Measurement System of Instantaneous Surface Temperature on Combustion Chamber Walls in an Internal Combustion Engine by Thin-Film Thermocouples

The state of heat loss from combustion gas to combustion chamber walls during the cycle in an internal combustion engine can be evaluated from instantaneous surface temperature of the walls measured by thin-film thermocouples (TFTs). Not only a suitable temperature probe but also an appropriate measurement system is necessary for accurate measurement.TFTs developed by the authors' group were designed and fabricated so that disturbance of the temperature filed could be minimized when they were embedded into combustion chamber walls. Appropriate measurement circuits and devices are necessary for accurate measurement of thermoelectromotive force generated by the TFTs because it changes very quickly as the crank angle, and the amplitude of its fluctuation is considerably small, usualy less than 3 mV. Therefore, the authors' group established a measurement system which consists of measurement circuits of thermoelectromotive force, an A/D (analog to digital conversion) system and a data processing device. The authors' measurement circuit has an advantage of being noise-free and quick in switching channels. On the other hand, the A/D system is of high accuracy and synchronizes with the engine operation. Furthermore, meaningfully reproductive data is generated by the data processing device. In this report, the authors' measurement system is presented.