Re: Another way to look at the Atkinson cycle
The octane rating of a fuel simply refers to its resistance to ignition. The higher the octane, the harder it is to ignite it. In many ways a higher octane fuel is truly better than a lower octane fuel, but only if engine design takes advantage of it. Many manufacturers of high-performance cars take advantage of this by designing engines with a higher compression ratio. This squeezes the air/fuel mixture more than, say, my Honda, essentially adding heat to this mixture on the way. If you squeeze a mixture too much it can "detonate," which is the early bulk ignition of the mixture. In its ligher form, "pinging," detonation is just a sign that the engine is out of its operating parameters. At its worst, this can completely destroy an engine. But I digress...
The advantage of burning high octane fuel in a high compression engine is increased thermodynamic efficiency. This is the case for both the atkinson cycle and the otto cycle, though it matters less in the atkinson cycle since its efficiency is inherently very high. You can use this efficiency to make more power or you can use it to make an engine that uses less fuel; manufacturer's choice. So the take home message is that lower octane fuels won't really buy you anything.
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