Muffler resonance frequency

[cid55]

Hi,

I am new to this forum

I am trying to design a muffler and so am in the process of determining how much fiber glass I need behind the perforated pipe. I was wondering if anyone knows how to workout the resonance frequency for a muffler? I have a 599cc engine with 11000 rpm and 70bhp. I know if I put 6 inches of fiber glass then it will absorb around 99% of the sound frequencies but I wanna reduce the amount of space needed for the fiber glass to say 3 inches. So it only absorbs to the required frequencies and hence reducing the overall size of the muffler. Its on be put on a race car with a skeleton chassis.

If I can get a resonance frequency then I can workout the diameter of the perforations required for the space available.

 

[Lou Scannon]

NACA published a report in 1954 titled Theoretical and Experimental Investigation of Mufflers With Comments on Engine Exhaust-Muffler Design. I think they took down the NASA server last year where I downloaded this report. If you can't find it on the web I can email it to you or we can figure out a way to fileshare.

"Schiefgehen will, was schiefgehen kann" - das Murphygesetz

 

[cid55]

Thx hemi, the article seems quite helpful but I didn't find any information on the perforations for the muffler pipe.

either way thx for the help

 

[SomptingGuy]

If I remember correctly, that paper deals with empty mufflers, whereas you appear to want to optimize perforates & packing. It does cover most of the simple designs you'd find on a race car system (FSAE I presume). Packing the resonator cavities with absorptive material (steel, glass,etc) will tend to raise the transmission loss across the whole frequency range. It'll also fill in the sharp troughs you see at the resonant frequencies (it kills strong resonances).

I don't see how the hole diameters of perforates relates to packaging constraints.

If this is FSAE, you could use one of the tools you'll have been provided by the sponsoring companies to test out some different muffler configurations. Your engine guys will probably have a performance model to hand.

- Steve

 

[Tmoose]

Is the engine speed going to vary during the sound test?