Dear Andrew,

Happy Hogmanay to you all as well.

Here is a blueprint of a Marine Compound Unaflow Steam engine. The
blue print is a sectioned arrangement or layout drawing. It has no
dimensions. The original is somewhere in Boxes 67 to 75 at the
Smithsonian Institute in Washington DC. I think it is in Box 74 or
thereabouts.

The engine shown is similar to the ones we will make. I have yet to
decide if we will use the "steeplejacked" compound setup with a high
pressure cylinder coaxial with the low pressure cylinder and connected
to the same piston rod. This fixes the same stroke for both
cylinders. There may be a small efficiency decrement as the steam
space aspect ratio cannot be ideal for both cylinders.

I am convinced we need a compound engine and we need two connecting
rods with a phase difference so the engine will "self start" at any
crank angle. It is possible we could use a single big end bearing
crank and a V-twin set up. Scott and I previously decided to build a
demonstration engine based on a V-twin 18 horsepower Briggs and
Stratton engine or a Harley Davidson engine.

My current focus is on replacing diesel engines for irrigation pumps.
These require engines of about 150 kW peak output. This suggest that
a large bore is required probably about 400 mm with a or 250 mm
stroke. This prevents us using the Harley or Briggs and Stratton
cranks. The high pressure cylinder would be 140 mm bore with same
stroke if we use the V-twin with one crank pin and two connecting
rods. Perhaps you could practice on that layout.

We will not be using the Woolf Cycle approach shown in the blueprint.
We will use two double acting cylinders of different bores and
probably the same stroke, for simplicity of crank design and
manufacture. The Woolf Cycle uses the LP cylinder single acting and
the HP cylinder is HP driven up and LP when driven down.

More tomorrow, also the NDA, I am going out with Chrissie now.

Regards,
Robert Mierisch, Mechanical Engineer
Tel +1 650 561 3273 Cell +1 650 862 4954
Email RMierisch@gmail.com

Andrew Murdoch Photography

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