The Effects of Piston-Head Shape, Cylinder-Head Shape, and Exhaust Restriction, on the Performance of a Piston-Ported Two-Stroke Cylinder Page: 7 of 42
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6 N.A.C.A. Technical Note No. 756
2. Compression ratio -- 7.
3. Fuel-air ratio ---- 0.227 by volume.
4. Ignition timing ---- 130 TC.
5. Port timing -------- (Sane as for the flow model)
520 - 550 BBC for inlet and 650 BBC for exhaust.
(See fig. 3a.)
Other timings were investigated (see fig. 18) with
several of the various combinations of porting, piston,
and cylinder head, but in each case optinun timing was
found to be the above. This timing was therefore adopted
as standard for the engine tests.
6. Port arrangement -- (see table I). Various port
arrangements were tried whenever indicated as
desirable by the flow studies. or by other con-
siderations, but usually the "E" arrangement
was found best.
7. Scavenging ratio -- 0.8 to 1.6.
The various combinations of piston, cylinder head,
and inlet ports tested in the engine are shown in table
III.
DEFINITIONS
"Scavenging Ratio," as defined in reference 1, is
the ratio of the volume of charge at inlet density pass-
ing through the engine cylinder per stroke, to the dis-
placement of the cylinder.
"Scavenging Efficiency" is the ratio of the weight
of fresh charge retained in the cylinder, per stroke, to
the product of total cylinder volume and inlet density.
Inlet density was taken at 750 F and 29.92 inches Hg in
every case. Since the indicated mean effective pressure
of the engine, with a given fuel-air ratio and compression
ratio, is proportional to the weight of fresh charge re-
tained per stroke, the indicated mean pressure is a meas-
ure of the scavenging_ efficiency. The friction mean ef-
ffective pressure was nearly constant at about 14 pounds
per square inch. This value is small enough so that the
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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/m1/7/: accessed July 17, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.