Effects of Biodiesel Fuels Use on Vehicle Emissions

Abstract

Many countries are using and considering the increased use of biodiesel blended fuels to slow their growth of fossil fuel use for transportation purposes. Before the use of these fuels increase, it is critical that we understand the effect of using biodiesel blends on vehicle emissions, so that we better understand what air quality impacts to expect. Many previous reviews of biodiesel effects on emissions have combined all of the emissions data available to find a single value for the effects of a biodiesel blend on pollutant emissions. This includes combining emissions data from both light-duty (LD) and heavy-duty (HD) diesel vehicles and engines, combining vehicle data from chassis dynamometer and on-road emissions testing, and combining data using different oil feedstocks for producing biodiesel fuels.
In this review, the effects of switching from petroleum diesel fuel to biodiesel blended fuels on relative vehicle emissions for LD and HD vehicles are determined separately. We will not include engine emissions data in this analysis. For HD vehicles, we will also separate results for on-road emissions testing from chassis dynamometer testing. For HD vehicles, hydrocarbon (HC) emissions were significantly lower for B20 and B100 fuels from dynamometer and for B20 fuels from on-road emissions testing. For LD vehicles, there was no significant effect on HC emissions for B5, B10, B20, B30, B50 or B100 fuels. Nitrogen oxides (NOx) emissions for HD dynamometer data was significantly higher for both B20 and B100, but no significant difference was found for the HD on-road emissions data. The NOx emissions for the LD vehicles were significantly higher for B10, B20, B30, B50 and B100 blends. For carbon monoxide (CO) emissions there was no significant effect for B20 and a significant decrease for B100 based on HD dynamometer data, and a significant decrease for B20 based on HD on-road emissions data. LD dynamometer data found a significant decrease in CO emissions only for B20 blends. No significant effect was found for carbon dioxide (CO2) emissions for HD vehicles using B20 fuels based on dynamometer or on-road emissions data. For LD vehicles a significant decrease in CO₂ emissions was found only for the B10 blend. Particulate matter (PM) emissions were significantly lower for B20 fuel in HD vehicles for both types of emissions tests. PM emissions decreased significantly for LD vehicles for B10, B20, B30 and B50 blends only. The HD dynamometer data showed a significant decrease in fuel economy for the B20 blend, but no significant effect was observed for either the HD on-road or LD dynamometer data. When the effects of a biodiesel blend on vehicle emissions in different categories were not significantly different, the results were combined to assess the effect of biodiesel use on the broader class of vehicles.