DOC AIRBUS | AMM A320FEXHAUST SYSTEM - DESCRIPTION AND OPERATION
** ON A/C NOT FOR ALL
** ON A/C NOT FOR ALL
1. General
The APU exhaust system ducts the engine exhaust gas overboard. Its secondary function is to decrease the exhaust noise level. To keep aerodynamic losses during APU operation to a minimum, the duct has a sufficiently large diameter. Also, the exhaust system discharge is positioned at the very aft end of the aircraft, where a low pressure area is generated during flight. Thus it is also made sure that exhaust gas does not re-enter the APU air intake system.
All components in contact with exhaust gas are made of corrosion resistant materials. All components exposed to high temperatures are made of fireproof or fire resistant materials. A flexible connection allows for relative movement between the APU and the muffler assembly and allows for any vibration and inertia loads during operation. Drainage provisions are incorporated into the muffler assembly. One ventilation louver each at the top and the bottom of the muffler compartment limit the structure temperature to 110 deg. C max. (Ref. 53-58-00). Muffler assembly surface temperature does not exceed 232 deg. C.
** ON A/C NOT FOR ALL The APU exhaust system ducts the engine exhaust gas overboard. Its secondary function is to decrease the exhaust noise level. To keep aerodynamic losses during APU operation to a minimum, the duct has a sufficiently large diameter. Also, the exhaust system discharge is positioned at the very aft end of the aircraft, where a low pressure area is generated during flight. Thus it is also made sure that exhaust gas does not re-enter the APU air intake system.
All components in contact with exhaust gas are made of corrosion resistant materials. All components exposed to high temperatures are made of fireproof or fire resistant materials. A flexible connection allows for relative movement between the APU and the muffler assembly and allows for any vibration and inertia loads during operation. Drainage provisions are incorporated into the muffler assembly. One ventilation louver each at the top and the bottom of the muffler compartment limit the structure temperature to 110 deg. C max. (Ref. 53-58-00). Muffler assembly surface temperature does not exceed 232 deg. C.
2. Component Location
** ON A/C NOT FOR ALL 
APU Exhaust Muffler Assembly Installation| ------------------------------------------------------------------------------- |
| FIN | FUNCTIONAL DESIGNATION | PANEL|ZONE|ACCESS | ATA |
| | | | | DOOR | REF. |
| ------------------------------------------------------------------------------- |
| EXHAUST MUFFLER BODY 315/ 315AL/ 49-81-41 |
| 316/ 316AR/ |
| 317 317AL |
| HOT NOZZLE ASSEMBLY 315/ 315AL/ 49-81-42 |
| 316 316AR |
| BELLOWS 315/ 315AL/ 49-81-42 |
| 316 316AR |
| V-CLAMP INSULATION SEGMENTS 315/ 315AL/ 49-81-41 |
| 316 316AR |
3. System/Component Description
(1) Exhaust Muffler Body
(a) Muffler Substructure
It is a riveted corrosion resistant steel (CRES) structure, made of frames, an outer tube and provisions for external seals and insulation segments. It has the subsequent functions:
It is a riveted corrosion resistant steel (CRES) structure, made of frames, an outer tube and provisions for external seals and insulation segments. It has the subsequent functions:
- it is the load carrying structure of the complete muffler assembly,
- it is the muffler resonator,
- to attach the muffler assembly to the rails in the tailcone muffler compartment.
(b) Tail Pipe Assembly
Its central part is made of feltmetal (sound attenuation CRES sheet metal). The end pieces are made of solid CRES sheet metal. The aft tube section is welded to the muffler substructure. The central tube section is put in from the front and positioned against the aft tube section. The forward tube section, which has a provision for the sealing ring, is then put in and riveted to the muffler substructure. Thus the feltmetal tube section is captured between the end sections with sufficient play to allow for thermal expansion differences.
Its central part is made of feltmetal (sound attenuation CRES sheet metal). The end pieces are made of solid CRES sheet metal. The aft tube section is welded to the muffler substructure. The central tube section is put in from the front and positioned against the aft tube section. The forward tube section, which has a provision for the sealing ring, is then put in and riveted to the muffler substructure. Thus the feltmetal tube section is captured between the end sections with sufficient play to allow for thermal expansion differences.
(c) Insulation Covers
The complete exterior surface of the muffler is covered with 2 large insulation blankets and several small insulation segments. These are held in position with lockwire, fastened to the buttons on the insulation components.
The function of these is to reduce the muffler assembly surface temperature to a maximum of 232 deg. C for all ambient temperatures or APU operating conditions.
The complete exterior surface of the muffler is covered with 2 large insulation blankets and several small insulation segments. These are held in position with lockwire, fastened to the buttons on the insulation components.
The function of these is to reduce the muffler assembly surface temperature to a maximum of 232 deg. C for all ambient temperatures or APU operating conditions.
(d) Sealing ring
This component is installed in a recess on the inner liner forward-tube-section. It is in continuous contact with the hot nozzle assembly. Thus it seals the clearance between these assemblies and allows for relative movement between them.
This component is installed in a recess on the inner liner forward-tube-section. It is in continuous contact with the hot nozzle assembly. Thus it seals the clearance between these assemblies and allows for relative movement between them.
(e) FR84 Fire Wall Seal
A circumferential fireproof seal is installed on a bracket on the muffler substructure. It seals the gap between the fire wall cutout in FR84 and the exhaust muffler assembly.
A circumferential fireproof seal is installed on a bracket on the muffler substructure. It seals the gap between the fire wall cutout in FR84 and the exhaust muffler assembly.
(2) Hot Nozzle Assembly
This component is directly attached to the APU turbine flange with a standard V-clamp. It is in contact with the tail pipe assembly through the sealing ring and the muffler body through the externally installed bellows. Thus APU movement is not transmitted to the rigidly installed muffler assembly. A drain port is installed at the lowest point (Ref. AMM D/O 49-17-00-00).
This component is directly attached to the APU turbine flange with a standard V-clamp. It is in contact with the tail pipe assembly through the sealing ring and the muffler body through the externally installed bellows. Thus APU movement is not transmitted to the rigidly installed muffler assembly. A drain port is installed at the lowest point (Ref. AMM D/O 49-17-00-00).
(3) Bellows
It is the flexible connection between the hot nozzle and the muffler body. It is also a back-up seal to prevent exhaust gas leakage into the APU compartment and thus compartment contamination. It is attached to both items with conventional band clamps. It is rigid enough to position the hot nozzle assembly, yet flexible enough to permit relative movement between the APU and the muffler body.
It is the flexible connection between the hot nozzle and the muffler body. It is also a back-up seal to prevent exhaust gas leakage into the APU compartment and thus compartment contamination. It is attached to both items with conventional band clamps. It is rigid enough to position the hot nozzle assembly, yet flexible enough to permit relative movement between the APU and the muffler body.
(4) V-Clamp Insulation Segments
To make sure that the surface temperature does not exceed 232 Deg. C, the connection between the APU turbine flange and the hot nozzle assembly is insulated. Two half-circle insulation segments cover the interface, held in position with lockwire fastened to the buttons on these items.
To make sure that the surface temperature does not exceed 232 Deg. C, the connection between the APU turbine flange and the hot nozzle assembly is insulated. Two half-circle insulation segments cover the interface, held in position with lockwire fastened to the buttons on these items.
B. Muffler Assembly Installation
Support rails align the assembly with the APU. Longitudinal positioning is provided at the rear attachment brackets only. Lateral positioning is made by fixing the assembly to the left rail. The distance between the rails is 6mm larger than the distance between the muffler assembly attachment brackets. Thus the muffler assembly is positioned 3mm to the left of the APU longitudinal axis. The attachment at the right rail allows for thermal expansion differences.
The 3mm displacement is taken up at the muffler assembly/APU turbine flange interface by the bellows and the sealing ring.
Support rails align the assembly with the APU. Longitudinal positioning is provided at the rear attachment brackets only. Lateral positioning is made by fixing the assembly to the left rail. The distance between the rails is 6mm larger than the distance between the muffler assembly attachment brackets. Thus the muffler assembly is positioned 3mm to the left of the APU longitudinal axis. The attachment at the right rail allows for thermal expansion differences.
The 3mm displacement is taken up at the muffler assembly/APU turbine flange interface by the bellows and the sealing ring.
4. Operation
APU operation will lead to thermal expansion of the complete muffler assembly.
APU operation will lead to thermal expansion of the complete muffler assembly.
- Radial expansion of approx. 6mm in diameter:
This leads to central positioning of the muffler assembly because of its assymetrical installation position at ambient temperature. - Fwd. axial expansion:
This leads to a reduction of the distance between the muffler assembly and the APU. This is taken up externally by compression of the bellows; Internally by forward displacement of the sealing ring along its contact surface on the hot nozzle assembly. - Aft. axial expansion:
This leads to a somewhat further extension of the muffler assembly into the airstream and an increase in compression of the access fairing seal.