Author Topic: Muffler for model i.c. engine  (Read 1331 times)

Offline Brian Rupnow

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Muffler for model i.c. engine
« on: August 23, 2018, 06:30:54 PM »
Just for the heck of it---has anyone ever built a muffler for a model i.c. engine? I have designed one this morning, based mainly on guess-work and size constraints. This muffler is designed to fit onto my flathead single cylinder engine which I designed and built a few years ago. This engine currently has a "straight pipe" on it, although the straight pipe has some fancy carving on the outside of it. Since I don't have a decibel meter, I will have to post a video showing the engine running in its current configuration, and a second video with the muffler installed on it.

Offline Brian Rupnow

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Re: Muffler for model i.c. engine
« Reply #1 on: August 23, 2018, 06:37:03 PM »
This picture shows the flathead engine in its current configuration.--The exhaust is really just a straight pipe, in spite of the fancy carving on the outside of it.

Offline b.lindsey

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Re: Muffler for model i.c. engine
« Reply #2 on: August 23, 2018, 06:37:39 PM »
Brian, I made one out of stainless to scale for the Briggs & Stratton engine. As I recall you have a digital copy of the plans so you can check that one out. It was made according to the B&S muffler just at half scale. Being stainless it should last forever. If you cant find it let me know and I will post that page of the plans here.

Bill

Offline Roger B

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Re: Muffler for model i.c. engine
« Reply #3 on: August 23, 2018, 06:43:55 PM »
I made one for my horizontal engine. Like you I don't know really how effective it is but here's the plan and some pictures.
Best regards

Roger

Offline b.lindsey

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Re: Muffler for model i.c. engine
« Reply #4 on: August 23, 2018, 07:05:29 PM »
Brian, if you have a smartphone, you should be able to fine a decibel meter app for it. Probably now quite as accurate as a dedicated meter, but close enough for this purpose. Just a thought.

Bill

Offline Brian Rupnow

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Re: Muffler for model i.c. engine
« Reply #5 on: August 23, 2018, 07:52:03 PM »
 I don't have a cell phone nor a smart phone. The smartest thing here is me.--and that's pretty scary!!!  This video shows my small flathead engine running, so you can hear the current noise level. Really, it isn't that loud even with a straight pipe on it.
https://www.youtube.com/watch?v=UjnlNpOcKGs

Offline Brian Rupnow

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Re: Muffler for model i.c. engine
« Reply #6 on: August 23, 2018, 10:20:30 PM »
One thing I have to be careful of.-I mix a bit of 2 cycle oil with my gasoline, for the sake of my Viton o-ring on the piston. None of my small engines run hot enough to burn this oil, so there is a steady fog of oil mist coming out the exhaust. I have to arrange things so there is not an oil trap built into the muffler.

Offline maury

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Re: Muffler for model i.c. engine
« Reply #7 on: August 23, 2018, 10:58:56 PM »
Brian, nice looking engine, and nice running too.

Currently, I'm building a Tank Mogul, one of Bob Bromps's old engine kits. At any rate, I wave always wanted an engine with a pot muffler. So I went and designed one, and made a pattern. Note, this is only the pattern, I need to make the castings yet.
Thought the board might be interested,
maury
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Offline Dave Otto

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Re: Muffler for model i.c. engine
« Reply #8 on: August 23, 2018, 11:45:46 PM »
That is going to be a good looking pot muffler Maury! Is that a freelance design or did did you find a picture somewhere?

Brian Asked if anyone had ever built a muffler? I think most anyone who has built a scale model of a real engine has probably built a muffler for it.
Here is one of mine; http://www.modelenginemaker.com/index.php/topic,1326.490.html starting at post #497.

Dave
« Last Edit: August 23, 2018, 11:54:59 PM by Dave Otto »

Offline Brian Rupnow

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Re: Muffler for model i.c. engine
« Reply #9 on: August 24, 2018, 01:08:45 AM »
Dave Otto--What a beautiful build and what a great muffler.--Thank you for the link.---Brian

Offline Dave Otto

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Re: Muffler for model i.c. engine
« Reply #10 on: August 24, 2018, 01:17:51 AM »
Thanks for the nice comments Brian.

Dave 

Offline zeeprogrammer

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Re: Muffler for model i.c. engine
« Reply #11 on: August 24, 2018, 02:37:30 AM »
I guess the sad thing is...my first understanding of a muffler was a piece of woman's clothing.
It was later that I understood the term also meant some hard, cold, object meant to suppress noise.
Something that you didn't want to remove in order to avoid the law.
I still prefer my initial thinking...something soft and warm that you wanted/tried to remove, regardless that it might involve the parents (the real/only law at the time).
Carl (aka Zee) Will sometimes respond to 'hey' but never 'hey you'.
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Offline Roger B

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Re: Muffler for model i.c. engine
« Reply #12 on: August 24, 2018, 09:25:24 AM »
One thing I have to be careful of.-I mix a bit of 2 cycle oil with my gasoline, for the sake of my Viton o-ring on the piston. None of my small engines run hot enough to burn this oil, so there is a steady fog of oil mist coming out the exhaust. I have to arrange things so there is not an oil trap built into the muffler.

I have drilled a small hole in the bottom of mine to avoid this problem.
Best regards

Roger

Online Allen Smithee

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Re: Muffler for model i.c. engine
« Reply #13 on: August 24, 2018, 12:06:24 PM »
It rather depends whether you want it to just collect exhaust gases or actually do any "muffling"...

I did quite a lot of work on silencers (as we call 'em over here) back in my aeromodelling days because we needed effective silencers to stop losing flying sites. From my work on this I established some basic principles.

The initial chamber of the silencer needs to be quite large (say >5 times the swept volume of the cylinder) and made of something rigid. The large space allows the exhaust gas to expand into the chamber which cools it, and that reduces the pressure (and thus the magnitude of the pressure pulses). The chamber needs to be rigid so that the pressure pulses don't just get transmitted through the walls, so a good solid thick-wall casting or machined lump.

After the initial expansion chamber you need to feed the gases into a second chamber that is at least five times the volume of the first one for further expmasion and cooling. This second chamber needs to have some sound-attenuating blanket around it to (again) stop the noise being directly transmitted through the walls. But whatever you use for this blanket mustn't thermally insulate the chamber because that negates its whole function (cooling the gases to reduce their pressure). Irvine came up with a superb and really effective solution to this problem with their "Q-type" silencers and "mouse" after-silencers where they used the cooled exhaust gas itself as the sound-attenuating blanket. If you don't have one to hand to cut up then let me know and I'll post a sketch of the concept.

Finally you need an exhaust pipe that is large enough to allow the pressure to drop, but small enough to present a reflection to pulsed pressure (this gets technical if you want to calculate it, but just experimenting with oriface sizes can find the answers quite quickly).

I found that the automotive approach of having a final chamber filled with some sort of sound adsrober (steel wool, glass wool etc) doesn't scale down - it just created backpressure in model sizes, causing the expansion chambers to stay hot and destroying their function.  Using these approaches it was possible to get a 6.5cc 2-stroke to chuck out over 1.2bhp at 11,000rpm with a peak noise output of 77dBA @7m from the back. At this point there was as much noise from the FRONT as there was from the back, because the prop noise and intake noise were becoming the longer poles in the tent.

In the design in the sketch above I would expect that the holes pointing directly at the side-wall will just make the sound pass straight through the sides. There doesn't seem to be enough volume in the expansion chambers and the outercasing would need to be quite thick-walled to keep the sound inside. Attenuation isn't about restricting gas flow - it's aboput expanding and cooling the gases to take the energy out. If you want it to be REALLY quiet the fil a turbocharger(!) or a pressure-wave supercharger (aka "tuned pipe") because that extracts the same energyu to do useful work.

As a final thought - if it's a 2-stroke and you want "quiet power" you can put a "folded wave" phelan-type tuned pipe inside the 2nd chamber of the silencer (the one that Irvine wrapped in the exhaust gas blanket). Irvine did this with the "40SP" engine they made for Sport 40 pylon racing in the early 90s. This knocked about 7dB off the output of a motor which was chucking out 1.95BHP at 17,000rpm...

€0.0003 suppliued,

AS
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Offline Brian Rupnow

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Re: Muffler for model i.c. engine
« Reply #14 on: August 24, 2018, 03:18:09 PM »
Went to bed last night and thought--and thought--With a bit of redesign I can make the two purple colored pipes identical. This also introduces another set of baffles ahead of the outlet, and gets holes down close to the bottom where any trapped oil can flow into the exhaust tube to be expelled.

Offline Brian Rupnow

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Re: Muffler for model i.c. engine
« Reply #15 on: August 24, 2018, 10:17:01 PM »
So--Here we are with the center parts all soldered together and the outer shell slid into place. The center consists of the two 5/16" o.d. tubes that extend out from each end plus the center plate with a bunch of holes drilled in it. I'm not going to show you the insides, because it is soooooooooo ugly. How ugly is it?--It's ugly enough that if it were a part that showed I would make it over again. However, that nice clean outer shell hides a lot of sin. Tomorrow I have the two endplates to make plus the flange which bolts to the engine.

Offline Brian Rupnow

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Re: Muffler for model i.c. engine
« Reply #16 on: August 25, 2018, 06:31:09 PM »
The new muffler is finished and installed on the engine. If you look on top of my ignition box you will see the old straight pipe setting in the lower left hand side of the picture. The new muffler turned out looking great. There was some really nasty blobby silver soldering inside, and of course the flat divider plate between the two tubes twisted and bent all to hell from the heat. Some quality time with a small body hammer and various pincer type tools got it sorted out to the point where it was good for functional but too nasty to show people. Next step will be to make a video to compare how loud the engine is now compared to what it sounded like with the straight pipe on it.

Offline Brian Rupnow

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Re: Muffler for model i.c. engine
« Reply #17 on: August 25, 2018, 06:56:11 PM »
And here we have a video of the engine running with a muffler on it. I think it is quieter than the video I posted earlier in this thread when it was running a simple straight pipe exhaust. Let me know what you think.---Brian
]https://www.youtube.com/watch?v=iggh3paQdMgl]
« Last Edit: August 25, 2018, 07:00:19 PM by Brian Rupnow »

Offline cfellows

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Re: Muffler for model i.c. engine
« Reply #18 on: August 25, 2018, 09:28:45 PM »
Sounds like a Briggs!

Chuck
So many projects, so little time...

Offline Brian Rupnow

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Re: Muffler for model i.c. engine
« Reply #19 on: August 25, 2018, 10:56:21 PM »
 Lets face it--we are generally happy just to see our engines run, and be able to rev up or idle down on demand. There IS a lot of mechanical noise from these small engines. I have removed the muffler and am doing some remedial work on the flange which attaches it to the engine. Although I did use a jig when I soldered the flange on, it was a crummy jig and the flange turned out quite crooked in respect to the muffler body. I was able to fully tighten the two top shcs, but not the bottom ones. I will show the new jig I am making to correct this issue, and then will repeat the sound test.---Brian 

Offline Brian Rupnow

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Re: Muffler for model i.c. engine
« Reply #20 on: August 26, 2018, 12:07:16 AM »
I have removed the flange from the muffler, made a new flange, and made a welding fixture to align the new flange properly with the muffler body. The four dark blue shcs are "sacrificial"--That is to say, they will end up silver soldered to the face of the flange--not on purpose, but unavoidable when soldering in such close proximity. The heads will be machined off after the flange is silver soldered to the muffler. Then the two pink/purple shcs will be removed and the green angle (with muffler and flange still attached) will be   pulled straight out of the blue fixture block. Then the dark blue shcs will be drilled out if necessary.

Offline rklopp

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Re: Muffler for model i.c. engine
« Reply #21 on: August 26, 2018, 12:49:14 AM »
Here’s one of the mufflers I made for my six Upshur Twins. It is a scaled version of the muffler on my Breisch Hired Man hit-and-miss, which in turn is a scaled version of the muffler that was on the Wisconsin V-4 haybaler engine I played with as a kid. For scale, the thread on the Upshur muffler is 1/4-40.

A lot of hit-and-misses have that style of muffler.


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Offline Brian Rupnow

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Re: Muffler for model i.c. engine
« Reply #22 on: August 26, 2018, 01:14:42 AM »
Thank you, Rklopp--I have seen that type of muffler before. I'm not really certain of how much noise they actually muffle, but it must be some.---Brian

Offline Brian Rupnow

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Re: Muffler for model i.c. engine
« Reply #23 on: August 26, 2018, 05:49:41 PM »
I reworked the muffler flange, and re-soldered it using the welding fixture shown in the previous post. I got lucky with the four dark blue socket head cap screws--Three of them unscrewed and I only had to drill one out. The muffler is reinstalled, and it seals properly to the engine now. The noise level has dropped a bit more, but trust me---Ya wouldn't want to have to sleep in a room with this engine running beside your bed.---Brian
t=6s

Offline Admiral_dk

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Re: Muffler for model i.c. engine
« Reply #24 on: August 26, 2018, 09:00:31 PM »
That muffler is officially a success Brian  :praise2: