Fuel And Fuel Metering Flashcards
Name two maintenance or inspection tasks performed during routine fuel system inspection and maintenance.
Drain sumps, change or clean filters, check linkages for smooth stop-to-stop operation, check fuel lines for cracks and hoses for deterioration , leak check , check pump operation and motor brush wear, check selector valve for wear, check fuel tanks for corrosion and leaks , check fuel quantity and pressure gauges for proper operation, check vents for obstruction, check function of warning system.
What checks of a fuel system can be made to verify proper operation?
A fuel system should have no external leaks. Make sure all units are securely attached. Drain plugs and valves should be opened to clear any water or sediment. Filter screens and auxiliary pumps must be clean and free from corrosion. Fuel system controls should move
freely, lock securely, and should not rub or chafe. Fuel vents must be in the correct position and free from obstruction. Overall engine performance checks give insight into proper fuel system operation. Check all fuel system related gauges for indications of fuel system operation. Carburetor air temperature, fuel flow, fuel pressure, and cylinder head temperature
indications can all indicate potential fuel system problems. An idle mixture check can also be performed.
What is the function and operation of a fuel boost (booster) pump?
A fuel boost pump is designed to provide positive fuel pressure to the engine fuel system. The boost pump forces fuel through the selector valve to the main line strainer. During starting, the boost pump forces fuel through a bypass in the engine-driven fuel pump to the carburetor or fuel injection system. Once the engine driven pump is up to speed, it takes over and delivers the fuel to the metering device.
What is the function of a fuel selector valve?
A fuel selector valve is controlled on the flight deck to select the tank from which tank fuel will be delivered to the engine.
What is done to inspect an engine driven pump for leaks and security?
If booster pumps are installed, they should be energized to check the fuel system for leaks. (During this check, an ammeter can be used to insure all boost pumps pull roughly the same amperage.) The drain lines of the engine drive pump should be free of traps, bends, or restrictions. Check for leaks and the security of the engine driven pump mounting bolts. Check the vent and drain lines for obstructions.
What is the function and operation of engine fuel filters on a turbine engine fuel system?
The function of the engine fuel filters is to remove micronic particles that may be in the fuel so they do not damage the fuel pump or the fuel control unit. Three kinds of filters are used: micron, wafer screen, and screen mesh.
What is vapor lock and how can it be avoided or remedied?
Fuel should be in the liquid state until it is discharged in the intake air stream for combustion. Under certain conditions, the fuel may vaporize in the lines, pumps, or other units. The vapor pockets formed restrict fuel flow through the units to the fuel-metering device. The partial or complete interruption of fuel flow is called vapor lock. The three general causes of vapor lock are low pressure on the fuel, high fuel temperatures, and excessive fuel turbulence. The most significant remedy for vapor lock is the use of boost pumps which pump the fuel from the storage tank to the metering devise under pressure so it cannot vaporize prematurely.
What is a possible reason for fuel running out of a carburetor throttle body?
The float level and fuel level in the float chamber of the carburetor must be below the level of the discharge nozzle or fuel will leak from the nozzle when the engine is not operating.
What are some indications that the mixture is improperly adjusted?
Carbon deposits on the spark plugs and spark plug fouling are signs that the idle mixture is not properly set. Also, faulty acceleration may be an indication of an excessively lean mixture.
What is the procedure for checking idle mixture adjustment on a reciprocating engine?
To check the idle mixture on a warmed up engine, move the mixture control slowly toward the idle cutoff position. Observe the tachometer for a slight RPM rise (10 – 50 RPM) before the engine cuts out. If this does not occur, adjust the idle mixture until it does.
What are possible causes of poor engine acceleration, engine backfiring or missing when the throttle is advanced?
A lean mixture is the most like likely cause. A cracked distributor block or high-tension leak between two ignition leads can also cause these symptoms and backfiring.
What are three types of fuel metering systems used on reciprocating engine and how do they operate?
Float-type carburetors, pressure carburetors, and fuel injection systems are all used on reciprocating aircraft engines. A float type carburetor uses the volume of air moving through a venturi to cause a suction that meters the fuel. A pressure carburetor uses a closed, pressurized fuel system. The venturi serves only to create pressure differentials that control the quantity of fuel to the metering jet in proportion to the airflow to the engine. A fuel injection system is a continuous flow system that measures engine air consumption and uses airflow forces to control the fuel flow to the engine. Fuel is injected into the airstream on a float type carburetor just before the throttle valve, just after the throttle valve on a pressure carburetor and directly into the cylinder head on a fuel injection system.
Name the fuel metering system components in a float type carburetor.
The main metering system components include the throttle, the venturi, the discharge nozzle, and the float and float valve in the float chamber. The idling system components include the idling jet and the idle mixture adjustment. The mixture control system includes either a needle valve or a back-suction line, the acceleration system including a piston/pump and the economizer system including the economizer needle valve.
What is the purpose of the part power stop on some engines when accomplishing engine trim procedure?
The engine is operated at full power or at the part power control trim stop for a sufficient amount of time to ensure it has completely stabilized. This is usually at least 5 minutes. Follow all manufacturer’s instructions.
Explain the operation of a fuel flow indicating system and where it is connected into the engine.
A fuel pressure gauge, calibrated in pounds per hour fuel flow, is used as a fuel flow meter with the Bendix/RSA fuel injection system for reciprocating aircraft engines. This gauge is connected to the flow divider and senses the pressure being applied to the discharge nozzles. This pressure is in direct proportion to the fuel flow and indicates engine power output and fuel consumption.
