Author Topic: Detonation  (Read 4388 times)

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Offline 2005yz250

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Detonation
« on: July 15, 2012, 06:55:49 AM »
What is detonation and how do you identify it as compared to two stroke rattle?  I'm simply curious and have never been 100% sure about it.

Offline Jeram

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Re: Detonation
« Reply #1 on: July 15, 2012, 09:09:37 AM »
I think the word explains it...

detonation!

it is a powerful shock-wave that goes through the combustion chamber when conditions are not idea (preignition, to lean, too hot etc)
This shock-wave can begin in several different ways

-hot spots on the piston dome and head can cause the fresh charge to pre-ignite it multiple locations simultaneously, causing a sudden impulse, can be caused by being too lean, too hot, or simply poorly designed (sharp angles/edges)

-as per the above but caused by a high concentration of hot exhaust gases re-entering the combustion chamber, acting like a million tiny embers. this effect was harnessed by Honda on the CRM250AR to perform controlled detonation to achieve a cleaner 2T combustion.

-the flame front travels too far if the  motors squishband is wrong causing it to build up mommentum as it moves accross the full bore length? confirm the definition of this one

- I believe also that extreme pressures can cause the mixture to self ignite also, technically I believe this is referred to as detonation also (high compression diesel trucks?)


-two stroke piston rattle is a mechanical rattling sound whereas detonation is a pinging sound (why its called pinging)

the pinging sound is the detonation/explosion occurring over a very short time span. Honda worked out in the 90s how to measure this shockwave pinging. They installed detonation sensors, a ring that went under the spark plug that transmitted some form of electrical pulse every time it detected a violent explosion.
by measuring the level of pinging they could determine the perfect bike tune up (a certain number of detonations per second indicates a perfect tunup for making HP but not enough detonations to cause damage.)



Offline scotty dog

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Re: Detonation
« Reply #2 on: July 15, 2012, 08:05:26 PM »
I was told it sounds like coins being rattled around in a tin can, you will only hear it when ya riding, under acceleration, my 05 CR 250 liked to do it until I dropped the clip down the needle
F**K THE WHALES......................SAVE THE 2 STROKE!!!!

The hardest part about riding a 4 stroke is telling your parents your ****!!

05 CR 250

Online beaner

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Re: Detonation
« Reply #3 on: July 15, 2012, 11:04:47 PM »
Somebody once described the sound to me like they had marbles in their engine. Not a bad description. You typically only hear it under load.
Ontario, Canada

Offline 2005yz250

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Re: Detonation
« Reply #4 on: July 15, 2012, 11:15:19 PM »
Thank you all so much for the detailed info.  So there really are no signs of detonation at idle? (I'm assuming unless it is way too lean etc.)

Offline scotty dog

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Re: Detonation
« Reply #5 on: July 16, 2012, 06:13:46 AM »
no you wouldnt get it at idle, two strokes do make funny little noises when idling, if you listen too hard it will get worse  :D :D
F**K THE WHALES......................SAVE THE 2 STROKE!!!!

The hardest part about riding a 4 stroke is telling your parents your ****!!

05 CR 250

Offline msmola2002

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Re: Detonation
« Reply #6 on: July 16, 2012, 06:24:58 AM »


this is a deto map from a logger on a Honda RS250 GP bike, fitted with a detonation counter. Toward the top end of the rev range and with a lot of throttle %.

Offline Jeram

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Re: Detonation
« Reply #7 on: July 16, 2012, 09:53:46 AM »
I beleive the reason  you dont get it at part throttle (including idle) is because the RPMs are low enough such that the piston and head can cool between cylces, and the load is much lower.

nice map there Michael ;)


Offline msmola2002

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Re: Detonation
« Reply #8 on: July 16, 2012, 10:10:24 AM »
Thanks, I like, totally made it myself

Offline 2T Institute

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Re: Detonation
« Reply #9 on: July 16, 2012, 11:40:20 AM »
Showing the reed engine deto-ing around WOT and within 1500rpm of the torque peak. A disc valve with deto at 50-70% throttle in the mid range.