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National Advisory Committee for Aeronautics, Technical Notes - Calculated Performance of a Compression Ignition Engine Compressor Turbine Combination Based on Experimental Data

Calculations based on test data taken on a single-cylinder
compression-ignition engine with a compression ratio of 15.1 and an
engine speed of 2200 rpm were made to determine the performance at
sea—level conditions of a compression-ignition engine geared
together with a compressor and a turbine. The maximum cylinder
pressure was assumed constant at 1400 pounds per square inch and
the effects of fuel-air ratio, compression ratio, exhaust back
pressure, and engine speed on the performance of the combination
were determined. The analysis indicated that the net specific
power output increased with decreasing compression ratio and
increasing fuel-air ratio and engine Speed. At an engine speed
of 2200 rpm and compressor and turbine efficiencies of 0.70 and
0.65, respectively, a minimum net specific fuel consumption of
approximately 0.40 pound per net horsepower-hour was obtained.

Increasing the compressor and turbine efficiencies to 0.85
decreased the minimum net specific fuel consumption to approxi-
mately 0.32 pound per net horsepower-hour. Decreasing the engine
speed to 1200 rpm decreased the minimum net specific fuel consump-
tion to 0.57 pound per net horsepower-hour when the compressor
and turbine efficiencies were 0.70 and 0.65, respectively. Come
parison with a compressionpignition engine using a turbosuper-
charger showed that little could be gained by gearing the turbine
to the engine, provided the turbosupercharger could be stably
operated with a closed waste gate.

The use of Jet-propelled aircraft has aroused considerable
current interest in aircraft-propulsion systems that utilize gas
turbines as the prime movers. (See references 1 and 2.) One of
the principal limitations in the use of gas turbines in the
energy-conversion process is the lack of materials that withstand
gas temperatures above approximately 16000 F. In order to maintain
the temperature below this limit, a large amount of excess air must
be supplied, which decreases the energy per pound of gas that can
be extracted by the turbine and consequently seriously reduces the
net power output of the system.