National Center for Sustainable Transportation

Given that today’s real-world diesel fuel supply is comprised of biodiesel as a blendstock with petrodiesel, understanding how addition of biodiesel affects exhaust particle properties and their subsequent effect on human health is critically important. Here, samples of a commercial waste vegetable oil biodiesel B100 fuel were subject to thermal oxidation at 110oC for 5, 10 or 20 hr before diesel engine dynamometer emissions testing as the neat fuel (B100) and as a 20% v/v biodiesel blend (B20) with petrodiesel. Exhaust particulate matter samples collected using impingers were tested for the ability of the particles to initiateformation of reactive oxygen species (ROS) using the abiotic dithiothreitol (DTT) assay. DTT Activity [nmol DTT consumed per minute per mg PM] of three B20, three B100 as well as petrodiesel (B0) fuels over a total of 13 emissions tests with a light-duty diesel engine were compared. Combining data for emissions tests by fuel blend and oxidation status, mean DTT Activity was similar between B0 and B20 (10hr oxidized), B100 (neat) and B100 (5 hr). Particles from the B20 neat and B20 (20 hr) fuels had the highest measured DTT Activity whereas the B100 neat and B100 (5 hr) had the lowest DTT Activity. Twenty hours of thermal oxidation conditions resulted in the highest measured DTT Activity (or highest potential to form ROS) for both B20 and B100 fuels and IP=0. An inverse relationship between storage stability (opposite of degree of fuel oxidation) of the biodiesel fuel as measured by induction potential (IP) and the ROS formation potential: higher DTT Activity was noted for the B100 fuels with the lowest IP. Results suggest that mixing of B20 from certified B100 fuel may lead to oxidation of unsaturated FAMES and subsequent higher ROS formation potential. Future work should examine how the detailed chemical composition of biodiesel exhaust PM, especially when waste oil B100 is blended with petrodiesel at 20 % v/v, may be related to DTT consumption or other metrics for ROS formation potential. Further, future emissions studies should provide information on property differences between Bxx blends and the neat B100 fuel that result not only from biodiesel storage, but from fuel handling. 

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