Fuel Metering Systems Flashcards
What are some of the sources used to heat the fuel in a turbine engine fuel system?
Bleed air and engine lubricating oil
When does a carburetor economizer system needle valve begin to open?
Approximately 60 to 70% of rated power
What are the most common types of metering systems use on small reciprocating engines?
Float type carburetors, pressure type injection carburetors, and direct fuel injection systems
What function does the mixture control perform?
Controls the fuel/air mixture
What generally causes spark plug fouling?
Operating the engine with an excessively rich mixture at idle
What is the purpose of an accelerating system in a float type carburetor when the throttle is open in a quick action?
It provides immediate brief increase in fuel flow in a Venturi to enrich the mixture
What is a carburetor economizer system?
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.
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?
The idle mixture is set correctly.
What is rpm indication when an idle mixture is set correctly, and the mixture control is placed to the idle cut off position
A slight rise in RPM prior to decreasing
Why should engine rpm be accelerated periodically when making carburetor adjustments?
To clean the engine
What maintains the fuel pressure in a fuel injection carburetor?
engine driven fuel pump
What happens if the manual mixture control of a pressure ejector carburetor is moved to the idle cut off position?
The engine stops
What are some of the advantages of fuel injection systems over carburetor systems?
- Less danger of icing induction
- better acceleration
- better fuel distribution
- better fuel economy
- reduce overheating of individual cylinders
How does an automatic mixture control function?
A sealed brass bellows connected to the fuel metering system expands and contracts with changes in pressure and temperature, adjusting the mixture accordingly
What purpose do turbine engine fuel control units serve?
They automatically meter fuel to the engine
What are two basic types of turbine engine fuel control units?
Hydromechanical
electronic and FADEC (full authority digital engine control)
What are the engine variables detected by the fuel control unit?
- Power lever position
- engine rpm
- compressor inlet temperature
- compressor inlet pressure
- compressor discharge pressure
- Burner pressure
What are the two major components of a supervisory electronics engine control?
The electronic control unit (ECU) and the Hydro mechanical fuel control
What are some of the advantages of a full authority digital engine control (FADEC) over a Hydro mechanical fuel control?
- Better fuel economy
- improved starts
- requires no engine trimming
- provides engine limit protection
- provides constant idle speed regardless of atmospheric conditions or bleed air requirements
- fully modulates the active clearance control and allows more repeatable engine transients
What do turbine engine fuel spray nozzles do?
They inject fuel into the combustion area
What are the different engine indications used for trimming a turbine engine?
Either (EPR) engine pressure ratio or RPM is used depending on the particular engine
What maintenance adjustments are normally allowed on an installed Hydro mechanical fuel control?
Specific gravity for fuel, idle rpm and maximum rpm
