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

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

Answer 2

Above approximately 60 to 70 % of rated power.

Question 3

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

Answer 3

Float-Type carburators, Pressure-Type injection carburators 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 (clog)?

Answer 5

Operating the engine with an excessively rich mixture at idle.

Question 6

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

Answer 6

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

Question 7

What is a carburator 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-cutoff position, a slight rise in R.P.M is noted prior to the engine decelerating. What does this indicate?

Answer 8

The idle mixture is set correctly.

Question 9

What is the RPM indication when an idle mixture is set correctly, and the mixture control is placed to the idle-cutoff position?

Answer 9

A slight rise in RPM prior to decreasing.

Question 10

Why should engine R.P.M be accelerated periodically when making carburator adjustaments?

Answer 10

To clean the engine.

Question 11

What maintains the fuel pressure in a fuel-injection carburator?

Answer 11

An engine-driven fuel pump.

Question 12

What happens if the manual mixture control of a pressure injection carburator is moved to the idle cutoff position?

Answer 12

The engine stops.

Question 13

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

Answer 13

(1)Less danger of icing induction,
(2)Better acceleration,
(3)better fuel distribution,
(4)better fuel economy,
(5)reduced overheating of individual cylinders
(6) Better fuel economy.

Question 14

How does an automatic mixture control (AMC) 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 the two basic types of turbine engine fuel control units?

Answer 16

Hydromechanical, eletronic and FADEC (Full Authority Digital Engine Control)

Question 17

What are the engine variables detected by the fuel control unit? (Turbine)

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 eletronics engine control?

Answer 18

The eletronic control unit (ECU) and the Hydromechanical fuel control.

Question 19

What are some of the advantages of a full-authority digital engine control (FADEC) over a hydromechanical 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
(6) speeds regardless of atmospheric conditions or blees air requirements,
(7)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 hydromechanical fuel control?

Answer 22

Specific gravity for fuel, idle RPM and maximum RPM.