Fuel Metering Systems Flashcards
(22 cards)
What are some of the sources used to heat the fuel and a turbine engine fuel system?
Bleed air and engine lubricating oil
When does a carburetor economizer system needle valve begin to open?
Above 60% to 70% of rated power
What are the most common types of metering systems used on small reciprocating engines?
Float type carburetors
Pressure type injection carburetors
Direct fuel injection systems
What function does the mixture control perform?
Sets the amount of fuel added to the intake airflow to control the fuel/air mixture
What generally causes spark plug fouling (clog)?
Operating the engine with an excessively rich mixture at idle
What is the purpose of an accelerating pump system in a float type carburetor when the throttle is open in a quick action?
It provides an immediate but brief increase in fuel flow in the 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 to help with engine, cooling and 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 the 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 and a fuel injection carburetor?
An engine driven fuel pump
What happens if the manual mixture control of a pressure injection 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
Reduced overheating of individual cylinders
How does an automatic mixture control functions?
A sealed brass Bellows is connected to the fuel metering system, which expands and contracts with changes in pressure and temperature. This adjusts the mixture accordingly.
What purpose do turbine engine fuel control unit serve?
They automatically meter fuel to the engine
What are the basic types of turbine engine fuel control units?
Hydromechanical
Electronic
Fuel authority digital engine control (FADEC)
What are the engine variables detected by the fuel control units?
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 and the Hydromechanical fuel control
What are some of the advantages of a full authority, digital engine control over a Hydromechanical fuel control?
Better fuel economy
Improved starts
Requires no engine trimming
Provides engine limit protection
Provides constant idle speeds, regardless of atmospheric conditions or bleeds air requirements
Fully modulates the active clearance control
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?
EPR (engine pressure ratio) or RPM is generally used, depending on the engine
What maintenance adjustments are normally allowed on an installed Hydromechanical fuel control?
Specific gravity for fuel, idle RPM and maximum RPM
