1 FUEL SYSTEM The fuel system is one of the major systems of the Airbus A320. This system, controls the entire fuel flow and fuel reservoir on board the aircraft. The primary use of the system is to suppl y fuel to then engine and the APU. It also contributes in the balancing of the center of gravity of the aircraft during flight. On Board the A320, the essential characteristics of the fuel system are: fuel pressurization, Engine Feed, Fuel Transfer, Defuel and Refuel. The fuel system uses a pump feed system to move the fuel in the desired location (tank, engine…).
1.1 FUEL TANKS AND PUMPS The fuel tanks are integrated into the center fuselage area and the wings. The center wing tanks are part of the center wing box. The wing tanks are divided into inner and outer cells as seen in Figure 1-1:Fuel tanks SchematicFigure 1-1. To 1-1. To reduce structural loads, the fuel in the outer cells is not used until the fuel in the inner cells decreases to a low level [1]. There is a vent surge tank outboard of the outer tank in each wing.
Figure 1-1:Fuel 1-1:Fuel tanks Schematic Schematic [1] [1] The main fuel pump system supplies fuel from the center tank or the inner wing tanks to the engines [2]. The system has six main fuel pumps, two are installed in the center thank and two are installed in each wing tank inner cell [1]. All wing tank pumps remain active throughout the flight. They are fitted with pressure relief relief sequence sequence valves; valves; these valves valves give priority priority to center center tank pump pump to supply fuel until it is low [3]. A specific fuel pump supplies the APU when tank pumps are not operating. This fuel pump is connected to the left supply line. This fuel line is critical at the procedure of engine starting [3].
1.2 FUEL SYSTEM VALVES The fuel system is run by a pressurized line made of pumps, pipes and valves. Valves play the roll of regulating the fuel flow and fuel directions. There exist 4 types of valves on board of the Airbus A320.
1.2.1 Transfer Valves Two electrical transfer valves are mounted in each wing to permit fuel transfer from outer to inner tank as seen in Figure 1-2 [2]. They turn active when the fuel reaches low level in the inner cells. The use of transfer valve instead of cross feed valves is due to the nature of transfer valves, transfer valves allow one way transfer of fluid instead the cross feed valve allows two ways of fluid movement. 1.2.2 Cross Feed Valve A cross feed valve controlled by a double motor allows both engine to be fed from one side or one engine to be fed from both sides. The cross-feed valve is normally inactive [2]. The activation of the cross-feed valve is temporary and allows the shortest route of fuel to flow. It is kept inactive throughout most of the flight, it is usually activated to balance the aircraft, or an engine is lost. 1.2.3 Engine Low Pressure Valves The low-pressure valve isolates the engines or APU from the fuel supply. This valve manages the fuel flow to the engine and APU. The Valve is active when the engines or APU system are running, it deactivates when the engine or APU is shut down or when FIRE pushbutton is released out [2]. 1.2.4 Suction Valves The suction valves are inactive in normal conditions, they allow the engines to be fed by gravity if the inner tank pumps fail. The center tank is not equipped with suction valves therefore in case of pump failure, the engines cannot be fed from the center tank [2]. 1.2.5 Sequence Valves Pressure relief sequence valves are integrated on the wing tank pumps as see in Figure 1-2, to give priority to center tank pump to supply fuel. The sequence valves give priority by limiting the wing tank pumps output pressure [3]. Sequence valves have external drain port to keep from trapping leakage oil. The sequence valves have the option to be internally pilot-operated, controlling fluid passing through fuel pumps. Sequences valves have some disadvantages; once a high pressure at a certain level is reached sequence valves switch to relief the pressure however, the actuator positioning cannot be known, the only information given when sequence valves are activated is that there is a high pressure in the fluid but the cause is unkown.
Figure 1-2:Detailed Fuel Line Schematic [3]
1.3 R EFUELING AND DEFUELING SYSTEM Refuel panels are located on the fuselage and wings as see in Figure 1-3. The refuelling system is Automatic, the refueling procedure starts by the outer cells. If the selected fuel loads exceed the wing tank capacity, the center tank is refuelled simultaneously. As the outer cells are being refuelled, fuel flows to the inner cell though a spill pipe. Refuel Valves close automatically when the tanks contain the preselected fuel loads [2].
Figure 1-3:Refuel Panel Locations [2]
1.4 FUEL RECIRCULATION SYSTEM The fuel recirculation system is used to cool down the engines. The fuel supplied to each engine goes from the high-pressure fuel line through the integrated drive generator (IDG) in which it releases the absorbs heat, to the fuel return line as seen in Figure 1-4. This operation ensures that the IDG cooler is operating when the oil temperature is high or when at low engine power [2].
Figure 1-4: Fuel Recirculation System [2]
Figure 1-5:Fuel System Architecture [2]
Figure 1-6: ECAM Display [1]
Fuel Sensors are installed in the Fuel tank to detect the quantity of fuel left in the tank, it is programmed to be triggered when the fuel system reaches 750 Kg. At this stage the Low Fuel sensor sends commands to the FQI Computer as seen in Figure 1-5 and the FQI sends signals to the ECAM Fuel Page Figure 1-6 to trigger the ‘LO LVL’ warning.
[1] AIRBUS S.A.S., "T1-28-Fuel," Airbus Training & Flight Operations Support and Services, Toulouse , 2005. [2] AIRBUS, "28-Fuel System," AIRBUS Training manuals, 2006. [3] AIRBUS, "ATA 28: Technical Training Manual," AIRBUS, Blagnac , 2000.
