POWER SECTION - DESCRIPTION AND OPERATION
_________________________________________
1. General
_______ The power section of the Auxiliary Power Unit (APU) supplies shaft power to drive:
-a load compressor,
-
an accessory gearbox,
-
an electrical generator.
It is a single-shaft assembly with:
-
a single-stage centrifugal compressor,
-
a two-stage axial flow turbine,
-
a reverse-flow, annular combustion-chamber. The single main shaft of the assembly is held with two bearings. The first bearing is a Duplex ball bearing located FWD of the L/C impellor and the second is a roller bearing located AFT of the second stage turbine. The power section compressor and the turbine wheel are given full hub containment. If a rotor hub or disc failure occurs, the debris is contained.
2. Description
___________
(Ref. Fig. 001)
A. Single-Stage Centrifugal Compressor
The compressor section includes:
-a single-stage, 7,5 : 1 pressure ratio, machined titanium, centrifugal impeller,
-single-stage, radial-flow, diffuser vanes,
-axial de-swirl vanes.
The centrifugal compressor is less likely to suffer blade or disc failure
than an axial flow compressor. The housing of the centrifugal compressor
will contain the debris should a compressor hub failure occur.
B. Reverse-Flow Annular Combustion-Chamber The compressor discharge air cools the reverse-flow annular combustion-chamber. The annular combustion-chamber surrounds the turbine hub containment.
C. Two-Stage Axial-Flow Turbine
The two-stage, axial-flow turbine includes:
-a cooled first stage nozzle,
-inserted first stage rotor blades,
-an uncooled second stage stator,
-a dual alloy second stage rotor,
-an annular exhaust diffuser. The turbine operates on a high cyclic (stop-start) life. The component is made from high temperature alloys. The turbine is provided with full hub containment, which will contain all the debris should a turbine hub or disc failure occur.
R EFF : 001-049, 101-105, 107-107, 151-199, 49-21-00Page 1 201-210, Config-2 Aug 01/05
CES
Power Section Figure 001
R EFF : 001-049, 101-105, 107-107, 151-199, 201-210, Page 249-21-00Config-2 Aug 01/05
CES
3. Operation
_________ The Fuel Control Unit (FCU), and the Electronic Control Box (ECB) 59KD, control the optimal fuel flow. This is necessary for the operation of the APU. To start the APU, 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 atomizers spray fuel into the combustion-chamber where it is mixed with the air and ignited. Additional air enters through holes along the combustion chamber. This additional air helps to contain the flame envelope, prevent torching of the combustion-chamber walls and complete the combustion process. The hot gas discharges from the combustion chamber and flows through the two-stage axial-flow turbine. The hot gas expands across the turbine where its energy is converted to mechanical power. This power is used to drive the:
-power section compressor,
-load compressor,
-gearbox,
-accessories for the APU operation.
A logic program in the ECB 59KD prevents engine compressor surge. The flow
of fuel is limited to do this as a function of inlet temperature, inlet
pressure and speed.
R EFF : 001-049, 101-105, 107-107, 151-199, 49-21-00Page 3 201-210, Config-2 Aug 01/05
CES POWER SECTION - DESCRIPTION AND OPERATION
_________________________________________
1. General
_______ The power section of the Auxiliary Power Unit (APU) supplies shaft power to drive:
-a load compressor,
-
an accessory gearbox,
-
an electrical generator.
It is a single-shaft assembly with:
-
a single-stage centrifugal compressor,
-
a two-stage, axial flow turbine,
-
a reverse-flow, annular combustion-chamber. The single main shaft of the assembly is held with two bearings. The first bearing is a ball bearing which is installed between the load compressor and the accessory gearbox. A second bearing, which is of the roller type, is installed at the end of the turbine. The power section compressor and the turbine wheel are given full hub containment. If a rotor hub or disc failure occurs, the debris is contained.
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