Vegetable oil

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This article is about vegetable oil used as fuel. For other uses of vegetable oil, see vegetable oil.

Waste Vegetable Oil which has been filtered.Many vegetable oils have similar fuel properties to diesel fuel, except for higher viscosity and lower oxidative stability. If these differences can be overcome, vegetable oil may substitute for #2 Diesel fuel, most significantly as engine fuel or home heating oil.

For engines designed to burn #2 diesel fuel, the viscosity of vegetable oil must be lowered to allow for proper atomization of fuel, otherwise incomplete combustion and carbon build up will ultimately damage the engine. Many enthusiasts refer to vegetable oil used as fuel as waste vegetable oil (WVO) if it is oil that was discarded from a restaurant or straight vegetable oil (SVO) to distinguish it from Biodiesel.

History

The first known use of vegetable oil as fuel for a diesel engine was a demonstration of an engine built by the Otto company and designed to burn mineral oil, which was run on pure peanut oil at the 1900 World's Fair. When Rudolf Diesel invented the diesel engine, he designed it to run on peanut oil after coal dust was determined to be unsuitable as a fuel but it was soon discovered that it would operate on cheaper petroleum oil. In a 1912 presentation to the British Institute of Mechanical Engineers, he cited a number of efforts in this area and remarked, "The fact that fat oils from vegetable sources can be used may seem insignificant today, but such oils may perhaps become in course of time of the same importance as some natural mineral oils and the tar products are now."[1]

Periodic petroleum shortages spurred research into vegetable oil as a diesel substitute during the 30s and 40s, and again in the 70s and early 80s when straight vegetable oil enjoyed its highest level of scientific interest. The 1970s also saw the formation of the first commercial enterprise to allow consumers to run straight vegetable oil in their automobiles, Elsbett of Germany. In the 1990s Bougainville conflict, islanders cut off from oil supplies due to a blockade used coconut oil to fuel their vehicles.[2]

Academic research into straight vegetable oil fell off sharply in the 80s with falling petroleum prices and greater interest in biodiesel as an option that did not require extensive vehicle modifications

Application and usability

Older diesel Mercedes are popular for conversions to biodiesel or waste vaetable oil.
While engineers and enthusiasts have been experimenting with using vegetable oil as fuel for a diesel engine since at least 1900, in all the literature, only one peer reviewed study exists that compares long term use of vegetable oil and #2 Diesel as fuels which shows no noticeable difference in rate of deterioration of the engine burning vegetable oil, for one particular model of engine, the German Deutz F3l912W .[3] (#1 Diesel has a cold-weather additive to reduce gelling)
Most diesel car engines are suitable for the use of SVO, also commonly called Pure Plant Oil (PPO), with suitable modifications. Principally, the viscosity of the SVO/PPO must be reduced by preheating it, typically by using heat from the engine or electricity, otherwise poor atomization, incomplete combustion and carbonization may result. One common solution is to add an additional fuel tank for "normal" diesel fuel (petrodiesel or biodiesel) and a three way valve to switch between this additional tank and the main tank of SVO/PPO. The engine is started on diesel, switched over to vegetable oil as soon as it is warmed up and switched back to diesel shortly before being switched off to ensure it has no vegetable oil in the engine or fuel lines when it is started from cold again. In colder climates it is often necessary to heat the vegetable oil fuel lines and tank as it can become very viscous and even solidify. Another solution (the one-tank system) is to add electric pre-heating of the fuel and, if necessary, upgrade the injection pumps and glow-plugs to allow SVO/PPO fuel use with one tank. One tank conversions are most viable in hot climates.
With unmodified engines the unfavourable effects may be reduced by blending, or "cutting", the SVO with diesel fuel; however, opinions vary as to the efficacy of this. Some WVO mechanics have found higher rates of wear and failure in fuel pumps and piston rings due to partially-combusted WVO/SVO droplets carbonizing in those components[citation needed]. For normal use, without either blending or a second tank and associated modifications in a petrodiesel engine, vegetable oil has to be transesterified to biodiesel.
Many cars powered by indirect injection engines supplied by inline injection pumps, or mechanical Bosch injection pumps are capable of running on pure svo in all but winter temperatures.* Turbo diesels tend to run better due to the increased pressure in the injectors. Pre-CDI Mercedes-Benz vehicles and cars featuring the PSA XUD engine tend to perform well too, especially as the latter is normally equipped with a coolant heated fuel filter.