Evaluation of the Impacts of Biodiesel and Second Generation Biofuels on NO^sub x^ Emissions for CARB Diesel Fuels

The impact of biodiesel and second generation biofuels on nitrogen oxides (NOx) emissions from heavy-duty engines was investigated using a California Air Resources Board (CARB) certified diesel fuel. Two heavy-duty engines, a 2006 engine with no exhaust aftertreatment, and a 2007 engine with a diesel particle filter (DPF), were tested on an engine dynamometer over four different test cycles. Emissions from soy- and animal-based biodiesels, a hydrotreated renewable diesel, and a gas to liquid (GTL) fuel were evaluated at blend levels from 5 to 100%. NOx emissions consistently increased with increasing biodiesel blend level, while increasing renewable diesel and GTL blends showed NOx emissions reductions with blend level. NOx increases ranged from 1.5% to 6.9% for B20, 6.4% to 18.2% for B50, and 14.1% to 47.1% for B100. The soy-biodiesel showed higher NOx emissions increases compared to the animal-biodiesel. NOx emissions neutrality with the CARB diesel was achieved by blending GTL or renewable diesel fuels with various levels of biodiesel or by using di-tert-butyl peroxide (DTBP). It appears that the impact of biodiesel on NOx emissions might be a more important consideration when blended with CARB diesel or similar fuels, and that some form of NOx mitigation might be needed for biodiesel blends with such fuels. [PUBLICATION ABSTRACT]