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AMT1220

Fuel Metering

QuestionAnswer
What is not a factor in the operation of an automatic fuel control unit used on turbine engines? Mixture control position
How is the fuel control adjusted when trimming a turbine engine? Set to idle RPM and maximum speed
How does an EEC obtain the most effective engine operation? By adjusting a standard hydro mechanical fuel control unit
What is generally turned off when trimming an engine> All accessory bleed air
What causes the automatic mixture control to respond in reciprocating engines? Changes in air density due to changes in altitude or temperature
What is the fuel metering force of a conventional float-type carburetor in its normal operating range? the pressure acting on the fuel in the float chamber and the discharge nozzle
How would the engine run if the main air bleed of a float-type carburetor becomes clogged? Rich at rated power
How would you adjust the level of the float in a float-type carburetor? Add or remove shims under the needle-valve seat
How would you achieve better fuel vaporization and control of fuel discharge, especially at lower engine speeds? Have a calibrated orifice in a main air bleed
How does the back-suction type mixture control system operate? By varying the pressure acting on the fuel in the float chamber
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
On an engine equipped with a pressure-type carburetor, how is fuel supply in the idling range insured? by the inclusion in the carburetor of a spring in the unmetered fuel chamber
If the bellows of the automatic mixture control (AMC) in a pressure carburetor ruptures while the engine is operating at altitude, how will the mixture be affected? It will become richer
Where do you NOT measure the fuel level of a float-type carburetor? the edge of the float
What component measures the amount of air delivered to the engine? Venturi
If the engine is not running and the carburetor leaks fuel, what is the likely cause? worn or otherwise not seated float needle valve
From where is fuel discharged during idling speeds on a float-type carburetor? The idle discharge nozzle
When air passes through the venturi of a carburetor, what three changes occur? Velocity increases, temperature decreases, and pressure decreases
The carburetor venturi does not do what? regulate the idle system
How is idle cutoff accomplished on a carburetor equipped with a back-suction mixture control? By introducing low pressure (intake manifold) air into the float chamber
What is the primary purpose of an air bleed in a float-type carburetor? To decrease fuel density and destroy surface tension
Where is the measurement usually made to determine the float level in a float-type carburetor? From the top of the fuel in the float chamber to the parting surface of the carburetor
What device controls the ratio of fuel/air mixture to the cylinders? mixture control
What device controls the volume of fuel/air mixture to the cylinders? throttle valve
What causes the pressure drop in the carburetor venturi? air velocity
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
What is the purpose of the carburetor accelerating system? Temporarily enrich the mixture when the throttle is suddenly opened
What carburetor component actually limits the desired maximum airflow to the engine at full throttle? Venturi
What will happen to the mixture on a carburetor without an automatic mixture control as you ascent to altitude? It will become enriched
How is the desire idle speed and mixture setting adjusted? With the engine warmed up and operating
What component in a float-type carburetor aids in emulsifying the fuel at idle speeds? The idling air bleed
What would be considered as the most desirable conditions for trimming a turbine engine? No wind and low moisture
In air-cooled reciprocating engines, when will the mixture be richer? At rated power and at idle
(During idle mixture adjustments) How do you know the correct mixture has been achieved? Changes in RPM or manifold pressure
When the mixture control is moved to IDLE CUTOFF, the manifold pressure decreases and RPM increases momentarily before the engine stops. What does this indicate? The optimum idle mixture has been obtained
When checking the idle mixture on a carburetor, how much of an increase in RPM should there be if the idling mixture is correct? 10-50
What will happen if the idling jet becomes clogged in a float-type carburetor? The engine will not idle
What are benefits of using water injection? Increase engine power and control detonation and preignition
What will an excessively lean fuel/air mixture cause? Increased cylinder head temperature
How much air to fuel is a mixture of 11:1? 1 part fuel to 11 parts air
What system in a float-type carburetor increases the fuel/air ratio at high power settings? The economizer system
What does the dump portion of the valve do in turbine engines that use a pressurization and dump valve? Drains the engine manifold lines to prevent fuel boiling
What has little to no effect on the operation of a jet engine? humidity
What position will the pressurization and dump valves be in when the engine is shut down? Pressurization valve closed, dump valve open
What would a ruptured balance diaphragm cause? A lean mixture and high cylinder temperature
What occurs when the air/fuel mixture burns too fast? Detonation
When should the needle valve and seat be replaced? When the carburetor is found to be leaking fuel from the discharge nozzle
When operating a gas turbine engine fuel control unit, what factor is NOT used? Mixture control position
Fuel control manufacturers recommend all final adjustments increase direction in order to stabilize what? Cams, springs, and linkages
Created by: Ms.Fietzek