There are already proposals to use compressed air as a power soruce for cars.

These proposals fall down, in part, because compressed air has a much lower energy density than fuel and you either need huge amounts of storage space or extremely highly compressed air.

How about rather than using compressed air we use dry ice?

You pull into the gas station, throw dry ice into a hopper, close it and the dry ice falls through into a fuel tank.

As the dry ice melts, gas pressure builds and that powers the car.

You still wouldn't get as much energy as from a petrol engine but you could use it as the back-up in a hybrid system.

As an added bonus, on hot days you get airconditioning by pumping air through a heat exchanger inside the CO2 tank.

Update: it appears I've reinvented a device already used for model aircraft engines.

So I guess the question is whether the idea could be scaled up for use in conjunction with a hybrid engine.

The CO2 engine would run at a constant speed and power a turbine to recharge the batteries. The benefit of this would be the higher power density of the co2 as compared with batteries.
-- Iangould, Sep 28 2006

Davis CO2 Motors for Model Airplanes http://www.davisdie...evelopment.com/co2/
We didn’t invent the CO2 motor, it’s been around for over 50 years. [baconbrain, Sep 29 2006]

CO2 steam engine Stanley_20Dryer
Courtesy of [theircompetitor]. [Shz, Oct 03 2006]

Interesting.[+] Trying to get energy from cold things. Theoretically, you'd need to put more energy into it to get it to melt/expand than you'd get as work-energy expanding it. But, you have limitless ambient temperature to work with... And of course, it's a battery, more than a fuel, as it takes more energy to make dry ice than it does to submlimate or melt it.
-- sophocles, Sep 28 2006


I dont think it would build up the amount of presseure you would need to power the car.But if it would work that would be great
-- anewgeneration08, Sep 29 2006


One gram of CO2 occupies somewhat less than a liter at room temperature and atmospheric pressure. So the absolute maximum potential energy available for harvest would be about 100j/gram. Quite respectable--higher than gasoline even. Unfortunately, the only way to get all that energy out would be to add a lot of heat. To be sure, heating the CO2 to ambient would suffice, but it's hard to do that quickly without adding energy.

On the other hand...

If a vehicle used the dry ice in addition to some other power source which tended to produce excess heat, that excess heat might be used to assist in the efficient vaporization of the CO2.
-- supercat, Sep 29 2006


The difficulty I see is stability. You are filling your tank at ambient pressure, then as it sublimates the pressure is going to rise until all the solid is converted. I would see it as very easy to overfill the pressure vessel and have it burst on you.
-- Galbinus_Caeli, Sep 29 2006


CO2 motors already exist, at least for model airplanes. They use liquid CO2, as it is easier to handle and contain than is dry ice. Squirting liquid through a valve is a lot easier than sealing up a pressure hatch on a hopper.

There have been some studies done on using other cryo gases for powering cars. CO2 doesn't have as much oomph as does liquid nitrogen. I'll see if I can find my links.
-- baconbrain, Sep 29 2006


I Googled for "cryo car" and found that University of North Texas developed a car that runs on Liquid Nitrogen (LN) and called their car Cryo Car. University of Washington in Seattle, converted an old mail truck to run on LN. They called their truck LN2000.

There are descriptions of how CO2 engines work, at various places on the internet. Liquid CO2 makes a good "fuel", and is easy to handle. The engines are simple, too. Solid dry ice, on the other hand, is a pain, although possible to make work, I guess. Liquid engines have the advantage of being able to inject liquid into the "combustion" chamber, which gives a lot more expansion than does a puff of gas.

As was said above, it's going to take energy to collect and freeze CO2, so it will not be a savings in overall costs. But a hybrid is a good idea for using CO2.
-- baconbrain, Sep 29 2006


I can see this going a different way, you could couple the CO2 engine to a small gas engine. The infinite ambient temperature is the difficulty I see, not that it won't work, but it will take a lot of work to get the heat transfer you need. traditional heat transfer improvements could work against you as fins fill up with frozen condensation in humidity prone areas, but adding a small gas engine (even one or two cylinder) could provide additional starting torque, a warmup cycle and, as an added power boost, the CO2 could be circulated into the cooling jacket of the gas engine to boost the pressure just before injecting into the cylinder.
-- cblunds, Oct 02 2006


OK, totally off the top of my head: what about using liquid oxygen? That way after it expands you can use it in the gas engine as a sort of turbocharger. Although that would probably make it the most dangerous car in existence.
-- omnilynx, Oct 02 2006



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