Landracing Forum
Tech Information => Technical Discussion => Topic started by: NathanStewart on April 23, 2015, 03:40:17 PM
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I've been doing a LOT of research on industrial "silencers" (mufflers basically) and am wondering if anyone on here has any experiencing designing and/or building them. I'm looking to do something like a hybrid silencer that has a reactive primary stage followed up with an absorptive secondary stage with the idea of killing both low and high frequency noise. There are plenty of companies that make industrial silencers that range from small engine mufflers to mufflers that are the size of buses but they're pretty expensive new and I'm not having much luck finding a pair of them used.
I'm thinking about adding some large, high flowing silencers for my dyno. Dyno noise has turned into a bit of an issue for me (Costa Mesa has lost its mind and is now building condos in commercial/industrial areas - there's a new condo complex across the street from my shop) and I think trying to add in some mufflers is going to be my cheapest/easiest solution to try and bring the noise down some. What I'd like to do is have two large silencers that'll hopefully support about 1000hp worth of exhaust flow each. As far as connecting the silencer inlets to the car's exhaust, I thought about using rubber exhaust bellows that seem to be common in marine applications. I don't know much about boats, but it seems like these rubbers bellows can hold up to exhaust temps.
There are a whole slew of other things to consider when trying to put something like this together but I thought I'd a least get the discussion started. Any thoughts and/or suggestions?
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Nate, no experience, but for 2 years, I lived across the street from the Waukesha/Dresser industries plant - now WPI. They have a test facility for large stationary engines, and the mufflers they used were enormous and effective. On the photo of the trailer to the right, you'll see what I'm talking about - this is what they use on their mobile units . . .
http://www.wpi.com/engine-solutions/power-generation/
I don't know what they flow - I doubt the engineers at Dresser could tell you - but they're hanging them on 2000 KW output engines, and even working third shift and sleeping in the morning with the windows down, they never woke me.
Just a thought.
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Nathan,
I think the rubber sections on the boats are cooled with water, at least all mine have been.
The water is pumped through the ex manifold to cool it and then it dumps into the last section just before the rubber connections.
Ex gasses are pretty hot when running making good power, especially on the rotary's.
John
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Nathan, PM sent.
Pete
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Nathan-
This may be (read: probably is) a stupid idea, but a few 55 gallon drums in series, baffled by cutting slits into the sides and welding in scrap metal, would make rudimentary, but large and inexpensive "mufflers"... Those can be had for scrap prices and could accept any type of coupling between your shop and each other. I'm sure someone in the industry has a better (informed) idea, but in theory it would work.
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Nathan-
This may be (read: probably is) a stupid idea, but a few 55 gallon drums in series, baffled by cutting slits into the sides and welding in scrap metal, would make rudimentary, but large and inexpensive "mufflers"... Those can be had for scrap prices and could accept any type of coupling between your shop and each other. I'm sure someone in the industry has a better (informed) idea, but in theory it would work.
That sounds like a good idea, but I wonder if the drums will resonate and flex making noise themselves. I imagine it would be minor compared to 1000hp even if it did but just kind of wondering
The other idea would be a bunch of tires , but a fire hazard.
Fire stations often have a flexible hose hanging down to attach to the exhaust when in the bay. It looks like a big dryer duct, but not sure what it's made out of.
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Nathan (and others if you have interest), :-D
The type silencer that you would probably need from what you describe is a "critical grade" silencer. Those are the types used at hospitals on stand by gen systems. :roll:
With the encroachment of dwellings and such around your shop, it is probably a good thing you are investigating the upgrade for noise abatement. A far greater problem might arise from the regional or sectional air management and resources control group because they will probably deem your dyno facility a "stationary stack emitter". The combination of the air resources management district and the "noise" might put you in a bind so be very wary as you try to improve your lot in the community of Californians around you. :? :dhorse:
Exhaust silencer companies are more than happy to help if you give them some guidelines but they will also have you pay dearly as that puts them in the potential litigation loop with wretched municipality and local government regulations. :-o
BTW - You can use an exhaust system that helps to decrease multiphase frequencies and still not have a problem with power losses from exhaust back pressure. The first 1% in power loss ticks over at approx 13.6"H2O (1"Hg).
Good luck as you look for solutions. :cheers:
Regards,
HB2 :-)
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Thanks for all the tips and ideas. I have heard of people making dyno mufflers by filling barrels with old tires and then burying the whole thing under ground. The rubber does a good job of absorbing sound and having them buried helps with noise insulation of the barrel itself.
Making a drum muffler is a pretty good idea. I think 55 gal drums would be really big but I think some 30 gallon drums could work. I could make the drum chambered and then use a standard absorptive muffler on the outlet. That should get me noise reduction across a wide frequency spectrum.
I think the biggest challenge will be getting this secondary muffler connected to the cars exhaust. I was hoping that the boat bellows would work and knew marine exhaust were liquid cooled but didn't know much more than that. Having a sealed connection would be best for noise suppression but that might be touch to do. I think a base layer of high temp header wrap might keep the direct heat off the rubber.
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I recently spent a bunch of time designing a silencer system for my business partner's RV generator. The end result was that I was able to knock down the 3600rpm Onan generator noise emission from 93dB to 83dB (at 10 feet) with just a little bit of effort. During this, I got some tips from my father who spent his career as an acoustical engineer. Key things are:
1. mass is your friend. If you have the ability to surround your dyno cell and all piping until the actual exit with as dense a material as possible, that is best. Burying system underground or behind layers of 5/8 plywood and 1/2" sheetrock also works. There is flexible sound absorption matting available at a reasonable cost too.
2. you are dealing with variable frequencies, but you can still attack them with a combination of Helmholtz resonator plus a multi band pass filter (muffler)
3. There are some good Helmholtz calculators out there. I made an Excel spreadsheet for mine and built the resonator as a small pipe leading to a larger plenum, with the small pipe mounted 90 degrees to the exhaust pipe. The key formula that you want to work with is w = c(sqrt(S/(Leff*V))) where w is the target frequency, c is the speed of sound at temperature (I used 4200 inches per second), S is the neck cross section area, Leff is the effective neck length and V is the chamber volume.
4. There are a number of muffler designs out there and a google search will quickly bring up different options of how to design a muffler that will target multiple frequency bands, if you want to build your own.
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Nathan, a few things I have noticed with my engine dyno noise issues & how I have worked with them in the same small industrial complex for over 21 years now.
I use diesel truck mufflers as they are inexpensive, easy to get, do not produce much back pressure, & do not take up a lot of space. They my not be as quite as you want so you might use multiples. The next step is to exit the exhaust upward as opposed to pointing at something.
I my case I have found that mechanical engine noise is almost as loud or louder than the muffled exhaust. My dyno cell is well insulated, we can talk with the engine under power, but it does have two 3' x 3' air vents in and out of the room so a lot of noise escapes this way.
I agree that a good connection from the exhaust to the mufflers is important. There are a couple cheep and easy ways to make a connection with little sound loss. Do a google search on dyno test cells and you will see how some of these are done that might work for you.
Lastly use caution if you build any type of inclosure for sound reduction. I know of one made with plywood that over time accumulated fuel & oil catching fire that was not easily extinguished. Another had an underground channel to a shed with 55 gallon drums constructed into silencers. The underground section collected explosive fumes that were ignited with a misfiring engine.
Best of luck on the project.
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When I worked for Montana Power we had problems with the diesel bucket trucks in the down town alleys. They would empty out the office buildings in a few minutes and they were mad plus we couldn't breathe either. They had a corrugated rubber 4 inch flex tube made up or bought about 75 ft long so we could run the exhaust out into the streets after it left the muffler. Maybe something like that would redirect the noise out of the mufflers away from the buildings. Just something to think about anyway. Cost wise I don't have a clue about or whether they would hold up to the heat of a wide open engine. Once the people move in youre probably on a down hill slide from there no matter what you do
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I've got some experience with exhaust silencers. My last run I kicked 2 rods out the pan and the exhaust got extremely quiet. :-D
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Pipe the exhaust to downtown Los Angeles and vent it there. Nobody would hear it, or smell it.
Doug :cheers: :cheers: :cheers: :evil: :evil: :evil:
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I think silicone coated fiberglass fabric may be my answer for a "coupler" to mate the silencer with the car's exhaust. I've found stuff that has a working temp range of 1500°F to 3000°F. Wrap it around the loosely coupled "joint" a couple times and then secure with some long worm drive hose clamps.
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Nathan,
Cant help with the design but I can give safety advice. Be very careful with engines that don't start up right away. Rick had a problem with the starter on Joe Fontana's dyno, when my engine finally started it ignited the fuel vapor in the system and blew down all the celling panels in the cell. Another time running Dale Smarts blown alcohol motor on Billy Williams dyno a similar occuance blew the mufflers off the top of the building and into a trailer park next door. All very exciting.
Jim
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Try to find an old copy of The Scientific design of Intake and Exhaust Systems. Technical, about open exhausts and explains how odd stuff like motorcycle "fish tale" tips were developed, exhaust pulses and sound deadening. When the SCCA had problems at the old Golden State Raceway we did a lot of Dyno work to hit 103db
We created a dyno-set that had no back pressure to use when testing our engines. Whether you could do that for a variety of engine types....dunno.
But, I'm willing to talk about it 8-5 Texas time and explain what we did.
Woody 90three-216-three115
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For stationary systems, size is your friend, to get good noise reduction with low back pressure. Using drums is a good idea, and if you make the first drum large and empty, the engine sees it almost like discharging into open air.
I'd avoid flat surfaces as much as possible, to avoid having the shell of the enclosure itself acting like a speaker. The ends of typical drums might pose a problem. Burying the whole thing might be a solution, but if it ever corrodes or gets plugged...
And, as jdincau said, be careful of engines that don't start easy. I've heard stories of engines filling the exhaust system fuel of air/fuel mixture, then lighting it off, and blowing man-hole covers in the system 30 feet up!
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There is a reason why gas engine boats have Bilge Blower vent systems
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I used one of these for exhaust vibration control on a home generator- http://www.ebay.com.au/itm/like/150869416070?limghlpsr=true&hlpv=2&ops=true&viphx=1&hlpht=true&lpid=107&chn=ps
It did leak some fumes, so I coated it in high temp silicone which solved that problem. The mufflers from turbo diesel applications don't actually have to muffle that much noise because the turbo itself acts as a sound deadener, so expect to run 2 in series for a non turbo app. I did try running my generators exhaust through a 60 litre drum that was filled with water to the 3/4 mark, but running the exhaust gas to the bottom of the drum (in order to force the gas/noise through the water) does create some backpressure, and there is a lot of evaporation so water levels need to be checked often. Unburnt fuel tends to collect in the water too, which was not a problem for my diesel application, but could pose problems for a gasoline set up. If I did it again I would just run more automobile mufflers, and would probably incorporate a large blow off valve or two for the occasional explosion.