Comparing Maximum Pressures in Internal Combustion Engines Page: 4 of 5
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This device has been used on several occasions to demonstrate
a fact frequently mentioned with reference to detonation, namely,
that under Certain conditions higher pressures result when firing
from one spark plug than when firing from two. For these demon-
strations the disk assembly was located as shown in Fig. 2 in an
extra spark plug hole in the side of an otherwise standard Liberty
cylinder. A thickness of diaphragm was selected which, with the
engine operating with a fairly early spark would withstand the ex-
plosion pressures for over five minutes, provided the engine was
fired from both plugs. If, however, after one minute of operation
the ignition wire was removed from plug A and the engine fired
from plug B alone the diaphragm would fail almost instantly. The
experiment merely constitutes a rather striking illustration.of
how the failure of one spark plug may result in a disastrous in-
crease of explosion pressure.
From the experiments made at the Bureau it appears that so
long as diaphragms are made of the same material, check results
can be obtained under the same engine conditions within rather
close limits. In any event, the simplicity of the device commends
its use for qualitative comparisons of a similar nature to that
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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/m1/4/: accessed January 21, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.