Experimental measurements of piston temperature and analysis of heat flux applying advanced infrared imaging in a compression ignition engine

The trend toward a new scenario in the transportation sector points to innovative technologies of propulsion for road vehicles. On the other hand, internal combustion engines (ICEs) still play a main role at the moment. The improvement of ICEs is necessary to fulfill emission regulations in the immediate future. For the improvement of engine efficiency, components design, combustion models, and resistance tests, the knowledge of the thermal status of the engine, especially pistons and cylinders, is required. This paper analyzes the temperatures and the heat flux in a research compression ignition engine by different perspectives. The engine has run three operating conditions of the Worldwide Harmonized Light Vehicles Test Cycle. First the injection and combustion processes have been visualized via visible and infrared imaging to get information about the parameters that mainly affect the combustion process. Then, thermal imaging has been applied to measure the temperature of the optical window in the piston, both in motored and in fired conditions. The knowledge of cycle-resolved temperature values allowed to calculate the heat flux resolved in the cycle. The evolution of the heat flux has been discussed with the rate of heat release and the luminous intensity of the sooting flames to analyze their mutual influence. The evaluation of the heat flux with a well-consolidated 0D correlation provided an indication of the heat flux behavior with low efforts, allowing to put in evidence the influence of time and location of sooting flames on heat losses during combustion.