MH's ideal coil and voltage question

[ramset]

Loner
Funny I was thinking about you today [the race track]
good to read you here and your valuable contributions.

I know few here have your experience with an ICE and Racing .
  I have to just drop this in from another racer/engine designer  "Johan 1955" for you to see , a very dependable 2 stroke
8HP per cubic inch N.A. and climbing ...as they continue to dial it in.

https://www.youtube.com/watch?v=1zDmlOYiaTI

Yes its a screamer [perhaps the NA[normally aspirated] goes out the window ??] ,But they also play with resonance and a huge standing wave in some very tricky ways.

BTW your comments here are in no way off topic !
regardless whichever side of the fence your on.



respectfully
Chet K

[tinman]

I fundamentally agree with you that it is a transmission line.  In the animation and the description they describe it as a "one-shot at the optimal engine RPM."  If you noticed they also discuss a modified shape to extend the RPM range with less than optimal performance and so on.  I am not going to try to become an "enthusiast" or "expert."  What I am seeing is a transmission line used as a delay line to synchronize pushing fuel back into the cylinder at the optimum RPM.

I tried searching on many variations on "delay line" and "exhaust," "engine" etc., but could not find a good link, probably because I am not using the right terminology for engines.  You can find all sorts of electronic acoustic delay lines, and of course you always find the ancient computer memory mercury delay line.  That's a trip in itself, to think that in the 50's mainframe computers used long tubes of mercury for memory!

Anyway, I am out of gas on this stuff and if Brad wants to believe what he believes so be it.  Or if he can find a link that makes his case, I will be happy to read it.  But I am seeing an acoustic delay line in the exhaust system to optimize the combustion process, and not resonance.

MileHigh

MH'
The resonance state is between the piston and pressure wave that returns the gas charge back into the cylinder. The timing is critical,and only happens at a set frequency(RPM) range--we are talking about the two stroke engine here. At a set RMP (frequency) range(the resonant range),the entire gas charge held in the expansion chamber,is returned to the cylinder ,through the exhaust port. If the RPM(frequency) is to low,then that gas charge will enter the cylinder,and begin to exit the cylinder again,before the piston closes off the exhaust port. When this happens,you will have very little compression,and thus,very little power--anyone that has ridden a high performance motocross bike will know this to be true--very little torque at low RPM. If the frequency(RPM) is too high,then the piston closes off the exhaust port before the complete charge can enter the cylinder,and so the engine will run lean,and once again,result in a power drop--along with a damaged motor soon enough.

At the resonant frequency(correct RPM), when all of the charge that was held in the expansion chamber will enter the cylinder,the result is a higher cylinder pressure--this is what can be seen as the supercharging effect,and the end result is a much higher explosion force within the cylinder--more power. The resonance is the precise timing between the pistons position,and the pressure wave created within the expansion chamber,where all of that wave front of gas charge has completely entered the cylinder at the precise time the piston closes off the exhaust port,so as that pressurized gas charge cannot escape the cylinder. This results in a maximum amplitude of pressure in the cylinder,and a maximum amplitude in power.

Perhaps this link can explain it a little better.

http://www.roost.si/articles/exhaust/exhausts_work.htm


Brad

[tinman]

Rats...

Tinman, I am sorry to have to respond to that, but I'm afraid I must "sorta" agree with MH on that specific point.

I want to ensure you understand what I mean, so I am posting this, even though I stated I would not comment.  This is really a matter of semantics.  Removing electrical resonance for a moment, though the data would apply in another way, the simplest way to describe physical/mechanical resonance would be an oscillation between potential and kinetic energy.  This IS what is happening inside the exhaust, and is what is providing the described pressure wavefront, however the alignment of the piston at the correct point on the exhaust's pressure wave would (In my opinion...) have to be considered "Timing" and not part of the actual exhaust resonance.  Yes, I am picking nits here, but that was the major point I was trying to make previously.

To put it another way.  Pick an RPM.  To make the best power at that RPM, you want to have the exhaust resonate at a specific frequency.  To get this effect, you ONLY have to modify the exhaust, as the action of the piston will not change.  (I'm not explaining this well, so please forgive me.  I'm trying...)  While the amount of power will change, due to increase charge density, the actual frequency (RPM) of the piston does not change.  The piston is acting as the signal injector, at a "Fixed" frequency and when the resonance of the exhaust matches, then...

This is where I always had so much trouble, as increasing the power in other ways could change the charge density enough to alter the exhaust freq. while the engine is still spinning the same RPM.  All of a sudden my tuning to increase power caused a decrease.  I do realize that 2 stroke is MUCH more sensitive to these effects than 4 stroke where the situation is different.  Therefore, while I would agree 100% that the exhaust has a physical resonance going on inside (Both acoustic and pressure...), the true physical resonance is ONLY going on in the exhaust.  The fact that this wavefront is matched to the correct position of the piston is not really part of the exhaust resonance, even though it IS dependent on it.  I'm quite certain you are aware of Q and bandwidth, although you might view it as the width of the power band instead.  Same thing to me.  So, while these are very synchronized, and very timing dependent, in the true sense of the concept the exhaust and engine are not in resonance with each other, they are just correctly timed for the desired effect.  The exhaust IS in resonance by itself and so is the engine.  (I doubt we need to discuss crankcase volume, etc., as that is another whole story.)

All it really comes down to is how nit-picky we all want to be.  There are those in the engine area that will lean more towards your view and discuss intake reed valve tensions as being part of the engine resonance and on and on and on, but I have always maintained that while they are timed and synchronized, the actual resonance applies separately to intake, engine and exhaust.  In real life I can accept that, while at the track, while you won't be doing engine mods, you will be re-jetting and swapping resonance chambers depending on conditions.  This makes it easier to look at the whole thing as a single resonant system, but I look at it as more complex than that and try to keep them separate in my mind.  End result?  While bolting on a different chamber between heats, it's a single resonant system.  While sitting on the couch or at the computer, it is three separate systems.  As to which is correct?  Ask the person sitting on the couch and he IS correct.  Ask the person who just won the race, HE is correct.  For me, both are correct for what they are trying to do.  There will always be differences in perception between the academics and application people in complex systems.

I am definitely too old for this stuff.

You are basically saying what i am.
The expansion chamber is the resonant source,but for that resonant source to have the desired effect,then the pistons position must also align to that resonant frequency of the expansion chamber. If the RPM of the engine is not correct,then the resonant chamber dose not have the desired efffect-->engine frequency must be the same as the resonant frequency of the expansion chamber.
This makes a resonant system as a whole,and for maximum pressure amplitude to be reached inside the cylinder,then this system as a whole must exist.

Hope that helps


Brad

[MileHigh]

Brad:

As Loner says, and as your link says. the tuning of the expansion chamber shape, and especially length, is an exercise in optimizing the exhaust timing to the engine at a certain RPM.

The correct technical term would be to synchronize the events for optimum performance at a given RPM.

This thread started a discussion about resonance in terms of the true scientific and engineering sense of the word.  And that is the basis for this thread, period.  So a huge chunk of this "ICE resonance" nonsense and berating over and over is because you failed to distinguish between true resonance and motor shop talk "resonance."

Why do they call it "resonance" for expansion chambers instead of "synchronization?"

The answer is simple, it's because "resonance" sounds way cooler and sexier than "synchronization."  That's all there is to it.

A whole mountain of endless discussion for something as nonsensical as this.  It has happened before with you.

From your link:

These waves have the caratteristics of reflecting as a negative wave (suction) if they meet an open end of a tube. On the other way if they encounter an closed end of a tube they reflect as a positive wave (stuffing).

Those are classic characteristics of an acoustic or electrical transmission line.

The rpm at which the pipe will be in resonance depend on the length of it and the temperature of the gasses.

There is your smoking gun.  Adjust the length of the transmission line to get the proper required delay to synchronize events with the cylinder at a given RPM.

For probably the sixth or seventh time, this is NOT resonance.

It annoys me to think of how much crap we went through when the whole time you damn well knew that I was talking about true resonance, not "resonance" for two-stroke engine enthusiasts.

MileHigh

[MileHigh]

You are basically saying what i am.
The expansion chamber is the resonant source,but for that resonant source to have the desired effect,then the pistons position must also align to that resonant frequency of the expansion chamber. If the RPM of the engine is not correct,then the resonant chamber dose not have the desired efffect-->engine frequency must be the same as the resonant frequency of the expansion chamber.
This makes a resonant system as a whole,and for maximum pressure amplitude to be reached inside the cylinder,then this system as a whole must exist.

Hope that helps

Brad

You are talking crap again to avoid the frying pan.