Nitrided-steel piston rings for engines of high specific power Page: 3 of 56
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NACA ARR No. 4D22
IrRODUCTION
For many years the NACA has been conducting tests of aircraft-
engine cylinders at specific power outputs in excess of their maxi-
mum ratings. The first engine parts to fail as the specific power
is increased are the piston rings; the failure manifests itself by
general increases in specific oil consumption, in rapid ring wear,
in blow-by, and in subsequent loss in power.
Variables that considerably. affect piston-ring and cylinder-
barrel wear are: dust; lubrication, both quantity and quality;
brake mean effective pressure; engine speed; and operating tem-
peratures. Both bench tests and engine tests were made on a
variety of piston-ring materials and ring designs. Some of the
materials and ring designs were eliminated by the bench tests.
The others were tested in single-cylinder engines. The choice
of the procedure for the engine-ring test covered by this report
was chosen with a view to picking test conditions that would give
the required results in the minimum time. The final combination
of nitrided-steel rings in both nitrided-steel and chromium-plated
cylinder barrels was performance-tested under a wide variety of
operating conditions in both single-cylinder and. multicylinder
engines.
The thin, nitrided-steel rings used in these tests were
manufactured by and tested in cooperation with the Borg-Warner
Corporation, Spring Division, Bellwood, Ill.
The nitrided-steel piston rings were performance-tested in
single-cylinder engines at Langley Memorial Aeronautical Labora-
tory from 1939 through 1942. At the recommendation of the
National Advisory Committee for Aeronautics, multicylinder and
single-cylinder engines were tested by the Bureau of Aeronautics,
Navy Department, at the Aeronautical Engine Laboratory of the
Naval Aircraft Factory in Philadelphia and by the Army Air Forces,
Materiel Command, at Wright Field.
DEFINITIONS
Piston-ring terms to be used in this report are defined as
follows:
face - The part of the piston ring that is adjacent to, or in
direct contact with, the cylinder wall.face width - The width of the ring face.
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Collins, John H., Jr.; Bisson, Edmond E. & Schmiedlin, Ralph F. Nitrided-steel piston rings for engines of high specific power, report, April 1944; (https://digital.library.unt.edu/ark:/67531/metadc279433/m1/3/: accessed March 28, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.