Lecture 17 Flashcards
List advantages of a fuel injection system*
Freedom from vaporization icing (carb icing)
More uniform delivery of air-fuel mixture to each cylinder
Improved control of fuel/air ratio
Instant acceleration after idling with no tendency to stall
Increased engine fuel efficiency and power
What are the advantages of fuel injection over carburetion?*
Fuel injection is more responsive than carburetion
Fuel injection does not have carb ice issues while carburetors do
Fuel injection does not have a float mechanism while carburetors do (fuel flow disturbances in aircraft maneuvers interfere with the float mechanism)
What is the Bendix RSA fuel injection system designed to do?
Meter fuel in direct ratio to the volume of air being consumed by the engine
How does the Bendix RSA system (servo) meter fuel to air?*
Impact tubes direct air to the air diaphragm
As the air diaphragm moves left, it pulls the fuel diaphragm with it
The diaphragms are linked together with a rod that has a ball valve on the end of it
Since the air and fuel diaphragm move together, it pulls the ball valve and allows metered fuel to exit the servo to the flow divider
How does the servo pressure regulator work when fuel and air pressures are equal?
Just enough metered fuel is allowed to discharge and maintains pressure balance
What is the servo pressure regulator?
Works to create the right air-fuel ratio using diaphragms and valves
How does the servo pressure regulator work when the throttle opens?
Airflow and differential pressure across the air diaphragm increases
The servo valve opens, decreasing the pressure in the meter fuel chamber
With the increase in fuel differential pressure
More fuel is increased to the engine to support the higher power level requested
What are the air diaphragm and fuel diaphragm connected by?
Servo valve
What is the idle valve?
Connected to the throttle linkage
Externally adjustable
At idle, the low airflow is not sufficient to accurately control the fuel flow
It limits the area of the main metering jet
Meters fuel accurately in the idle range
Idle mixture is correct when the engine gains 25-50 rpm from idle speed when mixture is placed in “idle cutoff”
What are the two primary functions of a flow divider?*
Ensure equal distribution of metered fuel to the nozzles
Provide isolation of each nozzle for clean engine shutdown
Where does the fuel air mix in a fuel injected system?*
Fuel injection nozzles right behind the intake valve as it goes into the cylinder
