Potential?

[tufty]

So, I've been thinking about force-fed ramjets for a while now. Particularly after Jonny69 (I think) posted his air-amplifier-fed-with-propane video. Spent a while scouring eBay for air amplifiers, was too cheap and got pipped at the post on a couple, so I've been thinking some more.

My original idea was an air amplifier front end fed off pressurised propane followed by something to promote mixing the largely laminar fuel flow with the entrained air, a flameholder, and a largely speaking conventional combustion chamber.

I also toyed with the idea of feeding the air amp with combusion chamber pressure, but I doubt there's enough pressure to do anything useful with.

Whatever happens, though, mixing the fuel and the air is going to be hard to do without buggering up the flow characteristics. So I started thinking about "inverting" the air amplifier part - making it a central part with a surrounding shell, leaving the back of it "flat" to promote turbulence (and therefore mixing).

I think this needs a picture: Here's one I did earlier.

I don't actually have time for this at the moment, been doing 18 hour days on a current project and won't have any time to weld'n'lathe untill Tuesday at the earliest.

Any thoughts? Viable? Not viable? waste o time?

[larry cottrill]

Simon -

Basically, a good idea - I like it a lot. The only thing wrong, I believe, is that you don't get the full action of the diffuser - the air going into the chamber will be faster than it enters at the front end. This could be corrected by using an expanding cone for the front end instead of a cylinder, though, so it would be an easy fix. Better yet, the diffuser could follow the separation point (sharp rear edge).

I have always liked the idea of smoothly flowing fuel over a "bullet" and then having it shear off at a rear edge where the air undergoes separation. I have no idea whether testing would prove it to be a good method, however - it just seems like it ought to work.

L Cottrill

[tufty]

Simon -

Basically, a good idea - I like it a lot. The only thing wrong, I believe, is that you don't get the full action of the diffuser - the air going into the chamber will be faster than it enters at the front end. This could be corrected by using an expanding cone for the front end instead of a cylinder, though, so it would be an easy fix. Better yet, the diffuser could follow the separation point (sharp rear edge).

Well, crappy drawing, but I was trying for (at least in the air amplifier part) a straight cylindrical casing, and doing the diffusion by tapering the centre "bullet" part. I agree, basically :)

I have always liked the idea of smoothly flowing fuel over a "bullet" and then having it shear off at a rear edge where the air undergoes separation. I have no idea whether testing would prove it to be a good method, however - it just seems like it ought to work.

Seems that way to me, too. Another possibility might be to taper the "bullet" down to a point downstream and injecting fuel there, much like a spray gun nozzle. Don't know if that would work without forced boundary flow, though, seems like it should, at least to me. Of course, that would mean (for ramjet applications, at least), a need for force air for static running, or carrying pressurised non-fuel gas, which I ws trying to avoid.

Simon