Low Heat Rejection From High Output Ceramic Coated Diesel Engine and Its Impact on Future Design

A high output experimental single cylinder diesel engine that was fully coated and insulated with a ceramic slurry coated combustion chamber was tested at full load and full speed. The cylinder liner and cylinder head mere constructed of 410 Series stainless steel and the top half of the articulated piston and the cylinder head top deck plate were made of titanium. The cylinder liner, head plate and the piston crown were coated with ceramic slurry coating. An adiabaticity of 35 percent was predicted for the insulated engine. The top ring reversal area on the cylinder liner was oil cooled. In spite of the high boost pressure ratio of 4:1, the pressure charged air was not aftercooled. No deterioration in engine volumetric efficiency was noted. At full load (260 psi BMEP) and 2600 rpm, the coolant heat rejection rate of 12 btu/hp.min. was achieved. The original engine build had coolant heat rejection of 18.3 btu/hp-min and exhaust energy heat rejection of 42.3 btu/hp-min at full load. With the insulated build, the heat rejection of the coolant was 9.7 btu/hp-min and exhaust energy heat rejection was 54.1 btu/hp-min. The large increase in exhaust heat rejection at the expense of lower coolant heat rejection of the insulated engine indicates that some type of exhaust heat utilization device would be useful.

The heat rejection results from the insulated engine indicate the probable direction of the insulated engine program whereby high power densities and high efficiency are desired. A diesel engine operating near stoichiometry with the insulated engine with turbocompound device offers the most horsepower for a given engine displacement at the highest thermal efficiency. An insulated engine was demonstrated operating near stoichiometry (18:1) air-fuel ratio with normal smoke and fuel consumption. Calculation of the combined insulated and near stoichiometric engine with turbo-compounding showed the highest power density and best fuel consumption. Conversion of the high exhaust heat rejection and the minimized parasitic power for the low coolant heat rejection are the most likely contributing factors for the higher engine efficiency. These two experimental programs have shown the potential capability of the insulated-stoichiometric-turbocompound engine referred to as the Turbocompound-Stoichiobatic Engine.