Self extinguishing hybrid.

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Joker050608

Joker050608

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Has anyone tried to make an extinguishing system for hybrid motors? I'm thinking about designing this to incorporate a 12oz Co2, braided steel micro line and an servo controlled micro "lightning" valve. This would be used with a magnetic apogee detector to.... Extinguish the motor grain.

Is this something that would fly for an RSO or make them frown upon the design?

Also if anyone has any input on optimizing this, that would be great.


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I noticed on a lot of hybrids that the grain continues to burn even after the tank is empty. Just want a way to keep everything from scorching or getting damaged.


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Joker050608 said:
I noticed on a lot of hybrids that the grain continues to burn even after the tank is empty. Just want a way to keep everything from scorching or getting damaged.


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Click to expand...

Makes sense, to introduce Co2 to remove any oxygen source and sufficate any residual burning. Personally, I do not believe that there is a real problem with scorching after motor burn out. I know that when I flew HyperTEK, the initial O2 ignition sequence would scorch the bottom of my rockets, but never at motor burnout. RATTWorks and Sky Ripper System (rest it's soul) products never burned my rockets either... I do not have experience with Contrail, but the videos I have witnessed have not raise any alarms.
 
The worst I've had (SRS 29, 38, 54 and RATT 29) was some soot on the bottom of the rocket and that could just as easily gotten there during start up as during tail off.

You would have to get the CO2 in up near the injector to do what you want. I can't think of any way of doing that without modifying the motor and that's a can of worms you don't want to open.
 
Well the motor itself was going to be of my own design. I want to have separate plumbing but only one point of injection for both gasses. I know it can be done but sure it would also have to be certified through NAR or tripoli before it is ever used.


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Joker050608 said:
Well the motor itself was going to be of my own design. I want to have separate plumbing but only one point of injection for both gasses. I know it can be done but sure it would also have to be certified through NAR or tripoli before it is ever used.

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Click to expand...

Once the Nitrous is gone there is very little oxygen left to burn any fuel that is still in the motor. Sure some can enter through the nozzle but not much if other combustion gasses are exiting.
The additional tankage, lines, valve and controls would require extra space in the rocket plus add weight with little or no added value.
OTOH I have thought for a long time that adding a small nitrogen tank and regulator to maintain a constant pressure in the nitrous tank would improve performance in large hybrid motors. Plus for your concern it would do the same as CO2 and eliminate the oxygen and extinguish the remaing fuel.
 
My design is going to be considered "self contained". Basically how the S'creamers worked. Although not great for long burn times with the small tanks I think if I go with their concept and modify it, I should have a functioning model if anything.
I would like to stick to using acrylic for the fuel grain because I have access to tons of it and I can make any size grain I want. Along with where the core shall be and what shape it should be in. Of course round is the easiest but I like to challenge myself sometimes. Even if it is impossible.
Also I will use braided steel micro line to run all the plumbing. There will be two separate tanks with two separate lines running into the booster section of the rocket. If there is a fire or other situation, the booster will be able to break away, leaving the tanks and electronics unharmed. Just need to figure out a good fail safe parachute deployment design to go along with it.


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If you're going to run a separate nitrous line, why not just install a solenoid in that line to cut off the nitrous flow?
 
billspad said:
If you're going to run a separate nitrous line, why not just install a solenoid in that line to cut off the nitrous flow?
Click to expand...

I'm having a hard time finding the micro line valve that can withstand the pressure from the nitrous tank. The one I have for the Co2 is a direct connection with a regulator that only goes up to 300 psi. The nitrous will be way above that. Somewhere around the 700-800 range.


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Um, look at the formula for CO2. There is plenty of oxygen there. If a fuel contains sufficient of the right metals and is hot enough then CO2 is a suitable oxidizer and the ISP isn't half bad. Most likely, hot 2(CO2) -> O2 + 2(CO) and then the O2 gets burned with the fuel providing enough heat to continue the reaction. The correct O:F ratio is a lot more critical than for N2O though as N2O is a monopropellant in its own right, being notably exothermic upon decomposition. N2, Argon, etc, would be better for motor blowdown.

https://www.sbir.gov/sbirsearch/detail/276324

Gerald
 
I'm familiar with the formulas and will be using a Co2 concentration similar to what is found in a fire extinguisher. The oxygen in such a concentration is quickly depleted. Although I am willing to try other gasses. Even thought about using compressed air @ 3000psi. Similar to a paintball tank with no regulator


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Fuel grains in a conventional hybrid do not contain an oxidizer so it will extinguished when you run out of nitrous. No oxidizer, no strong propulsive burning.

Some limited afterburning continues to occur in the blow down phase as the gaseous nitrous pressure in the tank bleeds down to zero, but this is a low energy release process compared with propulsive operation, and even after the nitrous is exhausted you still have a hot propellant grain in the motor so hot pyrolized gases can be generated and can burn outside the motor with ambient air. All rocket engines experience this type of after burning and it shouldn't be a problem in a properly built rocket.

Bob
 
Joker050608 said:
I'm familiar with the formulas and will be using a Co2 concentration similar to what is found in a fire extinguisher. The oxygen in such a concentration is quickly depleted. Although I am willing to try other gasses. Even thought about using compressed air @ 3000psi. Similar to a paintball tank with no regulator


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Click to expand...

What happens when you blow on a hot coal? Bad plan.

N2O is stable at room temperature - ie, not an oxidizer. Same with CO2. At sufficient temperature (perhaps 600C for N2O but it's exothermic so it will get hotter; 10% dissociation at 1 atmosphere for CO2 at 1500C, 90% dissociation at 2000C at 1 atmosphere), these molecules dissociate. N2O does so exothermically; CO2 endothermically. All it takes for CO2 to be burned as an oxidizer is for the combustion temperature to be high enough to trigger the dissociation and a fuel to burn in the resultant gasses which puts out enough heat to maintain or increase the temperature. Presence of any remaining other oxidizer will make this easier.

CO2 hybrids have been demonstrated.

Things which will put out a fire at low temperature may be a fuel or an oxidizer for a higher temperature flame. You don't put out a metal fire with water, for example. Water is an oxidizer under these conditions. (That is, not unless you can dump enough water fast enough to suck out the heat) Look up ALICE rocket motor.

Gerald
 
FWIW ALICE was considered to be a proof of concept for a CO2/Al or CO2/Mg rocket motor. Of course, things didn't work out so hot (ouch) for that plan, but not because of temperature limitations.
 
G_T said:
What happens when you blow on a hot coal? Bad plan.

N2O is stable at room temperature - ie, not an oxidizer. Same with CO2. At sufficient temperature (perhaps 600C for N2O but it's exothermic so it will get hotter; 10% dissociation at 1 atmosphere for CO2 at 1500C, 90% dissociation at 2000C at 1 atmosphere), these molecules dissociate. N2O does so exothermically; CO2 endothermically. All it takes for CO2 to be burned as an oxidizer is for the combustion temperature to be high enough to trigger the dissociation and a fuel to burn in the resultant gasses which puts out enough heat to maintain or increase the temperature. Presence of any remaining other oxidizer will make this easier.

CO2 hybrids have been demonstrated.

Things which will put out a fire at low temperature may be a fuel or an oxidizer for a higher temperature flame. You don't put out a metal fire with water, for example. Water is an oxidizer under these conditions. (That is, not unless you can dump enough water fast enough to suck out the heat) Look up ALICE rocket motor.

Gerald
Click to expand...

Honestly this here had slipped my mind when drawing it up. I never bothered to think of the grain temp and take into account the atmosphere I might have to re think this whole thing here.


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