from The American Heritage® Dictionary of the English Language, 4th Edition
- n. The ignition of fuel in an internal-combustion engine before the spark passes through the fuel, resulting from a hot spot in the cylinder or from too great a compression ratio for the fuel.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. The premature detonation of a fuel charge in Four-stroke cycle engines.
from the GNU version of the Collaborative International Dictionary of English
- n. Ignition in an internal-combustion engine while the inlet valve is open or before compression is completed.
from The Century Dictionary and Cyclopedia
- n. An ignition of the combustible charge of fuel and air in an internal-combustion engine before the piston, on its compressing stroke, has reached the inner dead-center, or completed the normal compression of the charge. See ignition, 5.
Sorry, no etymologies found.
But, to overcome preignition you can inject water or adjust the fuel or higher octane or a combination thereof but there is also the compression ratio to consider.
However too much advancement is preignition that will increase cylinder pressure to the point of depositing the bottom end in to the pavement.
After taking lead out of the gasoline the compression ratios had to be dropped to 8 and 9 to 1 in order to avoid preignition igniting of the fuel which the lead was in there to prevent.
It is a measure, on a scale 1 to 100, of the resistance of a fuel, usually gasoline, to preignition or knocking in an internal combustion engine.
Under those conditions, the engine is generating a lot more heat and I would expect preignition to be more likely.
However, because of ethanol's resistance to preignition, it should be theoretically possible to design an engine with a much higher compression ratio, which could then extract more useful work from the ethanol.
The reason for premium: higher octane fuel has a higher threshold for preignition
Octane, at the root, is the resistance of a gasoline fuel to preignition, aka "knock".