The Auxiliary Power Unit (APU) on the A330 aircraft is a Gas Turbine Engine Compressor Power (GTCP) 331-350 and it is a compact, self-contained gas turbine engine designed to provide electrical power and bleed air for essential aircraft systems.
The key sections of this are the Power Section (the engine), the load compressor (creates pneumatic pressure), the accessory gearbox (drives multiple components including electrical power generation).
Power Section
Centrifugal Compressor: This two-stage design compresses intake air, increasing its density for optimal combustion.
Reverse Flow Combustion Chamber: The annular (donut-shaped) combustion chamber provides a controlled environment for fuel and air to combust.
Three-Stage Axial Turbine: Expanding combustion gases drive this turbine, which powers the compressor, load compressor, and accessory gearbox. The first stage utilizes air cooling for thermal efficiency.
Load Compressor
Single-Stage Centrifugal Design: Similar to the power section compressor, this component generates a pressurized bleed air supply.
Inlet Guide Vanes (IGVs): These adjustable vanes regulate airflow into the load compressor. Their position is controlled by a fuel-driven actuator to optimize bleed air output based on system demand.
Accessory Gearbox
Power Transfer: The gearbox receives rotational power from the load compressor and distributes it to vital APU accessories.
Mounted Components: The gearbox houses the oil pump (which also drives the Fuel Control Unit), generator, starter, and compartment cooling fan.
Oil Reservoir: The gearbox serves as the APU’s oil reservoir and includes critical oil monitoring sensors.
Additional Considerations
Mounting System: The APU utilizes a three-point mounting system with vibration isolators to minimize structural stress transfer between the APU and airframe.
Electronic Control Box (ECB): The ECB monitors APU operation, controls systems, and stores fault codes for troubleshooting purposes.
Understanding the APU’s design and functionality is crucial for maintenance technicians and engineers responsible for ensuring its reliable operation.
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