Experimental study on influence of high exhaust backpressure on diesel engine performance via energy and exergy analysis

Marine diesel engines can be exposed to high backpressure conditions, because various aftertreatment systems and waste heat recovery devices have been widely applied to reduce the emission level, and the outlet of its exhaust manifold is normally below sea level. This article aims to understand the influence of exhaust backpressure on turbocharged engine performance. Diesel engine tests under high backpressure was conducted and it has been found that engine output power drops sharply. To explore the reasons and further study the recovery method, analysis of energy and exergy was carried out. With the increase of backpressure, turbo expansion ratio reduces sharply. But the energy upstream turbine doesn't decrease necessary due to the increase of exhaust temperature. Simultaneously, the exhaust exergy gradually increases by 10.3% when the backpressure increases from 0 bar to 0.55 bar at 75% load, leading to improved energy grade. The turbine output power reduces 56.7% because of the combination results of reduced expansion ratio and increased exhaust energy grade. The method of power recovery should balance these two factors. The study can enlighten the method of power recovery of diesel engine confronted by high backpressure conditions.