Pratt & Whitney Canada PT6A Turboprop, Instruction Manual

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Air is directed to a compressor consisting of three axial stages (Four
axial stages on large PT6A engine models) and one centrifugal stage.
Compressed air leaving the compressor passes through diffuser pipes
which turn the flow 90 degrees, reduce its speed and direct the air into the
combustion chamber.
In the annular combustion chamber the air is mixed with fuel and burned.
Two igniter plugs are used to light the fuel/air mixture when the engine is
started. They are not required to maintain the combustion process and can
be shut off once the engine has reached idle speed.
The expanding hot gases are directed first through the compressor turbine
and then through the power turbine. After passing through the power
turbine, the gases are exhausted through ports on each side of the engine.
(Some engines are fitted with a single-port exhaust.) The exhaust stubs
fitted to the engine are normally directed to utilize the remaining energy of
the gases in the form of thrust for additional aircraft propulsion.
Two bleed air systems are incorporated in the PT6A engine. Automatic bleed
air from the compressor prevents compressor stall during acceleration from
low engine speeds or deceleration from high engine speeds. For aircraft
use, air may be bled for heating or pressurizing aircraft cabins.
Airflow
Medium PT6A Engine
Air is directed to a compressor consisting of three axial stages (Four
axial stages on large PT6A engine models) and one centrifugal stage.
Compressed air leaving the compressor passes through diffuser pipes
which turn the flow 90 degrees, reduce its speed and direct the air into the
combustion chamber.
In the annular combustion chamber the air is mixed with fuel and burned.
Two igniter plugs are used to light the fuel/air mixture when the engine is
started. They are not required to maintain the combustion process and can
be shut off once the engine has reached idle speed.
The expanding hot gases are directed first through the compressor turbine
and then through the power turbine. After passing through the power
turbine, the gases are exhausted through ports on each side of the engine.
(Some engines are fitted with a single-port exhaust.) The exhaust stubs
fitted to the engine are normally directed to utilize the remaining energy of
the gases in the form of thrust for additional aircraft propulsion.
Two bleed air systems are incorporated in the PT6A engine. Automatic bleed
air from the compressor prevents compressor stall during acceleration from
low engine speeds or deceleration from high engine speeds. For aircraft
use, air may be bled for heating or pressurizing aircraft cabins.
Airflow
Medium PT6A Engine