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The Air Car Nears Completion
torok writes "According to an article on Gizmag, Tata, India's largest automotive manufacturer, has developed a car that runs on compressed air. It costs less than $3 USD to fill a tank on which it can run for 200 to 300km. The car will cost about USD $7,300 and has a top speed of 68mph. About once every 50,000 km you have to change the oil (1 liter of vegetable oil). Initial plans are to produce 3,000 cars per year."
IC engines generate a lot of waste heat that can be used to warm the passenger compartment with little additional cost. On the other hand, IC vehicles need complicated a power hungry air conditioners to cool the passenger compartment during hot weather.
The compressed air powered car operates the other way around. Compressed air cools as it decompresses. The exhaust from this vehicle is below zero Celcius. That cold air acts as free AC. A heating system for a vehicle like this is going to be very expensive from a power consideration.
If these vehicles are not a scam then I think we can expect their adoption only in warm climates. In cold weather, I would not be surprised if the decompressed air freezes the components that transfer power to the wheels.
The French guy who invented the car has been working on it for years. The car has been announced several times before and they are able to produce working prototypes. This counts as one of those technologies that is almost there but there is some small, pesky, won't-go-away, details that keep it from being economic. In that regard, it is similar to the plant that converts turkey guts to oil. The process works but isn't quite there.
The best thing about this car is that air-conditioning is very easy and costs no energy. As the air decompresses in the engine, it cools off. Directing that air into the cabin would provide air-conditioning with just about no effort.
While I agree in principle, I'd be interested in the assumptions you used to reach that conclusion (e.g. how much energy it takes to move the machine a km).
The amount of energy needed to move a person that far is not that much. An average cyclist can produce something like 3watts/kg. A 75kg cyclist produces something like 225 watts; assuming he can travel at about 20km/h, we can put a lower bound on the energy needed to move a typical person 200km at 2250 watt hours.
Let's assume we have an engine that is as efficient as the rider (for setting the lower bound) and weighs as much as the rider. Lets suppose that we need twice the energy to move engine and rider the 200km. So we need 4500KWh.
Assuming that electricity costs $0.10/KWh, then such a machine would consume forty five cents to move a person 200km.
To put it in perspective then, the claim is that this car can move a person from place to place using only fourteen times the energy a reasonably fit cyclist would use.
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This is incorrect. SCUBA tanks are generally filled with plain old air, compressed to between 2500 and 3500 psi. The only thing special about the air is that it is dried and filtered -- dried so that the tanks don't rust and filtered because you don't want to breathe compressed crap that has settled out in the bottom over multiple fills.
Sometimes tanks are filled with other mixtures. One common recreational mixture is Nitrox, which is mostly regular air, but with some pure O2 added to increase the ratio of oxygen from its normal ~21% to a higher value, usually 32% or 36%. The reason for adding oxygen is to reduce tissue absorption of nitrogen, allowing for longer bottom times without risking the bends (though the higher oxygen ratio limits depth due to oxygen toxicity).
In technical diving, tanks are filled with mixtures of pure gases, rather than air. Helium is used to replace nitrogen, either entirely, making "heliox" or partially, making "trimix". Gas ratios are precisely tuned for the dive profile. Deep mixes use small amounts of O2, to avoid oxygen toxicity, and more helium, to reduce nitrogen absorption and minimize nitrogen narcosis. Shallower "deco" bottles may use all sorts of mixes depending on the decompression technique being used and indeed divers often breathe from two or more bottles during a single decompression stop in order to maximize the rate at which they safely offgas their absorbed inert gas load. For example, it's common for technical divers to breathe from bottles of pure O2 for short periods even at depths which would normally cause severe toxicity because doing so accelerates the offgassing of nitrogen.
Getting back to the question at hand, it does not cost $5-$10 to fill a SCUBA tank with compressed air, anywhere in the world. You may well *pay* that much, but that's not what it costs. Dive shops are small scale operations with enormous overhead, so they mark everything up by huge amounts, including air and gas fills. Were a typical shop's compressor to be run on an industrial scale, fills would be at least an order of magnitude cheaper. Take out the requirement for filtering (though drying is probably still a good idea) and it should cost even less.
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-Jay-
Compressed air is not a power source, since the energy has to come from some other source, such as electricity. Storing energy as compressed air is not a more efficient process than storing electricity inside a battery. There ARE electric cars today with more range than the Air Car. And they are not all ultracompact cars but some more reasonable formats. So we have already a technology that is simpler, proven, has better performance, it is likely to be much more reliable (fewer moving parts) and has constant performance (a vehicle run by compressed air will lower its performance as it runs out of "gas"). I'm not completely sure it is cheaper today, but it certainly will be as batteries progress (they have been progressing at a steady 10% increase in capacity or decrease in cost every year for the last few decades, it is expected that the trend continues). The Air Car is not so proven, and the manufacturing costs will surely go up as they near production (they always do). I'm not saying this project has no value, but investing the same money and effort in developing electric cars will certainly produce better results faster.
Well obviously, dumping a few heavy metals into the environment is preferable to releasing more CO2 into the atmosphere. I'd rather have mercury poisoning than live in a world that's a few degrees warmer. ;)