> In fact, it looks as if the Stirling (which I recall reading
> that Ford Motor was interested in PM or PS magazine some
> twenty plus years ago!) engine is a step *back* in technology.

The principle itself is technology independent as it is the physical
implementation of the Carnot cycle. The Carnot cycle is the most efficient
way of converting thermal energy to mechanical energy. Present engines all
use less efficient cycles - including internal combustion (petrol) engines
(Rankine?>), Diesel engines (Otto), gas turbine, steam et al. As I noted,
the actual IMPLEMENTATION is another matter and you can certainly make some
very inefficient Stirling Engines
(as I have done :-) ).

> It looks to be a variation of the "basic steam cycle" (and
> steam "cars" predate internal combustion engines by quite
> a margin).

The main similarity between steam and Stirling engines is that both are
external combustion.
The first Stirling Engine was produced in about 1860. There may have been
Carnot cycle engines before then that we are unaware of but they weren't
made by Mr Stirling :-). He was, incidentally, a Pastor who sought to make a
safer & more efficient engine for use in his brother's mines. Steam engines
of the day had a bad habit of destroying themselves and people nearby. Then
as now the main problems experienced with the SE were materials related.
Modern SE's typically run at internal pressures of 3000 psi+ and use Helium
gas or, for the really brave, Hydrogen. Temperatures are 'as hot as the
materials can be made to stand" as Carnot efficiency increases with
temperature.  (Cycle efficiency = (Thot-Tcold)/Thot ). Hydrigen is a superb
gas thermally but has some extremely nasty habits, even more so at such
elevated pressures and temperatures - it will cheerfully diffuse through
steel pressure vessels and cause hydrogen embrittlement along the way as a
bonus.

> Recall also that Chrysler experimented with TURBINES (internal
> or external combustion?) too, back some twenty years ago. That,
> IMO would represent a step forward in technology.

Technology quite possibly, but not in "cycle" used. Ultimately its better /
cheaper / faster that wins the day and so far Stirling Engines have not done
so except in niche applications. Some of the best domestic market units
("Whispergen" co-generation units) were designed in New Zealand and are now
selling internationally at exhorbitant prices.

Once one was perfectly in control of all aspects of the materials used then
the SE would probably be the winner but don't expect it to happen any day
soon. Until then a 100 year old "one lunger" diesel will probably do about
as well as anything you can get for home power generation.




        RM

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