The Effects of Piston-Head Shape, Cylinder-Head Shape, and Exhaust Restriction, on the Performance of a Piston-Ported Two-Stroke Cylinder Page: 8 of 42
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N.A.C.A. Technical Note No. 756
"gross" brake mean effective pressure may also be used
as a measure of scavenging effiCiency. This quantity,
defined as the brake mean effective pressure calculated
from the dynamometer brake load, is plotted herewith for
all engine tests.
"Net brake mean effective pressure" is calculated
by assuming 70 percent adiabatic blower efficiency and
subtracting the resulting blower mean effective pressure
from the engine gross mean effective pressure.
Port shapes.- Various combinations of port inserts
were used in both engine and flow model. The inlet-port
arrangements used are designated in table I.
Because no inserts were used in-the top of the hori-
zontal (0o) ports, they opened about 30 of crank travel
before the 300, 450, or 600 ports.
The height of the exhaust ports was also varied by
inserts as shown in figure 3.
Piston-top shapes.- Seven piston-top shapes were
tested as follows:
No. Name Figure
1 Deflector 6
2 Deflector 6a
3 Flat 7
4 Round edge, 5/8 in. radius 7
5 Domed, sharp edge -
6 Domed, 3/4 in. radius 7
7 Flat, 3/4 in. radius 7
Pistons 1 and 2 were developed as a result of flow-
model tests. The procedure followed in developing these
pistons was one of trial and error, in which a clay pis-
ton head was gradually modified to obtain the desired
result in the flow model. As no definite pockets or flow
peculiarities had been noted with the best port arrange-
ments, the objective was an accentuation of the type of
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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/m1/8/?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.