Attempts have been made to use raw oils in engines since at least 1900 when the Otto company demonstrated the use of peanut oil in a diesel engine at the Paris Exhibition.

Blends of 10-40% ethanol in diesel fuel have been tested extensively. Recent developments have shown some promise of solving the chronic problems with these fuels. One of the primary problems is that ethanol has a low cetane number. Modern diesel engines need a cetane number of 40 or higher to give their intended performance and emissions. This problem can be solved with cetane enhancing additives.

The lubricity of the fuel is another concern. The diesel fuel injection system relies on the fuel for the lubrication of its closely fitting parts. Ethanol has poor lubricity so it degrades the lubricity of the diesel fuel.

However, this problem can also be solved with a lubricity additive.
Finally, the flashpoint of ethanol-diesel fuel blends is a problem and it cannot be corrected with an additive. The flashpoint of a fuel is the temperature where the vapors above the liquid fuel can be ignited. Ordinarily, diesel fuel has a flashpoint that is around 125^oF to 150^oF. This means that there is little chance of accidentally igniting diesel fuel and it is sometimes called an “intrinsically safe” fuel. However, with ethanol present, the flashpoint will be below ambient temperatures and the fuel needs to be treated with the same precautions as gasoline.

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