Term question

[godale03]

Hey Guys,

When you say a motor detenates, or stalls, what do you mean by that? I am just trying to follow the lingo, and I read alot of threads with these terms. Just wondering what they mean. I am pretty sure I know what you mean by stall, its the detination I am having a bit of a problem with. I am sure it doesn't mean blowing your mill up. Thanks

Tom

 

[Rolex]

Detonation is the term for firing on each stroke. Basically it means it's doing what it's supposed to do.
The fuel and air enter the chamber, the piston compresses it, the glow plug is hot, and at the top of the stroke, the mixture detonates, provides the power stroke, and the cycle starts over.

 

[godale03]

Thank you Rolex. I know it was a dumb question, I just wanted to make sure. I am picking up on the lingo pretty well for a noob, but there are still a few I am not sure of. Thanks again my friend. I owe you big for all the help you provide. Between you and Plaidfish, I would owe you two alone a small fortune!

 

[retarded pilot]

rolex... i belive what he means is you hear people talking about dentonation like when people want to remove head shims to increase power...and people reply "as long as you dont hear any dentanation you should be fine" ...I've been wondering what that souns like as well ..i belive it has to do with the timing being advanced and the engine firing before it should?

 

[bashaholic]

I'm not trying to contradict you Rolex, well I guess I am because Traxxas describes detonation as "A popping or clattering sound when decelerating" which is a symptom of overheating according to traxxas.

 

[Rolex]

Detonation IS the mixture firing within the cylinder. However, timing affects when that occurs. Nitro content, shims, and what type of plug you use will alter the timing. It can pre-detonate, meaning it will fire before the piston reaches TDC, or it can detonate after TDC.
Exactly when the mixture detonates determines how efficiently the engine produces power or RPMs.

 

[Candyman]

Yeah, detonation is usually used to describe a condition where the air/fuel mix is violently exploding rather than it's typical combusting. It usually happens when the engine is running too hot or with too much compression. Long-term running under detonating conditions can lead to excessive glow plug failure and physical damage to the head and face of the piston.

 

[Candyman]

Taken from the RC Nitro article on glow plug technology:

"Detonation occurs when the fuel mixture explodes quickly rather than burns. You don't want this to happen because it can damage the engine. The telltale signs of detonation are a "miss" in the exhaust tone at high speeds and a pitting of the cylinder head around the glow plug and the top of the piston. Severe detonation can cause the coil element of the glow plug to come loose, and this can severely damage the engine. The primary cause of detonation, however, is excessive compression."

 

[Rolex]

Perhaps the word takes on a different meaning with nitro engines. With 1:1 engines, it's always been described the way I explained it.
When it's been through its' intake stroke, it goes to the compression stroke, the spark plug fires and the mixture detonates, creating the power stroke. When it fires can be controlled by the ignition timing. The timing being off is what causes the jingling noise when going up hill. Low octane gas has the same affect.
Candyman's explanation gives it a somewhat different meaning, and I now know what caused the pitting on top of a friend's piston.
Sorry if I had it wrong, but you now have the correct explanation.

 

[Candyman]

Don't sweat it R. When I read your post, I realized there are 2 different definitions. I guess the RC community just decided to redefine it. In 1:1 terms, isn't that considered predetonation?

 

[Rolex]

In 1:1 terms, it's described as pre-ignition.

 

[CorradoPsi]

Detonation IS the mixture firing within the cylinder. However, timing affects when that occurs. Nitro content, shims, and what type of plug you use will alter the timing. It can pre-detonate, meaning it will fire before the piston reaches TDC, or it can detonate after TDC.
Exactly when the mixture detonates determines how efficiently the engine produces power or RPMs.

actually Rolex, I'm sorry terminology is wrong.

PRE-DETONATION is the mixture igniting before its intended to, all engines ignite before TDC, its nessessary to make good power. as you explained it has to due with how fast the piston is traveling vs. how fast the mixture can burn, to time them so that the mixture is at its most powerful state just as the piston reaches TDC.

BURNING is what happens when the mixture ignites inside the combustion chamber properly.

DETONATION is what happens when the mixture explodes due to: too lean condition, or compression too high, or timing to far advanced (too hot a plug) or any combination of the 3.

i know it sounds wierd but the mixture is actually burning when everything works right, just like in a real engine, its a very fast controlled burn.

detonation will sound like popping when you hear it, most noticable under deceleration, but if its bad enough you can hear it when accelerating too. your engine can also be detonating without you hearing it, signs of this are:
high temps, a frosty finish on the button or top of piston, plugs seem to not last long even with a proper tune, the plug coil is distorted.

 

[CorradoPsi]

ok i read on and see you guys got it covered. i pulled a newb and half read the thread.

 

[Rolex]

ok i read on and see you guys got it covered. i pulled a newb and half read the thread.

You'll have to be punished now. We are considering detonating something next to you.

 

[Candyman]

Shall I warm up the tank?

 

[Rolex]

Yes. I'm running out the spool of wire now.

 

[CorradoPsi]

man you guys are rough :shrug:

 

[godale03]

Ok, first off, I want to thank you guys for all of the good information. I think I have this understood. When folks talk about there Nitro mills detonating, they are talking about the fuel actually exploding, and not burning. The question I have now, is how can you tell on a nitro mill if you are detonating? Thank you.

Tom

 

[rocknbil]

^ ^ ^ ^ ^

.....detonation will sound like popping when you hear it, most noticable under deceleration, but if its bad enough you can hear it when accelerating too. your engine can also be detonating without you hearing it, signs of this are:
high temps, a frosty finish on the button or top of piston, plugs seem to not last long even with a proper tune, the plug coil is distorted.

Plus it tends to run hotter.