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Basics for Vegetable Oil Vehicle Conversions (Diesel Engines ONLY)
VO = Vegetable Oil
SVO = Straight Vegetable Oil
WVO = Waste Vegetable Oil
"The diesel engine can be fed with vegetable oils and would help considerably in the development of agriculture of the countries which use it."
"The use of vegetable oils for engine fuels may seem insignificant today. But such oils may become in course of time as important as petroleum and the coal tar products of the present time."
Rudolf Diesel, 1911
Now that we know that the original diesel engine was designed to run on vegetable oil, modern diesel engines, however, have been designed to run on petroleum diesel fuel. This creates several issues, which must be overcome in order for a modern Diesel engine to efficiently run on vegetable oil without causing damage to the engine.
Using Vegetable Oil as a Motor Vehicle Fuel?
Vegetable oil is nearly 12 times as viscous (thick) as petroleum diesel fuel and trying to spray it through an injection system designed to deliver and properly atomize a fluid so much less viscous, such as petroleum diesel fuel, is similar to trying to spray liquid butter through a Windex bottle. An improper spray pattern will result in incomplete combustion and incomplete combustion will result in carbon deposits being formed in the engine. The carbon deposits will build and cause engine damage. There are several ways to reduce the viscosity of vegetable oil, the simplest being thermal degradation (heating). When vegetable oil is heated to 160°F, its viscosity is very close to that of petroleum diesel fuel.
Another issue that needs to be dealt with is the polymerization of vegetable oil when it contacts metal below an optimum temperature. The simplest way to explain this is with a simple analogy: If a pan is filled with water and then placed on a burner at HIGH to heat the water, the pan begins to heat up first and then the water begins to boil, and eventually the water is transformed to vapor. Alternatively, if the pan is placed on the stove and heated on HIGH first and then droplets of water are placed on the pan, the droplets will dance around the pan on a layer of vapor, none of it sticking to the pan.
This same principle applies inside the combustion chamber of an engine, so injecting vegetable oil into an engine at a low temperature could result in carbon deposits being formed on the piston crown and cylinder walls, eventually causing engine damage.
Now have two major problems to overcome:
- The vegetable oil must be heated to at least 160°F before being injected so that it can be atomized properly by the injectors, like petroleum diesel fuel.
- The engine must be at operating temperature before vegetable oil is injected.
Since an engine that is cooled with radiator coolant (typically 50% Distilled water, 50% Ethylene Glycol) has an abundance of coolant that has been heated to 180°F by the time the engine is up to operating temperature is available - a ready heat source is available. The requirements set by problem #2 above (engine at operating temp) is met, and by using the heated coolant to fuel a heat exchanger with the coolant, vegetable oil can be easily supplied above 160°F, meeting the requirements of problem #1 above (heating the vegetable oil to at least 160°F).
Next is a need to have a vehicle with two independent fuel systems, one for diesel (or biodiesel) and one for the vegetable oil. The vehicle will start on diesel fuel and run on that fuel until operating temperature, at this point vegetable oil fuel can be supplied above 160°F and the fuel supply can be switched. Of course when the vehicle is turned off, the fuel system will still be filled with vegetable oil, which will cool and become useless as a starting fuel, prohibiting restarting the vehicle as the conditions to solve problems #1 & #2 above are no longer being met. To solve this issue the vegetable oil in the fuel system will need to be purged and diesel fuel introduced before the engine is turned off.
Vehicle Conversion to Bi-Fuel VO by Alternative Fuel Concepts
Alternative Fuel Concepts installs VO bi-fuel conversion systems that utilize advanced component technology.
The following components are typically installed by Alternative Fuel Concepts to have the most reliable and functioning VO bi-fuel system:
- Separate VO fuel tank. The tank is required to separately contain the vegetable oil and have an area around the fuel pickup tube being heated to insure that the VO is thin enough to be drawn into the VO fuel supply line without restriction.
- VO fuel (supply & return) lines. The lines supply VO fuel to the engine and return unused VO fuel to the tank during purging and should be heated to thin the VO fuel enough to move through the lines without restriction.
- A heated VO fuel filter. Heated VO can be filtered easily; in addition the filter or filtering element should be easily replaced and readily available.
- VO fuel heat exchanger. The heat exchanger uses the engine coolant to heat VO fuel to the required temperature.
- Switching valve. This valve allows switching between the two fuel systems. It independently controls the fuel flow so that cross contamination of fuel is eliminated and aids in the purging of VO fuel from the system before turning the engine off.
- Controller. Controls the activation of the switching valve until the engine is at operating temperature and the VO fuel is at the proper temperature, to provide status indicators (diesel of VO mode), provides an alarm if the vehicle is turned off while running on VO fuel, and to activate the purging function when the VO fuel system is turned off.
Both SVO & WVO vehicle conversions require the same components. WVO requires proper filtration and dewatering before using as a fuel source. Any water remaining in the WVO will cause engine damage. Many WVO filtration and dewatering systems, kits, and plans are available if it is going to be used.
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