APU Flashcards
Engine
Solar T62-T-2C gas turbine rated at 95shp
Sections of APU Engine
- Annular air inlet
- Compressor section
- Combustion
- Turbine section
- Engine accessories section
- Reduction drive assembly
Air Inlet
Annular air intake screen
Air inlet DUCT assembly is contoured cylindrical casting is is bolted to APU
Compressor Section
Single stage centrifugal compressor
Fixed guide vanes
Bolted onto flange which is integral to APU rotor shaft
Rotor shaft is supported by forward ball bearing and at aft end with roller bearing
Forward bearing resists THRUST and RADIAL loads
Aft bearing resists RADIAL loads only
Combustion Section
Annular combustion burner assembly, air flows between walls of combustion housing and liner and reverses direction to flow forward through burner section
Single igniter mounted at the AFT LEFT side of combustor housing ignites fuel air mixture supplied by start fuel nozzle during starting
6 equally spaced main fuel injectors mounted on combustor housing supply fuel to 6 vaporizing tubes
Tubes direct fuel into chamber of combustion liner for burn
Port in sump on lowest portion of combustor housing vents excess fuel after false starts and malfunctions
Exhaust gas temp monitored by single thermocouple on aft section of combustor housing
2 section thermal blanket laced around combustor housing and exhaust duct to protect people from heat
Turbine Section
Turbine wheel is pressed onto aft end of rotor shaft
This connection causes the turbine rotor shaft to turn the compressor and output pinion in to the reduction drive assembly
Reduction Drive Assembly
Single piece reduction drive housing made of magnesium
APU output pinion enters reduction drive and moves 3 planetary gears that drives short output shaft
Output shaft drives accessory drive gear and oil pump drive gear
Accessory drive gear drives APU speed detector and fuel control assembly
Oil pump drive gear drives APU lube system, which consists of:
- Pump
- Filter
- Pressure relief valve
- Oil jets
- Connecting passages
- Oil sump
Hydraulic APU Motor/Pump
Mounted to front of reduction drive housing and splined to reduction drive output shaft
Acts as a motor to start APU
Acts as a pump to turn the AGB
APU Fuel
Fuel comes from LH tank and is sucked by APU fuel booster pump (DC powered) and then pushed through APU fuel shutoff solenoid valve and filter, then to the engine mounted pump and control unit
Booster pump operates when APU switch is at start and continues operating until switch is off
Shutoff valve is energized open during APU start and remains open until start switch is OFF or APU button is pressed
APU Fuel Control System
Engine driven fuel pump pushes fuel to engine governor assembly
From the governor fuel is split into:
- Start fuel
- Main fuel
During start, fuel flows through a start solenoid valve (energized open by ESU) to the start fuel nozzle (only 1). During normal ops the start solenoid valve is closed and main fuel solenoid is open
Fuel is then provided via main fuel line to 6 main fuel injectors
Fuel control system is mounted to at top section of reduction drive assembly
APU Start Fuel Solenoid Valve
Energized open by 28vdc from ESU at 5% rated APU speed
Valve de energized off at 70% rated APU speed
APU main Fuel Solenoid Valve
Energized open by 28vdc from ESU triggered at 14% APU speed
Normal shutdown of APU is accomplished by de energizing this valve
APU Fuel System Operation
APU switch moves from RUN to START:
- Airframe fuel pump takes fuel from LH fuel tank and pressurizes fuel through airframe shutoff valve
- A. Hydraulic start valve opens, causing motor pump to turn, which turns compressor
- As turbine speed increase APU fuel pump output increases, forcing fuel through start fuel valve, which opens at 5%
- Single igniter is activated at 5%, causing combustion
- At 14% the main fuel solenoid opens, allowing max fuel flow to fuel manifold and to 6 vaporizing tubes
- A. All fuel flow is controlled in proportion to compressor pressure
- At 70%, igniter, hydraulic pump, and start fuel solenoid are all switched off
* if engine fails to reach 90% in 40 seconds, ESU will shut engine down with “Fail to Start” indication*
APU speed is governed by flyweight assembly within the governor housing. APU slows causes more fuel to flow, APU goes to fast it restricts the fuel flow to APU
If APU load is significantly reduced, a minimum flow orifice in fuel control housing bypasses the governor, which allows a small amount of fuel under pump pressure to flow to fuel nozzles, which is enough to maintain combustion
Moving APU switch to OFF position removes 28vdc from airframe fuel pump solenoid and ESU. Fuel pump stops, fuel solenoid closes the valve, and starves APU of fuel
APU Oil Pump
2 gear pump housed in reduction drive housing
APU Oil Filter
Contains bypass, located on reduction drive housing
Angled tube on No. 2 side of reduction gear housing