I build electric bicycles and scooters as a hobby, and have briefly toyed with the idea of using liquid Nitrogen as a power source.

Liquid nitrogen can be stored relatively easily. I've seen engineers with older design thermal cameras arrive with a thermos flask slightly unscrewed and full of liquid Nitrogen.

Futhermore, one of these stuck his finger in quickly to show that the Nitrogen does not stick like liquid helium.

The idea is to store the Nitrogen in an insulated container which is pressure regulated to approx 10 bar. Excess pressure is boiled off through a relief valve, thereby keeping the Nitrogen cold.

When power is required, a valve lets the Nitrogen gas from the top of the container out through a heat exchanger to fully expand the gas. The gas then drives a compressed air motor which supplies power to the Bicycle.

I made some calculations in the past, and I remember that I would need about a gallon of Nitrogen for about 30 mins of use.

I dismissed the idea at that time in favour of battery storage, but Nitrogen does have advantages: Instant refill, no need to change cells after 500 charges, easy to see remaining capacity.

The disadvantages are that the bicycle cannot be stored in a sealed room, Nitrogen is not exactly available in everyones home, risk of cold burns, cannot use well in cold climate and the energy density is not good.

I didn't consider power density.

Anyhow, I think it is possible to do it.
-- Ling, Jan 17 2004

LN2000 http://www.aa.washi...CRYOCAR/CryoCar.htm
[Fussass, Oct 05 2004, last modified Oct 17 2004]

CoolN2Car http://www.mtsc.unt.edu/CooLN2Car.html
Plummer et al. Built a compressed air bike too [thisispeterstanley, May 26 2007]

Pneumatic locomotives http://quasiturbine...ocoValen030908.html
Thermo-Pneumatic Quasiturbine Locomotive [TIB, May 26 2007]

theaircar http://www.theaircar.com/
compressed air motor [M Carter, Jan 20 2008]

Some one has made a liquid-nitrogen "steam" engien - however, it was table monted. :(
-- my-nep, Feb 25 2004


I have a vision of a bicycle's back wheel doing sudden half rotations while accelerating from rest, to the sounds of chuff, chuff....... [my-nep], do you have a link?
-- Ling, Feb 26 2004


Interesting! Years ago I thought of a design for propelling a small vehicle, but using a cylinder of liquified CO2 to drive a "motor" similar to those used in compressed air powered tools. Admittedly I don't know how to calculate the available energy from, say, a cubic foot cylinder (although it can't be very difficult and intuitively it would seem to be a fair amount, considering the volumetric increase from the phase change - too bad the change in temperature couldn't also be converted to useful energy too!). This would have the advantages of CO2 being readily available, easily transportable, no waste to keep itself cool, no problem in a sealed room, and little chance of cold burns. I wouldn't think the efficiency would drop a whole lot in cold climates (isn't the liquification pressure of CO2 at room temperature around 800 psi?) My only concern was of course the worst case scenario of catestrophic failure, which would turn the apparatus into anything from a rocket to a bomb.
-- WindPwr, May 25 2004


[Fussass], thank you very much for the link. It's reassuring to know that I'm not raving mad.
-- Ling, May 26 2004


As a quick note, the cold temperature could be used to create electrical energy using a peltier junction or sterling engine.
-- nathanEE, Jan 25 2005


What about a compressed air asisted bike. In this design a compressor (which also acts as a brake) is built into the rear hub. The compressed air is piped to a storage tank (two paint ball gun tanks mounted on either side of the front wheel would do) and when power assist is needed the compressed air is valved into a pheumatic motor enclosed in the front hub. This comes originally from an "April Fools" article written by Dan Henry for "Bicycling" magazine in the sixties. This machine is not intended to provide long distance effort free riding, but rather to smooth out the hills and increase the efficiencey of the machine by using energy that would otherwise be thrown away to heat the brake pads.
-- Shiboleth, Dec 14 2006


//The disadvantages are that the bicycle cannot be stored in a sealed room//

How come? The weight of one gallon of liquid nitrogen is less than 7 pounds. Evaporate all of it, and that will displace about 9% of the air in a room ten feet on a side. No problem.
-- ldischler, Dec 14 2006


Ling, seeing as your also a bike builder, I just wanted to point out that I have an 80cc 2 stroke on my mountain bike with a clutch and it gets me to 35+km/h and about 300bpm on my heart. My neighbors think I'm insane.

These motors give you about 125mpg and are very fun and inexpensive.

Just thought you would find it interesting :/
-- Giblet, Dec 14 2006


Giblet, I know the feeling. I rebuilt a cyclemaster, which was a two stroke inside the backwheel, and put it on an old Raleigh which had pull-rod brakes with very hard pads.
The available controls were:
Left brake
Right brake
Back pedal brake (absolutely required!)
Hand clutch on left
Thumb Throttle on right, with latch

Coming up to a junction was 'comical'. I actually got it through an MOT (English test for road vehicle worthiness), and it made the tester's day. Finally it was sold on ebay for a few hundred quid.

ldischler, I take your point. Assumption is the mother of all cock ups.

Shiboleth, thanks for the comments. I think your idea has been previously discussed in some form on this site, and I know that there have been suggestions to use the frame itself as a reservoir. I'm not sure if anyone has ever done it, however. I expect it could be done, but I wonder how many seconds the acceleration would last.
-- Ling, Dec 15 2006


I think you are right Ling. No one has ever done it. The article by Dan Henry (it was supposed to be a spoof) did propose storing the compressed air in the frame, but I think this is impractical because the frame is just too open. For instance, holes are drilled inside all the joints so that the frame will drain after being dipped in treating fluids and how would one seal the crank hanger or the seat post or the head post where the stem goes through. On the bright side I just looked up paint gun air tanks and some of them hold incredibly high pressures up to 4500 psi which I think is over 300 BAR. Wow! that'll blow your socks off! They also sell filling stations so you could charge your tanks before you hit the road.
-- Shiboleth, Dec 15 2006



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