Biodiesel1,2 is defined as the mono-alkyl esters of vegetable oils or animal fats. It can also be derived from used frying oils. Biodiesel is produced by transesterifying the parent oil or fat to achieve a viscosity close to that of petrodiesel. Biodiesel standards have been developed in the United States, Europe,and elsewhere around the world. Advantages of biodiesel include domestic origin, reducing the dependency on imported petroleum, biodegradability, high flash point, and inherent lubricity in the neat form.1,2 Improvement of the oxidative stability and low-temperature properties remain technicalchallenges. Most regulated exhaust emissions (particulate matter ) PM, hydrocarbons ) HC, carbon monoxide ) CO) with the exception of nitrogen oxides (NOx) are reduced through the use of biodiesel.3-5 Thus, the reduction of NOx exhaust emissions is another technical challenge facing biodiesel, especially in light of the increasingly stringent exhaust emissions regulations affecting diesel engines and becoming effective in the next few years (Table 1). This development is connected with the introduction of ultralow sulfur diesel fuel (ULSD; for example, less than 15 ppm sulfur in the United States). Several engine or aftertreatment technologies, such as selective catalytic reduction (SCR), exhaust gas recirculation (EGR), diesel oxidation catalysts
Summary and Conclusions
The exhaust emissions of commercial biodiesel and petrodiesel, three components of biodiesel fuels, methyl laurate, methyl palmitate, and methyl oleate (technical grade), and two components of petrodiesel, dodecane and hexadecane, were studied in a 2003 model year heavy-duty 14 L six-cylinder diesel engine with EGR. The commercial biodiesel fuel, as well as the fatty compounds, significantly reduced PM exhaust emissions (75-83%) compared to the petrodiesel base fuel, while the two hydrocarbons found in petrodiesel achieved reductions of only 45-50%. However, NOx exhaust emissions were slightly increased with commercial biodiesel and technical grade methyl oleate, while methyl laurate and methyl palmitate as well asdodecane and hexadecane led to a slight decrease of NOx compared to the base fuel. The chain length of the compounds had little effect on NOx and PM exhaust emissions, while the influence was greater on HC and CO, the latter being reduced with decreasing chain length. Unsaturation in the fatty compounds causes an increase in NOx exhaust emissions. The present results differ from previous literature data showing the effect of newer engine technology on exhaust emissions. The low levels of PM observed with the ester fuels may influence emissions reduction technologies when using biodiesel.
From
Energy and Fuels Abstract here:
http://pubs.acs.org/cgi-bin/abstract.cgi/enfuem/asap/abs/ef0502711.htmlText