leaking pen wrote:
becuase... running a sirling off the heat from the engine coolant and
block is innefficient?
Who says the actual engines they're using aren't similar to Stirling
engines? They pipe the hot fluids to a pair of "expansion units" but
the article doesn't say what's inside those "units".
In any case recapturing 80% of the exhaust heat sounds pretty impressive
to me.
Looks like they had a glance at steam locomotives before they designed
it :-) ... notice that both circuits, low and hi temp, first make steam
(or should we say "steam" -- not sure it's actually water they're
boiling!) and then superheat it at the back of the exhaust pipe? The
old steam locomotives used a very similar trick, boiling the water and
then running the steam through the boiler again before using it. Of
course the second pass is "upstream" of the first pass in the exhaust
circuit.
Did you notice the photo of a man holding his hand on the exhaust pipe
with the engine operating? Pretty "cool"...
Notice also that both system, low and high temp, use the radiator of the
car for the "cold reservoir". The first stage of the low-temp circuit
appears to suck hot water directly from the engine and dump the heat
from it into the radiator. In fact, the diagrams make it appear as
though there is no longer any direct connection from the engine to the
radiator.
And elsewhere, Merlyn said:
Yup, but do they run into problems with backpressure?
Cooling the exhaust necessitates that it becomes
denser. I have heard that backpressure can be a
problem with exhaust cooling, but do not have the
references handy.
[Again, that's Merlyn, not LP!]
I would suspect not, for a couple reasons.
First, muffling an engine puts a _lot_ of backpressure on it, and takes
away about 10% of its power IIRC. (This is one reason small airplanes
are often so noisy -- a muffler would be too big a power drain.) But
note that they can probably ditch at least one muffler when they put
this in the exhaust system: going through a heat exchanger very
probably has about the same effect on the noise as going over the
baffles of a conventional muffler. So, they're most likely trading one
source of backpressure for another, rather than just adding one. (I
assume BMW's normally have more than one muffler, of course!)
Second, boat engines have used water-cooled manifolds for just about
ever and they apparently work just fine. No doubt a little power is
stolen, but that's the only bad consequence AFAIK. And according to the
numbers, BMW's seeing a significant increase in power from this, so
they're clearly reclaiming more energy than they're losing through the
backpressure increase.
Keep in mind that the "cost" of the backpressure is really just the
"cost" of pumping the exhaust through the heat-exchanger. Surely, one
can arrange a heat-exchanger to extract more heat from hot gasses than
the pump that operates it consumes; otherwise steam engines couldn't work!
On 12/20/05, [EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]>* <[EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]> > wrote:
Finally, someone finds a practical way to use the wasted ICE heat:
http://www.gizmag.com/go/4936/
"The concept uses energy from the exhaust gasses of the traditional
Internal Combustion Engine (ICE) to power a steam engine which also
contributes power to the automobile ? an overall 15 per cent
improvement for the combined drive system."
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