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mileage and energy efficiency mathematical correlation?

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  • murdoch_1998
    Rick, et. al.: Lord knows I have to defer to your judgment and other experts in an EV-making discussion. But, with respect, on this more general science
    Message 1 of 3 , Jul 31, 2004
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      Rick, et. al.:

      Lord knows I have to defer to your judgment and other experts' in an
      EV-making discussion.

      But, with respect, on this more general science issue, I want to try
      to understand something here about this relationship between energy
      efficiency and mileage. I do not think there is necessarily a
      linear relationship between the percentage energy efficiency and
      miles per unit energy. My reasoning is something along these lines.

      Theoretically, in the ideal, one can get an infinite distance from a
      miniscule energy input. "A body in motion stays in motion unless
      acted upon by an outside force".

      So, if we had an ideal car on a non-friction surface and no
      resistance (wind or otherwise), after the original "impetus" of
      energy, the car should go forever. The distance traveled would be
      infinite.

      Now, if we include real-world performance issues of acceleration and
      deceleration, wind resistance, etc. then do we come closer to a
      linear mathematical correlation between energy efficiency and
      mileage?

      I don't know the upper limits on mileage per MegaJoule, given
      idealized thought experiments or alternatively given some defined
      real-world constraints (a certain weight to a vehicle, some internal
      friction, acceleration and decelleration, wind resistance, etc.).
      I've just always wondered about this question as to what we mean
      when we say "energy efficiency" and relate it to mileage.

      It seems to me I have read once or twice articles about college-type
      contests where teams shoot for the most awesome mileage they can get
      and throw away virtually every other consideration. The speed
      traveled, the number of possible passengers, etc. etc... these
      factors are all subordinated to mileage. And in those contests I'm
      pretty sure the mileage figures attained have been astounding, I
      think well into the hundreds of miles per gallon (but I could be
      wrong... haven't seen this data for years).

      In any event, I'm not sure how I should view this issue of mileage
      and energy efficiency.


      --- In evworld@yahoogroups.com, Rick Woodbury <rick@c...> wrote:
      > Al Zelicoff, MD wrote:
      >
      > > 5. Yet, the MDI is advertised as being able to travel about 200
      > > kilometers on an air-charge. Given that it is no more
      aerodynamic than
      > > battery powered cars (although it is less weighty) and that
      electric
      > > motors are, for all intents and purposes nearly 100% efficient in
      > > converting on-board energy into movement, this suggests that the
      MDI is
      > > 20 to 30 times more efficient yet. That just doesn't make sense.
      >
      > No it doesn't. If a vehicle were 60% efficient and traveled 60
      miles on a
      > charge for example, as it became 100% efficient it would go 100
      miles. That
      > would mean no heat loss from friction, no aerodynamic drag, or any
      other
      > factors, i.e., impossible. Obviously 20 to 30 times more efficient
      is 20 to
      > 30 times impossible.
      >
      > There was an electric motor company in China advertising that
      their motor
      > was so efficient that it could get several times the range of a
      conventional
      > motor. Obviously they were smoking the same stuff. Current
      electric motors
      > are 85% efficient or more, meaning that there is very little heat
      loss. If a
      > motor were 100% efficient (absolutely impossible since there is
      always some
      > friction and other losses) it could go 15% further on a charge.
      Obviously
      > range must be increased by carrying more energy not so much through
      > efficiency gains. A lithium-ion pack can carry many times the
      energy per
      > weight and volume of lead acid. That makes sense.
      >
      > Thanks for doing the energy calculations for compressed air. I've
      always
      > thought it was highly suspect, but never took the time to disprove
      it. I
      > know that it takes a 6 hp air compressor to run a 1 hp or less air
      tool and
      > the compressor can't keep up at that. There is a lot of loss in
      heat when
      > the air is compressed too.
      >
      > A compressed natural gas car can get a 200 mile range using all of
      the
      > energy in the gas itself from a 5,000 psi cylinder. A home
      compressor works
      > for many hours to reach that pressure. To think you could throw
      away the
      > energy in the gas and run 200 kilometers on the pressure is
      ludicrous.
      >
      > It's hard to get 200 Wh/mi with an electric car with it's highly
      efficient
      > motors. How can one expect to get the same or better efficiency
      out of a
      > reciprocating engine. An internal combustion engine is about 13%
      efficient.
      >
      >
      > Rick Woodbury Phone: (509) 624-
      0762
      > President, Commuter Cars Corporation Toll-free: (800) 468-
      0944
      > Doubling the capacity of freeways Fax: (509) 624-
      1466
      > Quadrupling the capacity of parking Cellular: (509) 979-
      1815
      > Zero to 60 in under 4 seconds
      > 715 E. Sprague Ave., Suite 114 Email: rick@c...
      > Spokane, WA 99202 Web:
      http://www.commutercars.com
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