Proposed Design - 'Reflector Bucket' Valveless Pulsejet

[larry cottrill]

Don -

I fully agree that the velocity is indeed the problem. Your test setup for the experiment sounds fine, with just one exception: You're not getting a real bang from the driving explosion. Note that we expect good bangs from pulsejet combustion, even from a nicely-running jam jar; I think the combustion you're getting is too rich, and the overall energy per burn is low [or at least, the average gas momentum is low at the interface]. I am not sure I agree that the blast needs to be supersonic as it impinges on the bucket throat, but it surely needs to be pretty fast to have enough momentum to perform any compression.

I'm sure that one problem in my design is that you start out trying to compress cold, dense air with hot, thin air. If the thing could be gotten to limp along under those conditions for a few cycles, that situation would change for the better. However, here's what we need to make the reflection meaningful, under ANY gas condition: The mean directed molecular momentum of the driving blast all across the opening MUST significantly exceed the mean undirected molecular momentum which represents the static pressure in the bucket. And what that means at the beginning is [because we're trying to compress dense air with thin air] there has to be a LOT of well-directed velocity to the driving blast.

Maybe experimenting above the throat of a good, running jam jar would be the way to test this. At least, you'd be starting from a setup that you know is producing the kind of combustion gas velocity that we care about. Of course, jam jars are relatively low energy devices on a per-cycle basis, so even here there might be problems getting a good start to the reflection cycle. What I'm thinking is, you'd get the jam jar running and then gradually lower the bucket 'onto' the ejected flame. Sounds tricky.

L Cottrill
----------

[Bruno Ogorelec]

Larry,

It could be a matter of timing. If you synchronize the refilling of the bucket with the blast from the chamber, you will have two fronts of gas traveling in the same direction -- fresh air followed by the hot blast. the energy of the blast will 'climb' on top of the kinetic energy of cold air and produce elevated pressure. One will not fight another.

But, for that kind of timing you need longer vessels. Longer vessels give you more volume, which dilutes the effect.

It all returns to my conceit that the reflecting chamber won't work, or at least won't work well. What you really want is two opposed combustion chambers blowing against each other.

Bruno

[George]

Hy Larry,

Without any joke, for me you didn'nt put the spark plug (and combustion chamber) at the right place !
I spent a lot of time to think how is it possible to compress fresh air to have a good compression ratio.
Finaly, i re-create an EYRNST engine with a sonic tube a the mouth of the pot, the only difference is that i've seen this tube with a counter-cone like an exhaust for a two-times engine to bring back a part of the detonation.

Look how is it near from your vision !

[Pieter van Boven]

George, I realy like to see your project-engine but I can't open the file. Wich program do I need to open it?

Thanks,
Pieter.

[Mike Everman]

Wich program do I need to open it?

It's power point. You can go to the Microsoft site for a free viewer.