> Russell, whatever happened to storage of energy by compressed air? 
> Or by
> inertial energy (a spinning weight) ?
> Since the issue for vehicles is really just THAT, storage of energy 
> in
> some form. I seem to recall an American city trying 
> inertially-driven
> buses for public transportation.

A key issue for vehicle transport is energy density (per mass and per 
volume) and most technologies struggle to compete economically (or at 
all) with the densities achievable with Hydrocarbon fuels.

Hydrocarbons such as petrol and diesel achieve around 10 kWh/kg and 
similar per litre.
Hydrogen is about 36 kWh/kg but has abyssmal volume density in most 
storage forms. (Compressed the containers get heavy. Absorbed is not 
too mucvh better and in chemical combinations it's still below 
hydrocarbons.)

Compressed air is bad on most density counts and it's hard to release 
the energy efficiently and it generally needs multistage expanders to 
do so.

Flywheel systems have their place but the speeds and masses needed for 
decent amounts of absolute energy place severe demands on materials. 
At the requisite speeds the stresses are severe and a high tech 
flywheel explosion is something you don't want to personally 
experience. Imagine ALL the energy in a tank of petrol being liberated 
inside a vehicle in a tenth of a second or so. That's approximately 
equivalent to the same mass of high explosive being detonated. :-(.

> I know that compressed air is the "starting fuel" of choice for the
> starting of ships' huge diesel
> engines; nothing else is able to start such huge cylinders, yet a 
> blast
> of compressed air turns
> them over in a twinkling of an eye.

In that context it's torque* rather than absolute power that counts. 
If you can inject air into a cylinder with a piston at tdc at quite 
modest pressures it WILL turn over. Most motors rely on higher torque 
and lower speed to produce power and require extra gearing etc to 
match their characteristics to the starting of a large prime mover. 
[[ Power (Watts)  ~= torque (kg-m) x RPM. ]] Infinite torque at no 
speed is "not much power :-)" (tm)  but helps heaps to get things 
moving.


> I think if platinum is a REQUIREMENT for fuel cell cars, only 
> wealthy
> people could afford to
> buy them. 'course, its almost at that point now for gasoline-fueled 
> cars...

Not much Pt is required per cell. But, worldwide, there's not a truly 
vast amount available.




        Russell

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