On Wed, 21 Dec 2005 16:58:29 -0000, "Ian_m" wrote:

"Ian Stirling" wrote in message
...
The3rd Earl Of Derby wrote:
Dave Plowman (News) wrote:
In Autocar this week.

BMW are experimenting with using the waste heat from an IC engine to
produce steam which drives a motor attached to the main engine. On the
test bed they're getting a 15% saving in fuel consumption - at the
same time as more power and torque.

Seems it's not a new idea, but BMW reckon it is practical and should
be in production within 10 years.

When I was a nipper my old man was a tinkerer in electric motors and
generators and although this is very vague he put together on a piece of
wood a small cycle light generator a 12 or 24 volt motor(?) and
rechargable
battery connected together whereby the battery started the motor which in
turn rotated the generator wheel thus fed power to the battery for
charging
purposes, obviously there was some electronics in between which as i said
was very vague recollection

http://en.wikipedia.org/wiki/Perpetual_motion

Alas, not.
However, the BMW gadget suffers from none of this - car engines are quite
inefficient (thermodynamically), and the exhaust temperature (at the
exhaust valve) is around 700C.

Current car engines are about 25% at best efficient, so 75% of power goes
out the exhaust pipe wasted.
Theoretically, about 66% of this could be recovered by a completely
efficient heat engine, but in practice, even large power stations only get
about 50%, and they start off a bit hotter, as well as having ready access
to cooling water.

10% is probably achievable - in the long term, for maybe a recovery of
7.5%,
or a gain in efficiency of 30%.
This means however major additional systems such as much, much bigger
radiators.

Best cars, maybe 18% efficiency, power stations lucky if 25%, fluidised coal
bed stations can reach 33% efficiency.

What class of power station? Coal fired steam turbine with/without
passout, gas turbine, gas turbine with cogen, Low speed heavy fuel
diesel engine with waste heat recovery,? There are many combinations
the most efficient of which is likely the slow speed heavy oil diesel
engine with waste heat recovery that will exceed 50% efficiency,
however, this type of generation is not, I believe, used in the UK.
Industrial gas turbine with cogen is probably a very close second,
again with 50% plus efficiency.