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#1 2025-03-10 10:19:04
- tahanson43206
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- Registered: 2018-04-27
- Posts: 23,376
Thermal Efficiency in Propulsion
This topic is offered for NewMars members who might wish to contribute to a collection of links and text about the efficiency that might be expected (or hoped for) from a propulsion system that depends upon heating of a working fluid.
As I open this topic, I do not know how the Carnot cycle relates to the topic, but I suspect that it applies.
This topic is inspired by work of kbd512 who has looked into (and written about) use of solar energy to heat liquid hydrogen to produce thrust.
This work is similar to the use of nuclear energy in a thermal engine to heat liquid hydrogen to produce thrust.
The difference is that one process uses fusion and the other uses fission.
What I'm hoping will happen with this topic is that NewMars members may attempt to explain how ordinary thermal efficiency (such as a steam engine application) compares to a thrust/propulsion application.
Energy invested in propulsion involves acceleration of mass.
There may be an upper limit to the efficiency with which energy is used to accelerate mass. If there is such a limit, this topic is available for a post in which that limit is defined and for which examples are provided.
I am hoping that NewMars members may find Real Universe examples of testing of the concept, including statements of efficiency of each such example compared to the theoretical maximum that might be calculated.
Because solar energy is essentially unlimited, the skill of the engineer/designer will be demonstrated by thrust achieved from the energy collected from a given area.
If agreeable to everyone, I'd like to suggest a collection area 200 meters on a side, for a total of 40,000 square meters.
If solation per square meter is 1000 watts, this array ** should ** deliver 40 MW to a propulsion device.
The question before the members is: What is the best possible design to generate thrust given this level of power?
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#2 2025-03-10 10:19:47
- tahanson43206
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- Registered: 2018-04-27
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Re: Thermal Efficiency in Propulsion
This post is reserved for an index to posts that may be contributed by NewMars members over time.
Index:
#3: Snippets by Google from Wikipedia about Carnot Theorem
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#3 2025-03-10 10:24:51
- tahanson43206
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- Registered: 2018-04-27
- Posts: 23,376
Re: Thermal Efficiency in Propulsion
This post is intended to hold a bit of output from Wikipedia about the Carnot theorem...
Carnot Cycle - Definition, Theorem, Efficiency, Diagrams ...
A Carnot cycle in thermodynamics refers to a theoretical, idealized thermodynamic cycle that represents the maximum possible efficiency for converting heat into work, consisting of four reversible processes: isothermal expansion, adiabatic expansion, isothermal compression, and adiabatic compression, all occurring between two heat reservoirs at different temperatures; it is considered the most efficient way to convert thermal energy into work, and is based on the work of
French physicist Sadi Carnot.
Key points about the Carnot cycle:
Idealized nature:A Carnot cycle is a theoretical concept, meaning it assumes perfect reversibility with no friction or energy loss, and cannot be perfectly replicated in real-world engines.
Four processes:
The cycle consists of four steps:Isothermal expansion: The working fluid expands at a constant high temperature, absorbing heat from the hot reservoir.
Adiabatic expansion: The working fluid further expands without heat exchange, causing its temperature to decrease.
Isothermal compression: The fluid is compressed at a constant low temperature, releasing heat to the cold reservoir.
Adiabatic compression: The fluid is further compressed without heat exchange, causing its temperature to increase back to the initial state.Efficiency:
The Carnot efficiency is calculated based on the temperatures of the hot and cold reservoirs, with higher efficiency achieved by increasing the temperature difference between them.Carnot's theorem:
This theorem states that no heat engine operating between two given temperatures can have a higher efficiency than a Carnot engine operating between the same temperatures.Carnot Cycle & Heat Engines, Maximum Efficiency, & Energy Flow ...
Dec 7, 2017 — so if we decrease the temperature of the cold reservoir and the efficiency goes up in order to increase the efficiency.YouTube ·
The Organic Chemistry TutorCarnot Engine, Carnot Theorem & Carnot Cycle - Working, Efficiency
A Carnot cycle is defined as an ideal reversible closed thermodynamic cycle. Four successive operations are involved: isothermal e...Carnot cycle - Wikipedia
A Carnot cycle is an ideal thermodynamic cycle proposed by French physicist Sadi Carnot in 1824 and expanded upon by others in the...Wikipedia
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Generative AI is experimental.Carnot's theorem states that all heat engines operating between the same two thermal or heat reservoirs cannot have efficiencies greater than a reversible heat engine operating between the same reservoirs.
Carnot's theorem (thermodynamics) - WikipediaWikipedia
https://en.wikipedia.org › wiki › Carnot's_theorem_(the...
Carnot Cycle
Carnot Engine, Carnot Theorem & Carnot Cycle - Working ...
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Carnot cycle
In the case of a (hypothetical) liquid hydrogen deep space vessel powered by solar energy, the goal for the engineer/designer is to achieve the maximum possible thrust given a certain amount of solar energy collected by a device that subtends a part of the sphere around the Sun.
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#4 2025-11-18 09:20:03
- tahanson43206
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Re: Thermal Efficiency in Propulsion
Today's post is about Thermal Efficiency in the context of the pipes to heat hydrogen for the (proposed) Optical Plane deep space vessel propulsion system.
The Python program to generate the data is posted in the Python topic.
The data itself covers a range of pipe radii from near zero to 5 centimeters.
The pipe radius of interest is 0.1778 cm. This value was chosen by NASA engineers as the optimum size for their CERMET study.
CERMET is an updated version of the NERVA engine. See posts by kbd512 for much more information and plenty of links.
The data posted below can be fed into any plotting software (such as in Excel or Calc). The result shows clearly how the efficiency varies along a hyperbolic curve, while the area of the cross section changes in a parabolic curve, and diameter and circumference show up as linear curves,
cat solar_rocket_pipe_efficiency.csv
Radius (cm),Diameter (cm),Flow_Area (sq cm),Wetting_Circumference (cm),A_to_C_Ratio_r_over_2,C_to_A_Ratio_2_over_r
0.0505149494949495,0.101029898989899,0.008016590854498074,0.3173947884595856,0.02525747474747475,39.59223992097549
0.10101989898989899,0.20203979797979799,0.032060015836382356,0.6347267450660993,0.050509949494949496,19.79807958628013
0.1515248484848485,0.303049696969697,0.07213027525981215,0.9520587016726132,0.07576242424242426,13.199155254063738
0.202029797979798,0.404059595959596,0.1282273691247874,1.2693906582791268,0.101014898989899,9.899529772335812
0.2525347474747475,0.505069494949495,0.20035129743130817,1.5867226148856408,0.12626737373737376,7.919702219196557
0.303039696969697,0.606079393939394,0.2885020601793744,1.9040545714921544,0.1515198484848485,6.599795406342403
0.3535446464646465,0.707089292929293,0.39267965736898613,2.221386528098668,0.17677232323232325,5.656994159010677
0.404049595959596,0.808099191919192,0.5128840890001433,2.538718484705182,0.202024797979798,4.949887390061876
0.4545545454545455,0.909109090909091,0.6491153550728459,2.8560504413116954,0.22727727272727274,4.399912001759964
0.505059494949495,1.01011898989899,0.801373455587094,3.173382397918209,0.2525297474747475,3.959929513254664
0.5555644444444444,1.1111288888888888,0.9696583905428874,3.4907143545247226,0.2777822222222222,3.5999424009215852
0.606069393939394,1.212138787878788,1.1539701599402266,3.808046311131237,0.303034696969697,3.299952150693815
0.6565743434343434,1.3131486868686868,1.354308763779111,4.12537826773775,0.3282871717171717,3.0461135437284987
0.707079292929293,1.414158585858586,1.5706742020595412,4.442710224344264,0.3535396464646465,2.828537082049718
0.7575842424242424,1.5151684848484848,1.8030664747815164,4.760042180950777,0.3787921212121212,2.639970432331158
0.8080891919191919,1.6161783838383839,2.051485581945038,5.077374137557292,0.40404459595959596,2.474974322141408
0.8585941414141415,1.717188282828283,2.3159315235501046,5.394706094163806,0.42929707070707074,2.32938929295035
0.9090990909090909,1.8181981818181818,2.596404299596716,5.712038050770319,0.45454954545454546,2.1999802001781985
0.9596040404040405,1.919208080808081,2.892903910084874,6.029370007376833,0.47980202020202023,2.0841929752170505
1.0101089898989901,2.0202179797979802,3.205430355014578,6.346701963983348,0.5050544949494951,1.9799843581235703
1.0606139393939396,2.121227878787879,3.5339836343858257,6.664033920589861,0.5303069696969698,1.88570027765508
1.111118888888889,2.222237777777778,3.8785637481986197,6.9813658771963745,0.5555594444444445,1.7999874000881992
1.1616238383838384,2.323247676767677,4.239170696452958,7.298697833802888,0.5808119191919192,1.7217277520600733
1.212128787878788,2.424257575757576,4.615804479148845,7.616029790409403,0.606064393939394,1.6499896875644524
1.2626337373737375,2.525267474747475,5.008465096286274,7.933361747015916,0.6313168686868688,1.583990622775513
1.313138686868687,2.626277373737374,5.41715254786525,8.25069370362243,0.6565693434343435,1.5230683704622272
1.3636436363636366,2.7272872727272732,5.841866833885773,8.568025660228944,0.6818218181818183,1.4666588444861626
1.414148585858586,2.828297171717172,6.2826079543478395,8.885357616835458,0.707074292929293,1.414278541873109
1.4646535353535355,2.929307070707071,6.739375909251451,9.20268957344197,0.7323267676767677,1.3655106492589344
1.515158484848485,3.03031696969697,7.2121706985966085,9.520021530048485,0.7575792424242425,1.319993928027931
1.5656634343434346,3.131326868686869,7.700992322383313,9.837353486655,0.7828317171717173,1.2774137507009644
1.616168383838384,3.232336767676768,8.205840780611561,10.154685443261512,0.808084191919192,1.2374948179904495
1.6666733333333335,3.333346666666667,8.726716073281356,10.472017399868026,0.8333366666666667,1.1999952000191998
1.717178282828283,3.434356565656566,9.263618200392697,10.78934935647454,0.8585891414141416,1.1647014290827709
1.7676832323232325,3.535366464646465,9.81654716194558,11.106681313081054,0.8838416161616163,1.1314244336477854
1.818188181818182,3.636376363636364,10.38550295794001,11.424013269687567,0.909094090909091,1.099996150013475
1.8686931313131314,3.737386262626263,10.970485588375986,11.741345226294081,0.9343465656565657,1.0702666834305743
1.919198080808081,3.838396161616162,11.57149505325351,12.058677182900595,0.9595990404040405,1.0421019174622648
1.9697030303030305,3.939406060606061,12.188531352572577,12.376009139507108,0.9848515151515153,1.0153814911338734
2.02020797979798,4.04041595959596,12.821594486333192,12.693341096113624,1.01010398989899,0.9899970795086153
2.0707129292929296,4.141425858585859,13.470684454535348,13.010673052720136,1.0353564646464648,0.9658509258851852
2.121217878787879,4.242435757575758,14.135801257179052,13.32800500932665,1.0606089393939395,0.9428545836804156
2.1717228282828285,4.343445656565657,14.8169448942643,13.645336965933163,1.0858614141414142,0.9209278338623862
2.222227777777778,4.444455555555556,15.514115365791094,13.962668922539677,1.111113888888889,0.899997750005625
2.2727327272727273,4.545465454545455,16.22731267175943,14.28000087914619,1.1363663636363637,0.8799978880050687
2.323237676767677,4.646475353535354,16.956536812169315,14.597332835752704,1.1616188383838384,0.8608675814790514
2.3737426262626267,4.747485252525253,17.701787787020752,14.91466479235922,1.1868713131313133,0.8425513271204675
2.424247575757576,4.848495151515152,18.46306559631373,15.231996748965733,1.212123787878788,0.8249982468787252
2.4747525252525255,4.949505050505051,19.24037024004825,15.549328705572247,1.2373762626262628,0.808161615996702
2.525257474747475,5.05051494949495,20.033701718224314,15.86666066217876,1.2626287373737375,0.7919984476830425
2.5757624242424244,5.151524848484849,20.84306003084193,16.183992618785272,1.2878812121212122,0.7764691266463498
2.626267373737374,5.252534747474748,21.668445177901088,16.501324575391788,1.313133686868687,0.7615370849137311
2.6767723232323233,5.353544646464647,22.50985715940179,16.8186565319983,1.3383861616161616,0.7471685143489939
2.727277272727273,5.454554545454546,23.367295975344046,17.135988488604816,1.3636386363636366,0.733332111113148
2.7777822222222226,5.555564444444445,24.24076162572784,17.45332044521133,1.3888911111111113,0.7199988480018431
2.828287171717172,5.656574343434344,25.130254110553178,17.77065240181784,1.414143585858586,0.707141771175137
2.8787921212121215,5.757584242424243,26.03577342982006,18.087984358424357,1.4393960606060607,0.6947358182840572
2.929297070707071,5.858594141414142,26.957319583528495,18.40531631503087,1.4646485353535355,0.6827576554115906
2.9798020202020203,5.959604040404041,27.894892571678472,18.722648271637382,1.4899010101010102,0.6711855305958907
3.0303069696969698,6.0606139393939396,28.848492394269993,19.039980228243895,1.5151534848484849,0.6599991420011154
3.0808119191919197,6.161623838383839,29.818119051303068,19.35731218485041,1.5404059595959598,0.6491795190550254
3.131316868686869,6.262633737373738,30.803772542777676,19.674644141456927,1.5656584343434345,0.6387089150893593
3.1818218181818185,6.363643636363637,31.805452868693834,19.99197609806344,1.5909109090909093,0.6285707102049025
3.232326767676768,6.464653535353536,32.823160029051536,20.309308054669952,1.616163383838384,0.6187493232429276
3.2828317171717174,6.565663434343435,33.856894023850785,20.626640011276464,1.6414158585858587,0.6092301318823236
3.333336666666667,6.666673333333334,34.90665485309158,20.94397196788298,1.6666683333333334,0.5999994000005999
3.3838416161616163,6.7676832323232325,35.97244251677392,21.261303924489493,1.6919208080808081,0.5910442115398576
3.434346565656566,6.868693131313132,37.054257014897814,21.57863588109601,1.717173282828283,0.5823524102080965
3.4848515151515156,6.969703030303031,38.152098347463244,21.89596783770252,1.7424257575757578,0.5739125444238743
3.535356464646465,7.07071292929293,39.26596651447022,22.213299794309034,1.7676782323232325,0.5657138169799801
3.5858614141414145,7.171722828282829,40.39586151591874,22.53063175091555,1.7929307070707072,0.5577460389608706
3.636366363636364,7.272732727272728,41.5417833518088,22.847963707522062,1.818183181818182,0.5499995875003093
3.6868713131313133,7.373742626262627,42.70373202214042,23.165295664128575,1.8434356565656567,0.5424653670109714
3.7373762626262628,7.4747525252525255,43.88170752691357,23.482627620735087,1.8686881313131314,0.5351347735575854
3.7878812121212126,7.575762424242425,45.07570986612829,23.799959577341603,1.8939406060606063,0.5279996620802162
3.838386161616162,7.676772323232324,46.28573903978454,24.11729153394812,1.919193080808081,0.521052316205177
3.8888911111111115,7.777782222222223,47.51179504788233,24.434623490554632,1.9444455555555558,0.5142854204083311
3.939396060606061,7.878792121212122,48.75387789042168,24.751955447161144,1.9696980303030305,0.5076920343196738
3.9899010101010104,7.979802020202021,50.01198756740256,25.069287403767657,1.9949505050505052,0.5012655689794587
4.04040595959596,8.08081191919192,51.28612407882499,25.386619360374173,2.02020297979798,0.49499976487511166
4.090910909090909,8.181821818181819,52.576287424688964,25.703951316980685,2.0454554545454546,0.4888886716050348
4.141415858585859,8.282831717171717,53.882477604994484,26.021283273587198,2.0707079292929294,0.4829266290304221
4.191920808080808,8.383841616161616,55.20469461974155,26.33861523019371,2.095960404040404,0.47710824978959043
4.242425757575758,8.484851515151515,56.54293846893017,26.655947186800226,2.121212878787879,0.47142840306128464
4.292930707070707,8.585861414141414,57.89720915256032,26.97327914340674,2.1464653535353535,0.465882199474099
4.3434356565656564,8.686871313131313,59.26750667063203,27.29061110001325,2.1717178282828282,0.46046497706872785
4.393940606060606,8.787881212121212,60.65383102314527,27.607943056619764,2.196970303030303,0.4551722882283343
4.444445555555555,8.88889111111111,62.05618221010007,27.92527501322628,2.2222227777777777,0.4499998875000282
4.494950505050505,8.98990101010101,63.474560231496405,28.242606969832792,2.2474752525252524,0.4449437202373663
4.545455454545454,9.090910909090908,64.9089650873343,28.559938926439305,2.272727727272727,0.43999991200001765
4.595960404040404,9.191920808080807,66.35939677761372,28.877270883045817,2.297980202020202,0.43516475865235016
4.646465353535353,9.292930707070706,67.8258553023347,29.194602839652333,2.3232326767676765,0.4304347171077605
4.696970303030303,9.393940606060607,69.30834066149725,29.511934796258853,2.3484851515151517,0.4258063966701423
4.747475252525253,9.494950505050506,70.80685285510131,29.829266752865365,2.3737376262626264,0.42127655092802646
4.797980202020202,9.595960404040405,72.32139188314692,30.146598709471878,2.398990101010101,0.41684207016066777
4.848485151515152,9.696970303030303,73.85195774563408,30.46393066607839,2.424242575757576,0.4124999742187516
4.898990101010101,9.797980202020202,75.39855044256278,30.781262622684906,2.4494950505050506,0.4082474058454678
4.949495050505051,9.898990101010101,76.96116997393304,31.09859457929142,2.4747475252525253,0.4040816244064975
5.0,10.0,78.53981633974483,31.41592653589793,2.5,0.4
The data above shows values over the range from near zero to 5 centimeters of radius.
Links to images go here: Three plots are available. the links will be posted shortly.
These links are on the Azure test server, so they are visible to those who sent IP address information to newmarsmember at gmail.com
http://40.75.112.55/phpBB3/download/file.php?id=101
http://40.75.112.55/phpBB3/download/file.php?id=100
http://40.75.112.55/phpBB3/download/file.php?id=99
This data is for all pipes, forever.
Here is a link to an image from GW Johnson that shows the same data with an image of a circle to add context
http://40.75.112.55/phpBB3/download/file.php?id=102
For those who might take the time to generate the graphs available from the above data, GW Johnson reminded me that the curve of 2 divided by radius (2/r) has the appearance of a hyperbola, but the curve is not a true hyperbola.
Curves such as these are more likely to be found in study of analytic geometry.
I attempted to obtain an explanation of curves of these types, but the result was not usable in the context of the forum
The practical application of the curve you see when you plot 2/r is the sizing of tubes for heat transfer, and that is precisely the problem the Optical Plane working group is addressing. kbd512 found a study done for NASA on a next generation nuclear thermal rocket. It is from that study we have the radius 0.1778 centimeters, which was chosen for the CERMET application.
Ultimately we find that a different radius is better for our application, but at the moment, 0.1778 centimeters is all we have to work with.
(th)
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#5 2025-12-04 02:58:40
- Calliban
- Member
- From: Northern England, UK
- Registered: 2019-08-18
- Posts: 4,266
Re: Thermal Efficiency in Propulsion
The new CatGen catalyst bed technology promisses more compact and fuel efficient GT engines.
https://youtu.be/-TDoteS9QZA
I can see a number of problems with this idea in practice.
1. Whilst the catalyst allows efficient combustion in a compact volume, its presence limits combustion temperature to the melting point of the catalyst and substrate. This places limits on cycle efficiency.
2. The catalyst bed adds weight.
3. The compressor must force air through the narrow channels of the cataylst bed, which increases pumping losses through the engine. In a conventional GT, compression already consumes at least half of the energy produced by the turbine.
4. Although the video talks about the tolerance of the catalyst to different fuels, the reality is that fuels containing sulphur or soot will poison the catalyst.
In spite of these problems, this engine concept may offer value in burning lean fuel mixtures that would not otherwise support combustion. In the Martian context, we know that the Martian atmosphere contains small amounts of CO and O2. If CO2 can be seperated from the bulk air, the remaining gas mix could be preheated and passed through a catalyst bed to extract energy. Given the small concentration of CO, this is unlikely to be a net energy producing reaction. But assuming we are inputting energy to extract specific gases from the Martian atmosphere, this reaction would allow some portion of input energy to be recovered. It also scrubs CO out of the N2/Ar gas mix, which is important if we are gathering life support gases.
Last edited by Calliban (2025-12-04 02:59:56)
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
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#6 2025-12-04 16:57:07
- kbd512
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Re: Thermal Efficiency in Propulsion
Calliban,
CO2 bubbled through a Gallium-Indium-Copper catalyst will produce pure O2 and flakes of pure Carbon that float to the top of the liquid metal column, very near room temperature. There will be plenty of other losses associated with obtaining CO2, compressing the O2 oxidizer, and possibly liquefying it to further reduce storage volume, but CO2 will always be plentiful on Mars and can be extracted at night and stored as LCO2 using minimal energy input. The Carbon powder can be pumped by fluidizing it with LCO2. Storing large amounts of O2, even somewhere pretty cold like Mars, is the most challenging issue. The exhaust effluent from a gas turbine burning pure Carbon and O2 is nearly pure CO2, which can be recaptured using appropriate cooling and recompression equipment.
The Allam-Fetvedt cycle uses a SCO2 power turbine and recaptures most of the CO2 effluent from combustion for heat re-injection. Approximately 95% of the "atmosphere" fed into the combustor is actually recycled hot CO2. The remainder is coal dust or natural gas and pure or O2-enriched "air". Re-heating of a larger volume of "cold combustible mixture" is not required. Here on Earth, this cycle is paired with an energy-robbing ASU to produce pure or enriched O2. Using the Gallium-Indium-Copper catalyst to produce coal dust and O2 would mean the major energy losses are limited to O2 compression and CO2 recompression.
We're going to start operating a 300MWe power plant in Odessa, Texas, starting in 2026. It was built by NetPower on land owned by Occidental Petroleum, who is presumably supplying the gas. A 50MWth demo plant has already been built and tested in La Porte, Texas. The utility scale plant will burn natural gas instead of coal powder, but that's because we have so much natural gas here. Another similar plant being built in one of the other midwest states will supposedly be rigged to burn coal brought in from the Powder River Basin. Plant construction for the Odessa facility is nearing completion. Certification to get connected to our grid is on track to begin next year.
An overhead shot of the La Porte, Texas demo facility:
I can't swear to it, but I believe the Odessa facility is merely a rework of part of an existing 1GWe natural gas fired power plant that's been in operation for some time now.
NET Power Consolidates Business to Gear Up for Allam Cycle Power Plant Deployment
Assuming all goes well in Odessa, and the engineers seem reasonably confident that it will, they're talking about converting 1,000 power plants here in the US and about 15,000 globally.
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#7 2025-12-05 06:13:19
- Calliban
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Re: Thermal Efficiency in Propulsion
Here is a similar paper, this time using cerium as the active catalytic surface instead of copper. Both use liquid metal as conductive carrier for the catalytic surface and dissolved CO2.
https://www.nature.com/articles/s41467-019-08824-8
Correct me if I'm wrong, but they are talking about electrochemical decomposition of CO2 into carbonaceous products. This is therefore an electrolysis process that needs electric current to work. The catalyst is essential for reducing the temperature at which this happens. But the electrical energy is still needed to reduce the carbon.
It would be neat if we found an efficient and rapid process for converting low-grade heat into stored chemical energy. But the second law of thermodynamics appears to be against it. Entropy always increases.
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
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#8 2025-12-06 12:14:14
- kbd512
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Re: Thermal Efficiency in Propulsion
Calliban,
This is the process I'm thinking of:
This is the device:
This CO2 splitting process does not directly consume electricity for the purpose of stripping the O2 from the CO2. There will obviously be the bath vibrator to help "bubble" (disperse and react the CO2 through the eutectic mixture) the CO2 through the column of liquid metal, which is electrical, and pumps to pump-in the CO2, and another pump to pump-out / compress the O2 if the O2 is also captured. I presume the pumps would be electrical because that's how we normally do it whenever we can. Maybe the pump doesn't have to be electrical and maybe some kind of mechanical device could vibrate the eutectic mixture tube in its hot water bath, but that seems like a lot of extra work when electrical pumps already get the job done.
All that said, there are combinations of purely chemical and electrocatalytic processes involving various room temperature liquid metals and lanthanide catalysts. IIRC, the express stated purpose of these catalysts is production of syngas (for fuels and plastics) and alcohols (presumably for Alcohol-derived fuels, but also for chemicals), not solid Carbon powder (as close as we're going to get to synthetic coal).
I believe the papers you're looking at are for partial CO2 splitting of syngas and other short-chain hydrocarbon molecules. Almost everyone is primarily interested in synthetic liquid fuels, not synthetic coal. The general idea is that refinement of these new processes or something similar can produce the gasoline, diesel, and kerosene fuels we prefer to use.
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#9 2025-12-06 16:04:00
- Calliban
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Re: Thermal Efficiency in Propulsion
From your link, the flow of liquid gallium over silver nanorods, creates triboelectric current. This breaks the C=O bonds in the CO2. So this process converts a mixture of mechanical and thermal energy into chemical energy. The energy consumption of 230kWh/tonne of CO2, is 810kWh per tonne of carbon. At an electricity cost of $0.1/kWh, that works out at $81/tonne carbon. That is assuming that the 230kWh is electrical energy. So this does look promissing.
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
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#10 Yesterday 14:08:16
- Calliban
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Re: Thermal Efficiency in Propulsion
It would be interesting to know how the 230kWh of electrical energy are consumed. Is this used in gathering and compressing the CO2? Is it the motor seperating the carbon flakes? On Mars, the ambient atmosphere is typically cold - far beneath the CO2 critical point and often beneath the triple point. CO2 could be gathered as liquid with relatively little compressor work. Or it could be allowed to accumulate as ice on a cold plate. What is the energy input creating motion in the nanoparticles? For particles this small, even brownian motion would generate triboelectric current through friction. It would be amazing if we could develop a process that could convert low grade heat into chemical energy. Such energy could be derived from the sun or waste heat from a nuclear reactor. There is even the potential for geothermal heat to be used in select locations.
Last edited by Calliban (Yesterday 14:11:32)
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