– Why are you supposed to put high octane gas in some (typically luxury brand) cars?
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When petroleum is pushed through an engine, the petroleum is compressed into a tight chamber before being ignited – this is important for effective combustion, though the reason doesn’t matter here. The problem is that compressing petroleum into a small space causes it to heat up.
If the fuel gets too hot, it might spontaneously ignite and burn while still in the compression chamber. We don’t want that – not only will the fuel and energy be wasted if it ignites while still in the chamber, but it will likely damage the engine too (This is called ‘knocking’).
Higher octane fuels are fuels which have been formulated to withstand higher pressure before they self-ignite. Basically, you can compress higher octane fuels far more.
Most average modern cars are built with the idea that most people will use cheaper, lower octane fuels. Therefore, they design their compression chambers around the idea that lower-octane fuels will go through them. There’s no real reason for them to use highly compressed chambers, because they cost more money to produce and most average drivers won’t benefit from it.
Sports cars, however, use tighter compression chambers that compress fuel more than average. This means they can benefit from higher octane fuels that can benefit from those tighter compression chambers – they can create more power with less fuel that way.
You may be thinking there’s a missing puzzle piece here – surely that should mean that putting lower octane fuels into a sports car would cause knocking? Well, yes and no – most modern cars’ internal computers are smart enough to detect when knocking is about to happen, and adjust the engine to minimise the chance. This does cause a little lost performance, but it’s better than the performance lost from engine knocking. With high octane fuels, however, they don’t have to.
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