Like I said, colloquially incorrect, but detonation is ignition under pressure by definition. Damn Finnish mother making me say these things that are correct English but not colloquially correct.

 

From a thermo standpoint, detonation by definition is an combusion event with a supersonic front (i.e shock wave), deflagration (subsonic front propagation) is what is typicaly desired in internal combustion engines. Its the pressure spike from the undesired supersonic front that kills rings/ hammers rod bearings, etc. Saying detonation is bad as it pertains to our motors is correct and is not a normal combustion event.

Richard, do some logs to check AFRs. Don't lower the octane!

 

Sorry, but that's incorrect. Detonation has nothing to do with whether it's sub- or super-sonic. It's the violent expansion of something after ignition. Here's my Finnish nature interfering with an otherwise sound argument that yes, he should absolutely check his AFRs to confirm what could be wrong (if anything).

 

Regardless of the side show above,
You have no way of knowing if your car is running rich without a durametric or an exhaust gas analyzer.
I have never heard of a post 90's car running rich for any extended amount of time without a getting a fault code ( i guess a 'cel' in the 996).
You certainly dont want to lower the octane at all. That just does not make any sense.

 

Yes sideshow aside listen to sound car advice.

 

OK Guys,Can I add my 2 cents here for what its worth......Normal combustion is a process where the air/fuel mixture burns in a smooth,steady motion with the flame front expanding from the spark plug until the entire mixture is burned........IF unburned air/fuel mixture is excessively elevated in pressure or temperature,,it will explode in several spots with out waiting for the flame front to ignite it...>>..This Results in DENTONATION/PINGING,,,which is a violent collision of flame fronts after the sparkplug fired....OK,,,,Just had to tell you what I know and think....Hope this helps the show........

 

guess I wasted my money on an MS in combustion and heat transfer...

http://en.wikipedia.org/wiki/Detonation

http://en.wikipedia.org/wiki/Deflagration

...sorry for the derail

 

Grammatical tangents aside, I hope that Richard-Mark has refilled his tank with some high octane fuel.

Jon

 

Its got to be one of the biggest misunderstandings about spark ignition engines, the number of times people post that after the spark plug ignites the mixture, it explodes and the explosion pushes the piston down the bore.

It does not explode at all, it burns rapidly at a speed that is many, many times slower than a true explosion such as a stick of dynamite.This is normal desired combustion.

At no time during normal combustion does the fuel air mixture ignite under compression and detonation is definitely not a natural part of a cars function

Also looking at your exhaust tips tells you nothing about what your fuel mixture maybe under boost or any other condition.

And

 

Hi,Sorry to disagree or should I say disagree on the defintions of certain words..lol..,,,But I guess explodes is in MANY basic definitions on ignition 101 principles,,,,I think we all know the basic concept only the defintions are different depending on how we were taught or read.....