Comments on: Chilled “Fizzy” Propellants for Vapor Pressurized Rockets http://selenianboondocks.com/2009/05/chilled-fizzy-propellants-for-vapor-pressurized-rockets/ Random Musings from the Warped Minds of Jonathan Goff, Ken Murphy, John Hare, and Kirk Sorensen Thu, 26 Jan 2012 21:26:05 +0000 hourly 1 http://wordpress.org/?v=3.3.1 By: Jonathan Goff http://selenianboondocks.com/2009/05/chilled-fizzy-propellants-for-vapor-pressurized-rockets/comment-page-1/#comment-4711 Jonathan Goff Sat, 16 May 2009 20:16:06 +0000 http://selenianboondocks.com/?p=991#comment-4711 Dan, Yeah, having never tried a system like that for real, I don't know what all the complexities end up being. That said, protoflight had both propellants at saturation I think, and they had several runs whose pressure traces were flat enough to eat off of. Not sure what they did to deal with those potential instability issues. I do know they used a pintle-injector, but that wouldn't solve feed-system instabilities... ~Jon Dan,
Yeah, having never tried a system like that for real, I don’t know what all the complexities end up being. That said, protoflight had both propellants at saturation I think, and they had several runs whose pressure traces were flat enough to eat off of. Not sure what they did to deal with those potential instability issues. I do know they used a pintle-injector, but that wouldn’t solve feed-system instabilities…

~Jon

]]> By: Dan Moser http://selenianboondocks.com/2009/05/chilled-fizzy-propellants-for-vapor-pressurized-rockets/comment-page-1/#comment-4710 Dan Moser Sat, 16 May 2009 20:07:29 +0000 http://selenianboondocks.com/?p=991#comment-4710 Bruno hit on a key issue: pressure drops in plumbing cause 2-phase flow which can cause serious flow rate fluctuations. Truax told me once that having one propellant in a near-saturated state should be OK, with proper precautions taken, but that having both propellants saturated causes flow stability problems. He didn't elaborate or provide back up data, so take it for what it's worth. My current system concepts, AVOx and ECPS, both attempt to use vapor pressurization with heat exchange between fluids so as to feed them through the plumbing & injector at sub-saturated conditions. Bruno hit on a key issue: pressure drops in plumbing cause 2-phase flow which can cause serious flow rate fluctuations. Truax told me once that having one propellant in a near-saturated state should be OK, with proper precautions taken, but that having both propellants saturated causes flow stability problems. He didn’t elaborate or provide back up data, so take it for what it’s worth. My current system concepts, AVOx and ECPS, both attempt to use vapor pressurization with heat exchange between fluids so as to feed them through the plumbing & injector at sub-saturated conditions.

]]> By: Jonathan Goff http://selenianboondocks.com/2009/05/chilled-fizzy-propellants-for-vapor-pressurized-rockets/comment-page-1/#comment-4709 Jonathan Goff Sat, 16 May 2009 17:14:32 +0000 http://selenianboondocks.com/?p=991#comment-4709 Bruno, Yeah, I wouldn't take it all the way down to -80C. -60C at the most, and -40C would be better. Fluorosilicone gives you most of the benefits of silicone while being oxidizer compatible... Anyhow, it'd be interesting to try the stuff. ~Jon Bruno,
Yeah, I wouldn’t take it all the way down to -80C. -60C at the most, and -40C would be better. Fluorosilicone gives you most of the benefits of silicone while being oxidizer compatible…

Anyhow, it’d be interesting to try the stuff.

~Jon

]]> By: anon http://selenianboondocks.com/2009/05/chilled-fizzy-propellants-for-vapor-pressurized-rockets/comment-page-1/#comment-4708 anon Sat, 16 May 2009 16:38:13 +0000 http://selenianboondocks.com/?p=991#comment-4708 "The fact that oxygen comes out preferentially in the vapor acts as a stabilizer against vapor phase detonation events. Unlike nitrous, oxygen won’t exothermically decompose if heated, so it acts like a heat sponge. Theoretically you need 10,000x as much energy to initiate a detonation in a oxygen/nitrous vapor compared to pure nitrous." Do you have test data on this, or was this a chemical sim? “The fact that oxygen comes out preferentially in the vapor acts as a stabilizer against vapor phase detonation events. Unlike nitrous, oxygen won’t exothermically decompose if heated, so it acts like a heat sponge. Theoretically you need 10,000x as much energy to initiate a detonation in a oxygen/nitrous vapor compared to pure nitrous.”

Do you have test data on this, or was this a chemical sim?

]]> By: Bruno Berger http://selenianboondocks.com/2009/05/chilled-fizzy-propellants-for-vapor-pressurized-rockets/comment-page-1/#comment-4707 Bruno Berger Sat, 16 May 2009 07:35:48 +0000 http://selenianboondocks.com/?p=991#comment-4707 We did that once a while back. The idea wasn't to get a high density propellant, the idea was to get a subcooled oxidizer which isn't at it's saturated point and therefore doesn't form bubbles at the slightest pressure drop (preventing "water hammering" effects). This was at ambient temperature (this was about 10 °C at that time) and pressurized it with nitrogen and later with oxygen to about 60 bar. As a nice side effect (We didn't knew that then) SPG showed with their great research work, that diluting the vapor phase with something else like helium, nitrogen or oxygen makes it more or less immune to vapor phase detonation. I think cooling it down to -80 °C makes it very unhandy. Imagine you have your rocket or VTOL vehicle sitting on the pad and the sun shines on it. With the cheap LOX you just vent it and so it keeps its temperature. You can't do that with Nytrox because you will loose the O2 fist (without much cooling effect because the N2O is still not at its vapor pressure). Cooling down to -80 °C isn't something you can do with a "fridge-like" aperture (maybe I am wrong, what is the lowest temp you can reach with a compressor fridge and a suitable coolant?). But I see a nice application for planetary missions (GLXP for example) where you probably can sustain the temperature without much effort, combined with blended fuel like propane/methane or ethane/methane. Just a hint about o-rings: Viton (and other brands) is chemical compatible, but not physically... it swells when exposed to N2O for a longer period. Our sealant supplier recommended silicone o-rings to us. The chemical compatibility isn't perfect though. Bruno We did that once a while back. The idea wasn’t to get a high density propellant, the idea was to get a subcooled oxidizer which isn’t at it’s saturated point and therefore doesn’t form bubbles at the slightest pressure drop (preventing “water hammering” effects). This was at ambient temperature (this was about 10 °C at that time) and pressurized it with nitrogen and later with oxygen to about 60 bar. As a nice side effect (We didn’t knew that then) SPG showed with their great research work, that diluting the vapor phase with something else like helium, nitrogen or oxygen makes it more or less immune to vapor phase detonation.

I think cooling it down to -80 °C makes it very unhandy. Imagine you have your rocket or VTOL vehicle sitting on the pad and the sun shines on it. With the cheap LOX you just vent it and so it keeps its temperature. You can’t do that with Nytrox because you will loose the O2 fist (without much cooling effect because the N2O is still not at its vapor pressure). Cooling down to -80 °C isn’t something you can do with a “fridge-like” aperture (maybe I am wrong, what is the lowest temp you can reach with a compressor fridge and a suitable coolant?).
But I see a nice application for planetary missions (GLXP for example) where you probably can sustain the temperature without much effort, combined with blended fuel like propane/methane or ethane/methane.
Just a hint about o-rings: Viton (and other brands) is chemical compatible, but not physically… it swells when exposed to N2O for a longer period. Our sealant supplier recommended silicone o-rings to us. The chemical compatibility isn’t perfect though.

Bruno

]]> By: Dan Moser http://selenianboondocks.com/2009/05/chilled-fizzy-propellants-for-vapor-pressurized-rockets/comment-page-1/#comment-4706 Dan Moser Sat, 16 May 2009 06:20:41 +0000 http://selenianboondocks.com/?p=991#comment-4706 Nytrox seems like an innovative VaPak choice. In the 60s Aerojet reportedly had some success with N2H4/NH3 fuel and N2O4/NO oxidizer blends, some seriously nasty stuff.. a classic trade off between higher performance cryogens and moderate performance mild cryogens. CH4/H2 "Mythrogen" fuel blends take that to an extreme. I used C3H8/C2H6 mixtures with H2O2 on the Comp-L system tests years ago. The blended fuel feed system worked fine, but we ended up going to all ethane anyway. You might want to investigate propylene or Dimethyl ether fuels. Nytrox seems like an innovative VaPak choice. In the 60s Aerojet reportedly had some success with N2H4/NH3 fuel and N2O4/NO oxidizer blends, some seriously nasty stuff.. a classic trade off between higher performance cryogens and moderate performance mild cryogens. CH4/H2 “Mythrogen” fuel blends take that to an extreme. I used C3H8/C2H6 mixtures with H2O2 on the Comp-L system tests years ago. The blended fuel feed system worked fine, but we ended up going to all ethane anyway. You might want to investigate propylene or Dimethyl ether fuels.

]]> By: Randy Campbell http://selenianboondocks.com/2009/05/chilled-fizzy-propellants-for-vapor-pressurized-rockets/comment-page-1/#comment-4704 Randy Campbell Fri, 15 May 2009 19:14:57 +0000 http://selenianboondocks.com/?p=991#comment-4704 Jon, and all ; SPG caught my interest a bit ago as the are the company that is commercializing the paraffin hybrid booster technology. I suspect this is going to fold into that concept. I'd originally heard of the concept they are working with from Dr. Bruc Dunn's site: http://www.dunnspace.com/index.htm Under "Low Cost Rockets" it has the information on his initial work on the concept: http://www.dunnspace.com/self_pressurized_rockets.htm While he was working on the assumption of upper-stage engines, for the longest time (since I couldn't find any actual information on the process :o) I was under that assumption that VPAK WAS this concept! Now that VPAK has been explained to me in simple terms, (by the Jon... just an FYI but some of us with ADOS or ADD can't STAND twitter so I don't suspect I'll visit much, though I recall my wife said the same thing about Facebook and she's got a page there now so....) I see the differences and this concept looks very interesting. Both for hybrid oxidizers and full-up liquid propellants. Thanks for point it out. (Oh and as to Eric question on the vapor pressure the Dunn page details how that works very well :o) Randy Jon, and all ;

SPG caught my interest a bit ago as the are the company that is commercializing the paraffin hybrid booster technology. I suspect this is going to fold into that concept. I’d originally heard of the concept they are working with from Dr. Bruc Dunn’s site:
http://www.dunnspace.com/index.htm

Under “Low Cost Rockets” it has the information on his initial work on the concept:
http://www.dunnspace.com/self_pressurized_rockets.htm

While he was working on the assumption of upper-stage engines, for the longest time (since I couldn’t find any actual information on the process :o ) I was under that assumption that VPAK WAS this concept! Now that VPAK has been explained to me in simple terms, (by the Jon… just an FYI but some of us with ADOS or ADD can’t STAND twitter so I don’t suspect I’ll visit much, though I recall my wife said the same thing about Facebook and she’s got a page there now so….) I see the differences and this concept looks very interesting. Both for hybrid oxidizers and full-up liquid propellants. Thanks for point it out.
(Oh and as to Eric question on the vapor pressure the Dunn page details how that works very well :o )

Randy

]]> By: Jonathan Goff http://selenianboondocks.com/2009/05/chilled-fizzy-propellants-for-vapor-pressurized-rockets/comment-page-1/#comment-4703 Jonathan Goff Fri, 15 May 2009 15:05:47 +0000 http://selenianboondocks.com/?p=991#comment-4703 Tim, As with all Vapak systems, as the propellant is forced out of the tank, a small bit of it vaporizes, keeping the vapor pressure nearly constant. In this case, most of the vapor boiling off will be oxygen. So yes, towards the end of the run, the liquid flowing out of the tank will have less and less oxygen, but the vapor left in the tank will have more and more oxygen (which keeps the pressure up). I'm not sure, but I think that the vapor composition actually ends up being relatively constant. But I could be wrong. It definitely will be a mix of vapors. You'd need to run a subscale test a few times to verify how consistent it would be, but my understanding is, it should be consistent. ~Jon Tim,
As with all Vapak systems, as the propellant is forced out of the tank, a small bit of it vaporizes, keeping the vapor pressure nearly constant. In this case, most of the vapor boiling off will be oxygen. So yes, towards the end of the run, the liquid flowing out of the tank will have less and less oxygen, but the vapor left in the tank will have more and more oxygen (which keeps the pressure up).

I’m not sure, but I think that the vapor composition actually ends up being relatively constant. But I could be wrong. It definitely will be a mix of vapors. You’d need to run a subscale test a few times to verify how consistent it would be, but my understanding is, it should be consistent.

~Jon

]]> By: Tim http://selenianboondocks.com/2009/05/chilled-fizzy-propellants-for-vapor-pressurized-rockets/comment-page-1/#comment-4702 Tim Fri, 15 May 2009 06:58:22 +0000 http://selenianboondocks.com/?p=991#comment-4702 Given that the gas phase of contains a greater amount of oxygen than the liquid phase (and I assume something similar would happen with a propane/methane mix), won't the oxygen be used up before the nitrous? Would this mean you would lose vapour pressure as the tanks empty? If the pressurant fuel/oxidiser does vary and isn't completely used up by the time you want to use the RCS, I would imagine the variable (and proably uncertain) propellant mixture would create some tricky control issues. Given that the gas phase of contains a greater amount of oxygen than the liquid phase (and I assume something similar would happen with a propane/methane mix), won’t the oxygen be used up before the nitrous? Would this mean you would lose vapour pressure as the tanks empty? If the pressurant fuel/oxidiser does vary and isn’t completely used up by the time you want to use the RCS, I would imagine the variable (and proably uncertain) propellant mixture would create some tricky control issues.

]]> By: Jonathan Goff http://selenianboondocks.com/2009/05/chilled-fizzy-propellants-for-vapor-pressurized-rockets/comment-page-1/#comment-4701 Jonathan Goff Thu, 14 May 2009 15:18:32 +0000 http://selenianboondocks.com/?p=991#comment-4701 Eric, Taking you questions in order: 1-Not sure. I imagine SPG has been doing a fair amount of experimentation, but I don't know how thorough they've been so far. 2-I would think it would be pretty simple. You'd have some similar parts, but there would be many you could leave out. My guess is that you'd only really need a prevalve, and a relief valve per branch, and then the on-engine solenoids. Compare that with accumulators, regulators, gas lines, valves, filters, pressurant fill plumbing, etc... 3-Yes, composites give you a lot more freedom in shaping your vehicle. Typically, for shapes that can be fillament wound, there is little to no penalty for taking the shape and aspect ratio you want. Admittedly, for the use I was thinking of, mostly plain-jane cylinders with elliptical heads would be fine for the most part. But if you needed to do say a conical tank, composites would make it easier to do so. ~Jon Eric,
Taking you questions in order:
1-Not sure. I imagine SPG has been doing a fair amount of experimentation, but I don’t know how thorough they’ve been so far.

2-I would think it would be pretty simple. You’d have some similar parts, but there would be many you could leave out. My guess is that you’d only really need a prevalve, and a relief valve per branch, and then the on-engine solenoids. Compare that with accumulators, regulators, gas lines, valves, filters, pressurant fill plumbing, etc…

3-Yes, composites give you a lot more freedom in shaping your vehicle. Typically, for shapes that can be fillament wound, there is little to no penalty for taking the shape and aspect ratio you want. Admittedly, for the use I was thinking of, mostly plain-jane cylinders with elliptical heads would be fine for the most part. But if you needed to do say a conical tank, composites would make it easier to do so.

~Jon

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