what would happen to the motor?? how can u tell if it has detonated??

 

i duno about the results for sure, but its bad for your engine. haha, durrr.....and you can hear the pingin sound from your engine. i think i will sorta sound like a diesel engine but not as loud.

 

Detonation can have MAJOR effects on your engine. I can be harmless if it is slight (IE you can't hear it but the knock sensor can). Most common failure from detonation are melted pistons (actual holes in the pistons), cracked pistons, broken ring lands, melted rings, blown head gasket, and a couple others.

One sure fire way to check and see if your engine has detonated is to pull the sparkplugs and look at them. If they are speckeled (looks like salt and pepper), you have detonated. That speckeling is actually the piston's material being burnt off and deposited on the plugs.

Most common definition of detonation is an "uncontrolled flame front", meaning the engine ignited the flame without the use of the spark plug. This usually happens at insanely advanced levels of the compression stroke. The piston has started on it's way up and the mixture ignites, trying to force the piston down as it is going up. The knocking and pinging sound is the piston rocking in the bore and the actual explosion. It's not a good thing, especially on blown, turbo'd or nitros'd engines...it will destroy a motor FAST.

 

When your engine goes.. tink tink tink..

 

Sounds to me like you are describing pre-ignition instead of Detonation. Pre-ignition is more of the "uncontrolled flame front" where detonation is more of a "spontaneous combustion".

 

pre ignition and detonation are one in the same.

Both are uncontrolled ignition of air fuel mixed BEFORE spark is applied.

 

well then what do you call it when your ignition timing is too far advanced and ignites the charge at TDC (or any point before the optimal angle of force)??

dave w

 

Even normal timing calls for spark BTDC -- usually 12-14 degrees BTDC for normal cruising. If you ignite the mixture at or after TDC, you will lose most of the energy because of the time it takes to propagate the flame.

 

well, yes...but that in no way even address the question.
If detonation and pre-ignition are the same thing then what do you call it when your ignition timing is so far advanced that you are trying to push the piston/rod straight down at TDC and causing the same pinging sound. Mr. Bone said both were cause from uncontrolled ignition BEFORE sperk is applied...i'm wondering then what its called when its caused from the spark being applied too early.

ohhh and by the way, the 1# type of damage from all det is bearing damage on the bottom end. they take most of the force....

-davew

 

Pre-ignition and detonation are definitely not the same thing. In fact, detonation is often called "Post Ignition". While yes, they are both uncontrolled combustion, they are quite different. Saying they are the same, is like saying Anthrax and Small Pox are the same, because they both infect your bloodstream.

Pre ignition is when something in the combustion chamber retains enough heat to ignite the fuel before the spark does (say, a glowing hot "bur" somewhere in the chamber, or a red hot carbon deposit particle, or some other glow spot). Pre ignition leads to much higher combustion chamber temperatures, which would melt the spark plug tip. But often times it won't damage the engine like detonation can, because the combustion process still expands from one spot, as opposed to detonation, where the entire air/fuel mixture combusts at the same time, causing much higher chamber pressures. With Pre-ignition, you have a flame front.

Detonation, is when the air/fuel mixtures flame front does not move smoothly from the spark tip to the opposite side of the chamber. It "spontaneously combusts" caused by high engine temps, and high compression. With Detonation, there is no flame front, because it all combusts at once.

They are two different things. But detonation can often lead to pre-ignition (in the next compression stroke), because often, a really hard ping will reshape the combustion chamber enough to give a new "hot spot". I could explain it more, if you would like..




[Modified by martini, 4:13 PM 12/6/2001]

 

okk...admittedly it was a trick question. I was trying to get at the fact that both don't occure Before spark is applied. as the previos post explains Pre ignition ocurrs when something ignites the charge before spark ignition and det usually occures long after TDC. If you advance the ignition timing too far (resulting in peak cylinder pressure at a less than optimal pin angle) it simply causes a significant increase in combustion chamber tems wich speeds up the reaction time and can lead to either det or pre-ignition or both, depending on the circumstances. , octane and quality of gas, etc....

I like to blame the free radicals. they are always causing problems wherever they go

later,
dave w

 

martini,

the subject of this thread is blasphamy as far as your rotary is concerned, figured you'd give a good detailed explanation ... one ping and you're ding in the FD.


Greg

 

Yes, it certainly is to my advantage to have a fair bit of knowledge on the subject.