www.pulse-jets.com

Hi,

Do you think this idea might work?? A valveless p-jet constructed from intersecting paraboloids. At the exit point of the combustion chamber the focal points overlap or coincide ensuring a transfer of combustion shockwaves and vectored thrust to the outside. While at the other end the focal point is after the intake aperture so that the majority of shockwaves are reflected back into the combustion chamber and may assist with the intake cycle (venturi??). Unlike the crude picture you could muck around with paraboloids of different geometry. Has it been done? Is this a wave engine??

mmm...well ok thx for the feedback...

I can't see why it wouldn't work in theory (assuming that you acoustically tune the inlet pipe and tailpipe). I'm just not sure whether you want to "focus" the acoustic energy - but its a very interesting idea. By the way, there are no shock waves in a pulsejet - the gas is subsonic everywhere.
Sam

I remember one fellow, Dick Klockner, EAA 3201 saying that one shape that will not work is the cigar shape. "The tube shapes which will resonate seem almost infinite (although it is hard to believe at times) if all other factors concerned are proper. There are a few conditions , however, which will not support resonance. One of the tube shapes which will not function either in theory or in practice is a cigar or aerodynamic shape. The critical portion of this shape is the exhaust end. The extreme tail end cannot be converging because a condenstion wave will not be reflected as a rarefaction wave from the open end of the tube, and consequently the valves will not open."
"And here is an obvious one, he says. "Another condition which will not support resonance is a tube which is too short. The longer the tube, the less critical are the other parameters. .... consequently it would be wise for the beginning experimenter to make his tubes long and then shorten them as experimenting progresses."
"If an increased diameter cylinder is added to the tail section of a pulsejet, theory predicts that during one working cycle intake and compression can occur twice. This is not a good condition for valve type units because it affects valve life. However, we have found it excellent for valveless units because the incoming charge can be doubled over a similar straight tail section. It is possible to have an engine which is much shorter using this technique."
Even a simple straight pipe will run as a pulsejet, which may come as a surprise to some, but it is perfectly logical when one considers a simple organ pipe. This configuration is very poor on performance, however. The best all around performance seems to be produced when the tail pipe has about twice the volume as the combustion chamber."
Just some other thoughts to muddle over. It was written in 1965.
Mark

Thanks for the replies....lots too think about....doesnt sound too promising. I guess the next step will be to build one to make sure it wont work..=)...I havent got the foggiest about how to accurately fabricate parabaloids. I was thinking of cnc machining a plug of the desired internal profile and then somehow casting around it. Maybe pottery is the way to go. Thx again.

if your gonna make a mold you could hydroform it. read the "tools and construction" part about it.