Investigation of the impact of biodiesel fuelling on NOx emissions using an optical direct injection diesel engine

The impact of biodiesel fuelling on NOx emissions was investigated using an optically accessible diesel engine. A soy-based biodiesel (B100) and three separate primary reference fuel (PRF) blends were evaluated over a range of loads at an engine speed of 800 r/min. Experimental operating conditions were carefully controlled to maintain a constant start of combustion (SOC), and a PRF blend was identified that would eliminate differences in premixed-burn fraction. A load-averaged NOx increase of ∼10 per cent was observed for B100 relative to the PRF blend with matched premixed-burn fraction. The results indicate that factors other than SOC and premixed-burn fraction affect the tendency for biodiesel to increase NOx. Equilibrium calculations reveal no significant differences in stoichiometric adiabatic flame temperature between the test fuels; however, experimental data suggest that actual flame temperatures may be influenced by differences in soot radiative heat transfer. The effect of biodiesel on mixture stoichiometry at the lift-off length may also play an important role in increasing NOx emissions. © IMechE 2006.