Compressed Air car?

This has been discussed before.

Note that compressing air generates heat. Lots of it. And compressing that much air will produce an awful lot of heat. Unless you have some use for a large amount of very low-grade heat, it's wasted.

In winter that heat could theoretically be used to heat the house. But the car's in the garage, and the heat is produced in the air tanks in the car, which would complicate matters greatly.

You rise a very good point about the noise. All night long!

Question for scuba divers: How long does a tank last? But these tanks are holding a lot more pressure, I presume.

 

I saw the Futurecar program too.

It did not make sense. They said to make a compressor engine to compress the air. And use the air engine to power the car and the compressor engine. Hence the car will never need to be refueled.

Uh... what kind of science is that? There is no such a thing as free energy.

Did I miss something?

 

<div class='quotetop'>QUOTE(dipper @ Feb 23 2007, 02:49 PM) [snapback]395496[/snapback]</div>

Yes. What you missed is that you plug the car into an electrical outlet to run the compressor. You never need to put gasoline in it.

 

<div class='quotetop'>QUOTE(daniel @ Feb 23 2007, 05:10 PM) [snapback]395478[/snapback]</div>

They will usually top your tank off at 2000-2500 PSI, some less legit places in the Caribbean will do 3000 PSI. How long it lasts you really depends on how good of shape you’re in, and your activity level when you’re down there. But I think what you meant to ask was how long they take to refill, I’m not exactly sure, and I couldn't find the answer online.

Needless to say, 4500 PSI is ALOT of pressure. To give an extremely rough comparison, my parents own a contractor-grade air compressor, and its two tanks equal about one scuba tank. It takes 3 minutes for it to fill from 0 to 150 PSI.

So, as other people have mentioned, there are a lot of downsides to it such as refill time, noise, and heat loss. I saw the show last night as well, and I think the most important thing to remember from it was when the narrator said, in reference to hydrogen "Hydrogen is the means of storage of energy, not creation". All of these systems, be they electric, hydrogen, or air pressure depend on the electric grid. The whole utopian idea though, is that we can eventually use clean sources of power as we perfect Solar, Wind, Wave, and dare I say nuclear power.

Another benefit to the air tanks over electric, is that while the tanks do take time to be recharged, it’s conceivable that they could be swapped out. You could go to a refilling station and have them swapped out for full ones on a long trip, much like pool owners trade out their empty chlorine jugs for new full ones (instead of refilling their old ones). This is all really hypothetical though.

One idea similar to the compressed air is compressed water, or hydraulics. It is possible to make a vehicle that, when breaking, compresses hydraulic cylinders. Think of it like mashing down a metal coil spring. When the power is needed (for acceleration), the hydraulic cylinders expand, pushing the vehicle forward and letting the engine slowly (and efficiently) come online. Not only is the engine stressed less under acceleration, but it can be weaker since so much acceleration is provided by the hydraulic cylinders. Both of these factors would improve mileage and emissions. Here is an example of this tried on an F150: http://www.allheadlinenews.com/articles/7002397595

and another: http://www.fordmuscle.com/blog/ford-to-bui...mpg-f150/112114

 

<div class='quotetop'>QUOTE(Stepclimb @ Feb 23 2007, 08:04 PM) [snapback]395560[/snapback]</div>

Amen to that. I cant help but think that switching directly from gas guzzlers to hydrogen is a bit much. Thats like a 6th grader saying "ah forget high school, im gonna take most of those subjects again in college anyways. Ill just go ahead and skip to the university". It also seems as though it could be a bit of a bait-and-switch trick, but I try to avoid pessimisim like this.

 

<div class='quotetop'>QUOTE(Jonathan Rohr @ Feb 23 2007, 03:17 PM) [snapback]395508[/snapback]</div>

NO! My question was, how many years or fills is the tank good for before it is considered unsafe to hold the pressure? That's the time after which you'd have the expense of installing new tanks. Does your scuba tank last forever? Or do you need to replace it after some number of years or dives?

The 3-minute fill assumes availability of very high-pressure air pumps at sufficient locations. At home it would take several hours.

The compressed-air engine would be roughly as complicated as a steam engine: pistons, valves, some sort of control mechanism to regulate acceleration, etc. By contrast, electric motors are simpler and more reliable.

 

<div class='quotetop'>QUOTE(daniel @ Feb 24 2007, 11:22 AM) [snapback]395784[/snapback]</div>

3K 4K 5K psi tanks can be filled in a water tank to keep them cool. (Used to dive commercially for Disney) They can be filled within a few minutes, this way. They have to be visually & hydrostaticly (sp?) tested every couple years (at least back in the 1990's). They don't last hundreds of thousands of refills (but yes, SOME do). They loose some of their ability to take a full charge (safely) after time, so the tank gets re-rated to something like an 80-90% refill standard. Usually after 8-12 years, the tank will fail the tests and can't be refilled any longer. The failure rate doesn't necessary turn on whether the tank is refilled 2X / year, or whether it's filled every day. But some DO last a long time. I had one set of twin 38's that was manufactured in the 1940's ! ! ! but that is not the norm. Lastly, the carbon fiber tanks have a rated life too. I've seen a few used on Disney's jungle boats in the scrap bins ... sawn into pieces.

 

Hi All,

No, you cannot compress water, oil or any liquid. That is actually the advantage put to good use in hydraulics. Hydraulic Hybrids use a compressed gas accumulator tank. Mechanical springs cause small area loads that are much more problematic to build mechanical structures to resist. Gaseous springs distribute the spring force evenly around the inside of the container resulting in a practical tank design.

As to quick recharging of compressed gas pressure tanks one could concievably catalytically combust a fuel air mixture, if one had a fuel/oxidizer pump that would exceed the storage pressure required. Combustion at high pressure would probably be much more complete. But, one would have to avoid hydrogen in the fuel, as the water would condense. So, one would need a liquid fuel that would combust catalytically, without hydrogen, and for which the combustion products would be inert, and dischargable. Not sure what that is. Too bad carbon has such a high melting point, but then that might aid the complete combustion. Might call it the Tar-Car or the Toner-Car? Run the car of a mixture of Oxygen and Carbon Black dust (aka Xerography Toner).

Scratch that. Just use liquid Nitrogen. Pump it up to high pressure, and through an electric heater and into the accumulator. That works for quick recharge, but not where the energy is going to come from.

 

I wouldn't want to be around if a 4500psi tank ruptures in an accident.
http://biobug.org/scuba/scubatank/
Scroll about half way down.

 

Okay, so the tanks are probably not a serious problem. I still suspect the mechanics of an air car would be more complex than an EV. Darell could certainly tell us everything we want to know about maintenance costs and component lifetimes for an EV.

There is (or was, I think) actually a nitrogen car prototype. They call it a cryogenic engine. It uses liquid nitrogen. The liquid nitrogen is boiled by ambient air, and otherwise it works basically like a steam engine: The nitrogen gas replaces the steam. The energy input is the point where the nitrogen is liquified. (Compared to a steam engine, which gets its energy from the on-board burning of fossil fuel.) If the energy used to liquify the nitrogen were obtained from renewables, the car would be very environmental. I don't know how practical it would be. You'd need either a nation-wide system for distributing liquid nitrogen, or nitrogen compressors at every gas station (probably prohibitively expensive).

Back to the wasted energy of the air car: Even if you filled the tanks rapidly using water-cooling, you still have a lot of very low-grade waste heat. As long as gas stations will let you fill your tank for free, you can pass your energy costs on to them. But once they realize what you're doing, and what it's costing them for all that compressed air, they'll make you pay. So which is more efficient: grid to compressor to car, or grid to battery to car? I don't know. I suspect it may be a wash, with EVs being easier to maintain.