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#1 2006-02-07 14:06:34

Designer
Member
Registered: 2006-02-07
Posts: 8

Re: Mars Crew Exploration Vehicle 2030"manned rover"

Hi, my name in Hirash Razaghi. I am a transportation design student in Sweden. www.dh.umu.se 

At the moment I am doing my thesis which is a visionary project about a crew exploration vehicle for explorations on Mars surface " a manned Rover"

I would appreciate if you could help me to get to know about possible materials which could be used to build the body of the vehicle, what composites/materials? Possible propulsion technology? what I am looking for are the possibilities which can be used in a future scenario "2030" So any conceptual ideas are welcome.

I would appreciate your opinions and looking forward to Your input and help!

Regards
Hirash Razaghi

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#2 2006-02-07 14:56:13

Rxke
Member
From: Belgium
Registered: 2003-11-03
Posts: 3,667

Re: Mars Crew Exploration Vehicle 2030"manned rover"

Hi, Hirash, and welcome to New Mars!

There's a whole section dedicated to land propulsion, see: http://www.newmars.com/forums/viewforum.php?f=23 (Edit: moved to that section)

And don't be surprized when some discussions there are rather heated, heehee, that's just proof people feel strongly about certain things.

Maybe there's some stuff in the Wiki (see link under the new mars banner) but I don't readily remember if that's the case (adds to to do list)

If you find something interesting, or have stuff to share, please do!

Looking forward to more news from you.

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#3 2006-02-07 15:47:28

GCNRevenger
Member
From: Earth
Registered: 2003-10-14
Posts: 6,056

Re: Mars Crew Exploration Vehicle 2030"manned rover"

What size of manned rover?

Small, light, unpressurized:
-Battery power coupled to electric motors, solar cells for supplimentary power perhaps. You won't be going very far, so stored power should do.

Big, heavy, pressurized:
-Fuel cells powerd by Hydrogen or Methanol with Oxygen, with capacitors or batteries for burst power
-Turbine burning Methane with Oxygen coupled to a generator, with waste heat regeneration if possible

Some kind of storage mechanism is needed, like a battery or a flywheel set. Propulsion will be by motors built into the wheels probobly for maximum maneuverability and duability (no transmission, axels) Solar power here will be helpful if you make stops in the day, but would only be a small bennefit if traveling alot.

Fuel cells would be more efficent, can use a lighter weight fuel (hydrogen), and are quite durable (few moving parts) but themselves are heavy and bulky per watt and hydrogen storage is difficult.

A turbine would be very light weight, use a denser and easier to get fuel (methane) but much less efficient. Some means of capturing waste heat would be very nice, but I am not quite sure how you would do it. Thermocouples for instance are very inefficient.


"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw

The glass is at 50% of capacity

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#4 2006-02-07 16:13:49

Designer
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Registered: 2006-02-07
Posts: 8

Re: Mars Crew Exploration Vehicle 2030"manned rover"

Hi Rxke,

Thank You! I am sure there some useful stuff there. No worris I understand the passion:)
Regards, Hirash

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#5 2006-02-07 16:21:13

Designer
Member
Registered: 2006-02-07
Posts: 8

Re: Mars Crew Exploration Vehicle 2030"manned rover"

Big articulated pressurized long distance truck...almost 9 meters with full "walk- through" articulation enough space for three person,driving/sleeping/small lab and spacesuit changings compartment.

Sketches on the way ...but do not know how to view it here:(

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#6 2006-02-07 20:46:54

Dook
Banned
From: USA
Registered: 2004-01-09
Posts: 1,409

Re: Mars Crew Exploration Vehicle 2030"manned rover"

Not sure if you've read all of my post "Simply Mars Exploration Vehicle" but in my opinion it really is the only way to go.  All life support and mission essential systems have at least one backup and it is just under 5,000 lbs, low enough to make the critical Mars Direct weight requirements (well, if they don't take one mini-truck)

For structure, you have to go with carbon composite for two reasons.  You can't beat it's strength to weight ratio and it will lose much less heat (may in fact keep in too much heat) but an aluminum structure would lose internal heat quickly in mars temperatures.

Propulsion is probably going to be fuel cell powered electric motors, solar power alone isn't nearly enough, internal combustion engines will not work because you need to carry a large and incredibly heavy LOX container, and PGM's with their needed radioactive shielding are way too heavy.  And fuel cells are not heavy at all, the space shuttle ones weigh 250 lbs. 

I disagree with GCN about having the motors in the wheels.  This exposes them to extreme vibration, there's going to be a lot, the cold, and mars fines (dust).  Even one of the wheel motors on Opportunity (or Spirit?) is having problems now.   

LOX is incredibly heavy.  I can't imagine trying to carry enough LOX to fuel a methane/oxygen turbine for more than a few minutes.

In my humble opinion, keep it simple and lightweight.  Four wheel drive vehicles on earth make it over incredibly rough terrain so why do we need a full articulating truck on mars?  Plus good luck (no way it's going to happen) getting it's weight under 5,000 lbs.

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#7 2006-02-08 05:50:58

Designer
Member
Registered: 2006-02-07
Posts: 8

Re: Mars Crew Exploration Vehicle 2030"manned rover"

Hi Dook,

Thanks for the advise! I will read your post carefully. What kind of carbon composites? there are so many different types of them. ...about the hub engines...but if they are well protected in some kind of case? with some water heating system?

cheers

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#8 2006-02-08 16:52:23

Austin Stanley
Member
From: Texarkana, TX
Registered: 2002-03-18
Posts: 519
Website

Re: Mars Crew Exploration Vehicle 2030"manned rover"

Propulsion is probably going to be fuel cell powered electric motors, solar power alone isn't nearly enough, internal combustion engines will not work because you need to carry a large and incredibly heavy LOX container, and PGM's with their needed radioactive shielding are way too heavy.  And fuel cells are not heavy at all, the space shuttle ones weigh 250 lbs.

LOX is incredibly heavy.  I can't imagine trying to carry enough LOX to fuel a methane/oxygen turbine for more than a few minutes.

You keep saying this, but you continue to be wrong.  A methane-02 combustion reaction and a methane-oxygen fuel cell use EXACTLY the same reaction (via diffrent methods) to produce their energy.  In both cases the formula is:

CH4 + 2O2 -> CO2 + H2O + 891 kJ

The same is basicaly true if you were going to use any other type of fuel cell or combustion reaction.  Be it H2-O2 or O2-Methanol.  A fuel cell is able to reclaim the energy a little bit more efficently (about 10% better) but that is it.  An interal combustion engine does not require radicaly more fuel than a fuel cell does.  To make up for that, they have about twice the power/weight ratio a fuel cell has.


He who refuses to do arithmetic is doomed to talk nonsense.

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#9 2006-02-08 21:08:09

GCNRevenger
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From: Earth
Registered: 2003-10-14
Posts: 6,056

Re: Mars Crew Exploration Vehicle 2030"manned rover"

A hydrogen fuel cell is going to require alot of oxygen too, and infact nearly as much as a combustion engine. Hydrogen also requires bulky tanks since its density is so low. There is no good reason a combustion engine can't burn hydrogen either if fuel mass is a problem.

The turbine I am talking about isn't like the big jumbo one on an M-1 battle tank or a ocean ship, I am talking small turbine(s) like six or eight inches in diameter, coupled to a generator, with waste heat and water reclemation perhaps. Couple the thing to a flywheel for battery-free energy storage perhaps.

That Shuttle fuel cell you cite is just for one cell, Shuttle packs three of them to generate its full power output. You are talking a metric tonne for the cells and support componets, versus what for a small turbine and generator?

"Full articulation" as you put it is absolutely vital for several reasons:

-If you get stuck far away from the HAB, you are going to die. The six-wheel no-axle arrangement maximizes agility, where each wheel can turn either direction, and is proven to work even on the tiny MER rovers. Traction is substantially less due to reduced gravity too... Your "humble opinion" is simply wrong.

-Compactness, that vehicle volume is also very important and is the #1 or #2 failing with MarsDirect. If there are no axles, the wheels can be "tucked in" tighter.

They also have some redundancy, where you could lose one or two motors and still get around. And that vibration? You aren't going to be racing this thing over the Martian landscape, and the reduced gravity will help. If its good enough for the special forces:

DARPA electric drive SpecOps hybrid vehicle

Its good enough for me. The things are just big magnets too, not much in the way of sensitive electronics, so the cold shouldn't be a problem. That leaves the Martian dust to contend with, and I think this could be overcome.

Fully independant drive over six wheels should make the ride smoother then axle drive over four, which might be important if you are trying to do anything sensitive (electron microscopy for instance) while driving.

A carbon composite shell might not be such a good idea, since ultraviolet light and the peroxides in the Martian dust could damage it. Aluminum metal is a known quantity, and as calculations have been done, keeping the vehicle cool may turn out to be a bigger problem then keeping it warm at night. Aluminum would be the clear winner here.

Also, if the electric motors are internal to the vehicle, and cooling is a problem, then you just made it ten times worse by putting the motors inside.

MarsDirect's cheif failings are that its too optimistic about mass and too optimistic about volume, and this is passed down to the pressurized rover. I don't think that it should be so constrained to the mass/volume requirements that Zubrin has set out, since he calls for pushing everything too far.


"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw

The glass is at 50% of capacity

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#10 2006-02-09 14:08:26

GCNRevenger
Member
From: Earth
Registered: 2003-10-14
Posts: 6,056

Re: Mars Crew Exploration Vehicle 2030"manned rover"

Furthermore, there is a neat technology you might not be aware of, the marvelous new trick of active suspension. Instead of relying on springs or gas/liquid cylinders to moderate the shock to the vehicle, the wheels will lift themselves up and over an obsticle (like a rock) or push themselves down into shalow depressions. This would probobly be accomplished with electromagnetic servos like those used on modern aircraft control surfaces.

This system works best with six wheels, where you can keep four opposing wheels on the ground at all times when going over objects smaller then the wheels base, or have better climbing power with two wheels over larger objects.

This system works even better I am sure if each wheel can be powerd independantly as nessesarry. It has already been tested in prototype high-end luxury cars on Earth.


"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw

The glass is at 50% of capacity

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#11 2006-02-09 15:29:19

Designer
Member
Registered: 2006-02-07
Posts: 8

Re: Mars Crew Exploration Vehicle 2030"manned rover"

thanks for your valuble advises! I will gather all information for further evaluations. Sinece I am a Transportation designer "not engineer is hart to understand at once:) but lets not  forget that this project should be conceptual to keep the inspiration up but in otherhand what you are saying will be in great concedration. Keep write please! I need to learn.
Thanx

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#12 2006-02-09 18:57:27

Dook
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From: USA
Registered: 2004-01-09
Posts: 1,409

Re: Mars Crew Exploration Vehicle 2030"manned rover"

Austin:  Certainly you are not arguing that all types of engines/fuel cells use exactly the same amount of oxygen per fuel and provide the same amount of power?

I didn't say an internal combustion engine would require more fuel than a fuel cell but it will require an incredible amout of oxygen.  So much that you can't carry enough to operate your ICE for more than a few minutes.  Go ahead, figure it out on your own.  Take a 2.5 liter diesel engine, multiply 2.5 by your given RPM (say 2,000?).  Hmm, that's 5,000 liters of oxygen per minute.  That's a whole lot of oxygen!  I'll let you figure out how heavy your LOX tank is going to be. 

GCN:  I'm not familiar with micro-turbines but I am familiar with large turbines.  They are incredibly dependable but use enormous amounts of oxygen.  Since it's your suggestion maybe you can compare the weight of your oxygen/fuel turbine power supply (two since you'd need a backup) with my double fuel cell powered idea.

Full articulation is not vital at all.  It wasn't needed on the moon where there is even less gravity for traction.  It is simply an expensive unnecessary toy.  Jeep 4x4's routinely climb over incredibly rocky terrain (Calif Rubican Trail) but for some reason they've never needed fully articulating wheels.  My humble opinion is not wrong. 

Motors in wheels will be exposed to the extreme cold, vibration, and mars fines while motors inside gearboxes would be guarded from all of these.

Hehe, Darpa vehicle?  I wonder what the weight of it is?  You forgot about something.  Oxygen is not provided by the martian atmosphere!  This thing may get you 35 miles on mars with batteries, that's 17 miles out then turn around and come back while my vehicle will get you a thousand miles range.  And there is nowhere for the crew to sleep and no depressure area. 

Servo controlled suspension would add unnecessary complexity and create a higher electricity need from your vehicle.  Why would anyone prefer that over simple, lightweight, composite leaf spring suspension?

As far as my vehicle idea goes, I expect it to have a top speed of 20 mph and I seriously doubt the carbon composite is going to be ruined in a few months of sitting on mars waiting for the first crew to arrive.  Carbon composites have been used on mars for all of the rover missions, even sojourner.  The tiny solar panels are mounted on carbon composite and the rovers have exceeded their life expectancy.  Each vehicle is not intended to be fully functional, although with refueling (oxygen/hydrogen) and a few spare parts it likely will be, for each subsequent crew.   

And the motors are not inside the vehicle.  They are in a separate unpressurized compartment below the floorboards which you can access from the inside by opening the hatch on top of the gearbox.

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#13 2006-02-09 22:50:13

GCNRevenger
Member
From: Earth
Registered: 2003-10-14
Posts: 6,056

Re: Mars Crew Exploration Vehicle 2030"manned rover"

You aren't following Dook, pay attention

The actual amount of oxygen reacted with a given amount of fuel is precisely the same reguardless what kind of power plant, so long as the same or similar chemical reaction is used. The power plant simply converts the energy yeilded in the reaction to mechanical or electrical energy, is doesn't have much to do with what or how much of reactant chemicals are used.

Fuel cells use about the reaction as simply burning Hydrogen or Methane in an ICE or turbine engine and yeilds aproximatly the same amount of energy. Fuel cells are somewhat more efficient, but only by tens of percent. I think that you are ignorant about the chemistry involved Dook, a fuel cell requires exactly the same amount of oxygen to react a given amount of Hydrogen or Methane, down to the very last milligram. Its a simple concept of stoichiometry and conversion of mass & energy.

"Take a 2.5 liter diesel engine, multiply 2.5 by your given RPM... That's a whole lot of oxygen!... "

Um, no. You do know that not all the gas in an ICE engine are fuel and oxygen, right? ICE engines draw in large amounts of gas, but most of it is there simply to provide a working fluid, and is not consumed. ~85% of the non-fuel gasses in an Earth ICE engine aren't oxygen, but they seem to run just fine.

Since you know so much about ICE engines, I am sure you are aware that only a tiny amount of fuel is injected for each cycle: hence according to stoichiometry again only a tiny amount of oxygen would be consumed too. If you are pumping up your ICE engine with O2, then the vast majority of that oxygen won't be consumed. This is not rocket science.

"Full articulation is not vital at all. It wasn't needed on the moon"

If you will note the landing sites, the Lunar missions didn't exactly deal with anything approaching "hostile" terrain. This rover is going to have to handle extremely rough terrain better then any regular Earth vehicle, for one simple reason: If you get stuck or have a wreck, you are all going to die. Simple, yes? So, if there is something that can be done to make it safer without a radical increase in system mass, then it should be done. Even if it weighs a bit more. Thats why you're wrong.

"Hehe, Darpa vehicle?"

It only uses the same highly durable motor-in-wheel concept, I was not suggesting we use that design, you idiot.

"Servo controlled suspension would add unnecessary complexity and create a higher electricity need from your vehicle. Why would anyone prefer that over simple, lightweight, composite leaf spring suspension?"

Again, radically reduced vibration for a modest increase in complexity and small increase in mass. This system will expose the vehicle and the wheels to vastly less shock and vibration. (This removes the vibration issue for articulation, but for axle + spring?). If you would bother to even consider that it might not take too much energy to move the wheels up and down, then you would have realized the electrical demand will be trivial versus these bennefits.

Because a simple, lightweight, composite leaf spring doesn't exsist. At Martian temperatures, the composite will be too rigid and brittle to use as a spring. It is, after all, just pencil lead and super glue. The active suspension system will also provide far superior performance without an increase (and perhaps a decrease) in net mass over metal springs. Here is a perfect illustration where the simpler solution is the bad solution.

"is going to be ruined in a few months"

Its going to be ~2.5 years before the crew will arrive if the rover is shipped seperatly, and will have to operate another 2.0 years while on the surface. Four years of unfilted UV rays and corrosive peroxides against super glue? Even just two years? And the composite is a great insulator: this is probobly a bad thing, since a cooling system is going to be heavy and inefficient. I bet the mass and complexity of a cooling system would outweigh using aluminum and adding extra heat.

"The tiny solar panels are mounted on carbon composite"... are shielded from the UV rays by said solar panels, and we have no idea if that composite could withstand internal pressure today safely. Aluminum is a known factor.

"They are in a separate unpressurized compartment below the floorboards which you can access from the inside by opening the hatch on top of the gearbox."

You must not be in the design business... So, you want to force the crew to depressurize their crew cabin before they can access the gear box under the floor? And make them do repairs in space suits in cramped quarters? What a splended idea! Unless, of course, you intend to make this compartment pressurizable, in which case it will have to have thick walls and be sealed against internal cabin pressure without leaking. How much mass and trouble is that going to be?

And you don't seem to know too much about heat transfer either... just where is the heat from the motors going to go? Its inside of a insulated (!) box that is immediatly under the crew cabin, seperated by only a hatch. That heat is going to go into the crew cabin, since the Martian atmosphere is too thin to transport it away and the motors are too close to use radiators... Unless you want to use active cooling, which heavy and prone to lethal failure, or blowers which will get clogged with dust... Are you sure your motors won't overheat on their own?

The heat from the motors in a closed compartment in close proximity to the crew cabin made of insulating composites is going to compound the problem of cabin over heating... Aluminum is a known quantity, six-wheel articulated drive is a known quantity, and so on and so forth. Its not broken! Its just not "cut-off-toothbrush-handles" like the wild-eyed liar Bob Zubrin demands to try and pass off his sham of a plan as gospel truth. It will be a better vehicle and it will be worth the extra mass.


"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw

The glass is at 50% of capacity

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#14 2006-02-09 23:14:34

GCNRevenger
Member
From: Earth
Registered: 2003-10-14
Posts: 6,056

Re: Mars Crew Exploration Vehicle 2030"manned rover"

Now for my next trick...

If you are pumping up your ICE cylinder with pure oxygen and injecting fuel, only a small amount of oxygen will be consumed. What happens to the rest? It would be pushed/sucked out with the H2O/CO2 exhaust.

This oxygen would not have to go to waste, and infact you could probobly burn more of that oxygen by re-injecting it into the cylinder with more fuel. You could do this several times infact, until the H2O/CO2 levels became high enough to impede combustion.

But, since Mars is fairly cold, it would be pretty easy to extract the H2O by condensing it out as a liquid or solid for later reclemation or drinking. Carbon dioxide could be removed by a selectively permiable membrane/sorbant and dumped overboard, if burning Methane or Methanol.

So what do you have left? Thats right, pure oxygen gas. Under pressure to boot... Back into the engine it goes.

The same method could be used for a turbine engine too.

Edit: Oh, and if the exhaust pressure is high enough, say 10atm or so, cooling the exhaust to Mars ambient temperature would cause the carbon dioxide to condense too. Condensed CO2 makes a great coolant too, if your vehicle runs hot. Don't worry, most of this heat energy would go to preheating the combustion gasses, and wouldn't go to waste. Only the final cooling would be dumped.

Edit edit: As a practical matter, the ICE engine with pure oxygen might actually burn too fast and cause engine knocking... maybe a minimum amount of H2O/CO2 could be included to slow combustion Austin?


"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw

The glass is at 50% of capacity

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#15 2006-02-10 02:22:20

Austin Stanley
Member
From: Texarkana, TX
Registered: 2002-03-18
Posts: 519
Website

Re: Mars Crew Exploration Vehicle 2030"manned rover"

Austin:  Certainly you are not arguing that all types of engines/fuel cells use exactly the same amount of oxygen per fuel and provide the same amount of power?

Actualy, that is pretty much exactly what I am saying.  The reactions involved are functionaly identical.  To produce so much energy, you burn a certian amount of fuel in combination with a certian amount of oxygen.  For methane this ratio is 1:2 stoichiometricly or 1:4 in terms of mass.  EXACTLY the same as it is for a fuel cell.  It may suprise you to find that most ICE operate at nearly stoichiometric ratios, which makes sense, since this is the most efficent ratio to run them at.  So oxygen is consumed at basicaly the same rate per-unit of fuel as it is in a fuel cell.

I didn't say an internal combustion engine would require more fuel than a fuel cell but it will require an incredible amout of oxygen.  So much that you can't carry enough to operate your ICE for more than a few minutes.  Go ahead, figure it out on your own.  Take a 2.5 liter diesel engine, multiply 2.5 by your given RPM (say 2,000?).  Hmm, that's 5,000 liters of oxygen per minute.  That's a whole lot of oxygen!  I'll let you figure out how heavy your LOX tank is going to be.

Your calcuation is simply bogus.  If we were to burn 5,000L of oxygen a minute we would have an engine producing 1.7MW of energy, that's like 2200 horsepower! A we bit excessive for a martian rover, thats more like a jet engine.  No 2.5L engine could possible produce energy at this rate, the cylinders would melt from the heat!  Your crazy engine is chugging through fuel (methane) at ~2kg a minute!  Which again, is more like an air-craft than a car.

But don't take my word for it.  I'll run throught the math with you, so you can see it for yourself.

2.5L of oxygen consumption per revolution doesn't tell us much, since the actual amount of oxygen (mass/moles whatever) could varry greatly depending upon the actual conditions (temperature and pressure) it is under.  In this case, however we are probably talking about oxygen close enough to standard temperature and pressure (STP, 273K, 100kPa) for goverment work, which is convient since 1L of any gas at STP is equal to 22.4mols so:

2.5L O2/rev * 1molO2/22.4L = .11 mol 02/rev

Now, the equation I gave earlier [CH4+2O2->CO2+H2O+891kJ] not only tells us how much oxygen is consumed in relation to methane, but how much energy this reaction produces per unit.  So, we can calculate the amount of energy thusly:

.11 mol O2/rev * 1 mol reaction/2 mol O2 * 891kJ/mol reaction = 50kJ/rev

Now, since we know how much energy is produced every revolution, we can figure out how much energy the energy the engine produces.

50kJ/rev * 2000rev/min * 1min/60sec = 1700kJ/sec = 1.7MW

The process I just went through is a simple stochiometric analysist of your situation, and shows just how silly it realy is.  Stochiometry is the bane of many an early chem-student, but you should learn to love it, because it provides such a powerfull tool for analyisis of many situations.  As you can see, all the units properly cancel out (a good way to double check) and every ratio I multiply bye is actualy equal to 1, so we can be sure our number has not actualy changed.

The reason why your reasoning is so silly is because the entire cylinder is not filled with oxygen.  Not on earth, and certianly not on Mars.  Instead, in modern fuel-injected ICE a tiny amount of fuel is injected to react with the realitivly small amount of oxygen in the air.  I really don't know how you came up with this method of calculating fuel consumption, but it is realy wrong-headed.

GCN:  I'm not familiar with micro-turbines but I am familiar with large turbines.  They are incredibly dependable but use enormous amounts of oxygen.  Since it's your suggestion maybe you can compare the weight of your oxygen/fuel turbine power supply (two since you'd need a backup) with my double fuel cell powered idea.

Again, you are simply not getting it.  If a turbine is designed to produce the same amount of energy as fuel-cell or an internal combustion engine it will consume it's fuel and oxygen at basiclly the same rate.  In fact, a turbine will probably do a little better than a fuel cell since they tend to be more efficent (the large ones at least).

::EDIT, Sorry didn't see this little part on GCRN's post:::

As a practical matter, the ICE engine with pure oxygen might actually burn too fast and cause engine knocking... maybe a minimum amount of H2O/CO2 could be included to slow combustion Austin?

Hmm... I would have to look into the kinetics of the reaction, which are actualy probably pretty complex, especialy in an ICE where the volume and temperature change dramaticly (and thus the rate of reation).  Generaly speaking, combustion reactions are governed by the fuel mixture, not the method of reaction at high temperatures.  An ICE takes advantage of this by compressing the mixture to make the reaction happen faster.  So in this sense, changing the mixture wouldn't have that drastic an effect on the rate of reaction.

On the other hand, burning the fuel with a great deal of excess oxygen would be similar to increasing the compression ratio (at least in comparision to a terrestial engine), since the partial pressure of oxygen would be ALOT higher.  A higher compression ratio can lead to knocking, so it might be an issue.  Also, methane (and methanol) reacts at a much lower temperature than traditional hydrocarbons and so would cause more knocking.  The total lack of Nitrogen (and thus NO2 emissions) also probably changes things.

Honestly I don't realy know though.  I don't design engines for a living :-).  The issue is pretty complex, but it has been delt with before on submarines and the like.


He who refuses to do arithmetic is doomed to talk nonsense.

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#16 2006-02-10 09:53:36

GCNRevenger
Member
From: Earth
Registered: 2003-10-14
Posts: 6,056

Re: Mars Crew Exploration Vehicle 2030"manned rover"

I see three routes forming here:

-Combust gasses in either an ICE or a turbine with stoichiometric ratios of gasses in as small a quantity as possible with as complete combustion as possible, and not recycling the gasses at all. Steam would preheat liquid fuel/oxidizer or provide heat for something else, and then all of it would be condensed. CO2 would be seperated from the condensed water and dumped overboard.

-Combust gasses in an ICE or turbine engine repeatedly, with continuous injection of fresh fuel/oxidizer and removal of waste products. This would provide gasses (H2O/CO2) to slow down the combustion and provide a "free" working fluid for the combustion to heat and expand.

-Combust gasses in an ICE or turbine engine in the presence of an inert gas, where the combustion products would be completly removed and the inert gas (Helium probobly) recycled. This would "thin out" the mixture and provide a working fluid for the engine to heat. It may also reduce the corrosive effects of hot oxygen and/or carbonic acids by reducing their concentration.


"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw

The glass is at 50% of capacity

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#17 2006-02-10 10:35:27

Dook
Banned
From: USA
Registered: 2004-01-09
Posts: 1,409

Re: Mars Crew Exploration Vehicle 2030"manned rover"

Sigh...you both avoided the problem and you know it.  Fine, don't fill your 2.5L diesel engine with oxygen. 

Please inform us all exactly what you want to fill it with (something that burns with fuel maybe?), then do some math and tell us all exactly how you will carry it to mars, (liquid/gas?) and include how much it weighs, if you please.

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#18 2006-02-10 11:34:53

GCNRevenger
Member
From: Earth
Registered: 2003-10-14
Posts: 6,056

Re: Mars Crew Exploration Vehicle 2030"manned rover"

No Dook, I think this is a simple case that you don't understand the chemistry or engineering involved.

For any kind of combustion engine, a fuel and an oxidizer are combusted to heat a working fluid (typically gas), which causes it to expand and drive a piston/turbine/etc.

As I outlined in my last post, there are three possible ways to do this on Mars, which I will explain in greater detail for you:

1: Just enough oxygen and fuel are injected into a cylinder/turbine such that there will be none left over. The resulting water and carbon dioxide gasses, heated by the chemical reaction, expand and drive the engine.

2: Lots of oxygen but only a little fuel are injected into the cylinder/turbine, with a great deal of oxygen being left over following the reaction, which is heated and expands. This left over oxygen is recaptured and put back in the engine.

3: Small amounts of fuel and oxygen are injected into the engine along with a large amount of inert gas. The combustion products are removed from the exhaust, and the inert gas used again.

So, we aren't talking much here just a few kilos of helium.


"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw

The glass is at 50% of capacity

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#19 2006-02-10 11:39:34

RobS
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From: South Bend, IN
Registered: 2002-01-15
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Re: Mars Crew Exploration Vehicle 2030"manned rover"

Dook, they just told you what they want to fill the cylinders with; the exhaust from the previous combustion, CO2. That can come from the atmosphere as well. The cylinders can burn the fuel with an atmosphere that is only a few percent O2. The rest could even be Martian air. Using recycled exhaust is better because it's already hot. If the methane or other fuel doesn't burn completely you can recycle IT through the cylinders again and give it another chance to burn.

The idea is, if you want 50 horsepower, just burn enough methane and oxygen to give you that much horsepower and recycle the rest back through the engine. That will raise the efficiency considerably. ICE engines already do this; cars eliminate unburned gasoline by recycling the exhaust through the cylinders a second time.

Everyone said this the last time we discussed this matter, too

                 -- RobS

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#20 2006-02-10 11:43:25

GCNRevenger
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From: Earth
Registered: 2003-10-14
Posts: 6,056

Re: Mars Crew Exploration Vehicle 2030"manned rover"

Dook, they just told you what they want to fill the cylinders with; the exhaust from the previous combustion, CO2. That can come from the atmosphere as well. The cylinders can burn the fuel with an atmosphere that is only a few percent O2. The rest could even be Martian air. Using recycled exhaust is better because it's already hot. If the methane or other fuel doesn't burn completely you can recycle IT through the cylinders again and give it another chance to burn.

The idea is, if you want 50 horsepower, just burn enough methane and oxygen to give you that much horsepower and recycle the rest back through the engine. That will raise the efficiency considerably. ICE engines already do this; cars eliminate unburned gasoline by recycling the exhaust through the cylinders a second time.

Everyone said this the last time we discussed this matter, too

                 -- RobS

Yes, something like that... and the oxygen can be conserved just like the fuel can by recombusting it.


"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw

The glass is at 50% of capacity

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#21 2006-02-10 13:16:34

Rxke
Member
From: Belgium
Registered: 2003-11-03
Posts: 3,667

Re: Mars Crew Exploration Vehicle 2030"manned rover"

Earth atmosphere contains 21% oxygen.
So your 50cc engine does NOT use 50cc Oxygen. 79% is other stuff that does NOT react with the fuel.
On Earth that's mainly Nitrogen, so if you could replace that with CO2 through an external compressor, you're there.

What's so hard about that to disagree with? Or is it impossible to run an engine with a mix of O2/CO2? (I could see a problem with that, possibly...)

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#22 2006-02-10 15:00:23

GCNRevenger
Member
From: Earth
Registered: 2003-10-14
Posts: 6,056

Re: Mars Crew Exploration Vehicle 2030"manned rover"

Because I know Helium will work... oh, and of that 21% oxygen, most likly only a portion of it is burned. CO2 as a diluent gas could be problematic in high concentrations for a number of reasons:

-High temperatures could cause conversion to oxygen and carbon black, which would be bad for the engine mechanically.

-CO2 in high concentration mixed with steam might force the equilibrium to create carbonic acid despite the high temperatures (though I think this is unlikly).

-CO2 could be a pain to bottle because of its ability to change from liquid to gas to solid at slightly reduced temperatures depending on pressure.

-CO2 might interfere with the combustion by reacting with intimediate fuel/oxidizer species, which would severely limit the efficiency of the engine (this is probobly unlikly too).


"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw

The glass is at 50% of capacity

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#23 2006-02-10 15:06:36

Rxke
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From: Belgium
Registered: 2003-11-03
Posts: 3,667

Re: Mars Crew Exploration Vehicle 2030"manned rover"

-High temperatures could cause conversion to oxygen and carbon black, which would be bad for the engine mechanically.

That was the first thing I thought about too, and the carbonic acid. But but that was only intuitivelty, so to speak.. has anyone tried this kind of stuff?

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#24 2006-02-10 17:09:19

Dook
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From: USA
Registered: 2004-01-09
Posts: 1,409

Re: Mars Crew Exploration Vehicle 2030"manned rover"

Exhaust Gas Recirculation (EGR) is already used on modern engines but only a very small amount is recirculated because it affects engine performance. 

A vehicles EGR line is about a tenth the size of an exhaust pipe but you are talking about injecting large amounts of C02 or Helium along with fuel and pure oxygen into an internal combustion engine. 

EDIT: found a reference.  5-10% of exhaust is recirculated.  Hardly 79%.

http://en.wikipedia.org/wiki/Exhaust_gas_recirculation

Can you provide a reference where this has been tested before and worked?

How are you going to remove the combustion products from the exhaust?
How are you going to transport the helium on the rover?

And fuel cells are still more efficient, provide pure hot water to the crew for drinking, food preparation, or washing.  And they've been launch tested many, many, times with only one failure. 

I said all this before as well.

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#25 2006-02-10 17:15:29

Rxke
Member
From: Belgium
Registered: 2003-11-03
Posts: 3,667

Re: Mars Crew Exploration Vehicle 2030"manned rover"

Can you provide a reference where this has been tested before and worked?

That's what I wanted to know too.

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