Whats the octane rating of diesel?

How about after mixing gas/oil in a 2 stroke?
While we’re at it can a gasoline/ oil mix be used in a diesel?

The end of my questioning will be can I use used cooking oil fuel in my 2 stroke lawn mower?

Diesel is measured in cetane, not octane. I believe pump diesel in the US is 40 cetane.

I don’t think mixing gas + oil for a 2-stroke changes the octane of the gas.

Hijack: Can lawn mowers (in general) run OK on E85 (85% ethanol)?


Petroleum is “cracked” (refined) into a variety of fractions with names you are probably familiar with. Each fraction has a different number of carbon atoms in it’s hydro-carbon chain:

1 C atom, methane
3 C atoms, propane
4 C atoms, butane
5 C atoms, pentane
6 C atoms, hexane
7 C atoms, heptane
8 C atoms, octane

Conventional automotive fuel (gasoline or petrol) is a mixture of octane and heptane, with the percentage (or effective percentage*) of octane given as the rating. This is because octane is less likely to sponteneously ignite when compressed, and so is more desirable in high compression engines.

Diesel fuel requires less refining than that used to produce gasoline. A more qualified person can come along and correct this, but IIRC, diesel fuel has 14 C atom hydrocarbon chains.

With regard to using diesel fuel in a gasoline engine, unless the engine has been designe for it, it won’t work. For one thing, diesel engines operate at far higher compressions, and don’t use spark plugs. A quick Google will undoubtably turn up a lot more information about how the various engines work.

To add the missing bit from my post above:

  • I say “effective percentage” because there are ways of using additives to make a given fuel behave as though it had a different percentage of octane. Lead (actually tetraethyl lead) was found circa WWII to make fuel behave as though it had a higher percentage of octane. This is how fuels can actually have an octane rating higher than 100 (“Super Test” is a name sometimes applied to such mixtures, I believe).


Last time I saw a diesel pump, it was marked with a 42 octane sticker.

The cetane rating for diesel is a measure of how quickly it spontainiously ignites at high temperature and pressure. A too low cetane rating may not work at all, or may be noisier.

This is nearly the opposite of an octane rating, which is a measure of how well a fuel resists detonation. But not an exact opposite or inverse. It is measuring a different property.

In both cases, this is a factor in how well they work in an engine designed for that particular fuel. But you can’t convert from one to the other. If Dave is 6’3" and Bill weighs 173#, then how much does Dave weigh? Human height and weight do, in general, have some corilation, but not really enough to be useful in any particular case.

In general, the octane rating for diesel fuel would be very low. The noise typically associated with a diesel IS a detonation of the fuel that was injected prior to combustion occuring. The burn rate for the remaining fuel is determined by the injection rate.