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For kbd512 re #125 and topic
You've been consistently trying to guide thinking toward a gas turbine vehicle design in this topic.
I've been focused on the original piston engine concept, starting with SpaceNut's original scenario.
Along the way, either you or GW Johnson pointed out the advantages of a hybrid design, with electric motors for interaction with the terrain, and a constant speed power source (with battery energy buffer) as the most efficient way to use a combustion engine.
I've been reluctant to consider a turbine because I cannot (easily at least) imagine it manufactured on Mars, using local materials.
Your point in post #125 about NOT needing to worry about lubrication finally caught my attention.
Am I correct in understanding that the bearings in a gas turbine do not require hydrocarbon lubricants?
Can such a turbine be manufactured on Mars from indigenous materials, preferably using 3D Printing to insure the knowledge to make the turbine is embodied in the 3D Printer instructions?
Thank you (again) for helping the topic along.
I'd like to see a practical business concept evolve from the discussion, and I would like to see the knowledge assembled in this topic collected in a Wiki type collection for use by future Mars settlers, as well as those planning to become Mars settlers.
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I do not dispute that there might be a way to "lubricate" gas turbine machinery with gas films instead of liquid films. But if gas, the pressure will have to be very high: thousands of psi, or even tens of thousands of psi. Film density is also important, not just viscosity.
That being said, the only gas turbine engines I am aware of, all use oil film lubrication for their machinery. Most of the time, it works pretty good, but there is a difficulty with cold-soaked lube oil not flowing, at about 10 F below zero and colder. Warmup times are over an hour long when cold-soaked that low. Been there and done that (old "war story").
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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tahanson43206,
I've been trying to guide the discussion towards two different practical solutions (one closed-loop gas turbine powered and the other battery powered) that have durable moving parts, low total parts count, and a minimal logistics tail attached to both solutions. Industrialization on Mars will not happen before the habitable space exists for such purposes, but we need simple and durable construction equipment in order to create that. You don't need a 3D printer to machine something a few inches in diameter. That's a waste of time. A desktop milling machine and a lathe are better tools for that purpose.
If you think a gas turbine the size of a coffee can is difficult to manufacture, then try 3D printing any type of diesel engine. The are far more total parts that also consume a substantially greater mass of materials while requiring significantly more machining time to fabricate, a variety of different manufacturing methods and source metal alloys, some of which are simply not amenable to 3D printing at the present time. All piston engines are significantly larger than gas turbines producing equivalent power output. The pistons themselves are significantly larger and heavier than the single moving part in a 250kW SCCO2 gas turbine. Any modern I6 / V8 / V12 diesel engine contains at least a thousand discrete parts. Beyond that, gas turbines that use gas bearings do not require hydrocarbon lubricants or coolants of any kind, unlike piston engines.
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GW,
The SCCO2 gas turbines that NREL is working on will use SCCO2 as the bearing surface, and yes, the working pressure is very high, because it has to be.
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For kbd512 re #128 and topic in general
Thanks for adding to the vision you are developing for delivery of reliable power to equipment on Mars.
It is possible (of course) that your vision of having skilled machinists in the population on Mars is reasonable and practical.
It is also possible that enough members of the population born there will want to become skilled machinists, and devote their lives to honing their skills while delivering much needed components to a grateful set of customers.
In some cultures in human history, needed specializations have been "assigned" to children. I read recently that China has stopped doing that, and has transitioned to American style incentive methods instead. When you design a machine infrastructure, you ** must ** plan ahead for the development of the needed work force. You can use authoritarian methods, or you can use incentives, or you can do without.
Your doubt about the ability of 3D printers to build (assemble the atoms of) objects needed for various applications on Mars is certainly justified at present.
I am looking at the longer term, where I see the trend line inevitably moving toward emulation of what Nature has been doing for thousands and quite likely millions of years. A tree assembles atoms (as molecules) one at a time, and it does so in parallel for many years.
A 3D Printer is an early example of precise placement of material. The advantage of a 3D Printer (evolved over time) is that the knowledge needed to create a part is embedded in the instructions coded for that part. All literate members of the population would be able to read such instructions and modify them as necessary to create new parts or to improve old ones.
Assembly is most likely to be carried out by robots whose instructions will also be examples of embodied knowledge which any literate member of the population can read and modify as necessary.
The advance of self-learning systems on many fronts suggests to me that robots will become interactive with their human companions at some point, so that the cadre of machinists you've implied may become available.
For the purposes of what I ** think ** this topic is trying to accomplish, design of a simple, understandable, achievable (on Mars) piston engine infrastructure makes a lot of sense. If a group takes on the turbine technology you've described, they'll need to take on all the responsibilities that come with it, including developing and retaining the work force needed to sustain it in the absence of resupply from Earth.
I'm hoping you ** will ** continue to develop this line of thought, and I'm hoping that SpaceNut will succeed in winning support from the Mars Society to facilitate storage of the insights and knowledge building up in this topic so it can be referenced reliably and easily by future readers, as well as current ones who want to refresh their understanding of a particular concept.
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Topic engines types with ratio given in post 122 with the respect that we will not be running the engine ever on red line RPM's. Most engines never will go to much over 2000 while in motion something less than forward motion of 30 mph probably at most.
Idling at just under 1000 rpm would be kept to a minimum and the electrical will be put into a standby mode to supply power as the batteries get lower than safe margins would provide to start the machine and to give life support needs.
This equals 22.17lbs of air per min at 7000 rpm
Assuming that rpm and use rates for oxygen stay then to operate at 1000 to 2000 would be much less and a multiple of time then gives the run time contained in the oxidizer tanks mass that you would carry. The above is also pressurize oxygen and not a liquid o2 which makes the tank heavier but smaller to hold for external or outside use.
Post 117 gives the size of methane tank for an 8 hour run of simular engine.
GW gave the air mix ratios more precisely back a page to be able to calculate the air tank required for mars.
A. outside engine use with plausible exhaust to be captured for reuse directly to reduce mixture air but are considered hazardous for inside use.
post 13 image is of a typical boxer engine
1. First up was a gasoline earth powered engine which for Mars may be a long ways from being able to be used on mars as that takes a fuel production plant to make it possible. Then the carrying of the air to mix with the fuel is another totally seperate issue of what would be used for a gas mixture.
2. Diesel engines seem possible with many different fuels and oxidizer mixtures with this type being better suited for heavy equipment as these are less of an issue in construction equipment.
B. Inside engine use with exhaust gas needing to be monitored for internal use but usually considered safe.
Post 30 image is of this engine
1. ULA IFV engine which uses the boiloff from Hydrogen and Oxygen tanks to generate power for the rocket ship and to control the boiloff rate. This is a very do able engine on mars as we can use the boiloff to make it a functional on demand power system as we will need to control the boiloff of these products.
2. As we make methane which is less boiloff sensitive. Methane can also be use in the same engine with adjustments to ration of fuel oxidizer. Methane is very simular to the natural gas and propane which is used here on earth in many an inside the warehouse style vehicles for human safety reasons.
Not to be included for active discussions as we have several fuel cell topics but to not connections as they relate.
category not being an engine are fuel cells that can be used with the liquid fuels and Oxidizers in both inside or outside equipment for direct power generators or for equipment electrical engines (Motors) Which relies more heavy on a battery energy density.
c.
The SCCO2 gas turbine is part of a very highly pressurized closed loop. The gas turbine itself is not combusting the fuel. SCCO2 flows from the heat exchanger, through the gas turbine, and back to the heat exchanger.
1.
An externally mounted combustor can blowing heat across a heat spreader block affixed to the gas turbine's intake pipe, like a blow torch heating a water pipe inside a boiler, externally heats the SCCO2 working fluid inside the gas turbine's closed loop.
2. Solar concentrating directionally controlled reflectors to provide the heat source is another option. Large Balloon floating reflection systems as well might be possible since mars air is not all that violent for blowing.
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For SpaceNut re development of topic ....
Thanks for the additional insights collected in Post #131
I'd like to see this topic trend toward actual hardware and performed experiments, with documentation collected for future Mars settlers to study and use on site.
Kbd512 is justifiably skeptical of 3D Printing as a means of production of the components of IC engines. I'd like to see progress on that front. My concern and interest is to see if the knowledge required to manufacture parts can be embodied in the 3D Printer command files as documentation accompanying the commands. This is comparable to the (occasional) practice of documenting code inside programs. There are even "self documenting" program languages, but those require the willing participation of the programmer to use meaningful variable names.
We can take a major leap forward by learning how to use the Marspedia system of the Mars Society IT structure.
(th)
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The main issue with 3-D printed engine parts is surface smoothness and dimensional accuracy; i.e. tolerances. Both gas turbine and modern piston engines are machined to extremely tight tolerances with very close fits between moving parts. That's why modern engine oils are very low viscosity now, like the gas turbine oils always have been.
Anything you 3-D print will still have to be machined by high-precision equipment to the high tolerance fits. If you don't, you have to return to the loose fits, thick oils, shorter life, and low performance of your piston engines of a century ago.
And you can forget any sort of gas turbine. That would be true even replacing oil film with gas film at extreme pressure: you still need the close fits and smooth surfaces. Plus that gas film thing is not yet a deployable technology. It is highly experimental.
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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For GW Johnson re #133 and topic ..
Thanks for your reminder that precision is the key to the success of the technical age in which we're living ...
When I read your comment/observation, I was reminded of at least one book that follows the theme that precision is the key to the success of most if not all of the objects we take for granted in 2021.
As things stand, I would imagine there are engineers working hard on the precision issue, because the better the performance of 3D Printers, the greater the potential savings to manufacturers. However, in the mean time, and if you are willing to engage a bit further ...
Can you imagine a scenario in which a group heading off to Mars packs ** just ** enough high precision equipment, and hires ** just enough ** qualified personnel, so that 3D printed roughs can be finished to work reliably in an IC engine on Mars?
Would it make sense to plan ahead to keep variety down, so that the equipment carried along can be minimized.
And .... looking ahead a bit ... since the history of technology on Earth is that crude equipment was used to make ever more precise successors, can you imagine that same scenario playing out on Mars?
I am still worried about the personnel education/training issue.
The competing teams in the recent Conference City-State videos seemed aware of the need for training of adult passengers landing in a steady flow from Earth, but there seemed little concern with how to carry important skill sets like machining precision parts forward.
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GW,
Entire working gas turbine engines have already been 3D printed.
RUSSIAN STATE SUCCESSFULLY FLIGHT TESTS 3D PRINTED GAS TURBINE ENGINE
This 3D Printed Turbine Replaced 61 Parts With 1: Here Is What That Means
Fraunhofer IFAM 3D prints fully functional, scaled gas turbine model
The only part that was not 3D printed on that last one was the drive shaft. The original engine used as the model contained more than 3,000 parts. The 3D printed engine contains 68 discrete parts. The drive shaft is a steel cylinder. Those don't need to be 3D printed. Bar stock spun on a lathe is the most efficient way to do that, which is why I told tahanson43206 that some parts won't be 3D printed.
Furthermore, if you want perfectly smooth fan blade surfaces, then tumbling media or post-printing machining to individual blades can be done using much smaller CNC machines that shave off a small amount of excess metal from slightly over-sized fan blades, in much the same way that aftermarket piston engine blocks and heads come from the factory, meaning the cylinder bores are rough-honed, for a final hone to exact diameter, and the cylinder bores are final-honed, the crank journals gun drilled, and the block decked by a local machine shop. Dart sells BBC / SBC / SBF / BBF engine blocks that way, for example. They can finish machine your block, but prefer that your local machinist performs a number of finishing operations so that you can have the exact bore diameter, stroke length, and valve train components that you want for your particular application. All engine overhauls that require re-dimensioning of parts are also done that way.
In the near future, nearly all of the components of small gas turbine engines except the fasteners and drive shafts or gears for engine accessories will be 3D printed, drastically lowering their production and assembly costs. The largest gas turbines will still need custom made composite fan blades for the fan section of the engine, but those things power intercontinental airliners. We're talking about gas turbines small enough to fit inside a shoebox.
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For kbd512 re #135
Thanks for news (to me at least) of the achievements of the Russians in advancing the state of the art of 3D Printing!
I'll follow the other links as well, as soon as possible.
The only remaining uncertainty I have is whether CO/O2 can provide the intake for the small gas turbine engines you've described.
I ** think ** you've already answered the question in earlier posts.
If you will provide a link, I'll set up a SearchTerm: for it.
My recollection is that you've looked at the possibility of recirculating CO2 to provide the buffer gas that GW Johnson says is needed for a piston engine.
I'm not clear on whether that same buffer gas is needed for optimum performance of a gas turbine. I would imagine a buffer gas is needed, because all turbines operating on Earth have one, but that could be because that's what the Earth provides, and not because the engine requires it.
My recollection of the explanation by GW Johnson for a piston engine is that the buffer gas helps to keep operating temperatures within the range the materials of the engine can tolerate, and it provides a useful working mass to deliver force to the piston head. I'm not clear on whether something similar is needed in a gas turbine engine.
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tahanson43206,
Alright, I guess I'll make another attempt at explaining this.
The SCCO2 gas turbine is part of a very highly pressurized closed loop. The gas turbine itself is not combusting the fuel. An externally mounted combustor can blowing heat across a heat spreader block affixed to the gas turbine's intake pipe, like a blow torch heating a water pipe inside a boiler, externally heats the SCCO2 working fluid inside the gas turbine's closed loop. SCCO2 flows from the heat exchanger, through the gas turbine, and back to the heat exchanger. There is no "exit" from this heat-exchanging turbine system, period, hence the term "closed loop". This is based off of an existing Oxy-Fuel burner or combustor design specifically used to test closed loop SCCO2 gas turbine technology for application to solar thermal and nuclear thermal power plants, in order to drastically reduce the size of the turbo machinery. Little to no diluent gas is required. Oxy-Fuel combustion uses 95% O2 mixed with 5% CO2 (to limit flame temperatures associated with combusting Methane), and CH4 here on Earth. All the relevant posts and links are in this thread.
Large quantities of buffer gas are only required for a piston engine, because the pistons compress cold gas and expanded heated gas. A closed loop SCCO2 gas turbine (the exact same device that NREL has already built and tested) does not require buffer gas or lubricants. The lubricant / bearing material in the SCCO2 gas turbine is the SCCO2 gas itself. Tiny channels further pressurize the SCCO2 and direct it around the shaft to act as the bearing surface between the shaft and engine casing.
GW keeps talking about aircraft engines and their operating requirements, which have no bearing whatsoever on SCCO2 gas turbines, because SCCO2 gas turbines are NOT aircraft engines. There is no suck-squeeze-bang-blow going on. The "squeeze" happens by externally heating the SCCO2 fluid trapped in the closed loop turbine inlet or "suck" tube, just prior to flowing through the turbine wheel. The "bang" happens using an external heating source that is the exact same technology used in a rocket engine's main injector. The "blow" happens by cooling the gas trapped in the closed loop using the heat exchanger and radiator. Every component except the combustor can is operating as part of a closed loop. To recap, "suck" / "squeeze" / "blow" all happen inside a closed loop, with "bang" happening external to the engine's closed loop.
The SCCO2 gas turbine is completely thermally soaked, meaning the turbine wheel, the turbine housing, the plumbing, and the radiator / heat exchanger all operate in the 700C range. That's why the radiator has to be Copper and all other components have to be Inconel. The temperatures involved would turn Aluminum into liquid.
GW is correct about buffer gas preventing metals from melting in engines combusting 100% O2 with hydrocarbon fuels. The flame temperatures get hot enough to melt steel. Again, that's a phenomenon that has very little bearing on this engine design.
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For kbd512 re #137 and topic in general
Thanks for taking the time to provide this concise and detailed explanation of the closed loop turbine design!
SearchTerm:turbine kbd512 explanation of closed loop SCCO2 gas turbine
http://newmars.com/forums/viewtopic.php … 63#p175763
I'd like to propose to you and to SpaceNut that we split this topic into two .... One for turbines, with concentration on SCCO2 under your stewardship
The second would be a concentration on piston engine designs for Mars, under SpaceNut's watchful eye.
I am interested in seeing the knowledge and insight flowing through the posts in this forum harnessed to perform long term good for humanity, and specifically settlers on Mars, and even more specifically, those who are alive on Earth today who ** will ** be in the population moving to Mars.
SpaceNut, when you opened this topic, it made sense (from my perspective) to keep the scope generic, and you've seen the topic grow nicely. It would appear to be time to allow the topic to fork (carefully), so that the two competing technologies compete separately, and not within one topic.
It is appropriate to attempt to recruit members who will want to specialize in one or the other of these technologies.
We already have a battery powered vehicle track, and I think it can continue for a while longer until a need for a split becomes apparent.
I ** think ** it was kbd512 (it might have been GW Johnson) who suggested a hybrid power train for Mars construction vehicles. In that track, were it to be created, a set of plans would evolve for IC power >> generator >> battery storage >> electric motor appendage movement (or hydraulic appendage movement in the case of blade or bucket lifts).
I'll offer these suggestions in housekeeping as well.
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This is for kbd512 ...
In thinking about your recent post, clarifying the nature of a closed turbine design, I realized you had said something I did not pick up on immediately.
If I understand the explanation correctly, there is an external source of energy that is directed at the turbine to excite the molecules of the working gas.
It is ** that ** source of energy that could be Carbon Monoxide.
Am I correct in thinking that CO could be used to heat the gas in the turbine system you've described?
Next ... if so, since you've shown that high temperatures are required to achieve the desired performance of the turbine, is it correct that CO/O2 could provide the desired heating, without the complication of a buffer gas?
Are there materials that can withstand (I'm pretty sure your earlier posts confirm this) the temperatures needed?
Finally .... is it your recommendation that a CO/O2 heater for a turbine should direct exhaust to the atmosphere of Mars?
SpaceNut had inquired about capturing the CO2 exhaust from an IC on Mars, because that exhaust would be purified (compared to the atmosphere of Mars) and therefore "worth" something. However, the cost (in terms of energy) of capturing the exhaust might easily outweigh any benefit.
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tahanson43206,
I gave up on the idea of running a diesel on Mars due to the requirement for petroleum-based lubricants, engine coolant, and all the large moving parts that can break. In general, diesels are efficient internal combustion engines that see frequent use in generators / off-road vehicles / construction equipment, but a closed loop gas turbine of equivalent power output can be even more efficient and be substantially lighter. The overall mass and efficiency of the engine, maintenance requirements, and input energy are taken to extremes here. There's a much shorter and smaller logistical tail associated with the gas turbine, in comparison to the diesel.
I wouldn't concern myself with 3D printing components on Mars when the single wear component is LITERALLY the size of a cookie (a 125kW SCCO2 gas turbine wheel, the part that the hot CO2 spins to make power, is a 30mm diameter miniature steel hockey puck), thus a lifetime supply of replacement turbine wheels and casing bolts can be carried in a single shoebox. Why would you even concern yourself with what you can or cannot make on Mars when you can ship a supply of wear components to cover the next century of construction operations for the same weight as a single DuraMax diesel? That makes no sense at all. The first priorities are creating habitable living spaces and growing crops- the same things that created technologically advanced human civilization here on Earth.
Yes, an external blow torch blows hot CO2 (combusted O2/CO) over the intake pipe of the closed-loop SCCO2 gas turbine. I guess you could think of this as an external combustion engine, similar to a boiler or Stirling engine (another type of piston engine that also uses an external heat source to drive pistons operating in a closed loop), but the basic principle of operation is that of a conventional gas turbine.
I don't believe any buffer gas would be required or even desirable, on account of the low thermal energy output of O2/CO.
Yes, there are materials such as Inconel that can withstand the heat required to achieve the level of performance that NREL achieved in testing (700C to 725C). Every component is Inconel, so far as I understand. We're introducing a Copper radiator plate in our vehicle engine because radiation is the only viable heat removal method in a near-vacuum. NREL extensively tested the sub-scale demonstrator gas turbines. They initially used 95% O2 mixed with 5% CO2 because they were using CH4 / Methane as the fuel. They fully intend to supply input heat within that temperature range from solar thermal or nuclear thermal. Initial testing used Oxy-Fuel combustion for the sub-scale demonstrators, followed by hooking up larger devices (in the multi-MW range) to actual operating solar thermal power plants. No tests using nuclear-supplied heat have been conducted yet, but the ultimate intent is to increase thermal efficiency of solar thermal and nuclear thermal power plants to 50%+ using SCCO2 gas turbines and heat supplied at very high temperatures. These systems have 2 closed loops- the secondary closed loop of the gas turbine itself and the primary closed loop (molten salt) of the solar or nuclear power plant. There's a third type of use (still closed-loop for the SCCO2 gas turbine) that uses a semi-closed primary loop to capture most of the CO2 effluent from burning coal. Some of the waste thermal power embodied in the hot CO2 effluent stream is converted into additional electrical power to drive pumps that compress the CO2 for storage.
If it's not possible to recompress the hot CO2 effluent from the combustor can, which will require additional input power to accomplish, then it would probably need to be exhausted to the atmosphere. The real question is how much additional power would be required to recompress the CO2 to reuse it, so that fresh CO2 doesn't have to be extracted by a multi-stage vacuum pump or MACDOF or some similar device. Generally speaking, from an energy input standpoint, it's "cheaper" to recycle than to collect and process the raw materials from scratch. The alternative is accepting the weight and performance penalties associated with much heavier and less energy dense batteries. A battery might be fine for a lightweight passenger vehicle operating on a paved roadway, but you'll have to accept a performance reduction for semi-trucks or construction equipment or heavy duty off-road vehicles, or accept that nearly the entirety of the vehicle will be batteries to provide equivalent power output over an equivalent period of time. As to which approach is preferable, I think we don't have good options at the present time, either way.
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For kbd512 ... Thanks for your response to questions about the turbine in Post #140
SearchTerm:turbine additional notes on use of closed cycle turbine ... this time covering external heating and gas recovery
http://newmars.com/forums/viewtopic.php … 78#p175778
Is there any way to guess the efficiency of the external heating component of the system?
In a hybrid construction vehicle, (as I understand the situation unfolding here) we would have:
1) External burner: CO/O2 without buffer gas
2) Closed loop turbine dumping waste heat to the atmosphere using copper radiator
3) Generator powered by turbine at a constant velocity
4) Power flowing to electric motors or to battery storage via electronic stage
5) Electric motors operating directly (wheels) and indirectly (pumps for hydraulic components)
6) Whatever I've missed.
The resulting vehicle would perform bulldozer (or other off-road) operations for as long as the vehicle mounted tanks can supply LCO and LO.
At some point, I'm hoping this discussion will result in a ballpark estimate of the size of the tanks needed for this vehicle and the amount of time the vehicle can perform its assigned task running at full tilt.
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tahanson43206,
1. Yes
2. Yes
3. Maybe (would be the most efficient way of doing it), but variable speed is why I suggested using a VFG
4. Yes, power is distributed from the generator to other parts of the vehicle or to something external to the vehicle that you need to supply power to, such as a habitat module of other piece of construction equipment (heavy duty off-road military vehicles have the option of functioning as a mobile generator while the vehicle remains stationary)
5. Yes, sealed heavy duty electric motors would be the best way of providing motive power
6. This vehicle has more in common with a hybrid M2 Bradley (or the new AMPV replacement for the Bradley that BAE designed and tested and pushed through to production, only to be cancelled by the Army after a handful of vehicles were made) or diesel-electric locomotive than a prototypical light off-road truck.
The result is a multi-purpose off-road vehicle chassis (bulldozer, backhoe, crane, dump truck, personnel carrier, with the appropriate tool additions bolted to the chassis, much like the armored recovery / engineering vehicles in current use with armies across the world) with the power output of a modern main battle tank, using an engine or battery pack design that is Mars-specific.
We've already estimated a size / weight for this vehicle using the T-55 bulldozer as an analog, along with the input power requirements to run at maximum power output for a given length of time. If you're using a 250kW electric motor, then you need to supply just over 250kWh to run the vehicle at maximum output for 1 hour, presuming 95% electric motor efficiency so commonly achieved in modern electric vehicles. Granted, I would use different construction techniques and materials since this vehicle is no longer an armored vehicle with a turret. For example, this vehicle would be constructed of all-welded stainless steel plate and use upgraded steel track links, but we're already in the right ballpark by using the weight of an existing Earth-bound analog.
If possible, I would like to make removable gas turbine or Lithium-ion battery power packs, such that the entire 1/3 rear or front end of the vehicle between the tracks is dedicated to a giant plug-in / removable power unit. If a given task is easier to accomplish with one or the other types of power pack, then use what's most appropriate. If the vehicle has to make a 500km round-trip transit to another outpost, then we'd need that gas turbine. If the vehicle will remain relatively stationary while removing overburden to pour a foundation for a new building on bedrock, then we use removable batteries and replace them with recharged packs, throughout the day, as required.
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For kbd512 re #142
Thanks for your encouraging reply, and for the details included in #142
This discussion is ** almost ** at the goal ... Given the prototype vehicle you've described, can you estimate the size of the tanks needed to hold enough LCO and LO2 to power the vehicle for that working hour you suggested?
As referenced earlier in this topic, I found that Caterpillar offers a working speed of 2.4 miles per hour for a fully engaged bulldozer. If we assume a push force of one ton, and a duration of 60 minutes, we can compute the amount of work to be done.
It should be possible to work backward through the chain of components to arrive at the fuel/oxidizer requirement.
From that set of figures, assuming liquid storage, it should be possible to compute the volume of the tanks.
***
SpaceNut ... are you willing to take a run at that?
We know (from the example provided by kbd512) what the base structure of the vehicle is going to look like. What we don't know is what the tanks mounted above the chassis are going to look like.
Given the information that GW Johnson and kbd512 have provided, I am hoping it is possible to determine the size of the tanks.
The tanks would be mounted above the chassis, because no one is going to be shooting at the vehicle, and that's a convenient place for them.
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It has been several years since I last gave serious attention to the SCO2 power generation cycle. It is being studied at MIT as the power generation cycle for a direct cycle gas cooled fast reactor. It is an interesting concept because it allows high whole system power density compared to competing concepts. It has been studied as the power generation cycle for sodium and lead cooled FBRs as well. Results are all promising. But it does require high reactor hotleg temperatures to achieve good efficiency overall. Temperature out of the primary heat exchanger (or reactor in direct cycle) must exceed 500C and pressure upwards of 15MPa. To achieve really high efficiency of greater than 50%, temperature must approach 700C. MIT chose to limit operating temperature to 550C, as this allows the use of low alloy steels, which dramatically reduces capital costs. This limits efficiency to between 40-45%, which is an acceptable compromise. Low alloy and carbon steels, typically lose 50% of the strength they have at room temperature at 550C and strength declines very rapidly with increasing temperature after that. But they are cheap, abundant and easy to work with and will therefore always be the designers first choice unless weight considerations rule them out.
The main challenge in making this into part of the power source for a vehicle, is not the turbine, but the heat exchangers. The heat exchangers in most nuclear power plants are considerably more bulky than the reactor itself. The most promising development of the past two decades is printed circuit heat exchangers, which are far more compact than traditional tube heat exchangers. Whether or not we can practically build SCO2 engines on Mars rests on our ability to produce printed circuit heat exchangers, with walls thin enough to allow high rates of heat transfer, without adding excessive pressure drop, which reduces net power output by pushing up pumping power and also introduces vibration problems. One way of improving the performance of heat exchangers is to allow higher temperature drop between the fluids on the two sides. But this again can cause thermal shocking problems and of course temperature drop eats into efficiency. It is a tricky engineering problem that can probably only be solved by a certain amount of trial and error, actually building the things and tinkering with them over a period of decades.
Printed heat exchangers are exactly the sort of product that 3d printing would be suitable for. Gas turbines are tricky, because blades are grown as single crystals of nickel alloy with internal cooling channels. But that applies to combustion chamber gas turbines, which see direct flame temperatures greater than 1000C. In an SCO2 turbine, which sees temperatures of 500-600C, high strength steels without cooling channels are a usable material. The growth of single crystals has more to do with rate of cooling when casting. Obviously heat treatment is out of the question. Temperatures of 550C are beneath phase transition temperatures for steel, so that will not limit its use in an SCO2 turbine at relatively low temperatures.
I like the idea of designing an SCO2 engine that can be 3d printed entirely from low alloy steels. Iron oxide is an abundant material on Mars and low alloy steel will almost certainly be the first metal that we are able to produce in abundance. Can we 3d print with steel? Carbon steels melt between 1400-1600C.
In terms of producing motive power in systems that are easy to build on Mars, the best option may be direct drive solar electric. Solar panels power DC electric motors directly without battery storage. A very simple system, but it limits the speed of the vehicle as a function of solar intensity on the panel. When the sun is low on the horizon, you drive more slowly until the motive force provided by the motors is insufficient to overcome static friction. Then you stop. This is something that you simply have to work around logistically. You use power when the sun is available and stop performing activities at night. I suspect that this is generally how solar power will be used on Mars, both for mobile and static applications. There will be minimal use of batteries. Instead, demand will adapt according to supply.
Last edited by Calliban (2021-01-11 23:03:19)
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
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Diesel engines for Mars research to use the Lco + Lo2/Lco2 needs some research on how a diesel works for engine compresses at a ratio of 14:1 to as high as 25:1 with and without a glow plug to raise the temperature to ignition.
https://auto.howstuffworks.com/diesel1.htm
gasoline is typically C9H20, while diesel fuel is typically C14H30
https://en.wikipedia.org/wiki/Diesel_engine
https://carbiketech.com/diesel-engine/
The temperature of the air inside the combustion chamber rises to above 400°c to 800°c. This, in turn, ignites the diesel injected into the combustion chamber.
So ignition under pressure temperature for Lco to ignite
http://www.uigi.com/MSDS_liquid_CO2.html
https://cameochemicals.noaa.gov/chemical/336
https://www.safetystoragecentre.co.uk/a … ure-5.html
Flammable Substance Temp (Deg C) Temp (Deg F)
Carbon monoxide 609 1128
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Calliban,
Yes, the NREL-backed SCCO2 gas turbines use Inconel to achieve 715C to 725C operating temperatures to permit 50%+ efficiency using a single-stage gas turbine. They use a diffusion-bonded Inconel PCHE (Printed Circuit Heat Exchanger) to achieve high power density (a reduction in heat exchanger volume / weight to transfer a given amount of thermal energy to a radiator, without an unacceptable pressure drop) in that sub-assembly as well. The high operating temperature also reduces the size of the radiator, but again, mandates the use of a heavier metal since Aluminum will melt at the temperatures it operates at. The use of Inconel for all components in direct contact with hot / highly-pressurized CO2 is all about maintaining acceptable strength at high operating temperatures and inhibiting the corrosive effects of hot flowing CO2 associated with the use of low-alloy Carbon steels. All of the Inconel components can survive decades of continuous use, whereas low-alloy Carbon steel cannot. Given the intended use case (reliably delivering power through decades of operations) and low total mass of Inconel components (less than 500kg per vehicle and several tons for a 10MW solar thermal power plant), I fail to see the point in using less durable steels that will only serve to reduce overall reliability, increase maintenance requirements, and decrease replacement intervals.
The single greatest cost, by far, even if Starship can deliver tonnage to Mars at the price points SpaceX is claiming, is the cost of transport to Mars. The single greatest issue affecting equipment after arrival on Mars, is durability / longevity in operation. As such, every aspect of the solution should minimize transport costs and the equipment's associated logistical tail. The best way to do that is to not compromise on the durability of the components used. Inconel is a very common alloy for high temperature parts and there's no good reason for not using the most suitable materials for the job.
As far as only using power when it's available, that's not how any cities with a million inhabitants were constructed here on Earth. I'm unopposed to taking opportunistic advantage of additional power, but construction work is inherently power-intensive. The best way to get jobs done is to assure the availability of power, personnel, and equipment.
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Turbines are unique in that they area rotating force engine and not a piston design.
As for capturing the exhaust we are going from a high pressure to a lower one with a greater volume to hold it in at the reduced pressure.
Mars is nearly a vacuum and its hard to recapture it in the wild but from a tank that even is 1 bar is easier than 100mb that mars is at its greatest.
Edit
so as to not miss the electronic sieve here it is for the above post # 104 which mentioned it.
Kbd512's post in the co topic
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For SpaceNut re #147
Thank you for bringing back kbd512's post on molecular sieve technology. I had read that a year ago, but failed to remember it when we started concentrating on Carbon Monoxide for engine applications recently.
Searchterm:MolecularSieve see post 147 above for link to kbd512's post on the subject.
(th)
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Calliban,
Yes, the NREL-backed SCCO2 gas turbines use Inconel to achieve 715C to 725C operating temperatures to permit 50%+ efficiency using a single-stage gas turbine. They use a diffusion-bonded Inconel PCHE (Printed Circuit Heat Exchanger) to achieve high power density (a reduction in heat exchanger volume / weight to transfer a given amount of thermal energy to a radiator, without an unacceptable pressure drop) in that sub-assembly as well. The high operating temperature also reduces the size of the radiator, but again, mandates the use of a heavier metal since Aluminum will melt at the temperatures it operates at. The use of Inconel for all components in direct contact with hot / highly-pressurized CO2 is all about maintaining acceptable strength at high operating temperatures and inhibiting the corrosive effects of hot flowing CO2 associated with the use of low-alloy Carbon steels. All of the Inconel components can survive decades of continuous use, whereas low-alloy Carbon steel cannot. Given the intended use case (reliably delivering power through decades of operations) and low total mass of Inconel components (less than 500kg per vehicle and several tons for a 10MW solar thermal power plant), I fail to see the point in using less durable steels that will only serve to reduce overall reliability, increase maintenance requirements, and decrease replacement intervals.
The single greatest cost, by far, even if Starship can deliver tonnage to Mars at the price points SpaceX is claiming, is the cost of transport to Mars. The single greatest issue affecting equipment after arrival on Mars, is durability / longevity in operation. As such, every aspect of the solution should minimize transport costs and the equipment's associated logistical tail. The best way to do that is to not compromise on the durability of the components used. Inconel is a very common alloy for high temperature parts and there's no good reason for not using the most suitable materials for the job.
As far as only using power when it's available, that's not how any cities with a million inhabitants were constructed here on Earth. I'm unopposed to taking opportunistic advantage of additional power, but construction work is inherently power-intensive. The best way to get jobs done is to assure the availability of power, personnel, and equipment.
Point taken. If the engine is going to be shipped from Earth, then it makes sense using the most robust materials possible. Also, there are lots of meteorite fragments scattered across the Martian surface that contain a high percentage of nickel. So nickel should be available in usable quantities on Mars.
Regarding the use of direct electric solar power on Mars and adapting demand to supply, I believe that this is the only way that Mars built PV power makes sense as anything more than a niche energy source. On Earth, the EROI of solar PV barely exceeds 10. Mars has only half the solar constant and a harsher UV environment. Now consider that batteries have a lot of embodied energy and there are sizable energy losses in charging, discharging and conversion to AC. The only way solar PV can provide a decent amount of net energy on Mars, will be to avoid unnecessary embodied energy and parasitic energy losses. That means adapting demand to supply. It may even mean low voltage DC power networks.
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
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The local 3D Printer group held it's monthly meeting this evening. The attendees could have been anywhere (of course) but as it happened we were all local. We used the gather.town system again, and I have to admit I ** really ** like it!
However, the reason I am posting now is to report that as I asked about 3D Printing:
1) a pencil
2) a piston engine
3) a turbine engineone of the attendees asked if we had considered a Wankel engine? We had not, and I'm definitely interested in tossing that question out to the Internal Combustion engine topic participants!
The piston engine will have hundreds if not thousands of parts, most of which needed to be given manual attention to bring them to the necessary precision.
The turbine idea met with approval, but with the observation that unlike with a forging, 3D printed parts may have flaws which would have to be detected before the parts are put into service.
The Wankel engine concept was offered as a simpler rotary engine that still has a decent track record on Earth.
(th)
The first several generations of builds for the Wankel were very leaky to oil seals and more and require even tighter tolerances than a regular block piston engine does. The Wankel would be simular to the turbine in that its a rotary type movement based on forces.
They are not dead or forgotten for what they could and can do.
These were a gasoline engine and it could use the gaseous fuels of hydrogen or methane but going for co and others might not be possible until some one does build one for its use. Of course could they also be done with diesel size and fuels is still another question?
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