Continuous detonation engine - general discussion

[ssabot25]

Hello everyone
I have been lurking for a while, consuming information rather than giving things out, but let's hope this will become profitable now that I have accounted (enmembered?) myself (sic)

There is little information on CDEs around the web, although from what I have seen it has been pondered in about two threads around here, in both as if apro-pos.


CDEs are about a standing wave. I guess most people here know it, as it was cited in other posts. The question is how?

To my logic, the combustible mixture is delivered to the point of detonation so fast that it's speed equals the speed of propagating shockwave. This can be achieved by pre-compressing the mixture and changing the pressure into velocity using De Laval nozzle, or at high velocities by directing enough air into the engine.

But what makes the reaction of the fuel a detonation?

Are we going to go chemistry-wise and optimize fuel, for instance use liquid Oxygen/Hydrogen mixture, or MAPP gas?
Alternatively, can we use high-density fuel, pre-compressed to be capable of sustaining detonation as-is? (liquid hydrogen injection into the air freezes it pretty well... Japanese were pursuing similar technology at Kawasaki I think, for hi-speed scramjet-like engines... multi-stage hydrogen injection during compression of air could allow the air to be greatly compressed without combustion taking place or water vapor freezing during the process... but still, after reaching desired speed upon exiting De Laval nozzle, it would have to maintain enough density to support detonation...)

Or am I missing a point here, and the pressure exerted upon the moving gas by the standing shockwave (and the pressure exerted upon the shockwave by the gas, for that matter) give enough of compression to sustain the detonation?

[ssabot25]

I've drawn a scheme to illustrate what I expect a CDE to look like. I don't expect it is anywhere near accurate in regard to angles, shapes and distances, so this is disputable as well .

CDE theoretical scheme

One thing for sure, fuel delivery system would be very energy-consuming.

This goes as follows:
-Fuel and oxidant are injected into a pressure chamber, where they mix.

-They exit through a De Laval nozzle, increasing in speed. The speed after the nozzle should be higher or equal to the speed of shockwave generated by the explosion.

-Fuel hits another De Laval nozzle, increasing pressure to the point where detonation could take place, and is ignited. BAM! we get a detonation.

-Part of the shockwave exits through the opening in the pipe, perhaps another De Laval nozzle, ass seen on the image. (possibly even overexpanded De Laval, which should give better efficiency?)

-Second part of the shockwave stabilizes around the entrance to the De Laval nozzle, and will move back and forth depending on amount of fuel injected.

I can think about a few flaws in this design that won't make it work, but I don't have the experience to judge it properly :/ For instance, won't the detonation decay to a deflagration as it tries to force itself back against the fuel flow in the De Laval? I would like to hear what you think.


This thing is constructable on a mini-scale, where a simple compressor (and possibly heating the pressure chamber with a blowtorch) would suffice to produce a stable detonation...
However, because fuel is present in the whole system, it should be extinguished by water/steam/co2 injection, not to get the flame sucked back into the oxygen-rich pressure chamber as the operating pressure decreases...

[ssabot25]

There is an interesting patent about generating a standing detonation for lab purposes...
http://www.freepatentsonline.com/20050079461.pdf

They apparently have developed a witty way to compress the gas... You get two containers, one with lean fuel/oxygen mix, the other with very rich fuel/oxygen mix. They are ignited, blow up generating enormous pressure, and are directed outwards through a nozzle... when they meet, remaining fuel and oxygen ignite vigorously, but are already accelerating at the speed of the shockwave...