Abstract
Biodiesel fuels may serve as a partial solution in the search for sustainable energy sources for the transportation sector. However, increased nitrogen oxide (NOx) emissions are a potentially significant drawback to the use of biodiesel fuels that must be addressed if biodiesel is to gain widespread acceptance. One approach is to identify specific biodiesel fuel properties that minimize NOx formation and use these to produce lower NOx fuel blends, In this work, seven biodiesel fuels were produced from high-erucic rapeseed, olive, palm, coconut, soybean, and fresh and used canola oils, with their chemical composition determined using gas chromatography mass spectrometry (GC-MS). The fuels were then burned in a single-cylinder direct-injection diesel engine and evaluated for both fuel consumption and exhaust emissions of nitrogen oxides, carbon monoxide (CO), unburned hydrocarbons, and particulate matter. While all biodiesels had higher brake-specific nitric oxide (NO) emissions than ultralow sulfur diesel (ULSD) at low engine loads, olive, palm, coconut, and canola biodiesels performed better than ULSD at 50% loading and above. Nitrogen dioxide (NO2), CO, and unburned hydrocarbon emissions were generally lower from the biodiesel fuels than ULSD. Palm biodiesel consistently generated the lowest brake-specific NOx levels of all tested fuels. Statistical analysis of the results showed that higher fuel hydrogen/carbon molar ratios, low polyunsaturation levels, and lower fuel density were all significantly associated with reduced NO emissions in the tested biodiesel fuels but no clear trends were observed for NO2. The results suggest that pathways exist for tailoring the fuel properties of biodiesel blends to reduce nitrogen oxide emission compared to current fuels.