Effects of high-pressure and donor-cylinder exhaust gas recirculation on fuel economy and emissions of marine diesel engines

Abstract

With the increasingly stringent emission legislation for marine diesel engines, a higher exhaust gas recirculation (EGR) rate is used to reduce NOx. However, a high EGR rate deteriorates brake specific fuel consumption (BSFC). Therefore, a suitable EGR pattern is critical to balancing NOx and BSFC. In this study, high-pressure EGR (HP-EGR) and donor-cylinder EGR (DC-EGR) were separately established by GT-Power, and NOx and BSFC comprehensive optimization was conducted by adaptive particle swarm optimization. The effect of the EGR-coupled high-pressure turbine on NOx and BSFC for HP-EGR and the effect of the EGR-coupled throttle valve on the inhomogeneity of different cylinders for DC-EGR were studied. Comparisons of two EGR patterns show that the achievable maximum EGR rate for HP-EGR is more sensitive to engine loads than DC-EGR. DC-EGR can achieve a higher EGR rate and lower NOx at low and medium loads. Under the same NOx, the required EGR rate, λ, boost pressure and exhaust pressure of DC-EGR are lower. However, the BSFC of DC-EGR is slightly higher at a 25% load. As the turbine flow characteristic of HP-EGR is insufficiently adjusted with loads, DC-EGR is more inclined to achieve comprehensive optimization of NOx and BSFC under full loads.