Page 12 – Don’t Re-invent the Wheel

Previous page______ Index______ Next page

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.”

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.

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 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, p
max/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.