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#276 2022-05-02 13:40:13

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 2,224

Re: Internal combustion engines for Mars

Kbd512, 9.76hp is 7.3kW.  Is that the fan power needed to remove 25kW of heat?  If so, it is damning for the case of using Martian air for convective cooling.  But remember that P expression in the equation is the dP across the fan, not total atmospheric pressure.  Typically, dP will be no greater than 5KPa here on Earth and typically no greater than 4KPa.  Fans get progressively less efficient as dP/P increases.

2dP/(ambient Rho) = v^2

Where v is flow speed through the fan.  A 4KPa dP will give a flow speed of 81.65m/s here on Earth.  On Mars, a 24.4Pa dP will give a flow rate of 61.3m/s.

On Earth a fan delivering 100,000m3/hr at 4KPa dP will consume a power of 120kW.  That is about 10% efficient in terms of kW of electric energy converted to air kinetic energy.
https://www.engineeringtoolbox.com/fans … d_197.html

One thing to keep in mind is that CO2 at 250K is over 50°C beneath it's critical point and only 30K above triple point.  This should make a fan a lot more efficient.  Friction will only consume 38% as much power on Mars.  That should help as well.

A 4% dP in the Martian atmosphere gives a flow rate of 61.27 m/s, taking ambient rho to be 13 grams / m3.  That is about 0.8kg/m2 swept area per second.  If dT is 200K and Cp is about 800, then heat removed would be a maximum of 128kW per m2 swept area.  The reason I say 'maximum' is that the heat exchanger will have a pressure drop across it that will reduce the effective driving dP.

Last edited by Calliban (2022-05-02 13:57:58)


"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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#277 2022-05-02 13:48:57

tahanson43206
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Registered: 2018-04-27
Posts: 12,051

Re: Internal combustion engines for Mars

For Calliban re cooling discussion .... out of curiosity, in your opinion, would it be feasible to use the regolith of Mars as a heat sink for a manufacturing plant?

I am "pretty sure" you've already addressed this question in your thinking about fission reactors on Mars.

The heat sink would need to enjoy the presence of water brine in some abundance, to carry the thermal energy to be sunk out into the terrain under the plant.  However, that thermal energy could itself serve to liberate water to be harvested.

(th)

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#278 2022-05-02 14:05:47

Calliban
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From: Northern England, UK
Registered: 2019-08-18
Posts: 2,224

Re: Internal combustion engines for Mars

tahanson43206 wrote:

For Calliban re cooling discussion .... out of curiosity, in your opinion, would it be feasible to use the regolith of Mars as a heat sink for a manufacturing plant?

I am "pretty sure" you've already addressed this question in your thinking about fission reactors on Mars.

The heat sink would need to enjoy the presence of water brine in some abundance, to carry the thermal energy to be sunk out into the terrain under the plant.  However, that thermal energy could itself serve to liberate water to be harvested.

(th)

I would imagine so.  Fine, dry regolith on Mars has about the same thermal conductivity as rock wool.  But if water can be used as a means of transferring heat to the surrounding permafrost, it would be a far more efficient heat sink.

A while back Robert Zubrin wrote an article about the possibility of inhabiting ice covered lakes on Mars.  One of the things that makes the idea so attractive is the presence of a heat sink that can be pumped through a compact heat exchanger.  If we are forced to rely on purely radiative heat sinks on Mars, the radiators for a light water reactor, with a condenser temperature of 300K, would have to cover an area about 20% the size of a solar power plant on equivalent power output.  None of that matters if we are using the waste heat to warm up greenhouses of course.

Last edited by Calliban (2022-05-02 14:13:15)


"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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#279 2022-05-02 15:32:58

tahanson43206
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Re: Internal combustion engines for Mars

For Calliban re #278

Thanks for the reminder that greenhouses are a logical destination for "waste" heat from manufacturing of liquefied gases for machery.

The transfer would be by convection to the atmosphere (presumably) at 1/2 Earth Standard that would be typical of Mars habitats, if the recommendation of RobertDyck is accepted and implemented.

There are some who suggest a lower pressure for greenhouses, but if the can be constructed at an energy cost that the settlement can afford, then it would be advantageous to be able to enter the greenhouse volume directly from habitat volume.

A cooling liquid could circulate between the manufacturing facility and the greenhouses (or habitats if they are located near by).

(th)

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#280 2022-05-02 15:45:40

Calliban
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From: Northern England, UK
Registered: 2019-08-18
Posts: 2,224

Re: Internal combustion engines for Mars

I would suggest transferring heat via a ditch that runs the length of the greenhouses.  This can then do three things simultaneously: (1) Heat the greenhouse; (2) Water it with dripping condensation; (3) Purify dirty water in the ditch.


"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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#281 2022-05-02 16:05:57

tahanson43206
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Posts: 12,051

Re: Internal combustion engines for Mars

For Calliban re #280

To clarify the mental picture I am creating to go with your post ...

A pipe containing hot liquid from the manufacturing plan is routed via a pipe (material to be defined), through a ditch containing some level of "dirty" water (it might be grey water from the habitat, for example).

After the coolant completes it's circuit, it is back at the plant, ready to take up another load of thermal energy.

? close ? ... needs adjustment ?

(th)

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#282 2022-05-02 16:17:42

Calliban
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From: Northern England, UK
Registered: 2019-08-18
Posts: 2,224

Re: Internal combustion engines for Mars

tahanson43206 wrote:

For Calliban re #280

To clarify the mental picture I am creating to go with your post ...

A pipe containing hot liquid from the manufacturing plan is routed via a pipe (material to be defined), through a ditch containing some level of "dirty" water (it might be grey water from the habitat, for example).

After the coolant completes it's circuit, it is back at the plant, ready to take up another load of thermal energy.

? close ? ... needs adjustment ?

(th)

Yes.  Grey water would work well.  It could in fact be salt water directly from the aquifer.  That would be even better in fact, as salt would suppress bacterial growth.  As the temperatures are low, a polypropylene pipe could be used to transfer heat into the ditch.  Concrete or high silicon cast iron could also be used.  The heat supply could be any form of waste heat from an industrial plant or indeed a nuclear power plant.

We could heat domed habitats in much the same way.  Water would condense on the roof and drip feed plants.  But I suspect that putting that much humidity into the air would not be ideal for a habitat.  But heat with a temperature of 30°C is ample for heating buildings and domes, with warm water running through concrete or plastic pipes within the structures and beneath the soil and streets.  Heat is then distributed by conduction and reradiated from all solid surfaces.  I think it very unlikely that any waste heat generated by industry or nuclear power plants would ever actually be wasted on Mars.

Last edited by Calliban (2022-05-02 16:32:53)


"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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#283 2022-05-02 16:36:05

kbd512
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Posts: 6,238

Re: Internal combustion engines for Mars

Calliban and tahanson43206,

Proving that this concept works seems to be a bit of a challenge, but now we're using WAVAR numbers for this calculation since they have actual fan modeling, pressure drops, and real experimental data under anticipated Mars atmospheric conditions.  WAVAR was designed by Department of Aeronautics and Astronautics University of Washington, Seattle, WA.

Extraction of Atmospheric Water on Mars in Support of the Mars Reference Mission - Mars Society Founding Convention, Boulder, CO, Aug 13-16, 1998

WAVAR's maximum fan power was 10kWe.  WAVAR's mass flow rate was 121.547 kg/h of Martian atmosphere.

They're using 0.017kg/m^3 as the Mars surface atmospheric density, so that's what we will use.

WAVAR could nominally push 121.547 kg/h of Martian atmosphere through a filter and zeolite bed.

US Patent US8978293B2 - Process for the production of useful materials for sustaining manned space missions on mars through in-situ resources utilization

I said I needed a flow rate of 10m^3/s to dissipate 25kWt.  That corresponds with a total mass flow rate of 0.17kg/s and 612kg/hr.

612kg/hr / 121.547kg/hr = 5.035

5.035 * 10kWe = 50.35kWe

That's a good deal more power than I'd hoped to consume, but still doable.

A non-communist from University of Seattle, WA (I know, right?  These days, what are the chances of that?) came up with a much smaller 85% efficient propeller:

FEASIBILITY STUDIES OF THE EXTRACTION OF WATER VAPOR FROM THE MARTIAN ATMOSPHERE BY ADSORPTION IN ZEOLITE 3A

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#284 2022-05-02 16:41:41

kbd512
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Posts: 6,238

Re: Internal combustion engines for Mars

tahanson43206,

Is it clear to everyone else that we either need a massive energy savings on synthesis of the fuel / oxidizer combo from room temperature processing, ala the NIST article I linked to, else this doesn't make much sense to do (with a gas turbine or any other kind of engine)?

The use of LPG fuel would make this a much more practical proposition.

I'm going to revisit your suggestion of using the intake charge as a heat sink, with and without cryogenics, but within reason.  Half the energy heat exchanged into the intake charge and the other half delivered by compression.

We need to find a way to get that power requirement down to something that only waste heat from the engine has to provide.

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#285 2022-05-02 17:18:39

Calliban
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From: Northern England, UK
Registered: 2019-08-18
Posts: 2,224

Re: Internal combustion engines for Mars

The pumping power is a strong function of the pressure drop across the heat exchanger, filter, zeolite bed, etc.  This isn't an easy thing to work out.  It would depend upon the shape of the heat Transfer surfaces, their size and the gaps between them and the roughness of the surfaces.

The zeolite bed and filters have a high pressure drop because the filter must be very fine to filter out Martian fines and the zeolite beads need a high surface area.  Also, pressure drop scales with the square of flow rate.

At present, we cannot really determine what flow rate per unit area we would need through the heat exchanger or what the pressure drop would be.  We can say that all else being equal, it is going to be more difficult designing a convective cooling system on Mars, because heat removal capability scales with flow velocity, but pressure drop scales with the square of flow velocity.  Because the air is much thinner, we need much higher flow velocity through the heat exchanger to remove the same amount of heat per unit surface area.  That means more pumping power per unit of heat removed than a comparable system on Earth.

Last edited by Calliban (2022-05-02 17:29:57)


"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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#286 2022-05-02 18:01:18

kbd512
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Posts: 6,238

Re: Internal combustion engines for Mars

Alright everyone,

Let's explore SpaceNut's suggestion of using molten salt as a waste heat sink while we're at it.

60% Sodium Nitrate / 40% Potassium Nitrate eutectic, aka "Solar Salt", has a specific heat capacity of 1.53kJ/kg K and it's liquid at 116°C.  We'll use 500kg of salt.

Let's assume we start off at 120°C or 393.15K and we take it up to 550°C or 823.15K.

Q· = m· * Cp * ΔT
Q· = 500kg * 1,530 * (550°C - 120°C)
Q· = 500 * 1,530 * 430
Q· = 328,950,000J
328,950,000J / 13,158 seconds / 219 minutes / 3.655 hours of run-time

If we take the salt to 650°C, then we get Q· = 405,450,000J (112.5kWh) and 4.505 hours of run time

NREL says we should get a 46.8% gross energy recovery with a 650°C "hot" tank and 470°C "cold" tank by using the thermal energy stored in the salt to generate electricity during the night or to keep the machine warm, but that's for a very large system, so we would probably get less than that.  Still, if we get 40% of 112.5kWh, that's still 45kWh.

Molten Salt Power Towers Operating at 600°C to 650°C

If we recovered 40% of the energy that a nuclear reactor dumps into molten salt tanks, then 45kWh is no better than Nickel-Metal Hydride batteries, except that the thermal battery will not store less energy over charge / discharge cycles.  With KiloPower, we can theoretically "recharge" this thermal battery at a rate of 30kW/hr, so the 12hour overnight period provides 360kWh of charging capability, but we would need 8 of these 500kg molten salt tanks to store that much power.  Once you add the tank mass, it's little better than Lead-acid, but again, no real temperature limits.  The tank stays hot and is recharged / discharged using a very small sCO2 gas turbine.

Unless we switch to using a better fuel, I say we leave the internal combustion engines at home.  If we can obtain salt from Mars, then our total thermal efficiency is no better or worse using nuclear and molten salt.  The electricity from the reactor can then be used to power the base.  Thermal can power the machines.  The only real "game changer" would be a high temperature fuel cell paired with a molten salt heat sink.

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#287 2022-05-02 18:23:51

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 26,791

Re: Internal combustion engines for Mars

tahanson43206 post 263 response,

page 1 post 30 is the ivf ula engine that uses the boil off at a pressure that is above 20 psi

Since we are using injectors for fuel, oxidizer and diluent gas we will not need the intake valves or anything else which would typically be used on earth as we are not using mars air pressure.

That extra valve being removed will allow for a thicker head wall for the temperatures to not be able to crack them quite so easily.

If we do have the temperatures we can also make it a combination sterling engine to produce power from what would be considered waste gas products.

https://en.wikipedia.org/wiki/Cummins_B_Series_engine

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#288 2022-05-02 21:45:56

kbd512
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Posts: 6,238

Re: Internal combustion engines for Mars

SpaceNut,

I don't know if making the head thicker where there's less heat transfer would be useful.  The exhaust valves and ports are where you typically see your most concentrated heat transfers into the head and water jacket.  That's why diesels frequently have Inconel exhaust valves these days, while the intake valves are either stainless steel or a much less expensive type of carbon steel.  Intakes don't see nearly as much heat as the exhaust valves, even under fairly high boost pressures.

To your point, the elimination of the intake valves would allow for larger exhaust valves with more heat sink surface area, there would be more room for extra injectors for the O2 and CO2, beefed-up exhaust valve rocker arms, and less total valve train mass to rob power from the engine.  However, if we do that we're no longer building a Cummins 6BT.  It's a kind of one-off engine design that won't be shared with any other designs.

If we're going to thermal sink into the intake charge, then we could still do compression ignition using far less compression.  Squirting in 4L of CO2 through something the size of a normal diesel injector would be highly problematic to say the least.  It would have to be the size of a normal intake valve to cram it all in fast enough.

A YouTube video of Carbon Monoxide combustion (blue flame):

The dancing flame: combustion of carbon monoxide

Apparently, CO will light off using normal atmospheric O2 content, no problem at all.

Maybe we should just do a CO / O2 / CO2 oxy-fuel combustor pintle that heats a sCO2 loop to drive a gas turbine, as Calliban suggested.

This diesel engine will be exceptionally heavy for the power it provides, unless we switch to a different fuel.

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#289 2022-05-03 00:32:26

Calliban
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From: Northern England, UK
Registered: 2019-08-18
Posts: 2,224

Re: Internal combustion engines for Mars

If a Kilopower unit is being used as a heat source for an S-CO2 power generation loop, then you won't need anywhere near as much molten salt, because heat can be generated on demand.  The salt can serve the two functions of absorbing decay heat when the engine is switched off and providing a gamma shield during reactor operations.  Within an hour of scramming the Kilopower unit, decay heat will be down to 1% of operating power.

The problem with CO/O2 in my opinion is relatively poor energy density at 6.4MJ/kg.  If a diesel engine working with this fuel is 40% efficient, then effective mass energy density drops to 2.6MJ of mechanical energy per kg.  When the weight of tankage, engine and heat exchanger are included, you would end up with a system providing only about the same mass energy density as state of the art Li-ion batteries.  Dimethyl ether would be a better direct substitute for diesel.  On Earth its vapour pressure is comparable to LPG.  At Martian temperatures, its vapour pressure would be low enough to allow storage in simple low alloy steel fuel tanks.  Oxidiser will be LOX.

The waste heat problem is not an easy one to solve.  It is made simplest if the bulk of waste heat is carried away with combustion products, with as little heat transfer into the engine as possible.  A gas turbine does this very effectively, with exhaust temperatures of 500°C.  A diesel engine exhaust can also reach temperatures of 500°C.  On Earth, small gas turbines are poorly efficient.  This is partly because of the large amount of work consumed by the compressor.  If fuel can be injected as liquid, oxidiser is cold and the combustion temperature buffer is injected as liquid, compressor work will be cut dramatically.  I'm not sure how easy an engine like this would be to start.

What we call radiators on Earth vehicles are actually forced convection coolers.  Air is blown through a heat exchanger consisting of thin metal fins carrying heat by conduction from a water jacket.  As things stand, it is uncertain how well they would work on Mars.  But early indications from literature review carried out by Kbd512, suggest that a high pressure drop would be needed to get sufficient air flow rate through these heat exchangers, due to low Martian atmospheric density.  This would place a heavy burden on the engine power.  An alternative might be to use radiator panels mounted on the vehicle.  At 100°C, a black body radiator would radiate 2.8kW of heat per square metre.  There should be enough surface area on a large digger or truck to mount some steel radiator panels.

Last edited by Calliban (2022-05-03 00:44:22)


"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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#290 2022-05-04 00:05:03

kbd512
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Registered: 2015-01-02
Posts: 6,238

Re: Internal combustion engines for Mars

Calliban,

I gave up on this idea awhile back because the energy density is so poor relative to Methane or Propane.  It was interesting at first because CO/O2 had the potential to eliminate water losses associated with combustion.  As I eventually found out, its gravimetric energy density made it no better than a battery.  As for batteries, we simply can't ship enough of them and at some point we're slowing the growth of the colony to appease "electronic everything" ideology.  If the battery control electronics ever fail, then the attached batteries are paperweights.  I have faith that the electro-chemistry of Lithium-ion batteries is every bit as rock-solid as Lead-acid.  What concerns me is the very real possibility of a catastrophic electronics failure.  People see the Mars rovers and think that level of technology represents something feasible for the rest of humanity to use, which is an absurdity.  I did not pay $1M/kWe for my solar panels.  The microchips in my car are not radiation hardened.  The wiring was not designed in such a way to prevent stray voltage from interfering with other circuitry.  The level of fault tolerance in the software and firmware is a joke compared to what JPL engineered for the Mars rovers.

Despite their inefficiency, we will need simple and reliable thermal engines that are not extremely costly to produce and ship, nor subject to radiation-induced electronics failures.  I think a sCO2 gas turbine powered by an external combustor pintle (rocket engine blowing hot exhaust over a heat pipe filled with sCO2) to heat the supercritical CO2 working fluid and drive it through the turbine.  We can still use molten salt as well if we don't care too much about gravimetric energy density.  Those are still the best alternatives to traditional diesel engines, especially for high power applications.  The combustor pintle could blow the exhaust over a Tungsten pipe so we don't have to worry about melting it, since pure CO/O2 combustion is 2947°C and Tungsten melts at 3422°C.  We could use Sodium rather than sCO2 in the turbine as well, so no worries about CO2 dissociation at elevated temperatures.

Molten salt is also a practical way to turn a very small 23% efficient simple cycle micro nuclear reactor into a 51% efficient device.  The radiators have to be stainless steel rather than Aluminum to withstand the temperatures and pressures involved, but it's workable.  Since we can operate those radiators at much higher temperatures when we're not subject to coolant temperature limitations of piston engines, the radiator surface area goes down as well.

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#291 2022-05-04 03:16:42

Calliban
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From: Northern England, UK
Registered: 2019-08-18
Posts: 2,224

Re: Internal combustion engines for Mars

kbd512 wrote:

Calliban,

Despite their inefficiency, we will need simple and reliable thermal engines that are not extremely costly to produce and ship, nor subject to radiation-induced electronics failures.  I think a sCO2 gas turbine powered by an external combustor pintle (rocket engine blowing hot exhaust over a heat pipe filled with sCO2) to heat the supercritical CO2 working fluid and drive it through the turbine.  We can still use molten salt as well if we don't care too much about gravimetric energy density.  Those are still the best alternatives to traditional diesel engines, especially for high power applications.  The combustor pintle could blow the exhaust over a Tungsten pipe so we don't have to worry about melting it, since pure CO/O2 combustion is 2947°C and Tungsten melts at 3422°C.  We could use Sodium rather than sCO2 in the turbine as well, so no worries about CO2 dissociation at elevated temperatures.

Molten salt is also a practical way to turn a very small 23% efficient simple cycle micro nuclear reactor into a 51% efficient device.  The radiators have to be stainless steel rather than Aluminum to withstand the temperatures and pressures involved, but it's workable.  Since we can operate those radiators at much higher temperatures when we're not subject to coolant temperature limitations of piston engines, the radiator surface area goes down as well.

There is truth to this.  A CO/O2 diesel or spark ignition engine is something that we can machine almost entirely from low alloy steels, maybe even 3D printing.  A much easier proposition than high performance batteries from an ISRU perspective.  A nickel alloy gas turbine is more difficult, as the blades must be cast as single crystals.  But we could do that by carefully controlling the rate of cooling in the mould.  If we are talking about Earth moving equipment and mining equipment relatively close to a fixed base, then energy density is a less pressing issue.  If propellants are compressed gases rather than cryogenics, then plain carbon steels can be used as pressure tanks for the CO and O2.  Refilling with CO and O2 is something that can be done quickly and simply using flexible hoses.  For cooling the engine, I would suggest compressed CO2, circulating through the engine to radiator panels by means of a fan.  Again, much of the waste heat will be removed by exhaust gases, so the radiator only has to handle the heat that is transfered into engine components and lube oil.

From what I have been able to read, the CO/O2 is produced by direct electrolysis of CO2.  The CO2 can be pumped into an evaporator as liquid, before entering the electrolysis stack.  The stack will therefore produce pressurised CO/O2.  No separate compression is needed.  In fact, the only pump needed in the whole propellant manufacturing process is the compressor that liquefies CO2 from the atmosphere.

If you have access to a portable nuclear heat source then things can be even simpler.  You put the Kilopower units in a bath of liquid sodium or have a heat exchanger between the sodium and a salt bath.  LCO2 evaporator tubes (stainless steel) would run through the sodium or salt tank, delivering hot dry CO2 to the turbine inlet.  You don't need any drying equipment, because the bath temperature is far above critical temperature for CO2.  Nor is there need to radiate much heat, because the turbine exhaust goes into the atmosphere.  A regenerator would improve efficiency, but would add weight.

You keep an LCO2 tank on site and when the tank level on the vehicle gets low, you refill by gravity through a flexible line.  The boiler on the vehicle can be pressure fed from the onboard LCO2 storage tank.  The turbine could power a hydraulic motor, charging a hydraulic accumulator, which provides motive power to move the vehicle and actuate its tools.  The vehicle would need regular refilling with LCO2.  The amount of mechanical work done per litre of LCO2 woukd be onntge order of a few hundred KJ.  So this isn't an option for a vehicle that needs to travel many miles.  But for mobile diggers and mining equipment, which can top up as they operate from a stationary tank on site, something like this may be the cheapest option.

Last edited by Calliban (2022-05-04 06:24:00)


"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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#292 2022-05-04 05:57:45

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 12,051

Re: Internal combustion engines for Mars

For Calliban and kbd512 ... the purpose of this post is to try to provide an easy-to-find tag for your collaboration.

SearchTerm:Snapshot description of a feasible scenario for heavy duty mining and construction equipment using CO/O2

SearchTerm:BiPropellant concept for CO/O2 engine/turbine equipment using CO2 as diluent

SearchTerm:Sodium coolant for heat engines working as part of construction/mining equipment

The opportunity is present for other forum members to contribute tags to help to find this discussion quickly.

The opportunity is present for forum members and readers to create 3D printer definitions for:

1) Piston engine to be made of Mars available materials
2) Turbine engine - blades (rotating and fixed), and shaft and cylinder components.

it is possible that existing turbine drawings can be adapted, if they are publicly available.

I would like to see this discussion progress toward action plans on several fronts.

This topic is available for coordination.

Some specifications would be helpful.  I'm inviting kbd512 and Calliban to collaborate on specifications for both designs, so 3D Printer designers have something firm to work with.

(th)

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#293 2022-05-04 06:16:53

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 12,051

Re: Internal combustion engines for Mars

For all regarding collaboration in design of equipment to use CO/O2 for mining and construction on Mars.

The NewMars forum is now able to store work products, using the NewMars Dropbox account.

Documents to be stored and made publicly available include:

Specifications of various kinds (scope, details, etc)
3D Printer instructions (Blender/Fusion 360/Other) delivered in universal stl format
Assembly instructions for components
Test procedures
Operating procedures

3D printers can render in plastic for testing designs with models, so work can begin immediately

(th)

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#294 2022-05-04 06:34:39

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 2,224

Re: Internal combustion engines for Mars

Back of the envelope propellant consumption estimate for a mobile digger employing a portable nuclear heat source and using CO2 as an open power cycle propellant.

Assumption: The turbine is fed with hot CO2 gas a temperature of 900K (623°C).  The turbine converts 1/3rd of thermal energy into mechanical energy and the exhaust is vented to atmosphere.

Qu: How much LCO2 will a 100kW machine consume in 1 hour?

Enthalpy CO2 at 900K = 37,252J/mol.  Mechanical power extracted = 12.4KJ/mol = 282KJ/kg.

Propellant consumption per hour = (100kW/282KJ) x 3600 =1275kg.

LCO2 has density of about 1100kg per m3 at 220K.  So a tank with volume just over 1m3 would allow 1 hour of continuous operation.  Refilling can then take place using a flexible hose from a static header tank at the building site, which would drain by gravity into the vehicle propellant tank.

Zubrin estimated that the electrical energy needed to harvest 1kg of LCO2 from the Martian atmosphere is 288KJ.  Interestingly, this is almost exactly the amount of power that an open cycle turbine would raise per kg propellant, with an inlet temperature of 900K.  So for each 100kW machine working on a construction site, we would need a 100kW stationary machine gathering liquid CO2 propellant from the atmosphere.  That machine would require an axial compressor, which woukd compress CO2 to 5-6 bar and then a refrigeration unit, cooling it to 220K, whereupon it will liquefy.  The heat exchanger wouod drain into the storage tank.

I suspect that Kilopower units would be too expensive to employ for digger units.  However, recent NASA work with lattice confinement fusion, may allow production of small portable heat sources using natural or depleted uranium.  These should be cheap to make in volume.  The world has plenty of DU.  It is waste from enrichment facilities.

Last edited by Calliban (2022-05-04 07:26:59)


"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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#295 2022-05-04 07:29:41

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 12,051

Re: Internal combustion engines for Mars

For Calliban re #294

Please confirm this rough draft of what I understand from your proposal...

Minining installation includes (at least) one mobile unit:

a. Nuclear heat source
b. Tank of liquefied CO2
c. Turbine engine driven by CO2 heated by fission source
d. Hydraulic subsystems for mobility and equipment

A detail ... suggestion for remove of debris from the work site?

Base unit:

a. Nuclear heat source (identical to mobile unit)
b. Tank of liquefied CO2 as output
c. Turbine engine driven by CO2 heated by fission source to drive compressor
d. Hydraulic subsystems for manipulation of tanks to be charged
e. Equipment for compressing CO2
f.  Equipment for delivering waste heat to useful destination (eg, greenhouse)

Have I missed something? Chances are at least 50/50 I have.

Detail: How will the automated operator manage the nuclear reactor to deal with fluctuating work loads?

I assume your design plans for rapid de-escalation of reactor activity as work load decreases, but that is a detail that could be defined further, if you have time.

(th)

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#296 2022-05-04 07:49:59

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 2,224

Re: Internal combustion engines for Mars

tahanson43206 wrote:

For Calliban re #294

Please confirm this rough draft of what I understand from your proposal...

Minining installation includes (at least) one mobile unit:

a. Nuclear heat source
b. Tank of liquefied CO2
c. Turbine engine driven by CO2 heated by fission source
d. Hydraulic subsystems for mobility and equipment

A detail ... suggestion for remove of debris from the work site?

Base unit:

a. Nuclear heat source (identical to mobile unit)
b. Tank of liquefied CO2 as output
c. Turbine engine driven by CO2 heated by fission source to drive compressor
d. Hydraulic subsystems for manipulation of tanks to be charged
e. Equipment for compressing CO2
f.  Equipment for delivering waste heat to useful destination (eg, greenhouse)

Have I missed something? Chances are at least 50/50 I have.

Detail: How will the automated operator manage the nuclear reactor to deal with fluctuating work loads?

I assume your design plans for rapid de-escalation of reactor activity as work load decreases, but that is a detail that could be defined further, if you have time.

(th)

All good.  Except the stationary facility producing liquid CO2 won't need hydraulics.  The tank will be static a hose will be used to connect it to the vehicle propellant tank.

The operator won't control the nuclear reactor.  It will be on a temperature switch activated by thermostats on the salt / sodium tank.  If the tank gets too hot, the reactor will switch off.  If the tank temperature drops too low, it will reactivate.  The salt or sodium tank should have sufficient heat capacity to absorb enough reactor heat to prevent continuous stopping and starting.  If the reactor fails to trip, we need a radiator panel that can radiate 100% of it's full operating power - 333kWth.  We could, say, have metal plugs that melt at 700°C opening the heat tank to a radiator.  At 700°C, that radiator would need to be 2.5 x 2.5m, ignoring conduction losses into the vehicle.

Last edited by Calliban (2022-05-04 07:59:11)


"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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#297 2022-05-04 08:01:10

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 12,051

Re: Internal combustion engines for Mars

For Calliban re #297

It is definitely encouraging to see progress in this topic! Thanks !!!

A detail... I predict there will be NO onsite (human) operator. The pace of development of remote control manipulators is high, and it is global.

A teleoperating robot seems like a useful addition to the site configuration.

There needs to be a way to connect the hose to the mobile unit.  I'm pretty sure automation exists today for this purpose.

I proposed hydraulics as a way to move filled tanks to temporary storage locations.

However, that may not be necessary if the mobile uinit(s) is/are considered the "temporary" storage locations.

Question ... do you have contacts that would allow the NewMars workforce to increase in size?

We have theoreticians here in great abundance.

We have artists here, Void being the most prominent, with a nod to RobertDyck for hand drawings and Blender renders.

What we do NOT seem to have are hands-on-craftspeople.

We (forum) are now positioned to move from fantasy through detailed vision to drawings and specifications.

What we appear to need are members who are inclined in that direction, as a natural addition to our existing (and very successful) visualization capabilities.

(th)

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#298 2022-05-04 08:10:19

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 12,051

Re: Internal combustion engines for Mars

For Calliban re radiator ...

At 700°C, that radiator would need to be 2.5 x 2.5m, ignoring conduction losses into the vehicle.

Please add detail ... we only (appear to) have 2 dimensions given in the specification.

I'm assuming there are pipes into which the sodium flows, separated by sections of flat metal.

Detail: between episodes, the sodium will solidify in the radiator pipes.  It this intended to be a one-time-usage emergency backup?

If so, would maintenance / remanufacturing consist of melting the entire device down and separating the elements for re-use?

I like the automatic safety feature for the base station.  It would (of course) not be available to the mobile units.

(th)

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#299 2022-05-04 08:33:55

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 12,051

Re: Internal combustion engines for Mars

For SpaceNut ...

There is only ** one ** topic that contains the words "internal" and 'combustion"

Due to evolution of this topic over time, I'd like to suggest you create two daughter flows:

Internal combustion piston engines for Mars
and...
Internal combustion turbine engines for Mars

Each appears (to me at least) to have a solid technical base on Earth, for development and deployment on Mars.

In addition, the direction Calliban seems to be heading deserves a topic of it's own...

I'm not sure what the topic title should be, but here are the elements I see as factors:

1) Nuclear power
2) Turbine to convert thermal energy to mechanical energy
3) CO2 as the working fluid

A variation on this theme was offered by Calliban some time ago....

That is the CO/O2 turbine, which would deliver CO2 in the exhaust.

That design would (probably) still require a nuclear powered base station, to prepare the CO/O2 propellant.

In all these situations, I see the theoretical work as nearly as far advanced is is possible.

It is time to recruit members who both want to work on moving to actualization, and have the ability to do so.

There is a remote possibility that existing members may be inspired to gain the education and skills needed to move from theory to practice.

(th)

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#300 2022-05-04 09:17:01

kbd512
Administrator
Registered: 2015-01-02
Posts: 6,238

Re: Internal combustion engines for Mars

Calliban,

That's not quite what I had in mind, although I'm sure what you proposed could also work, assuming you can make a properly shielded nuclear reactor small enough to mount inside a vehicle and use DU as the reactor fuel.

I want a closed-loop sCO2 gas turbine that uses re-heat between expansion stages to improve thermal efficiency.

1. Injectors supply pure CO and O2 to a combustor can.  This is a rocket engine pintle, or a blow torch, or a burner similar to those on gas stoves or inside jet engines, dependent upon what analogy / visualization works best for you.  This device operates at CO/O2's stoichiometric combustion temperature of 3,220K.  It's made from a conductive Tungsten-Nickel-Iron or Tungsten-Copper-Iron alloy that can expand and contract without becoming brittle.

2. The combustor can directly heats a Tungsten alloy pipe containing a supercritical CO2 (sCO2) working fluid.

3. The sCO2 is fed through a multi-stage expander gas turbine that generates electrical power.  Hot gas from before the first stage turbine inlet is re-injected just before the second and third stages.  This increases thermal efficiency to at or above 50%.  More stages and re-injections could produce greater thermal efficiency, but for some reason NREL and General Electric stopped at three stages for the ongoing sCO2 project.  I'm going to go way out on a limb and say that GE knows how to make gas turbines and there must be a good reason why 3 stages was better than 2 or 4.

4.  Behind our sCO2 turbo expander, we have an electric generator and a printed circuit heat exchanger.  The heat exchanger contains a Labyrith with hot sCO2 on one side and NaK or pure Sodium metal on the other side.  The Sodium metal extracts the heat from the sCO2 working fluid without a dramatic pressure loss.  The waste heat is radiated away by high temperature stainless steel radiators affixed to the exterior of the vehicle.

5. The electric generator provides life support and motive power to the vehicle.  A 1MWt sCO2 gas turbine is approximately the size of a beer can, and 500kW (50% thermal-to-electric conversion efficiency) is 670hp, which is more power than most diesel-powered heavy duty trucks have.  On Mars, with 38% Earth gravity, a vehicle so-powered has rough equivalency with the AGT-1500 gas turbine that powers the M1 Abrams main battle tank.  The latest versions are around 72t.  For heavier mining-type equipment that requires more power, you could use more turbines or larger turbines.

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