Exhaust Mufflers/Silencers

[YT2095]

I have a plan to make an exhaust muffler, basicly it`s a tin can with a screw top lid cylindrical and about 1 litre capacity.

I`ll use a 15mm copper pipe going into this can about 2/3`s its length, and 4x 8mm copper pipes from the other end of the can also going in about 2/3s of the can length.

so any gas will have to do a letter `S` path to escape, the can will be filled with course grade wire wool.

the single 15mm pipe is the inlet and the 4 8mms the outlets.

that`s about the best I can come up with as an idea.

 

I`de welcome any comments or improvements to this as long as they`re DOable.

 

I also considered leaving the inlet pipe free (not fixed position) so I can slide it in/out the can for tuning purposes first before I fix it in place.

 

my generator already has a baffle silencer and is reasonably quiet at 68db, I`de like to take this even lower, a gentle HISS would be ideal!

[Klaynos]

put it on a sprung mounting so that it down't vibrate the floor

[DV8 2XL]

If the generator runs at a fixed RPM you might look into a tuned exaust.

[YT2095]

actualy the speed govenor should alter the RPMs according to load, thus delivering the preset voltage per load (I can set this manualy from 750vac downwards).

 

I conducted an experiment today (just for a giggle) and used 2x 15mm copper pipes offset inside a beer can so it still had to do the `S` path (-leakages), it knocked down alot of the low freq sound!

it`s the low freq that I want shifting really, so I`m guessing that a 1 litre metal tin as opposed to a 440ml tin (with leakage) should perform alot better.

 

Klaynos: the gen is on concrette with rubber shoes on it, although it DOES vibrate (even though the cement is 18 inch deep and 10 foot by 8 foot) it`s the best I can possibly hope for in this case.

[DV8 2XL]

My father-in-law made a exhaust muffler once for a fixed powerplant, so I just asked him what exactly he had done. He made the thing out of cast iron, as weight wasn't an issue and the added mass of the material, he felt helped. The geometry was rather simple: A center 1.75in pipe perforated with 0.5in holes terminated at one end with a plug, inside a 4in sewer pipe with end caps. the small pipe passed through the end cap at one end, and an exit pipe was attached at the other end cap. The total length was 22in, because "that was what I had on hand."

[doG]

actualy the speed govenor should alter the RPMs according to load, thus delivering the preset voltage per load (I can set this manualy from 750vac downwards).

That's a bad thing if we're talking AC. The speed governor should try to maintain a constant RPM regardless of load so that the AC frequency doesn't vary. The voltage should be controlled by a variable voltage across the exciter winding. As load increases, amperage, it will try to pull the engine RPMs down and the governor should try to rev it back up to maintain the required frequency. Ideally the RPMs will be constant and a tuned exhaust will offer the most efficient attenuation.

[insane_alien]

depends if it is designed to give a set frequency. my grampa had an old generator that was used for lighting. since the lighting only needed > 25Hz that was the only thing the govenor kept track of. it sometimes went up to 75Hz

[Flunch]

doG is right - almost any AC generator in common use will run at a fixed speed in order to generate a constant frequency output. I believe you're on 50Hz in Europe so a common engine speed there is 1500 rpm (4-pole generator)

 

I don't know what size generator you have but 15mm pipe seems pretty small. You want to ensure you don't create excessive backpressure on the engine. You can measure the pressure easily by installing a simple water manometer near your engine exhaust outlet.

[YT2095]

I think there`s a little misunderstanding here, under load the revs try and drop, the govenor detects this and up`s them again to the correct output RPMs, thus maintaing the speed and current as well as voltage. however I CAN set this to anything I like by adjusting a screw, and so 240vac need not be the default setting, but anything from about 90v upto 750vac, it could probably go higher as the engine will easily allow this but the exciter cap for the generator is only 750v rated, so it`s not something I`de even try and risk.

the output is 1200watts.

the engines a 4 stroke 80ml displacement (2.4 HP), so the exhaust outlet is only small, a 15mm copper pipe fits nicely over it.

 

edit: if it`s of any help its a Robot Model RBT1000A A152F.

[DV8 2XL]

Here's the gen on building a tuned exhaust

 

L = (850 (180 + N)/RPM)-P

 

 

where L = length of pipe in inches

N = degree before BDC exhaust valve opens

P = distance from exhaust valve to manifold

and RPM = desired RPM

 

 

The diameter of the pipe needs to be calculated so that the volume of the exhaust pipe attached to each cylinder is twice the volume of each cylinder. The exact diameter of the pipe, incidentally, is not critical and should only be used as a guide in determining which standard sized pipe diameter should be used.