The purpose of this book is
to “fast track” newcomers to Stirling engine
boat building.
Such
people are likely to be innovators.
Being strong willed and
independent it is likely that ”taking
advice” in an anathema.
Please,
put your pride and strong
wilfulness aside.
This book is reporting the experience
of 15 years of a group of Stirling devotees and their
successes
in matching the Stirling engine to the task of small boat
propulsion.
As one (very highly skilled) newcomer to
Stirlings said:-
”My
first four engines wouldn’t even run – let alone pull
the skin off a rice pudding.”
So,
please,
take the ideas that are presented here. Reproduce them. Learn.
Then
improve, evolve and develop.
To
quote Tom Lehrer – “Don’t shade your eyes -
plagiarise”
There are three basic types of
Stirling engine and many variants within those types.
Why
have I presented the beta engine, rather than the alpha or the
gamma?
Because we have built alphas, gammas – and
transferators.
Each engine can take many months to build.
And we have had the best success with the pumped
beta.
We don’t claim to be “great men”
– but please stand on our shoulders.
See
further.
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Some “why nots”.
The
alpha engine needs two pistons (or more).
The gas seal of
the piston is crucial. It is also a good source of friction.
For
the private workshop builder, one piston/cylinder is quite
enough.
The gamma design brings with it dead space.
Looking carefully at commercial engine designs, these
issues of friction and dead space are overcome by raising the
pressure. This raises the power. Gas pressures
are usually many tens of bar. This just
raises the fabrication challenge to new heights.
Heater
tubes? Even more dead space.
Meanwhile, the beta –
as Dennis put it – “It has negative dead space.”
And one piston.
So, we have spent,
literally years, building and learning from various variants of
the Stirling engine. We would like to save you a lot of
time.
The other engine types all work.
But
of the boats that we have and use, the betas work well.
Consistently.
Going back to the beta, one of the
fundamentals is how big is the pressure
oscillation inside
the engine. In an atmospheric 90 mm hot cap diameter beta,
the
peak was measured at 22 psi absolute. The trough at 8 psi. A ratio
of 2.75.
This ratio, pmax/pmin
is a fundamental ratio for the
engine. It is an indicator
of the power of each engine cycle.
Looking at the reference books of major engines,
they are all lower (weaker) near 2.0 - because of the higher dead space.
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