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EVT Layout |
The EVT design
differs from conventional practice in the following
ways:
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The Steam and
Exhaust Ports (stationary ports) are 150% the diameter of
the cylinder port. However, the size of the Cylinder
Port (traveling port) remains the same as that established
in past practice (its size is determined by the displacement
of the engine).
-
The distance
between the adjacent edges of the stationary ports (web
width) is the same for the EVT design as in the Typical
design. (Approximately 110% of the cylinder port diameter.) design as in the Typical
design. (Approximately 110% of the cylinder port diameter.)
-
The Cylinder
Port traverses the larger diameter Stationary Ports for an
engineered amount of time, as opposed to the momentary
alignment of ports in the Typical design. See
illustrations below)
-
The additional
travel of the Cylinder Port is effected by increasing the
distance from the trunnion to the Cylinder Port. In
other words, the arc length of the port path increases as
the distance from the trunnion increases.
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EVT Animation
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| This
animation shows the relationship between crank position
and port alignment. Notice the length of time that
the cylinder port remains fully in communication with
each of the stationary ports. (The crank position
diagram is synchronized with the port motion, but is not to scale.) |
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EVT
vs. Conventional Flow Potential
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This graph
shows the total potential flow capacity of the EVT and a
conventional (Typ.) design.
Notice
the more rapid opening and closing of the EVT ports.
Notice
also the flow at 20 degrees past TDC on the admission
curves. The conventional design yields roughly 25%
while the EVT design delivers twice that.
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The following
illustrations capture the important events through a single
revolution of a single acting oscillating steam engine.
The illustrations depict both the EVT and
"Typical" layout in a single model to better compare the
similarities and differences. The illustrations are
correctly scaled so that the relative difference in the size and
location of the ports may be appreciated. The actual
engines would, of course, have only one set of ports. Click
on images to enlarge. Use your browser's "back"
button to return.
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Note:
*It
seems reasonable to assume that in the past 150 years, someone
else would have also discovered this method of port
proportioning and layout - yet I am unable to find any
documentation supporting a prior claim to its development.
I would be very interested in hearing from anyone that has had
any experience with a similar approach, or knows of an engine
design employing the principles described.
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