Abstract
Biofuel has lately attracted considerable attention as an effective renewable energy and as a countermeasure against global warming. This paper presents results of improvement of combustion in a 4 stroke cycle medium speed marine diesel engine using marine diesel oil (MDO), marine fuel oil (MFO) and biofuels without esterification such as rapeseed oil and used vegetable oil. The authors systematically investigated the effect of biofuel content of fuel oil, the effect of fuel injection timing, and the effect of assist injection system which is a new fuel injection system composed of a common rail system and a cam drive pump. The findings are the following: (1) In high engine load conditions, it is possible to reduce CO, PM and smoke by mixing used vegetable oil with MFO because the combustion of biofuel achieves low CO, PM, and smoke emissions in these conditions. (2) In low engine load conditions, the combustion of biofuel results in higher CO and smoke emissions, but it is possible to reduce CO and smoke significantly by using assist injection system (a small amount of low pressure pre-injection).
