There are at least 3 methods to run a diesel motor on biofuel utilizing veggie oils, animal fats or both. All 3 are used with both fresh and used oils.
1. Use the oil just as it is-- usually called SVO fuel (straight grease);
2. Mix it with kerosene (paraffin) or petroleum diesel fuel, or with biodiesel, or mix it with a solvent, or with fuel;
The first 2 approaches sound most convenient, however, as so frequently in life, it's not rather that simple.
1. Mixing it
Vegetable oil is far more viscous (thicker) than either petro-diesel or biodiesel. The function of mixing it or blending it with other fuels is to reduce the viscosity to make it thinner so that it flows more easily through the fuel system into the combustion chamber.
If you're blending veg-oil with petroleum diesel or kerosene (same as # 1 diesel) you're still using fossilfuel-- cleaner than most, but still not tidy enough, many would say. Still, for each gallon of
grease you use, that's one gallon of fossil-fuel saved, and that much less climate-changing carbon in the atmosphere.
People use different blends, varying from 10% veggie oil and 90% petro-diesel to 90% grease and 10% petro-diesel. Some people simply utilize it that method, begin up and go, without pre-heating it (which makes veg-oil much thinner), and even utilize pure grease without pre-heating it, which would make it much thinner.
You might get away with it with an older Mercedes 5-cylinder IDI diesel, which is a really tough and tolerant motor-- it won't like it but you most likely won't kill it. Otherwise, it's not sensible.
To do it properly you'll require what totals up to an SVO system with fuel pre-heating anyhow, ideally utilizing pure petro-diesel or biodiesel for starts and stops. (See next.) In which case there's no requirement for the mixes.
Blends with numerous solvents and/or with unleaded fuel are "experimental at finest", little or absolutely nothing is understood about their effects on the combustion qualities of the fuel or their long-term results on the engine.
Higher viscosity is not the only issue with utilizing vegetable oil as fuel. Veg-oil has various chemical homes and combustion qualities from the petroleum diesel fuel for which diesel engines and their fuel systems are developed.
Diesel engines are state-of-the-art makers with really precise fuel requirements, especially the more modern, cleaner-burning diesels (see The TDI-SVO debate).
They are difficult however they'll just take a lot abuse. There's no assurance of it, however utilizing a blend of approximately 20% veg-oil of great quality is stated to be safe enough for older diesels, especially in summertime.
Otherwise utilizing veg-oil fuel requires either an expert SVO solution or biodiesel. Mixes and blends are generally a poor compromise. But blends do have a benefit in cold weather.
Just like biodiesel, some kerosene or winterised petro-diesel fuel blended with straight veggie oil reduces the temperature at which it starts to gel. (See Using biodiesel in winter) More about fuel mixing and blends.
