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Post by RiftandRend on Jan 22, 2017 5:58:59 GMT
I was wondering, is there any reason why some sort of Chemical/Nuclear rocket wont work? For example you could burn LOX Decane and then pass the resulting H2O and CO2 through an NTR. This seems like a way to use the chemical energy of propellent that would normally be wasted in an NTR.
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utilitas
Junior Member
I can do this all day.
Posts: 59
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Post by utilitas on Jan 22, 2017 6:59:41 GMT
I'm guessing that it might result in a lower overall exhaust velocity due to the cooling propellants used. I've been thinking the same, actually, but the opposite way around. First superheat the chemical propellants in the nuclear core separately, (probably requires two asymmetric chambers to heat both as much as possible, because both of them are unlikely to have the same thermal properties) only then let them combust together in the nozzle.
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Post by caiaphas on Jan 22, 2017 7:14:17 GMT
<abbr>I'm guessing that it might result in a lower overall exhaust velocity due to the cooling propellants used. I've been thinking the same, actually, but the opposite way around. First superheat the chemical propellants in the nuclear core separately, (probably requires two asymmetric chambers to heat both as much as possible, because both of them are unlikely to have the same thermal properties) only then let them combust together in the nozzle.</abbr> I think the main issue with that is that most of the chemical propellants will either completely destroy the reactor by virtue of being stupidly reactive (fluorine and hydrazine spring to mind) or they're powerful oxidizers and will set your reactor on fire if you superheat them (hydrogen peroxide, LOX). The only way I can see this working is if you choose two propellants that, when they react, produce a relatively stable and inert molecule that won't dissociate when you heat it up (maybe one of the LOX-hydrocarbon mixes? too lazy to look up the physical properties right now) and then feed it through your reactor. I'm not convinced that you'll get that much better performance from that, though, because the product of the combustion reaction is going to be rushing through your reactor really quickly, so you'll either need a very long and skinny reactor or a lot of potentially fragile heat sink-like vanes of fissile material that might not be the best design for a reactor to increase the surface area. EDIT: doy, of course one of the LOX-hydrocarbon mixes will work, the products are flipping carbon dioxide and water. 'bout as inert as you can get. |
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Post by RiftandRend on Jan 22, 2017 7:15:08 GMT
<abbr>I'm guessing that it might result in a lower overall exhaust velocity due to the cooling propellants used. I've been thinking the same, actually, but the opposite way around. First superheat the chemical propellants in the nuclear core separately, (probably requires two asymmetric chambers to heat both as much as possible, because both of them are unlikely to have the same thermal properties) only then let them combust together in the nozzle.</abbr> I imagine both setups would work, depending on wether the reactants or products have higher molar mass. |
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Post by RiftandRend on Jan 22, 2017 7:17:02 GMT
Platinum coated internals might help resolve reactivity issues with less volatile propellents.
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Post by caiaphas on Jan 22, 2017 7:23:04 GMT
Platinum coated internals might help resolve reactivity issues with less volatile propellents. Maybe. I sincerely doubt that anything will help with fluorine without drastically cutting into your mass budget, though, that stuff eats through glass and it gets nastier the hotter it goes. And even then it's still going to limit your reactor performance. I mean, as an example, I run my decane NTRs at 3000 K, but I'm going to need to drop that by 1000 K to keep the platinum from melting. |
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Post by RiftandRend on Jan 22, 2017 7:41:04 GMT
Because of that LOX-Hydrogen/Hydrocarbon systems are probably going to be the only viable use of this system.
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Post by caiaphas on Jan 22, 2017 8:02:05 GMT
Because of that LOX-Hydrogen/Hydrocarbon systems are probably going to be the only viable use of this system. And even then you'd probably need to run it colder than a normal NTR. I'd need to look up the specific reactions, but I think that you'd get non-trivial conversion of water to peroxide when you run it at several thousand Kelvin. EDIT: bleh, meant "you'd get decomposition of water back into H 2 and O 2, and as stated above I am incredibly leery about letting a powerful oxidizer come in contact with my fissile materials". Sorry for the brain fart. |
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Post by RiftandRend on Jan 22, 2017 8:23:16 GMT
Perhaps injecting LOX into a jet of superheated NTR hydrogen exhaust would bypass the reactivity issue.
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Post by darthroach on Jan 22, 2017 10:34:13 GMT
I was wondering, is there any reason why some sort of Chemical/Nuclear rocket wont work? For example you could burn LOX Decane and then pass the resulting H2O and CO2 through an NTR. This seems like a way to use the chemical energy of propellent that would normally be wasted in an NTR. If you burn it before passing it through the reactor, all you're going to do is get way less energy out of the reactor, ending up with a very heavy, slightly hotter chemical rocket. If it even works. What you're proposing has already been considered, btw. LANTR, or LOx-augmented NTR, proposes injecting LOx in the exhaust stream. Increases thrust at the expense of about 1/3 of the exhaust velocity. Essentially a more efficient form of dumping remass into the exhaust to increase thrust since the remass recovers some energy from chemical combustion. |
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Post by ash19256 on Jan 22, 2017 12:35:28 GMT
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Post by bigbombr on Jan 22, 2017 13:27:09 GMT
A hybrid NTR-resistojet seems interesting: most of the heat comes from the reactor (which is temperature limited to the melting point of your fissile) and the resistojet heats the propellant further (increasing exhaust velocity at the cost of a small amount of energy).
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Post by caiaphas on Jan 22, 2017 22:09:14 GMT
Yes, we did see roach's post. Well, I did. |
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Post by theholyinquisition on Jan 22, 2017 22:13:02 GMT
Yes, we did see roach's post. Well, I did. Besides, I think LANTRs don't burn the LH2-LOX, they just use it as an additive. |
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Post by caiaphas on Jan 22, 2017 22:25:58 GMT
Yes, we did see roach's post. Well, I did. Besides, I think LANTRs don't burn the LH2-LOX, they just use it as an additive. Atomic Rockets doesn't specify? |
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