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National Advisory Committee for Aeronautics, Technical Notes - Dynamics of the Inlet System of a Four Stroke Engine

Tests were run on a single-cylinder and a'multicyl-
inder four~stroke engine in order to determine the effect
of the dynamics of the inlet system upon indicated mean
effective pressure.

Tests on the single-cylinder engine were made at
various speeds, inlet valve timings, and inlet pipe
lengths. These tests indicated that the indicated mean
effective pressure could-be raised considerably at any
one speed by the use of a suitably leng inlet pipe.

Tests at other speeds with this length of pipe showed
higher indicated mean effective pressure than with a very
shOrt pipe, although not so high as could be obtained '
with the pipe length adjusted for each speed. A general
relation was discovered between optimum time of inlet
valve clasing and pipe length: namely, that longer pipes
require later inlet valve c105ing in order to be fully
effective.

Tests were also made on three cylinders connected to
a single pipe. With this arrangement, increased volumet—
ric efficiency at law speed was obtainable by using a “
long pipe, but only with a sacrifice of volumetric effi- i
oieney at high speed Volumetric effi_ciency at high
speed was pregressively lower as the pipe length was in—
oreased.

It has long'been recognized that the'VOlumetric er . ; ;—e~
ficiency and hence the mean effective pressure of an in- ” "
ternal combustion engine is affected by the dynamics of
the inlet system. (See references 1 to 19.) The present
work was undertaken in order to make a more systematic
and extensive investigation than had been made before,
and to attempt to devise a mathematical analysis which
would lead to a better understanding of the observed phe—
nomena.

The work was done under the auspices of the National
Advisory Committee for Aeronautics, The experimental
work Was done in the Sloan AutOmotive Laboratory at the
Massachusetts Institute of Technology under the superviv
sion of Professor E. S. Taylor. A theoretical analysis of
this problem may be feund in Item 4 of the Bibliography.