Making a muffler

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n2xlr8n
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Re: Making a muffler

Post by n2xlr8n » Thu Jun 29, 2017 8:49 am

ptuomov wrote: Even for supersonic blast waves? Those are quite far from the acoustic waves which are assumed to move at the speed of sound and be small. These are big and fast. It's my reading that the acoustic theory is not very predictive when waves get bigger aka finite waves, and it's pretty far off for shock waves in general and supersonic blast waves in particular.

My thinking is that the first section of the exhaust needs to deal with the supersonic blast waves one way or another. Methods that I'm thinking about is a single large pipe that combines all eight pulses per revolution. I don't have room for acoustic packing there, so I just have to try to use geometry there. I need to reduce the amplitude of the shock wave enough, as the amplitude determines the wave speed. If I can get it down to sonic velocity, then the shock wave will die and turn into a normal finite wave. I think.

Then the middle section can be tuned and predicted more with the 1D finite wave sort of methods. Finally, if the middle section has enough volume and dampening, then the rear muffler can is probably adequately modeled with the acoustic tools you reference.

This is all wild speculation on my part, so don't take any of the above as facts, just food for thought.
Right- the turbine, header and collector.

The muffler/ and remaining pipe are designed to shape/filter the resultant waves, which imo (empirical) are not supersonic.
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Re: Making a muffler

Post by ptuomov » Thu Jun 29, 2017 9:01 am

n2xlr8n wrote:
ptuomov wrote: Even for supersonic blast waves? Those are quite far from the acoustic waves which are assumed to move at the speed of sound and be small. These are big and fast. It's my reading that the acoustic theory is not very predictive when waves get bigger aka finite waves, and it's pretty far off for shock waves in general and supersonic blast waves in particular.

My thinking is that the first section of the exhaust needs to deal with the supersonic blast waves one way or another. Methods that I'm thinking about is a single large pipe that combines all eight pulses per revolution. I don't have room for acoustic packing there, so I just have to try to use geometry there. I need to reduce the amplitude of the shock wave enough, as the amplitude determines the wave speed. If I can get it down to sonic velocity, then the shock wave will die and turn into a normal finite wave. I think.

Then the middle section can be tuned and predicted more with the 1D finite wave sort of methods. Finally, if the middle section has enough volume and dampening, then the rear muffler can is probably adequately modeled with the acoustic tools you reference.

This is all wild speculation on my part, so don't take any of the above as facts, just food for thought.
Right- the turbine, header and collector.

The muffler/ and remaining pipe are designed to shape/filter the resultant waves, which imo (empirical) are not supersonic.
When do the supersonic blast waves lose enough amplitude to turn into finite waves moving at sonic speed? How do we know at which point of the exhaust that happens? How much does that depend on the turbine speed and/or the turbine pressure ratio? How about the wastegate circuit when that's open? It would be nice if I could somehow convince myself that under 3000rpm and part throttle, the supersonic blast waves have died by the time they come out of the turbine, but how would I know that?
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Re: Making a muffler

Post by Kevin Johnson » Thu Jun 29, 2017 9:34 am

Tuomo, if you have a chance you should look at the referenced JSAE papers in the link you provided recently. They are not pay-walled and the diagrams are in English. I think a translate program could be used on the Kanji manuscript to extract even more information.

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Re: Making a muffler

Post by ptuomov » Thu Jun 29, 2017 9:56 am

Kevin Johnson wrote:Tuomo, if you have a chance you should look at the referenced JSAE papers in the link you provided recently. They are not pay-walled and the diagrams are in English. I think a translate program could be used on the Kanji manuscript to extract even more information.
I've tried to look at the papers, although I remember exactly zero of the 150 Kanji that I learned in college...

The paper that I linked to is the latest and greatest in this series of research. It reverses some of the earlier conclusions, because it considers packed mufflers. This strand of literature advocates placing a "pre-muffler" shortly after the collector or integrating same features in the catalytic converter (which is placed close to the collector for temperature reasons). In this setup, the pre-muffler is designed to kill the supersonic blast (shock) waves. The earlier papers came to the conclusion that a multi-chamber muffler is the best pre-muffler to kill the blast waves. However, this latest paper finds that a simple large chamber with acoustical packing is even better. Other things that those earlier papers seem to find is that conical baffles (an internal cone pointing upstream with its nose cut off) are effective in mitigating shock waves. However, for a performance exhaust, I'm not sure that those would give an acceptable trade off between the pre-muffler volume and and back pressure on their own.

What I haven't seen studied anywhere is a muffler that has a perforated pipe in the middle and conical baffles inside the can that is filled with acoustic packing, such that the perforated pipe is perfectly straight thru and passes thru the cut-off nose sections of the conical baffles which themselves are filled with acoustic packing material. I'm talking about like the gun silencers but with a perforated pipe thru is to hold acoustic packing in the cavities:
GunSilencer.jpg
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Re: Making a muffler

Post by ptuomov » Thu Jun 29, 2017 7:39 pm

MadBill wrote:
ptuomov wrote:...I don't know. All the research that I've been able to find says or hints that the early part of the exhaust wave is a supersonic blast wave and that blast waves generate broadband noise...
Here's an only vaguely related thought: If, as widely stated, the cylinder pressure of an NA engine at WOT/EVO is typically in the range of 50-100 psi, then if you pressurized the cylinder with a leakdown tester to 100+ psi and momentarily popped open the exhaust valve by striking the tip with a dead-blow hammer, a sonic pulse should result. I can say it is loud... :-k
While I'm struggling to understand what exactly happens inside a car exhaust, my thinking is that that sort of supersonic (and at 100 psi it will be supersonic) blast waves are exactly what I'd need to take care hopefully relatively high upstream in the exhaust system.
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Re: Making a muffler

Post by pdq67 » Fri Jun 30, 2017 3:36 am

What is you opinion of putting a big open can on the front end of a long Walker/Dynomax/Thrust smooth perforated inner pipe old-fashioned glass pack?

Of course, bell-mouth the glass pack and if still too loud increase the length of the glass pack.

pdq67

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Re: Making a muffler

Post by n2xlr8n » Fri Jun 30, 2017 9:43 am

ptuomov wrote:I'm talking about like the gun silencers but with a perforated pipe thru is to hold acoustic packing in the cavities:

GunSilencer.jpg
Tuned cavities, aka waveguides (without E and H fields).

One can see the different cavity sizes based on the frequency spectrum of the projectile and charge.

I'd love to know which specific calibers they were designed for.

If the reference manual didn't help you, I'll buy it from you- I have two already (one w notes), but they are great Christmas presents :lol:
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Re: Making a muffler

Post by ptuomov » Fri Jun 30, 2017 11:25 am

n2xlr8n wrote:
ptuomov wrote:I'm talking about like the gun silencers but with a perforated pipe thru is to hold acoustic packing in the cavities: GunSilencer.jpg
Tuned cavities, aka waveguides (without E and H fields).

One can see the different cavity sizes based on the frequency spectrum of the projectile and charge.

I'd love to know which specific calibers they were designed for.

If the reference manual didn't help you, I'll buy it from you- I have two already (one w notes), but they are great Christmas presents :lol:
It takes a long time to read! I've started, but not finished.

It's still the case that I think that these shock wave attenuators (including those in the gun silencers) are going to be a little different animals from tuned resonators of acoustic waves. This is why I think the gun silencer has conical baffles:

http://www.m-hikari.com/astp/astp2012/a ... 8-2012.pdf
The most effective configuration among three obstacles to attenuate incident shock strength is a conical baffle. In the case of a conical baffle, the high-pressure region in front of the inlet of the baffle is not created, since a part of shock front propagates further outside of the baffle. It means that the pressure increase behind reflected shock waves cannot be realized.

The role of jet formation appeared around the inlet region of the obstacles is important. In both the case of an orifice and a diverging nozzle, the jet is clearly generated, when the high-pressure gas behind reflected shock waves flows out from the inlet region to the downstream.

In the case of an orifice and a diverging nozzle, the high-pressure region behind reflected shock waves is realized between the reflected shock front and the baffle plate of obstacles. The supersonic jet is created when the high-pressure gas flows downstream. In the case of the orifice, the strength of transmitted shock waves is not so diminished, since a supersonic jet compresses the flow behind transmitted shock waves. Although the expansion rate of shock front is very large by the sudden expansion of cross-sectional area, the transmitted shock front is accelerated by supersonic jet.
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Re: Making a muffler

Post by ptuomov » Sat Jul 15, 2017 6:09 pm

New bigger quarter wave resonator pipes, also known as wastegate dump pipes:
IMG_0204.JPG
IMG_0205.JPG
IMG_0206.JPG
IMG_0207.JPG
IMG_0208.JPG
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Re: Making a muffler

Post by ptuomov » Sat Sep 30, 2017 3:59 pm

There's been a snafu and a delay. The welding stand collapsed and took with it a lot of expensive parts. The hardest one to replace was the prototype cast exhaust manifold. Also a lot of other stuff. Nobody was injured, so after licking the mental wounds it was time to get back to the saddle.

Here's the cracked exhaust manifold:
cracked.jpg
Here's what came from the 3D mold printing and foundry (with a big bill):
NewCasting.jpg
The empirical shrinkage factor is better calibrated for this second generation prototype, so the machining steps have to take off less metal:
NewCastingMachined.jpg
So now the project team is back to square one refabricating the downpipes. After downpipes, the cats and test pipes. Then rest of the exhaust. Then, and only then, the custom muffler that is the topic of this thread.
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Re: Making a muffler

Post by ptuomov » Sat Sep 30, 2017 4:04 pm

John Kuhn is back working on this exhaust.

Here are the newly (re)fabricated but still uncoated downpipes installed on the car for test fitting. There's so little room that one needs a fixture locating everything all the time during the fabrication:
NewDownPipes.jpg
And here are the cats. They don't flow as much as a straight 3.5", shocker there, but they shouldn't be too awful either. And with high octane gas runs, they'll be replaced with "test" pipes:
TaggedCats.jpg
And here's the difficult divorce from the center-section "inifity pipe" into the two legs:
CenterDivorce.jpg
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Re: Making a muffler

Post by ptuomov » Sat Sep 30, 2017 5:14 pm

The infinity pipe will basically be the biggest structurally-sound non-drumming pipe you'll be able fit in that location:
IMG_0623.JPG
IMG_0622.JPG
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Re: Making a muffler

Post by ptuomov » Sat Sep 30, 2017 5:55 pm

And here's the planned transition from the cats to the infinity pipe:
CatsWithClamps.jpg
print.jpg
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Re: Making a muffler

Post by pdq67 » Sat Sep 30, 2017 6:32 pm

pdq67 wrote:
Fri Jun 30, 2017 3:36 am
What is you opinion of putting a big open can on the front end of a long Walker/Dynomax/Thrust smooth perforated inner pipe old-fashioned glass pack?

Of course, bell-mouth the glass pack and if still too loud increase the length of the glass pack.

pdq67
Nobody answered my question?? Whatcha guys think?

pdq67

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Re: Making a muffler

Post by ptuomov » Sat Sep 30, 2017 8:10 pm

pdq67 wrote:
Sat Sep 30, 2017 6:32 pm
pdq67 wrote:
Fri Jun 30, 2017 3:36 am
What is you opinion of putting a big open can on the front end of a long Walker/Dynomax/Thrust smooth perforated inner pipe old-fashioned glass pack?

Of course, bell-mouth the glass pack and if still too loud increase the length of the glass pack. pdq67
Nobody answered my question?? Whatcha guys think? pdq67

Thanks for bringing that up. I'm not sure what would happen if you'd do that.
[b]Paradigms often shift without the clutch[/b] -- [url]https://www.youtube.com/watch?v=cxn-LxwsrnU[/url]

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