Open main menu
Home
Random
Recent changes
Special pages
Community portal
Preferences
About Wikipedia
Disclaimers
Incubator escapee wiki
Search
User menu
Talk
Dark mode
Contributions
Create account
Log in
Editing
Pre-ignition
(section)
Warning:
You are not logged in. Your IP address will be publicly visible if you make any edits. If you
log in
or
create an account
, your edits will be attributed to your username, along with other benefits.
Anti-spam check. Do
not
fill this in!
'''Pre-ignition''' (or '''preignition''') in a [[spark-ignition engine]] is a technically different phenomenon from [[engine knocking]], and describes the event wherein the [[air–fuel ratio|air/fuel mixture]] in the [[cylinder]] ignites before the [[spark plug]] fires. Pre-ignition is initiated by an ignition source other than the spark, such as hot spots in the [[combustion chamber]], a spark plug that runs too hot for the application, or carbonaceous deposits in the combustion chamber heated to [[incandescence]] by previous engine combustion events. The phenomenon is also referred to as 'after-run', or 'run-on' or sometimes [[dieseling]], when it causes the engine to carry on running after the ignition is shut off. This effect is more readily achieved on carbureted gasoline engines, because the fuel supply to the [[carburetor]] is typically regulated by a passive mechanical [[float valve]] and fuel delivery can feasibly continue until fuel line pressure has been relieved, provided the fuel can be somehow drawn past the [[throttle]] plate. The occurrence is rare in modern engines with throttle-body or [[electronic fuel injection]], because the injectors will not be permitted to continue delivering fuel after the engine is shut off, and any occurrence may indicate the presence of a leaking (failed) injector.<ref name=b1/> In the case of highly supercharged or high compression multi-cylinder engines, pre-ignition can quickly melt or burn pistons since the power generated by other still functioning pistons will force the overheated ones along no matter how early the mix pre-ignites. Many engines have suffered such failure where improper fuel delivery is present. Often one injector may clog while the others carry on normally allowing mild detonation in one cylinder that leads to serious detonation, then pre-ignition.<ref>{{cite book|url=https://books.google.com/books?id=b2kQLVszg88C&pg=PA165|page=165|title=Automotive fuels & emissions|author=Barry Hollembeak|publisher=Cengage Learning|year=2004|isbn=1-4018-3904-5}}</ref> The challenges associated with pre-ignition have increased in recent years with the development of highly boosted and "downspeeded" spark ignition engines. The reduced engine speeds allow more time for autoignition chemistry to complete thus promoting the possibility of pre-ignition and so called "mega-knock". Under these circumstances, there is still significant debate as to the sources of the pre-ignition event.<ref name=solutions>{{cite web |title=solutions for pre-ignition ("mega-knock"), misfire, extinction, flame propagation and conventional "knock |publisher=cmcl innovations, UK |url=http://www.cmclinnovations.com/print/cmcl_user_story_07_knock.pdf |accessdate=12 June 2010 |url-status=dead |archiveurl=https://web.archive.org/web/20110708170503/http://www.cmclinnovations.com/print/cmcl_user_story_07_knock.pdf |archivedate=8 July 2011 |df=dmy }}</ref> Pre-ignition and engine knock both sharply increase combustion chamber temperatures. Consequently, either effect increases the likelihood of the other effect occurring, and both can produce similar effects from the operator's perspective, such as rough engine operation or loss of performance due to operational intervention by a powertrain-management computer. For reasons like these, a person not familiarized with the distinction might describe one by the name of the other. Given proper combustion chamber design, pre-ignition can generally be eliminated by proper spark plug selection, proper fuel/air mixture adjustment, and periodic cleaning of the combustion chambers.<ref name=b2>{{Cite book|url=https://books.google.com/books?id=U4TBoJB2zgsC&pg=PA630|page=630|title=Automotive technology: a systems approach|author=Jack Erjavec|publisher=Cengage Learning|year=2005|isbn=1-4018-4831-1}}</ref>
Edit summary
(Briefly describe your changes)
By publishing changes, you agree to the
Terms of Use
, and you irrevocably agree to release your contribution under the
CC BY-SA 4.0 License
and the
GFDL
. You agree that a hyperlink or URL is sufficient attribution under the Creative Commons license.
Cancel
Editing help
(opens in new window)