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apu and turbine lecture

Turbine Engine Main Sections

  • Compression

    • Process of compressing incoming air for increased efficiency and pressure.

  • Aircraft

    • Refers to the interaction between the turbine engine and aircraft components.

  • Exhaust

    • Where spent gases exit the engine, affecting thrust and performance.

  • Accessories

    • Additional components contributing to engine functionality (e.g. fuel pumps, ignition systems).

  • Ground Power Unit (GPU)

    • Provides electrical power for starting the APU and other systems.

  • Starter Motor

    • Key component that initiates engine rotation when powered by the GPU.

APU (Auxiliary Power Unit) Operation

  • Electrical Power to Starter Motor

    • The GPU supplies power to the APU's starter motor.

    • Starts the accessory section, rotating essential components.

  • Components powered by Starter Motor

    • Rotates:

      • Cooling fan

      • AC Generator

      • Lubrication System

      • Fuel System

  • AC Generator

    • Activated by the starter, it sends power to the ignition system.

  • Drive Shaft Rotation

    • As the drive shaft spins, it powers:

      • Loading Compressor

      • Power Compressor

      • Turbine

      • Power Turbine

  • Compressor Function

    • The load compressor increases the air pressure before it reaches various systems including:

      • Pneumatic System

      • Bleed Control Valve

Air Compression and Mixing

  • Airflow Process

    • Air flows from the APU to the compressor, then to:

      • Diffuser (increases pressure, decreases velocity)

      • Manifold (directs air to mixed zones)

  • Fuel Mixing

    • Mixes compressed air with fuel in the combustion zone; fuel is dosed via fuel control units.

    • Types of fuel nozzles are Simplex or Duplex.

  • Ignition Process

    • The igniter plugs produce sparks igniting the fuel-air mixture.

Turbine Operations

  • High-Pressure Combustion

    • High velocity, high temperature air from combustion drives the turbines.

    • Turbines rotate blades for energy extraction and compressor work.

  • Turbine Blade Design

    • Shrouded blades with impulse and reaction types.

  • Turbine Temperature Monitoring

    • Thermocouples measure temperature at the turbine inlet (TIT) and guide fuel flow control.

  • Exhaust Section

    • Convergent and divergent nozzles regulate airflow for optimal thrust.

    • EGT (Exhaust Gas Temperature) sensors monitor exhaust conditions.

Airflow and Engine Efficiency

  • Bypass Ratio

    • Represents the ratio of secondary (bypass) airflow to core airflow in high bypass turbofans:

      • Low: < 2:1

      • Medium: 2-4:1

      • High: 5-6:1

      • Ultra High: > 7:1

  • Engine Cooling

    • Bypass airflow contributes to cooling and overall thrust generation.

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