Quote:
Originally Posted by jkv45
What are the common urban legends?
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That "higher-octane petrol burns slower". Flame-front propagation speed will vary in an engine based upon compression-ratio, throttle-opening, RPMS, etc. However, on exact same engine under same operating conditions, combustion speed will be exactly same ~16.5m/s for both 87 or 91-octane petrol.
The exact opposite is true. Higher compression, larger throttle openings and higher-RPMs results in faster combustion speeds and more power. Similar to black-powder vs. modern smokeless gunpowder, faster combustion generates more power. Oxygenated fuels like nitro-methane or race-gas carries their own on-board oxygen-supply to increase octane-rating AND increase combustion speed for more power.
Or we can go back to basic physics, P=W/S or work/sec. Let's say you can lift 4-bushels of oranges into lorry in 4-seconds; you've generated P=4/4=1 amount of power to do this. Another bloke comes along and shoves identical 4-bushels in only 2-seconds. He's generated P=4/2=2 or twice amount of power. Things happening FASTER is what makes more power, not slower.
Here's some more info on octane, combustion speeds and power.
https://www.scribd.com/document/270451669/What-s-Octane <-- review references at end
https://www.caranddriver.com/feature...ar-or-premium/
https://oppositelock.kinja.com/the-r...ane-1785829176
https://www.2strokeheads.com/index.p...-of-detonation
https://link.springer.com/article/10...430-013-0094-y < -- really good
back-to-back dyno testing
https://nasaspeed.news/tech/engine/o...es-more-power/
https://www.hotrod.com/articles/fuel...ng-comparison/ <-- read last paragraph
https://www.hotrod.com/articles/0901...pump-race-gas/
In end, only difference between fuels of different octane-ratings is speed of radical-akyl groups formation during combustion. These are highly sensitive and unstable compounds that cause spontaneous ignition in areas other than flame-front, causing detonation & knock (pre-ignition is something completely different altogether). Higher octane fuels resists formation of radical-akyl groups better and their formation-rate is
slower. That's where "slower" comes from since flame-front prop speed is exactly same 16.5m/s with same base petrol.