Emission reduction methods and split fuel injection in a marine four-stroke engine

The new emission legislation for sea-going vessels issued by the International Maritime Organization (IMO) requires drastic reduction in exhaust gas nitrogen oxides (NOx), and the combination of different primary methods can be an interesting solution without increasing remarkably the machinery. In this paper, the Miller cycle and the dilution with exhaust gas in the combustion chamber were tested to reach the Tier III limits for a four-stroke marine engine. In particular, the Miller cycle is used to reduce the in-cylinder temperature, and lower oxygen content in the combustion chamber is realized with cooled exhaust gas recirculation (EGR). Despite a remarkable reduction in NOx, the main drawback was a significant increase in fuel consumption. Split injection is combined with the abovementioned methods, in order to improve the engine efficiency. The novelty of this study consists in the simultaneous use of a split fuel injection, the Miller cycle and EGR in a marine-size application. Along this study, combining Miller timing with a relatively low EGR rate reduces NOx emissions by 90%. On the other hand, split injection does not bring significant advantages in fuel economy, although the results with very early pilot injection suggest further studies to be realized.