A Study on Reducing Cooling loss in a Partially Insulated Piston for Diesel Engine

To improve the thermal efficiency of an engine, it is particularly important to reduce the cooling loss from the combustion gas to the combustion chamber wall, which constitutes a major proportion of the total loss [1]. Previous studies addressing cooling loss reduction attempted to use ceramic in place of the conventional aluminum or iron alloys, but this led to a reduction in the volumetric efficiency and increased smoke emissions. This was caused by the ceramics having both a low thermal conductivity and high heat capacity, relative to aluminum and iron. These characteristics cause the piston wall temperature, which rises during combustion, to remain high during the intake stroke, thus increasing the intake temperature and reducing the volumetric efficiency. This increases the smoke emissions [2]. This paper presents the concept of a technology that applies an insulation coating to part of the combustion chamber wall to reduce the cooling loss while simultaneously suppressing the increase in smoke emissions caused by the drop in volumetric efficiency. The usefulness of the technology was evaluated by applying it to a diesel engine.