Search Results

The horse power and emissions of a heat insulated engine with high heat insulation rate* over 70% was investigated, as a result, a deterioration of power and emissions has become clear to be caused by change of combustion in the tests. Therefore, the observation of the combustion process in high temperature air has been carried out in the engine by using a high speed camera. We have investigated the combustion process included progress of injected fuel spray, ignition, extension of flame, and formation of soot in a vessel charged with air of high temperature and pressure with the gas condition in an engine cylinder. The test result showed that diesel fuel did not penetrate straight forward in the high temperature air, and the tip of the jet stream spread in such a shape like a lump of cloud and the spray is ignited in a short ignition delay. The flame extended widely in the free jet stream, however we observed soot formations here and there in the flame.

For the purpose of eliminating a cooling device from conventional diesel engines, a heat insulation structure referred to as thermos structure was adapted in a low heat rejection (LHR) diesel engine. The thermosstructure is constructed by a combustion chamber wall made of Si3N4 monolithic ceramics having higher strength and fracture toughness at much higher temperature and the heat insulation layers combined with air gap and gaskets with low thermal conductivity that are located behind the combustion chamber wall. Although the insulated engine achieved reduced heat rejection from the combustion chamber with the thermos structure, improvement in fuel economy and exhaust emissions could not be realized in the case of a diesel engine with Direct Injection (DI) system.