Air breathing engines on Mars

RobertDyck · 2012-04-12 16:53:34

Yup, atmosphere breathing. There has been work on engines that burn in the CO2 atmosphere of Mars.

John Wickman did work in the 1980s on a jet engine for Mars. It uses powdered magnesium for fuel. Here is his website:
http://www.wickmanspacecraft.com/marsjet.html

There is also trisilane. Silane is silicon and hydrogen, SiH4. This is (was) used to ignite the Space Shuttle's main engines. It spontaneously ignites upon contact with oxygen, so immediately burns on contact with Earth's air. If you've ever seen video of a launch, it's the burning liquid they spray sideways beneath the main engine. Trisilane has the formula Si3H8, it's liquid between -117°C and +53°C. Mars never gets hotter than that, and only the poles in winter get colder. We would never send humans to a location below -117°C, so this means it remains liquid outdoors on Mars. In the CO2 atmosphere of Mars, it's about as stable as gasoline. Just make sure you never expose this fuel to oxygen in a pressurized garage; it wouldn't explode but would immediately catch fire.

The advantage to air (atmosphere) breathing engines is you don't have to carry oxidizer. This gives a Mars airplane or rover a lot greater range. That is, carry more fuel because you don't have to carry oxidizer. And the fuel tank for liquid silane is about the same as a gasoline tank, you don't need a heavy pressurized methane tank. Note: natural gas is mostly methane, so look at the fuel tank on a natural gas car. That's what a methane rover would require. Liquid fuel means more fuel, less tank.

There are a couple catches to trisilane. When it burns in CO2, the waste product is steam, soot, and silica scale. Steam obviously isn't a problem, soot would produce black smoke like a badly tuned 18-wheel truck, but silica scale requires special engineering. Scale would quickly clog a piston engine, but a jet engine can be designed for it. The jet engine for an A-10 Warthog aircraft was designed to withstand small arms fire, so American engineers already know how to design a robust turbine engine. This turbine engine would power the wheels through a transmission, like the engine of an Abrams tank. The blades and internal air flow channel would be coated with Teflon. Silica scale would build up until a large heavy scale accumulated, then flake off. The turbine would have to be designed to withstand a certain amount of blade imbalance.

As Robert Zubrin said, there's no EPA on Mars. So we don't have to worry about dirty exhaust. He was talking about dumping CO after extracting oxygen from CO2, but the same principle applies. After all, millions of cars in a single valley (Los Angeles, San Francisco, etc) cause significant environmental problems, but a single rover on the entire planet is not significant.

Trisilane is made from rock and water. Burn silicon with hydrogen, the hydrogen comes from electrolysis of water. Silicon an be made by burning silica (SiO2) in pure carbon. Either find a deposit of white silica sand, or a type of feldspar called bytownite. There's a lot of bytownite all over Mars. That mineral can be separated with sulphuric acid into alumina (Al2O3) which can be melted with electrolysis to form aluminum metal. The byproduct of the initial step is silica gel, which can be calcinated with heat to drive off water to form pure silica. That silica can be melted to make glass; useful for windows, fibreglass insulation, or by adding resin can be fibreglass for construction. Or as I said, burn the silica with carbon soot to form CO2 and pure silicon. So trisilane is made from a byproduct from smelting aluminum.

GW Johnson · 2012-04-13 11:47:23

I have lots of experience designing, repairing, and operating piston and turbine engines on a lot of weird fuels. But, I cannot imagine using a slag-forming reaction (from burning tri-silane with atmospheric CO2) inside anything with moving parts. I just do not see how it could survive the grit and other solids for more than a few seconds. Blades, valves, pistons, makes no difference.

On the other hand, a device without moving parts could survive such abuse, so long as one you periodically (or continuously) get rid of the slag buildup inside. I also have decades of experience with ramjet engines, so that does come to mind. Not the ones with the baffle or colander flameholders, the simple dump combustors, which had wider flameout limits here on Earth, anyway.

I'm not sure how any "air"-breathing engine could ever produce useful power relative to its weight on Mars, because the atmosphere is so thin. Nor am I sure that airplanes would ever be practical there, for the same reason. But, under the assumption that low engine cycle pressures and high wing loads can feasibly be addressed, one might consider a ramjet airplane with a rocket booster for planetary transport on Mars.

Use the tri-silane or some other fuel with some oxygen in a separate rocket motor to takeoff and accelerate to supersonic-type ramjet speed, generally Mach 2-ish here on Earth, probably similar there. Then switch to tri-silane (or magnesium powder) burning with Martian atmospherioc CO2 in the ramjet (and shut the rocket down). You cut all power to decelerate and glide to landing, with some reserve rocket propellants to support go-around or divert.

I picked the supersonic-inlet ramjet variant because the performance potential is much higher (higher cycle pressures in the engine) than the subsonic variety. This plus other extraordinary design measures would be needed to counter the disadvantage of the extremely thin "air" there. This is still subsonic combustion, though, not "scramjet", which simply is not yet ready for prime time. Flight speeds will be in the Mach 2 to Mach 4 range quite easily.

Air transport on Mars? Maybe. That "air" is awfully thin. Engine thrust and power, and wing lift, will be more-or-less proportional to atmospheric density (as a ratio to here: pressure ratio .006 times molecular weight ratio 1.57 divided by temperature ratio something like 1.2, for .0079). The weights to be moved are proportional to gravity's pull (as a ratio to here: 0.38 gee). Power to weight, and wing loading, will be more or less in density/gravity ratio to here: 0.02.

It'll be 50 times harder than here to get decent power out of an airbreathing engine, and 50 times harder than here to balance structural weights against wing lift required to fly. Very tough to engineer.

GW

Last edited by GW Johnson (2012-04-13 11:50:19)

SpaceNut · 2012-04-13 20:57:14

I thought that the fuel from the site was meant as a solid propellant ...like an srb type useage

I remember that we talked about ICE and what fuels might be useful for them which included compressed air to making 2CO+ O2 reaction in a chamber plus others to make a simular rover powered vehicle movement possible...in threads long ago with DOOK ....I think he was a teacher in France...

clark · 2012-04-13 23:15:51

What are the requirements to boot strap a minimum level manufacturing base to produce a jet engine on mars? Fuel?

How about a ramjet?

Void · 2012-04-13 23:50:12

I have more imagination than skill in these matters, but so far I have been stimulated to visualize:
1) A rocket with a propeller at the top, which has airplane wings for blades, and that that propeller would have intake holes where the pressure were the highest.
The propeller would be rotated with rotons. I'm sorry, I am stuck on rotons. The "Propeller" would be an "Air" compresser, and that compresser would feed the rotons, and also the main rocket stack with compressed Martian gas. The "Propeller" might give some lift, but actually it is to be an "Air" compressor primarily.
I was thinking solid rocket fuel, both for the rotons and the main stack. Although the fuel may not have any Oxydizer, it is not a law that it would not. So the Oxydation part could be partially Martian air and partially solid fuel. I was thinking also that Aluminum powder could be included.

I was thinking that the solid "Jet?" boosters could be "Printed" with metal powders.

So actually I have no notion of a useful device in this case, just maybe something that could go up, and if it had on board oxydizer for when the atmosphere runs out, maybe even to orbit.

2) Replace the propeller with a cage fan, a rotating nose cone, again propelled by rotons, and that having a greater circumference than the rocket body, so that the cage fan would feed both the rotons and the main engine. The rocket itself would operate in a greater vacuum, because it would travel through the vacuum bubble left by the rotating cage fan, so you could drop the atmospheric drag load. Maybe this would be a good one for Earth? I am more leaning towards solid fuels, Magnesium and Aluminum also. To do useful work these would be strapped on to a load, and there would be at least two of them.

If this is a polution, I appologize in advance for the intrusion.

RobertDyck · 2012-04-14 06:06:03

NASA has already built unmanned aircraft with glider wings that fly so high into Earth's stratosphere that the pressure and density are the same as low altitude atmosphere on Mars. So the issue of wing load is already solved.

GW Johnson · 2012-04-14 11:08:14

The high-altitude NASA craft was very subsonic. Not compatible with supersonic flight with ramjets, so the propulsion would have to be something very subsonic, like propellers. There might be a way to do that with a combination of solar PV and chemical or battery storage of electricity. I have no idea what takeoff might look like in "air" that thin. Probably JATO-assist would be required.

GW

RobertDyck · 2012-04-14 15:41:24

Or simply subsonic with a turbojet engine.

GW Johnson · 2012-04-14 18:17:43

Turbojet? That gets us right back to the question of how to build such a thing. How to build a gas turbine that thinks CO2 is an oxidizer, and can generate a useful cycle pressure level in a 6-7 mbar atmosphere.

Like I said, that will be a really tough thing to do.

I really do have to wonder whether rocket-powered vehicles augmented a tad by aerodynamic lift while cruising supersonically wouldn't be just about as practical. But I sure would like to see some sort of "air"-breathing engine developed. We'll need a lot better compressors than we know how to build right now, of that I'm sure.

GW

SpaceNut · 2012-04-14 21:07:03

Sounds like scram or ram jet inputs where the oxidizer is scooped from the atmosphere, sort of of course some would need to be stored on board until the craft did get going fast enough....

SpaceNut · 2012-04-14 21:10:03

Question is anyone else getting an explore box indicating that ajaxfunc[1].html~ can not load....

RobertDyck · 2012-04-15 08:38:43

No rover will ever drive supersonic, so ram jet is not a solution.

Sorry GW Johnson, I respect your experience, but don't give up that easily. This reminds me of development of Canada's RadarSat. The Canadian Space Agency wanted to partner with NASA to develop a high resolution radar satellite. The purpose was to map arctic ice. Ships travelling through Canada's arctic can break ice, but how do you tell if it's ice over deep water or ice over land? Furthermore sand bars move due to currents. So this satellite would map sea ice and send that data to ships, so they can plot a safe course. But NASA said resolution that Canada wanted was impossible. So the Canadian Space Agency just did it without NASA. When they were finished they called NASA and asked them to launch it, offering 30% of observation time in exchange for the launch. NASA was amazed that the CSA actually built it! They called the US military to evaluate this design; they said it has significantly higher resolution than anything America has. In fact it can map the wake of a ship at sea, so can detect every moving ship in the ocean, even the US military doesn't have anything that can (at that time) do that. So the military said no, they wouldn't allow it to be launched. The CSA didn't get upset, they said fine, then they'll ask Russia to launch it, offer them the 30% observation time instead. NASA called back 24 hours later and said "When do you want it launched?" Since then Canada launched RadarSat2 with even higher resolution, it can see the metal hull of a ship directly, it doesn't have to depend on a wake, and it had a completely different financial arrangement. But the point is NASA said the first one couldn't be done, so Canada just did it.

Last edited by RobertDyck (2012-04-15 12:17:49)

GW Johnson · 2012-04-15 09:16:15

RobertDyck:

I quite agree with you about NASA. I am pleased with what happened in Canada with the RadarSat. Sounds like Canada's space agency has not stultified with "bureaucratic disease" the way the US agency did.

Part of our problem here in the US is that we allowed Congress to make pork-barrel political footballs out of every little project NASA does, which means NASA does nothing Congress cannot play for politics. That is precisely why American astronauts have not left Earth orbit for 4 decades now.

I hope Canada can avoid that mistake - it is fatal.

As for gas turbine or any other combustion engines on Mars, if they suck the local "air", they have to compress it to useful pressures inside the engines. Those are cycle pressures measured in tens of atm. Here, the source is 1 atm, for a compression ratio of tens. On Mars, the source is 0.0068 atm (at 7 mbar), for a required compression ratio in the thousands. The most extreme gas turbine ratios are around 30-something with known technology.

The most extreme recip compressors are in submarines, which for the high pressure air banks are around 480 atm and around 480 compression ratio. Those are not exactly the transportable-weight devices you could make a part of an engine, either.

You could in a vehicle carry both a fuel and liquid oxygen, and operate a turbine or a piston engine with it. The problem is the around-6000 F (3300 C) stoichiometric flame temperatures with just about any fuel and straight oxygen, again at tens of atm cycle pressure. Except for rockets, you'll need huge volumes of colder diluent gas to bring the stream temperatures down to something the hardware can withstand. Gas turbines do this with excess air, here on Earth. Due to the difficulties of compressing on Mars, that's not really an option.

The closest thing I know to a practical piston engine system independent of atmospheric oxygen was attempted for submarines decades ago. Diesel fuel plus hydrogen peroxide actually did work from storable liquids while submerged. It's somewhat similar to the propulsion of the torpedoes, but more suited to a reusable vehicle. There were great difficulties with it, and it was superseded by atomic power in submarines, then forgotten.

Given some sort of fuel that could replace the diesel, and some way to make hydrogen peroxide on Mars, that technology might lead to practical internal combustion or gas turbine power plants on Mars. The storable liquids are pressurized at around 1 atm, like here. Hydrogen peroxide decomposes to oxygen and steam. Steam is the diluent gas that reduces stream temperatures to something you can confine with cooled steel.

It can be done, but needs some development before we take it to Mars and count on it at the risk of lives.

GW

GW Johnson · 2012-05-05 13:07:49

See the "Gator" thread this same topic, for info about "air breathing" engines for Mars. I looked up a bunch of submarine and torpedo propulsion stuff.

GW

NeoSM · 2012-07-16 18:36:58

RobertDyck wrote:

No rover will ever drive supersonic, so ram jet is not a solution.

He was thinking in terms of aircraft - not a rover.

As GW mentioned, a ramjet engine is an attractive option for Mars - in terms of air breathing propulsion; they have been known to operate efficient sustained flight on earth at heights up to 80k - 85k feet (I imagine one could be designed to operate even higher) - NASA has a concept for an ionospheric ramjet - able to operate above 100km - point being, a ramjet can be designed to work perfectly fine in the thin martian atmosphere. The issue is getting the ramjet up to mach .5 - 1 just so it can start, and mach 3 to achieve the best efficiency (as you know simple ramjets can't take off, land, or work at slow speeds).

Last edited by NeoSM (2012-07-16 20:07:50)

Antius · 2012-08-17 07:10:46

For a ground vehicle, I would suggest decomposing the silane in a small chemical reactor, to yield silicon and hydrogen gas.

The H2 can then be burned in a fuel cell or small IC engine and the silicon collected as a solid for reuse. Some fuel cell vehicle concepts use a similar principle with gasolene or methanol.

A molten carbonate fuel cell might be used to burn the silane directly.

RobertDyck · 2012-08-17 07:45:57

That would defeat the point. The point of this discussion thread is "Air breathing engines on Mars". That means your vehicle does not carry any oxygen or other oxidizer at all. None, zilch, nada. So what fuel will burn in Mars atmosphere?

Antius · 2012-08-17 08:51:23

Hydrogen burns in a CO2 atmosphere, so the concept is in fact airbreathing. The question is whether it would be easier, cheaper, etc, to use a small gas turbine to burn the silane or an adapted fuel cell. Would a molten carbonate fuel cell work at all with silane as the fuel and compressed CO2 as the oxidiser?

GW Johnson · 2012-08-20 10:56:20

You're going to have a lot of carbonate slag clogging up any imaginable heat engine, if you use "molten carbonate fuel". Or a silane burning with CO2. Same thing may well be true of a fuel cell using that kind of fuel. I dunno for sure, but I had some experience with a silicone / magnesium ramjet fuel decades ago, burning with air. Fortunately, the ramjet had no moving parts. If it had had some, they would have been slagged solidly immovable. Good for internal heat protection, bad for part functionality.

GW

elderflower · 2016-06-20 03:23:44

GW Johnson wrote:

You're going to have a lot of carbonate slag clogging up any imaginable heat engine, if you use "molten carbonate fuel". Or a silane burning with CO2. Same thing may well be true of a fuel cell using that kind of fuel. I dunno for sure, but I had some experience with a silicone / magnesium ramjet fuel decades ago, burning with air. Fortunately, the ramjet had no moving parts. If it had had some, they would have been slagged solidly immovable. Good for internal heat protection, bad for part functionality.
GW

A Sterling engine would avoid this as its moving parts are in a clean environment and the heat source is external.

GW Johnson · 2016-06-20 14:12:49

The heat source is some kind of burner can. It is subject to slagging inside, and has to be designed for periodic but frequent cleaning. Like flushing out coal ash, just a whole lot worse and harder to do. Slag tends to stick tightly to surfaces.

GW

SpaceNut · 2016-06-20 16:44:46

The sterling also keeps the mass of the propellant and does not give the change in momentum for burning it until it is cleaned from the can it has been burnt in. Sure it can be used to create electrical power but we can not make props spin that fast or have great enough surface area to have the lift needed in the thin atmosphere.....

RobertDyck · 2016-06-20 21:43:39

NASA has designed a couple aircraft for Mars. And stratospheric aircraft designed to measure Earth's atmosphere for climate have operated so high that air density is the same as Mars. That is Earth atmosphere at very high altitude is the same as Mars at low altitude.

I was thinking of a robust turbine engine for Mars. But a Sterling engine could work on a rover. Built as a hybrid: engine generates electricity to recharge batteries, wheels driven by electric motors. Perhaps an easily replaceable burner "pot" to contain combustion byproducts. When it gets coated with silica scale, replace it with a new one. Then refurbish the "pot" by scraping/grinding off silica scale.

elderflower · 2016-06-21 02:32:42

Sterling engines work with any heat source of sufficient temperature, eg methanol/ LOx or radio isotopes as well as Silanes/CO2. Also they are not subject to slagging internally, unlike an IC engine of any type.

elderflower · 2016-06-21 11:24:12

Reading back, I should have been clearer. I was proposing stirling engines for surface use (stationary or rover mounted), not for flight.

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Air breathing engines on Mars

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