Analysis and modeling of the thermal soak phase of a vehicle — Temperature and heat flux measurements

The thermal soak phase of a vehicle results from driving the vehicle at high load followed by shutting off the engine. The present work deals with the analysis and modeling of the thermal soak phase of a vehicle through temperature and heat flux measurements. Measurements are carried out on a passenger vehicle in wind tunnel S4 of Saint-Cyr-France. The underhood is instrumented by alsmot 120 surface and air thermocouples and 20 fluxmeters. Measurements are performed for three thermal functioning conditions, with the engine in operation and the front wheels positioned on the test facility with power-absorption controlled rollers. It was found that in thermal soak the temperature of certain components can increase by almost 80°C (pre-catalyst) and that of air zones by alsmot 40°C (crawl area). These components correspond to areas that heat up after stopping the engine for 3 to 24 minutes, depending on their position in the underhood and on the thermal operating point considered.