Analysis on capability of power recovery of marine diesel engine at high backpressure conditions

Abstract

Marine diesel engines can be exposed to high backpressure conditions in the scenario of maritime, because the outlet of its exhaust manifold is normally below the sea surface to reduce the emission level. The performance of the engine has been confirmed to drastically deteriorate due to the high exhaust backpressure. The current methods for turbo-engine matching and power recovery at high backpressure conditions are specific instead of general. This article aims to understand the mechanism of influence on turbocharged engine performance by exhaust backpressure, and to develop a performance evaluation method as well as optimized methods of turbo-engine matching at high backpressure conditions. Firstly, numerical method is established for a 16-cylinder V-type turbocharged diesel engine and calibrated/validated based on experimental results. The influence of the backpressure on engine and turbocharger performance is discussed by the numerical method. The power recovery efforts are founded to be constrained by the maximum cylinder pressure and exhaust temperature. The influence of the effective flow area of the turbine and turbocharger efficiency on the operational constraints are discussed. It is concluded that the influence on intake air mass flow and fuel margin is the source of the influence on the constraints. Based on the findings, a capability region of engine power recovery is proposed, which is bounded by curves of maximum cylinder pressure and maximum exhaust temperature, respectively. Furthermore, the availability of exhaust gas is the root of influencing the boundaries of the region. According to the mechanism, a universal evaluation method based on the available energy of the exhaust gas is proposed which is tailored for turbo-engine matching at different exhaust backpressures.