flask of vegetable oil in front of palm leaf

Vegetable Oil Fuels

There are two main types of vegetable oil fuels:

Straight vegetable oil, or SVO, is exactly what it seems: vegetable oil, just like the kind available in the grocery store. In fact, many people buy vegetable oil from the grocery store to use as fuel. SVO will work in a diesel engine, though for best results the engine needs to be modified. The second type is waste vegetable oil, or WVO, which is oil that has already been used for cooking and can no longer be used for that purpose. Fast food establishments and potato chip factories produce huge amounts of WVO. This oil can be collected, purified, and used as SVO fuel.

Both SVO and WVO can be used just as they are in engines modified to use them. They can also be mixed with diesel fuel or kerosene to combine the benefits of biofuels with the advantages of fossil fuel. Or they can also be converted to biodiesel. Current use of vegetable oil fuels are mainly used in diesel engines, however nearly all diesel engines are designed to work with petroleum-based fuel, so running such engines on vegetable oil is not entirely straightforward.

The first problem is one of viscosity: vegetable oil is a lot thicker than conventional diesel fuel. This means that it has a harder time atomizing, which in turn reduces its ability to burn. One way to reduce the viscosity is to mix it with ordinary diesel fuel, and most of the diesel engines used in cars and light trucks will run quite happily on anywhere from 10% to 50% vegetable oil—poured right into the gas tank along with the diesel from the pump. Another way to thin the vegetable oil is to heat it; heating is the primary function of conversion kits you can buy to run your vehicle on vegetable oil.

But using pure vegetable oil is still problematic because the fuel sitting in your engine (and your fuel line) will be cold when you initially start your car. (This is especially true, of course, in colder climates and during the winter months.) One way of solving this problem is to use two fuel tanks—one for regular diesel and one for vegetable oil. You start your engine with regular fuel, and as it warms up, the heat is used to thin the vegetable oil. After a few minutes or so, you use a dashboard control to switch over to the vegetable oil tank. Dual-tank systems also mean that a vehicle can, if necessary, refuel at a regular gas station. Another approach is to use a special additive (which contains a small amount of petroleum); this enables the vegetable oil to flow more easily, even when cold.

In most cases, you can outfit your existing vehicle with a second tank, heater system, switch, and other necessary apparatus for under US $1,000; if you go with the additive-based approach instead, you eliminate your up-front costs in exchange for somewhat more expensive fuel. Either way, you'll save an enormous amount of money on diesel fuel—assuming that you run your vehicle on used vegetable oil.

Some proponents of vegetable oil fuel claim that you'll never have to buy fuel again, as long as you are willing and able to obtain used cooking oil from a restaurant or food processing facility. Many restaurants are apparently happy to give away their used oil, because otherwise they'd have to pay to have it disposed of properly. Even if you do have to pay for it, the cost would be a mere fraction of what you'd pay for diesel fuel.

If you're using waste oil, you'll need to filter it first—which potentially involves setting up some equipment in your garage and spending a bit of time doing the processing. The inconvenience of obtaining and filtering used vegetable oil is one of the biggest reasons this process hasn't caught on more widely. But when gas prices rise this extra step looks like an increasingly minor hassle. As for supply, the United States produces about 3 billion gallons (roughly 11 billion liters) per year of waste vegetable oil, which should keep quite a few cars on the road.

Some people mix vegetable oil into diesel fuel or kerosene. These blends can contain various proportions of vegetable oil to petrodiesel, mixed according to personal preference and what is available. Though mixed fuel can work in an ordinary diesel engine, the best results come from using a two-tank system such as the one that can be used with SVO.

People who use biofuels often see mixes as a poor compromise. The engine still must be modified as if it were running on SVO, and the user is still consuming fossil fuels and emitting pollutants. On the other hand, mixing SVO with petrodiesel or kerosene offers some advantages over straight SVO. It avoids some pollution caused by burning straight fossil fuel, and the engine starts better in cold weather than when it's powered by either biodiesel or SVO.

Pros and Cons of Vegetable Oil Fuels

Using vegetable oil for fuel has many benefits. According to some sources it's better for your engine, providing additional lubrication and reducing engine deposits. It's also less likely to cause a fire or explosion in the case of an accident. Vegetable oil supposedly gives you equivalent fuel efficiency to petroleum-based diesel fuel, which is to say, substantially more than gasoline. It also results in lower emissions. Because the carbon dioxide produced by burning vegetable oil is less than the amount absorbed by the plants from which the oil is obtained, vehicles running on vegetable oil produce no net increase in atmospheric carbon dioxide. And, finally, vegetable oil fuel is indefinitely renewable.

But using SVO or WVO in engines requires modifying them, which is inconvenient and expensive. SVO is not a direct substitute for diesel, unlike biodiesel, and cannot be used alternately with petrodiesel. Even though using SVO does not require the user to make biodiesel, it still must be prepared before it is burned; WVO especially must be cleaned of all food particles.
The economics of using vegetable oil for fuel depend somewhat on whether the oil fuel is new or used. Purchasing new vegetable oil can potentially cost more than purchasing diesel fuel. However, in many cases WVO is free for the taking. Factories and restaurants must pay to dispose of their WVO in the garbage. Therefore, they are often willing to donate it to anyone who wants to collect it.

Using WVO for fuel is an excellent way of getting rid of waste oil and avoiding the consumption of fossil fuels. On the other hand, vegetable oil must come from plants, and these plants must be grown — substituting vegetable oil for fossil fuels on a large scale would require vast stretches of land devoted to growing crops that can produce it.