Deposit Formation on Cylinder Head of Small DI Diesel Engine

Abstract

When diesel fuel was evaporated on a high temperature wall in a combustion chamber, a deposit was formed on the wall. Deposit formation on the wall of the combustion chamber affected a decrease of thermal conductivity. However, it is difficult to investigate directly a behavior of a diesel deposit in a diesel engine. Therefore it is necessary to develop the measurement technique for understanding the behavior of the deposit in the combustion chamber. In this study, an engine head of a small DI diesel engine was drilled in order to insert a plug for sampling of the deposit in the combustion chamber, and the deposit on the surface of the plug was collected. By using the measurement system developed, effects of wall temperature of the cylinder head and excess air ratios on the deposit formation were investigated. Moreover, thermal resistance of a PM deposit layer was estimated using a simplified engine head wall model. As the results, deposit mass in the lower wall temperature was larger than that in the higher wall temperature under the condition of the same excess air ratio. It was also clear that the deposit mass in the lower excess air ratio was larger than that in the higher excess air ratio under the condition of the same wall temperature. According to estimation of thermal resistance of the PM deposit layer, it was clarified that thermal resistance of the deposit layer with around 10μm thickness was higher than that of aluminum diecast aroy with 5mm thickness.