If seeking the same moderate pressure and performance, a hydrogen staged combustion cycle is simpler (drawing) than a gas generator cycle.A single stage hydrogen pump after the (not represented) 20b booster pump achieves 123b in the pre-chamber, and the smaller pumping power leaves 103b in the main chamber, which gives the same performance as a gas generator cycle.The hot gas' maximum expansion speed can be shared as 691m/s and 421m/s in the single-stage turbines that power pumps with 528m/s and 141m/s tip speed.Marc Schaefer, aka Enthalpy
Please remember I'm no chemist, so better advice is necessary before any attempt.Marc Schaefer, aka Enthalpy
Quote from: Enthalpy on 10/04/2011 05:40 pmThe amines I cite are not hydrazine nor its parents, precisely because of safety.I understand. However in *common* rocket engineering usage that is what is being referred to. It's something you might like to keep in mind. Like using PSIA or PSIG instead of bar, Pascals or other more rational units.QuoteTEPA is a very safe amine, dirt-cheap and produced in huge amounts (by Huntsman and more) as well as triallylamine. Divinylcyclobutane gives properties similar to the cyclopropyl-things. UV dimerization of butadiene produces it with good yield and looks scalable to mass-production; electricity for the lamps would amount to 300€/t.And, yes, heat of formation isn't the whole picture, of course - if it were, I'd have included things like acetylene.You might like to consider Propyne, which is used as part of the industrial fuel "MAPP" gas. Nearly as simple as most HC's but the strained bond gives it a useful higher level of Isp.QuoteI prefer the glow-plug I described here to a catalytic igniter. Starts quickly, not sensitive to contamination, less specialized on one propellant. And with the glow-plug, hypergolic ignition isn't necessary neither, as soon as one propellant produces heat by decomposition.I gave a thought to hydrazine replacements (at Saposjoint.net > Science > Technology) but I believe it's a dead end. I prefer the MON decomposition cycle, or pressurized methane-oxygen. Somewhere at the other site, I describe a cryocooler to keep oxygen, methane and even hydrogen liquid indefinitely.The cycle that decomposes MON runs oxygen-rich, as Soviet engines have over decades. The cycle that recomposes amines runs fuel-rich and I too see it as an advantage. So does the hydrogenolysis cycle and it is one efficient way to burn propellants with performance similar to methane, which would otherwise prefer an oxygen-rich staged combustion.You need to understand something about the way rocket engineering is done.Most of it is expendable. It's used once and thrown away. You get *one* shot to do it right and because the hardware is either in free space or small pieces at the bottom of the ocean it's *almost* impossible to establish *exactly* what went wrong.This makes rocket engineers *very* cautious. They like things *simple* and they like things with *long* histories. The fact the *existing* solution is very dangerous and expensive is effectively *irrelevant*. The dangers are known and the costs (in terms of staff training, special equipment etc) are known and probably written off. I'm unaware of *any* rocket engine using a glow plug ignition system. The ones that need ignition uses spark plugs with a side propellant flow (called augmented spark ignitors). The rest are hypergolic.Your preference is irrelevant unless you're building rocket engines or you've been hired to do so by someone else. If you are *then* they matter. I think you may have confused "different" (or merely complex) with *better*. So what if your amine fuels are safer to handle. They are unproven (look up "Technology readiness level"), add complexity and deliver poorer performance. These are what *really* concern the people who write cheques for this stuff. They'd only be used if you could demonstrate they would drop into *existing* systems with no change and lower the overall weight *more* than enough to compensate for the loss in performance.But you can't. A safer, lower performance alternative to the amines already exists and has flight experience. It's called high test peroxide and peopel *could* use if they wanted to. You can handle this information in several ways. 1) re-work your ideas to fit them better to what is actually wanted, possibly along the way accepting that this is not possible. 2) Give up the idea entirely for the time being and learn more about the subject.3) Insist you're right, "People don't understand my vision," etc etc and generally become yet another internet crackpot, one "resource" that the internet has *never* been short of.You might like to note I'm the only person who's bothered to respond to your multiple posts. It's not about how much effort you put in. It's about working out weather it was necessary to put *any* effort in in the first place. Solving a problem no one else feels *is* a problem given the number of *real* problems that exist is pretty pointless. If you want to go with 1) I'll suggest you consider catalytic ignition. Iridium (the active ingredient of the Shell 405 catalyst used in both MMH decomposition for the Shuttle APUs and the aerojet GO2/LH2 cat ignitor) seems an efficient low temperature catalyst but I don't if this is the *best* transition metal for the job or merely the first one that worked (quite a lot of rocket engineering developed on this basis under the pressure of the Cold War. It was good enough to get the job done at the time and no one ever bothered, or could afford to find anything better).Is it good enough for your amines? Is there a better catalyst?BTW the idea of cracking a fuel to a more reactive one was suggested (IIRC) by Bob Zubrin for a US Navy hypersonic missile project. The standard US navy fuel (JP7?) is used to cool the skin and is cracked into ethyne (acetylene) which was expected to burn fast enough to be usable in a scramjet. I'll leave it there.
The amines I cite are not hydrazine nor its parents, precisely because of safety.
TEPA is a very safe amine, dirt-cheap and produced in huge amounts (by Huntsman and more) as well as triallylamine. Divinylcyclobutane gives properties similar to the cyclopropyl-things. UV dimerization of butadiene produces it with good yield and looks scalable to mass-production; electricity for the lamps would amount to 300€/t.And, yes, heat of formation isn't the whole picture, of course - if it were, I'd have included things like acetylene.
I prefer the glow-plug I described here to a catalytic igniter. Starts quickly, not sensitive to contamination, less specialized on one propellant. And with the glow-plug, hypergolic ignition isn't necessary neither, as soon as one propellant produces heat by decomposition.I gave a thought to hydrazine replacements (at Saposjoint.net > Science > Technology) but I believe it's a dead end. I prefer the MON decomposition cycle, or pressurized methane-oxygen. Somewhere at the other site, I describe a cryocooler to keep oxygen, methane and even hydrogen liquid indefinitely.The cycle that decomposes MON runs oxygen-rich, as Soviet engines have over decades. The cycle that recomposes amines runs fuel-rich and I too see it as an advantage. So does the hydrogenolysis cycle and it is one efficient way to burn propellants with performance similar to methane, which would otherwise prefer an oxygen-rich staged combustion.
One oxidizer is Mon-33, or 33% NO dissolved in 67% N2O4. It freezes at -107°C, so if paired for instance with 2,4,6-trimethyl-tridecane (freezes at -102°C), they stay indefinitely on Mars or an asteroid or a Moon just in white tanks.
This is mass where not desired, and an expansion cycle performs better, but the electric pump is simpler.
As an alternative to heavy pressurized tanks and to complicated turbopumps,
My suggestion is fully supported by maths, of course and as always.Progress does exist. Batteries and electric motors are wrongly perceived as heavy, which suffices to explain that no-one was trying.
...Progress does exist. Batteries and electric motors are wrongly perceived as heavy, which suffices to explain that no-one was trying.
The propellant tanks for a pressure system are not heavy.
[Batteries and motors] are still much heavier than a gas generator or the like for the same power.
