Biodiesel fuels may serve as a partial solution in the search for sustainable energy sources for the transportation sector. However, increased nitrogen oxide (NO x ) 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 NO x formation and use these to produce lower NO x 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 directinjection 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 (NO 2 ), CO, and unburned hydrocarbon emissions were generally lower from the biodiesel fuels than ULSD. Palm biodiesel consistently generated the lowest brake-specific NO x 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 NO 2 . The results suggest that pathways exist for tailoring the fuel properties of biodiesel blends to reduce nitrogen oxide emission compared to current fuels.

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Biodiesel can be produced from a variety of feedstock oils and, as a result, may have a diverse set of properties based on the oil used to produce it. An understanding of the effects of these properties on engine usage and emissions is needed in order to improve biodiesel production and engine calibration. In this study, four biodiesels, produced from palm, jatropha, soybean, and beef tallow oil, are used to fuel a single-cylinder compression-ignition engine to investigate the effects of individual fuel properties on combustion phasing and behavior and exhaust emissions. This engine uses a common-rail fuel system with electronic control. Electronic control of injection is used to investigate the effects of biodiesel on combustion when combustion phasing is adjusted. Findings indicate that fuel viscosity, energy content, and molecular structure are all critical properties that alter engine combustion behavior. The combined effect of injection timing and biodiesel characteristics is found to produce lower NO x emissions compared to ultralow-sulfur diesel.

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