Effects of the Combustion Characteristics of Diesel Engine by the Intake of Exhaust Gas from Gas Engine

The authors have investigated on a ship installed some conventional marine diesel engines and lean burn gas engines, and have proposed a C-EGR (combined exhaust gas recirculation) system to reduce the slipped methane from the gas engines and the Nitrogen oxides (NOx) from the marine diesel engines. This system can consist of a marine diesel engine and a lean burn gas engine, and the exhaust gas emitted from the lean burn gas engine is provided to the intake manifold of the marine diesel engine. This system thus could reduce both the NOx from the marine diesel engine and the slipped methane from the lean burn gas engine simultaneously because of the EGR effect and the re-burning of the slipped methane. This paper introduces the effects of the intake gas compositions on the combustion characteristics of diesel engine simulated as our C-EGR system. In the experiments, oxygen(O2), methane(CH4) and carbon dioxide (CO2) concentration of the intake gas was changed by mixing nitrogen(N2), CH4, and CO2, the cylinder pressure and gas temperature of the diesel engine were thus investigated at the high and low load conditions. From the results, it was confirmed that, when CH4 concentration was increased or O2 concentration was decreased, NOx emission was decreased and CH4 emission was increased because the cylinder gas temperature was decreased, especially in low load condition. The reason can be decreased of cylinder gas temperature. On the other hand, the increase of CO2 concentration did not influence to the CH4 emission. These results might show that the reductions of slipped methane and NOx are trade-off depending on the O2 or CH4 concentration in intake gas as well as the load condition.