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National Advisory Committee for Aeronautics, Technical Notes - A Preliminary Motion Picture Study of Combustion Ignition Engine

Motion pictures'were taken at 1,850 frames per second
of the spray penetration and combustion occurring in the
N.A.C.A. combustion apparatus arranged to operate as_a com—
pression—ignition engine. Indicator carat W??%Ftaken si—
multaneously with the motion pictasss by meahs’of the
N.A.C.A. optical indicator.

The motion pictures showed that when ignition occurred
during injection it sta.rted in the spray envelope. If igi
nition occurred after injection cut— off, however, and. after
considerable mixing had taken place} it was impossible to
predict where the ignition wouldnstart'. The pictures also
showed that ignition usually started at several point_s in “
the combustion chamber. With this apparatus, as the injec—
tion advance angle increased frOm 0° to 40° before top cen—
ter, the rate of flame sprea.d increased and the duration of
burning decreased.

Many methods have been used to study the combustion
process in an internal—combustion engine. including: anal~_
ysis of indicator cards; cheervation of the flame by a
stroboscope; continuous, or "streak", photography of a narL
row band of the flame as shown through a slit}_analvbis"bf
gas samples taken progressively throughout the cjblb by‘a‘
stroboscopic Valve; recording of flame traVel by electric de-
vices; and stroboscopic photographing of the spec_trum of the
gases in the cylinder. Although each o?_these methods has
advantages over the others for_studying some_particular phase
of the combustion process, all of thanhave definite limitaL
tions. When making a photographic investigation of combus—
tion it is desirable to obtain e progressive picture of the
combustion as complete as possible;“ih respect to both time
and included field.

In previous nork on the effect of fuel vaporization on
combustion with the N. A. G. A. combustion apparatus some con—
tinuous photographic records of the flame were obtained
through Buinch round windows fitted in the sides of the com«
01stion chamber (reference 1). These pictures gave the ap~
oroximate location of the ignition relative to the spray
311d an idea of the rate of fle.me spread through the combus-
tion chamber. However, they showed the flame spread only
"hen the progress of the flame was slow and toward the sides
of the chamber, giving the speed of flame in only one direc—
tion.

This report presents some of the preliminary work dbne
using the N. A. C. A. combustion apparatus in con.junction with
a hi~h~speed motion- picture camera c-apable of taking pic—_
VUres at rates up to .250 fra.mos per second Motion pic—'
t res t‘- -ken at this rate through 2—1/2— inch—diameter glass
windoWs in the combustion ch.amber give a fair_l_v complete and
progressive picture of—ncrmal combustion. Under knocking
conditions, however, the combusti on- process is s_9 speodedup
that, even with the present Gamers speed, the flame fills
almost the entire cha.mber in the interval .h-et'ween succesu
sive frames.