Abstract
From the global environmental point of view, drastic fuel efficiency improvement is required for engines. Cooling heat loss is one of the most dominant losses among the various engine losses to be reduced. Although many attempts to reduce it by insulating the combustion chamber wall have been carried out, most of them have not been successful. Charge air heating by the constantly high temperature insulating wall is a significant issue of these attempts, because it deteriorates charging efficiency, soot and NOx emission in diesel engines, and the tendency of knock occurrence in gasoline engines. Authors have developed a new concept heat insulation methodology, which can reduce cooling heat loss without heating the charging air. Surface temperature of insulation coat changes rapidly, according with the quickly changing in-cylinder gas temperature in each engine stroke. Reduced temperature differences between them lead to lower heat transfer. During the intake stroke, surface temperature of the insulation coat goes down rapidly, and prevents intake air heating. To realize the above mentioned functionality, a thin coating layer with low thermal conductivity and low heat capacity was developed. It was applied on the pistons of diesel engines, and showed improvement of fuel efficiency, and increased exhaust gas temperature which contributes to earlier light off of the aftertreatment catalyst. As the result of energy balance analysis, cooling heat loss was reduced, on the other hand, break power and exhaust loss was increased. In addition, unburnt fuel emission reduction in the low temperature starting was observed.
