DOC AIRBUS | AMM A320FPOWER SECTION - DESCRIPTION AND OPERATION
** ON A/C NOT FOR ALL
** ON A/C NOT FOR ALL
1. General
The power section of the Auxiliary Power Unit (APU) supplies shaft power to drive:
** ON A/C NOT FOR ALL The power section of the Auxiliary Power Unit (APU) supplies shaft power to drive:
- a load compressor,
- an accessory gearbox,
- an electrical generator.
- a single-stage centrifugal compressor,
- a two-stage, axial flow turbine,
- a reverse-flow, annular combustion-chamber.
APU Power SectionA. Single-Stage Centrifugal Compressor
The compressor section includes:
The compressor section includes:
- a single-stage, 8:1 pressure ratio, machined titanium, centrifugal impeller,
- single-stage, radial-inflow, diffuser vanes,
- axial de-swirl vanes.
B. Combustor Assembly
The combustor assembly is the point in the engine where compressed air and fuel are mixed and ignited. The combustor assembly is made of high-temperture resistant steel alloy and has an inner combuster chamber assembly. The forward end of the combuster housing assembly attaches to the engine power section turbine casing and the aft end attaches to the engine exhaust casing, turbine ring support and containment shield. The main fuel nozzles and pilot fuel nozzles are installed around the circumference of the combustor housing assembly. The main fuel manifold and pilot fuel manifold connect to the respective nozzles. A combuster drain valve is installed in the bottom, centre of the combustor housing assembly (Ref. AMM D/O 49-30-00-00). Two igniters are also installed in the combustor housing assembly (Ref. AMM D/O 49-40-00-00).
The combustor assembly is the point in the engine where compressed air and fuel are mixed and ignited. The combustor assembly is made of high-temperture resistant steel alloy and has an inner combuster chamber assembly. The forward end of the combuster housing assembly attaches to the engine power section turbine casing and the aft end attaches to the engine exhaust casing, turbine ring support and containment shield. The main fuel nozzles and pilot fuel nozzles are installed around the circumference of the combustor housing assembly. The main fuel manifold and pilot fuel manifold connect to the respective nozzles. A combuster drain valve is installed in the bottom, centre of the combustor housing assembly (Ref. AMM D/O 49-30-00-00). Two igniters are also installed in the combustor housing assembly (Ref. AMM D/O 49-40-00-00).
C. Two Stage Axial Flow Turbine
The turbine consists of:
The turbine consists of:
- the first stage nozzle guide vanes (22),
- the first stage turbine wheel with inserted blades (37),
- the second stage nozzle guide vanes (26),
- the second stage turbine wheel with inserted blades (31).
The turbine rear shaft is supported by a roller bearing mounted in a flexible cage. A stainless steel diffuser guides the exhaust gas to the exhaust muffler. Insulation mats, installed around the exhaust muffler, prevent high surface temperatures in the APU tailpipe.
3. Operation
The Fuel Control Unit (FCU), and the Electronic Control Box (ECB) 59KD, control the optimal air and fuel flow. This is necessary for the operation of the power section module.
After the APU starts, air moves through the plenum chamber to the compressor of the power section. It then passes into the primary zone of the reverse-flow annular combustion-chamber. The main and pilot fuel injectors provide the air and fuel mixture for combustion. Additional air enters through holes along the combustion chamber and through secondary tubes. This additional air helps to contain the flame envelope, prevent torching of the combustion-chamber walls and completes the combustion process. The hot gas discharges from the combustion chamber and flows through the turbine. The hot gas expands across the turbine where its energy is converted to mechanical power. This power is used to drive the:
- direct-drive load compressor,
- APU generator,
- necessary controls and accessories for the APU engine operation.
A logic program in the ECB 59KD prevents engine compressor surge. The fuel flow is limited as a function of inlet temperature, inlet pressure and speed.
The Fuel Control Unit (FCU), and the Electronic Control Box (ECB) 59KD, control the optimal air and fuel flow. This is necessary for the operation of the power section module.
After the APU starts, air moves through the plenum chamber to the compressor of the power section. It then passes into the primary zone of the reverse-flow annular combustion-chamber. The main and pilot fuel injectors provide the air and fuel mixture for combustion. Additional air enters through holes along the combustion chamber and through secondary tubes. This additional air helps to contain the flame envelope, prevent torching of the combustion-chamber walls and completes the combustion process. The hot gas discharges from the combustion chamber and flows through the turbine. The hot gas expands across the turbine where its energy is converted to mechanical power. This power is used to drive the:
- direct-drive load compressor,
- APU generator,
- necessary controls and accessories for the APU engine operation.
A logic program in the ECB 59KD prevents engine compressor surge. The fuel flow is limited as a function of inlet temperature, inlet pressure and speed.