Page 154 - Aeronautical Engineer Data Book

Principles of propulsion 127
Table 8.3
Afterburner
A tailpipe structure attached to the back of military fighter
aircraft engine which provides up to 50% extra power for
short bursts of speed. Spray bars in the afterburner inject
large quantities of fuel into the engine’s exhaust stream.
Airflow
Mass (weight) of air moved through an engine per
second. Greater airflow gives greater thrust.
Auxiliary power Units (APUs)
A small (< 450 kW) gas turbine used to provide ground
support power.
Bleed air
Air taken from the compressor section of an engine for
cooling and other purposes.
Bypass Ratio (BPR)
The ratio of air ducted around the core of a turbofan
engine to the air that passes through the core. The air
that passes through the core is called the primary airflow.
The air that bypasses the core is called the secondary
airflow. Bypass ratio is the ratio between secondary and
primary airflow.
Combustion chamber
The section of the engine in which the air passing out of
the compressor is mixed with fuel.
Compressor
The sets of spinning blades that compress the engine air
stream before it enters the combustor. The air is forced
into a smaller and smaller area as it passes through the
compressor stages, thus raising the pressure ratio.
Compressor Pressure Ratio (CPR)
The ratio of the air pressure exiting the compressor
compared to that entering. It is a measure of the amount
of compression the air experiences as it passes through
the compressor stage.
Core engine
A term used to refer to the basic parts of an engine
including the compressor, diffuser/combustion chamber
and turbine parts.
Cowl
The removable metal covering of an aero engine.
Diffuser
The structure immediately behind an engine’s compressor
and immediately in front of the combustor. It slows down
compressor discharge air and prepares the air to enter the
combustion chamber at a lower velocity so that it can mix
with the fuel properly for efficient combustion.