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Space Forum / Space Flight / December 2003Peroxide biprop ignition
Some methods I've seen mentioned for peroxide biprop ignition are: Decompose the peroxide with catalyst pack. Pyrotechnic igniter in the chamber. Dissolve catalyst in fuel. Hypergolic starting slug in fuel feed line. How about mixing some liquid catalyst into the peroxide feed for a few seconds until there is stable self-sustaining combustion in the chamber? Liquid catalysts for monoprops have been abandoned in favor of catalyst packs for good reasons but they seem to have some desirable properties for biprop ignition: Usable with high concentration peroxide. Can be used with strongly stabilized peroxide. No hazardous materials. Restartable and reusable. The catalyst is mixed into the peroxide just before injection into the chamber. This cannot be done safely with a fuel but catalytic decomposition is slow enought to give some time for mixing. The injector is optimized for operation with uncatalysed peroxide. It may not perform optimally with the mixed-phase decomposing peroxide; it just needs to be good enough for the ignition phase. The injector and mixing chamber are flushed of any residues by ample amounts of peroxide (except on some emergency shutdowns) so the catalyst should not contaminate the upstream oxidizer lines . Oren >How about mixing some liquid catalyst into the peroxide feed for a few >seconds until there is stable self-sustaining combustion in the >chamber? This is a minor variant of the "hypergolic starting slug" approach. > No hazardous materials. Depends on what catalyst you're using. Even permanganates are not exactly mother's milk, and things like TEA are definitely hazardous. > Restartable and reusable. Subject to the need for yet another fluid system, with the added complexity that entails. >The catalyst is mixed into the peroxide just before injection into the >chamber. This cannot be done safely with a fuel but catalytic >decomposition is slow enought to give some time for mixing. I have real doubts about that part of the idea. Catalystic decomposition will not be slow with high-concentration peroxide and an effective liquid catalyst mixed well together. Mixing *in* the chamber sounds both better and safer.  SignatureMOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer pointing, 10 Sept; first science, early Oct; all well. | henry@spsystems.net >> Restartable and reusable. > [quoted text clipped - 9 lines] > catalyst mixed well together. Mixing *in* the chamber sounds both better > and safer. Once the rocket is firing, is it possible to use non catalysed HTP? >> I have real doubts about that part of the idea. Catalystic decomposition >> will not be slow with high-concentration peroxide and an effective liquid >> catalyst mixed well together. Mixing *in* the chamber sounds both better >> and safer. > >Once the rocket is firing, is it possible to use non catalysed HTP? Yes, definitely. As with any propellant combination, once it's lit it will generally stay lit, modulo combustion-stability issues. People have built rocket engines using peroxide as oxidizer with no catalyst at all, just a conventional ignition system. SignatureMOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer pointing, 10 Sept; first science, early Oct; all well. | henry@spsystems.net >>>I have real doubts about that part of the idea. Catalystic decomposition >>>will not be slow with high-concentration peroxide and an effective liquid [quoted text clipped - 7 lines] > built rocket engines using peroxide as oxidizer with no catalyst at all, > just a conventional ignition system. Thanks Henry. I'm one step closer :-) Julian <<Catalystic decomposition > will not be slow with high-concentration peroxide and an effective liquid > catalyst mixed well together. >> I've only heard of solid catalyst beds. What's a [non-exotic] liquid catalyst for HTP, [High Test Peroxide over 85% pure]? ^ //^\\ ~~~ near space elevator ~~~~ ~~~members.aol.com/beanstalkr/~~~ > Some methods I've seen mentioned for peroxide biprop ignition are: > [quoted text clipped - 13 lines] > No hazardous materials. > Restartable and reusable. It could probably work, but I think you overstate the case for it. Various platinum based catalysts will work fine with 98% peroxide, it is only the classic silver ones that have issues. The commercial catalysts we are using for our mixed-monoprop engines would work fine with 98%, for instance. High concentration and highly stabilized is really only a condition that happens at the amateur experimental stage where people are concentrating cheap peroxide on bench level equipment in small batches. Anything resembling a commercial rocket is almost certainly going to be using unstabilized peroxide. Adding a third consumable and the associated plumbing is a non-trivial increase in system complexity. We have only done a few tests with liquid catalysts, but we have had much better success with solid catalyst packs. Compared to almost any other biprop, cat-pack decomposition auto-ignition biprops are really easy to make work at good efficiencies. John Carmack www.armadilloaerospace.com >High concentration and highly stabilized is really only a condition >that happens at the amateur experimental stage where people are >concentrating cheap peroxide on bench level equipment in small >batches. Anything resembling a commercial rocket is almost certainly >going to be using unstabilized peroxide. Why is this so may I ask? D. SignatureThe STS-107 Columbia Loss FAQ can be found at the following URLs: Text-Only Version: http://www.io.com/~o_m/columbia_loss_faq.html Enhanced HTML Version: http://www.io.com/~o_m/columbia_loss_faq_x.html Corrections, comments, and additions should be e-mailed to om@io.com, as well as posted to sci.space.history and sci.space.shuttle for discussion. >>High concentration and highly stabilized is really only a condition >>that happens at the amateur experimental stage where people are [quoted text clipped - 3 lines] > >Why is this so may I ask? A commercial rocket is going to be using peroxide in sufficient quantity to get reasonable cooperation from peroxide suppliers (from new ones created to serve it, if not from existing ones). So it will have access to high-concentration peroxide that is either unstabilized or, at worst, lightly stabilized. Whereas amateurs have to work with existing peroxide suppliers, who are unhelpful (to put it mildly). So they are likely to have to do their own concentrating, and most of the easy bench-scale processes concentrate stabilizers as well as peroxide. Back when Beal was a going concern, buying high-concentration unstabilized peroxide in quantity and gearing up to buy it in QUANTITY, for a little while amateurs could piggyback on that new peroxide infrastructure and buy small amounts of rocket-grade peroxide without much difficulty. Not any more, as John can tell you at some length. SignatureMOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer pointing, 10 Sept; first science, early Oct; all well. | henry@spsystems.net Thanks Henry, John. All else being equal, would you not prefer your 98% peroxide stabilized? After all, stabilizers are not added by manufacturers to make life harder for rocket builders. They are supposed to make peroxide safer. You've explained why all else is not exactly equal but the bottom line is a tradeoff between complexity perceived safety. Such perceptions are not an exact science and are liable to change quickly on certain circumstances. Oren >All else being equal, would you not prefer your 98% peroxide >stabilized? After all, stabilizers are not added by manufacturers to >make life harder for rocket builders. They are supposed to make >peroxide safer. It's actually more a matter of making it less prone to deteriorate due to contamination, and giving it a longer shelf life. I can't speak for John, but if I were doing peroxide rocketry, I'd be willing to accept constraints like a short shelf life and a need to be fussy about cleanliness, in return for less hassle with catalyst poisoning etc. All else being equal, yes, I'd be happier with *lightly* stabilized peroxide using stabilizers compatible with my catalysts. (There is some choice about just which stabilizers are used, and if you're buying in bulk, you should have some voice in that decision.) The less fussy I have to be about procedural details like cleaning and shelf life, the more time and effort I can spend on design and development problems. But there are a lot of assumptions in that (e.g, *are* there such stabilizers?) and just getting it unstabilized might well be less hassle all around. SignatureMOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer pointing, 10 Sept; first science, early Oct; all well. | henry@spsystems.net |
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