The electric car killer?

This website is a bit more detailed for English readers.

http://www.theaircar.com/

 

<div class='quotetop'>QUOTE(vtie @ Jul 3 2007, 04:00 AM) [snapback]472127[/snapback]</div>

I guess the question is, how much energy is used to compress the air? Certainly that's lossy: aside from the "pumping losses" of air friction, compressing air heats it (Boyle's law?), and the heat is going to represent wasted energy. Every place I looked suggested that compressing air to 300 atmospheres (4500 psi?) would create a lot of heat. I searched for some clear calculation but found only internet chatter. But several plausible-sounding sources suggested that the energy available from the bottle of compressed air would be only about one-third of the energy that was required to compress it. Others said this would be one-third to one-half as efficient as an EV.

Yeah, here's a discussion with link to a citation suggesting 40% "compressor to wheel" efficiency for an air car versus 80% for an EV:

http://www.greencarcongress.com/2007/02/tata_motors_sig.html

So the issue is the amount of electricity required to compress the air.

Actually, that whole thread is a pretty intelligent discussion of the issues. For a familyi-sized passenger vehicle, range of an air car would be appear to be extremely limited. That matches what I read elsewhere, that the energy density of compressed air in standard steel containers is about the same as lead-acid storage batteries. (Ignoring the fossil-fuel option for this car.) So unless you devote most of the vehicle space to the batteries/air tanks, it won't go very far.

Other than possibly a low production cost, this would not appear to be a promising technology. It does not appear as efficient or practical as an EV.

Although, to tell the truth, I did not grasp how you could stretch 80 km range to 1500 km range by heating the air on expansion. In fact, reading between the lines, I'm pretty sure that what you have at that point is just a tiny, light car with an ICE. Again, reading between the lines on their website, they couldn't make this work in a traditional (read: crash-worthy) heavy steel-body car, so the car is fiberglass over tubing with carbon-fiber air tanks.

So, to unscramble what they say on the website: This is a small, ultralight fiberglass-body car using some exotic materials (carbon-fiber tanks) that can go 50 miles (80 km) on compressed air. And, you can use the engine as a traditional ICE and get great mileage because the car is small and light. (I did not see specifications on the weight of the car.)

All of that makes sense to me, and suggests no great breakthrough, just a particular set of choices in the engineering of the vehicle. On air power alone, it's an ultra-light limited-range vehicle. With the ICE running, it's an ultra-light high-mileage vehicle. It's the air-power equivalent of the PHEV (air + ICE instead of battery + ICE). Only the air-powered portion of it is not as efficient as the electric portion of a PHEV.

 

You could alway compress the air using a hand pump everytime you ran out. I like the new idea, but I don't think this better or a break through. If you could liquify the air then fine that would be some storage, but your not going to do that with a plug in.

 

<div class='quotetop'>QUOTE(vtie @ Jul 3 2007, 08:45 AM) [snapback]472178[/snapback]</div>

Adiabatic heat generated from compression is the same no matter what the compression speed. Compressor efficiency and speed are factors that can be controlled to some degree, but adiabatic losses are fixed unless you find some way to keep the heat from escaping, which is not practical over anything but short time periods.

Tom

 

This to me is a very interesting concept. The price they are looking at will make it very competitive. If they start selling it here, and there is no EV on the market then this will be my next car. It doesn't have the creature comforts I want in a car but it's still a promising city car

 

<div class='quotetop'>QUOTE(vtie @ Jul 3 2007, 11:39 AM) [snapback]472282[/snapback]</div>

True. Either way you are going to have a hard time doing anything useful with the heat energy as far as the car is concerned. If you have another use for it, that would be good, but you can't really figure that into the efficiency of the engine.

Tom

 

I see several major obstacles to a compressed air car.

• The United States Department of Transportation bans all air cylinders over 230 bar from being transported on public roads, regardless of rated pressure. For this reason 300 bar European scuba diving tanks are banned in the US.
• Every compressed air cylinder must be visually checked every year.
• Every compressed air cylinder must be tested in a hydrostatic (underwater) chamber every 5 years. This would mean the tank must be completely separated from the car and tested in equipment that car shops do not possess and would probably be too large for scuba shops to handle.
• In the event of a catastrophic failure while fully charged (Read: a high-speed accident), "The explosive potential in a fully charged 80cf aluminum SCUBA cylinder is approximately 1,300,000 foot pounds -- enough to lift a typical fire department hook-and-ladder truck over 60 feet in the air," claims scuba inspection expert A. Dale Fox.
• Heat is a big issue when filling a compressed air cylinder from a compressor. I don't have the calculations handy, but to compress enough air to fill a cubic yard with 300 bar (4350 psi) in 5 minutes would require a MASSIVE active heatsink.
• One of the things that appeals to me about electric cars are their silent operation. Wouldn't compressed air be just as loud as a traditional ICE?
• Another draw of the electric car is it can be charged at home with minimal investment in solid-state recharging equipment. To buy an electronic air compressor rated at 200 bar is about $1500 USD, plus it has moving parts and must be serviced (and probably certified) as often as a tank.

 

I agree that this is far from a perfect car. All that said I still think it can be built cheaper and even with higher operating costs I think it wil be a very affordable alternative fuel car.

 

<div class='quotetop'>QUOTE(Elephanthead @ Jul 3 2007, 07:07 AM) [snapback]472229[/snapback]</div>

I have a Logun S-16xs pre-charged pneumatic airgun that takes a 400cc air cylinder (that's 0.014 cubic feet) and is rated at 200 bar. I also own a $200 Air Venturi hand pump with a fairly substantial heatsink to relieve all the heat that's generated. It takes between 10-15 minutes to get the tank up to pressure. By the time I get to 160 bar I'm having to put my entire body weight (145 lbs) into pumping. It's definitely good exercise.

 

I've been watching MDI for about 8 years now. I don't personally believe they're any closer to offering a vehicle now than they were then.

 

http://www.popularmechanics.com/automotive...rs/4217016.html

Here's another link to the same technology going into production in India.

 

<div class='quotetop'>QUOTE(Mick @ Jul 3 2007, 04:01 PM) [snapback]472491[/snapback]</div>

The French patent holder has partnered with Tata, a Indian car company to build the car.

 

<div class='quotetop'>QUOTE(jhinton @ Jul 3 2007, 02:17 PM) [snapback]472509[/snapback]</div>

Perhaps you are seeing a solution for transportation of the 1 - 2 billion Indians and Chinese who are waiting for a car they can afford? 1 - 2 billion new cars based on current ICE technology will put us into terminal global warming territory....

 

<div class='quotetop'>QUOTE(apriusfan @ Jul 4 2007, 12:17 AM) [snapback]472797[/snapback]</div>

Though, perhaps not. ICE's don't produce GHGs when they can't run because oil costs $300/barrel. Global oil production has basically been flat, adding that much demand would cause a MASSIVE spike in the price of oil.

It seems this is a idea worth exploring. If it works, great. It's just one more solution to our problems. The tank safety issue would take a while to overcome. The carbon fibre tanks have been used for H2 compression and the state of the art ones are, I think, 700bar tanks (10K psi). You can shoot one with a .50 cal (12.7mm for everybody using that "crazy" metric system :lol: ) and they can take it. 0.50 cal rounds are BIG. I can't imagine an auto accident that could equal the concentrated force (that's stress right?) of one of those rounds. Still, a catastrophic failure would be... ugly. So how much energy does it take to fill one of these tanks?

 

<div class='quotetop'>QUOTE(Alan D @ Jul 3 2007, 04:12 PM) [snapback]472462[/snapback]</div>

I can only assume Mr. (?) Fox based that statement on the straight-up calculation of 1.3 million divided by the weight of the truck (in pounds) = distance of travel (in feet).

His argument would be easier to accept if he described the energy potential in terms of horizontal motion (60 ft. forward on level ground) or as applied to some sort of closed-circuit system (truck on a pneumatic lift?). As is, the terribly impractical nature of his (dramatic) scenario overshadows any technical value it might have.

I don't think they meant to suggest real-time compression. They are transferring compressed air from another (larger) tank into the vehicle's tank.

I'm sure you're right about the source tank's compressor having a large heatsink. We should also keep in mind that the compressor can be sized more in line with average flow rate requirements; so long as the storage tank has enough capacity to meet peak demand, the compressor doesn't have to replace the dispensed air in real-time.

Howstuffworks has an article describing air-powered cars (http://auto.howstuffworks.com/air-car.htm). They claim the e.Volution model they feature can travel up to 124 miles (200 km) on 79 gallons (300 liters) of air, at a top speed of 60 MPH (96.5 km/h). (Above 60 MPH, it runs on fuel instead of air.) Imagine owning a vehicle that gets 1.57 MPG (of air) and feeling good about it! :lol:

- Justifyd

 

<div class='quotetop'>QUOTE(tripp @ Jul 4 2007, 11:06 AM) [snapback]472969[/snapback]</div>

$300/barrel oil would actually help address the GHG emission issue in a major way - it would shut down all manner of processes that use petroleum as a feed stock. Nothing like a carbon tax....