Re: Hybrid Propellant Concept

Stephen Holden wrote:
> Hello,
> I am developing a new hybrid propellant concept that I would like to 
> discuss...It's basically very similar to any hybrid, except that the 
> propellant consists of a cylindrical grain of lightly bonded magnesium 
> powder onto which is sprayed through injectors the oxidizer. The 
> oxidizer is a solution of water and various nitrates and perchlorates 
> at high concentrations. There are many possibilities for testing and 
> would like to get people together to explore the concept.
> 
> I have placed a brief description on the Australian Experimental web 
> site, which I will update with any developments made.  
> 
> The motor is a concept at this stage, but tests of the reactivity of 
> lightly bonded magnesium powder and water / oxidizer solutions indicate 
> a highly energetic reaction that with a little luck will produce a 
> workable hybrid propellant.
> 
> Any and all ideas and help is welcome...I think it's an interesting 
> idea worth some investigation...

I see "lightly bonded" as a red flag on this -- if the stuff is bonded 
lightly, I see a serious possibility of cracking or shedding of the fuel 
grain, which could lead to significant pressure excursions from the 
change in burning area or from nozzle restriction.  Neither is quite the 
issue with a hybrid that it would be with a conventional solid, but on 
top of that you have the traditional problems with metallic fuels, in 
that the primary combustion products are likely to be or become solid 
before the exhaust is beyond the nozzle; though the phase change gives 
up heat to the remaining gas in the exhaust, it also reduces the amount 
of gas and in general is a net loss (not even to mention the nozzle 
erosion problems resulting from particle impacts at transonic speed).

Overall, I'd be interested in seeing static tests, but I'd also want to 
see tests where the motor is fired vertically in a test stand that 
simulates the vibration (and ideally acceleration) environment of rocket 
flight -- I'm inclined to believe there will be serious problems under 
flight conditions that might not show up on a solid test stand.  Using 
water as an oxidizer (which it certainly is for magnesium, at least once 
combustion is established) sounds interesting (agueous solutions are 
much safer to handle than most liquid oxidizers), but I'd have to 
suggest a high solids percentage traditional composite over whatever 
"lightly bonded" might mean.  I'd also suggest testing aluminum as a 
fuel in a similar motor, preferably milled and bonded in vacuum or 
nitrogen to prevent surface oxidation; a strong perchlorate solution 
should react nicely with aluminum, though the problem of solids in the 
exhaust remains.

Of course, there are significant handling hazards with both magnesium 
and aluminum as fine powders prior to bonding, especially if the powder 
is prepared in a manner that prevents oxide layer formation; both 
metals, when powdered, are pyrophoric and can also self-ignite if 
exposed to high humidity or actual liquid water.  Both are nearly 
impossible to extinquish once ignited in air.

-- 
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                                                     -- E. J. Fudd, 1954

Donald Qualls, aka The Silent Observer
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Opinions expressed are my own -- take them for what they're worth
and don't expect them to be perfect.