Mikes dominant mode...

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Mikes dominant mode...

Post by serverlan » Wed Oct 05, 2005 6:11 am

oooh Mike,
you one sick puppy!

>>BTW, another neat thing about sinusoidal pressure inputs is that you can start the run with different dominant modes. You might (and I wish I had time to) see if it's worth kicking the frequency up to the second harmonic, or if it's possible to do so.

As if it wasn't hard enough already!.

I've often wondered about frequency of operation.
I suspect that a long exhaust makes it easier to start,
but if you half the length, then it should run at twice the frequency,
and (all other things being equal) should develop twice the power.
Same shart pulses (not long waves) twice as often.

So, short stubby engines should be more desirable for power, but harder to start?

Unless, as you say, you can kick them into a higher mode.
I'll still think and write in terms of pulses travelling according to wave theory (a la UFLOW) rather than sinusoidals, but the concepts can parallel a fair bit.
Whats to stop the tailpipe accommodating two pressure pulses at different locations in the tailpipe at the same time, with the combustion chamber firing twice as often?

It would require a more elaborate starting setup, perhaps with both pressure and mass flow as astarting conditions to get the waves to move in only one direction.

Hmmmm. Tricky. I'll have to think about it.


larry cottrill
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re: Mikes dominant mode...

Post by larry cottrill » Wed Oct 05, 2005 1:29 pm

Don -

Alas, you will probably never get more power by increasing the fundamental frequency. Shortening the engine does increase the frequency, of course, but it also reduces the internal volume. An engine of a given design will only replace a certain fraction of its volume with each breath. Making the same design shorter to increase frequency will reduce the total explosive volume taken in, so less power will be delivered per explosion cycle. And on top of that, the Q of the pipe will be reduced, so the breathing will be inherently less efficient, and yes, starting will probably be more difficult as well.

There are a lot of different shapes and sizes of organ pipes - but there aren't any barrel shaped ones.

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re: Mikes dominant mode...

Post by Eric » Wed Oct 05, 2005 7:10 pm

Every once in a while some of us get an engine that will run at a much higher frequency when its started in a certian way.

One of the engines I made, if you have the air probe all the way in the intake and get the engine shreaking like a banshe you can turn the fuel all the way up and have the engine sustain like that. Its like nails being scratched down a chalk board, except as loud as a pulsejet. Its the kind of noise that makes you wish your head would just explode, and I think normal pulsejet sound is relaxing.

There was no power gain at all in this mode, infact there was much less power produced than normal, but it did produce thrust. The wave form would of had to be very "sharp" for it to be that annoying, and it was running on a much higher frequency.


Talking like a pirate does not qualify as experience, this should be common sense, as pirates have little real life experience in anything other than smelling bad, and contracting venereal diseases

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