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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The use of biofuels for transportation has grown substantially in the past decade in response to federal mandates and increased concern about the use of petroleum fuels. As biofuels become more common, it is imperative to assess their influence on mobile source emissions of regulated and hazardous pollutants. This assessment cannot be done without first obtaining a basic understanding of how biofuels affect the relationship between fuel properties, engine design, and combustion conditions. Combustion studies were conducted on biodiesel fuels from four feedstocks (palm oil, soybean oil, canola oil, and coconut oil) with two injection systems, mechanical and electronic. For the electronic system, fuel injection timing was adjusted to compensate for physical changes caused by different fuels. The emissions of nitrogen oxides (NO x ) and partial combustion products were compared across both engine injection systems. The analysis showed differences in NO x emissions based on hydrocarbon chain length and degree of fuel unsaturation, with little to no NO x increase compared with ultra-low sulfur diesel fuel for most conditions. Adjusting the fuel injection timing provided some improvement in biodiesel emissions for NO x and particulate matter, particularly at lower engine loads. The results indicated that the introduction of biodiesel and biodiesel blends could have widely dissimilar effects in different types of vehicle fleets, depending on typical engine design, age, and the feedstock used for biofuel production.

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