Lynn E. Hanover

The sound is detonation. Piston engines can do it for long periods of time and survive it. grandpa going uphill in the old pickup truck at 25 MPH in top gear.



That dreadful sound like an engine that won't stop when the ignition is turned off.

It just keeps trying to run with a metallic clinking sound. That is the detonation sound.



Don't count on hearing it in a rotary. It won't last long before damage is done, and you may not hear it at all. Usually in turbo engines. It can be induced by lugging the engine. Going to a high throttle setting while at low speed in a gear that is too tall for the performance being demanded. If you need power, rev the engine to an RPM, and select a gear, where that amount of power is available. Pay attention to your RPM.



I have read that the actual sound is that of the two flame fronts colliding. How this was determined, I have no idea. I suspect that if you took a hand grenade into a phone booth and set it off you might be able to tell us if the explosion was the loud part, or the sound of you head being shattered by the fragments was louder.

We will never know for sure, and, It won't matter. lambda knock sensors react to the shock wave, and report it to the computer so that timing can be retarded to cure the problem.



Preignition, is just ignition before the planned event. So it may make no unusual sound at all. There may be no symptoms at all. Or, the engine may seem to loose some power, and or, suddenly overheat, or begin to detonate audibly.



Lynn E. Hanover

j9fd3s

a couple of us read smoeky yunicks book, and his symptoms for detonation are when the rod bearings spin for no reason.



they know its 2 flame fronts colliding, because they put pressure sensors all over the rotor housing, in kenichi yamamotos book you can actually "see" it

Lynn E. Hanover

We run out our lives betting the farm on unsupported evidence that we think, in good faith, is pointing us this way or that. So it is with reports on conditions that are at the very edge of being impossible to collect data on, such as, what the hell was going on in there just before everything went south.



It is easy to find an expert on this or that until some new data shows up to render their opinions useless.



Cold fussion my ***. Yes world, me and my overeducated friends have been able to fuse hundreds of hydrogen atoms, and contain the resulting energy in this jug of water here. And other overeducated experts gathered in Chicago to see the car battery and water jug lashup that was fusing hydrogen with the flip of the switch.



So, was the world energy supply changed over to the new fusion generators that would fit into the glove box of a VW?



I am as sad as anyone that they didn't do it. They were not even close. They can liberate hydrogen from water with electricity, with some major energy expenditures as in charging a battery, but you sure as hell cannot fuse hydrogen atoms with a car battery.



The first clue should have been that the damn building was still there. Anyone with a calculator could have cut them off at the knees, but nobody said anything, for fear of being wrong. Or more accurately fear of being embarrassed for asking the "stupid" question.



So we look at an outcome, and make a determination with what we believe is good evidence that this is what happened. For example, the Lambda sensor has activated and has retarded my timing a bunch, therefor my engine was detonating. Seems logical enough right? Well, it turns out Mr Hanover was tapping on the block with his little hammer. The lambda sensor doesn't know about detonation, only shock waves above a certain amplitude, so a little hammer tap is as good as a shock wave to Mr Lambda.



The point is never stop thinking, and never stop asking questions. There is more to everything than you and I will ever know.



So is that the sound of two shock waves colliding, or just the sound of one hell of an explosion that we call detonation. Whatever you want is fine. Like adding zeros to zeros, it still works.



Lynn E. Hanover

RE4

ingnorance to the above is why I hate pop culture.The same pop culture that feeds my generation's willing apathy/disintrest in their own lives, political participation, education, and just flat out being a sheep because everyone else is a ******* sheep being blindly lead around.



RE420B

MazdaManiac

Here are some in-chamber pics of detonation taking place:

http://www.efi101.com/forum/viewtopic.php?t=131

Baldy

I just got around to reading the rest of this thread.



Ok, so finally, I understand why it's generally preferred to use lower compression and much higher boost, rather than the other way around. It seems like every time I saw this question, none of the answers were actually answers.



So if you increase the boost to high heavens, you can still cool down the heat from compression before it gets to the combustion chamber. But if you increase the compression by changing the engine internals, the heat of compression will always be higher than the lower compression engine.



Using higher boost and lower compression rotors lets you control the heat. Do I have that right?

BDC

Basically, that's right. The term you're looking for here is called effective compression ratio. Take the standard compression ratio and multiply it by the number of atmospheres you are cramming into the chambers, all else remaining equal (because temperature does and will change this). If you are running 15psi of boost, that's twice the atsmophere, which is basically twice the effective compression ratio. The higher the effective CR, the more load and resulting heat is generated. Make sense?



B

Baldy

Yep!

BLUE TII

That dreadful sound like an engine that won't stop when the ignition is turned off.

It just keeps trying to run with a metallic clinking sound. That is the detonation sound.



Don't count on hearing it in a rotary



I thought the metallic clinking sound in a piston engine was when the shockwave of detonation cannot move the piston down fast enough (or at all if before TDC) to match the expansion rate it rocks the piston about the wrist pin axis slamming the piston skirt into the cylinder wall.



In a rotary if the detonation shock wave cannot move the rotor fast enough it can't easily rock the rotor sides against the sidehousing walls because of the huge bearing area of the e-shaft lobe in this "short" axis, but it can easily rock the rotor front to back taking up the gear lash on this long axis. So our knock sensor mics have to listen for this more subtle sound.



I heard detonation many times when my turbo rotary was on stock turbo and 150,000mile engine, it is much quieter than in a piston engine.



At low HP levels (150-200RWHP) the rotary can withstand moderate bouts of detonation, but with enough air and fuel packed in for 400RWHP the first event usually takes it out, you feel a slight hesitation and then the bouncing boost gauge

Lynn E. Hanover

Nope.



The piston rocking makes little sound at all. Stock engines run about .0015" to .0018" of piston to wall clearance. (For cast pistons with expansion straps, zero clearance when cold). For forged racing pistons more like .004" to .005".

So you could hear a racing piston going over TDC (piston slap) if it were not for the exhaust noise.

The surfaces that will be touching are bathed in oil so even the race engine is not so bad in that regard.



The two flame fronts colliding makes the noise.



Now the piston or rotor not moving out of the way fast enough (not enough RPM for the throttle setting in use) can cause detonation, (It in effect makes the burn rate higher) but does not generate the sound. Long term light detonation also tends to fatigue fail the stationary gear teeth. (Cracks between the teeth) And can have the rotor gear walking out and running tight on the irons.



Lynn E. Hanover