A Study on the Wall Heat Loss from Diesel Spray Flame with Rapid Compression and Expansion Machine

抄録

Recently, fuel efficiency requirements has been stricter, and then diesel engines with high efficiency are focused in automotive industry. However, about 30% of the input heat quantity is lost as cooling loss inside the combustion chamber, therefore reduction of this is required to further improve the thermal efficiency in diesel engines. Cooling loss is mainly due to wall heat loss caused by convective heat transfer of the spray flame impinging on the chamber wall. From Newton's cooling law, wall heat loss is determined by physical factors, which are heat transfer coefficient, flame temperature, wall temperature, flame contact area and flame contact time on the wall. And these physical factors are affected by control factors. Therefore it is important to investigate the correlation among physical factors, control factors and the wall heat transfer with impinging flame on the wall for reducing cooling loss. In this study, it is investigated that the mechanism of the wall heat transfer under the low flow field with a rapid compression and expansion machine for reduction of wall heat loss in diesel engines. And in this paper, it is focused on that the correlation between diesel spray flame and wall heat loss by changing fuel temperature. In this experiment, temperatures on the wall surface and the wall inside are simultaneously measured with coaxial thermocouples, which are embedded in the piston, and heat flux is assessed from the difference of these temperatures. In addition, image correlation method and two-color method were performed from luminous flame images to calculate flame velocity and flame temperature. From the measurement result of the heat flux, it was found that wall heat loss is reduced with increasing fuel temperature.