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National Advisory Committe for Aeronautics, Research Memorandum - Investigation of Operating Characteristics of an Engine Equipped with Modifications to Eliminate Fuel Evaporation Icing

Two modified fuel-injection systems, a drilled-inducer type and
a spinner type, that prevent serious fuel-evaporation icing were
installed on.a V—type, liquidscooled aircraft engine’and a preliminary
investigation was conducted to determine the effect on engine operating,
characteristics. The spinner system was also ground- and flight-tested
on a twin—engine fight er airplane. Flight measurements of cylinder-
head temperatures over a range of fuel-air ratios and engine power
conditions were made at an altitude of approximately 10,000 feet.

1 Starting and acceleration of the engine on the ground were
unaffected by the fuel-injection modifications. During the flight
1nvestigation, no apprec—iable variation occurred between the maximum
and minimum cylinder-head temperatures with the standard and modified
system for the same power condition and no irregularity of mixture
distribution could be detected throughout the power range of the engine
Normal mixture distribution was also indicated by a similar response
of cylinder-head temperatures for variations of fuel-air ratio at
manifold pressures of 25 and 35 inches of mercury absolute.

Both modified fuel-injection systems required less fuel-nozzle
pressure than the standard system to obtain the desired fuel-air ratio
for a given aireflow condition.
An investigation of the icing characteristics of- an aircraft-
engine induction system in a laboratory setup consisting of a super-
charger assembly and a carburetor resulted in the design of two
fuel- -inJection modifications, a spinner fuel- -injection system and a :
drilled- inducer fuel— injection system, both of which satisfactorily "
prevent the formation of fuel- -evaporation icing (references 1 and 2).

An electric. motor was used_ to drive the engine—stage supercharger
during icing investigations to avoid operation of the entire engine.
The investigation _was extend_ed “3138 both. fuel— _injection modifica-
tions on a full- scaIe laboratOry engine, to determine Whether the
modifications affected carbure.tor metering and general engine perform-
ance. The spinner system was further investigated on an airplane
during ground and fligh.t tests to obtain a comparison of engine oper-
ation wi.th the standard system. “

The results are based on observations of the ease of starting
and acceleration of the engine, as well as on measurement of the
cylinder-head temperatures, which roughly indicate the nature of mix-
ture distribution to the cylinders.