Currently, the improvement of fuel economy is the most important issue in automobile engine development. To improve fuel economy via greater thermal efficiency, the enhancement of the compression ratio and the reduction of thermal losses because of cooling have been widely investigated. These efforts to improve thermal efficiency increase the thermal load on pistons. Ensuring the reliability of the pistons and the antiknocking capacity of engines require a better understanding of piston temperature distributions through accurate measurements under various engine operating conditions.
Thus, direct and indirect measurement methods have been developed to estimate the actual piston temperature. Direct methods, such as linkage-type measurements, are not typically applicable under higher engine speeds because of the poor durability of linkages. Indirect methods, such as material hardness-type measurements, can measure neither real-time piston temperature nor the temperature of piston skirts, which are thin-walled. Therefore, the conventional measurement systems no longer satisfy the measurement requirements under various engine operating conditions.
In this work, we have developed a telemetry-type method in which thin diametric thermocouples are installed at six points in each piston.
This method enables the measurement information to be transferred wirelessly at the bottom dead center using electromagnetic induction. This approach has enabled real-time and transitional measurements at engine speeds up to 6500 rpm in a four-cylinder gasoline engine. In addition, the experimental and calculated results are compared via 1-dimensional analysis to validate the accuracy of our method.