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#101 2020-12-30 21:04:21

tahanson43206
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Registered: 2018-04-27
Posts: 8,029

Re: Internal combustion engines for Mars

For SpaceNut re #100 ... thanks for bringing that entire discussion over to this topic ... it is definitely a good fit.

However, in the absence of updates in that topic, I'd like to see an answer to the questions that arose there ....

Louis proposed collecting CO and O2 from the atmosphere ... that would involve filtering molecules and compressing the CO and O2, and both those activities will consume energy, so I'd like to know how much energy would be required to deliver a Kg of CO and the corresponding supply of O2.

Someone else reminded the readers that CO and O2 can be produced by electrolysis of CO2 using a catalyst and high temperature, and I would like to see a report on how much energy is required to filter the atmosphere for that operation, plus the energy to produce on Kg of CO and the corresponding quantity of O2.

The energy costs would factor into a decision on which way to proceed, although the cost of the equipment and its maintainability would also be factors.

This forum contains reports of alternative ways of producing CO and O2 from CO2, in addition to electrolysis with a catalyst.

(th)

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#102 2020-12-30 21:13:39

SpaceNut
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Posts: 23,851

Re: Internal combustion engines for Mars

PPM is kind of a funny way to express pressure for a volume in molecules and that is where the electrolysis will win as you are starting out with a greater amount of molecules in the electrolysis than what you get from the natural atmosphere. Which brought about the apples to oranges comparison for water in another topic....you must start out with the same volume density to say that one process over the other is better with its use of energy.

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#103 2020-12-30 21:33:05

tahanson43206
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Re: Internal combustion engines for Mars

For SpaceNut re #102

The Kg of CO will be collected in a container, regardless of whether it comes from electrolysis, filtering the atmosphere, or some other process.

What I'm hoping someone will contribute (or if already contributed, found again) is the energy required to produce 1 Kg of CO using Louis' preferred method, or by electrolysis with a catalyst at high temperature, or some other method.

One of those methods will be less expensive (in energy required) than the others.

Energy cost is only one factor in determining the optimum method for Mars.   The complexity of the equipment, and the ease of difficulty of maintenance are factors.

Louis' preferred method of filtering may require distillation of the atmosphere after it has been liquefied .... that is an energy intensive process.

Is that what he had in mind? 

The gases admitted to the separation subsystem must be cleaned of non-gaseous contaminants such as sand.

What filter method did Louis have in mind?

Can the filters be sourced on Mars?

Can they be cleaned?

How much atmosphere can they filter before they are clogged?

Those questions would apply to the electrolysis system as well ... the input to the electrolysis needs to be as clean as possible.

Energy is required to move gases from one place to another in a system, and from one state to another.

(th)

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#104 2020-12-30 22:02:32

SpaceNut
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Re: Internal combustion engines for Mars

why would we bother to calculate out the energy as the energy is already used to gather in all air contents... we are left after processing Carbon monoxide 0.0747% from a cubic meter of mars air...

https://en.wikipedia.org/wiki/Atmosphere_of_Mars

Average surface pressure: 610 Pa (0.088 psi)
Carbon dioxide: 95.32%
Nitrogen: 2.6%
Argon    1.9%
Oxygen    0.174%
Carbon monoxide    0.0747%
Water vapor    0.03% (variable

All of Mars atmosphere has a mass of just 25 teratonnes which sounds like a lot but its not …
https://nasa.fandom.com/wiki/Atmosphere_of_Mars

with an mars air Surface density: ~0.020 kg/m 3 
https://nssdc.gsfc.nasa.gov/planetary/f … sfact.html

So carbon monoxide is 0.0747% of the ~0.020 kg/m 3 which you have now captured....you end up in a meter cube just 0.0001494 kg of co.

So we will move 6,693 cubic meters to get 1 kg of co...that must then add in the energy to electronically move it through a sieve to seperate the co from it....

So first we are going to cool the air that we have captured to seperate out the co2 where we would then move the rest to a tank for later processing... co will seperate out at a different temperature as will all of the other constituents there in which we will do when we have greater quantities of them later.....

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#105 2020-12-31 08:01:49

tahanson43206
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Re: Internal combustion engines for Mars

For SpaceNut re #104

Thank you for moving the ball forward here .... Post 104 is good for a first down, with the entire field to go before a touchdown.

A touchdown in this instance is to know with precision, which approach is the most energy effective.  Louis proposed collecting CO from the atmosphere of Mars, so your post shows that energy is required to collect the molecules.  Your post shows that the molecules must be cooled to separate the CO2 from other gases that are present.  Post #104 did not specifically mention the energy required to separate gas molecules from solid debris that may be (and surely will be) suspended in the mix. 

The idea of an electronic sieve is interesting and I'd like to learn more about that.  If there is a post earlier in the forum that explains that idea I'd be happy to look at it.

One suggestion is to try to keep units of measurement consistent ... a cubic meter is a measure of volume, and Kg is a measure of mass.

The mass in a volume varies depending upon the nature of matter inside, the pressure if the matter is gaseous, and the temperature.

A Kg is a reliably consistent measure of mass. 

In the case of Post #104, I deduce that a Kg of Mars atmosphere contains 0.0747 Kg of CO (74.7 milligrams).

That same Kg of Mars atmosphere would contain 953.2 milligrams of CO2.

It will take some amount of energy to separate the CO and O2 in that 953.2 mg

We will put the ball over the next 10 yard marker if we can find those two energy amounts, starting from a Kg of Mars atmosphere.

Since a viable CO/O2/CO2 industry on Mars depends upon knowledge of these energy amounts, this is a worth while exercise.

The end result will look something like this:

Louis' method: X ergs to make 1 Kg of CO by collecting CO from Mars' atmosphere

Electrolysis method: Y ergs to make 1 Kg of CO by splitting CO2

Another method (there are several proposals for low energy splitting of CO2): Z ergs to make 1 Kg of CO by splitting CO2

I'm looking forward to the NewMars forum collecting that data and finding a way to make it permanently accessible to future Mars settlers.

Edit#1: The energy required translates to what kind of energy supply is optimum to meet the need for a supply of CO/O2/CO2 to a customer.

The customer requirement suggested earlier, based upon the design of kdb512 for a bulldozer, would be ability to exert 1 ton of force against regolith for 8 hours in a work period.

Another data point that would added to the collection in this topic is a calculation of the amount of work to be done by the hypothetical bulldozer working on the surface of Mars.

Ultimately, it is that amount of work that any successful solution will perform, starting with solar panels in Louis' configuration, or nuclear reactors in everyone else's.

Edit#2: Oldfart1939 just introduced a challenge to the CO infrastructure idea in another topic.  I'm hoping someone in the current membership will consider taking up the challenge of approaching a nearby advanced high school or a junior college with vocational school features, to see if anyone there would be interested in pursuing the CO/O2/CO2 idea for an infrastructure on Mars.

It ** should ** be within the range of students, given the right leadership, to build and test an IC using this combination of gases.  For the purposes of the experiment, an existing Earth-proven engine design should be more than sufficient.  The project would include creating the CO input, taking risks carefully into account considering the age group.  Earth atmosphere can substitute for the CO2 buffer gas and the O2 oxidizer.

Since this technology has been demonstrated on Earth many decades ago, it is the demonstration by a living group of students that is of interest, in the context of a sustainable technology for Mars.

(th)

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#106 2020-12-31 11:13:02

SpaceNut
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Posts: 23,851

Re: Internal combustion engines for Mars

The moxie numbers for energy used to draw in Mars atmosphere and to seperate are contained in the topic Moxie and only Moxie
Remember this is a sub scaled unit capable of growing in size and numbers….

What moxie does talk about is relationship of input at 50 g/hour to be converted to 6 grams of o2.
So it runs many hours to draw in just a cubic meter of mars air in to process which we have given grams that we will get of each gas earlier.

It appears that it takes about 350 watts to do everything so number of hours x wattage is the whrs we will need to create the 2co + o2 from 2co2
so for the hour thats 50 g of co2 - 6 g of O = 44 g co produced not counting any of the initial amounts which are trace in the exhausted blend. This is all in gaseous form at this point and need to be cooled to make it liquid at the correct pressure.

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#107 2021-01-03 13:06:36

GW Johnson
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From: McGregor, Texas USA
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Posts: 4,690
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Re: Internal combustion engines for Mars

I looked really hard at the chemistry and thermochemistry of burning carbon monoxide as fuel.  That was with air,  with oxygen,  and with oxygen diluted with carbon dioxide.  I used the same oxygen percentage in the diluted case as exists in air,  on a mass basis. 

To evaluate energy storage density as it relates to the time integral of IC engine shaft power it can deliver,  you need to consider different storage densities for the different oxidant cases.  That is because you have to store the oxygen or the oxygen and the dilution gas,  in addition to storing your fuel,  if you aren't burning with Earthly oxygenated air.  The energy conversion efficiencies of typical IC engines at cruise power settings vary between about 10 to 20%.  The energy efficiencies of manual transmissions exceed about 85%,  with automatics a bit lower due to the slip inherent in some aspects of their operation. 

The deliverable time integral of shaft power to the wheels of the vehicle is the energy storage density times the conversion efficiency factors. But the energy storage density is not always the fuel lower heating value,  unless you are burning with Earthly oxygenated air not stored aboard the vehicle. 

For the fuel burning with Earthly air,  there is an air/fuel ratio by mass at stoichiometry that you compute from its oxygen/fuel ratio by mass from the chemical balance.  The mass percentage oxygen in Earthly air is 23.15%.  There is also a combustion heat release from the chemical balance,  that when divided by the fuel mass from the chemical balance,  is the upper heating value of the fuel,  with condensibles like water in the exhaust condensed.  The lower heating value is that with exhaust water uncondensed,  and is the more realistic value for IC engine work.  There is no water in carbon monoxide's exhaust,  so the two heating values are the same for that fuel.  The appropriate energy storage density for stored carbon monoxide burned with ambient air is 2417 cal/gram = 4350 BTU/lbm.

For the fuel and oxygen are both stored aboard the vehicle case,  the appropriate energy storage density is the fuel lower heating value divided by a factor that is 1 plus the oxygen/fuel ratio by mass.  That is effectively the chemical equation heat released by combustion (with water uncondensed generally),  but divided by the sum of the fuel and oxygen masses in the chemical balance.  For carbon monoxide burned with oxygen,  both stored aboard the vehicle,  the appropriate energy storage density is 1538 cal/gram = 2769 BTU/lbm.

For fuel,  oxygen,  and the oxygen dilution gas all stored aboard the vehicle,  obviously this depends upon how much dilution gas you use.  I analyzed the case where the oxygen mass percentage in the oxygen-dilution gas mixture ("effectively,  the "air") was the same as that in Earthly air (23.15% by mass).  For that choice,  the factor by which you divide lower heating value is 1 plus the air/fuel ratio by mass.  It is effectively the combustion heat release from thermochemistry (with water uncondensed generally) divided by the sum of fuel,  oxygen,  and dilution gas masses from that same chemical balance.  For a vehicle burning carbon monoxide with oxygen diluted by carbon dioxide (or nitrogen,  or any other inert gas),  with all three gases stored aboard the vehicle,  the appropriate energy storage density is 697.1 cal/gram = 1255 BTU/lbm.

I looked at methane fuel burned with air,  with oxygen,  and with oxygen diluted by nitrogen (or any other inert gas) in the same way.  The oxygen/fuel ratio for stoichiometry is much higher,  as is the lower heating value when burned with air.  The resulting energy storage densities for otherwise the same cases are:

stored methane with ambient air                                  14,038 cal/g = 25,269 BTU/lbm

stored methane with stored oxygen                               2810 cal/g = 5058 BTU/lbm

stored methane with stored oxygen and stored diluent    769.9 cal/g = 1386 BTU/lbm

Now,  I know that calories and grams are not SI metric.  Chemistry was always metric,  but my training in it,  and my sources for it,  long predate the advent of SI metric.  What I was working with was known as "cgs metric",  for which the cm the gram,  and the second,  were the fundamental units,  and the preferred unit of heat was the calorie,  defined as the heat that raised the temperature of 1 gram of water by 1 C. 

Pretty much the same thing can be done for any fuel, if you know its lower heating value,  and its stoichiometric oxygen/fuel ratio,  and using that 23.15% figure for the mass percent of oxygen in air.

GW

PS  -- When I started college,  the military air fleets were still more propeller-driven that jet-driven,  and the Navy still had operational diesel submarines.  I learned both cgs and mks metric in high school,  alongside the "British gravitational" version of US units.  I learned the "US customary" version of US units in college.   In the workplace,  I learned early on that there is German metric that uses kg-force for torque and likes pressures in atmospheres,  French metric that prefers bars for pressure,  and more versions in other countries,  in addition to the SI metric that only the US now demands in its government military work,  but does not actually generally use in civilian practice.  (How hypocritical is that?)

PPS -- I have my entire analysis reported in full detail in a word.docx file that I can email to somebody.  If that should be desired,  please let me know,  and where to email it.

Last edited by GW Johnson (2021-01-03 13:50:42)


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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#108 2021-01-03 13:17:29

tahanson43206
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Re: Internal combustion engines for Mars

For GW Johnson re #107

Thanks very Much!

SearchTerm:CO GW Johnson analysis: http://newmars.com/forums/viewtopic.php … 72#p175572
SearchTerm:CarbonMonoxide

Is there a member of the forum who can pick up the ball here?  I'd like to see specifications evolving from this discussion, for a bulldozer per the suggestion of kbd512 earlier, able to push 1 ton for 8 hours.

Given that work requirement, I'm hoping it is possible to know the quantity of CO/O2/CO2 needed, and the volume of fuel and oxidizer mix in liquid form, which seems to be the consensus form required for this application.

It should (I'm hoping) be possible to design a vehicle for Mars using these parameters as the starting point.

I would like to see the design flow into the Marspedia format of the Mars Society, if they are willing and if this is a good fit.

(th)

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#109 2021-01-04 17:04:32

kbd512
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Re: Internal combustion engines for Mars

GW,

Is that for a conventional open-cycle where we don't recirculate any of the exhaust gas to economize on diluent gas storage?

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#110 2021-01-04 18:03:50

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 23,851

Re: Internal combustion engines for Mars

Another piece of the fuel equation can also come from all types of waste recovery from a vareity of methods depending on what it is.

So plastic can be turned back into methane chains that will burn while paper can become with pyrolysis a mixed methane co and co2 output.

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#111 2021-01-04 18:30:16

tahanson43206
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Re: Internal combustion engines for Mars

For SpaceNut re #110

Once a foundation business plan for Mars is put firmly into place, it can be augmented with streams of input material that may become available, as you have suggested in this post.

My concern is that such streams are hypothetical at this point.  They may very well become important after a settlement is established.

For now, to repeat the previous post:

Is there a member of the forum who can pick up the ball here?  I'd like to see specifications evolving from this discussion, for a bulldozer per the suggestion of kbd512 earlier, able to push 1 ton for 8 hours.

Given that work requirement, I'm hoping it is possible to know the quantity of CO/O2/CO2 needed, and the volume of fuel and oxidizer mix in liquid form, which seems to be the consensus form required for this application.

It should (I'm hoping) be possible to design a vehicle for Mars using these parameters as the starting point.

I would like to see the design flow into the Marspedia format of the Mars Society, if they are willing and if this is a good fit.

Edit#1: The estimates for efficiency provided by GW Johnson seem reasonable to me, for the vehicle itself.

The efficiency of a plant to split CO2 to make the CO/O2-CO2 components, and to liquefy them for delivery to the customer is going to be knowable when the NASA experiment on Perseverance completes its experiment runs.

(th)

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#112 2021-01-04 19:48:18

GW Johnson
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From: McGregor, Texas USA
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Posts: 4,690
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Re: Internal combustion engines for Mars

The answer to Kbd512's question in post 109 is "yes".

GW


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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#113 2021-01-04 20:28:16

SpaceNut
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Re: Internal combustion engines for Mars

An idling not at work is a waste of fuel and energy. Earth usage of the bulldozer with a union worker and a business that runs on cash is a bad comparison to how we will run them on Mars let along fueling capacity for run time as it only needs to be running when it's moving material not idling waiting to work.

Also the limit of runtime is not just the tank size but the work distance that it can move the material. This is no reason not to be able to bring fuel to the bulldozer. Or to set up production on site to keep it working.

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#114 2021-01-04 22:17:38

tahanson43206
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Re: Internal combustion engines for Mars

For SpaceNut re #113

Thank you for pointing out the missing specifications for performance of a bulldozer to be designed for Mars.

I asked Google for help, and found a number of web sites set up to help owner/operators to estimate fuel consumption for various kinds of construction equipment on Earth.  I'll investigate further tomorrow.

What I was trying to do, and am still trying to do, is to see if it is feasible to power a bulldozer on Mars, using CO/O2-CO2.

I suggested the power (push capability) of the machine, and suggested a work stretch of 8 hours of continuous duty.  The purpose was to try to set up conditions that would allow computation of system performance.

After fuel requirements are known, it should be possible to work out the fuel tank capacity that would be needed.

From earlier posts in this topic (and elsewhere in the forum) I know that the energy carrying capacity of CO/O2-CO2 can be determined for a given volume of these materials in liquid form.

Also from earlier posts (primarily provided by GW Johnson in this topic) I know that the efficiency for an IC engine (of power delivered to the crankshaft) can be estimated.

By extending the specification to include work actually done (including moving the vehicle itself) it should be possible to compute the total fuel/oxidizer requirement, and from that the volume should fall out, and the size of the tanks will be known.

Your prediction that it may not be practical to mount tanks large enough to power the hypothetical bulldozer for 8 hours at full throttle could turn out to be right.  At this point, without facts to work with, we are guessing.

Thanks again for keeping the topic moving along.

(th)

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#115 2021-01-05 09:19:13

GW Johnson
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Posts: 4,690
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Re: Internal combustion engines for Mars

The energy conversion efficiency of an IC engine depends dramatically upon how it is used.  Those used in automobiles and trucks have to function across wide ranges of variable speeds and at highly-variable throttle settings. 

On the dynamometer,  at typical highway cruise settings,  the efficiency is usually in the ballpark of 15-20%,  a bit higher for diesel than gasoline, due to throttle losses in gasoline that are not incurred in diesel.  In city driving,  efficiencies run half,  or under,  cruise efficiencies. 

So-called "stationary engines" operating equipment at a single speed can run higher efficiency,  maybe 25% or even a tad higher.  Such run at one speed,  and maybe only two power settings (working power and idle).  The efficiency corresponds to the working power setting.  Size matters:  bigger is usually a tad more efficient. 

One of the most efficient uses of IC engines is in a true hybrid propulsion system featuring all-electric final drive.  In such a system,  the engines are essentially stationary,  with only a variable power setting at near-constant speed,  driving only generators.  Surge power comes from the battery,  not the IC engines.  You size the generators to have a slight excess capability at cruise power setting,  to recharge the battery after a surge draw. Such was in deiesel submarines,  and in railroad locomotives,  for decades. 

You can do the same sort of thing for construction equipment.  Usually these are either electric or hydraulic final drive,  with the electricity or the hydraulic pressure created by the engine,  operating as a more-or-less stationar power supply.  Hydraulics create far larger forces,  but electrics are more efficient.  You can even do this with both electric and hydraulic:  High-force hydraulic vehicle motion and implement action,  with an efficient electric-driven hydraulic pump,  running off a battery, that you only need to keep charged with the "stationary" IC engine. 

That last is of particular interest for stuff operating on Mars,  because it's mostly the same equipment,  with you having a choice about how you keep the on-board battery charged.  You can use an IC engine,  or solar,  or nuclear.  If you plug in to charge up when not working (solar or nuclear),  then you need a bigger battery to get through the work day.  The advantage of the IC engine and its propellant supply is supposed to be higher energy storage density than a battery.  But when you have to carry the oxygen and maybe the diluent gas,  that energy storage density advantage may not actually be there.  That's what my chemistry numbers showed. 

Just food for thought.

GW

Last edited by GW Johnson (2021-01-05 09:25:30)


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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#116 2021-01-05 09:37:40

tahanson43206
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Re: Internal combustion engines for Mars

For GW Johnson ... re Post #115

Thank you for another substantial addition to the topic!

The folks who will settle Mars are alive on Earth right now.  I would very much like to collect a few of them to develop their plans in association with each other and under the guidance and with the encouragement of the older members of this forum.

Picking up on the combination of your suggestion here, and kbd512's several earlier posts about electric bulldozer designs, I'm encouraged to think that a business model designed along the lines you've suggested might work for Mars.

I'm still concerned that electric motors and their related support structure may be a bit to much of a reach for manufacture on Mars, but perhaps this topic will attract young engineering students who are inspired by your post to come up with a set of plans that will result in a viable, sustainable business.

Working from the example of an Earth-designed military earth mover provided by kbd512, we can imagine a hybrid version of that tracked vehicle with electric drive and a constant speed IC, supported by enough battery capability to buffer the changing loads the vehicle will experience in the field.

My question remains ... do we have someone in the Registered Membership who is willing to take on the computations needed to determine the volume of tankage that would be needed to hold CO (in liquid form) and a mixture of O2/CO2 (also in liquid form) to power a bulldozer able to push a load with a force of one ton for eight hours?

SpaceNut has provided a reminder that my specification is missing an important element: The velocity of the push!

I could look up the performance of bulldozers on Earth, but I have my hands full right now trying to finish my daily ration of defunct ID's.

Is there someone in the Registered Membership who would be willing to finish the specification for the bulldozer, so we can move on to answering the primary question of tank capacity.

The whole point of the immediate exercise is to find out what volume of tankage is needed for the specified work load.

It may turn out that the volume is ridiculous for the 8 hour shift at full throttle.  To know what the actual volume is would be helpful, because if it cannot be carried on the vehicle itself it ** can ** be stored in tanks on site.

Thanks again for your helpful addition to this topic!

***
Here is an example of ** not ** helpful advice sometimes delivered by Google:

How do you calculate fuel consumption for construction equipment?
Fuel consumption figures for excavators are usually expressed as gallons per hour. To calculate the fuel consumption, simply divide the number of gallons of diesel required to fill the excavator's fuel tank by the number of hours that the machine has worked.Mar 3, 2013

(th)

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#117 2021-01-05 17:32:01

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 23,851

Re: Internal combustion engines for Mars

While a forklift is smaller its still a piece of equipment that we would want for inside and out for our engines.

https://www.forkliftpropane.com/advantages/

Forklift Propane

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storage-cage-propane

Because propane is the most portable forklift fuel option, the propane cylinders can be stored nearly anywhere at your place of business

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#118 2021-01-05 20:03:37

tahanson43206
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Re: Internal combustion engines for Mars

The pdf at the link below is from Caterpillar ...

http://nheri.ucsd.edu/facilities/docs/P … k_416C.pdf

It appears to contain quite a bit of information.  It may be suitable as a starting point for further study with respect to the adaptability of IC powered equipment to Mars, and specifically to the CO/O2-CO2 mixture under discussion in this topic.

(th)

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#119 2021-01-06 11:54:59

kbd512
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Registered: 2015-01-02
Posts: 4,899

Re: Internal combustion engines for Mars

GW,

If you're using a closed-loop SCCO2 gas turbine, then you're not carrying much in the way of diluent CO2.  The oxy-fuel combustion processes used here on Earth are 95% O2 and 5% CO2.

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#120 2021-01-06 17:25:38

SpaceNut
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Registered: 2004-07-22
Posts: 23,851

Re: Internal combustion engines for Mars

The pushing force is a function of grip and torque and that grip is a part of the mass of the object while the traction is tires versus tracks of which we do have a topic....

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#121 2021-01-06 23:04:31

tahanson43206
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Registered: 2018-04-27
Posts: 8,029

Re: Internal combustion engines for Mars

For SpaceNut re #120 and topic in general ...

Speaking of tracks, here is a web site Google found ....

https://drawingdatabase.com/caterpillar-973c/

I haven't explored the site yet, but thought the images of a Caterpillar scoop machine are pretty impressive.

The site seems to have something to do with layouts for 3D printing, but I didn't see anything that looked related to 3D Printing.

It is possible (for me at least) to imagine this machine fitted with an airtight cabin for the operator, but the fuel and oxidizer tanks would be MUCH larger than the diesel fuel tank in this machine.

The reduced gravity on Mars is going to have an effect on the traction of a regolith moving machine.

The Caterpillar pdf document I reported a few posts back is infused with the default gravity of (1), so that the author is probably unaware of it.

A version of any of the Caterpillar machines for Mars would (presumably) have to be redesigned to take lower gravity into account, to varying degrees, depending upon the function it is to perform.

A simple truck-transporter might be lower in mass for a given volume of load, but not a LOT lower, because the mass will be the same, even if the pull of gravity is less. 

(th)

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#122 2021-01-07 18:30:18

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 23,851

Re: Internal combustion engines for Mars

Still reviewing the 1034 page of caterpillar vehicles that it makes. Every thing from gas tank size ad engine to mass of the machine details.
Which brought me to look at gasoline comparison for the vehicles other fuels from the propane, methane ect which also showed methanol was in it as well.
Pluses for it are that its not a cryogenic or pressurized fuel to make use of....

http://www.differencebetween.net/scienc … -gasoline/

Mixtures of carbon monoxide and hydrogen are converted into methanol during a chemical process.
Methanol vehicles give a brisker performance, and are less prone to form Ozone
Engines use much more fuel with methanol than with gasoline, thereby the amount of fuel that gets into the crankcase is diluted with methanol. The separation can be a serious problem, and methanol is a very poor lubricant, which in results in a corroded valve stem, guide or valve seat. Methanol can rust metals and soft materials in fuel systems easily.

https://www.topspeedparts.com/blogs/new … omparision

GASOLINE
Gasoline is a mixture of hydrocarbons. Its chemical formula is C8H18. The air fuel ratio for complete combustion is 14.7:1 called stoichiometric. This means that our engine consumes 14.7 pounds of air for 1 pound of fuel. Gasoline has approximately 18,400 BTU/lb . Using an air flow calculator this focus engine would consume 247cfms at 7000rpms with 100% VE.  This equals 22.17lbs of air per min.  Divide by the 14.7:1 ratio and that would get you  1.5lbs of fuel.  Multiply that by the 18,400 and your engine would produce  27,600btu’s of energy at 7000rpms.

METHANOL
CH3OH is the chemical formula. Methanol burns at a much richer mixture than gasoline does, between 5.0:1 – 6.0:1. That’s 6lbs of air to one pound of fuel. Methanol has approximately 9,500 BTU/lb. Using our Focus engine from above with a 6.0:1 ratio our motor would use 3.69lbs of fuel.  Multiply that by the 9,500 btu’s per lb of alcohol and our motor would be making 35,055btu’s at 7000rpms.


Disadvantages of alcohol

First of all Methanol uses 2 times the amount of fuel that gasoline does.  This means you need twice the fuel system you had.  If you had 1 255lph pump and 1000cc injectors to make the power you had on gas, now you need 2 pumps and 2000cc injectors.  Also, you need bigger fuel lines and you might need more capacity in your tank.

Secondly Methanol is extremely corrosive.  When methanol comes in contact with bare aluminum it can corrode the metal.  Any aluminum surfaces should be hard anodized to prevent this.

https://afdc.energy.gov/fuels/fuel_comparison_chart.pdf

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#123 2021-01-07 18:50:46

tahanson43206
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Registered: 2018-04-27
Posts: 8,029

Re: Internal combustion engines for Mars

For SpaceNut re #122

Thanks for this (to me for sure) interesting review of differences between gasoline and methanol in a reference engine!

There are numerous points to be explored here, but the one I'd like to focus on is the mention of lubrication ... Methanol is reported to be not only a poor lubricant, but destructive as well.  That leads me to wonder what the situation might be for the CO/O2-CO2 mixture we've been thinking about in recent posts.

I asked Google about CO2 lubrication properties, and got an article about lubricants in engines instead.  The CO2 was mentioned in the article as a result of combustion, and not in the context of lubrication.

https://dannysengineportal.com/home/lub … car-alive/

I'll try to find something about how CO2 performs as a lubricant, but it is possible no one has ever studied that, so a document may not exist.

The article you quoted is helpful in pointing out that with a fuel that is lower in energy density than gasoline, the injectors and fuel lines need to be larger than would be required for gasoline.

(th)

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#124 2021-01-07 19:57:24

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 23,851

Re: Internal combustion engines for Mars

Lubricants for the arms on the Rovers (Curiosity, Spirit, Opportunity and the new Perseverance) and the one that was on the (Phoenix) polar lander shovel would be where to look for some applications.
Internal engines may be able to use them in some instances but I would need to deep dive for the information.

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#125 2021-01-08 12:40:15

kbd512
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Registered: 2015-01-02
Posts: 4,899

Re: Internal combustion engines for Mars

tahanson43206 and SpaceNut,

You don't need any hydrocarbon-based lubricants for a gas turbine that uses compressed gas as the bearing surface and labyrinth seals.

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