Potential flow in engine valves Page: 9 of 29
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N.A.C.A. Technical I'emorandum No. 343 8
nation of the relations for any desired variation of m would
mean much work. It was therefore a great advantage that the
special form of equations (3) and (4) (which could be written
in the form m = - f1 -+4g a and n = f2 K + K g2 a) allowed
the employment of nomographic methods, by means of which it was
possible to find the corresponding K, a and n for m from
0 to w vhich were then combined in the following manner.
a) Velocity plotted against the valve-lift.- n = f K
(Fig. 6). K increases almost linearly at first and, with in-
creasing n, approaches asyiptotically the value 1. It is
noticeable that all the curves in = const. lie very close to-
gether, so that any change in the overlapping has but little
effect on the velocity. For the valve-lifts occurring in prac-
tice up to n = 1, the n curve closely approximates a straight
b) a = g K (Fig. 7).- The overlapping has, as was to be
expected, a greater effect on .a, For small values of m,
a increases with relative rapidity and tends toward a limit,
as n increases. This limit falls for larger values of m,
so that at mi = m only a = 0 is possible. It is noteworthy
that, with positive overlappings, the maximum attainable angle
c) Coefficient of contraction (Fig. 8).- It can be readily
shown that a criterion for the contraction of the emergent
stream is given by k = n, when 6 denotes the thickness of
the stream. The course of these values indicates a very slight
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Eck, Bruno. Potential flow in engine valves, report, December 1, 1925; (digital.library.unt.edu/ark:/67531/metadc65148/m1/9/: accessed August 20, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.