Combustion and Emission Characteristics of Biodiesel and Renewable Diesel in a 4-Stroke Locomotive Engine

Rail transportation in North America consumes substantial amounts of fossil fuel, raising energy security and supply chain resilience concerns. Adopting renewable or alternative fuels is a practical approach to reduce petroleum dependence and improve supply security. The objective of this paper is to investigate the combustion and emission characteristics of biodiesel and renewable diesel as a drop-in fuel without engine modification. In this study, a single-cylinder, four-stroke locomotive engine was employed to investigate the combustion and emissions characteristics of four fuels: conventional Diesel No. 2, plant-based biodiesel, animal-based biodiesel, and renewable diesel. The experimental campaign was carried out under both part-load and full-load operating conditions at the constant load, with injection duration adjusted to achieve the targeted engine’s load and speed. Results indicate that biodiesel and renewable diesel deliver comparable peak in-cylinder pressure, indicated thermal efficiency, and start of combustion relative to Diesel No. 2, demonstrating their possibility to use as drop-in fuels. A reduction in smoke emissions was observed with both biodiesel and renewable diesel. However, plant- and animal-based biodiesels show an increase in NOx emissions under part-load conditions. The effect on NOx emissions was not observed at full load, due to increasing EGR ratios at full load operating condition, which suppressed NOx formation. Among the fuels tested, renewable diesel provided an additional advantage of reducing CO₂ emissions compared to both biodiesels. This study suggests that renewable diesel emerges as a promising option for rail applications, combining operational performance comparable to petroleum diesel with reduced smoke and CO₂ emissions. Biodiesel, while effective at reducing smoke, may require further strategies to control NOx emissions under part-load conditions.