Fuel Metering Systems

Question 1

What are some of the sources used to heat the fuel in a turbine engine fuel system?

Answer 1

Bleed air and engine lubricating oil

Question 2

When does a carburetor economizer system needle valve begin to open?

Answer 2

Approximately 60 to 70% of rated power

Question 3

What are the most common types of metering systems use on small reciprocating engines?

Answer 3

Float type carburetors, pressure type injection carburetors, and direct fuel injection systems

Question 4

What function does the mixture control perform?

Answer 4

Controls the fuel/air mixture

Question 5

What generally causes spark plug fouling?

Answer 5

Operating the engine with an excessively rich mixture at idle

Question 6

What is the purpose of an accelerating system in a float type carburetor when the throttle is open in a quick action?

Answer 6

It provides immediate brief increase in fuel flow in a Venturi to enrich the mixture

Question 7

What is a carburetor economizer system?

Answer 7

It is a power enrichment system that provides a richer mixture at high power settings, where the excess fuel aids in engine cooling to prevent detonation. This system functions at throttle settings above cruise power settings.

Question 8

When the mixture is placed in the idle cut off position, a slight rise in RPM is noted prior to the engine decelerating. What does this indicate?

Answer 8

The idle mixture is set correctly.

Question 9

What is rpm indication when an idle mixture is set correctly, and the mixture control is placed to the idle cut off position

Answer 9

A slight rise in RPM prior to decreasing

Question 10

Why should engine rpm be accelerated periodically when making carburetor adjustments?

Answer 10

To clean the engine

Question 11

What maintains the fuel pressure in a fuel injection carburetor?

Answer 11

engine driven fuel pump

Question 12

What happens if the manual mixture control of a pressure ejector carburetor is moved to the idle cut off position?

Answer 12

The engine stops

Question 13

What are some of the advantages of fuel injection systems over carburetor systems?

Answer 13

1. Less danger of icing induction
2. better acceleration
3. better fuel distribution
4. better fuel economy
5. reduce overheating of individual cylinders

Question 14

How does an automatic mixture control function?

Answer 14

A sealed brass bellows connected to the fuel metering system expands and contracts with changes in pressure and temperature, adjusting the mixture accordingly

Question 15

What purpose do turbine engine fuel control units serve?

Answer 15

They automatically meter fuel to the engine

Question 16

What are two basic types of turbine engine fuel control units?

Answer 16

Hydromechanical
electronic and FADEC (full authority digital engine control)

Question 17

What are the engine variables detected by the fuel control unit?

Answer 17

1. Power lever position
2. engine rpm
3. compressor inlet temperature
4. compressor inlet pressure
5. compressor discharge pressure
6. Burner pressure

Question 18

What are the two major components of a supervisory electronics engine control?

Answer 18

The electronic control unit (ECU) and the Hydro mechanical fuel control

Question 19

What are some of the advantages of a full authority digital engine control (FADEC) over a Hydro mechanical fuel control?

Answer 19

1. Better fuel economy
2. improved starts
3. requires no engine trimming
4. provides engine limit protection
5. provides constant idle speed regardless of atmospheric conditions or bleed air requirements
6. fully modulates the active clearance control and allows more repeatable engine transients

Question 20

What do turbine engine fuel spray nozzles do?

Answer 20

They inject fuel into the combustion area

Question 21

What are the different engine indications used for trimming a turbine engine?

Answer 21

Either (EPR) engine pressure ratio or RPM is used depending on the particular engine

Question 22

What maintenance adjustments are normally allowed on an installed Hydro mechanical fuel control?

Answer 22

Specific gravity for fuel, idle rpm and maximum rpm