Comparing Maximum Pressures in Internal Combustion Engines Page: 3 of 5
This report is part of the collection entitled: National Advisory Committee for Aeronautics Collection and was provided to Digital Library by the UNT Libraries Government Documents Department.
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As shown in Fig. 1, the diaphragm is mounted in a spark plug
shell between two metal washers. The metal disk which serves as
the.diaphragm is selected of a thickness such that, when subject-
ed to the explosion pressure of the engine, the exposed portion
will be sheared from the rim in a aca.paratively short time. If
this is to take place, two requirements must be satisfied.
First, the pressure must be high enough to produce shear. Second-
ly, the pressure must endure long enough or be repeated often
enough to effect the complete shearing of the center from the rim.
It is evident from this second requirement that the time required
for a disk to fail as well,..as its thickness should be considered
when comparing pressures by this method.
Fig. 3 shows the time of failure for aluminum diaphragms of
three thicknesses. A fourth diaphragm .046 inch thick had not
failed at the end of 11 minutes. There is little need for any
further explanation of the-method of using this device. With the
engine operating under a definite set of conditions the time re-
quired to shear a certain thickness of diaphragm is noted.
Changes are then made to produce the conditions under which a com-
parison is desired and again the time required to shear a disk of
the same thickness is ncted. An alternative method of comparison
Ls to substitute successively disks* of, various thicknesses until
one is found which fails in the same length of time as under the
original engine conditions.
* The miateria of which all the disks are made should be the same
and should have received.the same treatment.
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Sparrow, Stanwood W. & Lee, Stephen M. Comparing Maximum Pressures in Internal Combustion Engines, report, June 1922; (digital.library.unt.edu/ark:/67531/metadc53785/m1/3/: accessed January 23, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.