Author Topic: Internal Combustion Engines (ICEs) on the Moon  (Read 135239 times)

Offline Warren Platts

The McKay thread was getting horribly off topic going for many posts on the virtues and vices of internal combustion engines (ICEs), so I thought I would start a new thread here.

ULA is currently developing an ICE for their Centaur stage that is expected to fly within the decade. They have great hopes that it will have widespread applications, including for use in lunar surface systems. IMO, ICEs will eventually become the motor of choice for rovers and especially eventual mining equipment on the Moon.

Honestly, what is better? Batteries? Nukes? Flywheels? Ultracapacitors? Laser beams? Fuel cells?
« Last Edit: 01/04/2014 09:19 pm by Warren Platts »
"When once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return."--Leonardo Da Vinci

Offline Warren Platts

Re: Internal Combustion Engines (ICEs) on the Moon
« Reply #1 on: 01/04/2014 09:57 pm »
This is how small they can be made: a 4-stroke with 0.9 cc displacement....

"When once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return."--Leonardo Da Vinci

Offline A_M_Swallow

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Re: Internal Combustion Engines (ICEs) on the Moon
« Reply #2 on: 01/04/2014 11:52 pm »
Such motors would be required in several sizes.  An ICE to power the lights would be smaller than one for the communications equipment or the main engine of an excavator.

Offline Lee Jay

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Re: Internal Combustion Engines (ICEs) on the Moon
« Reply #3 on: 01/05/2014 12:01 am »
Honestly, what is better? Batteries? Nukes? Flywheels? Ultracapacitors? Laser beams? Fuel cells?

If your primary source of energy is electricity generated by solar or nuclear, you're not going to beat battery-electric.  Everything else has a round-trip efficiency under 50% (usually well under), while electric is going to be above 85%.

Offline Lar

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Re: Internal Combustion Engines (ICEs) on the Moon
« Reply #4 on: 01/05/2014 12:31 am »
I think battery vs fuel/ICE is a fascinating topic so I am going to repost what I said on that other thread... (here http://forum.nasaspaceflight.com/index.php?topic=33583.msg1142793#msg1142793 )

Apples and oranges. Oppy's battery has a specific energy of about 500 kJ/kg. GH2/GO2 has a specific energy of 13 MJ/kg;
These numbers have very little relevance to the system efficiency

Since we're talking about the Moon and the PSRs are where the action is on the Moon, the relevant number is how many hours a lithium battery powered rover can operate in a PSR compared to an ICE-electric hybrid of the same mass. Under this measure of efficiency, I believe the ICE-electric hybrid would last longer, but I am open to correction.


I think ICE is a better choice for PSRs but to be fair, a solar powered rover (or later, digger, driller, hauler, maintenance mech for the ISRU, etc. etc.) might well "dip in" to the PSR to do some work, then "climb back out" by traveling back to sunlight, and get recharged and then go back in, many many times... as long as nothing bad happened.

If it got stuck or broke down, it would have a limited amount of time to free itself before it froze out or ran out of juice.

So you're kind of counting on things going right for that rover so it can get back to safety many times and dip back in to that PSR to work. Or else it has to carry a backup power supply (RTG?).  Or you run cables down into the crater (eventually).

The higher energy density of the H2 ICE means it has a lot more dwell time before it has to refuel, IMHO anyway. And refueling can well happen where it is working, but I would think requires tankers since the ISRU has to be in sunlight (the whole thing that makes this work is that you ARE using sunlight to power things, you're just storing the energy in a more versatile way.)

A battery rover could be refueled by a "battery tanker" that swapped out batteries or recharged it. But that seems like fairly complex infrastructure.

PS: I am mostly talking to Warren, who I broadly agree with, rather than to savuporo, for example.

---

I think the "getting lost in the dark" argument really does weigh against battery for PSRs... maybe not.
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Offline Lar

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Re: Internal Combustion Engines (ICEs) on the Moon
« Reply #5 on: 01/05/2014 12:32 am »
Honestly, what is better? Batteries? Nukes? Flywheels? Ultracapacitors? Laser beams? Fuel cells?

If your primary source of energy is electricity generated by solar or nuclear, you're not going to beat battery-electric.  Everything else has a round-trip efficiency under 50% (usually well under), while electric is going to be above 85%.

I don't think efficiency is the key metric, I think energy density and ease of storage / refuel are more important metrics.  Optimise for cost, not efficiency.
"I think it would be great to be born on Earth and to die on Mars. Just hopefully not at the point of impact." -Elon Musk
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Offline jg

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Re: Internal Combustion Engines (ICEs) on the Moon
« Reply #6 on: 01/05/2014 12:41 am »
Actually, the mass saved by the ice system is amazing, as is the flexibility of the resulting system.  This is really first rate work.

Offline Lee Jay

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Re: Internal Combustion Engines (ICEs) on the Moon
« Reply #7 on: 01/05/2014 12:41 am »
Honestly, what is better? Batteries? Nukes? Flywheels? Ultracapacitors? Laser beams? Fuel cells?

If your primary source of energy is electricity generated by solar or nuclear, you're not going to beat battery-electric.  Everything else has a round-trip efficiency under 50% (usually well under), while electric is going to be above 85%.

I don't think efficiency is the key metric, I think energy density and ease of storage / refuel are more important metrics.  Optimise for cost, not efficiency.

Well, if your round-trip efficiency is 33% instead of 85% your source of power has to be increased in size by a factor of 2.6.  That might be quite a cost and weight penalty.

Offline Warren Platts

Re: Internal Combustion Engines (ICEs) on the Moon
« Reply #8 on: 01/05/2014 12:46 am »
Honestly, what is better? Batteries? Nukes? Flywheels? Ultracapacitors? Laser beams? Fuel cells?

If your primary source of energy is electricity generated by solar or nuclear, you're not going to beat battery-electric.  Everything else has a round-trip efficiency under 50% (usually well under), while electric is going to be above 85%.

I see what you are saying, but what about when you might have a surfeit of solar energy on the one hand, but you also want to conduct extended operations within a permanently shadowed region (PSR)? Or you might be a prospecting rover that is to descend into a PSR that is offloaded off of a lander that still contains many kilograms of residual propellant on board? Or you might be operating a real heavy piece of equipment that needs 400 kW (500 hp) of power? Or you're running a tank farm containing hundreds of tonnes of LH2/LO2 for export to L2/Mars and you've got skads of boiloff that you need to do something with? Or you're a rover on Titan where there's plentiful CH4 in the atmosphere, but little sunshine?

I can see how one might want to trade a bit of marginal efficiency for the high specific power and extended range of an ICE-electric hybrid system, especially if the heat produced by the ICE could be put to a productive purpose (e.g., in the ULA Centaur plan, the excess heat is used to vaporize cryogenic liquids to keep the propellant tanks pressurized).

Attached is a very interesting paper on a H2O2 ICE that is proposed as a nice "anaerobic" (and, I might add, a nice "heterotrophic") power supply for robots. There's been some talk the proposed RPM/RESOLVE lunar rover might be landed by a MoonEx lander running H2O2. Presumably they will land with a certain amount of margin; perhaps the residual propellant could be leveraged to power a small 25 cc ICE that would last longer within the PSR than the battery it's currently configured to use?
« Last Edit: 01/05/2014 12:51 am by Warren Platts »
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Offline Lee Jay

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Re: Internal Combustion Engines (ICEs) on the Moon
« Reply #9 on: 01/05/2014 12:54 am »
If you're running on otherwise-to-be-vented H2 and O2, then you could look into high-specific-power devices like ICEs and turbines engines, especially when you have a severe mass penalty.  However, if this were a surface situation and thus has a much less severe mass penalty than something like a turbopump has for a stage, then I'd be looking to long-term reliability and efficiency, and thus fuel cells.  A 500kW fuel cell is not a large device at all.  I rode in a prototype Hydrogen fuel cell car and the fuel cell was in the center console between the two front passengers, yet it produced over 100kW.

As I said, if the source of power were not excess H2 and O2, such as solar, I'd be shocked if you could beat battery-electric.

Offline savuporo

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Re: Internal Combustion Engines (ICEs) on the Moon
« Reply #10 on: 01/05/2014 12:59 am »
If you're running on otherwise-to-be-vented H2 and O2, then you could look into high-specific-power devices like ICEs and turbines engines, especially when you have a severe mass penalty.  However, if this were a surface situation and thus has a much less severe mass penalty than something like a turbopump has for a stage, then I'd be looking to long-term reliability and efficiency, and thus fuel cells.  A 500kW fuel cell is not a large device at all.  I rode in a prototype Hydrogen fuel cell car and the fuel cell was in the center console between the two front passengers, yet it produced over 100kW.

As I said, if the source of power were not excess H2 and O2, such as solar, I'd be shocked if you could beat battery-electric.
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Offline A_M_Swallow

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Re: Internal Combustion Engines (ICEs) on the Moon
« Reply #11 on: 01/05/2014 01:07 am »
{snip}
As I said, if the source of power were not excess H2 and O2, such as solar, I'd be shocked if you could beat battery-electric.

On a long term off-Earth mission the steam produced by the ICE will need recycling.  So the complexity and mass of the condenser, water tank and water need including.

Offline Warren Platts

Re: Internal Combustion Engines (ICEs) on the Moon
« Reply #12 on: 01/05/2014 01:21 am »
{snip}
As I said, if the source of power were not excess H2 and O2, such as solar, I'd be shocked if you could beat battery-electric.

On a long term off-Earth mission the steam produced by the ICE will need recycling.  So the complexity and mass of the condenser, water tank and water need including.

Maybe not. ULA was running their ICE extremely rich (O2/H2 ratio by mass = 1.0), which I guess is functionally equivalent to running extremely lean like most H2 ICEs on Earth run. Thus the reaction is 2 O2 + 16 H2 ==> 2 H2O + 14 H2. 7/8 of the H2 is unused.

Moreover, ULA said that by running their engine so rich, the exhaust temperature isn't all that hot, and in fact the exhaust temperature is "hundreds of degrees less than gasoline" exhaust. Thus if gasoline exhaust is ~500 C, then we're looking at an H2 ICE exhaust temp of maybe 100 to 200 C. Thus run the exhaust back through your LO2 tank; this will have the double effect of vaporizing more O2 for the ICE, and condensing out the H2O, leaving pure GH2 to be cycled back to the combustion chambers.
« Last Edit: 01/05/2014 01:53 am by Warren Platts »
"When once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return."--Leonardo Da Vinci

Offline Warren Platts

Re: Internal Combustion Engines (ICEs) on the Moon
« Reply #13 on: 01/05/2014 01:27 am »
Oooh, I just thought of something: the current plan is that the proposed RPM rover total mass be no more than 80-100 kg. And this mass has to contain the entire power train, including the batteries.

Or does it.

The power system on a battery powered rover consists of a BIG battery and an electric motor; using an ICE, the power system consists of the electric motor, a small battery, a small generator/starter, a small ICE, a fuel tank, AND the fuel.

Thus if the rover were to use only the residual propellant of the landing module, the rover would not need to count its fuel against the mass budget, and so could use that extra mass for other fun things like more instruments, bigger drill, or simply a lighter rover that can allow more delta v for the lander....

I like this! ;D
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Offline joek

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Re: Internal Combustion Engines (ICEs) on the Moon
« Reply #14 on: 01/05/2014 01:34 am »
Honestly, what is better? Batteries? Nukes? Flywheels? Ultracapacitors? Laser beams? Fuel cells?

I would think it would depend heavily on application.  Fixed installations might trade for higher end-to-end efficiency (e.g., centrally generated power and storage).  Mobile and mass-limited applications might trade for lower end-to-end efficiency and higher power density (e.g., portable generator or automobile).

ULA's ICE application appears to be in the latter category--a good portion of the end-to-end efficiency penalty has already been paid for by the presence of the stage's H2/O2.

Offline beb

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Re: Internal Combustion Engines (ICEs) on the Moon
« Reply #15 on: 01/05/2014 01:36 am »
On a long term off-Earth mission the steam produced by the ICE will need recycling.  So the complexity and mass of the condenser, water tank and water need including.

Why would a long-term mission need to recycling the water produced by the ICE? It's not like you can recycle the water back into hydrogen and oxygen, and robotic missions have no need for water. Now if you were talking about a manned mission recovering the waste water might make sense but that wasn't mentioned.

Offline Warren Platts

Re: Internal Combustion Engines (ICEs) on the Moon
« Reply #16 on: 01/05/2014 01:46 am »
A 500kW fuel cell is not a large device at all.  I rode in a prototype Hydrogen fuel cell car and the fuel cell was in the center console between the two front passengers, yet it produced over 100kW.

Well, the Frank Zegler paper said they looked at FCs for their application and decided that a 20 kW FC (which is as much power as was produced by the Shuttle orbiter):

Quote
"is a relatively large fuel cell for flight applications and because all power is produced as electricity (as compared to per 10% for the IC engine) it must be converted via motors to shaft power with their attendant switching systems and losses. This grows the fuel cell to address conversion efficiencies."

Their flathead, 6-cylinder ICE is about 0.7 m long, and the final flight ready version is expected to weigh about 50 kg.
"When once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return."--Leonardo Da Vinci

Offline Warren Platts

Re: Internal Combustion Engines (ICEs) on the Moon
« Reply #17 on: 01/05/2014 01:50 am »
On a long term off-Earth mission the steam produced by the ICE will need recycling.  So the complexity and mass of the condenser, water tank and water need including.

Why would a long-term mission need to recycling the water produced by the ICE? It's not like you can recycle the water back into hydrogen and oxygen, and robotic missions have no need for water. Now if you were talking about a manned mission recovering the waste water might make sense but that wasn't mentioned.

Well, the ULA paper does say that FCs produce liquid water, and that this might be a decisive consideration for a crewed vehicle. On the other hand, if you're at an ISRU mine that's producing 15,000 tonnes of H2O per year anyway, who cares if you vent off a little exhaust? Simply venting off the hot exhaust would go a long way toward relieving the heat budget.
"When once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return."--Leonardo Da Vinci

Offline savuporo

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Re: Internal Combustion Engines (ICEs) on the Moon
« Reply #18 on: 01/05/2014 01:58 am »
I would think it would depend heavily on application.  Fixed installations might trade for higher end-to-end efficiency (e.g., centrally generated power and storage). 
Stationary power storage systems do everything to maximize efficiency. Look up pumped storage for example - you convert power to "potential energy". Entirely doable by moving in-situ available mass.
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Offline Warren Platts

Re: Internal Combustion Engines (ICEs) on the Moon
« Reply #19 on: 01/05/2014 02:08 am »
Honestly, what is better? Batteries? Nukes? Flywheels? Ultracapacitors? Laser beams? Fuel cells?

I would think it would depend heavily on application.  Fixed installations might trade for higher end-to-end efficiency (e.g., centrally generated power and storage).  Mobile and mass-limited applications might trade for lower end-to-end efficiency and higher power density (e.g., portable generator or automobile).

ULA's ICE application appears to be in the latter category--a good portion of the end-to-end efficiency penalty has already been paid for by the presence of the stage's H2/O2.

Yes, I was thinking of mainly mobile, mass-limited applications (rovers/miners). However, consider perhaps the early stages of a lunar base that must survive 2 weeks of darkness. Batteries would be the most efficient end-to-end system, at least as far as electricity is concerned, but you'd have to haul in a huge load of batteries, most likely from Earth. Any heating you did would have to come from electric heaters, and any shaft power you needed would require electric motors.

Meanwhile, you could crack water during the day, and then use the LH2/LO2 to drive an ICE generator during the night. Yes, you're not getting as much electricity out for the number of Joules put in, but since its the lunar night, you're going to need some heating, and the heat from the exhaust can be used for that. Also, there might be some condensers or something to run the crycoolers to suppress boiloff on your tank farm that require some shaft power: this could be taken directly from the ICE, rather than having to be converted into rotational motion via an electrical motor. Granted, that might be a case where you'd rather have a fuel cell; on the other hand, if this were a commercial venture, up front costs would need to be minimized and so the lighter weight and cheaper cost and good reliability of ICEs might possibly be more optimal.

Although if you're going solar, probably the best thing would be to have a space-based system at one of the L points that could beam you power during the night. This would quadruply save mass on your solar system by not having to double or triple your capacity in order to store energy, you don't need nearly as much mass for bracing, and you save on all that propellant that would be required to land all those solar panels. In this case, you would need a backup system, and an ICE or an FC might be a good choice.
"When once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return."--Leonardo Da Vinci

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