The effects of recirculated exhaust gas on fuel economy and exhaust emissions in marine diesel engines

摘要

The effects of recirculated exhaust gas on the characteristics of specific fuel consumption rate, and NO{sub}x and soot emissions are investigated by using an eight-cylinder, four-stroke, direct injection, water-cooled marine diesel engine operating at several loads and speeds. The experiments in this study are carried out at the fixed fuel injection timing of 38° BTDC regardless of experimental conditions. The intake oxygen concentration is measured by the intake air flow and the oxygen concentration in the recirculated exhaust gas. The exhaust oxygen concentration is measured in the exhaust manifold. And the mean equivalence ratio, calculated by the intake oxygen and fuel consumption rate, is used to analyze and discuss the influences of exhaust gas recirculation (BGR) on NO{sub}x and soot emissions. It is found that the specific fuel consumption rate is not greatly affected by the EGR rate. And NO{sub}x emissions decrease markedly owing to the reduced concentrations of intake and exhaust oxygen, and the increase of the equivalence ratio as the EGR rate is increased, while soot emissions increase with increasing EGR rates at a given engine load and speed, especially higher loads. The optimal EGR rate for the respective engine conditions without degrading the specific fuel consumption rate can be roughly estimated within the emissions standards of Korean heavy-duty diesel engine, based on the correlations between NO{sub}x and soot emissions.