modeling, which relies on a constant effective turbulent thermal conductivity. Improvement in the unsteady thermal boundary layer simulations is expected in the future when the temporal and spatial variations in effective turbulent conductivity are correctly modeled.