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General Automotive General automotive discussion. This is intended to be a discussion about other not VW and Diesel cars you may have or interested in.

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Old August 31st, 2007, 02:44   #1
LargePrime
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Default A very different Hybrid?

I was poking around the interwebs an i saw an article on steam engine cars.

Turns out a R&D group at VW has the bestest high tech steam engine around.

So I was thinking, A typical Infernal Combustion engine would make a right proper heat source for a high tech steam engine.

Assuming a Diesel gets ~40% efficency, and a high tech steam engine gets about ~30%, we get about 58% all up!

What think ye about a diesel/steam hybrid?
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Old August 31st, 2007, 08:47   #2
TDIMeister
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Individually each cycle may be able to reach the efficiencies you state, but put into combination (by that I assume you mean employing the steam portion to use the waste heat of the Diesel engine in a bottoming cycle), you can never reach any significant improvement over the Diesel engine alone. The reason is the temperature of the waste exhaust heat is relatively low, and therefore so is its "exergy" or availability to do useful work.

Secondly, when tossing around efficiency figures, we're always dealing with peak values. Even a Diesel engine with a peak efficiency of 40% is not the problem. The problem is that, like every other thermodynamic cycle, the engine is rarely operating at a point of peak efficiency. Far from it. Whether Diesel or otherwise, the power at the wheels is less than about 20% of the energy latent in the fuel.

Even doubling the peak efficiency of any engine process will at part loads bring relatively small improvements in the whole scheme of things. On top of that, you add all the extra complexity, bulk and the dreaded C-word -- cost -- with a small steam engine, and you can understand why nobody is beating down doors to get this to consumers' hands.

BMW has demonstrated a small auxiliary steam engine running off the exhaust heat, but it's just that: it's a technology demonstrator, not something that will be cost effective anytime soon. And its coupled to a gasoline engine. With a Diesel, there would not be enough exhaust heat to justify the steam bottoming cycle, and Diesel already has a cost disadvantage to begin with.

Nice idea for laboratories and maybe massive combined-cycle stationary generators, not quite ready for prime time automotive production.
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Old September 3rd, 2007, 19:46   #3
bugablue
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Quote:
Originally Posted by LargePrime
bestest
I love that word
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Old September 3rd, 2007, 20:02   #4
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Our cars have trouble keeping themselves warm in the winter!

When I was a kid we still plowed crop ground in the fall. (we no-till now) This plowing took weeks and generally we worked 12 hour shifts and in those days we didn't have a permanent cab on the tractor. Can you say cold?
We put on what was called a 'heat-houser' than was canvas and funneled the engine heat back around the operator seat. It was open on the top and back. When you faced the wind you cooked and when the wind was at your back you froze. We had one field that had 1.5 mile long rows....

When you just couldn't feel your fingers any more, and ONLY if you were on a diesel tractor (all non-turbo in those days) you could grab the muffler coming out of the hood and it would warm your hands right through your gloves.
If you tried it on a gas tractor, you burned your hands rather badly.
Not that much waste heat from those diesel tractors compared to the gas ones.

Bill Lear (google him) spent millions trying to bring back the steamer. I'd like one myself!

Bill
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