– Why are you supposed to put high octane gas in some (typically luxury brand) cars?
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When you compress a gas vapor, it causes heat. When the piston in an ICE compresses the fuel vapor in the cylinder too much and the temperature gets high enough, the fuel will burn of its own volition (how a diesel works). This happens as the fuel is being compressed on the upstroke (compression stroke) of the engine, so the fuel is combusting before it is supposed to which causes intense strain on all the components.
You can think of octane as an inhibitor. The higher the octane rating, the less prone the fuel is to combusting from pressure/temperature rise. Many expensive cars have high compression ratios and often require octane ratings above 90 to compensate for this. There are other ways to help avoid this, like adjusting the timing, but all of those also inhibit performance.
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