Fuel Metering Systems

fikenowu's version from 2018-03-13 13:50

Section 1

Question Answer
Which of the following is least likely to occur during operation of an engine equipped with a direct cylinder fuel injection system?Backfiring
If a float-type carburetor leaks fuel when the engine is stopped, a likely cause is that theFloat needle valve is worn or otherwise not seated properly
The active clearance control (ACC) portion of an EEC system aids turbine engine efficiency byensuring turbine blade to engine case clearance are kept to a minimum by controlling case temperatures
On a float-type carburetor, the purpose of the economizer valve is toprovide a richer mixture and cooling at maximum power output
A reciprocating engine automatic mixture control responds to changes in air density caused by changes inaltitude or temperature
What is the relationship between the accelerating pump and the enrichment valve in a pressure injection carburetor?No relationship since they operate independently
Which of the following is NOT an input parameter for a turbine engine fuel control unit?Ambient humidity
Under which of the following conditions will the trimming of a turbine engine be most accurate?No wind and low moisture
To determine the float level in a float-type carburetor, a measurement is usually made from the top of the fuel in the float chamber to theparting surface of the carburetor
Generally, the practice when trimming an engine is toturn all accessory bleed air off
During engine operation, if carburetor heat is applied, it willdecrease the air density to the carburetor
An excessively lean fuel/air mixture may causean increase in cylinder head temperature
What is the possible cause of an engine running rich at full throttle if it is equipped with a float-type carburetor?Clogged main air bleed
When air passes through the venturi of a carburetor, what three changes occur?Velocity increases, temperature decreases, and pressure decreases
When troubleshooting an engine for too rich a mixture to allow the engine to idle, what would be a possible cause?Economizer valve not operating correctly.

Section 2

Question Answer
For what primary purpose is a turbine engine fuel control unit trimmed?To obtain maximum thrust output desired
Detonation occurs when the fuel/air mixtureburns too fast
If an engine is equipped with a float-type carburetor and the engine runs excessively rich at full throttle, a possible cause of the trouble is a cloggedmain air bleed
Which of the following causes a single diaphragm accelerator pump to discharge fuel?An increase in manifold pressure that occurs when the throttle valve is opened
Where is the throttle valve located on a float-type carburetor?After the main discharge nozzle and ventri
The fuel level within the float chamber of a properly adjusted float-type carburetor will beslightly lower than the discharge nozzle outlet
If an aircraft engine is equipped with a carburetor that is not compensated for altitude and temperature variations, the fuel/air mixture will becomericher as either the altitude or temperature increases
What will occur if the vapor vent float in a pressure carburetor loses its buoyancy?The amount of fuel returning to the fuel tank from the carburetor will be increased
What factor is not used in the operation of an aircraft gas turbine engine fuel control unit?Mixture control position
Reciprocating engine power will be decreased at all altitudes if thehumidity is increased
One purpose of an air bleed in a float-type carburetor is todecrease fuel density and destroy surface tension
What is a function of the idling air bleed in a float-type carburetor?It aids in emulsifying/vaporizing fuel at idle speeds
When checking the idle mixture on a carburetor, the engine should be idling normally, then pull the mixture control toward the IDLE CUTOFF position. A correct idling mixture will be indicated byan increase of 10 to 50 RPM before decreasing
A supervisory electronic engine control (EEC) is a system that receives engine operating information andadjusts a standard hydromechanical fuel control unit to obtain the most effective engine operation
During idle mixture adjustments, which of the following is normally observed to determine when the correct mixture has been achieved?Changes in RPM or manifold pressure

Section 3

Question Answer
At what engine speed does the main metering jet actually function as a metering jet in a float-type carburetor?All RPM above idle range
A punctured float in a float-type carburetor will cause the fuel level torise, and enrich the mixture
Which of the following is NOT a function of the carburetor venturi?Regulates the idle system
The use of less than normal throttle opening during starting will causea rich mixture
Select the correct statement concerning the idle system of a conventional float-type carburetor.The low pressure between the edges of the throttle valve and and the throttle body pulls the fuel from the idle passage
In turbine engines that utilize a pressurization and dump valve, the dump portion of the valvedrains the engine manifold lines to prevent fuel boiling and subsequent deposits in the lines as a result of residual engine heat (at engine shutdown)
An aircraft engine equipped with a pressure-type carburetor is started with theprimer while the mixture control is positioned at IDLE CUTOFF
Select the statement which is correct relating to a fuel level check of a float-type carburetor.Do not measure the level at the edge of the float chamber
The function of the altitude compensating, or aneroid valve used with the Teledyne-Continental fuel injection system on many turbocharged engines is toprevent an overly eich mixture during sudden accerleration
A carburetor is prevented from leaning out during quick acceleration by theaccelerating sytem
How will the mixture of an engine be affected if the bellows of the automatic mixture control (AMC) in a pressure carburetor ruptures while the engine is operating at altitude?It will become richer
The primary purpose of the air bleed openings used with continuous flow fuel injector nozzles is toaid in proper fuel vaporization
The fuel metering force of a conventional float-type carburetor in its normal operating range is the difference between the pressure acting on the discharge nozzle located within the venturi and the pressureacting on the fuel in the float chamber
The purpose of the back-suction mixture control in a float-type carburetor is to adjust the mixture byregulating the pressure on the fuel in the float chamber
What carburetor component actually limits the desired maximum airflow to the engine at full throttle?Venturi

Section 4

Question Answer
An indication that the optimum idle mixture has been obtained occurs when the mixture control is moved to IDLE CUTOFF and manifold pressuredecreases and RPM increases momentarily before the engien ceases to fire
An aircraft carburetor is equipped with a mixture control in order to prevent the mixture from becoming toorich at high altitudes
The throttle valve of float-type aircraft carburetors is locatedbetween the venturi and the engine
When a new carburetor is installed on an engineand the engine is warmed up to normal temperatures, adjust the idle mixture, then the idle speed
Which statement is correct regarding a continuous-flow fuel injection system used on many reciprocating engines?Fuel is injected at each cylinder intake port
What carburetor component measures the amount of air delivered to the engine?Venturi
What method is ordinarily used to make idle speed adjustments on a float-type carburetor?An adjustable throttle stop linkage
What could cause a lean mixture and high cylinder head temperature at sea level or low altitudes?Automatic mixture control stuck in the extended position
The economizer system of a float-type carburetor performs which of the following functions?It supplies and regulates the additional fuel required for all engine speeds above cruising
Under which of the following conditions would an engine run lean even though there is a normal amount of fuel present?Incomplete fuel vaporiization
The device that controls the volume of the fuel/air mixture to the cylinders is called athrottle valve
If the volume of air passing through a carburetor venturi is reduced, the pressure at the venturi throat willincrease
The generally acceptable way to obtain accurate on-site temperature prior to performing engine trimming is tohang a thermometer in the shade of the nose wheel-well until the temperature reading stabilizes
During the operation of an aircraft engine, the pressure drop in the carburetor venturi depends primarily upon theair velocity
Why must a float-type carburetor supply a rich mixture during idle?Because at idling speeds the engine may not have enough airflow around the cylinders to provide proper cooling

Section 5

Question Answer
Float-type carburetors which are equipped with economizers are normally set fortheir leanest practical mixture delivery at crusing speeds and enriched by means of the economizer system at higher power settings
In order to stabilize cams, springs, and linkages within the fuel control, manufacturers generally recommend that all final turbine engine trim adjustments be made in theincreases direction
On an engine equipped with a pressure-type carburetor, fuel supply in the idling range is ensured by the inclusion in the carburetor ofa spring in the unmetered fuel chamber to supplement the action of normal metering forces
A major difference between the Teledyne-Continental and RSA (Precision Airmotive or Bendix) continuous flow fuel injection systems in fuel metering is that theContinental system uses fuel pressure only as a metering force
If the main air bleed of a float-type carburetor becomes clogged, the engine will runrich at rated power
The metered fuel pressure (chamber C) in an injection-type carburetoris held constant throughout the entire engine operating range
When trimming a turbine engine, the fuel control is adjusted toset idle RPM and maximum speed or EPR
The device that controls the ratio of the fuel/air mixture to the cylinders is called amixture control
If the idling jet becomes clogged in a float-type carburetor, theengine will not idle
What occurs when a back-suction type mixture control is placed in IDLE CUTOFF?The float chamber will be vented to a negative pressure area
(Refer to Figure 6.) Which curve most nearly represents an aircraft engine's fuel/air ratio throughout its operating range?2
In a supervisory EEC system, any fault in the EEC that adversely affects engine operationcauses an immediate reversion to control by the hydromechanical fuel control unit
On a carburetor without an automatic mixture control as you ascend to altitude, the mixture willbe enriched
What effect does high atmospheric humidity have on the operation of a jet engine?Has little or no effect
One of the best ways to increase engine power and control detonation and preignition is touse water injection
What is the purpose of the carburetor accelerating system?Temporarily enrich the mixture when the throttle is suddenly opened
Which of the following best describes the function of an altitude mixture control?Regulates the richness of the fuel/air charge entering the engine

Section 6

Question Answer
The desired engine idle speed and mixture settingis adjusted with engine warmed up and operating
One of the things a metering orifice in a main air bleed helps to accomplish (at a given altitude) in a carburetor isbetter fuel vaporization and control of fuel discharge, especially at lower engine speeds
(1) The mixture used at rated power in air cooled reciprocating engines is richer than the mixture used through the normal cruising range.(2) The mixture used at idle in air cooled reciprocating engines is richer than the mixture used at rated power.both No. 1 and No. 2 are true
Idle cutoff is accomplished on a carburetor equipped with a back-suction mixture control byintroducing low pressure (intake manifold) air into the float chamber
The economizer system in a float-type carburetorincreases the fuel/air ratio at high power settings
A nine-cylinder radial engine, using a multiple-point priming system with a central spider, will prime which cylinders?one, two, three, eight, and nine
Fuel is discharged for idling speeds on a float-type carburetorfrom the idle discharge nozzle
What are the positions of the pressurization valve and the dump valve in a jet engine fuel system when the engine is shut down?Pressuriztion valve closed, dump valve open
What is the relationship between the pressure existing within the throat of a venturi and the velocity of the air passing through the venturi?The pressure is inversely proportional to the velocity
What should be checked/changed to ensure the validity of a turbine engine performance check if an alternate fuel is to be used?Fuel specific gravity setting
Which method is commonly used to adjust the level of a float in a float-type carburetor?Add or remove shims under the needle-valve seat
What component is used to ensure fuel delivery during periods of rapid engine acceleration?Acceleration pump
A mixture ratio of 11:1 normally refers to1 part fuel to 11 parts air
The back-suction mixture control system operates byvarying the pressure acting on the fuel in the float chamber
The density of air is very important when mixing fuel and air to obtain a correct fuel-to-air ratio. Which of the following weighs the most?100 parts of dry air
An aircraft engine continuous cylinder fuel injection system normally discharges fuel during which stroke(s)?All (continuously)
What corrective action should be taken when a carburetor is found to be leaking fuel from the discharge nozzle?Replace the needle valve and seat
A full-authority electronic engine control (EEC) is a system that receives all the necessary data for engine operation anddevelops the commands to various actuators to control engine parameters
If a float-type carburetor becomes flooded, the condition is most likely caused bya leaking needle valve and seat assembly
Which type of fuel control is used on most of today's turbine engines?hydromechanical or electronic
An aircraft should be facing into the wind when trimming an engine. However, if the velocity of the wind blowing into the intake is excessive, it is likely to cause afalse high compression and turbine discharge pressure, and a subsequent low trim.