Intake (& Fan):
Turbofan- turbojet w/ shrouded fan prior to compressor. Fan driven by low-pressure compressor shaft. Intake air divided into bypass air or inlet air to gas turbine. Large volume of bypass air provides moderate acceleration, good takeoff performance, low-altitude/speed efficiency, & quieter operation. Turbojet core provides large acceleration & high cruise speed, with relatively small volume of air.
Bypass air- ratio of air flowing through fan to amount of air flowing through gas turbine. Higher bypass ratios yield greater fuel efficiency at low altitude.
Compressor:
Low-pressure compressor- forward most compressor. Driven by rearmost low-pressure turbine. Rotational speed of low-pressure compressor shaft, read in % design RPM, known as N1. N1 shaft turns freely inside of N2 shaft. N1 is primary means of setting power on “speed rated” engine.
High-pressure compressor- second or intermediate compressor. Driven by the high-pressure turbine. Rotational speed of high-pressure compressor shaft, read in % design RPM, known as N2. N2 shaft counter-rotates concentrically around the N1 shaft. Triple spool engines have an additional high-pressure compressor (N3).
Spool- combination of compressor, shaft, & turbine.
Centrifugal-flow compressor- forces air outward, into diffuser. Diffuser slows velocity, & increases air pressure.
Axial-flow compressor- forces air along longitudinal axis, into stator vanes. Stator vanes reduce rotational flow, slow velocity, & increase air pressure.
Compressor stall- distorted inlet air exceeds the fixed pitch compressor blade’s critical angle of attack. Airflow to compressor slows or stagnates, resulting in flow reversal. Indicated with loud “bang.” Reduce power setting, reduce angle of attack, & increase airspeed to correct.
Bleed Air- air tapped from compressor section to used for pressurization, heating, air-conditioning, thermal anti-ice, and other systems.
Combustion:
Burner Can (combustion chamber)- outer casing, with inner liner, which contains fuel injection, ignition, & self-sustaining “fireball.” Combustion chamber ports expanding combustion gases via high-pressure turbine nozzle into high-pressure turbine rotor.
Turbine:
Combustion chamber ports expanding combustion gases via high-pressure turbine nozzle into high-pressure turbine rotor, then into low-pressure turbine rotor.
High-pressure turbine- extracts sufficient energy from expanding combustion gases to drive high-pressure compressor (& accessory section). High-pressure spool % design RPM indicated with N2.
Low-pressure turbine- extracts sufficient energy from combustion gases to drive low-pressure compressor & fan. Low-pressure spool % design RPM indicated with N1.
TIT- Turbine Inlet Temperature. Highest temperature in a turbine engine.
ITT- Inter-stage Turbine Temperature. Measured between compressor & power turbines.
TOT- Turbine Outlet Temperature.
TGT- Turbine Gas Temperature.
Flameout- fuel/air mixture is not sufficient to sustain combustion.
Exhaust:
Accelerated exhaust gasses provide thrust. Turbojet exhaust- hot exhaust gases rip into cool atmosphere, resulting in loud wind shear. Turbofan exhaust- tapered cone & struts mix hot primary exhaust with cool bypass airflow to produce total thrust. Cool bypass air mixing with hot exhaust air, insulates/disperses hot exhaust gasses & muffles loud wind shear.
EPR- Engine Pressure Ratio “eeper.” Ratio of turbine discharge (exhaust) to engine inlet pressure (intake). EPR used to measure thrust produced, especially for takeoff, of “pressure-rated” engine.
EGT- Exhaust Gas Temperature. Usually, main engine temperature gauge used to prevent heat damage to turbine blades or other systems.
Accessory: (may not be considered major section in some applications)
Gear assembly, driven by high-pressure rotor shaft, which functions to drive various accessories (oil pump, fuel pump, hydraulic pump, fuel control unit, starter-generator).
