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National Advisory Committee for Aeronautics, Technical Notes - Influence of Fuel Oil Temperature on the Combustion in a Prechamber Compression Ignition Engine

The influence of fuel-oil temperature on combustion
was investigated by injecting the fuel into the prechamber
of a single—cylinder. 4—strbke—cyc1e, water—cooled, com—
pression-ignition engine Operating at 1,500 r.p.m. and at _u_ _fi
a compression ratio of 13.5. Indicator cards, exhaust—gas -
samples, and engine—performance data were obtained for
changes in fuel temperature from 124° to 7500 F. The in— .__
jection characteristics of the fuel system and the appear— 4
ance of the fuel spray were studied by injecting the fuel
into the atmosphere. A common-rail fuel—injection system
was used with a hydraulically controlled fuel—injection
valve operating at a pressure of 8,800 pounds per square
inch. The fuel was heated by passing it through an elec—
tric heater inserted between the pump and the injection
valve.

The results showed that heating the fuel 011 to 750°
F. increased the injection period, changed the rate of in-
jection, and eliminated the spray core. Engine tests
showed that the ignition lag, rate of pressure rise, and ,H
maximum cylinder pressure were reduced. The indicated __
mean effective pressure, the fuel economy, and the thermal
efficiency were slightly increased. Operation of the en— :_r
gine when the fuel was heated to 7500 F. was smoother, the
exhaust clearer, and the carbon formation in the combus—
tion chamber considerably less than when the fuel was
heated to 124°.

The present methods of proportioning the fuel to air
and the utilization of air flow in combustion chambers to
mix the fuel with the air have resulted in some improve-
ment in the combustion process. but the fuel still burns
throughout a large portion of the power stroke. No great
improvement in the engine performance can be expected as
long as the fuel is burned late in the cycle.

Attempts to increase the thermal efficiency by in—
Jecting the fuel during the earlier part of the_compres-
sion stroke and thus to obtain a more uniform mixture
throughout the combustion chamber have not been satisfac—
tory. The early injection resulted in the accumulation of
a considerable quantity of fuel in the combustion chamber
and, upon ignition, high cylinder pressures were devel—
Oped. knocking occurred, and the engine operation was
rough.