05/16/16
Overview
The thermal management system transfers hot fuel from the engines to the wing tanks.
Switch/lights on the FUEL control panel manually control the fuel return-to-tank (FRTT) shutoff-valves. When the fuel temperature in the left or right wing tank is too low, the WING FUEL LO TEMP caution message shows on the EICAS display. The pilot can set the L and R RECIRC switch/lights to ON to open the FRTT shutoff-valves. The FRTT shutoff-valves will open in approximately 3 seconds if the engine fuel flow is approximately 2,000 lb/hr (910 kg/hr). When the FRTT shutoff-valves are opened, the L- R FUEL RECIRC ON status messages show on the EICAS display. Fuel, made warm by the engine, then goes back to the wing tanks through the aft fuel transfer tubes.
After the WING FUEL LO TEMP caution message goes off, the pilot sets the L and R RECIRC switch/lights to OFF. If the fuel temperature in the left or right wing tank gets too hot, the WING FUEL HI TEMP caution message shows on the EICAS display.
There is also an EICAS caution message for L-R RECIRC FAIL On A/C 9090 and Subs and Post SB 700-31-013 for Global Express, or on Global 5000/XRS. This message will show when the left (right) FRTT shutoff-valve is commanded open with the valve indication shown as closed. The message will also show when the left (right) FRTT shutoff-valve is commanded closed with the valve indication shown as open.
05/16/16
Fuel Return-to-Tank (FRTT) Check-Valve
On A/C 9100 and subs and Post SB 700-28-001 for Global Express, or on Global 5000/XRS:
The FRTT check-valves are spring-loaded, poppet-type valves. The FRTT check-valves are installed in the aft transfer fuel lines, at the aft transfer shutoff-valves, near FS877.25 for Global Express/XRS and are installed in the transfer fuel lines near FS877.25 for Global 5000. The FRTT check-valves control the flow of fuel to the wing tanks. The FRTT check-valves prevent the flow of fuel from the engines and the aft transfer pumps to go in the opposite direction.
09/21/18
Fuel Return-to-Tank (FRTT) Shutoff-Valve
On A/C 9076, 9078 and Subs and Post SB 700-73-006 for Global Express, or on Global 5000/XRS:
The FRTT shutoff-valves are electrically operated solenoid valves. Approximately 2,000 lb/hr (907 kg/hr) of fuel flow is necessary to open the FRTT shutoff-valves. The FRTT shutoff-valves control the flow of fuel from the engines to the wing tanks. The FRTT shutoff-valves are installed on the engines near FS945.50.
Note:
Information on the FRTT shutoff valve is also available in chapter 73 of the Rolls-Royce Engine Manuals.
System Operation
FRTT Valve
The purpose of this valve is to maintain the fuel tank temperature above a minimum value during high altitude, long-range flights. The fuel return to tank (FRTT) valve is solenoid-controlled and is activated by the pilot. For Global 5000/Express/XRS, the operation is controlled automatically by the FMQGC. The FRTT valves (one on each engine) are controlled by two PBA switches located on the fuel control panel. For Global 5000/Express/XRS, the PBAs inhibit the system. The valve is basically a two position/three-port device which takes hot fuel from the excess capacity of the engine HP pump and recirculates it back to the aircraft wing tanks.
With the FRTT valve de-energized, the excess fuel that passes from the fuel metering unit to the FRTT valve is then sent to the inlet of the fuel cooled oil cooler. With the FRTT valve solenoid energized powered, the fuel is directed back to the aircraft wing tanks and the path to the fuel cooled oil cooler is closed.
The valve is spring-loaded closed (fuel routed to fuel cooled oil cooler), with an internal pressure balanced spool valve. When the solenoid is energized, the spool valve moves and ports to allow fuel flow to be diverted to the wing fuel tanks. A single position indication micro switch provides feedback of valve position.
Fuel Recirculation System
The fuel recirculation system has been installed to permit the Global to conduct long-range, high altitude flights in cold ambient conditions. The aircraft wing tank fuel must be heated to prevent bulk fuel temperatures from approaching/reaching the freezing point of the fuel. This situation is most likely to occur when the aircraft flies within or across the tropics at high altitude.
The engines generate the heat. The hot engine oil is cooled in the FCOC (fuel cooled oil cooler), where the oil heat is rejected into the feed fuel. The FRTT (fuel return to tank) valve allows the hot fuel, downstream of the HP pump, to return to the fuel tank via the A/C fuel recirc system. With the FRTT valve closed, engine internal fuel recirculation is allowed for heat management purposes, as per the already certified baseline A/C configuration.
Note:
The FRTT valve is fuel pressure actuated. The A/C fuel pumps pressure is not sufficient to activate the valve, thus the engine must be running for the FRTT valve to open.
With the FRTT valve open, hot fuel is returned back to the wing fuel tanks. The recirc line taps into the existing aft transfer line which runs below the floor in the cabin. A distribution manifold is added at the end of the transfer line to allow distribution of the hot fuel to bay 1 and bay 2. Even though cooling is more extensive at the wing tip, no heat is added there because bay 3 empties before the local fuel temperature gets close to −40 °C.
A check valve is fitted before the tap-in point with the aft transfer system to prevent leakage of fuel from the aft tank in the aft equipment bay, in the event of a ruptured line that may result from a rotor burst. Another check valve is fitted in the aft transfer pump branch to prevent FRTT flow from propagating to the aft tank.
Note:
The Global 5000 does not have an aft tank system, so the aft tank lines are used solely for thermal management.
There are two types of operational control system available for the thermal management, manual and automatic, both of which are controlled through the cockpit fuel control panel. All Global Express/XRS/5000 aircraft are equipped with the automatic system.
The manual system uses L and R fuel recirc ON PBAs on the cockpit control panel that the pilot will select to open the FRTT valves. When the corresponding valve is commanded open, the PBA illuminates ON in white. If the pilot gets a low temp message, or suspects that conditions are such that one may occur, the PBAs can turn on the system for each respecting wing. Once the wing fuel temperature is warm enough (>10 °C), a WING FUEL HI TEMP caution message will appear reminding them to turn the system OFF.
Also, if the pilot commands the system ON below 34,000 feet or 600 lb fuel quantity, or in the near ground mode, a FUEL RECIRC ON advisory message will appear, instructing the pilot to turn it OFF.
The automatic system uses L and R recirc OFF PBAs. Normally, the pilot will not select these inhibits, but if he does, the FMQGC will be unable to command the recirc valves to open. Otherwise, the FMQGC will command the recirc valves open whenever the A/C altitude is above 34,000 feet with the average fuel temperature drops below −9 °C or the coldest temperature drops below −20 °C.
