preignition
American Heritage Dictionary:
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pre·ig·ni·tion
(prē'ĭg-nĭsh'ən) 
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.
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.
McGraw-Hill Dictionary of Aviation:
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preignition
The ignition of the fuel-air charge prior to the spark plug firing. Preignition caused by some other ignition source such as an overheated spark plug tip, carbon deposits in the combustion chamber, and, rarely, a burned exhaust valve. All act as a glow plug to ignite the charge. Preignition occurs during the compression stroke, and the engine continues to fire with the ignition system switched off, although probably not all its cylinders. There is no explosion as in a detonation and the rise of temperature and pressure is much greater, probably resulting in catastrophic consequences. Preignition is often experienced when attempting to start a hot engine or during an attempt to shut down a hot engine, and it usually results in a backfire through the intake manifold.
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American Heritage Dictionary
The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.
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