Fuel metering systems Flashcards
Where are the fuel spray nozzles located in a turbine engine
They are located either externally or internally on the combustion chamber
Name the heat sources for the operation of fuel heaters used in turbine engine’s
Turban engines use heat exchangers to heat the fuel and prevent the possibility of ice crystal formations
Fuel lines are routed through the fuel heater, which uses a heat source, either bleed air or engine lubricating oil. If pleat air is used as the heat source it is called an air to liquid heat exchanger. When oil is used, it is a liquid to liquid heat exchanger
What engine variables are sensed by a Hydro mechanical fuel control
The fuel control senses power lever Position, RPM, compressor inlet pressure temperature, burn pressure, or compressor discharge pressure, and EGT or TIT
What are the most commonly used carburetors and small reciprocating engines
Float type carburetor and pressure type carburetor
What type of fuel control unit is used in turbine engine’s
Hydro mechanical and electric fuel control units
What is meant by trimming a turbine engine
Adjusting the fuel control for the proper specific gravity of the fuel and for the proper idol and full throttle RPM
When should a turbine engine be trimmed
Whenever there is a loss of engine power, or the manufacture specifies
What specifications are used to trim a turbine engine
Data plate on the engine typically contains the trimming specification
What are two types of electric fuel controls for turban engines
Electric engine control EEC and FADEC for authority digital engine control
What is a FADEC
A full authority digital engine control. Is a high Percision digital electrical fuel control that utilizes an electronica engine control and flight management computer to measure the fuel nozzle that prevents over speed and over temperature conditions
Does a turbine engine Controlled by the FADEC require manual trimming
No it’s self trimming
What is the purpose of a mixture control in a float type carburetor
Control the fuel air mixture as air density changes with altitude change
What is the purpose of an accelerating system on a float type carburetor
When the throttle is opened rapidly, the fuel air mixture will lean out momentarily
To overcome this tendency a charge of fuel from Excelerator pump or temporarily Enrich the mixture in the Venturi
Describe the purpose in operation of the Venturi
As the velocity of a gas or liquid increases the pressure decreases
It proportions to fuel air mixture, lowers the pressure at the discharge nozzle, and limits airflow at full throttle
What is the function of the metering jet
Limit the fuel flow when the throttle valve is wide open
What is the fuel metering force on the float type carburetor
Differential pressure between the pressure in the float carburetor and at the nozzle
What will be the result of using excessively rich idol mixtures
Excessively rich Idle mixtures will cause carbon fouling of the spark plug
What is the purpose of the economizer system in a float carburetor
Is essentially a valve which is closed at throttle settings below 60% to 70% of rated power, but provide additional fuel for cooling the engine to prevent detonation at higher throttle settings above 60 to 70%
Where does pressure injection carburetor obtain fuel pressure
From the booster pump for starting and from the engine driven fuel pump for normal operations
What operates an automatic mixture control on a pressure carburetor
The AMC contain sealed Bellows that expand or contract with changes in atmospheric pressure
And what position do you place the mixture control of a pressure injection carburetor to stop the engine
Idle cut off position
What RPM indication should results when the mixture control is placed in the idle cut off position when the idle mixture is set correctly
Slight increase in RPM, followed by a rapid drop in RPM to zero
What is the purpose of filling a pressure injection carburetor full of fuel and allowing it to soak for a period of about eight hours prior to installation
Soften the diaphragms and make them as pliable as they were when the carburetor was originally calibrated
What are the three types of carburetor icing
Throttle icing, impact icing, fuel evaporation icing
What is the typical fuel pressure in a float type carburetor
3-5 psi
