New Mars Forums

Official discussion forum of The Mars Society and MarsNews.com

You are not logged in.

Announcement

Announcement: As a reader of NewMars forum, we have opportunities for you to assist with technical discussions in several initiatives underway. NewMars needs volunteers with appropriate education, skills, talent, motivation and generosity of spirit as a highly valued member. Write to newmarsmember * gmail.com to tell us about your ability's to help contribute to NewMars and become a registered member.

#126 2020-02-17 20:56:09

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 28,716

Re: Running on Compressed Air?

The moxie process creates the possible fuel for land based crafts to be created and used early plus it requires no water mining for a trip with all that is required is to super cooling it to liquid. pg 50 shows the tracked verion of a vehicle using it.

http://www.niac.usra.edu/files/studies/ … 40Rice.pdf
ADVANCED SYSTEM CONCEPT FOR TOTAL ISRU BASED PROPULSION AND POWER SYSTEMS FOR UNMANNED AND MANNED EXPLORATION

The rover mission was defined as a 300 km one day trip. A system of gravel roads was assumed. Based on a trip distance of 300 km and a transit time of 10 hours, a velocity of 30 km/h was used. Turbine efficiency was assumed same for all fuels at 65% chemical potential to mechanical energy conversion efficiency.

For the initial iteration, the structural mass penalty for storing propellant was a 100 kg storage tank. The propellant mass penalty was ½ the mass of the propellant. For example, a 2000 kg rover that burns 200 kg of propellant and stores the byproducts has a mass of 2300 kg for the entire duration of the trip (with the tank mass penalty), while a 2000 kg venting rover has a mass of 2200 kg at the beginning of the trip and 2000 kg at the end. The mass used to calculate the propellant usage was therefore 2100 kg.

Offline

#127 2020-09-22 19:38:37

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 28,716

Re: Running on Compressed Air?

Calliban wrote:

Addressing post 207.  Pneumatic transport, that is to say a vehicle pushed along by differential pressure, is definitely an option worth considering on Mars.  The interesting thing about the idea is that the vehicle need not carry its own power supply.  A rail based or wheeled vehicle propelled by differential pressure could simply be a set of carriages, equipped with brakes to control its speed.

On Earth, atmospheric railways have found niche applications, but were largely rendered obsolete following the application of electricity to railways.  However, small pneumatic pipelines carrying wheeled vehicles could be very useful for transporting bulk materials on both Earth and Mars.  A square conduit just 20cm wide, carrying wheeled vehicles at 10m/s, could move up to 1500 cubic metres per hour of freight or bulk materials between any two points.  The vehicle would have a loose seal at its front and back, to minimise gas leakage past it.

The required differential pressure needed to drive the vehicle would be a function of its mass (weight), the friction coefficient of the wheels and the cross-sectional area of the vehicle.

The minimum force needed to move a vehicle is given by: F = W x C, where W is weight in N, and C is coefficient of rolling resistance, typically 0.002 for steel wheels on steel rails.  A 1 tonne mass would weigh 3679N on Mars.  To move this mass in a rail vehicle will take a minimum force of 7.4N on Mars.  For a vehicle 20cm wide, this amounts to a required differential pressure of 184Pa per tonne.  This of course assumes a perfectly flat surface.

Hydraulic capsule pipelines are a related concept in which neutrally buoyant capsules of material are carried through a water pipe.  Typically, this carries capsules very slowly, about human walking speed.  The concept is one of the most energy efficient transportation methods known to man, but it has the limitations of low speed and the need to load and unload the capsules with whatever is being transported and handle them at both ends.  An added problem exists on Mars - low temperature.  Operating hydraulic pipelines on Mars would require either heating the pipes or using brine as a carrying fluid.  The first solution is an option if we have access to nuclear waste heat.  The low thermal conductivity of Martian regolith would make it an excellent insulator.  Using cold brine is problematic, because water at subzero temperatures becomes progressively more viscous, which pushes up pumping power.

One significant advantage of low speed pipelines on Mars is the extremely low vapour pressure of water at temperatures close to zero.  The pipelines would barely need to be pressurised.  They could be constructed from cast basalt, concrete, steel or polymer.  We would lay them between our colony and numerous mine sites, allowing colonists to access materials from hundreds or even thousands of kilometres away.  The water would carry the capsules along at speeds of no more than a few metres per second.

A pipe some 10cm in diameter, carrying capsules at a speed of 1m/s, could transport up to 250,000 tonnes of material per year.  If the pipe is made from steel with a wall thickness of 1mm, it would weigh 2.5 tonnes per km. A 1000 km long pipe would therefore weigh 2500 tonnes.  The pipe could therefore carry 100x its own weight in freight every year.  Useful, if we wanted access to resources from a large area to support the needs of a growing city.  We could for example, build a city under a polar ice filled crater.  We could grow food in an agricultural colony closer to the equator.  A pipeline would deliver water from the polar city to the agricultural colony during the spring and summer months.  During the autumn and winter, the same pipeline would be used to transport food north in capsules.

Offline

#128 2022-10-08 17:19:09

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 28,716

Offline

#129 2022-10-09 11:05:21

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 3,335

Re: Running on Compressed Air?

Compressed air energy storage has always interested me.  Despite it's excellent ESoEI, progress in expanding CAES has been slow.  The problem is that pressure vessels are expensive and CAES projects therefore rely on underground air storage.  This limits CAES to areas with suitable geology, like underground salt deposits, which tend to be few and far between.

Other options have been explored over the years.  Subsea air storage in tanks or rubber bags.  Prestressed concrete storage vessels.  Even liquid air energy storage.  But none of these concepts have caught on in a way that would allow CAES to expand as a mainstream solution.

As a local offgrid solution, it may be possible to store low-pressure compressed air in pits or covered trenches.  This would work for storage of small quantities of energy at pressures <1 bar(g).  Vacuum can be stored in entirely compressive vessels made from concrete.  Again, this is not something that scales to large sizes, but may be a niche solution in situations where we need to store <1kWh and discharge it at high power.

Last edited by Calliban (2022-10-09 11:12:51)


"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."

Offline

#130 2022-10-12 19:40:02

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 28,716

Re: Running on Compressed Air?

Why yes you did see a topic

Mars_B4_Moon wrote:

I remember seeing SpaceNut maybe post news and Calliban discussing Air Compression the other day, I might search again for the thread later.

'China turns on the world's largest compressed air energy storage plant'

https://newatlas.com/energy/china-100mw-compressed-air/

The Chinese Academy of Sciences says the Zhangjiakou plant is capable of supplying the local grid with more than 132 GWh of electricity annually, taking on the peak consumption of some 40-60,000 homes. It'll save around 42,000 tons of coal from being burned in power stations, and reduce annual carbon dioxide emissions by around 109,000 tons – the equivalent of taking about 23,700 average American cars off the road.

The Academy says this design's low capital costs, long lifetime, safety and efficiency, along with its green credentials, position it well as "one of the most promising technologies for large-scale energy storage."

Offline

#131 2022-10-12 21:43:16

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 28,716

Re: Running on Compressed Air?

Offline

#132 2023-11-18 17:54:52

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 28,716

Re: Running on Compressed Air?

This topic has come up again.

Offline

#133 2023-11-18 19:12:43

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 3,335

Re: Running on Compressed Air?

Long term, I think L-CO2 could be a valuable resource on Mars and a convenient way of storing energy.  It can be stored as liquid at 5.1 bar at -56°C.  If exposed to a modest heat source above 304K, high pressure, dry CO2 gas is generated.  This gas could be used to power tools and even short range vehicles.  Nuclear waste heat could provide the heat.  We could store almost endless amounts of L-CO2 in thin walled steel vessel, insulated with regolith.  Natural circulation could cool the liquid CO2 using a surface radiator exposed to the cold of night.  If we can subcool the CO2 in the tank during night, we can refill it using solar electricity during the day, by compressing atmospheric CO2 to 5.1 bar and pushing it into the tank.  The gas that bleeds off will be enriched in non-CO2 atmospheric fractions.

Last edited by Calliban (2023-11-18 19:17:59)


"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."

Offline

#134 2023-11-18 20:20:41

kbd512
Administrator
Registered: 2015-01-02
Posts: 7,319

Re: Running on Compressed Air?

Calliban,

The bleed-off could become our source of Argon (electric propulsion and welding) and Nitrogen (for a breathable atmosphere).  There are other trace gases that will also prove useful, such as Carbon Monoxide and water vapor.  There's very little Neon, Krypton, and Xenon, but those trace gases would also need to be collected.  Neon is presently required to make CPUs, for example.

Offline

#135 2023-12-19 17:51:32

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 3,335

Re: Running on Compressed Air?

I managed to find a copy of this article:
'Experimental Investigation of A Compressed Air Vehicle Prototype With Phase Change Materials for heat Recovery'

https://sci-hub.ru/10.1002/est2.159

This is a prototype compressed air powered vehicle, with an exergy efficiency of 61% and a range of 87 miles.  The high exergy efficiency is achieved by storing compression heat in a paraffin phase change material onboard and then preheating the compressed air prior to expansion.

The range and efficiency allows the vehicle to compete with electric vehicles and will considerably outperform them when embodied energy is factored in.  The thing I have always liked about the idea of compressed air vehicles is that exotic materials are largely avoided.  We need fibre glass for the tanks, and paraffin wax as phase change material, but almost everything else is steel and plastic.  That should make these cars cheaper to build at volume.  Another positive attribute is the compressed air can be generated mechanically, without the prior need to generate electricity.

Whilst the prototype discussed here stores compression thermal energy onboard, another option would be to store cold energy from expansion and use it to precool air reducing the energy needed for compression.  This may work better, because the heat of fusion of water is substantially greater than paraffin and a smaller volume is needed to store the same amount of heat.

Last edited by Calliban (2023-12-19 17:58:30)


"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."

Offline

#136 2023-12-19 20:42:19

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 16,651

Re: Running on Compressed Air?

For Calliban re #135 ...

Thank you for finding the link you showed us in #135

I followed the link (to Russia without incident) and discovered the email addresses are for authors in Canada.

The image of a hybrid car, with both electric driven wheels and air motor driven wheels is definitely interesting.   I like the option of running on electric batteries to get home if the compressed air runs out.  Nice!

(th)

Offline

#137 2023-12-20 02:22:27

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 3,335

Re: Running on Compressed Air?

I hadn't noticed the link was from Russia.  From Russia with Love, perhaps, though I doubt :-)

Integrating the compressed air into an electric hybrid drive train, dillutes a lot of the advantages.  It means having all of the electric car components with just a smaller battery.  Maybe more work can eliminate the need for this by using a hybrid hydraulic drive train.  So long as the world remains fixated on a shiny electric future, progress will be slow unfortunately.  It is an ironic turn around that people that green movements are actually pushing the world into less sustainable practices.  Then again, being a Green is not the same as being an Environmentalist.

Last edited by Calliban (2023-12-20 02:25:41)


"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."

Offline

#138 2024-01-23 13:32:56

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 28,716

Re: Running on Compressed Air?

Calliban wrote:

SpaceNut, I wonder if the situation would be better if we transition to compressed air vehicles instead of battery-electric?
https://en.m.wikipedia.org/wiki/Compressed-air_car

Back in 2020, a prototype was able to achieve a 140km range and a roundtrip efficiency of 74%.  We would need to scale up generating capacity just as much using compressed air.  But the distribution pipework and charging infrastructure will be made from steel and synthetic rubber.  The pressure tank in the vehicle would be glass fibre wound around a carbon steel liner.  This idea at least does not present us with any unsustainable materials problems.  If we corrosion protect the steel pipes and avoid heavy pressure cycles, they should last for a very long time.  Same with the glass fibre tanks.  They should last for the life of the vehicle.

Offline

#139 2024-01-23 13:50:34

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 16,651

Re: Running on Compressed Air?

This topic certainly has legs, but after all the posts, we don't seem to be any closer to having a working system ...

I went back to Palomar's original post, and followed the discussion for a short distance ... Early in the series I found was I was looking for ... a proposal to store air (atmosphere in the case of Mars) as a liquid (Earth) or a solid (Mars).

I have two questions for Calliban (if you are willing to consider them and have the time)...

1) The vehicle in my garage can go 500 miles with a topped off tank using fossil fuel.

If air were liquefied and loaded into a suitable tank before a trip, could that charge carry the vehicle 500 miles?

I don't think the size of the gasoline tank is relevant, but it might turn out to be.  The volume of the tank is (about) 10 US gallons.

2) If paraffin is used to heat the LOX, what size paraffin tank is needed?

I'm assuming some thermal energy can be collected from the air along the way, but the system should be able to operate in a cold climate as well as a hot one.

(th)

Offline

#140 2024-03-11 17:17:34

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 28,716

Re: Running on Compressed Air?

tahanson43206 wrote:

For Calliban re air pressure energy storage ...

In the forum archive, there are posts between you and kbd512 (and perhaps others) about use of compressed air to store energy.

I was inspired by the discussion to invest in a generator/alternator that is designed for the golf cart market.  The machine is brand new and ready to go into service. My test plan was to drive the device from an air motor, to produce current to light a string of 12 volt DC bulbs. 

The automobile marketplace appears to include a few attempts at production of air pressure powered automobiles, and the tanks designed for that market would surely serve as energy reservoirs for my test.  I found an air motor that would be suitable for the experiment, but the Critical Path items is the air tank. Commercially available air tanks for air tools do not appear to have the capacity needed for the experiment, which was intended to produce 20 amps at 12 volts for some period of time (which I've forgotten but it might have been an hour).

I'd like to see the air stored energy discussion continue, if possible.

The cost of a suitable air tank may be out of reach for my budget, but at this point, I have no idea where to find one, let alone ask for price.

In the automobile application, I assume the engineers must have provided a regulator to deliver air to an air motor, so that would need to be part of the apparatus.

Follow up 2024/03/11 ... in a quick review of the compressed air automobile industry, I found hints that the air pressure in tanks may reach into the hundreds of atmospheres.  Safety would be a concern if air pressure driven equipment is supported by a store of that magnitude.  However, safety issues must have been addressed, if working automobiles have been developed and placed on the market.  I am interested in the application of this technology for on site power generation, whether for an electric generator via an air motor, or standard pneumatic tools.

(th)

Offline

#141 2024-03-12 03:51:03

kbd512
Administrator
Registered: 2015-01-02
Posts: 7,319

Re: Running on Compressed Air?

SpaceNut,

Practical air powered vehicles will use scuba diving tank or Hydrogen gas storage technology, either high strength corrosion protected (galvanized) steel or CFRP high pressure air cylinders with HDPE liners (Type IV H2 storage tanks).  CFRP is the safest and lightest and least affected by water vapor in the compressed air, but also the most costly by a considerable amount.  This is not the sort of equipment you can pick up at a home improvement store.  It must be ordered online or through a dive shop or from a company that makes H2 storage tanks, and then hydrostatic tested periodically by placing the high pressure air tanks underwater, taking them up to test pressure, holding for a specified period of time to assure no leaks, reinstallation in the vehicle, followed by leak testing.  This is also an ideal time to inspect the material condition of air feed lines and valves.

Hydrostatic testing is required every 5 to 10 years as a rule of thumb.  If you live near the coast, then retest every 2 years.  Ignore the 5 year requalification requirement and retest every 2 years.  Cylinder service life is normally 10 to 15 years, but this is something to ask the manufacturer of your particular air cylinders.  There is steel, Aluminum, and GFRP or CFRP with various types of liners.  CFRP overwrap tanks are designed to resist a set number of pressure cycles.  Going beyond that is a bad idea.  The steel is typically good until unacceptably corroded, damaged, or a service life or calendar life limit is reached.  Type IV CFRP H2 tanks can legally go to higher pressures, in accordance with US DOT regulations, as they were designed and intended to do when storing compressed H2.  Legal is important here, but not getting seriously injured or killed is infinitely more important.

You also need a much thinner / lighter hot water tank to contain hot water heated to just below its normal boiling point.  This tank can be corrosion protected steel (a standard water heater tank) or plastic, with an insulating foam used to retain heat.  A vacuum jacketed vessel such as a LN2 dewar is theoretically ideal, but again, more cost.  At some point, you have to give up on total optimization and aim for the most practical and cost effective solution.  Hot water tanks are pretty cost effective.  Anyway, the hot water tank goes inside your engine compartment, along with the air motor or turbine.

The entire system consists of one or more high pressure compressed air cylinders mounted below the passenger cabin or in / under a truck bed, a hot water tank to add thermal energy back to the "cold" expanding air to both maintain flow volume and preclude freezing from residual water vapor, plus an automotive air conditioning refrigerant loop with the radiator mounted inside the hot water tank standard location for a car, and the other side of the loop wrapped around the high pressure air line feeding expanding compressed air into the vehicle's air motor.  The refrigerant loop and pump attached to your air motor are using heat from the hot water to "gain efficiency" or "get extra air volume" to provide more power, however you wish to think about it.  In theory, your air motor could be a refurbished air cooled motorcycle engine.  A purpose-built air motor will be more efficient, but again... money.  A turbine is even more efficient for cruising at relatively constant speed, but not required, and the torque output from a stop will not be as good as a piston-driven air motor.

When the air is compressed using your onsite air compression pump, presumably solar or wind turbine powered, at least until hot water is provided as a grid service, the waste heat from the compression process is used to reheat the water in your vehicle's hot water tank.  If you have extra hot water or the water gets too hot, then some of that water goes back into your home's potable water heater tank or kitchen sink or bath or whatever else you use boiling hot water for.  That means the air compression piston cylinders of your stationary air compressor are surrounded by a water jacket, sort of like a normal combustion engine, to collect the waste heat.

For that burst of energy required for brisk acceleration, you're using a much larger turbine at low-speed, or a simpler / lower cost piston pump air motor which has greater friction losses than a turbine.

With 8X 45L 310bar compressed air tanks, you have 4.273hp-hr / 3.186kWh of energy from the compressed air alone, to work with.  100kg of hot water, cooled from 99C to 20C by adding heat / volume to the compressed air adds 9.186kWh, so 12.372kWh, maximum.  In other words, not a lot of energy.  That would give you about 35 miles of driving range at 350W/mile.  The vehicle will weigh about as much as a Tesla Model 3.  At this point, you probably understand why the engineers went for Lithium-ion batteries, 677kg / 18.275Wh/kg of weight for this setup, excluding the motor, for 35 miles of range vs 300+ miles of range.

The real difference, of course, is cost-over-time, of pay-as-you-drive energy consumption, vs lots of high energy materials.  If you have CFRP tanks, then your energy density looks much better, with 309kg of weight, or 40Wh/kg at the same 310bar operating pressure, which is about the same as Lead-acid batteries, but without the batteries.  The CFRP tanks are rated at 25,000 cycles.  At 720bar pressure of the Type IV CFRP H2 tanks, you get 80Wh/kg.  That's about half as good as Lithium-ion at the pack level.  Your battery, of whatever type, will never give you the same total Wh/kg after 25,000 cycles, yet simple heat and pressure will.  In reality, your system doesn't work at zero pressure, so you don't get quite as good as what's described here, but you can see how we rapidly achieve a meaningfully "more renewable" energy system that will last dramatically longer than electro-chemical batteries will.

If someone figures out battery and photovoltaic cell recycling, and we come up with 4 billion tons of conductor wiring, then we can go gangbusters on all-electric.  Until then, combustion where required plus a much more "natural energy system" anywhere we can, looks like a winner.  It doesn't catch fire or combust, because it's non-electric and non-combustion.  Anyone can figure this out, because it's so simple, even if it requires real engineered systems.  People who balk at natural energy due to the limitations are essentially asserting that natural energy doesn't work.  For "green energy" to be truly environmentally friendly, it has to.  Let's try something we haven't meaningfully tried before, and see where that leads us.  I'm tired of dead-ends.  There has to be something to serve as an adjunct to combustion or wild computerization, or normal folks are never going to switch, because they can't afford it.

Offline

#142 2024-03-12 03:58:59

kbd512
Administrator
Registered: 2015-01-02
Posts: 7,319

Re: Running on Compressed Air?

I did a poor job of explaining the refrigerant loop concept, but you're piping "cold" expanding air through your "hot water refrigerant loop", to pick up heat energy from the water to increase the volume of air through the air motor, so that by the time it's finished expanding, you get a multiple of the total stored compressed air volume to use to push / drive / pump your non-combustion air-pump.  You can do fancier stuff with primary and secondary loops to increase or temporarily store "hot air" for acceleration, but you don't need to.  You regulate pressure down at the compressed air tank outlet to something a standard car AC radiator core can work with, you increase the volume or force with the energy in the hot water, the hot air goes into the air motor to expand and drive the piston(s) to produce mechanical pony power output, and then you exhaust the "colder" air.

Offline

#143 2024-03-12 11:47:04

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 3,335

Re: Running on Compressed Air?

Kbd512, many thanks for an excellent description of an air powered car.

I wonder how much the compressor needed to charge the car will actually weigh?  Would it make sense to integrate a compressor into the vehicle?  One thing that does interest me about this concept is that charging an air vehicle can be accomplished using mechanical energy.  This could be in the form of pressurised water, LP compressed air or even direct shaft power from a mechanical windmill.  The systems involved can be simple and don't rely on any exotic resources.

We can build machines like that out of brick, stone, wood and welded steel.  If someone told me today that I had to build a photovoltaic powerplant from scratch with only basic materials that I could find, I would be lost.  But I am confident that I could build a mechanical windmill that pumps water.  I think a lot of people could do that.  And if we have a supply of pumped water at a pressure of 5-10bar, then we have a hydraulic power source for a compressor that can charge our vehicles.

Last edited by Calliban (2024-03-12 11:50:37)


"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."

Offline

#144 2024-03-12 11:59:53

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 16,651

Re: Running on Compressed Air?

Is there any chance at all this interesting topic could be tweaked to yield a practical recommendation?

I remain interested in finding a compressed air solution that can deliver 7 CFM for 20 minutes. This would be a solution for a remote location, without electrical supply to refill the traditional steel tank. 

The energy storage capacity of tanks designed and build for the automotive market appear to have the capability of meeting this requirement. So far I have not seen any down-to-earth practical information moving through this topic or ** any ** similar topic.

***
In order to advance this initiative, I just ordered a V-Belt for the drill press I have on a  nearby work bench. My plan is to mount the 12 volt generator/motor purchased earlier, on a frame so that motion from the drill press will drive the generator.  The purpose of the exercise is to confirm that the generator works and that it can light a string of 12 volt bulbs.

An air motor is available but I'll hold off on making that investment until a solution to hold compressed air for the required time period is available.

(th)

Offline

#145 2024-03-13 01:13:15

kbd512
Administrator
Registered: 2015-01-02
Posts: 7,319

Re: Running on Compressed Air?

Calliban,

A 300-350 bar compressor is reasonably small, light, affordable, and typically water-cooled to get rid of waste heat (heat we want to store for later use in the car).  Perhaps $500 to $1,000.  Some individuals own these if they do a lot of diving or paintball or air rifle practice.  A 700 bar compressor is not small, light, or affordable, at least several thousand dollars, but more like $5K to $10K for a machine that can get the job done in a reasonable amount of time.  A gasoline pump at a gas station costs a lot more than that, so it's a machine that a gas station can pay for by charging customers to refill their car.

I don't see the point to owning potentially very dangerous charging equipment at home, whether it's a high power battery charger or 700 bar air / H2 compressor.  Knowing how to charge or refuel a car is one thing.  Knowing how to service the charging or fueling equipment is different.  Yes, some people do it.  It's not something I want my wife or children messing with.  As I said before, it belongs at a gas station / service station / servo.

You're looking at 35kg to 55kg for a good 300 to 350 bar unit, commonly used by SCUBA and paintball shops.  I don't know about a 700 bar unit, but I know it's not going in a car.  700 bar paintball and air rifle units are not at all suitable for filling 360L of tank volume with 700 bar compressed air, because they're not intended for extended duration / continuous duty use.  Most of those recreational compressors have a 30 to 45 minute operating time cutoff.

45L 300 bar steel compressed air cylinders weigh 65kg to 75kg each.  The industrial compressed air tanks I looked at were about 68kg each, less fittings and hardware, so 544kg for 8 tanks.  It's a two man lift, and you need to be reasonably strong to do it.  It has the benefit of being cheap, because it's steel.  Let's call it $1,200 worth of steel.

nuvtr-s6-7000-asme.jpg

I would skip Aluminum tanks entirely, even though they're a good "in-between" CFRP and steel.  Salt water dive shops near the equator use Aluminum instead of steel because scratched or unprotected steel corrodes way too fast.  They won't pay to shot blast and repaint the steel tanks, so they get scratched being dragged back into the boat or along concrete piers, but mostly accumulate water vapor inside during filling, so then they rust, and then they're junk in a year or two.  The inside rust is way more problematic than the outside, though.  Someone could invent a machine to shot blast inside the tank and that would solve the rust problem.  Aluminum has a strict service life limit, but is essentially zero maintenance, which is why dive shops like them.  Aluminum is also very easy to recycle.  Someone else can make the case for Aluminum, but I view the most realistic options as CFRP (maximum performance) or hot-dipped galvanized steel (maximum economy to the consumer for very short-range vehicles).

Type IV (high modulus fiber with a HDPE liner) 700 bar / 10,000psi CFRP is less than half as heavy as 350 bar steel, about a quarter the weight of steel in an optimal configuration.  As the images below indicate, this is why you really want Hydrogen or Methane or Propane, rather than Lithium-ion batteries or compressed air and hot water.

hydro_slide01.png

hyd-spec.jpg

image-20210401204716-4.png

360L of volume for 350 bar steel is 544kg.
360L of volume with 700 bar Type IV CFRP / HDPE is 143kg in a mass-inefficient configuration, so 3.79X lighter.
360L of volume with 700 bar CNT would be about 75kg or less, same mass-inefficient configuration (using a bunch of little tanks).

CNT tanks buy 160Wh/kg.

What does 160Wh/kg represent?

A 100kWh Tesla Lithium-ion battery pack weighs 625kg, so 160Wh/kg.

CNT 700 bar compressed air tanks achieve Tesla battery pack performance without a battery.  CNT fiber doesn't have a functional service life limit.  The plastic liner and resin will eventually degrade, but the fiber will not.  NASA gave up on breaking the fiber after bending it back and forth over 1,000,000 times.  At the point at which we achieve Lithium-ion battery pack level performance without any Lithium-ion batteries, nor power-robbing performance degradation, we have to question the reason to use Lithium-ion or Sodium-ion batteries for vehicle applications, because it won't make any economic or environmental sense.

Offline

Board footer

Powered by FluxBB