Development of Instantaneous Temperature Measurement Technique for Combustion Chamber Surface and Verification of Temperature Swing Concept 2016-01-0675

To improve the thermal efficiency of an internal combustion engine, the application of ceramics to heat loss reduction in the cylinders has been studied [1-2]. The approach taken has focused on the low heat conductivity and high heat resistance of the ceramic. However, since the heat capacity of the ceramic is so large, there is a problem in that the wall temperature increases during the combustion cycle. This leads to a decrease in the charging efficiency, as well as knocking in gasoline engines. To overcome these problems, the application of thermal insulation without raising the gas temperature during the intake stroke has been proposed [3-4]. As a means of achieving this, we developed a "temperature swing heat insulation coating" [5, 6, 7, 8, 9]. This reduces the heat flux from the combustion chamber into the cooling water by making the wall temperature follow the gas temperature as much as possible during the expansion and exhaust strokes. On the other hand, in the intake and compression strokes, the heating of the intake air is prevented by suppressing an increase in the wall temperature. The temperature change within a single cycle is called the "temperature swing." A thermal insulation coating with a low thermal conductivity and low thermal capacity was developed in order to achieve this temperature swing. To validate the swing concept, we set out to devise a technique to measure the temperature in a diesel spray flame impingement section where a large heat loss reduction would be expected. Measuring the lifetime of laser-induced phosphorescence (abbreviated to LIP, below) was selected to measure the surface temperature which changes with a high responsiveness. First, we confirmed that the sensitivity and the response of this technique are sufficient for the investigation. Then, this technique was applied to a diesel spray flame impingement section. To reduce the occurrence of bright flames when attempting optical measurements, we selected an oxygen-containing fuel in place of normal diesel fuel. Also, by adjusting the fuel pressure and oxygen concentration, we identified the combustion conditions needed to produce a flame with low luminosity. Temperature measurements of the insulation coating revealed a steep temperature rise during the combustion period and a temperature drop during the intake stroke. The swing width in one cycle was approximately 140 K. On the other hand, the swing width of a non-insulation coating was about 45 K. In this way, we found that there is a clear difference between the insulation coating and non-insulation coating, thus confirming the temperature swing phenomenon of the insulation coating. Comparing these measured values with the results of the one-dimensional heat conduction calculation, the values were found to be almost consistent. It was also confirmed, from the results of a single-cylinder engine test, that the insulation coating we developed offers the required functionality.