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 (NO_x), 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 NO_x 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 NO_x.