Positive Displacement Pumps and Burners
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Questions and Answers

What happens to the flow of a positive displacement swash plate pump when the swash plate is perpendicular to the axis of the pump?

  • The flow is zero. (correct)
  • The flow is unpredictable.
  • The flow is maximum.
  • The flow is reversed.

    • What moves the swash plate away from the minimum stroke position in a fuel pump?

  • Increased servo pressure.
  • A spring. (correct)
  • Pump delivery pressure.
  • Reduced inlet pressure.

    • At what condition is the burner fuel flow at maximum?

  • At altitude.
  • Below I.S.A. sea level.
  • I.S.A. sea level. (correct)
  • 10°C above I.S.A. sea level.

    • How is servo pressure, used to control fuel pump 'Swash Plate' angle, obtained?

    <p>From pump delivery pressure through variable restrictions.</p> Signup and view all the answers

    What would be the effect on the engine if the B.P.C half ball valve in the servo line sticks open?

    <p>An increase of fuel flow, therefore an increase in RPM.</p> Signup and view all the answers

    What is the purpose of an A.C.U fitted to a gas turbine engine?

    <p>It limits the rate of increase in fuel flow during sudden acceleration.</p> Signup and view all the answers

    What happens to the pump output if fuel pump servo pressure is reduced?

    <p>The pump output decreases.</p> Signup and view all the answers

    What is the function of the swash plate in a fuel pump?

    <p>To control the direction of fuel flow.</p> Signup and view all the answers

    What is the purpose of the Barometric Pressure Controller in a gas turbine engine fuel system?

    <p>To control fuel flow to suit atmospheric pressure changes</p> Signup and view all the answers

    What must be done after the fuel control unit has been replaced on an aircraft gas turbine engine?

    <p>Retrim the engine</p> Signup and view all the answers

    What is the function of a kinetic valve in a gas turbine engine fuel system?

    <p>To control high-pressure pump output through the movement of a knife blade</p> Signup and view all the answers

    What is the effect of increasing air intake pressure on fuel flow to the burners?

    <p>Fuel flow decreases</p> Signup and view all the answers

    What is the purpose of the attenuator in a gas turbine engine fuel system?

    <p>To damp out pulsations in the fuel delivery to the BPC</p> Signup and view all the answers

    Why is a hydromechanical governor fitted to a gas turbine engine fuel pump?

    <p>To enable the engine to operate over a wide range of fuel specific gravities</p> Signup and view all the answers

    What is the normal fuel-to-air ratio for successful combustion in a gas turbine engine?

    <p>15:1</p> Signup and view all the answers

    What influences the operation of an automatic fuel control unit on a turbojet engine?

    <p>Burner pressure</p> Signup and view all the answers

    What happens to specific fuel consumption at altitude?

    <p>It increases</p> Signup and view all the answers

    During stabilized running conditions, the spill or half-ball valve is typically?

    <p>Lightly seated</p> Signup and view all the answers

    What is the purpose of the L.P. pump?

    <p>To prevent cavitation of the H.P. Fuel pump</p> Signup and view all the answers

    How are the fuel pump plungers lubricated?

    <p>The Fuel</p> Signup and view all the answers

    Which forces control the maximum RPM governor in a non-hydromechanical swashplate type of pump?

    <p>Rotor centrifugal pressure opposed to tension spring loading</p> Signup and view all the answers

    Why do the holes in the body of the duple burner provide air to the shroud around the burner head?

    <p>To minimise carbon formation on the burner face</p> Signup and view all the answers

    What does a fuel heater prevent?

    <p>L.P. filter icing</p> Signup and view all the answers

    What is the main purpose of the Barometric Pressure Control?

    <p>To vary pressure pump output in relation to intake pressure</p> Signup and view all the answers

    What is the function of the E.E.C. on a FADEC engine?

    <p>Electronic control of the hydro-mechanical fuel control unit in all modes</p> Signup and view all the answers

    During normal running conditions, is combustion?

    <p>Self supporting</p> Signup and view all the answers

    What occurs when the swash plate of a positive displacement swash plate pump is perpendicular to the axis of the pump?

    <p>The flow becomes zero</p> Signup and view all the answers

    What is the primary cause of surge in a jet engine?

    <p>Over-fuelling during acceleration</p> Signup and view all the answers

    What happens when the channel reset is activated on a FADEC engine?

    <p>It selects standby which becomes active on the next start</p> Signup and view all the answers

    How is servo pressure obtained in a jet engine fuel system?

    <p>From pump delivery pressure through variable restrictions</p> Signup and view all the answers

    What happens to the maximum RPM of a turbine engine when the fuel specific gravity decreases and the engine is fitted with an uncompensated fuel governor?

    <p>It increases</p> Signup and view all the answers

    What is the primary function of the fuel control unit in a jet engine?

    <p>To control fuel flow to the burners</p> Signup and view all the answers

    What limits the maximum RPM of a turbine engine?

    <p>Reduction of the fuel pump stroke by a spill valve sensitive to centrifugally generated fuel pressure</p> Signup and view all the answers

    Why is it necessary to control fuel supply during rapid acceleration?

    <p>To prevent excessively high EGT and possible compressor surge</p> Signup and view all the answers

    What type of fuel control unit is most commonly used in modern jet engines?

    <p>Hydro-mechanical</p> Signup and view all the answers

    What is the purpose of the kinetic valve in a fuel pump?

    <p>To control H.P pump output</p> Signup and view all the answers

    What is the position of the swash plate in a fuel pump when static?

    <p>In the maximum position</p> Signup and view all the answers

    During stabilized running conditions, the spill or half ball valve is?

    <p>Lightly seated</p> Signup and view all the answers

    What is the primary function of the high-pressure fuel pump in a gas turbine engine aircraft?

    <p>To provide the majority of the fuel pressure to the engine</p> Signup and view all the answers

    What is the position of the pressurization valve and the dump valve in a jet engine fuel system when the engine is shut down?

    <p>Pressurization valve open, dump valve open</p> Signup and view all the answers

    Which of the following air mixtures weighs the most?

    <p>100 parts of dry air</p> Signup and view all the answers

    What does a mixture ratio of 11:1 normally refer to?

    <p>1 part fuel to 11 parts air</p> Signup and view all the answers

    What is the primary purpose of trimming a turbine engine fuel control unit?

    <p>To obtain maximum thrust output when desired</p> Signup and view all the answers

    What type of fuel control is used on most of today's turbine engines?

    <p>Hydromechanical or electronic</p> Signup and view all the answers

    When is the trimming of a turbine engine most accurate?

    <p>No wind and low moisture</p> Signup and view all the answers

    What signal does an H.M.U receive?

    <p>E.E.C</p> Signup and view all the answers

    When trimming a turbine engine, the fuel control is adjusted to:

    <p>Set idle RPM and maximum speed or E.P.R</p> Signup and view all the answers

    What is the function of a supervisory electronic engine control (E.E.C)?

    <p>Adjusts a standard hydromechanical fuel control unit to obtain the most effective engine operation</p> Signup and view all the answers

    What causes the fuel divider valve to open in a turbine engine duplex fuel nozzle?

    <p>Fuel pressure</p> Signup and view all the answers

    What is the safety backup available for the engine fuel flow if the valve on a vane type fuel flow measuring device becomes stuck?

    <p>A differential pressure bypass valve</p> Signup and view all the answers

    What is the primary advantage of the duplex fuel nozzle used in many turbine engines?

    <p>Provides better atomization and uniform flow pattern</p> Signup and view all the answers

    What is the purpose of the flow divider in a turbine engine duplex fuel nozzle?

    <p>Creates the primary and secondary fuel supplies</p> Signup and view all the answers

    Which of the following turbine fuel filters has the greatest filtering action?

    <p>Micron</p> Signup and view all the answers

    Where is the engine fuel shutoff valve usually located?

    <p>Downstream of the engine driven fuel pump</p> Signup and view all the answers

    If a FADEC loses its ADC input, what will it do in the short term?

    <p>Go into soft reversion</p> Signup and view all the answers

    The primary purpose of an E.E.C is to:

    <p>Save fuel, reduce crew workload and reduce maintenance costs</p> Signup and view all the answers

    When both FADEC channels are healthy, what happens?

    <p>They alternate on each engine start</p> Signup and view all the answers

    What is the purpose of the LP fuel pump?

    <p>To ensure the H.P fuel pump does not cavitate</p> Signup and view all the answers

    What is the primary function of a FADEC system?

    <p>To reduce pilot workload and maximize engine efficiency</p> Signup and view all the answers

    What type of filter is typically used on the inlet side of a fuel pump?

    <p>Wire mesh filter</p> Signup and view all the answers

    What happens to the pressure drop across the Fuel Control Unit throttle orifice when the throttle is selected to increase power?

    <p>It drops then increases due to increasing pump output</p> Signup and view all the answers

    What action does the E.E.C take when it senses a fault on the engine?

    <p>Removes fuel and down-trims the signal immediately</p> Signup and view all the answers

    What does the E.E.C control in-flight?

    <p>Fuel flow</p> Signup and view all the answers

    What does a FADEC system not have?

    <p>Automatic control of engine fire bottles</p> Signup and view all the answers

    What prevents fuel from spilling out of fuel tank vents during aerobatic maneuvers?

    <p>Float-operated valves</p> Signup and view all the answers

    What is the purpose of the low-pressure fuel pump in a FADEC system?

    <p>To maintain a minimum of 40 psi to the inlet of the high-pressure pump</p> Signup and view all the answers

    Where would you disconnect the system to carry out flow checks after a bag tank replacement?

    <p>At the engine</p> Signup and view all the answers

    What happens when Channel A fails to receive information from a sensor in a FADEC system?

    <p>Channel A will take the information from Channel B</p> Signup and view all the answers

    What is the purpose of a silver strip on a fuel filter?

    <p>To detect sulphur in fuel</p> Signup and view all the answers

    How is fuel flow controlled in a FADEC engine with a hydromechanical fuel system?

    <p>By electro-hydraulic servo valves (E.H.S.Vs)</p> Signup and view all the answers

    What should the RPM be set to on approach for maximum acceleration?

    <p>Above minimum idle</p> Signup and view all the answers

    What is the primary purpose of cross-feeding fuel from one tank to another?

    <p>To supply fuel to the engines</p> Signup and view all the answers

    What type of pressure controls the swash plate in the fuel pump of an axial flow gas turbine engine?

    <p>Servo fuel pressure</p> Signup and view all the answers

    What happens if the air data inputs to the FADEC E.C.U fail?

    <p>The E.C.U reverts to the fail-safe mode</p> Signup and view all the answers

    Why are the end fittings on a fuel non-return valve normally of different sizes?

    <p>To prevent incorrect installation</p> Signup and view all the answers

    What components make up a FADEC system?

    <p>H.M.U, sensors, and an E.E.C</p> Signup and view all the answers

    What does a fuel heater prevent in a FADEC system?

    <p>Entrained water in fuel freezing</p> Signup and view all the answers

    What type of sensors does the E.E.C receive signals from?

    <p>Pressure and temperature sensors</p> Signup and view all the answers

    When re-light is required in flight on a FADEC engine, what happens to the igniter selection?

    <p>The FADEC chooses whichever igniter it wants</p> Signup and view all the answers

    When does the E.E.C channel change over occur?

    <p>On engine start up</p> Signup and view all the answers

    Where is the fuel heater located in the fuel system?

    <p>Before the LP fuel filter</p> Signup and view all the answers

    What is the combined output of all the scavenge pumps in a lubrication system compared to the pressure pump output?

    <p>Greater than the pressure pump output</p> Signup and view all the answers

    What is the primary power source for the E.E.C?

    <p>Separate permanent magnet alternator</p> Signup and view all the answers

    What happens when the knife-edge blade in a kinetic valve is fully in?

    <p>Servo pressure is being bled off</p> Signup and view all the answers

    What is the purpose of the kinetic valve in a gas turbine engine fuel system?

    <p>To regulate fuel flow to the burners</p> Signup and view all the answers

    What is the purpose of the acceleration control unit?

    <p>To prevent compressor surge and overheating</p> Signup and view all the answers

    In a FADEC system, what does the E.E.C measure along with RPM?

    <p>Pressure and Temperature</p> Signup and view all the answers

    What is the purpose of trimming in a gas turbine engine?

    <p>To control the idle speed and maximum thrust</p> Signup and view all the answers

    How are the power supply windings for channel A and Channel B wound in a FADEC system?

    <p>On one generator with 2 separate windings</p> Signup and view all the answers

    What happens if an Engine FADEC system loses air-data permanently?

    <p>The pilot will switch to Alt on the relevant E.E.C</p> Signup and view all the answers

    What is the main purpose of the fuel boost pumps in a gas turbine engine?

    <p>To increase the fuel pressure</p> Signup and view all the answers

    What is the function of baffles in a rigid fuel tank?

    <p>To prevent surge</p> Signup and view all the answers

    What is the forward idle setting of the thrust lever resolver angle?

    <p>40 degrees</p> Signup and view all the answers

    How are fuel pumps cooled?

    <p>Using fuel</p> Signup and view all the answers

    What happens to the fuel flow governor when the engine is at altitude?

    <p>It adjusts automatically to compensate for EGT change</p> Signup and view all the answers

    Study Notes

    Swash Plate Pump

    • If the swash plate is perpendicular to the axis of the pump, the flow will be zero
    • The swash plate angle is controlled by servo pressure, which is obtained from pump delivery pressure through variable restrictions
    • A spring moves the swash plate away from the minimum stroke position

    Fuel System

    • The burner fuel flow is at maximum at sea level (ISA)
    • Fuel flow responds to mass airflow rate through the engine during aircraft acceleration
    • Fuel flow is increased at a controlled rate during acceleration to prevent surge and the risk of flame-out
    • The barometric pressure controller (BPC) controls fuel pump output in relation to the pressure variation at the intake

    Fuel Pump

    • The high-pressure fuel pump is fitted in a gas turbine engine aircraft to provide the majority of the fuel pressure to the engine
    • The low-pressure pump prevents cavitation of the high-pressure fuel pump
    • The fuel pump plungers are lubricated by the fuel itself

    Governor

    • The hydromechanical governor is fitted to a gas turbine engine fuel pump to enable the engine to operate over a wide range of fuel specific gravities
    • The governor controls the maximum RPM of the engine by reducing the fuel pump stroke when maximum RPM is reached

    Fuel Control Unit (FCU)

    • The FCU is trimmed to obtain maximum thrust output when desired
    • The FCU is adjusted to set idle RPM and maximum speed or EPR
    • Trimming is most accurate in no wind and low moisture conditions

    Electronic Engine Control (EEC)

    • The EEC receives engine operating information and adjusts a standard hydromechanical fuel control unit to obtain the most effective engine operation
    • The EEC is a system that controls engine operation according to ambient temperature, pressure, and humidity

    FADEC System

    • FADEC (Full Authority Digital Engine Control) system has electronic control of the hydro-mechanical fuel control unit in all modes
    • Active control switchover occurs on engine start-up only
    • Channel reset selects standby, which becomes active on the next start

    Fuel Nozzle

    • The duplex fuel nozzle provides better atomization and uniform flow pattern
    • The flow divider in a turbine engine duplex fuel nozzle creates the primary and secondary fuel supplies
    • The valve on a vane type fuel flow measuring device becomes stuck, and a differential pressure bypass valve is the safety backup available for the engine fuel flow### Engine Fuel Shutoff Valve
    • Located downstream of the engine driven fuel pump

    FADEC System

    • Consists of H.M.U, sensors, and an E.E.C
    • Primary purpose is to save fuel, reduce crew workload, and reduce maintenance costs
    • Receives primary power from a separate permanent magnet alternator
    • E.E.C measures pressure and temperature along with RPM
    • Can change digital inputs into analogue format to provide glass cockpit information and reduce flight crew workload
    • Has an automatic starting capability
    • Does not have automatic control of engine fire bottles

    Throttle and Fuel Control

    • Throttle position is controlled by the crew or autothrottle
    • Fuel flow is controlled by the E.E.C in flight
    • Trimming is adjusting idle speed and maximum thrust
    • Fuel trimmer unit is adjusted automatically at altitude

    FADEC Channels

    • Both channels are operating, but either one can be in command if they are both healthy
    • If a channel fails to receive information from a sensor, it will take the information from the other channel
    • If all air data input fails, the E.C.U reverts to an alternate (Fail-safe) mode

    Engine Performance

    • Optimized performance is the reason FADEC was introduced
    • FADEC ensures efficiency is always maximum

    Fuel System

    • Engine fuel pump has a wire mesh filter
    • Pressure drop across the Fuel Control Unit throttle orifice drops then increases due to increasing pump output
    • Fuel boost pumps are cooled using fuel
    • Main purpose of the fuel boost pumps is to provide fuel pressure to both engine pumps

    Sensors and Valves

    • Silver strip on a fuel filter detects sulphur in fuel
    • Baffles in a rigid fuel tank prevent surge
    • End fittings on a fuel non-return valve are different sizes to prevent incorrect installation

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    Description

    Test your knowledge of positive displacement pumps and burners, including swash plate pumps and fuel flow. This quiz covers key concepts and principles related to these mechanical systems.

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