Effect of Biodiesel on Thermal NO Formation

Biodiesel is an attractive alternative to diesel fuel which is renewable in nature. This fuel has excellent lubricity, low smoke and potential for replacement of fossil diesel without major engine modifications or requirement of any additives. However, a higher nitric oxide (NO) emission from biodiesel is widely cited as their undesired emission characteristics. The present study analyses and describes the various reasons for higher NO formation with biodiesel relative to diesel fuel. To explore this so called biodiesel NO penalty, experiments were conducted on a four cylinder compression ignition engine with neat Karanja biodiesel and fossil diesel. Neat Karanja implies an unblended pure biodiesel. The experimental NO concentration with biodiesel and diesel fuel is validated using extended Zeldovich mechanism. Results suggest that the increase in NO emission with biodiesel fuel could not be opined to a change in a single fuel property but rather, it is the result of a number of coupled pathways whose effects may dominate or cancel one another under different conditions, depending on biodiesel compositional characteristics.