Straight Vegetable Oil SVO as Diesel replacement fuel

Waste vegetable oil

Waste Vegetable Oil (WVO) is vegetable oil that has become unfit for food preparation. The common causes of this degradation are: chemical degradation (including oxidation and hydrogenation) and the accumulation of contaminants.

Apart from being discarded, waste vegetable oil can be used in animal feed, can be burned as fuel in waste-to-energy plants, home heating furnaces, modified diesel engines. It can also be used as fatty acid feedstock for the production of soap and biodiesel.

Animal feed

As of 2003, the use of waste vegetable oil in animal feed is no longer permitted in the European Union, but continues in the United States.

Use in diesel engines

One of the first demonstration diesel engines ran on peanut oil. However, modern diesel engines are designed to run on petrodiesel. They run poorly on unmodified vegetable oil, with a risk of damage - the fine ports of injectors can be clogged by carbon which forms from the slow or incomplete combustion of heavier fractions of vegetable oil, while the injection pump may suffer premature wear due to the fuel's relatively poor lubricating properties. Similar problems were noted when the levels of sulphur in UK petrodiesel were reduced to counter emissions.

There are two solutions to this, both of them technically successful and growing in popularity:

* Convert the oil to biodiesel.
* Convert the engine to run on straight vegetable oil.

Biodiesel

Biodiesel has similar characteristics to petrodiesel, notably its viscosity. It can be produced by transesterification of WVO. Since the early 1990s, the use of waste vegetable oil to produce biodiesel has been growing steadily. Biodiesel and petrodiesel may be mixed in the same fuel tank.

Straight vegetable oil

The other approach is to convert the engine. The most common conversion simply provides a way of heating the fuel to reduce its viscosity. Such engines often have two fuel tanks, one for petrodiesel, biodiesel or a mixture of the two, for use in starting the engine, the other for the vegetable oil which is the main fuel. After starting and running for a short time to allow the fuel heating system to come into operation, the fuel supply is swapped to the heated vegetable oil feed. There are many theories of the best way of preparing WVO to be used in diesel engines. Most agreed upon is to let the oil settle for at least two weeks to allow suspended sediments (food particles) and water to settle out in the bottom. Allowing that, a good filtration system in addition to the heating system is all that is required to run most diesel engines on vegetable oil- be it virgin, unused oil, or waste vegetable oil (WVO).

Home heating

With often minimal modification, most residential furnaces and boilers which are designed to burn No. 2 heating oil can be made to burn either biodiesel or filtered, preheated waste vegetable oil. These are generally not as clean-burning as petroleum fuel oil, but if processed at home, by the consumer, can result in considerable savings. Many restaurants will give away their used cooking oil either free or at minimal cost, and processing to biodiesel is fairly simple and inexpensive. Burning filtered WVO directly is somewhat more problematic, since it is much more viscous, but with suitable preheating, it can be accomplished with a bit of ingenuity. WVO can be a very economical heating option for those with a mechanical inclination and the drive to put a little work into it.

The quantities involved

As of 2000, the United States were producing in excess of 11 billion liters of waste vegetable oil annually, mainly from industrial deep fryers in potato processing plants, snack food factories and fast food restaurants.

Waste vegetable oil has a stable market value of approximately USD 0.40 per US gallon (10 ¢/L) or USD 120 per metric tonne as of 2003, enough to make collection economically viable.

If all those 11 billion liters could be collected and used to replace the energetically equivalent amount of petroleum (a rather utopical case), almost 1% of US oil consumption could be offset.