Temperature Measurements of the Piston Optical Window in a Research Compression Ignition Engine via Thermography and Templugs

Internal combustion engines are characterized by high pressure and thermal loads on pistons and in cylinders. The heat generated by the combustion process is dissipated by means of water and oil cooling systems. For the best design and optimization of the engine components it is necessary to know the components temperature in order to estimate the thermal flows. The purpose of this work is to measure the piston sapphire window temperature in a research optically accessible engine by combining two different techniques: measurements with templugs and with thermography. The method is very simple and can provide a reliable value of temperature within a small interval. It fits well for applications inside the engine because of its low technical level requirements. It consists of application of temperature sensitive stickers on the target component that makes it a very robust method, not affected by piston movement. The huge limitation of this method lays in the possibility of a single-shot measurement. To this aim, a second technique as infrared thermography is proposed. It is non-invasive and easy to apply as well. The high-speed camera used in this work provides images resolved in the combustion cycle and then high temporal resolution of the temperature measurements. On the other hand, setup, interpretation, and analysis of thermographic images is very complex; hence, templugs measurements will be used for the validation and calibration of thermographic results. Temperature measurements have been used to calculate the convective heat transfer coefficient resolved in the combustion cycle and to evaluate the thermal flow to the sapphire window. The field of temperatures detected in this work could be useful for the design of engine components, the refinement of numerical models and the estimation of the optical window contribution in infrared imaging of combustion process.