Figure 1.17. OnePiece Compressor Case.
1.21.
Today, three basic combustion chambers are in use. They are
the annular combustion chamber, the can type, and the combination of
the two called the canannular. Variations of these basic systems
are used in a number of engines. The three systems are discussed
individually in the following subparagraphs. The most commonly used
gas turbine engine in Army aircraft is the annular reverseRow type.
The combustion section contains the combustion chambers, igniter
plugs, and fuel nozzles or vaporizing tubes. It is designed to burn
a fuelair mixture and deliver the combusted gases to the turbine at
a temperature which will not exceed the allowable limit at the
turbine inlet.
Fuel is introduced at the front end of the burner in a highly
atomized spray from the fuel nozzles. Combustion air flows in around
the fuel nozzle and mixes with the fuel to form a correct fuelair
mixture. This is called primary air and represents approximately 25
percent of total air taken into the engine. The fuelair mixture
which is to be burned is a ratio of 15 parts of air to 1 part of fuel
by weight. The remaining 75 percent of the air is used to form an
air blanket around the burning gases and to lower the temperature.
This temperature may reach as high as 3500 F. By using 75 percent of
the air for cooling, the temperature operating range can be brought
down to about half, so the turbine section will not be destroyed by
excessive heat. The air used for burning is
35
Previous Page
