The different ways you can use vegetable oil for biofuel all consist of altering either your vehicle or the oil. Vegetable oil may be modified to work in a regular diesel vehicle by adding substances such as ethanol, gasoline, or kerosene, though this may damage the engine. It can also be modified into biodiesel through a more complex process known as transesterification. The other ways to use vegetable oil for biofuel are to install a two tank system on your vehicle or modify your diesel engine to run on the thicker vegetable oil. It is sometimes also possible to use regular vegetable oil in an unmodified vehicle, though this is not usually recommended.
Since vegetable oil is more viscous than petrodiesel, it does not behave the same way in an unmodified diesel engine. One common way that people get around this fact is by thinning it out with other substances, such as petrodiesel or kerosene. This simple process of using vegetable oil for biofuel is sometimes sufficient to allow the vegetable oil to combust normally in an unmodified engine, though there may be undesirable results.
Vegetable oil can also be modified into biodiesel using the transesterification process. This can be done in an industrial setting, though you can also do it at home. The process typically consists of combining vegetable oil with alcohol and a catalyst. Vegetable oil is made up of compounds known as triglycerides, which can be combined with alcohol and a catalyst, such as lye, to form fatty acid methyl-esters. In addition to the fatty acid methyl-esters, also known as biodiesel, glycerin is also produced as a byproduct.
The process of transesterification can result in biodiesel that is very similar to the fuel you would purchase at a filling station, and can typically be used in any unmodified diesel engine. It does require very precise amounts of each ingredient, so while it can be done at home you need to be certain that you are capable of performing the procedure safely. The biodiesel created in this manner must be treated with care and stored safely, and the byproducts typically need to be disposed of in a particular manner.
You can also make use of straight vegetable oil for biofuel by modifying an existing vehicle. Kits are typically available if you have good mechanical skills, though you can also hire an expert to do the conversion. One way of converting a vehicle to use vegetable oil for biofuel is to use a two tank system. This system has one tank for vegetable oil and another for petrodiesel. The vehicle typically runs on the diesel fuel until it has warmed up and then switches to vegetable oil.
It is also sometimes possible to convert an engine to run on straight vegetable oil. This is typically a more complex process that involves higher pressure injectors, a preheating system for the vegetable oil, stronger glow plugs, and other modifications. A properly modified diesel engine can typically use straight vegetable oil for biofuel, though additional work usually needs to be done before putting any waste vegetable oil into the system.