Biodiesel Later-Phased Low Temperature Combustion Ignition and Burn Rate Behavior on Engine Torque

Finding a replacement for fossil fuels is critical for the future of automotive transportation. The compression ignition (CI) engine is an important aspect of everyday life by means of transportation and shipping of materials. Biodiesel is a viable augmentation for conventional diesel fuel in compression ignition engines. Biodiesel-fuelled diesel engines produce less particulate matter (PM) relative to conventional diesel and biodiesel has the ability to be a carbon dioxide (CO₂) neutral fuel, which may come under government regulation as a greenhouse gas. Although biodiesel is a viable diesel replacement and has certain emissions benefits, it typically also has a known characteristic of higher oxides of nitrogen (NO_x) emissions relative to petroleum diesel. Advanced modes of combustion such as low temperature combustion (LTC) have attained much attention due to ever-increasing emission standards, and could also help reduce NO_x in biodiesel. LTC has the ability to simultaneously reduce soot and nitric oxide (NO) emissions by having lower local equivalence ratios and combustion temperatures in order to significantly reduce soot and NO formation.

Results in this study - taken from a medium-duty diesel engine using 100% petroleum diesel, 100% palm olein biodiesel, and a 20%-v blend of biodiesel into petroleum diesel - demonstrate the attainment of later-phased low temperature combustion and the ability of biodiesel to sustain near-similar torque levels as of conventional combustion. The shorter ignition delay and combustion duration of B100, the latter of which is relatively shorter than petroleum diesel because of the burn characteristic of the studied biodiesel, allow biodiesel low temperature combustion to take place earlier in the combustion stroke than if petroleum diesel were used. Comparatively, the 20%-v blend also shows improved sustained torque, but less so than the 100% biodiesel. The biodiesel fuels also show improved combustion efficiency relative to the petroleum diesel at the low temperature combustion condition, further improving the engine's torque. Results of nitric oxide and soot concentrations are compared; differences in combustion phasing, exhaust gas recirculation level, and initial temperatures, however, render a direct comparison in these exhaust species among the fuels invalid.