The Effects of Piston-Head Shape, Cylinder-Head Shape, and Exhaust Restriction, on the Performance of a Piston-Ported Two-Stroke Cylinder Page: 6 of 42
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N.A.C.A. Technical Note No. 756
these variables had a noticeable effect on the type of
flow obtained with a given port arrangement. It was
found that port timing did not affect the flow. Air ve-
locities between a flow sufficient to give a definite
indication with the cotton tufts and one sufficient to
destroy the tufts, were investigated, with the conclusion
that the type of flow did not change over this range.
The type of flow was found to be unaffected by piston
position, except in the case where the ports were just
uncovered.
All flow-model runs were therefore made under the
following conditions:
1. Port timing of 520 - 55o before bottom center for
inlet and 650 before bottom center for exhaust.
This was the timing found best in the engine
(reference 1).
2. Constant inlet pressure of 0.6 inch alcohol, which
resulted in moderate air velocity in the flow
model.
3. Piston position 200 before bottom center.
The flow was explored and plotted at 0, 3/2, and 1
inch above the piston and at every inch thereafter to the
top of the cylinder. Typical plots are shown in figures
12, 13, and 14. The length of the arrows in these plots
indicates the relative horizontal component of the flow
direction. The relative magnitude of the vertical compo-
nent of the flow direction is indicated approximately by
the shading, a dark shading indicating a large vertical
component. Two arrows at one point indicate a fluctuation
of the horizontal flow direction within the angle included
between the arrows. A dot indicates upward flow with no
horizontal component. A cross indicates downward flow
with no horizontal component. Arrows with crosses at the
tail indicate a downward vertical component. Plain arrows
indicate an upward vertical component. Small circles in-
dicate stagnant or indefinite flow. The boundary between
regions of up-and-down flow is indicated approximately,
by means of a dot-dash lino.
Engine test procedure.- Tests with the engine were
made under the following conditions:1. Engine speed -- 1,800 rpm.
5
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Rogowski, A. R.; Bouchard, C. L. & Taylor, C. Fayette. The Effects of Piston-Head Shape, Cylinder-Head Shape, and Exhaust Restriction, on the Performance of a Piston-Ported Two-Stroke Cylinder, report, March 1940; (https://digital.library.unt.edu/ark:/67531/metadc54614/m1/6/?rotate=270: accessed July 17, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.