On Fri, 16 Sep 2005, David Van Horn wrote:

> I rather liked that one in California, like a flower. A field of 
> mirrors concentrates sun on a heat chamber. I think it's metallic 
> sodium or some such, maybe oil, but from there it's a steam turbine.
>
> The mirrors all need servos to track the sun, but that's not a huge 
> problem.

Water is not an ideal fluid for use in small heat engines. Other liquids 
and gases are better afaik. The highest efficiency Stirlings use Helium 
as working gas afaik. Almost any gas can be used but most gases that 
work very well are either very expensive, very explosive, or both. Plus 
some are toxic (ammonia is one f.ex., ethyl ether another). Also high 
efficiency heat engines either do not use phase change or use both phase 
changes to recover latent heat. That can make them bulky and inefficient 
if built small. Think about it: the most efficient known thermodynaic 
machines are diesel engines, stirlings and turbines. Neither use phase 
change internally.

So I do not think that it is simple. James could make a trial with a 
stripped down model aircraft engine, just to see if it works. Imho, the 
injector can be deleted and water can be injected at the 'intake' cycle. 
The latent heat would keep it liquid until TDC is reached if this is 
done right. Still, the latent heat will be lost unless the steam is 
recirculated through a condenser and the heat recovered. As a 'hack' 
such an engine could be interesting to make.

On the other hand, imho, if some trick could be devised to inject 
superheated water into the cylinder of a small engine, maybe compress it 
further under a gas cushion (air, nitrogen), and trigger nucleation at 
TDC, and repeat the process in a repeatable and stable way, then 
something might come of it.

Peter
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