On Feb 12, 10:35 pm, "The Pre-Meltdown Kid"
<entropic3.14de...@[EMAIL PROTECTED]
> wrote:
> Awl--
>
> Even tho "gasoline mpg's" may be obsolete with the advent of electric
cars,
> I thought it would be interesting to see at least what the upper limit
of
> gasoline mpg's are.
> The calcs reveal an additionally compelling feature about electric cars,
> namely that in addition to a myriad of other electric car advantages,
they
> operate under a *fundamentally higher thermodynamic efficiency*, because
the
> efficiency of a charging cycle of a battery is double-triple that of a
> Carnot-limited heat engine.
>
> My calcs and values follow--would be interesting to see what others
might
> get.
>
> The drag equation (http://en.wikipedia.org/wiki/Drag_equation)
is
> Force = .5 p v^2 Cd A
> p = density of air, v = velocity, Cd = drag coeff, A = net frontal area
of
> object.
>
> F x 1 mile is the energy needed to overcome aerodynamic drag for one
mile.
>
> A gallon of gas has about 131 megajoules.
> Net engine efficiency is about 32% (about 60% thermodynamic/Carnot eff,
and
> we realize about half of that).
>
> Aerodynamic drag supposedly accounts for 60% of the energy needed to
propel
> a car, at highway speeds.
>
> Using a CdA of about 5.5 for my Honda Fit (auto), at 65 mph, and the
60/40
> energy ap****tionment, I get a "theoretical" mpg of about 54.
>
> On an upstate drive, I was thrilled to achieve 46.4 of those 54 mpg's,
much
> better than Consumer Re****ts results.
> City driving, however, esp. with Yonkers hills, is not much better than
> 25-30.
> Hummers have a CdA of about 25, which means they consume 5 times the
> aerodynamic energy of my Fit.
>
> As stated above, perhaps the biggest energy hit occurs from middling gas
> engine efficiency, where 67% of the energy in a gallon of gas goes right
out
> the radiator/tailpipe--up the proverbial chimney. wow....
>
> And, another 40% of the paltry energy extracted from said gallon goes to
> sundry mechanical inefficiencies, likely consistent with the large
> difference between crankshaft hp and rear-wheel hp: Transmission
losses,
> driveline losses, sundry power-assists, etc.
>
> So from a pure energy pov, the comparison between gas and electric looks
> like this:
>
> Gas: 131 Megajoules x 32% (thermo) x 60% available for aero drag = 25
> megajoules applied to aero drag.
> Electric: 131 x 80% (batt/elec motor eff) x 85% (assuming only 15% loss
for
> car internals) = 89 megajoules applied to aero drag.
> Of course, the electric is not using a gallon of gas, this is just
supplying
> a 131 megajoule "initial equivalent".
>
> Thus, an electric car can be 350% the energy efficiency of an IC engine
> driven car. Mebbe more.
>
> One can fudge the numbers quite a bit either way, but it is unlikely
that an
> electric will fall below 200% the total energy efficiency of gas.
>
> In addition, the energy/resources consumed in the mfr of an electric car
are
> likely a small fraction of that of a gas car, esp. if we dispense with
the
> 300 hp bull****.
> VWs did fine with 42 hp.
>
> If we factor in the overall lower-power of an electric, say, 40 vs 200
hp,
> we have *another* factor of 500%.
>
> Overall, the energy savings of automotive trans****tation could drop to
1/5
> to 1/10 of current usage, which is pretty astounding.
>
> Also, the automotive service industry will be revolutionized--or
destroyed,
> depending on your perspective. "Check the brushes on your permanently
> lubed DC motors, sir?"
> Might not even have brushes!
>
> Yeah, batteries are still a problem, but proly not for long.
> With a small good hub motor on each wheel, even lead-acid batts are
viable,
> at least in-town.
>
> If all this indeed happens, I guess guys will have to go back to wearing
> decorated/bejweled codpieces, instead of their Vettes, Vipers, and
Carreras.
> :)
>
> Info for the above calcs:
>
> p = rho = 1.293 (metric units); v = 65 mph; CdA = 5.5 sq ft
> Conversions:
> .447 mph to m/s
> 10.76 sq ft to sq m
> 1610 meters/ mi
> .6 = fraction of energy applied to aero drag
> 131,000,000 joules/gal
> .32 gas engine eff.
>
> All data from the below peer-reviewed sources: :)
>
> http://en.wikipedia.org/wiki/Drag_equation
>
> http://en.wikipedia.org/wiki/Drag_coefficient
60%
>
>
http://en.wikipedia.org/wiki/Automobile_drag_coefficientshttp://en.wikipedia.org/wiki/Automotive_aerodynamics
CdA's
>
> http://ecen.com/content/eee7/motoref.htm
enginen eff
>
> http://photovoltaics.sandia.gov/docs/PDF/batpapsteve.pdf
95% batt
eff.
>
> --
> ------
> Mr. P.V.'d (formerly Droll Troll), Yonkers, NY
>
> Stop Corruption in Congress & Send the Ultimate Message:
> Absolutely Vote, but NOT for a Democrat or a Republican.
> Ending Corruption in Congress is the *Single Best Way*
> to Materially Improve Your Family's Life.
> The Solution is so simple--and inexpensive!
>
> AND,
> Make sure whomever you do vote for believes in
> ABSOLUTE separation of Church & State--ferchrissakes
>
> entropic3.14decay at optonline2.718 dot net; remove pi and e to
reply--ie,
> all d'numbuhs
Remember, that thirty percent or so efficiency number is only at
nearly full throttle.
When you are driving at part throttle it is not anywheres near as
efficient.
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