Fuel Metering System Flashcards
What factor is not used in the operation of an aircraft gas turbine engine fuel control unit?
mixture control position
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 the
increase direction
When trimming a turbine engine, the fuel control is adjusted to
set idle RPM and maximum speed or EPR
A supervisory electronic engine control (EEC) is a system that receives engine operating information and
adjust a standard hydro mechanical fuel control unit to obtain the most effective engine operation
A full-authority electronic engine control (EEC) is a system that receives all the necessary data for engine operation and
develops the commands to various actuators to control engine parameters
In a supervisory EEC system, any fault in the EEC that adversely affects engine operation
causes an immediate reversion to control by the hydro mechanical fuel control unit
The active clearance control (ACC) portion of an EEC system aids turbine engine efficiency by
ensuring turbine blade to engine case clearance are kept to a minimum by controlling case temperatures
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
The generally acceptable way to obtain accurate on-site temperature prior to performing engine
trimming is to
hang a thermometer in the shades of the nose wheel well until the temperature reading stabilizes
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 a
false high compression and turbine discharge pressure, and a subsequent low trim
Generally, the practice when trimming an engine is to
turn all accessory bleed air off
A reciprocating engine automatic mixture control responds to changes in air density caused by changes in
altitude or temperature
On a float-type carburetor, the purpose of the economizer valve is to
provide a richer mixture and cooling at maximum power output
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 pressure
acting on the fuel in the float chamber
If the main air bleed of a float-type carburetor becomes clogged, the engine will run
rich at rated power
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
What is the possible cause of an engine running rich at full throttle if it is equipped with a float-type carburetor?
clogged air bleed
One of the things a metering orifice in a main air bleed helps to accomplish (at a given altitude) in a carburetor is
better fuel Evaporation and control of fuel discharge, especially at lower engine speeds
A punctured float in a float-type carburetor will cause the fuel level to
rise and en-richen the mixture
The back-suction mixture control system operates by
varying the pressure acting on the fuel in the float chamber
If an aircraft engine is equipped with a carburetor that is not compensated for altitude and temperature variations, the fuel/air mixture will become
richer as either the altitude of temperature increases
Float-type carburetors which are equipped with economizers are normally set for
their leanest practical mixture delivery at cruising speeds and enriched by means of economizer
system at higher power settings
If a float-type carburetor becomes flooded, the condition is most likely caused by
a leaking needle valve and seat assembly
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 clogged
main air bleed
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
Which of the following best describes the function of an altitude mixture control?
regulates the richness of the fuel/air charge entering the engine
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 the throttle body pulls the fuel from
the idle passage
On an engine equipped with a pressure-type carburetor, fuel supply in the idling range is ensured by the
inclusion in the carburetor of
a spring in the unmetered fuel chamber to supplement the action of normal metering forces
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
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 fuel level within the float chamber of a properly adjusted float-type carburetor will be
slightly lower than the discharge nozzle outlet
The metered fuel pressure (chamber C) in an injection-type carburetor
is held constant throughout the entire engine operating range
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
What carburetor component measures the amount of air delivered to the engine?
venture
If a float-type carburetor leaks fuel when the engine is stopped, a likely cause is that the
float needle valve is worn or otherwise not seated properly
Fuel is discharged for idling speeds on a float-type carburetor
from the idle discharge nozzle
When air passes through the venturi of a carburetor, what three changes occur?
velocity increases, temperature decreases, and pressure decreases
Where is the throttle valve located on a float-type carburetor?
after the main discharge nozzle and venture
An aircraft carburetor is equipped with a mixture control in order to prevent the mixture from becoming
too
rich and high altitude
Which of the following is NOT a function of the carburetor venturi?
regulates the idle system
Idle cutoff is accomplished on a carburetor equipped with a back-suction mixture control by
introducing low pressure (intake manifold) air into the float chamber
One purpose of an air bleed in a float-type carburetor is to
decrease fuel density and destroy surface tension
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 the
parting surface of the carburetor
The throttle valve of float-type aircraft carburetors is located
between the venture and the engine
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
What component is used to ensure fuel delivery during periods of rapid engine acceleration?
acceleration pump
The device that controls the ratio of the fuel/air mixture to the cylinders is called a
mixture
The device that controls the volume of the fuel/air mixture to the cylinders is called a
throttle valve
Which statement is correct regarding a continuous-flow fuel injection system used on many
reciprocating engines?
fuel is injected at each cylinder intake port
During the operation of an aircraft engine, the pressure drop in the carburetor venturi depends
primarily upon the
air velocity
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
At what engine speed does the main metering jet actually function as a metering jet in a float-type
carburetor?
all RPM’s above idle range
An aircraft engine continuous cylinder fuel injection system normally discharges fuel during which
stroke(s)?
all (continuously)
What is the purpose of the carburetor accelerating system?
temporary enrich the mixture when the throttle is suddenly opened
When troubleshooting an engine for too rich a mixture to allow the engine to idle, what would be a
possible cause?
a primer line open
What is the relationship between the accelerating pump and the enrichment valve in a pressure
injection carburetor?
no relationship since they operate independently
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
Which of the following is least likely to occur during operation of an engine equipped with a direct
cylinder fuel injection system?
backfiring
What carburetor component actually limits the desired maximum airflow to the engine at full throttle?
venture
On a carburetor without an automatic mixture control as you ascend to altitude, the mixture will
be enriched
During engine operation, if carburetor heat is applied, it will
decrease the air density to the carburetor
The desired engine idle speed and mixture setting
is adjusted with engine warmed up and operating
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
What is a function of the idling air bleed in a float-type carburetor?
it aids in emulsifying/vaporizing the fuel at idle speeds
If the volume of air passing through a carburetor venturi is reduced, the pressure at the venturi throat
will
increases
(Refer to Figure 6.) Which curve most nearly represents an aircraft engine’s fuel/air ratio throughout its
operating range?
2
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 method is ordinarily used to make idle speed adjustments on a float-type carburetor?
an adjustable throttle stop of linkage
For what primary purpose is a turbine engine fuel control unit trimmed?
to obtain maximum thrust output when desired
Which type of fuel control is used on most of today’s turbine engines?
hydromechanical or electronic
Under which of the following conditions will the trimming of a turbine engine be most accurate?
no wind and low moisture
(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.
Regarding the above statements,
both no.1 and no. 2 are true
Under which of the following conditions would an engine run lean even though there is a normal
amount of fuel present?
incomplete fuel vaporization
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
An indication that the optimum idle mixture has been obtained occurs when the mixture control is
moved to IDLE CUTOFF and manifold pressure
decreases and rpm increases momentarily before the engine ceases to fire
The use of less than normal throttle opening during starting will cause
a rich mixture
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 by
an increase of 10 to 50 rpm before decreasing
When a new carburetor is installed on an engine,
and the engine is warmed up to normal temperatures, adjust the idle mixture, then the idle speed
The purpose of the back-suction mixture control in a float-type carburetor is to adjust the mixture by
regulating the pressure on the fuel in the float chamber
Reciprocating engine power will be decreased at all altitudes if the
humidity is increased
If the idling jet becomes clogged in a float-type carburetor, the
engine will not idle
An aircraft engine equipped with a pressure-type carburetor is started with the
primer while the mixture control is positioned at idle cutoff
One of the best ways to increase engine power and control detonation and preignition is to
use water injection
An excessively lean fuel/air mixture may cause
an increase in cylinder head temperature
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
A mixture ratio of 11:1 normally refers to
1 part fuel to 11 parts air
The economizer system in a float-type carburetor
increases the fuel/air ratio at high power settings
A carburetor is prevented from leaning out during quick acceleration by the
accelerating system
In turbine engines that utilize a pressurization and dump valve, the dump portion of the valve
drains the engine manifold lines to prevent fuel boiling and subsequent deposits in the lines as a
result of residual engine heat (at engine shutdown)
What effect does high atmospheric humidity have on the operation of a jet engine?
has little or no effect
What are the positions of the pressurization valve and the dump valve in a jet engine fuel system when
the engine is shut down?
pressurization valve closed, dump valve open
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
Which of the following is NOT an input parameter for a turbine engine fuel control unit?
ambient humidity
Detonation occurs when the fuel/air mixture
burns too fast
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 major difference between the Teledyne-Continental and RSA (Precision Airmotive or Bendix)
continuous flow fuel injection systems in fuel metering is that the
continental system uses fuel pressure only as a metering force
The function of the altitude compensating, or aneroid valve used with the Teledyne-Continental fuel
injection system on many turbocharged engines is to
prevent an overly rich mixture during sudden acceleration
The primary purpose of the air bleed openings used with continuous flow fuel injector nozzles is to
aid in proper fuel vaporation.
