Impact of Test Cycle and Biodiesel Concentration on Emissions

A series of paired fuel tests were conducted comparing certification-grade highway diesel fuel with 5 to 50 vol% soy-methyl-ester biodiesel blends. Each fuel pair was tested for up to seven transient cycles representing various load conditions, using a 2006 model year Cummins ISB compression ignition engine equipped with exhaust gas recirculation. Except for the most lightly-loaded cycle, the results show statistically significant differences in NOx emission for all fuel pairs. The average NOx emissions due to biodiesel increased over each cycle, ranging from 0.9 to 6.6% and from 2.2 to 17.2% for the B20/B0 and B50/B0 fuel pairs, respectively. Significant reductions in CO and PM were observed over a majority of the cycles tested. The data also reveal that the change in NOx emissions increases linearly with the average cycle load. To complement the transient results, a single modal point was monitored daily to investigate biodiesel effects on engine operating parameters. Apart from the distinct changes in the brake specific fuel consumption and exhaust temperature, a preliminary examination of both steady-state and transient data indicates noticeable shifts in certain engine operating parameters between the base fuel and biodiesel blends for this Cummins ISB engine. The parameters that appear to be impacted by biodiesel blends are associated with air/fuel intake and exhaust gas recirculation.