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National Advisory Committee for Aeronautics, Technical Notes - Considerations of Air Flow in Combustion Chambers of High Speed Compression Ignition Engines

The air flow in combustion chambers is dIivided into
three fundamental classes - induced, forced and residual.
A generalized résumé is given of the present status of air
flow- invest-i-gatipns- and of- the- Iw_orkI -done_ at this_ and other
laboratories :to de-te rmine. the dir_ection and ve1_ocit_yI of
air' movement in auxilia—ry and inmtegral combustion .chambers.
The effec-ts' of air- -flew on eng-iIne .performance are mentioned
to show that” a_lth0ugh air.- flow improv-es-I the _combustion ef—
ficiency, considerable: Iinduction,. fri-ct1on, and thermal-
losses must be guarded:against.

The'movement-of air in the combustion chambers of
high—speed internal—cembustion engines afterIthe inlet
valves» or ports, close has-been the subject of cpnsider7
able speculation but of insufficient.experimentation as to
the exact nature of this air movement. Authors have ex—
presse:d opi-nions ranging from the belief that all movement
stop s the instant induction ceases , to the conviction that_
an orderly flow persists during c ompression, combustion!
and expansion until the gases are_ released. Also, the
works. of Neumann (reference 1) and of Bird (reference 2)
have shown that air movement has importan_t .influences_ on '
ignition and cembustion of fuel .and air. -- - '

The movement_- -of air i-n. an engine cylinder and cembus-
tion chamber is of especial importance in a high—speed_ com—
pression~igniItion engi-ne since the miinng of fuel and air.
must occur in an extremely-- short;time. The fuel—injection
system‘can be much-simpler if air movement is used to assist
the-mixing-of fuel and air-in the combustion chamber.

The purpose of this discussion is to give a summary
of the present knowledge and_importance of air movement in
cylinders and combust ion chambers, _A_ir movement caused by
the us‘e df air injection'will be disregarded.

The term "air flew" as used in this discussion refers
to the orderly movement of air throughout an engine cyl—
inder or combustion chamber. The more commonly used term
"turbulence" is regarded _as the disorderly movement of air
and is nIot considered here.—' No distinction is made between
flow of pure air and of air mixed with residual gases or
with fuel.