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National Advisory Committee for Aeronautics, Technical Notes - The Effect of Connecting Passage Diameter on the Performance of a Compression Ignition Engine with a Precombusion Chamber

The diameter of the passage connecting the precombus—
tion chamber with the cylinder was varied through a range
from 3/16 inch to l-l/lfi inches. The auxiliary chamber
contained 50 per cent of the total clearance of the E by 7
inch cylinder at a compression ratio of 13.5.

Results of motoring tests are presented showing the
effect of passage diameter on chamber and cylinder com—
pression pressures, maximum pressure differences, and
f.m.e.p. over a speed range from 300 to 1,750 r.p.m.”

Results of engine—performance tests are presented
which show the effect of passage diameter on m.e.p., ex—
plosion pressures, specific fuel consumption, and rates of
pressure rise for a range of engine speeds from 500 to
1,500 r.p.m.

The cylinder compression pressure, the maximum pree~
sure difference, and the f.m.e.p. decreased rapidly as the
passage diameter increased to 29/64 inch, whereas further
increase in passage diameter effected only a slight change.
The most suitable passage diameter for good engine per—
formance and operating characteristics was 29/64 inch,
Passage diameter became less critical with decrease in en—
gine speed; therefore, the design should be based on max~
imum operating speed. Optimum performance and satisfac-
tory combustion control could not be obtained by means of
.any single diameter of the connecting passage,

The precombustion-chamber type—.nr cylinder head em—.
ploys forced air flow to mix air with fuel _in the auxil—
iary chamber. Combustion later expels part of the burn—
ing mixture into the cylinder where combustion continues.
The completeness and control of mixing and combustion de«
pend upon a number of factors which for convenience may
be divided into two groups: first. chamber position,
clearance distribution, and clearance shape; scoond the
connecting—passage area, shape, and direction. Several
of these factors have been investigated theoretically (see
bibliography) but there has been little engine investiga—
tion. The effect of clearance distribution on motoring
charact.eristics and engine performance has been experimen—
tally investigated at this laboratory and reported in ref-
erence l.