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Post by matterbeam on May 4, 2017 16:28:31 GMT
Hello. I'd like to know if the following design is possible:  The Dicyanoacetylene Ozone rocket apparently produces 5000K+ temperature flames. The products of combustion are not particularly lightweight, so it is outperformed by Hydrogen/Oxygen rockets. But, if hydrogen (as H2, then dissociates) is added as an inert propellant to be heated by the flame, could extreme exhaust velocities be possible? The method of operation would be similar to a solid nuclear thermal engine where the heating element increases the temperature of the propellant. |
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Post by bigbombr on May 4, 2017 16:33:10 GMT
Hello. I'd like to know if the following design is possible: The Dicyanoacetylene Ozone rocket apparently produces 5000K+ temperature flames. The products of combustion are not particularly lightweight, so it is outperformed by Hydrogen/Oxygen rockets. But, if hydrogen (as H2, then dissociates) is added as an inert propellant to be heated by the flame, could extreme exhaust velocities be possible? The method of operation would be similar to a solid nuclear thermal engine where the heating element increases the temperature of the propellant. The average atomic mass goes down (which would raise exhaust velocity) but the exhaust temperature goes down (as the hydrogen absorbs heat). Overall, it might perform slightly better or worse, but it would be heavier, more complex and you'd have to carry 3 propellants instead of 1. You might be better of using a LH 2/LOX engine, and if you can get away with it, a hydrogen-fluorine engine will perform considerably better. Ozone and FOOF are viable oxidizers too. |
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Post by newageofpower on May 4, 2017 16:35:17 GMT
At work (and sicker than a dog) but I don't think so. You need to vent your oxygen/acetylene byproducts along with the hydrogen, and due to the differences in density most of the momentum and energy would remain in the heavier byproducts.
Did I recommend the molten Lithium Hydride + Flourine rocket to you yet? More hydrogen per volume than liquid hydrogen, plus the highest exhaust velocity from any known chemical reaction. Downside is the rarity of Flourine. Plus extreme danger in such a rocket design. And the handling of Molten Lithium Hydride. And Flourine.
Try to imagine a premixer injection setup that doesn't cause spontaneous detonation...
=D
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Post by matterbeam on May 4, 2017 18:05:08 GMT
At work (and sicker than a dog) but I don't think so. You need to vent your oxygen/acetylene byproducts along with the hydrogen, and due to the differences in density most of the momentum and energy would remain in the heavier byproducts. Did I recommend the molten Lithium Hydride + Flourine rocket to you yet? More hydrogen per volume than liquid hydrogen, plus the highest exhaust velocity from any known chemical reaction. Downside is the rarity of Flourine. Plus extreme danger in such a rocket design. And the handling of Molten Lithium Hydride. And Flourine. Try to imagine a premixer injection setup that doesn't cause spontaneous detonation... =D But doesn't gas mixing homogenize the the temperatures? I understand that mixing 1 part C2N4+O3 to 10 parts H2 will lower the overall temperature, but is it possible to get a ratio that allows for an average exhaust velocity higher than possible before? For example, and I'm not fully grasping all the maths involved here, but a 1:10 ratio of fuel to propellant in mass should lead to hydrogen containing 90% of the combustion energy. |
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Post by alias72 on May 4, 2017 19:09:31 GMT
gas mixing will bring your hydrogen propellant into contact with your 5000k ozone (not all of which will combust instantly) thus causing a reaction. In fact that is this designs biggest flaw.
You cannot mix all three products because then ozone will burn with hydrogen at a lower temperature.
You cannot burn the fuel earlier because you need the hydrogen to form a gas wall preventing your rocket from melting.
also your estimates of mass fraction and isp are off even if you solve the above two because you will need to constantly burn fuel and oxidizer to create the heat for the propellant.
NTR's work because they have such an insane energy density that they need not undergo a notable mass change as they release energy. The result is that they can be thought of as a stationary heat source. Your chemically fueled heat source will require a substantial mass flow that will impact your ships mass fraction.
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Post by samchiu2000 on May 4, 2017 22:55:42 GMT
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Post by matterbeam on May 5, 2017 0:34:08 GMT
gas mixing will bring your hydrogen propellant into contact with your 5000k ozone (not all of which will combust instantly) thus causing a reaction. In fact that is this designs biggest flaw. You cannot mix all three products because then ozone will burn with hydrogen at a lower temperature. You cannot burn the fuel earlier because you need the hydrogen to form a gas wall preventing your rocket from melting. also your estimates of mass fraction and isp are off even if you solve the above two because you will need to constantly burn fuel and oxidizer to create the heat for the propellant. NTR's work because they have such an insane energy density that they need not undergo a notable mass change as they release energy. The result is that they can be thought of as a stationary heat source. Your chemically fueled heat source will require a substantial mass flow that will impact your ships mass fraction. Well, the quantity of hydrogen would normally dwarf any amount of oxygen available after combustion with the C-N fuel, so there'll always be a lot of inert hydrogen to heat up. Also, fluid dynamics can be used maintain a hot, high pressure flame in the center that excludes colder hydrogen from mixing in immediately. The hydrogen 'gas wall' can be very thin relative to the size of the chamber. Constantly burning fuel and oxidizer is not really a problem, but instead a characteristic of the design of chemical rockets. If the average exhaust temperature can be increased from, say, 3500K in a LH/LOx rocket, to 4500K in a LH/C2N4/O3 rocket, then it would be worthwhile. A increase in exhaust velocity by 20% can lead to a decently smaller rocket. |
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Post by n2maniac on May 5, 2017 4:59:11 GMT
Energy density of the reactants is what needs to be maximized for high exhaust velocities (and minimizing energy lost in rotational vibrational modes that do not transfer fast enough during expansion). The main remarkable property of NCCN + O3 combustion is the abundance of heavy products, which results in a high flame temperature (that does not necessarily translate to high exhaust velocity).
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Post by RiftandRend on May 6, 2017 22:19:06 GMT
I tested this while trying to implement C2N4+O3 combustion a few months ago. The specific heat of hydrogen in game (14 Mj/kg/k) is so incredibly high that it lowers the exhaust temperature faster than it improves the average exhaust mass, leading to lower total exhaust velocity.
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Post by Rocket Witch on May 6, 2017 23:06:18 GMT
Did I recommend the molten Lithium Hydride + Flourine rocket to you yet? More hydrogen per volume than liquid hydrogen, Something to bear in mind is that the intention of the mod is to emulate a Li-H-F tripropellant rocket, not a LiH-F bipropellant rocket. Some values may be off with regard to a LiH-F rocket specifically. In this tripropellant scenario one wouldn't realistically get good hydrogen storage as it is kept separate from the lithium. plus the highest exhaust velocity from any known chemical reaction. IIRC the other tripropellant rocket using beryllium was faster. |
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Post by Enderminion on May 7, 2017 0:00:29 GMT
if hydrogen (as H2, then dissociates) is added as an inert propellant hydrogen is not inert, use a (heavier) noble gas |
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Post by newageofpower on May 7, 2017 6:59:27 GMT
IIRC the other tripropellant rocket using beryllium was faster. Wasn't there problems in building an engine that would even burn most of the Beryllium? NASA publications that I've just read do indicate that Be/H/O has about a theoretical 39s impulse advantage over F/Li/H, but I'd like to see both modded in. |
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Post by Rocket Witch on May 7, 2017 13:58:49 GMT
IIRC the other tripropellant rocket using beryllium was faster. Wasn't there problems in building an engine that would even burn most of the Beryllium? NASA publications that I've just read do indicate that Be/H/O has about a theoretical 39s impulse advantage over F/Li/H, but I'd like to see both modded in. Ah. I wouldn't know actually. Do you have links for these? |
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Post by zorbeltuss on May 7, 2017 14:04:20 GMT
Wasn't there problems in building an engine that would even burn most of the Beryllium? NASA publications that I've just read do indicate that Be/H/O has about a theoretical 39s impulse advantage over F/Li/H, but I'd like to see both modded in. Ah. I woudn't know actually. Do you have links for these? I can not guarantee that this is the paper spoken of but the first ten pages seems to be on point. Current Evaluation of the Tripropellant Concept |
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Post by n2maniac on May 7, 2017 19:33:15 GMT
IIRC the other tripropellant rocket using beryllium was faster. Wasn't there problems in building an engine that would even burn most of the Beryllium? NASA publications that I've just read do indicate that Be/H/O has about a theoretical 39s impulse advantage over F/Li/H, but I'd like to see both modded in. Was it something in addition to the extreme toxicity of the BeO exhaust? |
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