Experimental measurements of piston temperature and evaluation of heat flux in engine at transient conditions

The heat losses in an internal combustion engine affect the efficiency and play a main role during the ignition delay and the combustion process. Moreover, complex combustion models use sub-models of heat losses that need to be properly calibrated. The present work contributes to the knowledge of the piston temperature by performing temperature measurements with a thermocouple. A K-type thermocouple is mounted on the piston, outside the optically accessible combustion chamber, in a re-search compression ignition engine. The signal is transmitted from two pins jointed to the moving piston to a couple of fixed contacts connected to an acquisition module. The temperature has been monitored only at the top dead center with closed valves with a frequency of a half engine speed. The transient temperature from the engine start to the regime conditions has been recorded and analyzed for different engine operating conditions with variable engine speed (1500-2000 rpm) in motored and fired modes. Moreover, both the temperature gradient and stationary values have been analyzed. The in-cylinder gas temperature, derived from the in-cylinder pressure signal, has been used together with the measured temperature and the calculated heat transfer coefficient to evaluate the heat flux from the in-cylinder gas to the piston during both the transition and the stabilization phases. These data could contribute to the lack of information on the piston temperature variation in the engine and to the evaluation of the heat flux with more accuracy.