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National Advisory Committee for Aeronautics, Technical Notes - Improving the Performance of a Compression Ignition Engine by Directing Flow of the Inlet Air

The object of this report is to present'the results of tests
performed by the National Advisory Committee for Aeronautics to
determine the effect on engine performance of directing the flow
of the inlet air to a 5-inch by 7—inch single cylinder, solid
injection, compression ignition engine. After a few preliminary
tests, comparative runs were made at a speed of 1500 R-P.H. with
and without directed air flow. It was found that directing the
flow of the inlet air toward the fuel injection valve gave stead—
ier engine operation, and an appreciable increase in power, and
decreased fuel consumption- The results indicate the possibility
of improving the performance of a given type of combustion Chem-
her without changing its shape and with no change in valve tim—
ing. They would also seem to prove that directional turbulence,
set up before the inlet valve of a four-stroke cycle engine, con-
tinues in the engine cylinder throughout the compression stroke.

During the inlet stroke of a compression ignition engine,
the air flow into the combustion chamber is given a turbulent
motion, due primarily to its passage through the inlet valves.
This turbulence persists throughout the compression stroke of
the engine and is of use in bringing about an intimate mixing of
the air and the injected fuel. For any given engine Speed and
volumetric efficiency, increasing the turbulence within a given
combustion chamber usually leads to increased power and decreased
fuel consumption.

The great disadvantage of a solid injection, compression igr
nition type of engine at high speeds is the failure to obtain
complete burning of the fuel charge in the short time available;
any factor, therefore, tending to improve the completeness of
combustion should be investigated. In the design of a compres—
sion ignition engine using airless injection turbulence is usual—
ly obtained by the shape of the combustion chamber and location '
of the fuel valve.