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Plant oil as fuel

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Vegetable oil can be used as a (bio)fuel. This is useful for transportation (use in vehicles), electricity generation (stationary use), ...

Diesel engines can be modified to run on straight vegetable oil or waste vegetable oil (used cooking oil). Problems can occur with some engine types when operated for extended periods at idle or low load as vegetable oil does not burn well in these conditions. Suitable engine modifications along with attention to fuel quality, ambient temperatures and operating regime generally avoids these issues.

Gasoline engines can only be made to run on ethanol. However, [biodiesel]] may also be used in gasoline engines, if mixed with ethanol[1] [verification needed] Some engines, oil types, and ambient conditions though can cause problems.

Finally, vegetable oils can also be used in stirling engines. This is slightly (10%) more efficient. Finally, the vegetable oils can be used in systems generate both heat and power (see Combined heat and power).

Vegetable oil extraction and conversion

The process of oil extraction is carried out the same way as for extraction of edible oil from plants. There are many crops grown in rural areas of the developing world which are suitable for oil production. Most of these have high energy contents; sunflower oil, for example, has an energy content of about 85% of that of diesel fuel.

There are two well-established technologies for oil extraction:

  • The simple screw press, which is a device for physically extracting the oil from the plant - this technology is well suited to small-scale production of oil as fuel or as foodstuff in rural areas. The press can be motorised or hand-operated.
  • Solvent extraction is a chemical process which requires large, sophisticated equipment. This method is more efficient - that is, it extracts a greater percentage of the oil from the plant - but is less suited to rural applications.

The oil, as well as being used for lighting and heating, can be used as a fuel in internal combustion engines.

Biodiesel production is not complex and can be done on a small scale. The vegetable oil is converted to a useable fuel by adding ethanol or methanol alcohol along with a catalyst to improve the reaction. Small amounts of potassium hydroxide or sodium hydroxide (commonly called lye or caustic soda, which is used in soapmaking) are used as the catalyst material. Glycerine separates out as the reaction takes place and sinks to the bottom of the container. This removes the component that gums up the engine so that a standard diesel engine can be used. The glycerine can be used as a degreasing soap or refined to make other products.

This article or section includes content from Original:Biogas and liquid biofuels by Practical Action. Used with permission.

Conversion of the engine

As stated above, pure vegetable oil can also be used in a diesel engine, and even then, modifications may still need to be done for running on pure vegetable oil. If the engine used is a gasoline engine, it can only be converted to run on either (very lean/good quality) biodiesel, or alternatively pure ethanol.

Vegetable oil is too thick to burn well in the engine unless it is hot. To deal with this problem, some vehicles use a two-tank system: one tank for biodiesel or petrodiesel, and one for vegetable oil. The engine is started on diesel and run until it heats up, then the driver switches to the vegetable oil tank. When done driving, the vehicle must be switched back to the diesel tank in order to get the vegetable oil out of the fuel lines; otherwise, the lines will still be full of vegetable oil when the car is next started, and it will be difficult to start. A single tank system can also be used, this system has the advantage that no petrodiesel (or another starting fuel -ie ethanol) needs to be carried in the vehicle, saving weight and thus fuel consumption.

Oil that is not hot enough when it enters the engine will not burn properly and will cause buildup that will damage the engine.

Waste vegetable oil can also be used, this is typically pure plant oil that has allready been used for frying food. It must be filtered and water must be removed before it can be used as fuel, or it will damage the engine.

See also

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