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 isdriven by the crankshaft and imposes a coolant flow, which transfers heat from the enginewalls 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 apressure increase inside the cooling circuit. A numerical dynamic model was developed topredict this phenomenon, often called after-boiling among engine manufacturers. Themodel structure includes thermodynamic equations to compute heat transfer as well asmass transfer equations to determine the vaporized mass of the coolant, which occurs incylinder head passages and the vapor condensation within the radiator. The developedmathematical model was validated against test data carried out on a production fourstrokespark-ignition engine, and simulation results show good agreement with experimentaldata.