Biodiesel is the type of the diesel fuel that is mostly manufactured from vegetable oils. Biodiesel is very similar to diesel based on petroleum though there are some differences that I will mention later in the article. Biodiesel can be used in its pure form or it could be blended with petroleum diesel at any concentration in most injection pump diesel engines, and though this is its main use it is not the only one as biodiesel could be also be used for some other purposes (for instance like heating oil).
If we compare biodiesel with standard diesel we can see that biodiesel has significantly better lubricating properties, meaning that engine will move more easily, which will increase diesel engine's life. Biodiesel also has higher cetane number which is a measurement of the combustion quality of diesel fuel during compression ignition. Having higher cetane number means that biodiesel fuel has shorter ignition delays that provide more time for the fuel combustion process to be completed. I should also mention here that biodiesel derived from animal fats has higher cetane number compared to biodiesel from vegetable oils.
Most diesel engines will have no problem with using biodiesel though some diesel engines may require few modifications, especially older diesel engines. Most diesel engines could use pure biodiesel (B100) but in most cases biodiesel is used together with standard diesel fuel (in most cases this mix consists of 20% of biodiesel and 80% of standard diesel fuel, known as B20).
Biodiesel produces fewer emissions that standard diesel. It is also very important to mention here that biodiesel has virtually no sulfur content meaning that it cannot contribute to formation of acid rain like this can be the case with standard diesel. This table below will give you better insight into comparison of emissions between biodiesel and standard diesel.
Biodiesel is also much safer to use compared to standard diesel, and has significantly higher flash point than standard diesel (130 °C, 266 °F compared to 64 °C, 147 °F). Flash point is the lowest temperature at which certain liquid can vaporize to form an ignitable mixture in air. Since biodiesel burns at much higher temperature compared to standard diesel the chances of biodiesel to accidentally combust are much lower compared to standard diesel.
The major setback that biodiesel has compared to standard diesel is the cost of biodiesel. Biodiesel costs higher than standard diesel, for instance a most common mix of 20% biodiesel and 80% standard diesel will cost in average around 30 cents more per gallon compared to standard diesel.
Biodiesel also has less energy content compared to standard diesel. The amount of energy per gallon of biodiesel is approximately 11 percent lower than that of petroleum diesel, meaning that with the most common mix B20 your car will achieve 2.2 percent fewer miles per gallon of fuel than with the standard diesel.
The problem with biodiesel is also the release of nitrogen oxide emissions which can contribute to the formation of smog. Because of this problem there are many ongoing researches that aim to find biodiesel formulations that do not increase nitrogen oxide emissions. Current solutions for this problem include blending the biodiesel with kerosene or Fischer-Tropsch diesel.