Combustion in Low-Heat-Rejection Diesel Engines

Abstract

This article provides an overview of the combustion and emission characteristics of the low-heat-rejection (LHR) diesel engine, the characteristic feature of which is that its combustion chamber wall components are of ceramic materials. The combustion chamber wall temperature of the LHR engines, which operate without cooling, increases more significantly at the high load condition compared with corresponding temperature of the water-cooled engines. The increased compression air temperature, which is due to the elevated temperatures of the combustion chamber walls, leads to a short ignition delay and increased combustion temperature. Combustion in LHR engines, therefore, is characterized by reduced premixed combustion and increased diffusion combustion. Degradation in combustion at high combustion temperature which results in a lower heat release rate and prolonged combustion duration may be attributed to poor mixing due to increased gas viscosity. The high combustion temperature and the change in the combustion mode are two competing influences that determine either the increase or the decrease in emissions such as NO, HC and particulates.