Please turn on javascript in your browser to play chess.
Science Forum

Science Forum

  1. 28 Feb '14 12:51 / 6 edits
    http://phys.org/news/2014-02-peugot-hybrid-cars-gas-compressed.html

    It is an interesting concept but, unless I am missing something, this appears to be a slightly flawed strategy as it would seem to be more cost effective to compress ordinary air i.e. air with 21% oxygen and the rest being mainly nitrogen rather than pure nitrogen that has to be purified at some expense.
    I cannot think why they didn't design it to run on plain ordinary air to make it cheaper. Does anyone know why not?

    I am also concerned with what would happen if the gas tank ruptured during an accident while it had max pressure -couldn't that cause it to release its pressure so violently that it would be a highly damaging explosion?

    Also, although I am not necessarily against the concept because I believe we should keep an open mind, with electric cars improving all the time, wouldn't electric cars make it become totally obsolete before they have a chance to mass-produce and sell these air-pressure-powered cars on mass? -even if I was a risk-taker, I would really hate to invest any money into this gambling that this will pan out. Peugot may have made a seriously bad investment here!
  2. Standard member sonhouse
    Fast and Curious
    28 Feb '14 14:42
    Originally posted by humy
    http://phys.org/news/2014-02-peugot-hybrid-cars-gas-compressed.html

    It is an interesting concept but, unless I am missing something, this appears to be a slightly flawed strategy as it would seem to be more cost effective to compress ordinary air i.e. air with 21% oxygen and the rest being mainly nitrogen rather than pure nitrogen that has to be purified at ...[text shortened]... into this gambling that this will pan out. Peugot may have made a seriously bad investment here!
    We use N2 inside some cylinders because it avoids the problem with water building up inside the pressure vessel. We have several compressors here at our plant and we have to take pains to get the water out of the compressed air because that leads to corrosion, rusting and it reduces the volume inside the cylinder, for instance, if the pressure vessel gets half filled with water, then if it was say 1 cubic meter internal volume, it would now be 0.5 meter^3 because it is half full of water. So we have to regularly drain our 'baby' compressors, they are small, only a few gallons of air storage and the water really screws things up in the pump and regulator and tank.

    So using just N2 avoids all that internal condensation.

    It also means you usually have to add some oil if there are cylinders involved that move back and forth under pneumatic power, 100% N2 also has the habit of drying up lubricated moving parts, seals and such so you usually add a device called an oiler that puts a very small mist of oil into the N2 to keep inner moving seals from drying out and losing compression.
  3. Subscriber Ponderableonline
    chemist
    28 Feb '14 14:47
    Originally posted by humy
    !
    A problem in using air could be the oxidising properties... The gas is presumed to stay in the cylinder all the time and is moved regularly by hydraulic fluid, whihc could be oxidised.

    The system described is for energy recuperation, meaning a limited amount of energy is won by braeking or idling and used later on.

    The concept of a compresssed air powered car was followed by "Aircar" around a decade before but went bakrupt.

    Today there seems to be some kind of interest group friming as Aircarfactory http://www.aircarfactories.com/ their last update was 2008
  4. 28 Feb '14 18:11
    thanks for the explanations. I now know.
  5. 28 Feb '14 19:09
    I had heard about Tata developing a compressed air only car a few years back but I see now that it has not yet got to market.

    I also notice that the picture of the Peugeot here:
    http://www.dailymail.co.uk/sciencetech/article-2568732/Car-runs-air-set-hit-streets-year-Peugeot-claims-new-hybrid-117mpg.html
    Was taken here in Cape Town - or was photoshoped onto a Cape Town background.

    It sounds like a good idea, as it gets the benefits of hybrid cars without the costs and problems associated with batteries. It might be much quicker to 'recharge' than electric cars. Also, many filling stations offer free compressed air
  6. 01 Mar '14 00:33 / 3 edits
    Originally posted by humy
    http://phys.org/news/2014-02-peugot-hybrid-cars-gas-compressed.html

    It is an interesting concept but, unless I am missing something, this appears to be a slightly flawed strategy as it would seem to be more cost effective to compress ordinary air i.e. air with 21% oxygen and the rest being mainly nitrogen rather than pure nitrogen that has to be purified at ...[text shortened]... into this gambling that this will pan out. Peugot may have made a seriously bad investment here!
    " ...if the gas tank ruptured during an accident..."

    Back in the days in the lab, it was universally believed that if a compressed gas cylinder fell over and the valve broke off, the cylinder would become a torpedo. I never saw one fall over.

    But watch this:

    https://www.youtube.com/watch?v=ejEJGNLTo84

    I didn't listen to the audio.
  7. Standard member sonhouse
    Fast and Curious
    01 Mar '14 01:53 / 1 edit
    Originally posted by twhitehead
    I had heard about Tata developing a compressed air only car a few years back but I see now that it has not yet got to market.

    I also notice that the picture of the Peugeot here:
    http://www.dailymail.co.uk/sciencetech/article-2568732/Car-runs-air-set-hit-streets-year-Peugeot-claims-new-hybrid-117mpg.html
    Was taken here in Cape Town - or was photoshope ...[text shortened]... icker to 'recharge' than electric cars. Also, many filling stations offer free compressed air
    Free except for the part where you would need 100% N2, not air. We already went over the problems using STP air, too humid and too much O2, spells oxidation disaster to metal parts and the compression tank.

    What about the idea of having a roof covered with PV cells and you use the cells to power a compressor that compresses the N2. Not sure how that would work. You would have to have a couple of tanks, one filled with enough N2 that you could compress it further into a higher pressure tank for driving. The problem is N2 has to by it's very nature be a closed system, you don't get N2 by itself. So you would have to have an N2 supply tank and a compressor system that compresses the stock of N2 into a higher pressure tank which would go to power the motor (turbine?) then back to the low pressure tank. Sound like too complicated. When they amp up batteries it seems like electric would be a lot less complex. But batteries right now don't have enough power density to do a car for 400 or 500 Kilometers. Maybe in 10 years.
  8. 01 Mar '14 05:28
    Originally posted by sonhouse
    Free except for the part where you would need 100% N2, not air. We already went over the problems using STP air, too humid and too much O2, spells oxidation disaster to metal parts and the compression tank.

    What about the idea of having a roof covered with PV cells and you use the cells to power a compressor that compresses the N2. Not sure how that woul ...[text shortened]... ht now don't have enough power density to do a car for 400 or 500 Kilometers. Maybe in 10 years.
    Need to factor in the option of starting with liquid N2. It is the immediate output of the distillation of air, and is dry. The O2 byproduct should help with the economics. Maybe this is the plan?
  9. 01 Mar '14 11:18
    I have not been able to find out just how far these cars can travel on just compressed nitrogen, so I am not sure what the benefits of 'filling up' would be. But lets assume it would be beneficial.
    Maybe you would hook up a motor to the car and it would compress the cars tank using the same mechanism the car currently uses. I don't know how long such a process would take. Would it be faster than recharging batteries? If so, would there be problems supplying enough electrical power to drive the system?
  10. 01 Mar '14 12:59
    Originally posted by twhitehead
    I have not been able to find out just how far these cars can travel on just compressed nitrogen, so I am not sure what the benefits of 'filling up' would be. But lets assume it would be beneficial.
    Maybe you would hook up a motor to the car and it would compress the cars tank using the same mechanism the car currently uses. I don't know how long such a p ...[text shortened]... batteries? If so, would there be problems supplying enough electrical power to drive the system?
    For liquid N2:

    "For an isothermal expansion engine to have a range comparable to an internal combustion engine, a 350-litre (92 US gal) insulated onboard storage vessel is required.[7] A practical volume, but a noticeable increase over the typical 50-litre (13 US gal) gasoline tank. The addition of more complex power cycles would reduce this requirement and help enable frost free operation. However, no commercially practical instances of liquid nitrogen use for vehicle propulsion exist."

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

    It is hard to believe that expansion of compressed nonliquid N2 could exceed this, but if O2 is the desired product of distillation of liquified air, the economics could be boosted.
  11. 01 Mar '14 14:12
    Originally posted by JS357
    "For an isothermal expansion engine to have a range comparable to an internal combustion engine, a 350-litre (92 US gal) insulated onboard storage vessel is required."
    The car is a hybrid, so it doesn't need to have a compressed N2 range comparable to a typical combustion engine car.
    In the past year, I have never once driven my car from full tank to empty. In fact, I typically don't even fill the tank full. I have known people who hardly ever fill their tank over the quarter mark.
    On a typical trip I do about 10km which is about 1/40th of my tank (and my car isn't very fuel efficient).
    So, if I could go 10km on compressed N2 only, I could manage 90% of my trips without petrol at all.
  12. Standard member sonhouse
    Fast and Curious
    01 Mar '14 14:56 / 1 edit
    Originally posted by JS357
    Need to factor in the option of starting with liquid N2. It is the immediate output of the distillation of air, and is dry. The O2 byproduct should help with the economics. Maybe this is the plan?
    That would be very difficult to implement in a car. The fact that you have a source of liquid N2 is great but that is in effect the nitrogen battery. So you either have a one use affair or you have onboard an N2 liquification machine that can take the room temperature N2 back to liquid, I seem to recall something like 80 degrees Kelvin or so, the amount of machinery involved would weigh more than the car I fear. If it could be done in a package the size of a breakfast toaster, fine, but if the equipment would only fit on the back of a pickup truck you would be in deep doo doo trying to get that to work in a car

    Also, you have to have a means of heating the N2 to room temperature or at least to gaseous form, maybe you could get by using it at say 100 degrees kelvin but that would have its own set of problems with mechanical devices having to work at those temperatures.

    The only use of liquid N2 I ever saw in terms of machinery was a report of a bottle of liquid N2 being used as a refrigerant in an aircraft air conditioner.

    That worked really well because the flights would last maximum 12 hours and the N2 capacity was able to accommodate that use.

    In a machine for transport, there would be a lot more energy expended than in a simple air conditioner so it just seems like too much trouble engineering wise to implement in a car.

    I am quite familiar with liquid N2, a plant I used to work for had a giant N2 tank some 20 feet tall and we had a service come and fill the liquid N2 about once a week. In order to have room temperature gaseous N2 we had to have a heater system that was a huge radiator affair whereas in a car the radiator wants to suck heat OUT of the system, this radiator used outside air to put heat INTO the incoming liquid N2 and it worked even in the dead of winter because even at zero degrees F that represents a super hot temperature compared to liquid N2! So the plant had a continuous supply of room temperature N2 which was used all over the plant for pneumatic cylinders, N2 injection into wafer furnaces and the like.

    The N2 generator system was extremely large and multifaceted however.

    We had the same thing for liquid oxygen but that system was about half the size of the N2 one because we used much less O2 in our work.