Noise Cancellation Corner

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leo
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re: Noise Cancellation Corner

Post by leo » Thu May 26, 2005 11:28 pm

Is a lockwood not the right shape for noise cancellation, maybe the bend has to be more to the back of the exhaust pipe, so that the waves from the intake and exhaust cancel each other out.
Only I think that the biggest pressure wave comes from the intake, and it will be hard to cancel it out with the pressure wave from the exhaust, maybe then you have to play around with the size of the ports to make the waves the same magnitude, but that will surely be a negative thing for the performance of the lockwood.

For Graham I always have flames when I have maximum power out of the tailpipe, only the are almost invisible outdoors with good light, the show up when its darker, I just notice that after a lot of testing.

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re: Noise Cancellation Corner

Post by Eric » Fri May 27, 2005 3:17 pm

Bruno I am also working on double and tripple clusters, as well as some totally different engine designs.

I might even post some stuff this weekend if I have time. Very exciting times.

Eric
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Re: re: Noise Cancellation Corner

Post by Bruno Ogorelec » Fri May 27, 2005 3:36 pm

Eric wrote:Very exciting times.
You bet! The world has not seen such a frenzy of pulsejet development in half a century. OK, it is largely amateur-driven now, in contrast to the 1950s, but it only makes for bolder approaches to design. :o)

Look at the Formula 1 field. 90 percent of designers working there were amateur builders at some point.

Mike Everman
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re: Noise Cancellation Corner

Post by Mike Everman » Fri May 27, 2005 5:08 pm

Exciting times to be sure!

Leo, the Lockwood and the straight pipe designs are by nature in phase front and rear. Bending them cannot get the outlets anything but fractionally out of phase.
If you look at the numbers, you'll see that the length of the engine is at cross-purpose to the effect we want. As the length of duct increases, the frequency goes lower, the wavelength of the pressure waves becomes longer, but the speed of sound in the ambient air remains largely the same.

Look at the attached motor length and frequency data below, the far right column calculates the half wavelength in 20c air; the linear distance required for the tail and intake pulses to be out of phase with each other. You see this distance loosely tracks the length of the engine, but a bit shorter. Linear designs could only have the intake bend around, for instance.

The notable exception is Bill's escopetta, which likely has the tail OUT of phase with the inlet. I can predict right now that Bill's bend couldn't be in the right place for the motor not to interfere with itself! I'll post that analysis later, but it's simple math after you look at the table.
Attachments
actuals with half wave distance.JPG
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leo
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re: Noise Cancellation Corner

Post by leo » Sat May 28, 2005 11:33 pm

I don’t believe the intake and exhaust are in phase with each other, the sound is produced in the CC and it will take a lot longer to reach the end of the tailpipe than the end of the intake, the only way to prove or disprove this is to stick a linear valveless thru a soundproof wall end record the sound in stereo, then analyzed it
After that it would be possible to find out the length you need between the in and exhaust ports to get the most noise cancellation, only I think that the waveforms are to different to get a good cancellation, and you have to put the jet into a duct to prevent noise to the side.
If you want to cancel out a lot of noise the waveforms have to be near to symmetric,
And I think this is not the case with these valveless pulsejets, but maybe we can get it to reasonable level.

So much to try, so little time.

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re: Noise Cancellation Corner

Post by Mark L » Wed Jun 08, 2005 5:37 am

Being a rank newbie, someone has probly tried this before.
Use a flowmaster muffler as a thrust augmenter/ muffler. The internal baffles split the incomming exaust in half and direct pressure waves against each other where they cancle with room for almost free flow for gasses. The company ocasionaly clames that they make more power than a straight pipe (even on race car)s by use of pressure pulses to scavange the exaust gasses. Spork it, add fuel at the cancelation point for an afterburner.

Must go read and think some more.
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re: Noise Cancellation Corner

Post by Dave » Wed Jun 08, 2005 11:01 am

"Use a flowmaster muffler as a thrust augmenter/ muffler. The internal baffles split the incomming exaust in half and direct pressure waves against each other where they cancle with room for almost free flow for gasses. The company ocasionaly clames that they make more power than a straight pipe (even on race car)s by use of pressure pulses to scavange the exaust gasses. Spork it, add fuel at the cancelation point for an afterburner. "

Interesting. Can you provide a link to the information?

Dave

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re: Noise Cancellation Corner

Post by Mark L » Thu Jun 09, 2005 6:48 am

Here is the claim http://www.flowmastermufflers.com/cgi-b ... round.html

A internal photo of the new kid.
http://www.flowmastermufflers.com/cgi-b ... aflow.html

I think the original design would be easier to tinker with, I'll start digging for a diagram.

on a different thought , I have only skimed the postings. Has a stratified fuel charge been tried? using a rich mix to compress/ignight a lean core?

Just rambling
A little soot won't kill you.

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