Electric Car? How about a Compressed Air Car?

On 21 Nov 2007 01:06:18 GMT, James Robinson wrote in
:

[snip]

Thank you for providing the information upon which your opinions are
based. It's refreshing to get the opinions on electrical vehicles of
a professional electrical engineer. Thank you for your contributions
to the debate.

I got pretty cynical about claims of energy saving after listening to all
the people who came to our company trying to sell various products that
guaranteed huge energy savings or emission reduction.

There are the snake oil salesmen who have the magic potion that can be
added to the fuel tank to virtually eliminate air pollution, plus it will
double engine life as a side benefit. I wonder why GM hasn't heard of
them? The people with a black box you simply have to hook up to the fuel
line that will absolutely, for sure, pay for itself in fuel savings many
times over, but they won't tell us what's inside it, or how it works,
because it's a company secret. You can trust us; The people who have
special ceramic magnets that can be put on either side of the fuel line
near the engine to align the fuel molecules so they will pass through the
injectors more easily, and therefore burn more efficiently; the people
who resurrect old ideas like water injection, without realizing why it
worked to increase power, but also why it won't improve fuel consumption;
I remember one person who claimed that when he applied his device to an
engine, the horsepower jumped by 20 percent, and he had dynamometer test
results to prove it. The only thing was that when he fudged the figures,
he forgot that RPM times torque equals Horsepower. The horsepower
certainly showed a jump in his test results, but when there was no
associated change in torque or RPM, it completely blew his credibility.
etc. etc. etc.

A new salesman with a new twist would appear at our door about once a
month, so we got lots of practice. It was sometimes really difficult to
keep a straight face during their presentation. After listening to their
pitch, our usual approach was to tell them to go to one of the reliable
engine testing labs and do a standardized test, and if the product worked
as claimed, we would buy all they could sell. We'd never see them again,
but some would even protest that we wouldn't see any improvement by
performing the tests, since the tests were wrong, and we should trust
their claims instead.

Just like the salesmen and women would appeared at our door, I just say
you can trust my calculations.

Ah. This explains your apparent cynicism.

So, let me see if I understand your position correctly. You believe,
that from a physics viewpoint energy recovery through regenerative
braking is marginally useful at best, that the current state of
technology cannot enable the production of useful electric vehicles,
and the emerging popularity of hybrid automobiles is just a vogue
based on marketing prowess? How far did I miss the mark?

[snip additional reasonable explanations]

and in heavy braking it
might be 10 times that required for acceleration. Consider that an
energy-efficient car might do zero to 60 in say 20 seconds, but is
able to stop from 60 mph in less than two seconds.

The prototype electric Mini Cooper and Tesla Roadster mentioned in
these links seem to do 0 to 60 mph in ~4 seconds:

http://www.teslamotors.com/performan...and_torque.php
The Tesla Roadster’s specs illustrate what it does (0 to 60 mph in
under 4 seconds)...

http://www.gizmag.com/go/6104/1/
In the MINI QED, this package offers a 0-60mph time of 3.7 seconds
and a 150mph top speed ...

Yes, that is true. However, they aren't selling those vehicles as
energy-efficient replacements for gasoline powered cars, any more than
Ferrari is trying to sell their cars for commuting.

While that may be true of the MINI QED (it's a prototype after all),
the Tesla Roadster IS being marketed as "high mileage" (as in MPG
presumably), as is apparent from the graph he

http://www.teslamotors.com/performan...tric_power.php
No More Tradeoffs
Up until now, if you wanted a car with amazing gas mileage, you’d
pick something like the leading hybrid; but when you pressed down
the gas pedal to zip up a freeway on-ramp, you'd likely be a
little disappointed — it takes over 10 seconds to reach 60 miles
per hour. On the other hand, if you demanded the 0 to 60 times of
a $300,000 supercar, you'd wind up with an embarrassing 9 miles to
the gallon in the city.

The graph below shows the Tesla Roadster (upper right) in a class
by itself with better acceleration than a Lamborghini Murcielago
and twice the mile-per-gallon equivalent of popular hybrids. The
highly efficient Tesla Roadster gets the equivalent of 135 miles
per gallon with an enviable 0 to 60 time of less than four
seconds.

And if the GM Volt (solely electrical propulsion) ever materializes,
it is also being marketed as "energy-efficient replacements for
gasoline powered cars" with "responsive acceleration" as stated he

http://www.greencarcongress.com/2007...evrolet-v.html
Comparing the fuel costs between old and new methods of
propulsion, GM estimated that driving costs in EV mode would be 2
cents per mile&mash;or 1 cent per mile if charged
off-peak—compared to about 12 cents per mile per gallon of
gasoline for a typical car today.

[snip]

The designer of a vehicle knows that the cost of the motor and control
system varies in about direct proportion to the power to be handled.
He would have to determine whether it would be economically reasonable
to provide a motor that is ten times the size and cost needed for
acceleration just to capture all of the small amount of braking energy
available.

That statement reveals a fundamental misunderstanding. While it may
be true that the active semiconductors may need to be sized for the
peak current, that reasoning is inappropriate for the motor and
conductors.

Yes, motors and conductors can be overloaded for a period of time. I am
well aware of short time ratings, since we rely on those on the machinery
in my business. My assumption is that they would normally be sized in a
car for typical acceleration and the power demand at constant speed to be
economic. The need to collect power at a minimum of ten times those
values suggests that they would have to be upsized to handle the power of
regeneration. There is no free lunch.

But there is a liquid cooling system designed in both the Tesla
Roadster, and the GM Volt, so "upsizing" may not be necessary.

For a real-world example, look at the current hybrids. They use
friction brakes at highway speeds, and do not recover braking energy
regeneratively,

Where did you get that idea?

http://www.toyota.com/prius/specs.html
Brakes Power-assisted ventilated front disc/rear drum with
Anti-lock Brake System (ABS) and integrated regenerative braking

Maybe I should have said that they primarily use friction brakes, with a
minor contribution to regeneration.

I'm unable to provide any research about the percentage of energy
recovery achieved through regenerative braking, but it appears to
theoretically very doable given the fact that the MINI QED is not
equipped with friction brakes at all, and solely relies on
regenerative breaking for deceleration; it needs to be chocked when
parked!

Otherwise, why are ventilated disc brakes even necessary?

I could speculate: For consumer acceptance. To meet government
standards. Lack of imagination. ...

My understanding is that the vast majority of
braking power at highway speeds is dissipated as heat, rather than being
recovered as energy.

Are you able to provide any evidence of the validity of that
understanding?