Mike Everman wrote: I must wonder though, if you aren't focusing on length overmuch, and not considering the impedence other than as a byproduct of intake length. In my opinion you're attacking the finer point of intake resonance when (I feel) it has little to do with getting it sustaining. The inlet area will determine all (if the heat release time and over-all length allow it), if the intake length is within a reasonably large range. My often wrong, but never uncertain opinion is that it looks ready to go if you choke down the inlet; then work the finer points on a running engine and thrust stand.
Perhaps try introducing a tapered stinger in your inlet to choke it down some, to find a running impedence, then play with intake resonance.
I've said it before, but I'm still not certain if our local intake mode should be in or out of phase with our main cycle, or at some odd harmonic that enforces one and draws out the other. If it's in, of course you get a bit (I mean 2%) more high and low pressure extremes in the CC; if it's out, you get it to dwell longer at the extremes, which may help with ingestion more than anything. Who's to say without a serious experiment? What do you think, M.? Ha,Ha.
OK--I'll go along with the recommendations of some of our more active participants here. I'll try a variable area "stinger" to see if we can find an improved impedance. This can be combined with my effort to find an optimum length, at the same time. Each length will be tested with the stinger, to see if a change in inlet area might create a sustaining engine
I'm not sure I completely agree with this approach, but since I lack any convincing argument to the contrary I'll give it a go.
My line of reasoning is that a properly designed intake provides its impedance through correct acoustic matching, and good plugging from the cold-air inflow velocity. A reduction in intake diameter may create a running engine but will sacrifice the breathing necessary to give it the higher performance the designer aspires to.
Having said that, I've observed that the Uflow sim shows an increase in end-of-cycle pressure in the combustion chamber as the intake tube is increased in length, up to a very obvious value--after that, the pressure falls off rapidly as the intake mismatch increases in value.
I have chosen to start with an intake tube length that is well above the indicated value and then shorten it until I get to the range where Uflow says it should be optimum.
I only have 2 hands (like regular people) so I can only handle that many variables at once. Since one hand is on the throttle (propane flow), I'll need to combine the proposed variable-diameter stinger with the start-air supply. The attached drawing shows a simple solution for this device. It's formed from a piece of straight metal tube and is pushed through a tapered piece formed from a length of hardwood dowel, and fastened (glued?) into place.
Does anybody else have a different (and possibly better) solution?
One of my goals here is to try and educate myself as well as others here about the problems associated with getting a new design to run. I would like to encourage as much participation in this discussion as we can get.
Acoustic Propulsion Concepts
".......some day soon we'll be flying airplanes powered by pulsejets."