Re: Why settle for a measly 230 MPG when you could get 1560 MPG?

On May 23, 5:12 pm, dkomo <dkomo...@xxxxxxxxxxx> wrote:
Paul Ciszek wrote:
In article <v62dnaOgVouUfqnVnZ2dnUVZ_jedn...@xxxxxxxxxxx>,
dkomo <dkomo...@xxxxxxxxxxx> wrote:

From a post of mine some years ago:

-----------------------------------------------------------------------
I ran across this interesting little problem in a Schaum's Outline on
physics. The problem states that a bicycle rider can go 100 miles on
2000 food calories and wants to know how many miles per gallon of
gasoline that translates into.

A gallon of gas contains 1.3 X 10^8 Joules of energy, a food
calorie (sometimes called a Calorie) = 1000 calories and 1 calorie
is equivalent to 4.2 Joules. So 2000 calories is equal to G
gallons of gas, where:

G = (2 X 10^6 cal)(4.2 J/cal) / (1.3 X 10^8 J/gal) = 0.06 gal

which is slightly less than a cup of gas.

So the rider gets

100 mi / 0.06 gal = 1560 miles per gallon.

This appears to be a pretty efficient form of transportation. The
Asians, particularly the Chinese, discovered this a long time ago.
Everybody tools around on a bike over there.

This is really neat. Do you have an estimate of how efficiently
humans (or other critters) are able to convert food calories into
mechanical work? I.e., a person on a pedal-powered generator can
do so many joules of work for each joule of food energy they burn off.

I don't have such an estimate, but I'll use this opportunity to present
some mind boggling facts about the inefficiency of automobile
transportation.

It turns out that only about 1% of a gallon of gasoline is actually used
to propel an average driver down the road, and 99% is wasted. So if a
gallon of gas actually costs $10.00, it costs only 10 cents to move the
actual driver, and $9.90 is thrown away.

At first the energy efficiency of the bicycle rider seems remarkable
until you stop to consider that the rider is moving only himself and a
relatively light weight bicycle.

Now consider a 100 pound woman driving a 3500 pound car to the
hairdresser's. Of the combined 3600 pound mass, the woman represents
only about 3%. The rest of the 97% mass is the steel, glass, rubber,
leather and plastic of the car itself, and the energy burned in the
gasoline has to move the whole mass down the road. But the mission in
this example is simply to get the lady to her hairdresser's.

Amory Lovins in a Scientific American article, "More Profit with Less
Carbon", gives a more detailed breakdown of where all the energy in the
gasoline goes. He says that only 13% of the fuel energy even reaches
the wheels, the other 87% is either dissipated as heat and noise in the
engine and drivetrain or lost to idling and accessories such as air
conditioners.

But it's an heat engine. Extracting more than 20% - 25% of energy from
gasoline is probably impractical.
(I don't know whether fuel cells are considered heat engines too).

More than half the energy delivered to the wheels heats
the tires, road and air. Just 6 percent of the gasoline energy actually
accelerates the car, and all this energy is normally thrown away when
the car brakes to a stop, ending up mostly heating the brakes.

Or when a large, non-aerodynamic car speeds, most mechanical energy is
lost in countering the air drag.

Finally,
because more than 95% of the accelerated mass is the car itself, less
than 1% of the fuel ends up moving the driver.

Hybrid cars can get fairly dramatic increases in fuel mileage because
they shut off the engine when the car stops, and convert much of the
kinetic energy of motion into electrical energy stored in the battery as
the car brakes to a stop. Also, electric motors are themselves much
more efficient than internal combustion engines.

Given the huge role that the mass of the car plays in all this, it's not
too surprising that cars of the future will be made from carbon-fiber
composites which will allow those cars to weigh less than half of
today's cars and be just as strong in collisions as steel. Carbon-fiber
composites can absorb six to 12 times as much crash energy per kilogram
as steel does.

Lovins believes that the introduction of ultralight bodies could nearly
double the fuel efficiency of today's hybrid-electric vehicles without
raising their sticker prices. This puts the fuel efficiency of these
future cars somewhere in the range of 80-100 miles per gallon.

There are problems associated with lightweight cars however:
They are less comfortable to drive. They are more easily swayed by
wind.
Their performances (including stopping distance) decrease noticeably
as the number of passengers increase.
Of course if gasoline gets expensive enough these problems will not
matter.

--dk...@xxxxxxxx

.

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