Factors affecting biodiesel engine performance and exhaust emissions – Part I: Review

Effects of variation in biodiesel fuel properties on engine performance are not completely understood and there is a need for further research. A review of literature studies on biodiesel engine performance and emissions is presented here, summarising known effects and highlighting aspects in need of further study. In particular, it is evident few studies have reported on the effects of biodiesel oxidation, and antioxidant additives. It is well known that physical properties of biodiesel such as the bulk modulus and viscosity alter the injected fuel-spray characteristics. Biodiesel's greater density and oxygenated structure results in proportionally lower energy content. Unsaturation level affects Cetane number and combustion characteristics. Maximum engine power usually decreases according to the lower volumetric energy content of biodiesel, and fuel consumption is expected to increase around 14%. Impacts on emissions are difficult to conclude generally due to contrasting reports. However, dominant emissions trends are usually an increase in oxides of nitrogen, and decreases in carbon monoxide, particulate matter, unburned hydrocarbons and aromatics. Changes in emissions of carbonyl compounds are less certain. The effect of alcohol type used in biodiesel production is not clear, neither is the effect of biodiesel oxidation and antioxidant additives.