Fuel Additive and Blending Approaches to Reducing NOx Emissions from Biodiesel 2002-01-1658

Blending of 20% biodiesel with petroleum diesel is well known to cause a significant reduction in PM emissions but also can cause NO_x emissions to increase by 1 to 3 percent. This study has examined a number of approaches for NO_x reduction for 20% biodiesel/petroleum diesel blends (B20). These approaches included blending with a nominally 10% aromatic diesel, zero aromatic Fisher-Tropsch (FT) diesel, and use of fuel additives. Biodiesel produced from soybean oil and from yellow grease was examined. Testing was conducted in at 1991 DDC Series 60 truck engine using the U.S. heavy-duty FTP. Emissions of NO_x, PM, CO, and THC are reported. Relative to certification diesel the B20 fuels exhibited 20% lower PM emissions but 3.3 and 1% higher NO_x emissions for soy and yellow grease based blends, respectively. The 10% aromatic fuel exhibited 12% lower PM and 6% lower NO_x. FT diesel had the lowest emissions with a 33% reduction in PM and 16% lower NO_x. For B20 (soy+cert fuel), lowering of the base fuel aromatic content from 31.9 to 7.5% lowered NO_x by 6.5%. Linear interpolation between data points for B20 produced using cert fuel and produced using 10% aromatic fuel suggests that, if all other factors are equal, a base fuel having 25.8 aromatics should provide a NO_x neutral B20 (relative to certification diesel having 31.9% aromatic content). Note that the cetane numbers of the certification diesel and the 10% aromatic diesel are essentially the same. Blending of FT diesel may produce a NO_x neutral fuel at biodiesel content as high as 55%. The cetane enhancers di-tert-butyl peroxide and 2-ethyl-hexyl nitrate are both effective at reducing NO_x from B20 blends in this engine, while retaining the PM emission benefits of biodiesel. Ferrocene was also examined but demonstrated no emission benefits.