Internal combustion engines for Mars

SpaceNut · 2022-05-01 19:40:06

15 hours of night duration to keep the block warm as well as the battery out in the open of mars means the block is frozen. The coolant will be frozen ect... The block will seem warm as compared to the fuel that is being fed into the chamber.

Molten salt requires 500c to keep it liquefied so not from a dip stick.

Sure for a propane oxygen warmer but for what as the coolant in the engine sees temperatures that are not normal for earth. Then should the battery stop supplying a voltage the engine freezes. So keeping the battery charging is a must all night long.

The coolant circulates so as to not become stagnant from the heat it absorbs it flows from cool into the engine where by it gathers the heat from the surfaces that its in contact with. The fluid flows as a result of the pump that pushes it through out the engine under pressure and that back out to the radiator to cool it once more.

Looks like we have an issue as a result of mars low pressure for the use of co2 that has lead to it being Lco2 and making the fuels high pressure rather than liquid.

SpaceNut · 2022-05-01 20:03:12

Here is the Toyota Mirai fuel tank mass.
https://en.wikipedia.org/wiki/Toyota_Mirai

The Mirai has two hydrogen tanks with a three-layer structure made of carbon fiber-reinforced plastic consisting of nylon 6 from Ube Industries and other materials. The tanks are 122 liter combined, and store hydrogen at 70 MPa (10,000 psi). The tanks have a combined weight of 87.5 kg (193 lb), and 5 kg capacity.

https://www.toyota-europe.com/download/ … 564265.pdf
Key Specifications The Mirai is a fuel cell vehicle (FCV)

High voltage from the fuel cell stack of 650v

tahanson43206 · 2022-05-01 20:47:48

For SpaceNut re #252

Thanks for the details you quoted for the Toyota Mirai, and specifically for the tanks. This evening, kbd512 invested a lot of Zoom time going over details of design considerations for the engine I'd like to see on Mars. Your post fits nicely into the flow.

kbd512 is arguing (leaning toward) an all gas design that uses a radiator to transfer waste heat to the (thin) atmosphere of Mars. He specifically mentioned 10,000 psi tanks, so your details from the Mirai are a good fit.

In holding out for a design that does NOT use a radiator, I learned (from kbd512) that an injector for the oxidizer would be necessary, due to the high pressure that would occur as the liquid oxidizer expands due to heating by the running engine.

We left for a future time the details of design that would allow an engine to operate productively with cryogenic fluids as inputs.

For SpaceNut ... there is a high probability that we (NewMars) are NOT the only people thinking along these lines. Please keep a lookout for links that might show what others are thinking, or perhaps even doing.

The environment of Mars can be emulated on Earth, with some effort. It would be possible to test an IC engine to see if would work as well on Mars as the comparable engine performs on Earth.

The advantage of the cryogenic fluids design (if it can be built at all) is that it will run happily on the Moon as well as on Mars.

A major difference is that the exhaust is captured by the atmosphere on Mars, but it would escape into the Universe on the Moon.

During the conversation, kbd512 reminded me of the ULA IC engine used in one of their rocket designs.

It burns hydrogen and oxygen which are boiling off of the rocket tanks, so it is an elegant solution for a particular use case.

(th)

tahanson43206 · 2022-05-01 21:51:19

For kbd512 re Zoom session ...

Thanks again for working on the CO/O2 engine this evening !!!

http://newmars.com/forums/viewtopic.php … 46#p193746

At the link above, Mars_B4_Moon provides a link to a report on MIT research to convert heat to electricity more effectively than the very inefficient Seebeck Effect.

I bring it up because I'm interested in the 2/3rds of energy we discussed as waste in an IC engine ....

some of that waste will be drawn off with the exhaust gases.

The rest goes into the cylinder walls, and from there into the primary coolant.

What I'm wondering is if any of that waste heat can be drawn off with these MIT chips.

I presume they need a cold sink, just like the Seebeck effect does, and the cryogenic fluid might provide it.

The output would be electric current that could (presumably) be fed into a battery and from there into onboard electrical systems.

A regular generator could draw mechanical power, but I'd rather apply as much mechanical power to the work face as possible.

(th)

kbd512 · 2022-05-01 23:58:18

SpaceNut,

The engine will be inside an engine compartment. If the engine compartment is well-insulated, then getting rid of waste heat will be a much bigger problem than retaining heat over 15 hours or so. Over longer periods of time, the block would eventually freeze. For waterless coolant that does not expand to nearly the same degree as water does (and is also capable of withstanding much higher temperatures without boiling), that is less of a problem from the standpoint of damaging the engine. For starting the engine again, you would need to re-warm the engine coolant and oil using external power. A molten salt could store thermal energy over a longer period of time, and a reasonably-sized tank of salt would retain sufficient heat for that purpose over at least several days, assuming it was well-insulated. However, over enough time even that salt tank would cool down and freeze. Therefore, delaying the inevitable will not be a long-term successful strategy. Using engine coolant that will not crack the cast iron block or cylinder head after it freezes is a more comprehensive solution. Evans waterless coolant remains liquid between -40°F and 375°F. When it freezes, its volume decreases slightly rather than increases.

Diesel engines such as the Cummins "B Series" (4BT and 6BT) contain engine block heaters as standard equipment, and the ones used up north also have oil heaters. These are normally electrical devices, so the vehicle (Dodge trucks or farming equipment) can remain plugged into a 120V AC power source, such as a standard wall outlet, using an extension cord. A nuclear reactor could also supply the electrical power, obviously, but why bother if the engine is in no danger of being damaged by its coolant?

However, in the interest of not requiring any external power sources like nuclear reactors or tanks of hot corrosive chemicals that could leak and spill all over the engine compartment or other parts of the vehicle, a simple CO/O2 burner can could also be used to heat the engine block. The burner solution would heat up the engine oil and coolant faster and require less total weight and/or complexity than competing solutions. Since it uses the same fuel and oxidizer to heat up the coolant system, so long as fuel and oxidizer are available, you can warm up and start the engine. I know a burner is not very high-tech or unusual, but it also happens to work.

kbd512 · 2022-05-02 04:23:49

tahanson43206,

Carbon Monoxide at 296K (73.13°F) / and 680ATM (9,993.28psi) of pressure has a bulk density of 783.9382kg/m^3.
Liquid Carbon Monoxide at 81.65K (-312.7°F) and 1ATM (14.6959psi) of pressure has a bulk density of 790.8kg/m^3.
Not a lot of difference there. I'm not real sure if that extra 6.8618kg/m^3 is worth the added hassle of messing with cryogenic liquids, but that wasn't what you were interested in, so let's explore what you wanted to do after first figuring out our mass differentials between the engine, fuel, and oxidizer (because this is pretty pathetic).

Oxygen at 296K and 680ATM of pressure has a bulk density of 895.9294kg/m^3.
Liquid Oxygen at -361.82°F has a bulk density of 1,141kg/m3.
There's a meaningful difference between LOX and high pressure O2 storage, but we need a lot more CO than O2 since 2CO + O2 = 2CO2.

CO produces 1.213kWh/kg. The Cummins 6BT's original rated output was 160hp / 119kW. 1m^3 of CO fuel (783.9382kg/m^3 * 1.213) provides a gross output of 950.917kWh. Divide by about 3 (at 33% BTE) and that's about how much mechanical power output we can actually expect (316.972kWh) to extract from our 1m^3 of CO fuel. Real diesel engines are usually a bit better than that, maybe 40% to 45%, but 33% is an old "rule-of-thumb". That means we can run the engine at full output for 2.66 hours using 1m^3 of CO fuel and about half as much O2. The 6BT weighs 545kg with standard accessories, 784kg for fuel, 392kg for oxidizer, 600kg for tankage mass, and that's 2,321kg without factoring in the CO2 diluent or tankage mass. Lithium-ion batteries at 179.83Wh/kg provide 396.5kWh is 3.33 hours of "engine runtime" at full rated output. The "net net" is that CO is a really poor fuel choice. The only real advantage is shipping 1,176kg less mass to Mars, because the oxidizer and fuel both come from Mars and there's a functionally limitless supply of that stuff on-hand, via the Martian atmosphere. Using CNG rather than CO would transform 2.66 hours of engine run time into 13.3 hours of run time, and again, the fuel and oxidizer come from Mars. Given the room temperature conversion of CO2 into CO and O2, may partially negate that advantage since the most of the energy loss comes from compression of the fuel and oxidizer, but that energy input is always present.

Comparison of CNG and LNG Technologies for Transportation - Final Subcontract Report June 1991 - December 1991
You lose about 8% of the energy in CNG by compressing it to 10,000psi (flip to Page 4). You lose about 5.625X as much energy in the liquefaction process at small scale (9,000BTU/lb for LNG vs 1,600BTU/lb for CNG at 10,000psi. Under very special operating conditions, sometimes no energy is lost (that will probably not apply to a small liquefaction plant on Mars).

And finally, we will address your question about heat-sinking the engine's waste heat into the CO2 diluent gas...

This will take some time, but I'll get there. First, we have to know some basic data about the 6BT engine and engines in general.

For internal combustion engines run under varying load conditions, approximately 1/3rd of the heat generated does mechanical work (produces power output), 1/3rd is rejected into the water jacket, and 1/3rd is rejected out the exhaust pipe. Diesels do a bit better than gasoline / spark-ignited engines in this regard, and some diesels do considerably better, as we'll discover.

Cummins 6BTA Marine Engine Specifications
Cummins 6BTA Fire Pump Engine Specifications
According to Cummins, a "factory standard" 6B/6BT/6BTA-M engine has a maximum allowable oil sump temperature of 120°C and maximum allowable engine coolant temperature of 96°C. The engine coolant volume is 12.9L, but total coolant volume with a heat exchanger (radiator) is 20.6L. The engine in question is 5.9L (360 cubic inches) in displacement and will run somewhere between 1,200rpm and 2,500rpm. Some of the "race" 6BT engines have been spun to 5,500rpm, but those don't live very long.

The Thermodynamic Design, Analysis and Test of Cummins’ Supertruck 2 50% Brake Thermal Efficiency Engine System

Current production heavy duty diesel engines have a brake thermal efficiency (BTE) between 43-46% [1]. In partnership with the United States Department of Energy (DOE) as part of the Supertruck 2 program, Cummins has undertaken a research program to develop a new heavy-duty diesel engine designed to deliver greater than 50% BTE without the use of waste heat recovery. A system level optimization focused on: increased compression ratio, higher injection rate, carefully matched highly efficient turbocharging, variable lube oil pump, variable cooling components, and low restriction after treatment designed to deliver 50% BTE at a target development point. This work will also illustrate the system level planning and understanding of interactions required to allow that same 50% BTE heavy duty diesel engine to be integrated with a waste heat recovery (WHR) system to deliver system level efficiency of 55% BTE at a single point. In addition to a test bench demonstration, the described system is also planned to be demonstrated at a vehicle system level. This paper summarizes the process and results of the 50% BTE engine development effort with a focus on efficiency and performance.

Cummins had an adiabatic diesel engine back in the day that they developed for TACOM (US Army), but those didn't live very long because they ran so hot that they required special ceramic metal to withstand the heat they generated.

Have a look here for diesel engine thermal efficiency improvement techniques and expected or measured results:
Engine Thermal Efficiency - From: Modern Engineering Thermodynamics, 2011

Look here for a paper detailing actual wall heat loss (15.1% for a large medium-speed diesel truck engine under 75% load at 1,200rpm):
Increasing Brake Thermal Efficiency of Heavy-Duty Diesel Engines for Long-Haul On-Road Vehicles up to 50% - FPT Motorenforschung AG - Swiss Federal Office of Energy SFOE

The goal was / is a 30 bar BMEP, which means a 300 bar peak cylinder pressure, 3,000 bar fuel injection pressure.

We're running this 6BT at significantly higher temperatures and plan to recover waste heat for various purposes, so let's presume we could realistically achieve 50% BTE. That means 25% of the thermal power is rejected into the water jacket and 25% goes out the tailpipe. In practice more goes out the tailpipe than into the water jacket, but still. That means 29.75kWt is being rejected into the water jacket. If you increased the engine coolant capacity to 29.75L, then each liter of engine coolant is rejecting about 1kWt if the engine's BTE is 50%. If the engine is run at 1,800rpm, then over 1 hour you have 108,000 revolutions, which means 54,000 intake charges per hour.

Let's say we run 4atm of pressure and pretend each cylinder is 1L for easy math, so 4L of intake charge CO2 gas is crammed into the cylinder on each intake stroke. Over 1 hour we will reject 29.75kWh into 216,000L of intake charge, so 1kWt is being rejected into 7.26L of intake charge.

How much would that heat up the CO2?
At STP, 1 mole of ideal gas occupies 22.4L and 1 mole of CO2 is 44.01g.
pv=nrt
58.8*1 = n * 0.1889 * 300K
58.8 = 56.67
56.67 / 58.8 = 0.963775510204082
0.963775510204082 = 42.415760204081633g of CO2 (assuming we could limit the intake charge temperature to 300K)
We're transferring heat at a rate of 1kJ/s since 1kWt is 1,000J/s...
CO2 requires 0.03735J/g/°C of input energy
Q=m*c*ΔT
We're using the autoignition temperature of Carbon Monoxide (620°C) subtracted from 300K / 26.85°C for ΔT, so 593.15°C
Q=42.42 * 0.03735 * 593.15
Q=939.78 Joules (very near to the total amount of waste heat generated before it's compressed by the piston)
So if we tried to "heat sink" the waste thermal energy from engine into the CO2 from a starting temperature of 300K, then we're not only igniting the mixture but melting the piston and cylinder walls using a 20:1 compression ratio (which takes / increases a "normal" diesel engine's air intake charge to 649°C), and will undoubtedly increase the temperature beyond what the engine can tolerate for any period of time.

I still need to figure out how much fuel and oxidizer we're injecting to determine if we have enough cryogenic LCO and LOX to remove enough heat from the CO2 intake charge so that when the piston compresses the CO2, it's near but not far above CO autoignition temperature. The intake charge needs to be just hot enough to ignite the mixture slightly before the piston reaches TDC. Remember what I said about massively de-rating the engine? That's what this is starting to look like to me unless we have enough fuel and oxidizer to heat sink our way away from destroying the engine. I think the answer is that you just end up dumping more heat from compression into the water jacket, which you cannot do. The heat needs to leave the engine.

Anyway... More time is required. I'm tired. I need to get a couple hours of sleep. Post "not done yet" as Void would say.

Edit: I'm sure my math is wrong somewhere as well (mass of the CO2 should be something between 13g and 15g, not sure what I did there and I'm too tired to figure it out right this second)

Last edited by kbd512 (2022-05-02 04:31:17)

tahanson43206 · 2022-05-02 07:34:53

For kbd512 re Post #256

Thank you for this massive study! I will plan to re-read it again, and (in particular) to check the math in the (unlikely) event there is an error.

As we proceed, it is worth keeping in mind that the total environment includes the manufacturing and storage facility, as well as the power supply for the entire operation.

The CO/O2 solution will require less manufacturing effort than any alternative that might be proposed for Mars.

This topic has room for evaluation of solutions that include Hydrogen.

Dr. Zubrin's studies from decades ago still stand as the benchmark for comparison.

While his interest at the time was in manufacture of methane for rocket fuel, methane is capable of serving as a fuel for an engine. The difference (of course) is that the landing party has to have water to make the hydrogen, which is why Dr. Zubrin planned to bring the hydrogen along.

***
For SpaceNut ... is the work that kbd512 did here something you'd be comfortable reviewing?

He's indicated an error might have crept into the flow of calculations, and if you have the time and energy to double check his work, it would be helpful. Even if your review shows that every number is correct, it would have the benefit of reducing uncertainty.

(th)

Calliban · 2022-05-02 07:51:40

I would propose using a small gas turbine, which vents hot CO2 directly into the Martian atmosphere. Given that your fuel and oxidiser are both compressed gases, you would effectively have zero compressor work and indeed, no need for a compressor. The low pressure Martian atmosphere allows excellent expansion ratio. Using nickel alloy blades, flame temperatures in a GT are limited to 1200K. The combustion product is pure CO2.

CO + 0.5O2 = CO2.

The combustion temperature of pure CO in O2 is 3220K. A few stats to help with the calculation of the amount of CO2 diluent that must be added to the combustion chamber to keep flame temperature at 1200K:

Internal energy of CO2 (3220K, 1200K, 200K) = 150, 43.78, 4.4KJ/mol, respectively.

By my calculations, we need to add 2.5 mol CO2 to each mol CO in the combustion chamber to keep flame temperatures at 1200K. That is 110 grams of CO2 for every 28 grams of CO or every 44 grams of CO/O2 bipropellant. That is a heavy addition. You could recirculate the CO2 through a heat exchanger and recompress it. But that would require a big heat exchanger and a lot of compressor power.

According to Zubrin, harvesting liquid CO2 from the Martian atmosphere would take about 288KJ/kg.
https://ntrs.nasa.gov/api/citations/199 … hment=true

To harvest the 2.5 mols needed as diluent per mol CO, would take 31.68KJ, which would be about one third of the shaft power of our engine. That could be an acceptable energy cost. But the axial compressor needed would be huge and heavy. So it is probably better to have a static machine producing LCO2 that you can top up with using a rubber hose. That isn't a problem for things like digging and soil moving equipment, which is what CO/O2 is best suited for. Waste CO2 can then be vented into the atmosphere, taking the waste heat with it.

Alternatively to CO2, it takes 4.57MJ/kg of heat to convert liquid water at 10°C into steam at 900°C. So if steam is used as diluent, the mass of water needed is around 23 grams for each 44 grams of bipropellant. A far better mass ratio. It would take about 1MJ/kg to harvest water from permafrost on Mars. So the energy cost of water and LCO2 are about the same in the quantities needed. However, ice is available in select locations on Mars, whereas CO2 is everywhere.

Last edited by Calliban (2022-05-02 08:02:59)

kbd512 · 2022-05-02 07:53:23

tahanson43206,

Thank you for taking me back to Junior High and Mr. Macey's chemistry class, BTW. I see what I did wrong.

CO2 molar mass = 44.01g/mol; 4L of CO2 at 300K = 28.612g

Q=mcΔT
Q=28.612 * 0.03735 * 593.15
Q = 633.875J (to raise 28.612g of CO2 to the autoignition temperature of CO gas with O2)

Q/mc=ΔT
ΔT = 1,000J / (28.612 * 0.03735) = 935.716°C

That's not a complete answer because the cryogenically cold O2 gas was not included in the intake charge, but give me a little bit and I'll get there.

Edit:
935.716°C = 1208.866K (very close to the temperature limit of Nickel alloy gas turbine blades, as Calliban stated, and this is before the engine compresses the gas to make any power)

Molar mass of O2 is 32g/mol. O2 is 21% of "air". Substituting CO2 for N2 and keeping the "intake charge air mix" the same, then if O2 was added in at the same ratio to the CO2, that's 6g of O2 per intake charge. LOX BP is -182.96 °C, and specific heat of Oxygen is 0.92 J/gK (0.00092J/g°C).

Q=mcΔT
Q=6 * 0.00092 * 802.96
Q=4.432J (to raise 6g of LOX to CO autoignition temperature)
That's all we get from the 6g of LOX, apparently.

Heat sinking our cylinder wall heat loss away using the intake charge isn't looking very promising. Even if we reduced the input cylinder wall heat loss value from 25% to 15%, a 900J vs 1,000J thermal power transfer doesn't change the results of the equations enough to make cryogenic 28.612g of CO2 and 6g of LOX provide a meaningful thermal mass to act upon. You need at least double the thermal mass to act upon than what the intake charge provides at reasonable volume (cramming more than 4L of intake charge into a 1L cylinder) and pressure, which is why the engine's water jacket is connected to a radiator with a fan attached to it.

Remember what I said about massively de-rating the engine?

Nominal engine output is 160hp / 119kW. You'd be lucky to get half that, and a third would be more practical.

2,321kg of weight to run a 53hp engine?

Nope.

Last edited by kbd512 (2022-05-02 08:31:26)

tahanson43206 · 2022-05-02 08:02:53

For kbd512 re #259

If Mr. Macey is still around, I tip my hat to his gifts as a teacher!

The direction I am headed is toward visualizing (and ultimately realizing) an industry on Mars.

The work you are doing is foundational. I logged in just now to post a collection of Google Snippets about MOXIE, which is (of course) an on-site demonstration of technology to make CO and O2 using a catalyst and energy.

While there are many demonstrations of technology done on Earth, using Hydrogen to make more complex Carbon based molecules, the MOXIE experiment is on site and working. The risks associated with the idea have been retired.

An entire industry can (and probably will) be built upon that demonstration.

Our mission here (as I understand it) is to visualize that industry, and to provide the knowledge others will need to implement it. A key to our contribution is our ability to make the knowledge easy to find.

Your work is an example of an element that needs to be easy to find, as it supports whatever the conclusion of this process turns out to be.

Thanks again for all your hard work!

(th)

tahanson43206 · 2022-05-02 08:04:02

For the record:

MOXIE snippets:

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MOXIE produces oxygen from the carbon dioxide in Mars' atmosphere using Solid Oxide Electrolysis (SOXE). MOXIE aims to produce at least 6 g/hr of oxygen, of at least 98% purity, on at least 10 separate occasions.
MOXIE (Mars Oxygen ISRU Experiment)https://an.rsl.wustl.edu › help › Instruments › M20 MOXIE
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A waste product, carbon monoxide, is emitted into the Martian atmosphere.” MOXIE is designed to generate up to 10 grams of oxygen per hour equivalent to about 20 minutes of air per hour for an astronaut on Mars.May 10, 2021
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The Mars Oxygen In-Situ Resource Utilization Experiment (MOXIE) is a technology demonstration on the NASA Mars 2020 rover Perseverance investigating the ...
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May 28, 2021 — Known as MOXIE, or the Mars Oxygen In-Situ Resource Utilization Experiment, the device is extracting small amounts of oxygen from the Martian ...
MOXIE Might Be the Most Exciting Thing Perseverance Has ...https://spectrum.ieee.org › moxie-might-be-the-most-excit...
May 28, 2021 — MOXIE has already run successfully a couple of times, producing 5.4 grams of 98% pure oxygen over the course of an hour on April 20. 5.4 grams ...

(th)

Calliban · 2022-05-02 08:16:28

In a compression ignition engine, you could spray that CO2 into the cylinder as compressed liquid along with some portion of the fuel gas. About half of the fuel gas and all of the oxidiser can be compressed and then the remainder of the fuel gas and LCO2 injected at peak compression. As the CO2 is in the form of droplets, it will phase change into gas as it absorbs heat from the combustion mixture. However, this will take finite time as it requires convective heat transfer into the droplets. By carefully tuning injection pressure, the CO2 will hold down reaction temperatures without quenching the reaction.

Another possibility is to use a tripropellant combination. Say, 80% Lox/CO with 20% methanol. That way, the gases can be compressed as a premixed charge, with the methanol injected at peak cycle to take the hot mixture over the combustible limit.

Last edited by Calliban (2022-05-02 08:23:06)

tahanson43206 · 2022-05-02 08:38:30

For Calliban re #262

Thanks for picking up on all that work by kbd512! And thank you for the (to me interesting) suggestion of a hybrid fuel mixture.

It **seems** to me yours is the first post to suggest employing and always limited supply of hydrogen on Mars, by adding what little there is to an engine designed for CO, to spice the mix and improve performance.

Since you have expressed interest in heat management, in many topics and in many posts, by any chance would you be willing to take a close look at the work of kbd512? I had asked for a vision of how an engine might be designed to use CO, and to NOT depend upon the atmosphere of Mars for cooling, but instead, to derive all cooling needed from the liquefied fuel and oxidizer in the tanks.

It seems to me that cooling using radiators is well understood in the context of Earth, but Mars will require a fragile radiator with many fins and furious fans to try to move the sparse atmosphere past those fins.

As kbd512 has pointed out, managing the thermal energy in a machine using liquefied inputs requires some adjustments on the part of the engineering team.

Fortunately, there ** is ** an example (which kbd512 pointed out (multiple times)).... The ULA engineering team modified an internal combustion engine to run on oxygen and hydrogen for a specific application in a rocket, where batteries and electrical systems would have been heavier.

***
For SpaceNut ... if you can find a link to a report on the ULA H2/O2 engine, it would be helpful.

(th)

kbd512 · 2022-05-02 08:48:36

tahanson43206,

Please see my Post #259 again.

This notion of heat-sinking the engine's waste heat into the intake charge instead of convecting it away appears unworkable.

The engine needs a radiator / heat exchanger and a powerful fan.

kbd512 · 2022-05-02 08:56:09

tahanson43206 or Calliban,

How about using the exhaust to drive a turbo that runs the radiator's fan instead of using the intake charge?

tahanson43206 · 2022-05-02 09:08:45

For kbd512 re #265

Thanks for continuing to work on this ... for fun, try embedding the engine inside the oxidizer tank.

If you have to release pressure, do so.

A radiator system on Mars is (probably) (to quote kbd512) "unworkable".

A system that works reliably on Mars without a fragile radiator system is needed, and if it can be done, it will be done.

NewMars has the opportunity to find the solution, if it can be found.

If you need to add an entire tank of liquid to cool the engine, add it!

(th)

Calliban · 2022-05-02 09:20:30

I'm not sure how effective a fan would be on Mars. The atmospheric density at Mars 'Sea level' is about 0.013kg/m3. If you could get a flow rate of 10m/s through a 1m2 radiator and let's say a temperature rise 300°C, then your radiator should be able to dump about 25kW. I don't know how much shaft power you would need to force CO2 through the radiator. It depends upon the viscosity of the CO2, the gap between the radiator fins, etc. Working out the heat transfer rates and pressure drop across the radiator is quite an involved design problem.

One of the reasons I suggested a gas turbine is that you don't have to remove as much waste heat from the engine. A much greater proportion exits with the exhaust gases. Both engines need diluent gases. That isn't about removing waste heat, it is driven by the need to keep combustion temperatures low enough to prevent engine components from overheating. There isn't anyway around that requirement that I can see. Water is the most efficient coolant in terms of heat absorbed per unit mass or volume. The mass of water needed to keep combustion temperatures down in comparable to the mass of fuel and about half the fuel propellant combination.

PS. Assuming the CO/O2 bipropellant is injected as cryogenic liquid, 1kg of bipropellant will consume 909KJ of heat energy as temperature increases from 100K to 1200K. Heat of combustion of 1kg of CO/O2 bipropellant will release 6.4MJ. Injecting fuel as cryogenics could reduce the amount of buffer gas required by about 20%. That is worth having, but thermal shock of injectors may be a problem.

This link examines convective cooling using the Martian atmosphere vs using a radiator.
https://www.osti.gov/biblio/5419527-con … nsfer-mars

It seems to be behind a paywall.

Last edited by Calliban (2022-05-02 11:31:38)

tahanson43206 · 2022-05-02 11:40:32

For Calliban re #267

Thanks for adding several new perspectives to the discussion.

It should be possible to test radiator/fan designs on Earth, using the conditions available in suitable environment test chambers, such as those NASA has to simulate deep space.

They have tested the Ingenuity helicopter in a chamber optimized for the Mars environment, and it seems to me the research team would be receptive to helping US industry to evaluate fan/radiator designs.

There is no need for a lot more hand waving. I am willing to write to the appropriate department at NASA to ask if their facility could be used for radiator testing. My guess is they would like to know the answer as well.

My guess is that no living being on Earth knows the answer.

The only clue we have is that the NASA Krusty design team went with radiative cooling.

My guess is that radiative cooling would work well for the fuel/oxidizer manufacturing plant on Mars.

I am looking for design solutions for Mars machinery that are as simple and durable as possible.

The manufacturing plant can have all the furious fans and delicate radiators anyone might want.

***
For Calliban ... I like the suggestion you provided, of pre-mixing the CO and O2 as a bipropellant.

kbd512 has offered the counter point view that such a bi-propellant would be dangerous.

That is also true of all bi-propellants in use on Earth (and in space) today.

From everything I am reading and learning, it would appear that a mixture of CO and O2 would NOT self ignite.

In fact, it sure ** sounds ** as though it will be just about at the limit of human capability to get it to ignite at all.

Pre-mixing the CO/CO2 and O2 at the point of fueling the machine would permit use of a single tank, or a set of interconnected tanks all holding the same liquid.

Thanks to ** everyone ** for giving this topic a new (and energetic) lease on life!

I am beginning to glimpse a possible glimmer of light at the end of the tunnel.

The goal is a robust specification for an entire industry that can be installed on Mars using known technology, with just a few tweaks for Mars.

There is more than enough talent assembled in this forum to pull this off.

Whether there is enough ** time ** is another question entirely.

This is an all-volunteer undertaking, so contributions come in as members are both inspired and available.

It is a lot to ask for professional level achievement under these circumstances.

however, I've seen it before, and figure it can happen again.

(th)

Calliban · 2022-05-02 11:53:30

This publication is accessible and suggests a convective heat transfer coefficient of about 5W/m2K at 4m/s Flow speed and ambient temperature of 250K.
https://www.researchgate.net/publicatio … an_Surface

tahanson43206 · 2022-05-02 12:15:43

For Calliban re #269

Thanks for the link, and for the summary of what it might provide

For kbd512 ... if you can find the time, and remain interested in the radiator question, please see of the link Calliban provided gives enough information so you can design a radiator system specifically for Mars conditions.

If you install that system on the fuel/oxidizer manufacturing plant, it would be an alternative to the purely radiative cooling system chosen by NASA for Krusty.

“Ingenuity is an experimental engineering flight test – we want to see if we can fly at Mars,” said MiMi Aung, project manager for Ingenuity Mars Helicopter at JPL. “There are no science instruments onboard and no goals to obtain scientific information. We are confident that all the engineering data we want to obtain both on the surface of Mars and aloft can be done within this 30-sol window.”

It would appear that MiMi Aung might be the right person to contact to inquire about testing kbd512's radiator design.

SpaceNut ... if you have time, please see what information might be available about MiMi Aung ... I expect there is a PhD on the wall, and perhaps other honors as well.

If a radiator system can work at all on Mars, it should be possible to prove it in that test facility on Earth.

(th)

kbd512 · 2022-05-02 12:39:06

tahanson43206,

A radiator is unworkable, hmm? Well, let's just see about that...

ElectronicsCooling.com - All you need to know about fans, by Mike Turner

I have a feeling Mike probably left some things out, but we'll humor him anyway. This was from May 1st, 1996. I was only 16 years old when this article came out. Edit: Correction, I was only 15.

Q· = m· * Cp * ΔT
Q· = heat transfer, in Watts
m· = mass flow rate, in kg/s
Cp = specific heat of CO2, in J/kg·K
ΔT = desired temperature differential (radiator to ambient outside air), in K

Q· = m· * Cp * ΔT
Q· = 0.02kg/s * 849J/kgK * (294K - 450K)
Q· = 16.98 * -156
Q· = -2,648.88J/s

25,000W (or Joules per second) / 2,648.88J/s = 9.44m^3/s (333.3705 cubic feet per second for Americans)

Engineer's Edge - Fans / Blower Horsepower Equation

Generalized fan / blower power equation:
P = (Q * p)/(229 * μ)
P = Power required, in good old fashioned American horsepower (and American horses are well known for being more powerful than metric horses)
Q = flow rate, in com
P = pressure in pounds per square inch
μ = fan efficiency coefficient (good propeller blades are about 85% efficient

Fan power at 85% efficiency (typical of good prop design)
P = (20,002.23cfm * 0.095 psi) / (229 * 0.85)
P = 1,900.21185 / 194.65
P = 9.76hp

A communist designs the fan, so only 75% efficiency (bunch of wastrels):
P = (20,002.23cfm * 0.095 psi) / (229 * 0.75)
P = 1,900.21185 / 171.75
P = 11.06hp

From Jack Kane, EPI Engineering, who I personally trust regarding such matters:

EPI Engineering - Propeller Performance Factors

From the article (the most important part):

NOTE: All our Products, Designs, and Services are SUSTAINABLE, ORGANIC, GLUTEN-FREE, CONTAIN NO GMO's, and will not upset anyone's precious FEELINGS or delicate SENSIBILITIES

Last edited by kbd512 (2022-05-02 12:42:06)

tahanson43206 · 2022-05-02 12:46:27

For kbd512 re radiator cooling ...

Posts are showing up faster than I can keep up, so this is just to note the arrival of your 1996 reference! Neat!

***
Please include dust on Mars in your design.

The radiator system you design for the manufacturing plant needs to be able to operate 24*7*668 (or whatever the number of Sols is), when the air is pure as it ever gets on Mars, and when it is choked with grit.

Ingenuity stopped working because of low solation (as I recall) and not because of dust.

However, NASA engineers may have taken dust conditions into account when planning flights.

Your radiator design needs to be able to operate without interruption, regardless of Mars weather conditions.

(th)

tahanson43206 · 2022-05-02 12:51:14

For Calliban re turbine for machinery ...

The machines I am thinking about would be operating inside the Mars terrain, and they would be needing to exert significant torque.

A turbine engine driving a hydraulic actuator might be successful in the Mars context. Are there any examples of that configuration on Earth.

An alternative is a turbine engine driving a generator, which then drives electric actuators.

I'm confident ** that ** configuration exists on Earth, in a variety of applications, on land, sea and air.

So! Can CO/O2 drive a turbine? I ** think ** you've already addressed that question, and I confess to being behind on the flow of messages, so apologize if you have. Just point to the post, to save time.

(th)

kbd512 · 2022-05-02 13:00:25

tahanson43206,

Since our turbo is cranking out at least double the amount of power required, I'm pretty sure "the fan" will work. On that note, let's skip the dust. Dust is bad for the fan. Anyway, I'm sure that Dyson can develop "the proper amount of suction" while spinning the dust out of the air. Otherwise their vacuums would go kaput. Our Dyson has been the longest lasting vacuum I've ever owned, but it doesn't use a filter.

Ingenuity's solar panels stopped producing enough power due to the dust, ergo the dust killed Ingenuity, just as dust ultimately killed Spirit and Opportunity. It doesn't matter if the dust is in the atmosphere or sitting directly on top of the panels- when there's enough of it, the solar powered whatever goes kaput. If we're half-way intelligent, which I'm sure we're not, then we won't repeat that mistake during missions with humans rather than electronics onboard.

kbd512 · 2022-05-02 13:33:27

tahanson43206,

Dyson's "bladeless" fan design sucks in 27L/s (64.8cfm) using 40W of electrical power. Dyson claims that 15X more "air" is entrained in the flow because their fan expels a jet of air at 55mph. If their marketing BS holds true, then 40W of fan power moves 1,036.8cfm through the fan, which means 772We of fan power is required to move the required volume of air through our radiator. If that is truly the case, then we may as well provide 1kWe from the engine's alternator to the radiator fan. I'm sure there's some kind of catch or their marketing BS is not true. It's a comparatively slow / gradual acceleration of a much larger volume of air. Volume is what we're after on Mars, even though mass flow is what ultimately affects cooling rate, so this is worth checking into.

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