Pressurize fuel tank with compressed air

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Alvaro

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Hello folks!

My father and I are starting the design and production of a rocket engine following this design guide ( HOW to DESIGN, BUILD and TEST SMALL LIQUID-FUEL ROCKET ENGINES - ISBN: 9600-1980-4) and we have some doubts about the design that maybe could be answered with your help.

The rocket engine is a model that uses petrol and oxygen. The oxygen is feed from a pressurized vessel to the combustion chamber and the petrol from another pressurized one. The thing is that in the design nitrogen is used to pressurize the fuel tank, but we do not see why simply compressed air wouldn´t make it.

Using this engine scheme, would it be possible to use compressed air instead nitrogen to pressurize the fuel tank( 4 )?
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Thanks in advance for any help!
 

dhbarr

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STOP! That is a BLEVE waiting to hurt you!

In general we don't discuss research rocketry in the open forum.
 

Alvaro

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okey...I see, it´s quite possible that for that pressures putting air and fuel in a tank would result in an explosion...similar to what happens in a diesel motor, isn´t it?

BTW where would it be the correct place to discuss this kind of questions?

Thanks a lot!
 

Alvaro

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Okey! Thanks guys, but I am afraid I don´t comply with several of the requeriments...

Do you know any other forum where I can put and discuss questions like this?

Thanks again!
 

Eric

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What requirements are you missing? Are you able to comply with them?
 

Alvaro

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What requirements are you missing? Are you able to comply with them?
Well I´m afraid almost none:


1) NAR or TRA senior member - This is the first time apart from fireworks we are dealing with rockets.
2) US Person (US Citizen or US Permanent Resident (Green Card Holder)) - Neither US citizens nor green card holders
3) High Power Certification (Level 1, 2 or 3) - No certification at all.

So it seems we are not getting to the research forum... :(
 

OverTheTop

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Fuel + air = possible explosive mixture. That's why aircraft nowadays use nitrogen to purge the ullage space in fuel tanks. A few aircraft have been destroyed by fuel tanks exploding in the past. The suggestion of using it in the rocket engine I'm sure is for the same reason. Not such a problem as the fuel is flowing out, but if a blowback happens you have a possible detonation in the tank.
 

jqavins

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If you have something against nitrogen (I can't see why anyone would) then use carbon dioxide, helium, or argon, which are all readily available.
 

heada

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High pressure air is fairly easy to get but air has enough oxygen in it to be an oxidizer and so you don't want to use it to pressurize your fuel. If your fuel tank were to have a double bladder system such that the fuel and the gas used to pressurize the fuel were not to be to be mixed, then using compressed air would be viable. I would still use nitrogen or helium, both are easily obtainable just not at high pressures.
 
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