Can compressed air run a dynamo which generates electricity to run a car?

Question

Can compressed air run a dynamo to generate electricity which runs a car and then replenish the battery ?Could the motion of the car be used to compress air to make the system totally self contained ?

Answer 1

Why suffer the losses by converting the mechanical energy to electrical energy and then back to mechanical energy? Simply use the compressed air to drive pistons.

Now, how much compressed air will it take to drive a car? Figure a car must expend an average of say 40 horsepower. I'm going to guess a small jackhammer exerts perhaps 4 horsepower and might run at 100psi, 50cfm. If so, a car would need something like 100psi, 500cfm. So for the car to run 100 minutes, it would need 100psi, 50,000 cubic feet. We can equate that to something more compact, similar to a high-pressure scuba tank - 3,000psi, 50,000/30=1,667cubic feet. This is a very heavy tank, perhaps a couple of tons, about 12-13 feet in diameter.

Hmmm, doesn't sound too practical..... but nice thought - 8^)

Answer 2

It is possible to make a car as you describe, but it would definitely not be a perpetual motion machine. Using the car's energy to compress air would slow the car down, so you would only want to compress air when you wanted to slow down (brake or deccelerate). Compressed air could be used to run a pneumatic motor directly, thus eliminating the electric motor.

If you can figure out a way to store enough compressed air safely and efficiently, to propel the car at reasonable speeds and accelerations for more than a 100 miles, then you might have a 'winner' of an invention.

.

Answer 3

Suppose you have a car with a small engine--fifty horsepower, and it's supposed to run for five hours on a compressed air 'charge.' And surprise: you'd need a fifty horsepower air compressor running for five hours to compress enough air into the tanks to run it for another five hours. Don't want to spend five hours at the compressor station? Well, let's see: ten minutes is 1/30 of five hours, so you could compress all of your air into the tank in ten minutes if your compressor was powered by a 50 hp x 30 = 1500 horsepower air compressor. I've never seen such a thing, but I'll bet it's impressive. They don't make air compressors that big. So why didn't anyone explain this when they said how great the compressed-air car was? Answer: they didn't know, and they hadn't thought it out. No such cars are in production, but there are outfits which would like you to give them money anyway.

Answer 4

There are actually some internal combustion engines which use compressed air to start them, instead of an electric motor.
Converting compressed air to rotary motion & back to compressed air is common. The issue is the inherited loss of energy anytime you convert one type of energy into another. The three stages of energy transfer you propose will each lose some efficiency, making the car require more power to operate.

Answer 5

Yes, it is definately possible. As pointed out the major limitations are power efficency and size/weight factors of storing the compressed air.

But instead of coming up with arbitrary values, we could actually calculate the volume a tank (1000 psig) would need to be to supply air for say 100 miles of travel at a constant velocity of 60 mph with sufficent gear reduction as to require a constant power requirement of 50 hp.


dW/dt = 50 hp(746 W/hp) = 37.3 kW

75 F ==> 23.89 C = 297 K

ds/dt = 60 mph ==> dt = 100/60 = 1.667 hr = 6000 sec

W = 37.3 kW * 1.667 hr = 62.166667 kWh * 3.6e6 J/kWh
= 2.238e8 J

This amount of work needs to be stored as PV potential energy because it is a gas.

/\(PV) = /\P * V + /\V * P = W
/\P = W
(Tank Pressure - Atm Pressure)*(tank volume) = W

1000 psi (1.013e5 (N/m^2) / 14.7 psi )*V (m^3) = 2.238e8 J

Therefore you need a tank with a volume of 32.476 cubic meters. Or a sphere with a diameter of about 6 feet across, which would probably be extremely heavy due to the pressures involved.

Now, if you lower the range and the power the car could work fine.

Answer 6

actually there might be a way to use the relief in yours advantage.... u have an air pressured tank that gives motion to the engine when going plain or up an you use the weight of the car when going down to refill the air tank. however u need a huge air tank and a low debit high pressure compressor. very close "gas" stations and a lot of free time to wait for the air tank to be refilled. Even if would be economic and ecologic it wouldn't be efficient and will cost you allot of time

Answer 7

a self contained system would be inefficient what u can do its to connect a turbine and use the exhaust gases to generate a small amount of energy to feed the battery to use a hybrid system.

but to run the compressor u must use a lot of energy and it will demand a big battery bank

Answer 8

use air to spin turbines to charge batteries

Answer 9

No. There is inefficiency and friction loss in every step you describe.