Analysis of ship propulsion system behaviour and the impact on fuel consumption

From fuel to ship moving, the overall energy conversion efficiency consists of three parts: the engine efficiency, the transmission efficiency and the propulsive efficiency. In off-design conditions, there are three factors, namely the engine speed, the propeller pitch ratio and the rudder activity, and an additional disturbance, ship loading factor that can impact the behaviour of ship propulsion system and influence the overall energy conversion efficiency. In this study, by means of computer simulation, four elementary types of off-design conditions, each of which is relevant to one of the impact factors, and entire voyage simulations which combines the off-design and design operation conditions, are investigated to reveal the behaviour of the ship propulsion system. The results demonstrate that, in terms of fuel consumption, the power specific fuel consumption is mainly determined by engine efficiency while ship speed plays the most important role in calculation of ton-mile specific fuel consumption. On the voyage basis, high percentage of manoeuvering stage and intensive rudder activity result in large ton-mile specific fuel consumption, while low cruising speed could improve the fuel economy on ton-mile basis.