Critical Milestone in Liquid Oxygen-Liquid Methane Engine

[scottb50]

Methane, kerosene and mono-methyl-hydrazine are all lighter than water.<br /><br />Of course they are, now add in the weight of LOX required to burn it and water looks pretty light. It doesn't matter what fuel you use if you don't have an oxidizer. <div class="Discussion_UserSignature"> </div>

 

[barrykirk]

And the boiling point of Methane is very close to the boiling point of LOX. Cool the Methane down to LOX tempertures and no insulation or little insulation is required between the two tanks. Maybe you can get by with a membrane.

 

[scottb50]

Water can only be used for electricity once more energy than it can produce has been added. <br /><br />Solar power is available half the time in LEO and all the time in deaper Space, why would it be wasteful to use solar power to produce Hydrogen and Oxygen from water and use them to power fuel cells that would provide continuous stable power. Once the Hydrogen and Oxygen are used in the fuel cells the water exhaust can be returned to the water supply for re-use.<br /><br /><br />And for propulsion, ion or plasma engines will provide much better ISPs than any combustion process....<br /><br />Yes they have higher ISP, but if the idea is to get from the surface to LEO or from one orbit to another they don't really fit the bill. They produce very little thrust continuously and it adds up in velocity, what is needed is on demand power to get from A-B in a useful time period. It would be much simpler to go to the moon in three days than 2 years as an example. <div class="Discussion_UserSignature"> </div>

 

[tap_sa]

<font color="yellow">"It doesn't matter what fuel you use if you don't have an oxidizer."</font><br /><br />And it doesn't matter if you have tanks full of light <i>oxide</i>, unless you have electrolizer, powersource for it, liquifier and associated plumbing/tankage. Add those into the picture and water starts to look pretty 'heavy'.

 

[barrykirk]

Actually, Methane is a much better hydrogen carrier than water for the following reasons.<br /><br />Methane contains 1 C at MW of about 12 and 4 H at MW of about 1 each.<br /><br />Total Hydrogen content of Methane is about 25% by weight.<br /><br />Water contains 1 O at MW of about 16 and 2 H at MW of about 1 each.<br /><br />Total Hydrogen content of water is about 11.11% by weight.<br /><br />So, Methane carries over twice as much hydrogen weight for weight as water.<br /><br />There are very few molecules other than H2 that contain more than 25% Hydrogen by weight.<br /><br />Now, as for water, it isn't very useful as fuel because it's heat of combustion is a non starter.<br /><br />Methane on the other hand generates a large amount of heat when combusted with Oxygen.<br /><br />Now let's look at the reaction.<br /><br />CH4 + 3O2 - /> 2 H2O + 1 CO2<br /><br />Gee, 66% of the combustion products are water. That's really close to what you get when you burn Hydrogen and Oxygen. Now at a given temperature, the velocity of the exhaust or the ISP should be proportional to the inverse of the square root of the MW of the combustion products.<br /><br />H2O is MW 18<br />CO2 is MW 44<br /><br />Yes, the CO2 sucks, but there is more water than CO2<br /><br />Typically, rocket engines are run fuel rich. Which is good and bad....<br /><br />With hydrogen, the excess is good in that it really kicks up the ISP, but bad in that it's so low density that it really is difficult to pump that much of it and the temperature is lower which lowers the velocity a little bit.<br /><br />With Methane, CH4 has a MW of 16 which is less than water and much less than CO2, so it does improve the ISP to a point which is the point at which it drops the temperature too much.

 

[scottb50]

It would also require storage and transfer systems for other propellants. Pumps that would need electrical power being a good example. electrolizers and fuel cells are the same thing so systems are much easier to build, make them small Modules that connect together as more power is needed.<br /><br />I think you could reliably store Hydrogen and Oxygen gasses at low to moderate pressures fairly simply. Tugs and other Vehicles would need liquid propellants, but that could be drawn off by a separate system and liquified.<br /><br />I was pointing out that methane is obviously lighter than water because water also contains the oxidizer.<br /><br />I've never heard of light oxide. <div class="Discussion_UserSignature"> </div>

 

[josh_simonson]

>And it doesn't matter if you have tanks full of light oxide, unless you have electrolizer, powersource for it, liquifier and associated plumbing/tankage. Add those into the picture and water starts to look pretty 'heavy'. <br /><br />This was the original plan for the propulsion system for reboosting space station freedom, before switching to russian hypergolics when they joined up.<br /><br />The whole idea behind shipping water or ammonia for fuel is that it minimizes the weight of the craft the actually transports the stuff from point A to point B. Water or ammonia can be shipped via solar electric propulsion in simple, passive tanks with zero losses. The hydrolysis and reliquification facility may be somewhat large, perhaps 1 HLV load to LEO and 1 HLV/EDS load to cislunar space, but once in place they never have to move again.<br /><br />What this buys you:<br />LEO station<br />A: Indefinite EDS loiter time in LEO awaying CEV.<br />B: Doubling of HLV/EDS payload to the moon.<br />C: Provides opportunities for launching low cost payloads to launch providers to improve economies of scale.<br /><br />Cis-lunar station<br />A: Don't have to carry descent/ascent propellant with crew, allowing fuel to be delivered via the least expensive means possible. Air, food, tools and other durable goods could also be delivered this way. This is another doubling of useful EDS cargo.<br />B: Ready location to use in-situ O2.<br /><br />Developing a supply chain represents a commitment to a sustained effort. With the current 'battlestar galactica' approach there is no commitment at all, and they're also having trouble shoehorning everything into their form factor. An LEO depot can apply to Mars as well as it can to the moon as long as it's left with a fair amount of excess capacity.

 

[jhoblik]

I was first that bring that idea store our hydrogen and oxygen in form of water. It was for mission to mars almost year ago and I am very happy that it is still alive. I would like to advance that concept little more forward. We don't need to liquefied oxygen and hydrogen for our engine. For interplanetary mission we don't need high thrust in manner of second or minutes, we could speed up for long time. <br />It means electrolyzing water and then using by engine. We will skip liquidation unit and the whole process will be easier.<br />It will save weight of tanks 1 ton 1m3(~10ft3), material could be something like rubber bag.<br />Problem with cryogenic if something failed your fuel vaporize in matter of hours. In case if our electrolyze unit failed you will have time, to fix it and you will not loose resources.<br />For long term mission I didn’t see any alternatives. <br />To expected that cryogenic not failed for years is very risk and one failed event could destroy whole mission.<br />Our mission has to be simple as could and have margin to handle hardware failure, it will increase probability of successfully mission.<br /><br />

 

[scottb50]

I was first that bring that idea store our hydrogen and oxygen in form of water. It was for mission to mars almost year ago and I am very happy that it is still alive....<br /><br />I've been pushing it for years here, well before the great dankening. <div class="Discussion_UserSignature"> </div>

 

[propforce]

<font color="yellow"><i>"....Methane, kerosene and mono-methyl-hydrazine are all lighter than water. ..</i><br /><br />Of course they are, now add in the weight of LOX required to burn it and water looks pretty light. It doesn't matter what fuel you use if you don't have an oxidizer. </font><br /><br /><br />You forgot that water (H2O) only has one oxygen atom, while LOX has 2 oxygen atom making up a molecule, e.g., LO2. So, you'll need about TWICE amount of water to make up the SAME amount of LOX required.<br /><br />Water doesn't look pretty light with TWICE of the amount now. <img src="/images/icons/smile.gif" /><br /> <div class="Discussion_UserSignature"> </div>

 

[propforce]

<font color="yellow">Trade them the integrated powerhead 'full flow' to get single shaft tech? </font><br /><br /><br />You work for Aerojet, don't you? <img src="/images/icons/wink.gif" /> My friends over there will just LOVE you ! <div class="Discussion_UserSignature"> </div>

 

[propforce]

<font color="yellow">CH4 + 3O2 -> 2 H2O + 1 CO2 </font><br /><br /><br />Hey, how about if you go collect the steam exhaust from a LOX/ Methane engine and we will separate out H2 from O2 and re-use them ???? Oh darn, now we will NEED a H2/ O2 engine <<kicking myself now />> <br /><br />OH WAIT !!! <<LIGHT BULB ON />>... .... how about if we just use catalysts and do a reverse reaction of the above ????<br /><br />2H2O + CO2 ----- /> CH4 + 3O2 <br /><br />then we can re-burn methane and oxygen, and do this all day long !!! <img src="/images/icons/laugh.gif" /><br /><br /><br />I have such GREAT ideas... I need to go patent this stuff ... be right back...... <div class="Discussion_UserSignature"> </div>

 

[henryhallam]

<font color="yellow">amount</font><img src="/images/icons/wink.gif" /><br />Sounds like some of these guys wouldn't know a mole if it hit them on the head...

 

[propforce]

<font color="yellow">mole</font><br /><br />Hey now, we don't need some CIA jargon from the world of intelligence << I laugh so hard at my own humor I can't stop... />><br /><br />Next thing I know you'll start introduce strange numbers like the Avagadro's <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> </div>

 

[henryhallam]

To address this water craziness here's a little back of the envelope calculation:<br /><br />Ballpark energy required for electrolysis is 285kJ/mol (2 * [H-O enthalpy] - [H-H enthalpy] - 0.5 * [O=O enthalpy] + heat of vapourisation of water). Best electrolysis systems at the moment are about 60% efficient, call it 75% to be generous. That gives (285/.75)*(1000/18) = 21MJ/kg. I really don't know how much extra to add for compression and refrigeration.<br /><br />If we assume a lunar mission similar to Apollo, the S-IVB had about 105 tonnes of propellants. Something like 3/4 of this was for TLI so call it 75 tonnes. That is 1.6*10^12 Joules required just for electrolysis, not including compression and refrigeration.<br /><br />At the moment under average lit conditions the ISS panels put out around 50kW. You spend half the time in night so that means the electrolysis for a single trans-lunar injection would take approximately 2 years. Add more time and mass budget to compress and liquify the propellants. Hang on a minute, now you have to insulate and keep them liquid for all this time. Why were we shipping up water again??<br /><br />Sure you could put up more panels, but look at how long it has taken to get the already fairly substantial system on the ISS operational, and how much all that infrastructure is going to weigh.<br /><br />Sorry guys but I really think this is a dead end. It is a different matter if you already have a multimegawatt nuclear reactor to hand and an abundant supply of in-situ water. (Martian poles, perhaps lunar south pole, comets if you're thinking really out of the box).

 

[henryhallam]

Oh there is one good propulsive use for large quantities of water in space but I don't think greenpeace would be too keen: http://www.npl.washington.edu/AV/altvw56.html

 

[scottb50]

Any other source of propullsion is going to have the same problem. It takes so much thrust to do something howwever you do it. You want to take up hydrocarbons and LOX or tempermental and corrosive hypergolics. I don't see that being any easier, in fact you would have to take up more mass for the same effect. <div class="Discussion_UserSignature"> </div>

 

[propforce]

WOW... you managed to do all these without even mention the Avagadro's number !! <img src="/images/icons/laugh.gif" /> <div class="Discussion_UserSignature"> </div>

 

[j05h]

On water-as-fuel, my prefered solution is to use the water directly in solar-thermal rockets. Nontoxic, available, and simple plumbing. Much better ISP than chemical rockets, much better thrust than regular electric thrust. <br /><br />And yes, NEO comets are my prefered source for that water. Once you can mine water on one dead comet, you have access to the rest. <br /><br />josh <div class="Discussion_UserSignature"> <div align="center"><em>We need a first generation of pioneers.</em><br /></div> </div>

 

[henryhallam]

<font color="yellow"><br />Any other source of propullsion is going to have the same problem. It takes so much thrust to do something howwever you do it. You want to take up hydrocarbons and LOX or tempermental and corrosive hypergolics. I don't see that being any easier, in fact you would have to take up more mass for the same effect.</font><br /><br />Sorry, I don't understand.<br /><br />I thought I just showed that lifting water and electrolysing it was ridiculously heavier, slower and more expensive than the existing, practical and known-working method of lifting ready-made cryogenic or hydrocarbon fuel + oxidiser along with a suitable engine?

 

[scottb50]

I thought I just showed that lifting water and electrolysing it was ridiculously heavier, slower and more expensive than the existing, practical and known-working method of lifting ready-made cryogenic or hydrocarbon fuel + oxidiser along with a suitable engine?>>><br /><br />And I'm saying water and Hydrogen/Oxygen is lighter than the other choices, easier and safer to handle and transport and also has numerous other jobs beyond propullsion. You have to have water anyway, might as well use it for as many jobs as you can which makes it cheaper in the long run. <br /><br />Lox and liquid methane require insulation, at least, which translates to higher costs and less payload. Either way it's going to take a lot of propellant uplift to get to Mars or the asteroids and moon however you do it. With your logic we should just abandon all hope and quit wasting our time. <div class="Discussion_UserSignature"> </div>

 

[tap_sa]

<font color="yellow">"Much better ISP than chemical rockets"</font><br /><br />Unfortunately not. Water steam will produce same Isp at same temperture no matter how it was heated. In fact you will likely get lower Isps using pure water because exhaust gas contain only water molecules. Chemical LOX/LH2 runs fuel rich so there are nice little light H2 molecules in it's exhaust to produce the high Isp.<br /><br />It is unlikely that solar thermal could produce temperatures as high as inside current conventional engines because instead of cooling the reaction chamber you'd need to heat it white hot so that the chamber itself can heat the propellant. IIRC the past NTR tests managed to produce ~2700K temps. SSME reaches ~3600K.

 

[propforce]

<font color="yellow">IIRC the past NTR tests managed to produce ~2700K temps. SSME reaches ~3600K. </font><br /><br />NTR gets a higher Isp than the SSME because it uses <i>pure</i> hydrogen as propellant, whereas the SSME use both oxygen and hydrogen. Same logic for a solar thermal orbital transfer vehicle (SOTV). When people says that a SOTV gets a great Isp, they're using pure H2 as propellant, not H2O.<br /><br />Oxygen flow rate is 6 times heavier than hydrogen for SSME, whereas in the case of water; oxygen is 8 times heavier than hydrogen. So water would produce a <i>lower Isp</i> than a conventional H2-O2 rocket. <div class="Discussion_UserSignature"> </div>

 

[tap_sa]

I've got nothing to add ... except THIS: 6.0221415 x 10²³ ! <img src="/images/icons/wink.gif" />

 

[webtaz99]

I'm not sure what you are discussing (it seems like 02/H2 combustion), but I'm talking about ion and plasma engines, which can produce ISPs of 1000+ or 10,000+, respectively. <div class="Discussion_UserSignature"> </div>