Abstract
Keywords - Diesel Engine, Low Heat Rejection, Ceramics, Functionally Gradient Material, Durability
Abstract - Experiments were conducted with a single-cylinder direct injection diesel engine to examine the effect of heat insulation on the engine performance. The focuses in the performances were on the heat rejection and the durability of the heat insulated engine. The combustion chamber of the low heat rejection engine was insulated by Functionally Gradient Material (FGM) ceramic coating, which consisted from NiCr Alloy and ZrO2 ceramics. The coating was applied to a piston crown, a cylinder liner, a cylinder head and intake/exhaust valves.
The effect of the insulation by the FGM ceramic coating on the heat rejection was investigated by parametric experiments with the single-cylinder engine. The heat rejection was calculated in the control volume of the engine. The test results showed that the heat rejection to the coolant of the insulated engine could be lower than that of a non-insulated engine, and the total heat rejection rate can be reduced by increasing the boost air temperature. Although it was found that insulation of the combustion chamber and the increased boost air temperature led deterioration of a thermal efficiency, it can be improved by operating the engine at higher fuel injection pressures.
Furthermore, the durability of the FGM ceramic coating was examined by 100-hour operation of the single-cylinder engine. After the endurance test, several cracks on the cylinder head and ablation on the surface of the piston crown were identified.
Especially, the cracks of the cylinder head were observed at the several portions between the intake and exhaust ports, which the thermal stress was considered as severe. However, those cracks and the ablation had no influence on the engine performances such as the total heat rejection rate and the specific fuel consumption.