Monday, November 24, 2008

Three ways of creating biodiesel

1. Mixing it

Vegetable oil is much more viscous (thicker) than either petro-diesel or biodiesel. The purpose of mixing straight vegetable oil (SVO) or blending it with other fuels and solvents is to lower the viscosity to make it thinner so that it flows more freely through the fuel system into the combustion chamber.

If you're mixing SVO with petro-diesel or kerosene you're still using fossil-fuel -- cleaner than most, but still not clean enough, many would say. Still, for every gallon of SVO you use, that's one gallon of fossil-fuel saved, and that much less climate-changing carbon dioxide in the atmosphere.

People use various mixes, ranging from 10% SVO and 90% petro-diesel to 90% SVO and 10% petro-diesel. Some people just use it that way, start up and go, without pre-heating it (which makes veg-oil much thinner). Some even use pure vegetable oil without pre-heating it.

You might get away with it in summer time with something like an older '80s Mercedes 5-cylinder IDI diesel, which is a very tough and tolerant motor -- it won't like it but you probably won't wreck it. Otherwise, it's not wise.

To do it properly you'll need what amounts to a proper SVO system with fuel pre-heating. (See next.) In which case there's no need for mixes.

Blends of SVO with various solvents, magical "secret" ingredients (turpentine, mothballs, paint-stripper) or with unleaded gasoline are "experimental at best" -- little or nothing is known about their effects on the combustion characteristics of the fuel or their long-term effects on the engine. Not recommended -- use such blends at your own risk.

Higher viscosity is not the only problem with using vegetable oil as fuel. Veg-oil has different chemical properties and combustion characteristics from the petro-diesel fuel that diesel engines and their fuel systems are designed to use. Diesel engines, especially the more modern, cleaner-burning diesels, are high-tech machines with precise fuel requirements (see The TDI-SVO controversy). They're tough but they'll only take so much abuse.

There's no guarantee of it, but using a blend of up to 20% veg-oil of good quality with 80% petro-diesel is said to be safe enough for older diesels, especially in summer. Otherwise using veg-oil as fuel requires a professional SVO solution -- or convert it biodiesel.

Mixes and blends are generally a poor compromise. But mixes can have one advantage in cold weather. As with biodiesel, some kerosene or winterised petro-diesel mixed with straight vegetable oil lowers the temperature at which the SVO starts to gel. (See Using biodiesel in winter)

More about fuel mixing and blends.

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