@MH

I am not going to look anything up, but I think in some engines they simply change the length of the exhaust expansion chamber to match the engine RPM.  That's to ensure a synchronicity between the piston pulse rate to empty the exhaust gasses and the tuned expansion chamber helping suck the exhaust gasses out of the cylinder, but it is not resonance.  It might be called a tuned exhaust port or a variable tuned exhaust port or something like that but it is not resonance.

Actually it is resonance MH just like a Helmholtz resonator and it is not designed to suck anything in a two stroke engine but rather push any excess fuel/air back into the cylinder also pressurizing the cylinder. Here is a pretty cool animation of the process, https://en.wikibooks.org/wiki/Engineering_Acoustics/Sonic_Supercharging_of_2_Stroke_Engines

We should also note it is more like a turbo charger than a supercharger as it is the reclaimed energy in the exhaust gas which aids the process.

AC

  When I was in my two stroke days we called it Kadenacy.
  I've got an LC 350 and it's just so much better than the
  air cooled I had previously.
  This whole thing just goes to prove that when you've dug
  yourself in to a hole-stop digging.
         John.

Thanks for the link and it was a very interesting read.   Note that the "straight pipe" helps draw out gases with a reflected negative pressure wave, and the "tune pipe" is essentially a "leaky" version of what appears to be a Helmholtz resonator but in fact it is not.   That is not what a Helmholtz resonator does, although I will agree that it is similar in function.

  So we are back at something that helps the engine run better with a synchronous event to the engine RPM with a fixed time delay, but it is not resonance.  And like I said before, if it is called "resonance" in the world of motor shop talk, that's fine, but on this thread and the Joule Thief 101 thread we are discussing resonance in the true scientific and engineering sense of the word.

MileHigh

I suspected that there was no resonance operating on the exhaust side of the engine, it is more of a fixed time delay event that promotes better engine operation at a certain RPM.

And as usual,you have got it all wrong again.
You obviously took no notice at all at the animation showing the precise timing needed in order for the returning pressure wave to re-inject the gas mix back into the cylinder at the correct position of the piston. When this timing between piston position and reverse gas flow is correct,the system is in resonance,and at this particular frequency(RPM) engine power and efficiency is at a maximum.

This is resonance in the purest sense,where maximum amplitude(maximum explosive force)is reached at the systems natural resonant frequency.
And do not get this mixed up with turbo charging or super charging of a 4 stroke engine,as they are not the same. The only thing they have in common,is that they all increase engine power.

This (in the animation)is the very same way your tuning fork work's,but where as maximum amplitude can be maintained in the two stroke resonant system,meaning it remains in resonance,while the tuning fork just ring's down-amplitude decreases the instant it has been struck-->Quote: In physics, resonance describes when a vibrating system or external force drives another system to oscillate with greater amplitude at a specific preferential frequency. Increase of amplitude as damping decreases and frequency approaches resonant frequency of a driven damped simple harmonic oscillator.

The "tune pipe" returns a reflected positive pressure wave as shown in the animation.

Just as i tried to tell you earlier on in this thread--but you knew better-once again-->hey MH
Like i told you,if you want to discus ICEs with me,then you need to brush up on how they work,as im simply not going to waste my time talking or arguing with some one that has no idea as to what they are talking about.


Brad

And as usual,you have got it all wrong again.
You obviously took no notice at all at the animation showing the precise timing needed in order for the returning pressure wave to re-inject the gas mix back into the cylinder at the correct position of the piston. When this timing between piston position and reverse gas flow is correct,the system is in resonance,and at this particular frequency(RPM) engine power and efficiency is at a maximum.

This is resonance in the purest sense,where maximum amplitude(maximum explosive force)is reached at the systems natural resonant frequency.
And do not get this mixed up with turbo charging or super charging of a 4 stroke engine,as they are not the same. The only thing they have in common,is that they all increase engine power.

This (in the animation)is the very same way your tuning fork work's,but where as maximum amplitude can be maintained in the two stroke resonant system,meaning it remains in resonance,while the tuning fork just ring's down-amplitude decreases the instant it has been struck-->Quote: In physics, resonance describes when a vibrating system or external force drives another system to oscillate with greater amplitude at a specific preferential frequency. Increase of amplitude as damping decreases and frequency approaches resonant frequency of a driven damped simple harmonic oscillator.

Just as i tried to tell you earlier on in this thread--but you knew better-once again-->hey MH
Like i told you,if you want to discus ICEs with me,then you need to brush up on how they work,as im simply not going to waste my time talking or arguing with some one that has no idea as to what they are talking about.

Brad

No Brad, I did not get it wrong, and you saying that "like usual I got it all wrong again" is just you doing your same old shtick.

I obviously took notice of the animation because I made reference to it.  You will also note in the great link provided by AC there is not a single reference to resonance and the word "resonance" or "resonant" is never used.

This is resonance in the purest sense,where maximum amplitude(maximum explosive force)is reached at the systems natural resonant frequency.

No, it is not even remotely close to resonance which by definition involves energy cycling back and forth between two different forms at the resonant frequency - like in a tuning fork or a wine class.  This has been covered for months now, has any of it sunk into your head?

In this case the maximum amplitude (maximum explosive force) is reached when the piston firing time lines up with the optimum timing for the returning pressure wave from the tune pipe.  Effectively it means that the echo off of the back of the tune pipe is at optimum timing.  This is not resonance in any way, shape, or form.  So a good chunk of the 75+ times you have been haranguing me about this "ICE resonance" business was you digging yourself into a hole.

I assume that you have heard of a PLC controller?

http://www.allaboutcircuits.com/textbook/digital/chpt-6/programmable-logic-controllers-plc/

They are used in all sorts of industrial processes and manufacturing processes.  One of the many things they do is orchestrate a sequence of events with the proper timing to operate some kind of production or process line properly.  For example, "When sensor switch A goes ON, turn on relay #5 exactly three seconds later."  That is akin to what is happening with the tune pipe when the engine is at the correct RPM - you get the optimal timing at that RPM.  That hasn't the slightest thing to do with resonance at all.

I will throw a hypothetical example at you.  In the Kellogg's factory they make Corn Flakes.  At the input to the production line there are corn kernels, sugar, salt, whatever else.  At the output to the production like there are raw unboxed Corn Flakes.  There is going to be a PLC controller that controls all sorts of stuff on the line.  For example, say 50 grams of salt are put into the liquid Corn Flakes goop every 20 seconds.  If the line stops, a signal goes to the PLC controller and the PLC controller stops adding the 50 grams of salt.

The PLC controller is critical in the production of the Corn Flakes and controls literally hundreds of events, and for each event there is a programmed timing that is entered into the PLC controller.  If the Corn Flakes tasters on the end of the line tell the production manager that the Corn Flakes are starting to taste too salty, the production line manager figures out where the problem is and corrects it.

Now, when the Kellogg's plant manager stops by and asks the Corn Flakes production manager how the line is running, do you think he says, "Good news Jim, the line is in resonance?"  The answer is NO, he says that the event timings for the PLC controller are all good, the sensors are all good, the actuators are all good, and the line is producing raw Corn Flakes without any problems.

So you are barking up a wrong tree Brad, you are just deceiving yourself about the exhaust cycling for a two-stroke engine, it has nothing to do with resonance.

MileHigh

I would think the tuned pipe is a slight variation of the Helmholtz resonator although they are so similar it's hardly worth debating.

They are actually very dissimilar and I will explain why.

The Helmholtz resonator is based on a "plug" of air mass in the neck that pushes against the "spring" of compressible air in the air cavity of the resonator.  So, this looks like any other LC-type resonator where the resonant frequency and associated cycle time is based on the square root of L x C.  There is no pressure wave at all in the model for the Helmholtz resonator.

For the tune pipe in your Wikibooks link, for starters, there is no resonant frequency at all, there is only a cycle time.  In addition the cycle time is dependent on the length of the tune pipe, just like the cycle time for an echo depends on how far you are away from the wall that the sound waves bounce off of.  From the link, "the goal is to have the diverging section create a returning rarefaction wave and the converging section create a returning pressure wave."  So there is no modelling of this in any kind of "resonant LC device" way.

In a nutshell, you are looking at the difference between a true LC resonator (that can be operating in a one-shot mode) with a cycle time, and a device that is based on a pressure wave bouncing off the back of the tune pipe with it's related speed of the wave and length of the pipe to give you a cycle time.

No matter how you look at it, those are two different beasts.  One is a resonant device, and the other one is simply a time-delay device.

MileHigh

Brad:

You clearly make no attempt to seriously respond to the technical argument that I made that clearly shows that there is no resonance at all in operation on the exhaust side as shown in the link provided by AC.

Instead, you do a chicken dance and try throwing spaghetti against the wall and hoping some of it will stick.  It's just a lousy performance and I will deal with it in another posting.

But the saddest thing of all, is that you simply couldn't admit that the way the exhaust system works to optimize the performance of the engine is a timing-based function and not a resonance-based function.  It is absolutely clear to me that this is the case and I am quite certain that the majority of readers would agree.  Instead of just admitting to it like a man, you shrink away from it and try to hide behind fake lol's and smiley faces.  And I have seen countless examples of this before and I think that is sad.

MileHigh

Brad:

contradicting myself.

This is smiley-faced dancing chicken bullshit.  You are ignoring everything technical I said and falling flat on your face.

Okay, now I am going to deal with your chicken dance.

Ha ha ha, big joke.  Here you are like a hawk plucking quotes of mine from way back in the discussion.  If you are such a hawk then you saw how several times that I expressed doubts that on the exhaust side that there was any form of true resonance in play.  The AC provided a good link and it confirmed my doubts as well as being informative and teaching me.
And all that you can do is dance like a funky chicken and try to do a "set up" to "prove" that I am

And that is what you have done time after time.
The fact is,that it is the exhaust side that dose 90% of the work by way of a resonant system. I tried to tell you this earlier on in this discussion,but you just kept on dribbling away.
I also tried to tell you to go and learn a thing or two,before trying to work out how it all work's,but i can see it was left for others to do for you--no surprise there.

And this says absolutely nothing about pressure waves inside the Helmholtz resonator.  Rather, it discusses how sound waves external to the resonator can be picked up and amplified by the Helmholtz resonator.  It also discusses how a Helmholtz resonator can generate sound waves external to the resonator.  So more useless dancing chicken.    See attached diagram.

Helmholtz Resonance

A Helmholtz resonator or Helmholtz oscillator is a container of gas (usually air) with an open hole (or neck or port). A volume of air in and near the open hole vibrates because of the 'springiness' of the air inside.

Sound-- is a type of energy made by vibrations. When any object vibrates, it causes movement in the air particles.

Plus I am pretty sure based on all of the discussion that you didn't have slightest idea how a Helmholtz resonator worked until I explicitly told you how one worked.

MH,you are clueless as to what i know.
You think that no one here knows anything ,unless you tell them.
The fact that pressure waves do exist inside a Helmholtz resonator,just shows how little you know.

I have not seen anyone try and steer people in the wrong direction more than you do.
I only hope that there is not to many that take notice of your rubbish.


Brad

Brad:

You are just throwing more useless spaghetti against the wall.

Helmholtz Resonance

A Helmholtz resonator or Helmholtz oscillator is a container of gas (usually air) with an open hole (or neck or port). A volume of air in and near the open hole vibrates because of the 'springiness' of the air inside.

Sound-- is a type of energy made by vibrations. When any object vibrates, it causes movement in the air particles.

Yes, the "'springiness' of the air inside" is the SPRING in the Helmholtz container.  Pressure waves do not travel through the spring, rather, the spring is a spring.

Your citing of a definition for "sound" is meaningless.  You make no attempt whatsoever to put your own intellectual content in here.  You are just throwing two strings of spaghetti against the wall and adding zero added value and zero brainpower.  You are just making another false equivalency, and a ridiculous one at that.

MH,you are clueless as to what i know.

Since you demonstrated no knowledge about what resonance actually is, I can make a very strong inference that you had no clue whatsoever how a Helmholtz resonator actually works.

The fact that pressure waves do exist inside a Helmholtz resonator,just shows how little you know.

That's my cue for 10 smiley faces.  The model for a Helmholtz resonator is such that the volume inside the resonant cavity acts like a spring.  That means that the wavelength of sound associated with the resonant frequency is much larger than the dimensions of the cavity.  Therefore, it's impossible for any pressure waves to exist inside the cavity.  At any given time, the pressure in the cavity is only a "small portion of a sine wave" and therefore the pressure is more or less constant throughout the cavity as it cycles up and down.  Another thing that you just learned Brad!

I have not seen anyone try and steer people in the wrong direction more than you do.
I only hope that there is not to many that take notice of your rubbish.

The truth is that you have learned a hell of a lot of stuff from me on these two threads but your big brain fry won't let you say that so all that you can say is the hollow fake-ass "rubbish" line.

MileHigh