Thermal Modeling of Engine Components for Temperature Prediction and Fluid Flow Regulation

The operation of internal combustion engines depend on the successful management of the fuel, spark, and cooling processes to ensure acceptable performance, emission levels, and fuel economy. Two different thermal management systems exist for engines - air and liquid cooling. Smaller displacement utility and spark ignition aircraft engines typically feature air cooled systems which rely on forced convection over the exterior engine surfaces. In contrast, passenger/light-duty engines use a water-ethylene glycol mixture which circulates through the radiator, water pump, and heater core. The regulation of the overall engine temperature, based on the coolant's temperature, has been achieved with the thermostat valve and (electric) radiator fan. To provide insight into the thermal behavior of the cylinder-head assembly for enhanced cooling system operation, a dynamic model must exist. In this paper, two multi-node thermal models will be presented to estimate the temperature of the in-cylinder and cylinder head components for air and liquid cooled engines. A lumped parameter approach has been pursued using both analytical and empirical relationships. To determined the appropriate number of thermal nodes and dominant heat transfer mechanisms (e.g., conduction, convection, radiation) between each node, thermal engine analyses have been performed. Representative numerical results will be presented and discussed for several operating cycles to demonstrate the performance of the dynamic model in predicting internal engine temperatures. To validate the thermal model, experimental testing has been conducted and temperatures logged at various engine locations. The paper will conclude with a discussion of mechatronic strategies to increase the engine's thermal efficiency while maintaining acceptable temperature limits for components.