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Protection from overtemperature during APU acceleration is provided by protective features incorporated in the ECU. The APU receives fuel from the right collector tank. The APU fuel system incorporates the right DC-powered fuel pump, fuel feed shutoff valve (SOV), fuel shutoff solenoid, fuel system filters, a high-pressure fuel pump (mounted on the APU), fuel control unit (FCU), and the fuel manifold assembly. COMPONENTS AND OPERATION APU FUEL SUPPLY The right DC-powered fuel pump delivers fuel under pressure to the APU fuel control unit. When the right engine is run-ning, the fuel pump ceases operation and fuel is delivered by the main engine ejector pump. FUEL CONTROL UNIT AND FUEL SHUTOFF SOLENOID The APU fuel control unit (FCU) meters fuel under command of the electronic control unit (ECU). During the start se-quence, the fuel shutoff solenoid, located between the FCU and the fuel nozzles is opened by the ECU at 5% rpm. Fuel is supplied in accordance with a schedule that accelerates the APU throughout the start sequence. When the APU is stabilized, fuel scheduling is influenced by the rpm and EGT as well as generator and bleed air demands. During normal or automatic APU shutdown, an overspeed signal closes the fuel solenoid valve and torque motor at the APU and causes the APU to shutdown. APU SHUTDOWN MODE Engagement of the APU master switch to OFF, remote stop, emergency/fire, or in the event of an exceeded limit, the ECU initiates the APU shutdown sequence by commanding the fuel off. When the shutdown sequence is complete, the ECU tran-sitions to idle mode and then powers down if the APU master switch is in the OFF position. The following is a list of all the APU protective shutdowns showing the ones that are inhibited in-flight (essential mode): * - An asterik indicates these shutdowns are inhibited in the essential mode. 28 VDC Power Loss Fire Indication* Reverse Flow* No Acceleration (during start)* Loss of EGT Signal* Overspeed Low Oil Pressure* Emergency Fire High Oil Temperature* Internal ECU Failure Overtemperature* Loss of Overspeed Protection Circuit No Flame (during start)* Volume 2 Flight Crew Operating Manual Sep 13/2004 CSP 100-6 REV 1 DESCRIPTION |
