Correlation of exhaust-valve temperatures with engine operating conditions and valve design Page: 2 of 26
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NACA ARR No. E5120
NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS
ADVANCE RESTRICTED REPORT
CORRELATION OF EXHAUST-VALVE TEMPERATURES WITH ENGINE
OPERATING CONDITIONS AND VALVE DESIGN
By M. A. Zipkin and J. C. Sanders
The theory correlating engine-cooling variables developed in a
previous report was used as a basis for the development of a semi-
empirical equation to correlate exhaust-valve temperature with engine
conditions. A term is included in the equation that is a measure of
the thermal resistance of the heat-flow path between the crown of
the exhaust valve and a point on the outside surface of the cylinder
head. A means for comparing exhaust valves of different designs
with respect to cooling is consequently provided. The necessary
empirical constants included in the equation were determined from
engine tests of a large air-cooled cylinder.
A number of investigations have been conducted on the operating
temperature of exhaust valves. As early as 1923, Gibson and Baker
(reference 1) measured the temperature of a hollow-stem exhaust
valve without internal coolant by means of a thermocouple and found
that the operating temperature of the exhaust valve in a cylinder
of low specific output (less than 0.25 hp/cu in.) varied between
6000 C and 7500 C, depending mainly on fuel--air ratio, cylinder
cooling, and spark timing. Reference 1 also states that under
abnormal conditions such as preignition, the valve temperature might
exceed 8000 C. Subsequent developments in valve and cylinder design
have permitted much higher specific outputs than 0.25 horsepower per
cubic inch with approximately the same range of exhaust-valve tem-
peratures. The operating temperature and the effects of several
operating variables on the temperature of a sodium-cooled exhaust
valve in current use are shown in reference 2 and an indication of
the extent to which valve temperatures can be influenced by valve
design is reported in reference 3. A review of available data on
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Zipkin, M. A. & Sanders, J. C. Correlation of exhaust-valve temperatures with engine operating conditions and valve design, report, October 1945; (digital.library.unt.edu/ark:/67531/metadc279466/m1/2/: accessed January 18, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.