Abstract
Genarally, NOx emission from medium-size four-stroke slow-speed engine is high level, comparing to the IMO NOx emission regulation, so some NOx reduction method is needed.
In this study, design parameters such as compression ratio, intake and exhaust valve timing, charge air pressure and injection timing are optimized, at first step. The engine performance tendency including NOx reduction effect is investigated from a simulation method, and the engine test using the modified engine components. The result is that NOx emission level is improved below IMO Regulation without drastic modification to the engine, and keeping same specific fuel consumption (SFC) and maximum cylinder pressure level as it is.
Also, further NOx emission reduction will be necessary, because NOx regulation will become more and more stringent. So, steam addition system, that adds steam to combustion air and to maintain the absolute humidity at a desired level, is developed at second step. NOx emission was decreased through steam addition, and virtually no decline was observed in SFC.
