kbd512 Postings

tahanson43206 · 2026-01-07 10:25:35

For kbd512 ...

This post picks up on #375...

I ran a search to see what is offered in topics ... we have nothing for SCO2. We have only one topic with supercritical...

Coal-fired Brayton Cycle Supercritical CO2 Boilers

That topic is probably a candidate for an update...

What do you think of creating a topic that is about the SCO2 concept over all?

Wikipedia has an article that appears to be an attempt to keep up to date.

If this forum had a dedicated topic, it could report on applications other than the coal fired boiler concept.

There must be reasons why SCO2 is not yet showing up in mass market applications.

Perhaps there is something about this technology that requires a massive investment to realize a return, and with existing systems performing reasonably well, perhaps investors simply aren't willing to take the risk.

Hybrid cars (that I know about) use piston engines to recharge the batteries for electric motors. It sounds (from Post #375) that SCO2 systems might be able to recharge batteries, so they might be candidates for hybrid vehicles as described in #375.

What would it take to put a vehicle like that on the road? What carbon fuels would it burn? It seems to me that having a carbon burning system in a vehicle would help deal with external cold while electric propulsion would eliminate complexity of mechanical drive trains.

(th)

tahanson43206 · 2026-01-07 11:12:01

For kbd512 ... we do not yet have a topic dedicated to SCO2 .... I'll put this analysis of SCO2 on Mars in your topic.

As a follow up... It sounds as though SCO2 is unlikely to achieve substantial market share compared to water based energy transformation systems. However, on Mars, the advantage of water is gone. There is water, but it will be enormously expensive. I contrast with Earth, Carbon Dioxide is readily available in great quantities. Please see if you can figure out how an energy storage system based upon the simple cycle: CO2 >> CO + O2 >> CO2 can be combined with SCO2 for energy transformation in a vehicle such as an Earth mover. Such a vehicle would need large tanks to hold CO and O2, but the output would be exhausted to the atmosphere. How might an SCO2 system recharge batteries for electric motors used for the drive train and manipulator operation?
***
On Mars, your proposed cycle—CO 2 →CO+O 2 →CO 2 —is more than just a chemical loop; it is a chemical battery that leverages the planet's atmosphere as both the fuel source and the carrier fluid.
Combining this with a supercritical CO 2 (sCO 2 ) system creates a high-efficiency power plant for heavy machinery that addresses the specific hurdles of the Martian environment.
1. The Energy Loop: "Mars Atmospheric Battery"
The system functions in two distinct phases: Recharge (at a base) and Discharge (on the vehicle).
Phase A: Charging (ISRU Base)
A stationary plant uses solar or nuclear power to "charge" the system by splitting atmospheric CO 2 .
Solid Oxide Electrolysis (SOXE): Using technology like NASA’s MOXIE, the base dissociates CO 2 into CO and O 2 .
Compression & Storage: These gases are compressed and stored in high-pressure tanks on the vehicle. Because CO 2 liquefies easily at Martian temperatures, the base can also provide the initial sCO 2 "working fluid" for the vehicle's internal loop.
Phase B: Discharging (The Vehicle)
The vehicle uses the stored CO and O 2 to generate heat via combustion.
2CO+O 2 →2CO 2 +Heat
This heat is then transferred to an internal sCO 2 power cycle to create mechanical motion and electricity.
2. The sCO 2 Power Transformation In an earth-mover or heavy rover, the sCO 2 system acts as the "Prime Mover" that replaces a traditional internal combustion engine.
How it recharges the drive batteries:
Direct-Fired or Indirect Heating: The CO/O 2 burns in a combustion chamber. In a Direct-Fired cycle (Allam-style), the resulting CO 2 from the flame becomes the working fluid. In an Indirect cycle, the flame heats a heat exchanger that warms a separate closed loop of sCO 2 .
Turbine Expansion: The high-pressure, high-temperature sCO 2 expands through a tiny, high-speed turbine.
High-Speed Generator: The turbine is coupled to a permanent magnet generator. Because sCO 2 turbines spin at extreme speeds (30,000+ RPM), they are perfectly suited for generating high-frequency AC power.
Power Electronics: This power is rectified and managed by a Power Distribution Unit (PDU) to:
Direct Drive: Power electric hub motors for the wheels.
Battery Top-off: Charge a Lithium-ion or Solid-State buffer battery that handles peak loads (like a sudden shove into a rock face).
Actuators: Power electric-hydrostatic actuators for the manipulator arms/shovels.
3. Why Mars makes sCO 2 more viable than Earth
The "headwinds" mentioned earlier are significantly reduced or turned into "tailwinds" on Mars:
Feature Challenge on Earth Advantage on Mars
Heat Rejection Needs water or massive fans. The cold Martian night (-60°C) is a perfect heat sink for sCO 2 condensation.
Atmospheric Gas CO 2 must be captured/stored. The atmosphere is CO 2 at 95% purity.
System Mass Steam is bulky; sCO 2 is just "smaller." Mass is the #1 cost in space. A desk-sized 1MW sCO 2 turbine is a massive logistics win.
Exhaust CO 2 is a pollutant. Exhausting CO 2 on Mars is harmless and returns the mass to the atmosphere.
4. Mechanical Design for an Earth-Mover
An sCO 2 earth-mover would likely follow a Hybrid-Electric architecture:
The "Engine" (sCO2): A modular, vibration-isolated "Power Box" containing the CO/O 2 burner and the sCO 2 turbogenerator.
The "Tanks": Cryogenic or high-pressure tanks for CO and O 2 .
The "Buffer": A relatively small battery pack. The sCO 2 turbine doesn't like to change speeds quickly, so it runs at a steady, efficient "cruise" while the battery absorbs the spikes in power needed for digging.
The Exhaust: Instead of a complex "condenser" to recycle every drop of CO 2 , the vehicle can afford a "Semi-Open Cycle." It exhausts the CO 2 byproduct of combustion into the Martian air, knowing the base station can always suck more out of the sky to "refuel" it.
Would you like me to look into the specific energy density (Wh/kg) of a CO/O 2 chemical storage system compared to modern batteries to see how much more range a Martian earth-mover might have?
***
Thank you for your helpful analysis and clear presentation! I will publish this in a forum devoted to Mars settlement. Hopefully there will be interest and follow up questions.
***
That sounds like an excellent plan! The Mars settlement community is exactly the right crowd for this—they value high-efficiency, closed-loop (or semi-closed-loop) systems where mass-savings are the highest priority.
To give your forum post a bit more "technical punch," here is a quick summary of the specific engineering synergy you've identified, which could spark deeper discussion among the members:
Key Talking Points for your Forum Post:
The "Atmospheric Battery" Advantage: Unlike Earth, where we struggle to store energy, Mars provides the "plates" of the battery for free in the atmosphere. We are essentially using solar/nuclear power to "un-burn" the Martian air into CO and O 2 , then "re-burning" it in the vehicle.
The Heat Sink Advantage: One of the biggest hurdles for sCO 2 on Earth is that the "cold" side of the cycle needs to be near 31°C to stay efficient. On Mars, the average temperature is -60°C. This makes the recuperation and condensation steps much easier and allows for a higher Carnot efficiency (1−T cold /T hot ).
Scale and Power Density: A steam-based earth-mover would be impractical due to the size of the boilers and condensers. An sCO 2 turbine the size of a watermelon could potentially power a 100-ton excavator.
A Technical Nuance for the "Follow-up Questions"
You might get asked about "Coking." When burning CO and O 2 , if the mixture isn't perfectly tuned, you can get carbon deposits (soot/coke) inside the machinery. However, in an sCO 2 environment, the high-pressure CO 2 actually acts as a solvent and a cleaning agent, which might help keep the turbine blades cleaner than a standard internal combustion engine on Earth.

(th)

tahanson43206 · Yesterday 14:32:52

For kbd512 ... thanks for this substantial update! https://newmars.com/forums/viewtopic.ph … 00#p237000

It appears that your consistent support of the SCO2 technology has a chance of paying off.

I doubt anyone who's invested has seen a return, but your reports seem to indicate that all that money may ultimately see a return.

FYI .... ChatGPT5.2 just created a utility program that allows us to "watch" the CFD model as it is running.

We are testing the 1 kg/s feed in this run. I am hoping it yields improved ISP at the price of reduced thrust.

If the improved ISP hypothesis pans out, as a flight director, you would have freedom to select the optimum run characteristics for a particular point in the flight plan.

There might be a minimum mass flow that is usable, but at this point I don't think we know anything. All we know for certain is that 2 kg/s works.

We have not tested 20 kg/s with the constricted nozzle. We know 20 kg/s works with the original large nozzle.

(th)

kbd512 · Today 01:53:31

tahanson43206,

Using materials like Alumina and BNNT, it's feasible to produce SCO2 engines with 1,300C TITs and 66% thermal-to-mechanical efficiency, with the weight of Aluminum metal and both absolute strength and strength-to-weight far surpassing any Inconel super alloy at 1,300C. At that point, there's little to argue over the benefits of this technology. It will be smaller / lighter / stronger / longer-lasting / more thermally efficient than any competing thermal engine technology. It's rapidly becoming a close runner-up to Solid Oxide Fuel Cells, but at much greater power density.

Reliable direct conversion (of hydrocarbon fuels) SOFCs are now approaching 5kW/kg in commercialized applications, and they achieve 70% to 80% thermal efficiency. I've read about lab-scale test articles achieving 8kW/kg. Plate-out of the electrodes and destruction of the membranes from Sulfur contamination continues to be a problem, although use of Methane vs denser fuels (Propane, kerosene, diesel) ameliorates this problem. SCO2 gas turbine engines are capable of power densities about 20X that of SOFCs by using CMCs combining Alumina with advanced fiber reinforcements like BNNT.

Do you see those big white components in these gas turbine engines?:

Those are Alumina-based CMCs. They're ceramic fiber reinforced metal oxide matrix composites (Alumina binder with Nextel fibers or something similar) with some plasticity to them, meaning they behave less like glass rods and more like sheet metal, but with significant thermal shock tolerance. They're not stronger than metals at room temperature, nor harder than pure ceramics, nor stiffer than Carbon fibers, yet they have a highly desirable mix of those properties combined with greater tensile strength than super alloys at combustion temperatures. Did I mention how light they are? They're similar in density to Aluminum. Even after hundreds of hours of operation, they still look brand new, because they're already oxidized to the point that no additional oxidation is possible. Have you ever noticed how metals exposed to such extreme temperatures look "rusted" or "blackened" or "every color of the rainbow"? That is actually surface oxidation damage to the base metal alloy. After a certain amount of accumulated oxidation damage, they become scrap metal.

A master's level thesis on testing these materials:
All-Oxide Ceramic Matrix Composites - Thermal Stability during Tribological Interactions with Superalloys - Daniel Vazquez Calnacasco - Luleå University of Technology, Department of Engineering Sciences and Mathematics

Preface
This project was performed between September 2019 and May 2021 as part of the Advanced Materials Science and Engineering (AMASE) Master Program, coordinated by the European School of Materials (EUSMAT) through an Erasmus+ scholarship.
The work focused on the interactions between a ceramic matrix composite and a superalloy when subjected to tribological testing and was carried out under the supervision of professors Marta-Lena Antti and Farid Akhtar at the Division of Engineering Materials of Luleå University of Technology (Sweden) in collaboration with GKN Aerospace Engine Systems, Sweden.
The composites studied in this work are often referred to in the literature with different terminologies involving the acronym “CMC” for Ceramic Matrix Composites, preceded by a suffix, such as in: i) “Oxide” or “All-Oxide” CMC (OCMC), ii) Oxide-Oxide CMC (Ox-Ox or Ox/Ox CMC), iii) Continuous-Fiber Ceramic Composites (CFCC), iv) Long Fiber Composites (LFC) v) Ceramic Fiber-Matrix Composites (CFMC) and vi) Fiber Reinforced Ceramics (FRC & FRCMC). In this work the term OCMC is preferred.
When addressing a composite in this document, the nomenclature will consist of three components, in the following order: fiber/(interphase)/matrix. If only two components are written, such as in “N720/A”, it will be understood that the composite has a porous matrix and no interphase.

A NASA CMC Development Partnership Project with Rolls-Royce and COI ceramics:
[url=https://ntrs.nasa.gov/api/citations/20150018257/downloads/20150018257.pdf]OXIDE/OXIDE CERAMIC MATRIX COMPOSITE (CMC)
EXHAUST MIXER DEVELOPMENT IN THE NASA ENVIRONMENTALLY RESPONSIBLE AVIATION (ERA) PROJECT[/url]

The very last slide shows pictograms of the process steps that COI Ceramics uses to make these parts.

Anyone who wants to see practical hybrid-electric aircraft take flight should be onboard with this tech, because every other energy storage and conversion technology is a pretender to their cause. At the present time, there are no electro-chemical batteries or fuel cells in existence that come within a country mile of the power-to-weight requirements for modern long range turbine-powered and kerosene-fueled aircraft.

Seeing designs with 20-30% increase in fuel economy over existing conventional gas turbine powered aircraft would be pretty spectacular.

This comment from Reddit User "discombobulated38x" is one of the best simplified explanations of current large turbofan engine design that I've seen in awhile:

Jet engine efficiency is made up of two things Thermal efficiency (Nth) and propulsive efficiency (Np).
Nth is 1 when all of the energy liberated by fuel is extracted (so exhaust gas is same temperature as at compressor exit) which is obviously impossible.
Np is 1 when the jet velocity matches the free stream velocity (so no thrust is created).
The goal of a turbofan is to lower the jet velocity, increasing the propulsive efficiency.
I'm struggling to think of a simple way to explain this, but if you take a turbojet, which has, say, Nth of 0.4 (in reality the faster you go the better this number gets), the mass flow is going to be low and the jet velocity (very) high. This means the engine doesn't generate much thrust when moving slowly, but still generates most of that thrust at high (supersonic) speeds, when the free stream velocity is close to the jet velocity (jet velocity not being supersonic as it is so much hotter than the free stream gas).
If you slap a power turbine on the back of that engine and hook it up to a fan it can comfortably generate an order of magnitude more thrust, but at a much lower jet velocity.
What this means is that your thrust at cruise greater, and is propulsively efficient, having a jet velocity as close as possible to the free stream velocity.
You also you have bucket loads more thrust at takeoff, which makes getting off the ground easier.
All of this is done for the same fuel burn. The higher propulsive efficiency at all stages of flight means more thrust is generated per kg of fuel burnt.
The biggest issue with high bypass turbofans is that the tip speed is limited to just over Mach 1 for a couple of reasons. This sets the speed of your low pressure rotor, which means you need a high diameter low pressure turbine with multiple stages to get the work extraction up.
It also means you need a much longer high pressure compressor, which comes with a whole host of its own issues. Pratt & Whitney and GE have mitigated this slightly by adding booster stages to the core, linked to the fan, which do a little but not much. Rolls-Royce on the other hand have gone for a three shaft architecture, which is substantially more complex, but allows for much more efficient compression, resulting in an engine that is substantially shorter and lighter than the competition at a cost of massively increased complexity/part count.
Pratt & Whitney (and RR, but they're behind the game here, partly because they don't have a competing product and partly because they have 3 shaft) have fixed both of these issues by developing a geared turbofan, in which the mass of a huge, slow LP turbine is removed, being replaced with a high speed intermediate/low pressure turbine and a big heavy gearbox. This drives an IP compressor at high speed, and then the fan via a reduction gearbox, decoupling fan diameter/tip speed and turbine speed.
It is a very nifty design, but the gearbox is incredibly hard to design, and to Pratts credit they appear to have nailed it on their PW1000 narrow body engine family. RR have a demo vehicle at the wide body end of the market called UltraFan, and that has the largest aerospace gearbox ever made, which has topped 87,000 horsepower. It's a thing of beauty.
I've not seen a GE9X cutaway yet (and suspect it will be a few years before I do), but GE are stuck with a huge, multi stage LP turbine, not that that seems to have deterred them from producing the biggest, highest bypass ratio having, most powerful aerospace gas turbine on the planet.

kbd512 · Today 02:11:09

This link covers some of the ceramic fibers being used in these parts:
Oxide-oxide ceramic matrix composites enabling widespread industry adoption

I would be remiss if I did not mention the role that NASA's and DOE's partnership programs as the genesis for the commercialization of a lot of these lab curiosities. Science for its own sake still matters, but so does directed science, aka "engineering", aimed at solving real world problems. NASA helps industry develop the basic "know-how" to retire risk to begin to apply aerospace technologies to the ordinary everyday world that the majority of us inhabit.

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#376 2026-01-07 10:25:35

Re: kbd512 Postings

#377 2026-01-07 11:12:01

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#378 Yesterday 14:32:52

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