Powerplant-Fuel
What is meant by a duplex nozzle in a turbine engine fuel metering system
A duplex fuel nozzle is one that has two fuel discharge passages. A flow divider sends fuel for low-pressure operation through one discharge passage, and when the engine demands more fuel, it is sprayed out through the second discharge passage. The spray pattern keeps the flame centered in the burner for all operating conditions.
What is FADEC
A Full-Authority Digital Electronic Control (FADEC) is a high-precision digital electronic fuel control that functions during all engine operations. It includes the Electronic Engine Control (EEC) and functions with the Flight Management Computer (FMC) to measure the fuel to the nozzles in such a way that prevents overshooting of power changes and over-temperature conditions. FADEC furnishes information to the Engine Indicating and Crew Alerting System (EICAS).
What would likely cause a reciprocating engine equipped with a float carburetor to hesitate momentarily when the throttle is rapidly advanced from idle to full power
A malfunctioning accelerator pump.
What is meant by a compensated relief valve in an engine-driven fuel pump
A pressure relief valve that is acted upon by a diaphragm as well as a spring. Atmospheric pressure acting on the diaphragm varies the pump discharge pressure so that it will remain a given amount higher than the pressure of the air entering the carburetor.
How does the exhaust gas temperature of a reciprocating engine tell anything about the fuel-air mixture being burned by the engine
A stoichiometric mixture produces the highest exhaust gas temperature. The mixture is adjusted to get the highest EGT, and then it is enriched to place it on the rich side of stoichiometric.
What is meant by trimming a turbine engine
Adjusting the fuel control for the specific gravity of the fuel and for the proper idle and full throttle RPM.
What are two types of fuel heaters used in a jet transport aircraft
Air-to-fuel and oil-to-fuel heat exchangers.
What should be done to an aircraft reciprocating engine if it has been operated on turbine engine fuel
All of the turbine fuel should be drained out & the system filled with the proper grade of aviation gasoline. The engine should be given a compression check, & all of the cylinders should be inspected with a borescope. The oil should be drained & the filters carefully examined. The engine should be given a complete run-up check.
When should a turbine engine be retrimmed
Any time there is a decrease in engine thrust, and after any maintenance that the manufacturer specifies as requiring trimming.
What are two locations water may be injected into a turbine engine
At the compressor inlet and at the inlet to the diffuser section
Where does an engine-driven fuel pump direct the excess fuel from its pressure relief valve
Back to the inlet side of the pump.
What is done in most aircraft fuel systems to prevent vapor lock
Boost pumps in the fuel tank pressurize the fuel in the lines & force the fuel into the fuel metering system.
Why is an aircraft reciprocating engine killed by placing the mixture control in the Cutoff position, rather than by using the magneto switch
By shutting off the fuel to the cylinders, the combustion chambers are left full of air with no fuel. This makes the engine less likely to fire if the propeller is pulled through with the ignition switch accidentally on.
What kind of boost pump is used in most aircraft fuel systems
Electrically operated centrifugal pumps.
What engine parameters are sensed by the fuel control unit of a turbine engine
Engine RPM, inlet air pressure, compressor discharge pressure, burner can pressure, and inlet air temperature.
Where are the fuel strainers normally located in an aircraft fuel system
Finger strainers are located in the tank outlet, the main strainer, located at the lowest point in the fuel system, and strainers in the carburetor or fuel injection system.
What is the purpose of the pressurizing & dump valve in the fuel system for a turbine engine
For normal engine operation, the pressurizing & dump valve acts a flow divider, directing the fuel into the main or pilot manifold so it will be discharged from the proper orifice in the duplex fuel nozzle. When the engine is shut down, the dump function of the valve dumps all of the fuel from the manifold.
Where is the heat taken from that is used to heat the induction air in a reciprocating engine
From a muff that is installed around some part of the exhaust system.
Where does the alternate air come from that is used with a pressure carburetor or a fuel injection system
From inside the engine cowling.
Does the application of carburetor heat cause the fuel-air mixture to become richer or to become leaner
Heated air causes the fuel-air mixture to become richer.
What are two basic types of fuel controls for aircraft turbine engines
Hydropneumatic and electro-hydromechanical.
Does the fuel-air mixture provided by a float carburetor become richer or leaner as the aircraft goes up in altitude
If the mixture is not adjusted, it will become richer as the aircraft climbs.
In which direction relative to the wind should a turbine-powered aircraft be positioned when the fuel control is being trimmed
If the wind velocity is less than 10 miles per hour, it can be faced in any direction. If the wind velocity is between 10 and 25 MPH, it should be trimmed facing into the wind. The engine should not be trimmed when the wind velocity is more than 25 MPH.
Where would ambient temperature be measured when trimming a turbine engine
In a shaded area as near the engine inlet as is practical.
In what position is the carburetor heat control placed when starting an aircraft engine
In the cold position.
In what position is the mixture control placed for starting an engine that is equipped with a pressure carburetor
In the idle cutoff position. The engine is started with fuel from the primer system.
Where does carburetor ice normally form in a carburetor
In the throat of the carburetor, on & around the throttle valve.
How does the automatic mixture control in a pressure carburetor keep the fuel-air mixture constant as the aircraft changes altitude
It automatically, and progressively, bleeds the air between the two sides of the air diaphragm and decreases the air metering force. This leans the mixture as the aircraft climbs.
What is meant by a compensated fuel pump
It is a fuel pump that senses the ambient air pressure and maintains the fuel pressure a specific amount above this air pressure.
Where is the fuel from a continuous-flow fuel injection system discharged
It is discharged through injector nozzles screwed into the cylinder heads near the intake valves.
What are two purposes of the manifold valve (or flow divider) in the fuel injection system of a horizontally opposed aircraft engine
It provides a constant discharge fuel pressure for idling, and it provides a positive shutoff for the fuel when the engine is shut down.
What are the two basic types of turbine engine fuel
Jet A & Jet A-1, which are special type of kerosine-base fuel. This is similar to military JP-^Jet B is a gasoline-base fuel similar military JP-4.
Are the instruments installed in an aircraft suitable for use when trimming a turbine engine
No, a special analyzer/trimmer such as JetCal should be used.
Does a turbine engine controlled by a FADEC require manual trimming
No, this is done by the FADEC.
What are two reasons Prist is used in turbine engine fuel
Prist is an antifreeze agent that lowers the freezing point of any water that precipitates out of the fuel. It also acts as a biocidal agent that kills the microbial growth that forms scum in fuel tanks. This scum traps & holds water against the aluminum alloy in the fuel tanks & causes corrosion.
Why must the diaphragms of a pressure carburetor be soaked before the carburetor is ready for flight
Soaking the diaphragms of a pressure carburetor restores them to the condition of flexibility that they had when the carburetor was calibrated.
What are two types of electronic fuel controls for turbine engines
Supervisory Electronic Engine Control and Full-Authority Digital Electronic Control.
What are two types of fuel injection systems used on modern reciprocating aircraft engines
Teledyne Continental (TCM) system and Precision Airmotive (Bendix) system.
Why do aircraft fuel metering systems for reciprocating engines have mixture controls
The air density increases as the aircraft ascends, causing the mixture to become richer. The mixture control allows the fuel to be decreased to maintain a fuel-air mixture ratio that produces the desired power.
What is the purpose of the bypass valve in an engine-driven fuel pump
The bypass valve allows fuel to flow around the engine-driven pump for starting & for emergency operation if the engine-driven pump should fail.
What specifications are used to trim a turbine engine
The data plate specifications for the specific engine. This data was obtained when the engine was calibrated in the manufacturer's test cell.
What is the function of the derichment valve in a pressure carburetor used on aircraft engine with an antidetonation injection system
The derichment valve automatically closes to lean the fuel-air mixture when ADI fluid is flowing. As soon as the ADI fluid stops flowing, the derichment valve opens and the mixture returns to its rich condition.
What is the function of the economizer system in an aircraft engine carburetor
The economizer system allows the engine to operate with an economically lean mixture for all conditions other than full power. When the throttle is opened for full power, the power enrichment system automatically enriches the mixture to remove some of the heat that is developed during this type of operation.
What is used in the TCM fuel injection system to control the amount of fuel sent to the nozzles
The engine speed determines the injector pump output pressure. The relief valve determines the fuel for low-speed operation, and the adjustable orifice determines the fuel for high-speed operation.
What is the function of a float carburetor
The float carburetor's function is to measure airflow through the engine induction system and dispense the appropriate amount of gasoline into the airflow for all engine operating perimeters and conditions. It must also provide the fuel in a state that is as vaporized as possible by the time ignition occurs in the engine cylinders.
What causes a vapor lock in an aircraft fuel system
The fuel becomes hot enough that it boils. Vapors are released from the liquid fuel, & these vapors block the fuel lines so the liquid fuel cannot flow to the engine.
Why do some turbine engine fuel systems incorporate a fuel heater
The fuel heater keeps the fuel warm enough that any water that precipitates out of the fuel will not freeze on the filters.
Where does the fuel metering system of a turbine engine discharge its fuel
The fuel is discharged through the spray nozzles into the combustion chambers.
What is controlled by the adjustment of the orifice in the fuel pump of a Teledyne-Continental fuel injection system
The high unmetered fuel pressure.
What is adjusted when the fuel control unit of a turbine engine is trimmed
The idle speed and the maximum-thrust speed.
What is used in the Precision Airmotive system to control the amount of fuel sent to the nozzles
The mass of the air entering the engine acts on air diaphragm that controls a servo ball valve in the line between the regulator and the flow divider.
Does the fuel-air mixture provided by a float carburetor become richer or leaner when carburetor heat is applied
The mixture becomes richer when carburetor heat is applied.
What would happen to the fuel-air mixture ratio in a float carburetor if the main air bleed were to become plugged
The mixture would become excessively rich.
On which side of the firewall is the engine fuel shutoff valve located
The shutoff valve must be on the side of the firewall away from the engine.
What two things are adjusted when adjusting the idling of a reciprocating engine
The throttle stop, to get the proper idling RPM, and the idle mixture control, to get the smoothest operation.
What is the significance of the letters that are stamped on the flats of a fuel injection nozzle
These letters designate the relative size of the orifice in the injector nozzle. The lower the letter in the alphabet, the smaller the amount of fuel the nozzle will flow.
Why do some aircraft fuel filters have a built-in relief valve
This relief valve will open & allow unfiltered fuel to flow to the fuel control device if the filter should become plugged with ice or other contaminants.
What are three purposes for the boost pumps in an aircraft fuel system
To provide fuel pressure for starting the engine, to pressurize the fuel lines to prevent vapor lock, & to transfer fuel from one tank to another.
How does the mixture control change the fuel-air mixture ratio on the Teledyne-Continental fuel injection system
When the mixture control is in its full rich position, all fuel goes to the manifold valve. When it is in the idle cutoff position, all fuel is returned to the pump inlet. Intermediate positions vary the amount of fuel that goes to the engine.
When does the acceleration system operate on an aircraft carburetor
When the throttle is suddenly opened.
What two things are adjusted when setting the idling conditions on a float carburetor
a. Idling RPM by adjusting the throttle stop. b. Idling mixture by adjusting idle needle valve.
What parameters are normally sensed by a turbine-engine fuel control
a. Power lever angle. b. Compressor inlet total temperature. c. Compressor RPM. d. Burner pressure.
