Achieving Higher Thermal Efficiency by Cooling Loss Reduction from a Heavy-duty Diesel Engine

抄録

For further increase in thermal efficiency of a heavy-duty diesel engine, improvement of cooling loss reduction must be essential. Many attempts to reduce cooling loss in a cylinder have been carried out by applying various ceramic coatings or monolith to the piston and/or other in-cylinder surface aiming to increase temperature swing. However, their advantage was mostly very little or sometimes negative by their complex phenomena caused by the cyclic and unsynchronized variation of working gas and wall temperatures. This study investigated into cooling loss mechanism of a diesel engine in detail by two new insulation layers. A titanium thermal spraying piston intended to increase temperature swing by its thermal properties. The other structure was made of the aluminum layer with 3-5 μm thickness by vapor deposition process on the mirror-polished stainless-steel layer of the piston and the cylinder head. Aluminum was initially selected by its high natural reflectance for flame radiation to selectively absorb radiation at the soot deposit to achieve higher local temperature where spray flame impinged. Although further cooling loss reduction was achieved with the latter structure, the heat loss mechanism seems to be more complex than our hypothesis.