|
|
Post by The Astronomer on Aug 19, 2017 13:56:33 GMT
Hydrogen is great. It is light and simple, so most rockets prefer it. However, storing hydrogen is a pain in the ass, because due to its small size and extremely low boiling point, it tends to boil off and leak out of your tanks. Water (H 2O), Ammonia (NH 3) and Methane (CH 4) are some of the lightest hydrogen-containing molecules. They are far easier to keep in tanks than hydrogen, so if you can find ways to separate hydrogen from those molecules, they looks promising. Water can be electrolyzed, producing hydrogen gas and oxygen gas. I suspect the same can be done for ammonia...? 2H 2O + energy ---> 2H 2 + O 22NH 3 + energy ---> 3H 2 + N 2For methane, the process is a bit more interesting. The most commonly used method is steam reforming, which reacts hydrocarbons with steam water. In methane steam reforming, this produces carbon monoxide and hydrogen gas. Carbon monoxide can react with another water molecule to form carbon dioxide and more hydrogen gas. CH 4 + H 2O ---> CO + 3H 2 (endothermic) CO + H 2O ---> CO 2 + H 2 (exothermic) Other possible storage molecules includes lithium hydride (LiH), which reacts with water to form lithium, hydrogen gas and hydroxide ion. 2LiH + H 2O ---> 2Li + 2H 2 + OH -Acids like plain hydrogen chloride should also work. Reacting them with some metal. Simple middle school chemistry. If you manage to find some, though. Hydrogen moles per molecular mole, hydrogen grams per kilogram of substance (approx.)Lithium hydride: 8 g/mol. 0.5 moles of hydrogen molecules for each molecular mole, ~125 g for each kilogram. Beryllium hydride: 11 g/mol. 1 moles of hydrogen molecules for each molecular mole. ~182 g for each kilogram. Methane: 16 g/mol. 2 moles of hydrogen molecules for each molecular mole. ~250 g for each kilogram. Ammonia: 17 g/mol. 1.5 moles of hydrogen molecules for each molecular mole. ~176 g for each kilogram. Water: 18 g/mol. 1 moles of hydrogen molecules for each molecular mole. ~111 g for each kilogram. Ammonia Borane: 29 g/mol. 6 moles of hydrogen molecules for each molecular mole. ~ 207 g for each kilogram. |
|
Enderminion on a tablet
Guest
|
Post by Enderminion on a tablet on Aug 19, 2017 22:39:08 GMT
What would you do with the extra stuff, it will kill you're mass ratio
|
|
|
|
Post by someusername6 on Aug 19, 2017 22:46:30 GMT
Water can be electrolyzed, producing hydrogen gas and oxygen gas. I suspect the same can be done for ammonia...? 2H 2O + energy ---> 2H 2 + O 2Are you suggesting a system where store water on the tanks, electrolyze it just in time, send it out to react as propellants on the engine, to have it come out as water again? That sounds fun. |
|
|
|
Post by matterbeam on Aug 19, 2017 22:47:51 GMT
Hydrogen is great. It is light and simple, so most rockets prefer it. However, storing hydrogen is a pain in the ass, because due to its small size and extremely low boiling point, it tends to boil off and leak out of your tanks. Water (H 2O), Ammonia (NH 3) and Methane (CH 4) are some of the lightest hydrogen-containing molecules. They are far easier to keep in tanks than hydrogen, so if you can find ways to separate hydrogen from those molecules, they looks promising. Water can be electrolyzed, producing hydrogen gas and oxygen gas. I suspect the same can be done for ammonia...? 2H 2O + energy ---> 2H 2 + O 22NH 3 + energy ---> 3H 2 + N 2For methane, the process is a bit more interesting. The most commonly used method is steam reforming, which reacts hydrocarbons with steam water. In methane steam reforming, this produces carbon monoxide and hydrogen gas. Carbon monoxide can react with another water molecule to form carbon dioxide and more hydrogen gas. CH 4 + H 2O ---> CO + 3H 2 (endothermic) CO + H 2O ---> CO 2 + H 2 (exothermic) Other possible storage molecules includes lithium hydride (LiH), which reacts with water to form lithium, hydrogen gas and hydroxide ion. 2LiH + H 2O ---> 2Li + 2H 2 + OH -Acids like plain hydrogen chloride should also work. Reacting them with some metal. Simple middle school chemistry. If you manage to find some, though. Hydrogen moles per molecular moleLithium hydride: 8 g/mol. 0.5 moles of hydrogen molecules for each molecular mole. Beryllium hydride: 11 g/mol. 1 moles of hydrogen molecules for each molecular mole. Methane: 16 g/mol. 2 moles of hydrogen molecules for each molecular mole. Ammonia: 17 g/mol. 1.5 moles of hydrogen molecules for each molecular mole. Water: 18 g/mol. 1 moles of hydrogen molecules for each molecular mole. Molar ratios are misleading. A much better comparison is kg of hydrogen in kg of storage chemical. For example, you'll find 112g of hydrogen in 1kg of water and 126g of hydrogen in lithium hydride. You mass ratio will therefore be strictly lower than 0.126! |
|
|
|
Post by jtyotjotjipaefvj on Aug 19, 2017 22:53:43 GMT
I guess you could do this for bipropellants. H20 to H2 and LOX should work. Just add in one part of LOX from a separate tank and you can have a 1:1 propellant ratio as well.
You'd probably have to have some buffer between the electrolyzer and thruster though, it might be difficult to electrolyze water fast enough to fuel a rocket.
|
|
|
|
Post by apophys on Aug 20, 2017 0:26:04 GMT
Diborane (B2H6): 27.6 g/mol. 3 moles H2 per mole. 9.2g / mol H2
Ammonia borane, a.k.a. borazane (BH3NH3): 30.8 g/mol. 3 moles H2 per mole. 10.3g / mol H2
Lithium borohydride (LiBH4): 21.8 g/mol. 2 moles H2 per mole. 10.9g / mol H2
Diborane will decompose to hydrogen and higher boranes when heated, eventually being just hydrogen and boron. Ammonia borane will decompose to boron nitride and hydrogen. Not sure how to get hydrogen off lithium borohydride, but I suspect it is similarly easy.
From the above data, methane seems the lightest storage method for hydrogen that is not hydrogen, at 8g / mol H2, followed by diborane.
Edit: Ethane (C2H6) is also good: 30 g/mol. 3 moles H2 per mole. 10g / mol H2
|
|
|
|
Post by The Astronomer on Aug 20, 2017 0:49:52 GMT
Diborane (B2H6): 27.6 g/mol. 3 moles H2 per mole. 9.2g / mol H2 Ammonia borane, a.k.a. borazine (BH3NH3): 30.8 g/mol. 3 moles H2 per mole. 10.3g / mol H2 Lithium borohydride (LiBH4): 21.8 g/mol. 2 moles H2 per mole. 10.9g / mol H2 Diborane will decompose to hydrogen and higher boranes when heated, eventually being just hydrogen and boron. Ammonia borane will decompose to boron nitride and hydrogen. Not sure how to get hydrogen off lithium borohydride, but I suspect it is similarly easy. From the above data, methane seems the lightest storage method for hydrogen that is not hydrogen, at 8g / mol H2, followed by diborane. Not sure about what to do with carbon dioxide, though. Oxygen can be used to breath, and nitrogen can be used to pressurize the module. But carbon dioxide? Feed them to your algae vats? Btw, lithium from lithium hydride, if you even managed to use them, can be used as remass. |
|
|
|
Post by Rocket Witch on Aug 20, 2017 7:31:39 GMT
Ammonia borane, a.k.a. borazine (BH3NH3): 30.8 g/mol. 3 moles H2 per mole. 10.3g / mol H2 Borazane. :p Borazine (B 3N 3H 6) is much worse hydrogen store. |
|
|
|
Post by n2maniac on Aug 20, 2017 8:43:00 GMT
Given that most rocket power densities are on the order of 4000m/s * 100 * 9.8m/s2 ~ 4000 kW/kg and typical good electrical power sources (IRL) top out around 8kW/kg (~20kW/kg for ingame reactors), doing this just in time will lead to a substantial performance hit.
...or just use resistojet/NTR
|
|
|
|
Post by beta on Aug 20, 2017 13:05:23 GMT
Interesting concept for water as a fuel storage medium - it is something companies are exploring today for mass and volume efficient engines that still provide good thrust. www.tethers.com/HYDROS.htmlWould be neat to have this modeled, though I imagine NTRs would still be better in most ways. |
|
|
|
Post by The Astronomer on Aug 20, 2017 13:24:33 GMT
Interesting concept for water as a fuel storage medium - it is something companies are exploring today for mass and volume efficient engines that still provide good thrust. www.tethers.com/HYDROS.htmlWould be neat to have this modeled, though I imagine NTRs would still be better in most ways. Wait a minute. I suppose this can be used to provide remass for NTRs? |
|
|
|
Post by beta on Aug 20, 2017 13:31:21 GMT
Yeah, you can electrolyze the water to produce the gases. The efficiency of reactor mass compared to the increased performance of hydrogen/oxygen gas may not provide enough of a benefit. Still, it could allow for a method of allowing for a "gearbox" for an NTR where you can use high-thrust water compared to high-efficiency hydrogen gas and oxygen gas.
|
|
|
|
Post by bigbombr on Aug 20, 2017 13:34:24 GMT
Yeah, you can electrolyze the water to produce the gases. The efficiency of reactor mass compared to the increased performance of hydrogen/oxygen gas may not provide enough of a benefit. Still, it could allow for a method of allowing for a "gearbox" for an NTR where you can use high-thrust water compared to high-efficiency hydrogen gas and oxygen gas. It's useful for chemical engines. In NTR's and resistojets, the propellant usually dissociates into ions. Without the dissociation, their exhaust velocities would be considerably lower. |
|
|
|
Post by beta on Aug 20, 2017 13:37:01 GMT
Well, hydrogen NTRs typically have higher exhaust velocity and delta v than a water NTR, right? A water NTR has much better volume of remass storage compared to hyrogen. This way, you can get the increased exhaust velocity and delta v of hydrogen gas (limited by the speed at which you can create the gasses from the water), while still retaining the high density of a water reaction mass.
|
|
|
|
Post by bigbombr on Aug 20, 2017 14:08:07 GMT
Well, hydrogen NTRs typically have higher exhaust velocity and delta v than a water NTR, right? A water NTR has much better volume of remass storage compared to hyrogen. This way, you can get the increased exhaust velocity and delta v of hydrogen gas (limited by the speed at which you can create the gasses from the water), while still retaining the high density of a water reaction mass. You're still stuck with all the excess oxygen. Carrying that around will more than ofset any benefit in exhaust velocity. Dumping it overboard means you've wasted it. Using it as propellant will give you lower exhaust velocities. In the end, I can't see this being better than a water NTR. If you really want high exhaust velocities out of dense propellants, try MPDT's. The reason they use this IRL is because they want an easy way to store oxygen and hydrogen for extended periods of time (it mentions it would mainly be too feed hydrogen/oxygen combustion rocket engines for station keeping), and not have all your hydrogen escape out of the tanks (which IRL is one of the main downsides of hydrogen, and isn't modeled in CoaDE). And most of the mass of you're 'storage molecule' will be non-hydrogen atoms, as hydrogen is extremely light. Not using those 'waste atoms' for propulsion and instead lugging them around would make your rocket so subpar you're better of with a monopropellant combustion rocket. |
|
