Carburetor/Fuel Injection Flashcards
Induction system
Brings outside air into the engine, mixes it with fuel in the proper proportion, and delivers it to the cylinders where combustion occurs
The volume of air flowing through the induction system is the primary fuel metering force
Purpose of carburetor
Provide engine with proper ratio of fuel to air
In an atomized state
Stochiometric Ratio 15:1
Accelerator pump
Pump squirts fuel into the carburetor throat during quick additions to power that would flood the engine with air and not enough fuel. Works like a syringe. When throttle is reduced the accelerator pump is filled with fuel.
Pressure type carburetor
Like a float type but uses diaphragms to regulate fuel flow.
Not as susceptible to icing
Used on large, high horsepower, high altitude piston engines.
Leaning
Controlling the amount of fuel entering the carburetor for altitude or air density changes.
Why lean?
Reduces fuel consumption
Stochiometric Ratio
●For efficient fuel combustion you need approximately 15 parts of air to 1 part of fuel
●Ratio 15:1
Prevents spark plug carbon/lead fouling
When to lean?
•Anytime there is a change in altitude or power setting
•Before takeoff at high altitude airports
When to enrich
•Altitude/power setting changes
•Full throttle operations
•Climb below 5,000’ DA
•Prepare for go-around
•Help cool engine
Conditions that produce ice
High humidity or visible moisture
Temperatures between 20 degrees and 90 degrees F
Pressure change
Expanding air exiting venturi causes
a temperature drop
Evaporation causes a
temperature drop
How ice forms
Cooling Effect
●Fuel vaporization
●Air pressure drop (expansion)
Types of carb ice
Impact – usually found on air intakes
Fuel – caused by the decreased temperature due to fuel evaporating. This type forms on the throat.
Throttle – forms due to change in pressure and evaporation of fuel. Air freezes at the throttle housing itself. Usually occurs at low power settings and lower temperatures than fuel icing.
How carb heat works
Shroud around exhaust stack heats up air
Pilot controls valve that lets hot air into the carburetor
Hot air melts ice and enriches mixture (hot air is less dense than cold air and moist air is less dense than dry air)
Fuel injection
Nozzles spray fuel directly into the intake manifold, near the cylinder head.
Types of fuel injectors
Meters the correct ratio of fuel for the air volume going into the cylinders at Fuel Injection Control Unit
Sprays atomized fuel directly into intake manifold by the Intake Valve.
Advantages of fuel injection
Better fuel flow
Better fuel distribution
Faster throttle response
Precise control of mixture
Less susceptibility to icing
Easier cold weather starts
Disadvantages of fuel injection
Difficulty in starting a hot engine
Vapor lock
Higher operational costs
Clogged injectors
