Vegetable oil is converted into biodiesel through the process of transesterfication and it produces biodiesel and glycerin. If methanol is used in the process, methyl ester and glycerol are produced. If ethanol is used, then ethyl ester and glycerol are produced. According to this article, written in 2003, methyl ester is cheaper due to lower cost for methanol. There are many things that we must consider when thinking of using biodiesel for our engines instead of diesel fuel. First, the viscosity of the fuel is important because it affects the atomization of the fuel being injected into the engine combustion chamber (Hofman 2003). A low viscosity of fuel is ideal to ensure complete combustion and a 20/80 mixture of number 2 diesel and biodiesel biodiesel has the closest viscosity similar to straight Number 2 biodiesel (Hofman 2003). Also, centane rating is a measure of the self-ignition quality of the fuel (Hofman 2003). The ignition quality affects the engine’s performance; it is better to have a low centane fuel, because a high centane fuel may lead to an incomplete combustion (Hofman 2003). Compared to Number 2 diesel, which has a rating of 45 and 50, biodiesel has a higher rating at 50 and 60 (Hofman 2003). Finally, the energy content of the fuel is important to understand efficiency of the fuel. Biodiesel has a low energy content, meaning biodiesel will require about 1.1 gallons of fuel to do the same work as 1.0 gallon of diesel fuel (Hofman 2003). According to this article, biodiesel begins to thicken when the temperature drops down to 30F and it thickens at warmer temperatures than Number 2 diesel; thus increasing the pour point of the fuel. A blend of biodiesel and number 1 diesel has a lower pour point than a mix of biodiesel and Number 2 diesel. Also, the article states that the cost of biodiesel is higher than diesel, but I am not sure if this stands true still.
The above information leads me to believe that pure diesel seems for efficient and cheaper than biodiesel; however the difference is not significant. The environmental consequences for using diesel are far worse than using biodiesel. According to the article, a U.S. Department of Energy publication shows that by using biodiesel there will be a reduction in most emissions except for an increase in nitrous oxide. If we used 100% Ester fuel (B100) hydrocarbon emissions would be reduced by 52.4% and carbon monoxide emissions would be reduced by 47.6% (Hofman 2003).
Also, the article looks into using vegetable oil to make biodiesel. It says for every gallon of vegetable oil, 1 gallon of biodiesel can be produced (Hofman 2003). The total input/output energy ratio shows a very positive return for the use of biodiesel from vegetable oil.
Overall, this article gave me a brief insight into the challenges that one would have to face when promoting biodiesel over diesel as a fuel source. Even though it may not be as efficient, I think it is important to focus on the positive impacts biodiesel would have on our environment.