Effect of Biodiesel Fuels on Real-World Emissions of Passenger Locomotives

Few data are available regarding the effect of biodiesel on exhaust emission rates of two-stroke engines used in many passenger locomotives. Using a portable emissions measurement system (PEMS), duty cycle average nitrogen oxides (NOx), hydrocarbons (HC), carbon monoxide (CO), particulate matter (PM), and carbon dioxide (CO2) emission rates were measured for three locomotives operating on ultra-low sulfur diesel (ULSD) and soy-based B10, B20, and B40 biodiesel blends. Measurements were conducted in the rail yard (RY) and over-the-rail (OTR) during passenger service. Compared to ULSD, B20 biodiesel had statistically significant average emission rate reductions in the RY of 58% for CO, 45% for PM, and 6% CO2 and OTR of 59% for HC, 50% for CO, 26% for PM, and 5% for CO2. The average differences in NOx emission rates for both the RY and OTR, and HC in the RY, were not statistically significant. The OTR findings typically agreed qualitatively with the RY findings; however, OTR provides a better basis for estimating the real-world impact of fuel switching. The results indicate substantial potential to reduce in-use locomotive emissions for existing older locomotives, with the exception of NOx.