[ausev] Series hybrids

[Christopher Robison]

On Mon, 2007-12-03 at 21:21 -0600, Donovan Becker wrote:
> The series hybrid will have greater efficiency than the parallel
> because the engine will be running at a relatively constant speed
> instead of the constant change of rpm's when using the it as a
> "driving" engine. I have read that the diesel engines in the
> locomotives are about three times as efficient as the ones in large
> trucks b/c of this reason. Locomotives have been similar to the series
> hybrid for a very long time, and GE's hybrid train is pretty similar
> to the Volt concept.

I'd be interested in a link to that efficiency comparison. Locomotive
engines are more efficient than truck engines for a number of reasons.
Among the most important would be frontal area versus mass and volume.
(High-speed Bonneville streamliners make use of this concept too.) A
train can move a lot more cargo for the single aerodynamic efficiency
hit of moving the air out of the way as it moves forward. Each car is
then well within "drafting" range of the car in front of it, and so
laminar flow is not highly disturbed by the gaps. Another huge reason is
rolling resistance. There was a really cool episode of Mr. Wizard I
remember seeing when I was younger, where they were at a rail yard and
demonstrated being able to push a huge set of wheels (weighing many
tons) with a single finger. The contact patch of each wheel to the rail
is about the size of a dime. Almost no material deformation = almost no
rolling resistance.

If you were to simply add a parallel hybrid system to a truck, allowing
the electric motor to help get the truck moving from a stop and
recapture braking energy, I think the overall efficiency would be
enormously improved. Perhaps a series hybrid system would be a further
improvement, but again I don't think the difference would be enough to
override other factors in dictating that design decision. 

Of course as the technology of series and parallel hybrid powertrains
from GM, Toyota and others improves, I may be proven false on my
assertions here.


-- 
Christopher Robison
chris at ohmbre.org
http://ohmbre.org          <-- 1999 Isuzu Hombre + Z2K + Warp13!