Temperature Measurements of the Piston Optical Window in a Research Compression Ignition Engine to Set-Up a 1d Model of Heat Transfer in Transient Conditions

The analysis of heat losses in internal combustion engines (ICEs) is fundamental to evaluate and to improve engine efficiency. Detailed and reliable heat transfer models are required for more complex 1d-3d combustion models. At the same time, the thermal status of engine components, like pistons, is needed for an efficient design. Measurements of piston temperature during ICEs operation represent an important and challenging result to get for the aforementioned purposes. In the present work, temperature measurements collected at different engine speeds and loads, both in motored and fired modes, have been performed and used to set-up a theoretical correlation and 1d model of heat transfer through the optical window of the piston. The in-cylinder gas and external ambient temperature, together with the thermodynamic and material properties are given. The model has been first calibrated in some selected operating conditions and then validated in the remaining. The aim of the 1d model is to simulate the transient of temperature during the engine warm up in motored, from the engine start up to the steady motored condition; and in fired mode, from motored up to steady fired condition. After tuning the model, a good agreement has been obtained in all the tested conditions; some refinements were needed when increasing the engine speed. The main peculiarity of the model is the possibility to get the steady temperature after long running time, not available from experiments because of technical limitations.