Gas Turbine Main Engine Components: Compressor, Combustor, Turbine, and Exhaust

The core components of a gas turbine engine are designed to process air through the Brayton cycle: Intake, Compression, Combustion, Expansion (Turbine), and Exhaust.

Compressor Section

The compressor increases the pressure of the air mass flow to supply the combustion chamber.

• Types:
  • Centrifugal: Accelerates air radially. Robust, simpler, max pressure ratio ~4.5:1 per stage.
  • Axial: Air flows parallel to the axis. Made of alternating rows of Rotors and Stators.
    • Rotor: Spins reduces volume, adds kinetic energy (Velocity increases, Pressure increases).
    • Stator: Stationary vanes. Converges kinetic energy into pressure energy (Velocity decreases, Pressure increases). Also straightens airflow.
• Overall Effect: Through the compressor, Pressure and Temperature increase, while Axial Velocity decreases.
• Compressor Stall/Surge: Can occur if airflow is disrupted (e.g., mismatched RPM and airflow).
  • Symptoms: High EGT, Vibration, loss of thrust, "banging" noise (surge).
  • Prevention:
    • Variable Inlet Guide Vanes (VIGVs): Before the 1st stage, adjust air angle.
    • Variable Stator Vanes (VSVs): Between stages.
    • Bleed Valves: Release pressure to prevent backflow.

Diffuser

Located between the compressor exit and the combustion chamber.

• Function: A divergent duct that decreases air velocity and increases static pressure.
• Purpose: Slows air to a speed compatible with flame propagation speeds, ensuring the flame burns continuously and isn't extinguished.

Combustion Chamber

Mixes compressed air with fuel and burns it.

• Process: Constant pressure combustion.
• Fuel Nozzles: Atomize fuel into a spray with axial and tangential velocity components.
• Drain Valves: Located at the bottom to remove unburnt fuel after a failed start (wet start).

Turbine Section

Extracts energy from hot gases to drive the compressor and accessories.

• Types:
  • Impulse Turbine:
    • Nozzle Guide Vanes (NGV): Convergent duct -> Velocity Increases, Pressure Decreases.
    • Rotor Blades: Bucket shape -> Velocity Decreases, Pressure Constant.
  • Reaction Turbine:
    • NGV: Directs air (Pressure constant).
    • Rotor Blades: Convergent shape -> Velocity Increases, Pressure Decreases (creating reaction force).
• Limitations: The turbine is the most stressed component (Heat + Centrifugal force).
  • Creep: Blades stretch over time due to stress/heat. Limits engine life and max temperature (TGT/EGT).
  • Active Clearance Control: Cools the casing to maintain optimal tip clearance.

Exhaust Section

Directs gases out of the engine to produce thrust.

• Jet Pipe: Conducts gas.
• Exhaust Cone: Smooths flow leaving the turbine.
• Propelling Nozzle: Usually convergent.
  • Function: Increases exhaust gas velocity and decreases pressure to maximize momentum and thrust.

Foreign Object Damage (FOD)

Ingestion of debris.

• Indications: High Vibration, High EGT, fluctuating RPM or parameters.