Influence of material of coaxial type thin-film temperature sensor on hot junction position and measurement accuracy

Abstract

Improvement of thermal efficiency is strongly required in internal combustion engine to promote environmental protections, it is important to clarify the mechanism and reduce cooling loss. Various methods have been proposed for measuring the cooling loss from the combustion gas to the combustion chamber wall, coaxial type thin-film temperature sensor is developed for wall temperature and heat flux measurement in this study. This sensor consists of thin-film and body and center wire, and there are three junction positions when the three materials are different. Therefore, it is necessary to use the same materials for thin-film and body or thin-film and center wire to make two junction points. In this study, as a method of forming thin-film on the sensor surface, not conventional metal plating method but sputtering method capable of forming various kinds of alloy materials and thickness of 0.1~1µm was chosen. It was evaluated the influence of differences in thin-film material on wall temperature and heat flux measurement by numerical analysis, as a result, the surface of sensor body (the same material as the combustion chamber) was hot junction by using the same material for the thin-film and center wire, it was suggested that high accuracy measurement is possible. And the sensor was attached to the cylinder head of gasoline engine and conducted experiments, and it was obtained the same result as the numerical analysis results. From these result, when high accuracy measuring wall temperature and heat flux with thin-film temperature sensor, it was found that it is important to use the senor body is the same material as combustion chamber wall and the thin-film is the same material as center wire.