There are at least 3 methods to run a diesel engine on biofuel using veggie oils, animal fats or both. All 3 are used with both fresh and used oils.
1. Use the oil just as it is-- normally 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 very first two techniques sound most convenient, however, as so frequently in life, it's not rather that easy.
1. Mixing it
Grease is much more thick (thicker) than either petro-diesel or biodiesel. The function of blending it or mixing it with other fuels is to decrease the viscosity to make it thinner so that it streams more freely 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 utilizing fossilfuel-- cleaner than a lot of, but still unclean enough, lots of would state. Still, for every single gallon of
grease you use, that's one gallon of fossil-fuel conserved, which much less climate-changing carbon in the atmosphere.
People utilize various mixes, ranging from 10% grease and 90% petro-diesel to 90% vegetable oil and 10% petro-diesel. Some people just utilize it that method, start up and go, without pre-heating it (which makes veg-oil much thinner), or perhaps use pure vegetable oil 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 difficult and tolerant motor-- it won't like it but you probably will not kill it. Otherwise, it's not sensible.
To do it correctly you'll need what amounts to an SVO system with fuel pre-heating anyway, ideally using 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 gasoline are "experimental at best", little or absolutely nothing is learnt about their effects on the combustion characteristics of the fuel or their long-term impacts on the engine.
Higher viscosity is not the only problem with using grease as fuel. Veg-oil has various chemical properties and combustion attributes from the petroleum diesel fuel for which diesel engines and their fuel systems are developed.
Diesel motor are state-of-the-art machines with really precise fuel requirements, particularly the more modern, cleaner-burning diesels (see The TDI-SVO controversy).
They're tough but they'll just take a lot abuse. There's no guarantee of it, however using a mix of up to 20% veg-oil of great quality is stated to be safe enough for older diesels, particularly in summer.
Otherwise using veg-oil fuel needs either an expert SVO option or biodiesel. Mixes and blends are generally a poor compromise. But mixes do have an advantage in cold weather.
Just like biodiesel, some kerosene or winterised petro-diesel fuel combined with straight veggie oil decreases the temperature level at which it starts to gel. (See Using biodiesel in winter season) More about fuel blending and blends.
