A Convective Mass Transfer Model for Predicting Vapor Formation Within the Cooling System of an Internal Combustion Engine After Shutdown

In the usual liquid cooling system of an internal combustion engine a centrifugal pump is driven by the crankshaft and imposes a coolant flow, which transfers heat from the engine walls to the radiator. Therefore, as the engine is switched-off, the coolant flow also stops, while metal temperature may be particularly high after a period of high load operation; coolant vaporization in the cylinder head passages may occur in these conditions, with a pressure increase inside the cooling circuit. A numerical dynamic model was developed to predict this phenomenon, often called after-boiling among engine manufacturers. The model structure includes thermodynamic equations to compute heat transfer as well as mass transfer equations to determine the vaporized mass of the coolant, which occurs in cylinder head passages and the vapor condensation within the radiator. The developed mathematical model was validated against test data carried out on a production four-stroke spark-ignition engine, and simulation results show good agreement with experimental data.