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National Advisory Committee for Aeronautics, Technical Notes - Compression Ignition Engine Performance with Undoped and Doped Fuel Oils and Alcohol Mixtures

Several fuel oils. doped fuel oils. and mixtures of
alcohol and fuel oil were tested in a high-speed. single—
cylinder, compression-ignition engine to determine power
output, fuel consumption. and ignition and combustion
characteristics.

Fuel oils or doped fuel oils of high octane number
had shorter ignition lags. lower rates of pressure rise,
and gave smoother engine operation than fuel oils or doped
fuel oils of low octane number. Higher engine rotative
speeds and boost pressures resulted in smoother engine op-
eration and permitted the use of fuel oils of relatively
low cetane number. Although the addition of a dope to a
fuel oil decreased the ignition lag and the rate of pres-
sure rise. the ensuing rate of combustion was somewhat
slower than for the undoped fuel oil so that the effective-
ness of combustion was practically unchanged. .

Alcohol used as an auxiliary fuel, either as a mixture
or by separate injection, increased the rates of pressure
rise and induced roughness. In general. the power output
decreased as the proportion of alcohol increased and, be-
low maximum power. varied with the heating value of the
total fuel charge.

Most published experimental investigations of fuels
for compression-ignition engines have been principally
concerned with ignition characteristics while en ine power
and economy were given but slight consideration freferenoes
1. 29 3. and 4). In order to improve the ignitibility of
fuel oils. various compounds have been added for the spe-'
cific purpose of reducing the ignition lag (reference 5).

The possibility has been suggested that fuel dopes might
be added or superior fuels obtained which will enable a
greater part of_the fuel charge to be burned during the
early part of the expansion stroke. French reports (ref—
erences 6 and 7) indicate that the use of ethyl alcohol

as an auxiliary fuel appreciably improved the engine power
and the ignition characteristics and decreased the rate of
pressure rise and the maximum cylinder pressure.