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As far as I know, the reason isooctane is better than octane in gasoline engines is because the octane is more prone to ignition by pressure. This makes it ignite when it is not supposed to, which damages the engine.

Isooctane, however, is somehow less prone to this. Why is that? Why is isooctane "more resistant to the potential of ignition incited by pressure"? How are the higher number of ligands involved in this?

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    $\begingroup$ Who says they are, by what quantitative measure? $\endgroup$ – Karl Dec 12 '20 at 20:30
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    $\begingroup$ Yes, branched isomers have a lower Bp., and that is of course one factor. The rest is debateable. Who taught you that, what was their reasoning? Do you know how the Diesel engine works? $\endgroup$ – Karl Dec 12 '20 at 20:45
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    $\begingroup$ Something tells me this is an extrapolation of the octane rating of a fuel, where 2,2,4-trimethylpentane (isooctane) is seen as a good fuel, whereas n-heptane is not. Whether this extrapolation is correct, and whether it has an explanation, I do not know. $\endgroup$ – Nicolau Saker Neto Dec 12 '20 at 22:14
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    $\begingroup$ Yes, diesel oil (very much linear alkanes) autoignites on compression. You don't want that in a regular gasoline engine, that's why gasoline has a high content of branched hydrocarbons. $\endgroup$ – Karl Dec 12 '20 at 22:14
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    $\begingroup$ @NicolauSakerNeto "Good" for a gasonline engine means no autoignition even at high compression. For a Diesel, you want autoignition without explosion. There is the cetane number for that. $\endgroup$ – Karl Dec 12 '20 at 22:21