h a l f b a k e r yMay contain nuts.
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A steam-car enthusiast says a pilot light will prevent the water from freezing when a steam car sits for up to two weeks
in sub-0°C weather. Aren't there working fluids other than water that don't have this problem? Why not a, hmm, an SF6 car? Or hey, why not a helium Brayton cycle.
Could one
have such a cycle with pistons and cylinders? As the piston squeezed the WF one would be removing heat, maybe by misting cool NaK through the helium. Then as it approaches minimum volume, start squirting in hot NaK. Some way through the expansion you want to drain off the partly cooled NaK, take it through a recuperator (a NaK/NaK heat exchanger) and then an air/sodium heat exchanger, aka "rad", then bring it back to cool the gas some more. Repeat.
The hot liquid metal (NaK is an alloy of sodium (Na) and potassium (K) that freezes at -11 Celsius) from the recuperator would go to the heat source, where combustion heat would be transferred to it through a big high-capacity thermal conductor, bigger than could fit in the cylinders.
If one does not like NaK, other liquids that could be used include ... well, nothing comes to mind right away.
It is certainly true that NaK is hazardous if it strays. It is entirely harmless to metal and helium, so if you must point out the hazards of NaK, go ahead, but I'm more curious about what else might be wrong with this idea.
Notice that the helium (or it might be nitrogen) never .leaves the cylinder.
External Combustion Car
http://www.1966batmobile.com/rear1.jpg
Circa 1966. [Cedar Park, Oct 04 2004]
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[Iodineman] What a great idea. How quick would the reaction be? And how would you power the compressors? I guess they could be electrically driven. This is one of the most intriguing ideas that I've seen yet on these pages. |
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This sounds like a Stirling engine to me, but I'm not an engine expert. |
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I'd be more inclined to favor a piston variation of a turbojet engine. Such a device could have a much longer combustion time than an internal-combustion engine, allowing for theoretically greater efficiency. |
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Is this like a non-water version of early steam-vacuum engines? |
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Without all the hot liquid metal and helium, what you are proposing a a heat exchange engine, |
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A Striling engine is an example of this, essentially a steam-less steam engine. Stirling engines work fine and have been used in cars. Tiny table top models are availible to demonstrate the principle, as my shop teacher showed us. Beyond compexity: Here are the problems- |
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1 Uses a lot of fuel- you need a hot fire all the time so polution and economy are bad
2 Warm up time- waiting +40 minutes to drive
3 Noisy as all HELL (the racket of a fractional horsepower toy was ridiculous!) |
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how would you contain the NaK in an accident also if helium were used it would have to be renewed on a regular basis (very often) because helium is natures most adept escape artist . As you will find if you study old research on this, the expense and mantenance for this kind of external combustion engine is far more than you might think at first and the containment and chemical renewal systems are so large and bulky (and extremly expensive) that for a car they are not practical. |
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This is a brilliant scheme as it opens up the possibility of a solar-steam-electricity conversion route appropriate to the third world, where old lorry engine cylinder blocks are available in abundance - but would be corroded immediately by conventional water-steam. NaK is a bit hairy though - is there an organic mineral alternative? Are there any chemists out there? |
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