Heat Release and Emission Characteristics of B20 Biodiesel Fuels During Steady State and Transient Operation

Biodiesel fuels benefit both from being a renewable energy source and from decreasing in carbon monoxide (CO), total hydrocarbons (THC), and particulate matter (PM) emissions relative to petroleum diesel. The oxides of nitrogen (NOx) emissions from biodiesel blended fuels reported in the literature vary relative to baseline diesel NOx, with no NOx change or a NOx decrease found by some to an increase in NOx found by others. To explore differences in NOx, two Cummins ISM engines (1999 and 2004) were operated on 20% biodiesel blends during the heavy-duty transient FTP cycle and the steady state Supplemental Emissions Test. For the 2004 Cummins ISM engine, in-cylinder pressure data were collected during the steady state and transient tests. Three types of biodiesel fuels were used in the blends: soy, tallow (animal fat), and cottonseed. The FTP integrated emissions of the B20 blends produced a 20-35% reduction in PM and no change or up to a 4.3% increase in NOx over the neat diesel. The neat diesel was a type-2 diesel with a cetane number of 49.9 and sulfur content of 320ppm. Although up to a 14% increase in NOx during steady state testing was observed during medium to high loads, no significant difference was seen in the heat release curves. At low loads (which had delayed injection) during steady state and transient testing, the start of combustion occurred earlier in the B20 fuels compared to the neat diesel fuel. The use of cetane improver additives 2-EHN (0.16% volume ratio) and DTBP (0.26% volume ratio) on the soy-derived B20 fuel provided no significant change with 2-EHN and up to a 2.4% decrease in NOx with DTBP on the heavy-duty transient FTP cycle.