Hybrid question

Discussions on hybrid rocketry including rockets, motors and technologies.

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air.command
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Hybrid question

Postby air.command » Wed Jun 24, 2020 9:11 am

Do you think it would be possible to build a hybrid motor that uses a slurry of say HDPE powder and nitrous? If you could mix the powder and nitrous inside the rocket before it gets injected into the combustion chamber, would that work? The thinking is that you would have maximum contact between fuel and oxidizer as it enters the combustion chamber greatly simplifying any injector design. You could also easily throttle the motor without ending up fuel or oxidizer rich.
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strud
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Re: Hybrid question

Postby strud » Wed Jun 24, 2020 1:17 pm

Hi AirCommand,

I think that there would be a few issues with this approach

- Safety : a premixed Ox/Fuel moves a long way away from the 'mix at time of combustion' approach normal hybrids have and may be much more prone to decomposition or similar issues
- If you made a slurry, then it may not actually be a hybrid anymore and be more of a liquid (not a problem, more of an issue with terminology)
- hard to see how you would ensure a homogeneous mix since the N2O is not a 'normal' liquid per se

The motivation for swirl injection is to overcome the issue of 'mixing' you have raised ie significantly improve the mixing of oxidiser and fuel at the grain surface.

strud
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Re: Hybrid question

Postby strud » Wed Jun 24, 2020 2:24 pm

Read slide 9

https://www.ibb.ch/publication/N2O/N2O_safety_e.pdf

quote from slide 9:

"• Very good solubility in oil grease and other hydrocarbons like plastics etc (That Very good solubility in oil, grease and other hydrocarbons like plastics etc. (That s' why it works so well for whipped cream). Also solid plastics like HTPB or fiber reinforced
plastics can be saturated when exposed to nitrous oxide for a long period and can
then transform to a high explosive. "

air.command
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Re: Hybrid question

Postby air.command » Wed Jun 24, 2020 2:32 pm

Haha... okay, yup probably not a good idea then. :D I realize that trying to come up with some way of mixing the two just prior to injecting it would be difficult, it was more a thought experiment than something that may be practical.
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DiscountBatman
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Re: Hybrid question

Postby DiscountBatman » Wed Jun 24, 2020 4:25 pm

Looks like NASA though it was a good enough idea to test out (with GOX and Al powder):

Powdered Aluminum and Oxygen Rocket Propellants: Subscale Combustion Experiments
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19940017287.pdf

They have a throwaway line in there about suspending Al particles in LOX to make a '"monopropellant".
So you might be able to premix NOX with a less spongy fuel and make it work.

air.command
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Re: Hybrid question

Postby air.command » Wed Jun 24, 2020 5:04 pm

Interesting article, thanks for sharing. For the mixing part I was originally thinking something along the lines of what abrasive water cutters do where they mix the abrasive into the jet of water just before it emerges out of the nozzle. But you could potentially get ignition inside this mixing chamber.
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