|Comparison of NOx emissions for conventional diesel and B20 for each vehicle tested and each cycle. Click to enlarge.|
A recent study by the US Department of Energy’s National Renewable Energy Laboratory (NREL) concludes that vehicles using a B20 biodiesel blend (20% biodiesel and 80% petroleum diesel) do not produce an increase in nitrogen oxide (NOx) emissions. These findings counter those of an earlier Environmental Protection Agency 2002 report showing a two-percent increase in NOx emissions for B20.
For the study, NREL tested entire vehicles on a heavy-duty chassis dynamometer at its Renewable Fuels and Lubricants Research Laboratory (ReFUEL). The vehicles included three transit buses, two school buses, two Class 8 trucks, and one motor coach.
Using the chassis dynamometer, NREL researchers simulated both urban and highway driving for each of these vehicles. In addition, NREL reviewed previously published results for engine and chassis testing of B20.
This is a major finding because the perceived small increase was leading some state regulatory agencies to consider banning B20 biodiesel. Our study helps remove a significant barrier to the expansion of biodiesel markets.
Our study shows that the NOx impact of B20 varies with engine design, such that some engines show a small increase while others show a small decrease. The EPA’s 2002 review was based on a data set made up primarily of data from one engine model that produces a small NOx increase. EPA uses these data to draw a general conclusion for on-highway engines that B20 causes a 2% increase in NOx. The chassis dynamometer testing along with careful review of previously published data suggest that their conclusion is not correct, and that on average B20 has no effect on NOx.—Robert McCormick, NREL Principal Engineer for nonpetroleum based fuels research
Effects of Biodiesel Blends on Vehicle Emissions (NREL/MP-540-40554)