Exhaust gas recirculation as a major technique designed to reduce NOx emissions from marine diesel engines

Abstract

The study objective is to identify to what extent the recirculation of exhaust gas from a low-speed marine diesel engine affects environmental, economic and power-related parameters in engine operation. Concentration of nitrogen oxides in exhaust gases was assumed to be the environmental parameter of an engine, specific fuel consumption as its economic parameter while effective (brake) power as its power-related parameter. Content of nitrogen oxides in exhaust gases discharged by low-speed marine diesel engines shall remain within the range of 3.4…14.4 g/(kW·h) depending on the area of marine vessel operation as specified by requirements of Annex VI MARPOL. Exhaust gas recirculation (EGR) was reviewed as a way to provide for such values. It was proven experimentally that recirculation of exhaust gas in the range of 4.7…18.8 % provides for reduction in concentration of nitrogen oxide (NO?) in the exhaust gases respectively down to 13.3…3.3 g NOx/(kW·h) depending on the rotation speed and load of diesel engine. Drop of NOx concentration in exhaust gases (as compared to NO? concentration without any circulation system used) was shown to reach 37.9…53.5%. It is proposed to apply the EGR system as a major technique to reduce NOx - emissions and bring the aforesaid parameter in compliance with requirements of international agencies.