Hybrid oxidiser system HELP?!?

[dhbarr]

As I have only ever handled medical grade like cylinder during my GOX/paraffin static fires, could you clarify what you mean by siphon tube?

All this help is much appreciated guys.

Pic is for CO2, but the concept's the same.

 

[jjrgray]

Okay so I either need to invert the fill cylinder or get one with a siphon/dip tube? I was hunting around for a nitrous fill cylinder, is the most commonly used type the ones for drag racing due to their siphon/dip tube?

 

[rocket_troy]

Yes, because (as you can imagine) inverting a cylinder requires some kind of stand (or at least a mounting pole) and accessing the valve wheel/handle is much easier done in the upright pos.

TP

 

[AeroTech]

A lot of information on N2O hybrids is posted here:

http://www.aerotech-rocketry.com/cu...tructions/RMS-Hybrid/54mm_hyb_in_man_6-98.pdf
AeroTech produced the first certified hybrid rocket motor system for consumer use in 1995. It is a sealed system as opposed to a vented system. They are no longer commercially manufactured but all documentation is available on the RCS website here:

https://www.rocketmotorparts.com/RMSHybrid_Data_Pack/p1577809_16042498.aspx
The “Pyrovalve” oxidizer control and ignition system was patented but the patent expired a number of years ago. You can find it here:

http://www.aerotech-rocketry.com/uploads/6eeae0f9-2526-45be-86bd-d132c28d6629_pyrovalve_5579636.pdf
They are still occasionally being flown at launches. I saw two of them flown at AirFest last year.

 

[jjrgray]

Yes, because (as you can imagine) inverting a cylinder requires some kind of stand (or at least a mounting pole) and accessing the valve wheel/handle is much easier done in the upright pos.

TP

So would you say that the drag racing bottles are the best way to go?

 

[rocket_troy]

If they're large enough for your flight/fill needs, then sure. That would be my recommendation at this point.

TP

 

[jjrgray]

If they're large enough for your flight/fill needs, then sure. That would be my recommendation at this point.

TP

Okay thanks for all your help mate, it's been invaluable.

 

[jjrgray]

A lot of information on N2O hybrids is posted here:

http://www.aerotech-rocketry.com/cu...tructions/RMS-Hybrid/54mm_hyb_in_man_6-98.pdf
AeroTech produced the first certified hybrid rocket motor system for consumer use in 1995. It is a sealed system as opposed to a vented system. They are no longer commercially manufactured but all documentation is available on the RCS website here:

https://www.rocketmotorparts.com/RMSHybrid_Data_Pack/p1577809_16042498.aspx
The “Pyrovalve” oxidizer control and ignition system was patented but the patent expired a number of years ago. You can find it here:

http://www.aerotech-rocketry.com/uploads/6eeae0f9-2526-45be-86bd-d132c28d6629_pyrovalve_5579636.pdf
They are still occasionally being flown at launches. I saw two of them flown at AirFest last year.

Thanks for the link, I've had a quick look and it will be of much help I am sure. Concerning pyrovalves, is any company producing them currently?

 

[cwbullet]

This is a fascinating topic. Paraffin and plastrics are common fuels. Well documented in international papers on the topics.

 

[jjrgray]

This is a fascinating topic. Paraffin and plastrics are common fuels. Well documented in international papers on the topics.

I'll be sure to look at those papers for fuel mixes/ratios. Don't want to cause any legal issues for TRF. Thanks for the tips!

 

[cwbullet]

I'll be sure to look at those papers for fuel mixes/ratios. Don't want to cause any legal issues for TRF. Thanks for the tips!

You have not done anything yet. I was just confirming that there are some out there.

https://www.sciencedirect.com/science/article/abs/pii/S0094576516302818
https://aura.alfred.edu/handle/10829/7457

 

[G_T]

It's in the Research forum, but I have a thread with a great deal of info on my designing, building, and static testing, a chilled nitrous hybrid: https://www.rocketryforum.com/threads/thrp-1-an-ex-hybrid-project.139372/

Gerald

 

[jjrgray]

It's in the Research forum, but I have a thread with a great deal of info on my designing, building, and static testing, a chilled nitrous hybrid: https://www.rocketryforum.com/threads/thrp-1-an-ex-hybrid-project.139372/

Gerald

Unfortunately as I am not a US citizen (I live in the UK) I cannot access the research forum . Thanks for your suggestion anyways.

 

[jjrgray]

https://aeroconsystems.com/cart/pressure-vessels/aluminum-pressure-vessel/

Does anybody have any thoughts on this? Would it be good enough to use as an engine tank for nitrous oxide? Apparently it is rated up to 1200 psi.

 

[heada]

Look at Rattworks, Alpha Hybrids (no longer in production?) and Skyripper (no longer in production for several years). They're monotube hybrids using a U-C injector (or similar) between a lower combustion chamber and an upper internal NO2 tank. They're standard 6061 Al tubes with a forward bulked acting as the top of the NO2 tank, a floating injector bulkhead that separates the NO2 tank from the combustion chamber and a nozzle (phenolic or graphite). Wide range if fuels and charged with NO2 at the pad so that you don't need high pressure tanks.

 

[jjrgray]

Look at Rattworks, Alpha Hybrids (no longer in production?) and Skyripper (no longer in production for several years). They're monotube hybrids using a U-C injector (or similar) between a lower combustion chamber and an upper internal NO2 tank. They're standard 6061 Al tubes with a forward bulked acting as the top of the NO2 tank, a floating injector bulkhead that separates the NO2 tank from the combustion chamber and a nozzle (phenolic or graphite). Wide range if fuels and charged with NO2 at the pad so that you don't need high pressure tanks.

Thanks man, I'll be sure to take a look at those designs. What do you mean by not needing high pressure tanks if it's charged with N2O on the pad?

 

[heada]

The monotube design is filled at the pad and so only is exposed to the pressure of your ground tank, normally less than 950psi if I remember correctly. The forward bulkhead is vented in a monotube design to allow for air to escape during fill and to give visual indication that the tank is full so there is no need for a high pressure tank like you showed.

If you wanted to use a pre-charged hybrid, then you'd need a separate oxidizer tank similar to what you showed. That was one of the reasons that monotube designs were more popular when hybrids were more in use.

 

[jjrgray]

The monotube design is filled at the pad and so only is exposed to the pressure of your ground tank, normally less than 950psi if I remember correctly. The forward bulkhead is vented in a monotube design to allow for air to escape during fill and to give visual indication that the tank is full so there is no need for a high pressure tank like you showed.

If you wanted to use a pre-charged hybrid, then you'd need a separate oxidizer tank similar to what you showed. That was one of the reasons that monotube designs were more popular when hybrids were more in use.

I'm not using a monotube design. The oxidiser tank will be a fair bit above the combustion chamber in the rocket's fuselage. However could you explain to me how you would still maintain pressure in the 'bulkheads' if it was being vented? I am quite sure this is an idiotic question but its been on my mind for quite a long time . Sorry for all the questions, keen to learn.

 

[heada]

Fill tube is 3mm to 6mm but the vent is at max 2mm. Pressure in the ground tank pushes liquid nitrous up into the oxidizer tank section and gas vents through the small vent hole. Once all the gas is vented, it is replaced by venting liquid nitrous. That is the sign to close the fill valve and fire the motor. The oxidizer flight tank never sees any pressure above the pressure of the liquid nitrous and is constantly venting so it can't build up pressure beyond what the ground supply tank can provide.

I understand you're not using a monotube design but they some of the easiest to design and use.

 

[Voyager1]

So would you say that the drag racing bottles are the best way to go?

Yes. I normally use a DE cylinder of engine grade nitrous from a local gas supplier. The D size bottle holds about 7kg of nitrous. The E refers to the fact that it has an extractor tube installed.

My Contrail hybrid motors typically use from about 350 to 1400 ml of nitrous, so there is generally enough for quite a few flights. You do lose a little when the bottle is nearly empty, because of the extractor tube.

I basically rent the bottle and just get it replaced when empty. You can get your own bottle and have it filled, but you do need to have it pressure tested.

 

[jjrgray]

Yes. I normally use a DE cylinder of engine grade nitrous from a local gas supplier. The D size bottle holds about 7kg of nitrous. The E refers to the fact that it has an extractor tube installed.

My Contrail hybrid motors typically use from about 350 to 1400 ml of nitrous, so there is generally enough for quite a few flights. You do lose a little when the bottle is nearly empty, because of the extractor tube.

I basically rent the bottle and just get it replaced when empty. You can get your own bottle and have it filled, but you do need to have it pressure tested.

Okay, good to know, thanks very much dude.

 

[jjrgray]

Fill tube is 3mm to 6mm but the vent is at max 2mm. Pressure in the ground tank pushes liquid nitrous up into the oxidizer tank section and gas vents through the small vent hole. Once all the gas is vented, it is replaced by venting liquid nitrous. That is the sign to close the fill valve and fire the motor. The oxidizer flight tank never sees any pressure above the pressure of the liquid nitrous and is constantly venting so it can't build up pressure beyond what the ground supply tank can provide.

I understand you're not using a monotube design but they some of the easiest to design and use.

Thanks for walking me through that, and I completely agree with you monotube designs are definitely one of the easiest types to design and use and if I could start all over again I would go down the monotube route, however I am stuck with what I've got and I'm just trying to work it not ditch it.

 

[AeroTech]

Thanks for the link, I've had a quick look and it will be of much help I am sure. Concerning pyrovalves, is any company producing them currently?

Not currently. A customer produced a small quantity for us for testing. The can be made from pressed black powder motors if you are very careful. That’s how we tested our first hybrid prototypes in 1994.

 

[dhbarr]

Thanks for the link, I've had a quick look and it will be of much help I am sure. Concerning pyrovalves, is any company producing them currently?

https://www.rocketmotorparts.com/RMSHybrid_Data_Pack/p1577809_16042498.aspx contains several drawings which would be useful for constructing a pyrovalve in the Aerotech style ( puck of compressed black powder, ptfe membrane ).

 

[jjrgray]

https://www.rocketmotorparts.com/RMSHybrid_Data_Pack/p1577809_16042498.aspx contains several drawings which would be useful for constructing a pyrovalve in the Aerotech style ( puck of compressed black powder, ptfe membrane ).

If I were to use an Aerotech style pyrovalve, what would the ignition system for the fuel grain look like? Would it be similar to the preheater solid propellant found in a U-C injector design?

 

[rocket_troy]

Generally, the pyro valve is the preheater. Like a U/C concept, it elegantly serves multiple purposes avoiding the need for additional mechanical parts and whatnot.

TP

 

[jjrgray]

Generally, the pyro valve is the preheater. Like a U/C concept, it elegantly serves multiple purposes avoiding the need for additional mechanical parts and whatnot.

TP

How would this work if I had a showerhead injector plate in between where I want to put the pyrovalve (in the end of the injector) and the fuel grain I want to ignite?

 

[kozuch]

This liquid nitrous oxide thing is very interesting! Thumbs up for letting the liquid N2O out from the gas cylinder via siphon tube or upside down!

However Ive got few questions. N2O gas cylinder has a pressure of 50 bars at 20C. What exactly happens to the liquid once it is out of the cylinder and has normal atmospheric pressure? Its boiling temperature at 1 bar is about -88C so I guess it will start start boiling violently? How fast does it boil/vaporize? Will it last longer (=vaporize slower) if you cool the cylinder down to -78C with dry ice before draining? N2O vapor pressure at -78C is about 2 bar.

I guess there are ways to run hybrid motors either with pressurized or unpressurized N2O? I saw the monotube motor diagram (cant find link now) and the N2O tank has a ventilation hole which means it is unpressurized. So the rocket logically has to stand upside down so that the oxidizer will not pour out. So do these monotubes have a gravity fed oxidizer system? Sorry I am not a rocketeer, just interested in the tech...

 

[jderimig]

This liquid nitrous oxide thing is very interesting! Thumbs up for letting the liquid N2O out from the gas cylinder via siphon tube or upside down!

However Ive got few questions. N2O gas cylinder has a pressure of 50 bars at 20C. What exactly happens to the liquid once it is out of the cylinder and has normal atmospheric pressure? Its boiling temperature at 1 bar is about -88C so I guess it will start start boiling violently? How fast does it boil/vaporize? Will it last longer (=vaporize slower) if you cool the cylinder down to -78C with dry ice before draining? N2O vapor pressure at -78C is about 2 bar.

I guess there are ways to run hybrid motors either with pressurized or unpressurized N2O? I saw the monotube motor diagram (cant find link now) and the N2O tank has a ventilation hole which means it is unpressurized. So the rocket logically has to stand upside down so that the oxidizer will not pour out. So do these monotubes have a gravity fed oxidizer system? Sorry I am not a rocketeer, just interested in the tech...

The N2O in a hybrid motor never sees atmospheric pressure (except right at ignition). When the motor is filled from the supply cylinder the motor tank is in equilibrium pressure with the supply cylinder. When fired the N2O expands into the combustion chamber while the N2O is changing its phase from liquid to gas, quickly.

 

[kozuch]

You typically have a vent orifice (tiny hole) at the top of your tank to let gaseous N2O to vent.

Does such vent orifice prevent the tank from reaching atmospheric pressure? Is the hole really very tiny? This does not make a lot of sense to me... looks like even the tiniest hole would bring the fuel tank to normal pressure quite fast.