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For a while now i've had this nagging need to produce a small scale device capable of producing and demonstrating Shock Diamonds. No interest in efficiency or using it for propulsion or anything. I really just want people to be able to see shock diamonds up close and safely.
doubtful, only high explosives by definition can produce a supersonic shockwave. Diamonds only occur for supersonic exhaust. The thing is any high explosive wouldn't be able to sustain a stream, it would destroy the engine and create, at best, a split second jet.
You would likely need to do it using jet engine principles, even if rudimentary in nature.
@L29Ah As I understand it that would only work with a pulse engine, which can be supersonic but wont produce diamonds without tuning the pulse frequency, even then might not... not really sure if or how pulse engines could produce diamonds as it usually requires a constant exhaust velocity.
Generally to create a constant supersonic stream youd need a compressor feeding the reaction chamber. At sufficient pressures fuels that are not normally capable of detonation like gasoline (which typically only deflagerates) will engage in detonation. Though jet fuel would require less pressure.
So I think the easiest design would involve a fairly enriched fuel source on the order of jet fuel plus a pressurized combustion chamber.
You could probably get away with a transient setup if you pass it over something like an oil-flow visualisation medium. The flow changes direction over each oblique shock, so there should be sharp corners in the traces. And that's likely safer anyway, because the observer doesn't have to get near the exhaust while it's moving at supersonic speeds, and the exhaust doesn't have to be hot enough to glow for visibility. Run the demo with everyone a safe distance away, then bring over the oil plate for everyone to see the streak pattern.
The problem is you only get diamonds in an overexpanded supersonic jet (i.e. lower pressure than ambient air), which means you need a good idea of what the properties of the high-pressure combustion products would be so you can design an appropriate nozzle to bring them down to below-ambient pressures. These combustion products are probably highly nonuniform and may even still be reacting as they pass through the nozzle, so the problem of nozzle design would be trickier than in steady flow.
@khird
Interesting points, and I hadnt looked into it enough to consider some of those points. sounds like it could be tricky for sure but thats half the fun if i ever took on such a project.
@L29Ah