Is detonation what I have always refered to as "pinging" ? I have thought over the years that "detonation" as everyone calls it, was more of a knocking sound from the piston resisting a premature cylinder firing due to excessive hot carbon buildup from improper fuel quality and fuel to air ratio. From reading many different posts in the archives.....it appears to me now that pinging and detonation are one in the same.

Is this true??? :confused:

 

vetman, i'm not exactly sure, i always thought pinging was something else as a knock is a loud distinctive sound, usually. out of curiosity are you in sebastopol california?

 

This is a complicated subject with many definitions and interpetations. You probably should buy some books. Oft times the three terms are used interchangably. *I* consider knock and ping, to be the same thing. It is usually caused by preignition. The knock or ping occures than the flame front from the preingnition meets the flame front of the intended combustion. *I* consider detonation to be a simiar malady, but caused by excessive heat and pressure. The heat and pressure of unburned gasses becomes so high, that those gasses self ignite as in a diesel engine. This self-ignition is a more powerful event. The collision of the two flame fronts is also more violent and damage causing. Higher octane fuels burn slower, causing a slower heat and pressure rise. They also resist ignition by heat and pressure to a greater degree than lower octane fuels. I AM assuming some basic knowledge of the heat and pressure relationships of a gas (gas as in air, not gasoline). That is just a start. Possibly it is more than you wanted. Good luck, and...

RACE ON!!!

 

Knock or ping is the same thing as detonation, the actual technical term for the phenomenon. In normal combustion the flame front consumes the fuel-air mixture in a predicable manner at finite speed. Detonation is abnormal combustion and occurs when the remaining unburned portion of the mixture reacts suddenly and spontaneously before being consumed by the normal flame front propagation.

This sudden reaction of what is known as the "end gas" creates shock waves that bounce around the combustion chamber. They essentially "ring" the structure of the engine, and this is the sound we hear and describe as knock or ping. 'Pinging" is used to describe light detontion, and "knocking" is perhaps more descriptive of moderate detonation. Another colloquial term is "rattling".

The problem with these detonation shock waves is that they increase the rate of heat transfer to the combustion chamber boundaries by nearly an order of magnitude, and can rapidly overheat piston crowns and exhaust valves.

If you've ever taken apart an engine and the piston crowns looked like someone attacked them with an ice pick, you are seeing the results of sustained moderate detonation. Localized heating actually causes the material to melt leaving little craters. Heavy detonation can hole a piston or take off a chunk of an exhaust valve in a matter of seconds on and engine that is running hard at WOT. If a racing engine gets into heavy detonation the results are often catastrophic because the sound may not register to the driver over the unmuffled exhaust.

Preignition and detonation are not the same thing, but one can lead to the other in a positive feedback loop. Detonation - say from insufficient octane or too much spark advance can cause hot spots that generate preigntion that leads to more severe detonation, and this is the usual death spiral scenario. Preigntion - say from too hot a spark plug - is the same as advancing the timing, which can lead to detonation.

Duke




[Modified by SWCDuke, 9:47 PM 8/25/2003]

 

Outstanding responses!!! Thank you for the info.


OatBoy: Yep...Sebastopol CA. Probably not far from you. The bad news is.....I sold the vette and went to the dark side!!!!! Ford :eek: :eek: :eek: Still have lots of chevy racing engines pushing all my other cars though. :steering:

 

Well, it depends what KIND of Ford. If you're talking about one of the new GT40's, the "GT", you're forgiven! I might even understand if you got a supercharged 32-valve Cobra, which kind of reminds me of the old muscle cars.
:D

Good response on the detonation issue. I think part of the reason for knocking, pinging, and rattling could be because of the absolutely horrible alcohol/gas blends that are common today. They cause havoc on carbureted engines at anything over 60 degrees F because the boiling point is lowered so much. The octane increases from adding alcohol do not have the same effect as the same octane level in a 100% pure gasoline. At least that's my personal belief.