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#26 2015-09-13 07:39:39

SpaceNut
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Re: Combustion engines ... - ... on Titan and Mars

To make the fuel not only do we pay a penalty in transported mass to mass to make the fuels and oxydized but also for the power source to power the processes to make hydrogen and to free the oxigen to use as oxydizer. Unless there is a freely available source of methane and oxygen I do not see man using then for any other than to power our rockets back to earth for quite some time.....

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#27 2015-12-09 09:46:05

knightdepaix
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Re: Combustion engines ... - ... on Titan and Mars

Tom Kalbfus wrote:

On Mars you need both the oxidizer and the fuel. Technically most rockets we use today are combustion engines. Mars' atmosphere lacks an oxidizer Zubrin talked about using combustion engines in rovers, the fact that the cars carry their own oxygen to burn methane with is somewhat compensated by Mars lower gravity.

On Mars, Zubrin's idea of reacting silane with Martian atmospheric carbon dioxide is a way to go for combustion engines, which do not have to be internal ones like on Earth. Imagine Intercity bus, coach services with refueling stops, which hold refining facilities that turn locally sourced silicon into silane while recycling the amorphous carbon or graphite, and silicon dioxide leftovers from the bus engines. The energy sources for these facilities would be one or combinations of uclear, geothermal or solar powers. Further, solar power could be transmitted by microwaves from Phobos, Deimos or artificial satallites. Given less Martian atmosphere content than Earth's, loss of energy would be considerably less.

Or Short Take-Off and Landing airplanes and airports -- in essence intercity bus operating on air -- remove the requirement of rail building.

For rail freight transport, it would be in demand only when the Martian population has gotten to a substantial numbers in hundreds of thousands at various settlement on the planet. Before that cargo flight or intermodal container truck from one settlement to another could be enough and with a few larger settlement capable of launching rockets for transportation to Earth.

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#28 2015-12-09 14:21:44

Void
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Re: Combustion engines ... - ... on Titan and Mars

knightdepax,

Very informative post.  Without in the least wanting to correct or divert from what you have presented,

http://phys.org/news/2015-12-metal-powd … fuels.html

Now first, let me humble myself.  I did not notice until now that you mentioned that the engine does not have to be internal.  May I suggest Magnesium?

And because I have very ulterior motives, may I suggest that the working fluid be some Cryogenic Martian or Earth smile Gas?

Of course on Earth we want Iron perhaps instead, and as a working fluid perhaps liquid air?

Imagine that also robots working in the fields squirting weeds with liquid air to kill them.

The method then allows such an air or Nitrogen powered steam engine to power from the air's heat against the stored cold of the Cryogenic fluid, and also the potential of a metal combustion, and then even solar effects.

Can we have a car like that?

Last edited by Void (2015-12-09 14:26:36)


Done.

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#29 2015-12-09 16:56:47

RobertDyck
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Re: Combustion engines ... - ... on Titan and Mars

knightdepaix wrote:

On Mars, Zubrin's idea of reacting silane with Martian atmospheric carbon dioxide is a way to go for combustion engines

Zubrin's idea used liquid methane and liquid oxygen, from the same ISPP that produced propellant for the ERV. It was my idea to use silane.

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#30 2016-04-11 14:50:12

knightdepaix
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Re: Combustion engines ... - ... on Titan and Mars

I am thinking of a fuel. Thank RobertDyck for reminder, my quote almost half a year ago was based on the book -- the Case for Mars. At any rate, my idea use a chemical mix mainly composed of butenes (1-butene Melting point −185.3 °C (−301.5 °F; 87.8 K) and  Boiling point    −6.47 °C (20.35 °F; 266.68 K) on Earth, the boiling point will be lower on Mars but 1-butene shall be a liquid.) and disilane (Melting point 132 °C (−206 °F; 141 K) Boiling point −14 °C (7 °F; 259 K) on Earth). 1-butene can be made from dimerization of ethene which can be made with various source of energy -- solar, nuclear geothermal -- on carbon dioxide and steam.). Corollary, disilane can be made from mono-silane.

The chemical composition of the mix can be tuned so silane and disilane can act as combustion starter in their reaction with Martian atmospheric carbon dioxide. The energy generated is going to drive the reaction between butenes and more carbon dioxide. The waste product would be water, carbon, carbon monoxide and silicon dioxide. Steam and carbon monoxide can escape into the Martian atmosphere -- the mass balance of the fuel is going to be decreasing. Silicon dioxide and carbon can be recycled. A design for combustion engine does not have to be thermal but fuel cell -- the electric power shall drive the vehicle. Extra energy is stored in batteries which themselves can be recharged or exchanged with new batteries when their energy level is low. All refuelling, recharging and exchanging can be done at fuel stop -- imagine driving your hydrid or electric car to a gas station for refuelling.

So a Tesla Model 3 on Mars with extra silane-butene fuel cells, I guess ?

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#31 2016-04-15 07:26:22

Antius
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Re: Combustion engines ... - ... on Titan and Mars

Silane may turn out to be a useful fuel for land transport on Mars.  I made a quick estimate of the heat output of silane–CO2 combustion using bond energy data.  One kg of silane yields 22MJ of heat if burned in CO2, making it about as energy dense as methanol burned on Earth – about half as energy dense as gasoline on a unit weight fuel basis.  A methane-oxygen bipropellant has energy density of about 10MJ/kg.  So even if a silane engine adds weight to the vehicle, it may still improve range for the same efficiency, provided it doesn’t double vehicle weight.

I then divided the heat output by the heat capacity of the products (water vapour, amorphous carbon and silica) to get adiabatic flame temperature.  It comes out at 3823K assuming a starting temperature of 0 degrees C which would make a silane-CO2 flame about as hot as an oxy-acetylene flame.  I’m not sure that I quite believe that, but it is safe to say that flame temperature is high in comparison to any flame burned in air on Earth.

The high flame temperature and the presence of solid particles (carbon and silica) in the flame suggest that the radiated heat fraction of a silane jet flame in CO2 will be high.  This has interesting implications for design of a light-weight boiler for an external combustion engine on Mars.  Jet flames are high momentum flames and the turbulent conditions induced by the boundaries of any boiler would have relatively little effect on flame shape.  This would be even more the case for the low atmospheric pressures prevalent on Mars.  In addition, the low density of the Martian atmosphere means that any momentum plume exposed to ambient pressure would experience negligible entrainment and should therefore keep a regular shape over much longer distances than on Earth.  Hence the shape of the flame can be predicted with good accuracy and a tubular boiler shell can be constructed for a silane-CO2 jet flame such that the flame and its products will not come into contact with the shell even over long lengths.  Hence, the majority of heat can be removed from the flame by radiation heat transfer without fouling the boiler heat transfer surface.

Dependent upon the fraction of heat that can be removed in this way, the combustion plume at the end of the tube boiler could be vented directly into the Martian atmosphere complete with solid products.  Alternatively, the flame could be vented into an ash box, such that residual heat could be removed by conduction.  The box would need to be emptied every 100km or so as to prevent it from blocking, as about 2.5kg of sand and carbon dust would accumulate for each 1kg of silane burned.  The water from the exhaust could be vented from the box as a gas and collected for re-use.  A single kg of silane fuel yields 1.125kg of water.

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#32 2016-04-15 11:30:50

Tom Kalbfus
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Re: Combustion engines ... - ... on Titan and Mars

RobertDyck wrote:
knightdepaix wrote:

On Mars, Zubrin's idea of reacting silane with Martian atmospheric carbon dioxide is a way to go for combustion engines

Zubrin's idea used liquid methane and liquid oxygen, from the same ISPP that produced propellant for the ERV. It was my idea to use silane.

On Titan those would make excellent fuels. Liquid oxygen could exist on the surface of Titan until it reacts with something, and methane exists in abundance on Titan. You could use LOx like gasoline is used on Earth. Of course you would need to expend energy to break it off of water molecules.

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#33 2016-05-26 18:21:27

kbd512
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Re: Combustion engines ... - ... on Titan and Mars

What exactly would we haul around on Mars that absolutely requires internal combustion engines?

Wouldn't electric vehicles be more efficient in an environment that has no readily available oxidizer or fuel?

There are no railroads, paved roads, airports, or space ports on Mars.  That has to be built with minimal startup resources.

I think the first order of business is to deliver power plants for mining operations.  We can mine zinc and manganese on Mars and then use those materials to create rechargeable batteries for use in electric vehicles.  The electric vehicles require far less maintenance and resources to operate than ICE equipped vehicles.  The only reason ICE equipped vehicles work so well here on Earth is the infrastructure built around extraction of liquid hydrocarbons and a readily available oxidizer for the ICE's to use.  None of that exists on Mars.  Why fight the natural environment there when we can use what is abundant and available there in as energy efficient manner as is practical?

If I wanted a sizable colony on Mars sometime this century, I'd limit our use of ICE's there to rocketry.  Even ICE equipped aircraft don't make much sense there.  Without ultra-low wing loadings and VTOL, landing speeds there make horizontal landings are a hazardous affair for routine operations.  Perhaps computers can reliably land aircraft at several hundred kilometers per hour.  A human pilot would need to be highly skilled.  The wide atmospheric pressure differentials also complicate stall characteristics.

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#34 2016-05-27 09:10:36

Antius
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Re: Combustion engines ... - ... on Titan and Mars

kbd512 wrote:

What exactly would we haul around on Mars that absolutely requires internal combustion engines?

Wouldn't electric vehicles be more efficient in an environment that has no readily available oxidizer or fuel?

There are no railroads, paved roads, airports, or space ports on Mars.  That has to be built with minimal startup resources.

I think the first order of business is to deliver power plants for mining operations.  We can mine zinc and manganese on Mars and then use those materials to create rechargeable batteries for use in electric vehicles.  The electric vehicles require far less maintenance and resources to operate than ICE equipped vehicles.  The only reason ICE equipped vehicles work so well here on Earth is the infrastructure built around extraction of liquid hydrocarbons and a readily available oxidizer for the ICE's to use.  None of that exists on Mars.  Why fight the natural environment there when we can use what is abundant and available there in as energy efficient manner as is practical?

If I wanted a sizable colony on Mars sometime this century, I'd limit our use of ICE's there to rocketry.  Even ICE equipped aircraft don't make much sense there.  Without ultra-low wing loadings and VTOL, landing speeds there make horizontal landings are a hazardous affair for routine operations.  Perhaps computers can reliably land aircraft at several hundred kilometers per hour.  A human pilot would need to be highly skilled.  The wide atmospheric pressure differentials also complicate stall characteristics.

I am inclined to agree, at least for ground vehicles.  A battery powered vehicle can carry light-weight solar panels to recharge those batteries.  The solar panels produce low voltage DC, batteries charge with low voltage DC, and permanent magnet motors run on low voltage DC. So no inverter or even power electronics are needed and the whole system can be very efficient.  The only weakness in the system is the need for lightweight, roll-up solar panels.  Not sure what the state of the art P/W is for these.

Internal combustion engines would have a much lower power-source to wheel efficiency, due to thermodynamic losses and inefficiency in the chemical engineering steps.  You are buying greater power, at the expense of needing a much more impressive energy source to manufacture the fuel.  At the base building stage, there will be a lot of demands upon that power and the inefficiency of chemical fule manufacture may not be tolerable.  A solar-electric vehicle has effectively infinite range.  Speed would be more limited.  The consequences of that are not trivial on Mars, as longer trips mean more consumable requirements and higher radiation doses to crew.  In addition, relying on solar electric power would make polar regions relatively less accessible.  You would need to borrow an RTG for those missions.

As for flight, how well would a helicopter work on Mars?  I am guessing that the blades would need a much higher swept area, which raises issues of rotational stability.  Would the tips need to approach the sound barrier and what would be the implications of that?  I would imagine that an aeroplane would need some sort of rocket assisted braking.  Friction is after all 3 times less effective on Mars, and drag is 10 times less effective.  Relying on these alone, would appear to require infeasably long runways.

Last edited by Antius (2016-05-27 09:21:13)

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#35 2016-05-27 10:03:46

GW Johnson
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Re: Combustion engines ... - ... on Titan and Mars

Things like the silane fuel will have lots of solids in the exhaust stream.  If you use it only as a source of furnace-like heat for other processes, you can cope with the solids.  They will greatly enhance radiation heat transfer,  but they will quickly clog passages, especially smaller ones.  I suspect the silica will be partly molten,  and will have soot incorporated in the droplets,  hardening them up considerably.  Deposits on solid surfaces will be very difficult to remove.  This stuff will not be a "clean sand" by any stretch of the imagination.

Gas streams with solids content are far less useful for extracting pressure driven work directly,  as in piston or turbine technology.  Aside from the horrific deposits problems,  the solid content in the stream is an incompressible substance.  It does no useful work in processes that reduce pressure (because there is no volume change).  The more solids content in the stream,  the less gas there is that can really do work. 

Just food for thought.

As for airplanes and helicopters on Mars,  there are two things to worry about.  The first is "wind pressure" (dynamic pressure) upon which aerodynamic forces are correlated.  It is 0.5 X density X velocity squared,  in appropriate units,  equivalent to 0.5 X specific heat ratio X absolute static pressure X Mach number squared,  if you like to work with Mach and pressure.  Both density and surface pressure on Mars range near 0.6% of typical Earth values.  To compensate,  you need just about factor-13 higher speed measures to achieve the same wind pressures you are familiar with here,  because the density factor is close to 167. 

Mach number is the second item.  Propeller and rotor blades as we know them become ineffective when tip speeds start exceeding the speed of sound (Mach 1).  There have never been any successful supersonic propeller designs,  although it has been tried many times over the decades.  We do have supersonic wing technology,  but typically they have poor handling qualities at low speeds for takeoff and landing.  That would not be the problem on Mars,  because you could never fly slowly in such thin air as an aerodynamic machine.  With similar-size wings,  landings and takeoffs will be closer to Mach 1 or more,  than the 50-200 mph stuff we use here.  Those are impractically-high speeds for takeoff and landing.  You will need very much larger wings,  a real strength/weight problem.

Assume we use a subsonic wing design and fly high subsonic with it,  say Mach 0.9 to cruise,  and that we accept a 300 mph (!!!) takeoff-landing speed,  compared to the normal,  say,  70 mph.  That's a factor 4 higher airspeed (factor 16 on velocity-squared) at near stall for takeoff and landing,  compared to factor 160-ish for compensating the density.  You will need something like factor-10 bigger wing areas.  In other words,  all dimensions of your aerosurfaces are at the very least about factor 3.3 times larger than here. 

If you restrict yourself to the same landing and takeoff speeds as we use here (and you may have to!!!),  then wing area must totally compensate the density factor of 160-ish.  Your wing and aerosurface dimensions are pretty near 13 times larger than here. 

Surfaces larger in dimension by a factor ranging from at the very least 3,  to far more likely around 13.  Somehow I don't think airplanes and helicopters as we know them are going to be a feasible transport mode on Mars.

I think any sort of aircraft we use there will resemble supersonic missiles more than conventional aircraft here.  You'll need a fast rocket launch to flying speed,  and a fast rocket deceleration into a rocket-powered propulsive landing. 

GW

Last edited by GW Johnson (2016-05-27 10:18:03)


GW Johnson
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"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#36 2016-05-27 11:17:19

Antius
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Re: Combustion engines ... - ... on Titan and Mars

Looks like purely ballistic vehicles may be way to go, considering how tricky the atmosphere is as an oxidiser source and how useless it seems to be for aerodynamic lift.  It is probably better to spend most of the journey above it, if you are travelling more than a few hundred km.  Such a vehicle could be provided a head start using a compressed gas rocket, basically a tough steel cylinder with a ball valve on the end that is charged up with compressed CO2 and used as a booster stage.  It could be recovered from the desert after each use.

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#37 2016-05-27 12:00:09

Antius
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Re: Combustion engines ... - ... on Titan and Mars

Antius wrote:

Looks like purely ballistic vehicles may be way to go, considering how tricky the atmosphere is as an oxidiser source and how useless it seems to be for aerodynamic lift.  It is probably better to spend most of the journey above it, if you are travelling more than a few hundred km.  Such a vehicle could be provided a head start using a compressed gas rocket, basically a tough steel cylinder with a ball valve on the end that is charged up with compressed CO2 and used as a booster stage.  It could be recovered from the desert after each use.

Actually a remarkably bad idea now I have worked out the performance of the rocket.  The final velocity would be about 40m/s.  With supercritical water, exhaust velocity would be 1600m/s and mass ratio would be ~1.25 (density = 322kg/m3) for the tank alone, perhaps 1.15 with the upper stage included.  So practical dV is 220m/s in vacuum.  Still not efficient.

Last edited by Antius (2016-05-27 13:00:59)

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#38 2016-05-27 14:38:54

GW Johnson
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Re: Combustion engines ... - ... on Titan and Mars

Well,  don't feel too bad.  Evel Knievel had a steam rocket designed for his Snake River jump.  Everybody today believes the steam rocket was "bad",  but it worked pretty well for a mile jump,  in spite of Knievel accidentally deploying the emergency chute on liftoff. 

If memory serves,  that was an 80 sec Isp supercritical water system designed by none other than Bob Truax.  I met him,  and saw his presentation on that event,  many years ago.  The chute actually caught some of the plume,  and yet it still flew over half a mile like that. 

GW

Last edited by GW Johnson (2016-05-27 14:40:22)


GW Johnson
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"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#39 2016-05-28 10:08:23

kbd512
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Re: Combustion engines ... - ... on Titan and Mars

Antius wrote:

I am inclined to agree, at least for ground vehicles.  A battery powered vehicle can carry light-weight solar panels to recharge those batteries.  The solar panels produce low voltage DC, batteries charge with low voltage DC, and permanent magnet motors run on low voltage DC. So no inverter or even power electronics are needed and the whole system can be very efficient.  The only weakness in the system is the need for lightweight, roll-up solar panels.  Not sure what the state of the art P/W is for these.

The overall energy efficiency of electric motors factored heavily into my selection of that technology when I was thinking about using light pressurized rovers and heavy nuclear powered rovers on Mars.  Current solar panel technology is sufficiently light, compact, and durable for use in light electric vehicles on Mars and the evidence for this is being driven around Mars right now.  The only real problem with current technology is the energy density of available batteries.  When the industry-manufactured batteries achieve a 500w/kg energy density, there's no functional alternative for this application that will provide better performance.  All current battery candidates for missions to Mars have more than adequate power density, so that's not a problem.

Antius wrote:

Internal combustion engines would have a much lower power-source to wheel efficiency, due to thermodynamic losses and inefficiency in the chemical engineering steps.  You are buying greater power, at the expense of needing a much more impressive energy source to manufacture the fuel.  At the base building stage, there will be a lot of demands upon that power and the inefficiency of chemical fule manufacture may not be tolerable.  A solar-electric vehicle has effectively infinite range.  Speed would be more limited.  The consequences of that are not trivial on Mars, as longer trips mean more consumable requirements and higher radiation doses to crew.  In addition, relying on solar electric power would make polar regions relatively less accessible.  You would need to borrow an RTG for those missions.

The Martian environment dictates what types of power sources and means of transport are most suitable for use there.  Land transportation provided by light electrically powered vehicles seems pretty obvious.

With respect to energy resources and electrical power production technology, the only sufficiently light and energy dense power source for use on Mars is the sort of fusion reactor that Lockheed-Martin is working on.  That's the only really "new" piece of technology we'll be taking with us that is a "mission enabler".  All other technologies for this mission are refinements to or evolution of existing technology.

Antius wrote:

As for flight, how well would a helicopter work on Mars?  I am guessing that the blades would need a much higher swept area, which raises issues of rotational stability.  Would the tips need to approach the sound barrier and what would be the implications of that?  I would imagine that an aeroplane would need some sort of rocket assisted braking.  Friction is after all 3 times less effective on Mars, and drag is 10 times less effective.  Relying on these alone, would appear to require infeasably long runways.

When I spoke of using VTOL aircraft on Mars, I wasn't thinking of helicopters or tilt wing / rotor aircraft.  Rocket-powered lifting bodies like the X wing concept I put forth are the most plausible form of air transport there.  There are runways and negligible atmospheric pressure dictates a rocket propulsion system to vertically land the craft, as approach and landing speeds would otherwise be unreasonable.

The X wing control surfaces were intended to be reconfigurable for different phases of flight, similar in concept to the aeroelastic wings that NASA and the military have done work on.  The wings, most of the vehicle actually, would be constructed of polymerized aerogel "foam" cores wrapped in graphene sheets.

In any event, the power-to-weight ratio of ICE's on Mars would be no greater than electric motors in any application except rocketry.  We're already experimenting with batteries that have 2.5kWh/kg - 3kWh/kg energy densities in labs.  Since ICE's are typically 25% to 30% efficient, and gasoline's energy density is around 12kWh/kg, it won't be long before there's no energy density argument to be made in favor of ICE's.  When industrially manufactured batteries reach 3kWh/kg, you won't see many new-built piston engined aircraft in general aviation.

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#40 2016-05-31 23:02:37

knightdepaix
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Re: Combustion engines ... - ... on Titan and Mars

Antius wrote:

The box would need to be emptied every 100km or so as to prevent it from blocking, as about 2.5kg of sand and carbon dust would accumulate for each 1kg of silane burned.  The water from the exhaust could be vented from the box as a gas and collected for re-use.  A single kg of silane fuel yields 1.125kg of water.

The filled box can be exchanged for an empty one at a refueling station... Imagine a truck driver taking a break off a highway... The Suez Canal is 193.3 km. So fuelling fully at the beginning, refuel at mid-point, refuel again at end point.

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#41 2016-06-03 06:32:28

SpaceNut
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Re: Combustion engines ... - ... on Titan and Mars

Batteries are a sub system for powering other things not related to movement of the vehicle as a result of captured energy being stored in a battery. There are several types of engines and each needs specific types of fuels to make them work. Now if the fuel is an excess creation for other purposes then fine lets use it but if we need to have additional processes and energy source to create this specific fuel then its not for early use....

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#42 2016-06-29 09:55:33

knightdepaix
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Re: Combustion engines ... - ... on Titan and Mars

https://www.ted.com/talks/boaz_almog_levitates_a_superconductor/transcript?language=en wrote:

But what is the future of quantum levitation and quantum locking? Well, let me answer this simple question by giving you an example. Imagine you would have a disk similar to the one I have here in my hand, three-inch diameter, with a single difference. The superconducting layer, instead of being half a micron thin, being two millimeters thin, quite thin. This two-millimeter-thin superconducting layer could hold 1,000 kilograms, a small car, in my hand.

About "cars", almost at the end of this talk, a car can be pushed upward from the ground -- a situation similar to levitation for propulsion. Then electric or chemical energy can be used for propulsion. With less gravity and car-frame made from aluminum/iron alloy, the wasted energy consumption is going to be less.

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#43 2016-06-30 21:52:23

SpaceNut
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Re: Combustion engines ... - ... on Titan and Mars

true a levitation via some sort of magnetically created source would work but as GW indicated thats centuries down the beaten path....

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#44 2016-07-05 03:39:42

elderflower
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Registered: 2016-06-19
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Re: Combustion engines ... - ... on Titan and Mars

karov wrote:

Only problem with the train track conducting electricity from solar cells is the fact that Mars is made of Iron... which conducts electricity granted not as good as copper or gold or other metals. One would need to insulate the tracks from the planet to make it work.

Insulation will be necesarry although I personally doubt that the natural conductivity of the Mars soil is so great to represent electricity leakage or short-cut problem. Mars soil has comperativelly big percent of iron oxides not pure iron. Regarding the direct maglev road-construction option and hence the need for superconductors, we could do the opposite: put the natural iron magnets as an armature in the glass-amorphic silicon road, include the superconductors with the criogenic equipment onboard the vehicles and power them by induction from the road...

The solution to integrate the electricity grid lines with the roads and railways and the bands of photovoltaic cells is just a way to arrange the hardware in spatial aspect.

Please, tell me exactly in what it differs to the way it is done the last hundred years here on earth?

In the UK one of the old railway companies installed a third rail when they electrified the lines. This rail is mounted on ceramic insulators. The system works, although not so well as overhead conductors which can run at a higher voltage.
The problem with railways is not that they wouldn't work but that of smelting sufficient iron, rolling rails from it then grading and installing track and ties. This is a large industrial operation so will not happen any time soon on another planet.

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#45 2016-07-09 11:59:19

SpaceNut
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Re: Combustion engines ... - ... on Titan and Mars

We had all but forgotten to discuss the rail holding tie's and the isolating effects that they give to the dirt that they set on.....So another reason that rail transportation will be centuries down the road for mars.....

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#46 2016-07-09 14:05:13

GW Johnson
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Re: Combustion engines ... - ... on Titan and Mars

The original thread topic was combustion engines on Mars and maybe Titan.  In neutral CO2 or N2 atmospheres,  you have to supply both oxidizer and fuel to run an engine of any kind.  The oxidizer far outmasses the fuel,  a situation unlike that we face on Earth with air-breathing engines.  Any sort of piston or turbine will require a dilution inert gas to reduce flame temperatures to something the hardware can handle,  which can come from the local atmosphere.  It too far outweighs the fuel,  and likely the oxidizer. 

Things like silane or magnesium can be made to burn with CO2,  but produce an overwhelming mass of condensed phase products in the exhaust stream.  You can burn as an external source of heat for some kinds of engines,  if you are prepared to clean the slag and clinker out of your firebox quite frequently.  But you cannot do internal combustion with such fuels and atmospheres.  The slag and clinker will put and end to your equipment in minutes,  if not seconds. 

I have no idea what might burn with nitrogen.  Not much does so here. 

These considerations are why so many look at electric surface propulsion for places like Mars. 

GW

Last edited by GW Johnson (2016-07-09 14:07:24)


GW Johnson
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"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#47 2016-07-10 11:01:11

knightdepaix
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Re: Combustion engines ... - ... on Titan and Mars

GW Johnson wrote:

The oxidizer far outmasses the fuel,  a situation unlike that we face on Earth with air-breathing engines.  Any sort of piston or turbine will require a dilution inert gas to reduce flame temperatures to something the hardware can handle,  which can come from the local atmosphere.  It too far outweighs the fuel,  and likely the oxidizer. 
Things like silane or magnesium can be made to burn with CO2,  but produce an overwhelming mass of condensed phase products in the exhaust stream.  You can burn as an external source of heat for some kinds of engines,  if you are prepared to clean the slag and clinker out of your firebox quite frequently.  But you cannot do internal combustion with such fuels and atmospheres.  The slag and clinker will put and end to your equipment in minutes,  if not seconds. 
I have no idea what might burn with nitrogen.  Not much does so here. 
These considerations are why so many look at electric surface propulsion for places like Mars.

I agree with almost all of your ideas. Can CO2 be reduced to CO, which is a gas ? Maybe organic derivatives of hydronitrogen could reduce carbon dioxide to monoxide and give nitrogen gas and water. Or derivatives of sulfur and fluorine could react with carbon dioxide to give carbon monoxide, sulfur hexafluoride, which a gas due to low Martian atmospheric pressure and contribute to greenhouse warming of Mars as it is released. In other words, the design of combustion fuel shall be linked to contribution to Martian global warming or greenhouse effect.

The following is far stretched. Could the carbon monoxide revert in contact to iron oxides on Mars surface with the more energetic solar radiation than on Earth to carbon dioxide again and leaving iron on the surface ? The speed of human contribution to global warming happens in decades. After decades or a century of human settlement on Mars, cities would have been founded and iron could be mined on surface due to the mentioned reaction.

Last edited by knightdepaix (2016-07-10 11:02:44)

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#48 2016-07-10 14:08:35

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,952
Website

Re: Combustion engines ... - ... on Titan and Mars

I dunno,  not being a real chemist.  I'm a mechanical engineer whose chemistry is mostly on-the-job experience making solid propellants and burning a variety of fuels with air. 

I do know there is trace amounts of gaseous CO in Mar's "air".  It's mostly CO2,  with traces of N2,  CO,  and O2,  and tiny traces of other things.  Not much water.  That's down in the ppm range.

GW


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#49 2016-07-11 06:09:57

Antius
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From: Cumbria, UK
Registered: 2007-05-22
Posts: 1,003

Re: Combustion engines ... - ... on Titan and Mars

knightdepaix wrote:
GW Johnson wrote:

The oxidizer far outmasses the fuel,  a situation unlike that we face on Earth with air-breathing engines.  Any sort of piston or turbine will require a dilution inert gas to reduce flame temperatures to something the hardware can handle,  which can come from the local atmosphere.  It too far outweighs the fuel,  and likely the oxidizer. 
Things like silane or magnesium can be made to burn with CO2,  but produce an overwhelming mass of condensed phase products in the exhaust stream.  You can burn as an external source of heat for some kinds of engines,  if you are prepared to clean the slag and clinker out of your firebox quite frequently.  But you cannot do internal combustion with such fuels and atmospheres.  The slag and clinker will put and end to your equipment in minutes,  if not seconds. 
I have no idea what might burn with nitrogen.  Not much does so here. 
These considerations are why so many look at electric surface propulsion for places like Mars.

I agree with almost all of your ideas. Can CO2 be reduced to CO, which is a gas ? Maybe organic derivatives of hydronitrogen could reduce carbon dioxide to monoxide and give nitrogen gas and water. Or derivatives of sulfur and fluorine could react with carbon dioxide to give carbon monoxide, sulfur hexafluoride, which a gas due to low Martian atmospheric pressure and contribute to greenhouse warming of Mars as it is released. In other words, the design of combustion fuel shall be linked to contribution to Martian global warming or greenhouse effect.

The following is far stretched. Could the carbon monoxide revert in contact to iron oxides on Mars surface with the more energetic solar radiation than on Earth to carbon dioxide again and leaving iron on the surface ? The speed of human contribution to global warming happens in decades. After decades or a century of human settlement on Mars, cities would have been founded and iron could be mined on surface due to the mentioned reaction.

Something like this does appear to be taking place on Mars.  CO and O2 are both produced by photo-dissociation of CO2.  From the chemical formula one would expected CO to be twice as abundant in the Martian atmosphere as O2.  But in fact, there is far more O2, which suggests that the CO is removed more rapidly than O2.  Some may result from dissociation of water vapour.  Another obvious mechanism if through oxidation of CO, which could occur as a result of photo-chemical reduction of FeO.  This would form CO3+ or H2O2 both of which would attack CO in the Martian atmosphere.

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#50 2016-07-11 08:58:12

RobertDyck
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From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 7,343
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Re: Combustion engines ... - ... on Titan and Mars

A smelter works by burning coke in a controlled reaction starved of oxygen to produce CO. That CO with heat strips oxygen from iron oxide to produce iron metal. It happens at temperatures cooler than necessary to melt iron, and old smelters kept the temperature down deliberately to control how much carbon got dissolved into steel. However, at low temperatures other impurities in ore tend to stay there. Modern smelters use higher temperature to melt steel, the molten steel accumulates as a pool at the bottom. This does a much better job of separating impurities, but produces steel with way too much carbon. In the late 1800s a separate device would re-melt steel to burn off excess carbon. We could go into modern techniques, but the point is CO does remove oxygen from iron oxide But it requires heat. Don't know if energy from UV light is sufficient for a low-level reaction on Mars.

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