I didn't see where you created the electricity, or an accounting for the
transmisison losses for sending he electricity to the charging location,
or
the cost of building the extra generating capacity needed to supply the
electricity, or the energy lost becasue batteies self discharge, etc.
Ed
"The Pre-Meltdown Kid" <entropic3.14decay@[EMAIL PROTECTED]
> wrote in
message news:47b27932$0$25060$607ed4bc@[EMAIL PROTECTED]
> Oh, might should have mentioned the overall strategy of the previous
> calcs:
>
> Notice that there is no mention of engines, cylinders, or any other
> specifics.
> The calculation of *theoretical mpg's* hinges on just a few general
> variables, some of which we can't do much about:
> gas engine eff, energy content of gas, the CdA, and internal losses of
> the car.
> Oh, and the the speed at which one drives.
>
> Only the CdA (wind resistance factor) can be manipulated to realize
> greater theoretical efficiences.
> And driving slower in top gear. Altho a previous thread on this topic
> suggested that this was not always the case, ie, slow speed in top gear
=
> best mpg's, but likely "second order" diffs.
>
> In *actual* efficiencies, the specifics of engine design of course come
> into play.
>
> In my Honda Fit, the only way to raise the "theoretical max mpg's" of 54
> is to lower the driving speed, or further reduce the CdA.
>
> It seems, tho, that for bitty cars like the Honda Fit genre, 50-60 mpg
is
> about the max mpg's that can be realized in a gas powered car--not the
> 100+ that some ballyhoo about.
>
> However, for all electric cars, the equivalent of 200-500 mpg's seem
> realistic--barring calculational errors.
> --
> ------
> 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
>
> "The Pre-Meltdown Kid" <entropic3.14decay@[EMAIL PROTECTED]
> wrote in
> message news:47b2737d$0$25054$607ed4bc@[EMAIL PROTECTED]
>> 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_coefficients
>> http://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
>>
>>
>
>
|
