An Observation of High Temperature Combustion Phenomenon in Low-Heat-Rejection Diesel Engines

Experimental research was carried out by a high speed camera to observe the effects of the ambient temperature, the pressure and the parameters of injection nozzle on spray development, the ignition delay, the location of ignition, the flame propagation and the combustion rate in a constant-volume bomb which simulates the high temperature and pressure condition of Low Heat Rejection (LHR) engines. The experimental results show that at high temperature the ignition delay becomes very short and the ignition occurs near the nozzle tip. The decreased premixed combustion can't provide enough energy for subsequent air fuel mixing. The spray is enveloped totally by the flame that prevents the air entrainment to the spray. Therefore the combustion duration is prolonged at high temperature compared with low temperature. Reducing the nozzle orifice diameter and employing the special type of impingement plate can accelerate air fuel mixing and therefore, reduce the combustion duration at high temperature.