The housing assembly has four connections:
-
a fuel inlet port,
-
a drain port,
-
a primary port,
-
a secondary port.
(3)
The FDDVA permits the metered fuel to flow through the primary drain valve to the primary manifold. The primary nozzles cause a back-pressure of 10,3 bar (150 psi) when the metered fuel flow is 20 kg/h (44 lb/hr). This causes the start sequence valve to open and fuel flows through the secondary drain valve and to the secondary manifold. The inlet fuel goes through a filter. This makes sure that the fuel is clean during the full operation. If the fuel filter is clogged, the fuel flows around the filter to the fuel nozzles to keep the engine in operation. The primary and secondary ports drain the fuel through the drain port into the drain line.
4. Operation/Control and Indication________________________________ (Ref. Fig. 002)
A. APU Fuel System For a usual start, operation or a second start, the fuel pressure at the APU fuel inlet is:
-a minimum 1,03 bar (15 psi) absolute (to ensure at least 0,69 bar (10 psi) above true vapour pressure),
-maximum 3,5 bar (51 psi) gauge.
If the minimum pressure (1.03 bar) is not available from the aircraft
main fuel pumps, the APU fuel pump will operate automatically.
(1)
Set the MASTER SW 14KD to the ON position. When you push the APU START switch 2KA, the engine starts to turn. At 7% engine speed, the ECB 59KD energizes the fuel solenoid valve to the open position and fuel from the pressurizing valve of the FCU will flow to the FDDVA. At the same time, the ECB 59KD energizes the ignition system. At a pressure of 7.5 psi (0.5171 bar) the primary drain valve in the FDDVA opens and fuel flows from the FDDVA to the primary fuel nozzles, combustion occurs and the engine continues to accelerate.
(2)
At 50% engine speed, the ECB 59KD de-energizes the starter motor 8 KA. The engine continues to accelerate under its own power to governed speed. The fuel speed and proportional governors in the ECB 59KD transmit a signal to the FCU. The FCU then increases or decreases the fuel flow as necessary for the changes in load. This keeps the speed of the APU constant.
(3)
As the engine accelerates, the ECB 59KD transmits a signal to the TM valve of the FCU. The TM valve of the FCU then controls the metered fuel flow. The fuel acceleration control in the ECB 59KD keeps the necessary fuel flow until the engine gets to governed speed. The engine accelerates, the fuel flow increases to a set level and the run sequence valve of the FDDVA opens at 150 psi (10.3421 bar). Then the secondary drain valve is opened by fuel coming from the run seqence valve. This permits a fuel flow to the secondary fuel nozzles, then the primary and secondary fuel nozzles are supplied with fuel.
APU Fuel Control - Functional Diagram
Figure 002
CES APU FUEL CONTROL - DESCRIPTION AND OPERATION
____________________________________________
1.
General
_______ The APU fuel control system operates fully automatically. During APU operation, the FCU, which is governed by the ECB, meters the fuel dependent on the APU load condition. The flow divider assy distributes the fuel via both fuel manifolds to the fuel nozzles. During APU start-up/shut-down, the FCU increases/reduces the quantity of fuel delivered to the flow divider assy. During APU start, the flow divider assy passes fuel to the combustion chamber via the primary fuel manifold only.
2.
Component Location
__________________
(Ref. Fig. 001)
-------------------------------------------------------------------------------FIN | FUNCTIONAL DESIGNATION | PANEL|ZONE|ACCESS | ATA | | | | DOOR | REF.
-------------------------------------------------------------------------------R FUEL CONTROL UNIT (FCU) 315 315AL 49-32-11 R FLOW DIVIDER 315 315AL 49-32-12
LOW PRESSURE FUEL FILTER 315 315AL 49-32-41
3. System Description
__________________ The FCU filters and pressurizes the fuel, delivered by the A/C fuel system, to operate the APU. During APU operation the FCU supplies the correct amount of fuel to support:
-
the initial combustion,
-
the programmed acceleration
-and the on-speed governing
of the APU.
The FCU is controlled by operating schedules of the ECB to meet the
different fuel demands of varying APU operating conditions.
The metered and filtered fuel is distributed to the Flow Divider Assy, from
where it is passed to the combustion chamber, via the fuel manifolds
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