Do Electric City Cars Dream Of Compressed Air Sleep?

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deadduck
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Re: Do Electric City Cars Dream Of Compressed Air Sleep?

Post by deadduck »

GigotHaricot wrote:
deadduck wrote:
Fair point. Refrigeration is not needed. It just helps because it stores extra energy if you have it. Some divers refill their tanks in a water bath to keep it cool for the same reason - it gets more air in for a given pressure.
:| Exactly. There are many ways of cooling without refrigeration. Cheap ways. Easy ways. It's not a valid argument.
This technology does have an intrinsically low efficiency compared to electric cars though.
Does it matter? It comes down to running cost.
Not just. Negative externalities and all that... The efficiency will eventually drive the running cost, if not now in a middle term.

Look at agro-carburant. They were the dogs bollocks on a small scale until they drove the colza prices off their tits.
Foreseeable negative externalities for compressed air powered cars:
-Pollution associated with the compression and transport of compressed air
-Safety risk of transporting highly compressed gases in a vehicle at risk of collision
-Noise

The first two can be overcome. Compared with battery powered electric vehicles and hybrids they compare very favourably.
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deadduck
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Re: Do Electric City Cars Dream Of Compressed Air Sleep?

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gibbothegreat wrote:
deadduck wrote: :| Exactly. There are many ways of cooling without refrigeration. Cheap ways. Easy ways. It's not a valid argument.
And yet it seems this is one area that has defeated Tata - without this it's nigh on impossible to achieve the requisite energy density, and no-one has really figured out how to make it work cost-effectively.

One other question to which I haven't seen any reference: how do these vehicles produce power for lights, steering, braking, defrosters, heaters, etc...?
I don't understand your point, when the air is compressed it creates heat, that is able to be removed by many methods, of which you just have to choose the one which combines cost effectiveness with highest efficacy. The energy density in the gas cylinder has nothing to do with Tata's technology, are you referring to something else?


With regards to your second point, surely they could use an alternator/battery system the same way petrol cars do?
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Re: Do Electric City Cars Dream Of Compressed Air Sleep?

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deadduck wrote:Foreseeable negative externalities for compressed air powered cars:
-Pollution associated with the compression and transport of compressed air
-Safety risk of transporting highly compressed gases in a vehicle at risk of collision
-Noise

The first two can be overcome. Compared with battery powered electric vehicles and hybrids they compare very favourably.
?? Really? Surely on the first one there's no difference except that compressed air vehicles are (currently) less efficient: both need large amounts of electricity, it's down to how cleanly that electricity is generated. But at current stage of development, for a given amount of electricity, battery technology will get you further and is therefore less polluting.

Whilst I don't doubt that the safety issue of compressed air can be overcome, clearly batteries are streets ahead on this one.

I'm curious about the third - again, noreferecne to this either way, but I had in my head assumed that it would be relatively simple to develop an extremely quiet compressed air vehicle, is that wrong?
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Re: Do Electric City Cars Dream Of Compressed Air Sleep?

Post by Leffe »

Fat Albert wrote:Do Electric City Cars Dream Of Compressed Air Sleep?
I guess they dream about oil. Dirty filthy oil *rubs thighs*
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Re: Do Electric City Cars Dream Of Compressed Air Sleep?

Post by deadduck »

gibbothegreat wrote:
deadduck wrote:Foreseeable negative externalities for compressed air powered cars:
-Pollution associated with the compression and transport of compressed air
-Safety risk of transporting highly compressed gases in a vehicle at risk of collision
-Noise

The first two can be overcome. Compared with battery powered electric vehicles and hybrids they compare very favourably.
?? Really? Surely on the first one there's no difference except that compressed air vehicles are (currently) less efficient: both need large amounts of electricity, it's down to how cleanly that electricity is generated. But at current stage of development, for a given amount of electricity, battery technology will get you further and is therefore less polluting.

Whilst I don't doubt that the safety issue of compressed air can be overcome, clearly batteries are streets ahead on this one.

I'm curious about the third - again, noreferecne to this either way, but I had in my head assumed that it would be relatively simple to develop an extremely quiet compressed air vehicle, is that wrong?
With batteries there are more externalities associated than just the power generation, such as the cost both financially and environmentally of producing them. Electric vehicles require rare earths, copper, lithium, semi metals etc none of which are particularly clean to produce. The batteries also need a recycling infrastructure to support them. Compressed air comes from the air and goes back to the air. It's a simple process with few hidden costs.

With regards to the noise, I would expect the noise of a compressed air car to be similar to that of a conventional ICE car. Not a major factor.
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Re: Do Electric City Cars Dream Of Compressed Air Sleep?

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deadduck wrote:I don't understand your point, when the air is compressed it creates heat, that is able to be removed by many methods, of which you just have to choose the one which combines cost effectiveness with highest efficacy. The energy density in the gas cylinder has nothing to do with Tata's technology, are you referring to something else?
Just shooting form the hip here, but there seems to me to be a few issues round this. First of all, if you don't cool the air as it's compressed into the tank, then you get less bang for your buck. Air being compressed will get hot, but it will then cool and lose pressure as it does so. Less pressure = lower energy density. OK, so you remove the heat, but that also requires a fair amount of energy, lowering the efficiency of the whole process.

I guess filling stations could work with a buffer of a tank of pressurised air? So they deal with the cooling, taking that weight away from the vehicle. But then how safe is it to handle an air supply with that pressure?

The sod is that you have the opposite problem when the air is used in the engine, as the energy latent in the pressure is converted to kinetic energy, the air (already at or near ambient temperature) will lose heat drastically, and will thus be below freezing: at which point the water vapour that's a normal constituent of air will freeze, quite rapidly. Can the engine be designed to deal with/survive this?
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Re: Do Electric City Cars Dream Of Compressed Air Sleep?

Post by slow wing »

Gibbo, yes, the freezing of water is another issue, although the concept is already dead on efficiency grounds imo.

To avoid that, they would have to dry the air on compression, like they do with compressors for divers' air tanks...

The compressed air output by the compressor must be filtered to make it fit for use as a breathing gas.[1] The following filters remove:
Water, using silica gel, activated alumina or a molecular sieve ...
http://en.wikipedia.org/wiki/Diving_air_compressor
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Re: Do Electric City Cars Dream Of Compressed Air Sleep?

Post by deadduck »

gibbothegreat wrote:
deadduck wrote:I don't understand your point, when the air is compressed it creates heat, that is able to be removed by many methods, of which you just have to choose the one which combines cost effectiveness with highest efficacy. The energy density in the gas cylinder has nothing to do with Tata's technology, are you referring to something else?
Just shooting form the hip here, but there seems to me to be a few issues round this. First of all, if you don't cool the air as it's compressed into the tank, then you get less bang for your buck. Air being compressed will get hot, but it will then cool and lose pressure as it does so. Less pressure = lower energy density. OK, so you remove the heat, but that also requires a fair amount of energy, lowering the efficiency of the whole process.

I guess filling stations could work with a buffer of a tank of pressurised air

The sod is that you have the opposite problem when the air is used in the engine, as the energy latent in the pressure is converted to kinetic energy, the air (already at or near ambient temperature) will lose heat drastically, and will thus be below freezing: at which point the water vapour that's a normal constituent of air will freeze, quite rapidly. Can the engine be designed to deal with/survive this?
You're assuming compression at point of service e.g. at a filling station. If the air is already compressed when it arrives at the filling station and is simply transferred under pressure to your vehicle then there are inherent efficiencies of scale to be gained in the cooling process.
With regards to your second point, I believe that's why the designers have incorporate a hybrid two-fuel system in some of their models, in order to increase open road efficiency they could use a second combustible fuel to generate heat to preheat the compressed air before it enters the engine. There are also simple chemical methods of drying the compressed air when it is produced, so that the water vapour component is negligible.
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Re: Do Electric City Cars Dream Of Compressed Air Sleep?

Post by Fat Albert »

Gibbo wrote:The sod is that you have the opposite problem when the air is used in the engine, as the energy latent in the pressure is converted to kinetic energy, the air (already at or near ambient temperature) will lose heat drastically, and will thus be below freezing: at which point the water vapour that's a normal constituent of air will freeze, quite rapidly.
Another perspective and you might say 'Free Air Conditioning' :D
Gibbo wrote:Can the engine be designed to deal with/survive this?
Are you serious? F1 engines are engineered to run at 20,000 explosions per minute producing 800bhp from 2400cc for 2,500km without servicing, do you really think there's an engineering issue making a compressed air engine run at a few degrees lower than ambient?

The miniCAT has recommended oil change intervals of 30,000 to 50,000km, and it's lubricating oil is vegetable based, compare that to ICE synthetic oil cycles
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Re: Do Electric City Cars Dream Of Compressed Air Sleep?

Post by gibbothegreat »

deadduck wrote: You're assuming compression at point of service e.g. at a filling station. If the air is already compressed when it arrives at the filling station and is simply transferred under pressure to your vehicle then there are inherent efficiencies of scale to be gained in the cooling process.
Yeah, I realised that afterwards and edited accordingly see- above. My next (again genuine) question would be: how safe is it then for members of the public to handle pressurised lines at 300 bar?
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Re: Do Electric City Cars Dream Of Compressed Air Sleep?

Post by gibbothegreat »

Fat Albert wrote:F1 engines are engineered to run at 20,000 explosions per minute producing 800bhp from 2400cc for 2,500km without servicing, do you really think there's an engineering issue making a compressed air engine run at a few degrees lower than ambient?
I was thinking about icing being the problem not the stresses within the engine, but I see that's been answered above - the compressed air would have to be dried. Seem to be an awful lot of ancilliary processes required to amke this work not even as well as batteries currently do...
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Re: Do Electric City Cars Dream Of Compressed Air Sleep?

Post by deadduck »

Drying it is dead simple, can be done in-process and at negligible cost. Not a problem.


With regards to the refilling at high pressure lines, well there are pump designs and attachments such as they use for LPG that can reduce the risk. No doubt there would be all sorts of electronic interlocks, leak detection and emergency cut offs. The pumps would likely have to be supervised more heavily but that's not a huge issue. If the impetus is there, the infrastructure will be developed. Obviously it will not be as simple as filling with petrol or diesel.
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Re: Do Electric City Cars Dream Of Compressed Air Sleep?

Post by Spell »

Im not sure either will be the solution

http://www.jouleunlimited.com/news/2011 ... tion-award
Unlike the costly, multi-step production of biofuels from biomass, Joule's Helioculture™ platform directly and continuously converts solar energy to infrastructure-compatible fuels and chemicals, including fungible diesel and ethanol. The platform combines breakthroughs in genome engineering, process engineering and solar capture and conversion to achieve productivities that will be up to 100X greater than biomass-dependent processes, while avoiding depletion of agricultural land or fresh water. Using sunlight and waste CO2 from industrial emitters or pipelines, with a modular SolarConverter® system that allows ease of scale, Joule targets commercial production of up to 15,000 gallons of diesel and 25,000 gallons of ethanol per acre annually, at stable costs as low as $20/bble and $0.60/gallon respectively, including subsidies.

Joule has been conducting pilot operations for over one year and will begin construction of its first demonstration-scale plant this quarter.
Im sure this has been discussed on the "Bored" before.
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Re: Do Electric City Cars Dream Of Compressed Air Sleep?

Post by TB63 »

deadduck wrote:
gibbothegreat wrote:
deadduck wrote: :| Exactly. There are many ways of cooling without refrigeration. Cheap ways. Easy ways. It's not a valid argument.
And yet it seems this is one area that has defeated Tata - without this it's nigh on impossible to achieve the requisite energy density, and no-one has really figured out how to make it work cost-effectively.

One other question to which I haven't seen any reference: how do these vehicles produce power for lights, steering, braking, defrosters, heaters, etc...?
I don't understand your point, when the air is compressed it creates heat, that is able to be removed by many methods, of which you just have to choose the one which combines cost effectiveness with highest efficacy. The energy density in the gas cylinder has nothing to do with Tata's technology, are you referring to something else?


With regards to your second point, surely they could use an alternator/battery system the same way petrol cars do?
Or a long extension lead..
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Re: Do Electric City Cars Dream Of Compressed Air Sleep?

Post by diom »

My approach to any of these "electric-alternatives" is that if it requires more energy transduction than are normally required by an electric car then it is almost certainly NOT as efficient.

Interesting, but as pointed out, unless the compression 100% efficient (impossible) then it will be less efficient at utilising energy than a battery equivalent.
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Re: Do Electric City Cars Dream Of Compressed Air Sleep?

Post by Fat Albert »

From Wiki wrote:Worldwide, there were 12.6 million natural gas vehicles by 2010, up 11.6% over the previous year

CNG is made by compressing natural gas, to less than 1% of the volume it occupies at standard atmospheric pressure. It is stored and distributed in hard containers at a pressure of 200–248 bar (2900–3600 psi), usually in cylindrical or spherical shapes.
There is an ISO standard for such storage tanks, ISO 11439. One might surmise that there has been some solid engineering behind the setting up of that standard.
SG wrote:At CNG fueling stations the gas is compressed before being provided to vehicles at 3000 to 3600 pounds per square inch (psi). Stations can deliver a “fast fill” to vehicles in minutes or, using a “slow fill” strategy, in a few hours to overnight.

In the US natural gas vehicles are subjected to the same federal government crash tests as other vehicles. CNG vehicle fuel systems must meet Federal Motor Vehicle Safety Standards 303 and 304. Natural gas cylinders are much thicker and stronger than gasoline or diesel tanks. Cylinders are designed not to rupture when fully fueled over six times a day, 365 days a year.

CNG vehicles have been used in the US since the early 1980s. Yet there has been only one fatality in the US caused by an CNGV fueling system failure in all that time. Insurance companies consider CNG fuelled vehicles lower risk than gasoline fuelled vehicles.
The CNG experience is directly applicable to compressed air engines, the tanks, pressures, re-fulling systems and infrastructure are all similar EXCEPT that CNG is volatile.

Atmospheric engines “suck” the piston up in the cylinder instead of pushing it down. The clever part of the French motor is that it takes advantage of the low temperature decompressed air to extract energy from air at the ambient temp.

The ignorance and prejudice on this Fred is remarkable only for it's similarity to discussions of atmospheric science

Compressed air may well be the truly green solution 'air heads' have been seeking for energy storage on a local level, imagine using sun/wind/water power to compress air into local storage tanks, overnight and/or when there's no wind the process could be reversed via the Negre atmospheric engine to GENERATE electricity.

Far less polluting than the manufacture, maintenance and disposal of batteries, however efficient.
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Re: Do Electric City Cars Dream Of Compressed Air Sleep?

Post by gibbothegreat »

Thanks for the info re CNG tanks and fuel handling, FA, that's just the sort of detail I was looking for.

Out of interest, what prejudice do you find on this thread?
Last edited by gibbothegreat on Thu Feb 02, 2012 10:57 am, edited 1 time in total.
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Re: Do Electric City Cars Dream Of Compressed Air Sleep?

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The only 'problem' I have with this technology is that according to the few academic research papers available online, it appears to be considerably less efficient as a storage medium than batteries, while batteries are becoming more efficient all the time as a consequence of pressure form the consumer electronics industry. Since the GHG and BEV emissions are both coupled with the greenness or otherwise of the power source used to compress the air (or charge the battery) then the efficiency difference makes compressed air commensurately less green, because more energy is required to achieve the same result. That's simple logic. Whether this is enough to outweigh the environmental cost of batteries is a matter for engineers. To say CAC is 'far less polluting' seems hopeful. It could easily be the other way round.
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Re: Do Electric City Cars Dream Of Compressed Air Sleep?

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6roucho wrote:The only 'problem' I have with this technology is that according to the few academic research papers available online, it appears to be considerably less efficient as a storage medium than batteries, while batteries are becoming more efficient all the time as a consequence of pressure form the consumer electronics industry. Since the GHG and BEV emissions are both coupled with the greenness or otherwise of the power source used to compress the air (or charge the battery) then the efficiency difference makes compressed air commensurately less green, because more energy is required to achieve the same result. That's simple logic. Whether this is enough to outweigh the environmental cost of batteries is a matter for engineers. To say CAC is 'far less polluting' seems hopeful. It could easily be the other way round.
Concentrating on the point of use efficiency is a fair red herring. There is much more energy involved in the manufacture of a battery than there is in filling a gas cylinder. You need to look at these options over the entire life cycle of the product not just the efficiency of the engine.
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Re: Do Electric City Cars Dream Of Compressed Air Sleep?

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CAR, April wrote:Peugeot have made a hybrid with a difference, one that dumps the batteries and electric motor for a compressed air energy storage system. The system can propel a 208 on fresh air, at speeds below 43mph. The Hybrid air system is claimed to reduce use of the accompanying petrol engine by 80% in town, slashing CO2 emissions.

Response is fast and the system uses regenerative techniques to recharge the air tank, working well in stop start traffic with the air tank able to recharge in under 10s.

Peugoet claims 97.4mpg beating the Yaris hybrid's 80.7mpg and with lower emissions at 69g/km. The mechanics are straight forward, robust and cheap compared with electric an hybrid's expensive batteries
Image

208 Linky | 2008 SUV Linky

How long before someone builds a Volt type hybrid that uses a small petrol engine to compress air, Peugeot claim 95% efficiency :shock:
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Re: Do Electric City Cars Dream Of Compressed Air Sleep?

Post by clifton cowboy »

my (limited) understanding is that compressed air has a big future in terms of energy storage - isothermal systems

still some effeciency improvement needed but could be v useful for eg storing wind turbine energy


(re powering cars - I expect hydrogen is much more effecient)


(NB: expect the compressors would be huge)
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Re: Do Electric City Cars Dream Of Compressed Air Sleep?

Post by Fat Albert »

Image Image
Auto Express wrote:With Hybrid Air technology PSA is addressing the biggest barrier to customers buying electric cars and plug-in hybrids – the cost. The simple but effective technology could be added to a wide variety of engines for a small price premium and boost economy significantly.

The Peugeot 2008 Hybrid Air prototype is the first fully-functioning showcase for PSA’s compressed air hybrid technology

The Hybrid Air system can operate in zero emissions air mode, petrol-engine-only mode, or petrol and air in combination. Driven carefully, it takes about 500 metres for the tech to exhaust itself around town, and the 81bhp 1.2-litre turbocharged three-cylinder petrol engine kicks in with a gruff low growl to help push things along. It's a momentary boost, as fully recharging takes no more than ten seconds at city speeds, and despite the apparently short range the centre display still claimed 60 per cent of our journey was emissions free.
Read more
gizmag wrote:The French automaker revealed its Hybrid Air technology last year and will showcase the 208 Hybrid 2L Demonstrator car at the Paris Motor Show next month. The latest iteration of the Hybrid Air design complements the gasoline-air powertrain with weight- and drag-cutting measures to offer fuel economy in the range of 117 mpg (2 L/100km)

The compressed air works in conjunction with a front-mounted hydraulic motor/pump system to power the car and refill in about 10 seconds during deceleration or by way of compressed air developed by the three-cylinder engine.
Read More

The 208L is scheduled for 2015/16 production and is expected to list for about £17,000 in the UK (more in an independent Scotland), it's entire manufacturing cost will be about the same as that of the Tesla S (300m range) battery pack!
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Re: Do Electric City Cars Dream Of Compressed Air Sleep?

Post by Yer Man »

gibbothegreat wrote:Looks very interesting... what infrastructure is there for refilling on compressed air at present?
Stick a tube up your arse and fart.
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Re: Do Electric City Cars Dream Of Compressed Air Sleep?

Post by merlin the happy pig »

deadduck wrote:
6roucho wrote:The only 'problem' I have with this technology is that according to the few academic research papers available online, it appears to be considerably less efficient as a storage medium than batteries, while batteries are becoming more efficient all the time as a consequence of pressure form the consumer electronics industry. Since the GHG and BEV emissions are both coupled with the greenness or otherwise of the power source used to compress the air (or charge the battery) then the efficiency difference makes compressed air commensurately less green, because more energy is required to achieve the same result. That's simple logic. Whether this is enough to outweigh the environmental cost of batteries is a matter for engineers. To say CAC is 'far less polluting' seems hopeful. It could easily be the other way round.
Concentrating on the point of use efficiency is a fair red herring. There is much more energy involved in the manufacture of a battery than there is in filling a gas cylinder. You need to look at these options over the entire life cycle of the product not just the efficiency of the engine.
Yes you do need to look at energy inputs for the whole life cycle.
But I think that is pretty much what 6Groucho says in the highlighted bit.

Until we find those numbers it's all pretty much piss and wind.
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