Effects of fatty acid methyl esters proportion on combustion and emission characteristics of a biodiesel fueled marine diesel engine

In this experimental investigation, four different types of biodiesel fuels were employed to investigate the effects of fatty acid methyl esters (FAMEs) proportion on emission and combustion characteristics of a marine diesel engine in terms of heat release rate, cylinder pressure, indicated power, brake specific fuel consumption (BSFC), CO emission, HC emission and NOx emissions. In accordance with international IS08178 standards, the experiments were carried out on a four cylinders direct injection diesel engine fueled with four different types of biodiesel fuels and pure diesel at two test cycle modes of E3 and D2. The experimental results showed that the kinematic viscosity and ignition delay time (IDT) of biodiesel fuel in combustion process played very important roles. The chemical IDT can be shorten by the higher saturation level and the kinematic viscosity will be increased due to the higher saturation contents like C18:0 and C16:0 together with C18:1 which is a single double bond methyl ester. The increased kinematic viscosity can result in poor evaporation process and poor fuel-air mixing. Lower kinematic viscosity methyl esters like C18:3 and C18:2 are beneficial for better combustion and fuel-air mixing, but the higher nitrogen oxide emission is discovered. Thus, the relationship between emission and combustion characteristics and proportion of biodiesel is not straightforward and simple, the balance of five majority components of biodiesel fuel is very significant. Compared with pure diesel, the oxygen content of biodiesel fuel improves the in-cylinder combustion. It is beneficial to decreasing HC and CO emissions and increasing NOx emissions. However, it is not obvious at low load.