Fuel metering systems

Question 1

Where are the fuel spray nozzles located in a turbine engine

Answer 1

They are located either externally or internally on the combustion chamber

Question 2

Name the heat sources for the operation of fuel heaters used in turbine engine’s

Answer 2

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

Question 3

What engine variables are sensed by a Hydro mechanical fuel control

Answer 3

The fuel control senses power lever Position, RPM, compressor inlet pressure temperature, burn pressure, or compressor discharge pressure, and EGT or TIT

Question 4

What are the most commonly used carburetors and small reciprocating engines

Answer 4

Float type carburetor and pressure type carburetor

Question 5

What type of fuel control unit is used in turbine engine’s

Answer 5

Hydro mechanical and electric fuel control units

Question 6

What is meant by trimming a turbine engine

Answer 6

Adjusting the fuel control for the proper specific gravity of the fuel and for the proper idol and full throttle RPM

Question 7

When should a turbine engine be trimmed

Answer 7

Whenever there is a loss of engine power, or the manufacture specifies

Question 8

What specifications are used to trim a turbine engine

Answer 8

Data plate on the engine typically contains the trimming specification

Question 9

What are two types of electric fuel controls for turban engines

Answer 9

Electric engine control EEC and FADEC for authority digital engine control

Question 10

What is a FADEC

Answer 10

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

Question 11

Does a turbine engine Controlled by the FADEC require manual trimming

Answer 11

No it’s self trimming

Question 12

What is the purpose of a mixture control in a float type carburetor

Answer 12

Control the fuel air mixture as air density changes with altitude change

Question 13

What is the purpose of an accelerating system on a float type carburetor

Answer 13

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

Question 14

Describe the purpose in operation of the Venturi

Answer 14

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

Question 15

What is the function of the metering jet

Answer 15

Limit the fuel flow when the throttle valve is wide open

Question 16

What is the fuel metering force on the float type carburetor

Answer 16

Differential pressure between the pressure in the float carburetor and at the nozzle

Question 17

What will be the result of using excessively rich idol mixtures

Answer 17

Excessively rich Idle mixtures will cause carbon fouling of the spark plug

Question 18

What is the purpose of the economizer system in a float carburetor

Answer 18

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%

Question 19

Where does pressure injection carburetor obtain fuel pressure

Answer 19

From the booster pump for starting and from the engine driven fuel pump for normal operations

Question 20

What operates an automatic mixture control on a pressure carburetor

Answer 20

The AMC contain sealed Bellows that expand or contract with changes in atmospheric pressure

Question 21

And what position do you place the mixture control of a pressure injection carburetor to stop the engine

Answer 21

Idle cut off position

Question 22

What RPM indication should results when the mixture control is placed in the idle cut off position when the idle mixture is set correctly

Answer 22

Slight increase in RPM, followed by a rapid drop in RPM to zero

Question 23

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

Answer 23

Soften the diaphragms and make them as pliable as they were when the carburetor was originally calibrated

Question 24

What are the three types of carburetor icing

Answer 24

Throttle icing, impact icing, fuel evaporation icing

Question 25

What is the typical fuel pressure in a float type carburetor

Answer 25

3-5 psi