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Yes, but this octane-fire mixing is a bunch of confusion to begin with.

Gasoline is less ready to ignite than diesel~=jet fuel, but has fumes.

Diesel~=jet fuel has little fumes, but is easier to ignite by heat, i.e. in an engine, but it will almost never be ignited outside of an engine. Meanwhile, gasoline is hard to ignite with heat and pressure in an engine, but easier to ignite in air than diesel.

Octane also has a higher boiling point than for example heptane, so higher octane fuel is probably not related to easy of ignition due to the fumes either.




The situation's more complicated than that.

Gasoline is easier to ignite than diesel fuel.

Both fuels burn as vapours rather than as liquids. The vapour pressure of gasoline at any given temperature is higher than diesel, that is, gasoline evaporates far more readily, making liquid gasoline far more hazardous to store, as the vapours can ignite and explode.

Diesel fuel resists autoignition under compression to a greater degree than gasoline, and so can be used in high-compression engines without spark ignition.

The flash point is the temperature at which vapours of a fuel can ignite given a spark. These are given for various fuels here: <https://www.engineeringtoolbox.com/flash-point-fuels-d_937.h...>

For gasoline: -42.5 C / -45 F

Diesel: 37.8 -- 54.4 C / 100 -- 130 F (depending on grade)

Kerosene / Jet Fuel: 37.8 -- 72.2 C / 100 - 162 F

Yes, the autoignition temperature of diesel is modestly lower than that of gasoline, but in practice the principle concern is vapours igniting from a spark rather than net ambient temperature reaching the autoignition point.

(I'd expected gasoline to have a lower autoignition temperature than diesel, this was a surprise for me, though multiple sources seem to indicate a lower ignition temperature for diesel. I learned something researching your comment.)

The autoignition point of various fuels is given here: <https://www.engineeringtoolbox.com/fuels-ignition-temperatur...>

For gasoline: 246 - 280C / 475 - 536F

Diesel: or Jet A: 210 / 410

Kerosene: 210C / 410F


Ah, I was actually trying to express precisely what you're saying here, and don't immediately see the difference between the views we're laying out.




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