Engine Fuel and Fuel Metering

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

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

Answer 2

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

Question 3

What function does the mixture control perform?

Answer 3

It controls the fuel air mixture

Question 4

What generally causes spark plug fouling?

Answer 4

Operating the engine with an excessively rich mixture at idle

Question 5

What is the purpose of an accelerating system?

Answer 5

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

Question 6

What is a carburetor economizer system?

Answer 6

It is a power enrichment system that provides a richer mixture at high power setting where the excess fuel aid in engine cooling. This system functions as throttle setting above cruise power setting.

Question 7

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 7

The idle mixture is set correctly

Question 8

What maintains the fuel pressure in a pressure injector carburetor?

Answer 8

An engine driven fuel pump

Question 8

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

Answer 8

To clear the engine

Question 9

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

Answer 9

The engine stops

Question 10

How does an automatic mixture control function?

Answer 10

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

Question 11

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

Answer 11

Less danger of induction icing, better acceleration, better fuel distribution, better fuel economy and reduced overheating of individual cylinders

Question 12

What purpose do turbine engine fuel control units serve?

Answer 12

They automatically meter fuel to the engine

Question 13

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

Answer 13

Hydro mechanical and electronic

Question 14

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

Answer 14

Power lever position, engine rpm, compressor inlet temperature, compressor inlet pressure, compressor discharge pressure and burner pressure

Question 15

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

Answer 15

The electronic control unit computer and the hydro mechanical fuel control

Question 16

What are some of the advantages of a full authority digital engine control over a hydro mechanical fuel control?

Answer 16

Better fuel economy, improved starts, requires no engine trimming, provides engine limit protection, provides constant idle speeds regardless of atmospheric conditions or bleed air requirements, fully modulates the active clearance control and allows more repeatable engine transients

Question 17

What do turbine engine fuel spray nozzles do?

Answer 17

They inject fuel into the combustion area

Question 18

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

Answer 18

Either epr or rpm is used depending on the particular engine

Question 19

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

Answer 19

Specific gravity for fuel, idle rpm and maximum rpm or maximum epr

Question 20

What type of pump can vary the amount of fuel discharged regardless of speed?

Answer 20

A variable displacement pump

Question 21

What is used to keep water, sediment and foreign matter out of the carburetor?

Answer 21

The main fuel strainer

Question 22

What is the purpose of a pressure relief valve in a constant displacement pump?

Answer 22

It returns excess fuel that is not required by the engine to the inlet side of the pump

Question 23

What type of engine driven fuel is widely used other than geared or piston pumps?

Answer 23

A rotary vane type

Question 24

What function do fuel boost pumps perform?

Answer 24

They supply pressurized fuel to the fuel pump, which helps prevent vapor lock and cavitation

Question 25

What is a commonly used type of fuel boost pump?

Answer 25

The centrifugal type

Question 26

What causes vapor lock and why is it a concern?

Answer 26

Vapor lock is caused by insufficient fuel pressure, high fuel temperatures and excessive fuel turbulence which may completely block any fuel flow, resulting in engine failure

Question 27

What function does the engine driven pump on a turbine engine perform?

Answer 27

It provides a continuous supply of fuel at the proper pressure while the engine is running

Question 28

Name the two categories of turbine engine pumps

Answer 28

Constant and variable displacement

Question 29

What category is a gear type pump classified in?

Answer 29

Constant displacement

Question 30

When performing an external inspection of an engine driven fuel pump, what should you look for?

Answer 30

Leaks and security of mounting

Question 31

What is the purpose of the sheer section of the driveshaft in a dual element constant displacement pump?

Answer 31

If one of the elements seizes, a portion of the driveshaft seizes, allowing the other element to continue the operation

Question 32

Where in a turbine engine fuel system is ice formation likely to occur and how is it prevented?

Answer 32

The fuel filter is most susceptible to ice formation, so a fuel heater is used consisting of heat exchanger using either engine oil or bleed air to warm the fuel

Question 33

What is the purpose of a bypass valve in an engine fuel system micron filter?

Answer 33

It is a safety feature that allows fuel to flow to the engine if the filter becomes blocked

Question 34

What is the purpose of a duplex fuel nozzle?

Answer 34

A duplex fuel nozzle discharges two different spray patterns. The spray pattern is wider during start up and acceleration and narrows when the engine speed increases above vital

Question 35

What are the functions of the pressurizing and dump portions of a pressurizing and dump valve?

Answer 35

The pressurizing portion provides primary and secondary fuel flow to dual line duplex fuel nozzles and the dump portion allows fuel to drain from the manifolds after engine shut down

Question 36

What purpose do fuel selector valves serve?

Answer 36

They allow tank and engine selection and allow a means for shutting off fuel flow