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

摘要

The authors have investigated on a ship installed some conventional marine diesel engines and lean burn gas engines, and have proposed a OEGR (combined exhaust gas recirculation) system to reduce the slipped methane from the gas engines and the Nitrogen oxides (NO_x) 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 NO_x 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 OEGR system. In the experiments, oxygen(O_2), methane(CH_4) and carbon dioxide (CO_2) concentration of the intake gas was changed by mixing nitrogen(N_2), CH_4, and CO_2, 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 CH_4 concentration was increased or O_2 concentration was decreased, NO_x emission was decreased and CH_4 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 CO_2 concentration did not influence to the CH_4 emission. These results might show that the reductions of slipped methane and NO_x are trade-off depending on the O_2 or CH_4 concentration in intake gas as well as the load condition.