Assessment of NOx Emissions during Transient Diesel Engine Operation with Biodiesel Blends

The target of the present work is to review the literature regarding the effects of biodiesel blends on nitrogen oxide (NOx) emissions during the transient operation of diesel engines (acceleration, load increase, starting, driving cycles). The most important mechanisms are analyzed on the basis of the fundamental aspects of transient conditions and the effects that biodiesel physical and chemical properties have relative to conventional diesel oil; biodiesel feedstock and driving cycle effects are also emphasized. In parallel, a comprehensive statistical analysis is presented regarding the effects of biodiesel blends on NOx emissions for engines running on transient cycles during the last 30 years. For the majority of the reviewed transients, an increasing trend in NOx emissions is established when the biodiesel ratio in the fuel blend increases. Moreover, the biodiesel NOx emission penalty seems to increase for more aggressive cycles and for increasing feedstock unsaturation. (C) 2014 American Society of Civil Engineers.