Reciprocating Engine Fuel Metering Flashcards
Where the fuel in a float chamber system is stored
Float chamber
The five air/fuel mixture settings
- Full rich 2. idle-cutoff 3. lean best power 4. rich best power 5. best economy
In the induction manifold, as the throttle is opened, the pressure_______
rises
Primary cause of Pre-ignition
Hot-spot
The two types of carburetors
Float type, Pressure injection
Why an increase in humidity will decrease engine performance
Water is incombustible
In Afterburning in a piston engine, fire may appear in_____
The exhaust
An airbleed system is a vented passage with a small calibrated orifice which overcomes
Surface tension of the fuel
Relationship between volumetirc efficiency and humidity
Inversely propotional
Aircraft with Constant speed propellers, the _____ gauge can be used to help adjust fuel mixture
MAP
To compare an engine to the manufactures specifications, the AMT will have to perform a(an) __________
engine run-up
The system out of the 5 carburetor systems which allows the pilot to control the mixture
Mixture control system
The idling system allows fuel
to continue to flow to the engine with the venturi butterfly valve in the closed position
The name for the pilot controlled restrictor plate installed in the Venturi
Throttle valve/ butterfly valve
The air/fuel mixture that a typical piston will generate maximum power at
12:1
The system which provides the engine with the correct amount of fuel for all speeds above idle
Main metering system
The ratio of fuel displaced by the piston to the piston’s swept volume
Volumetric efficiency
The most likely condtion of an engine that continues to fire after the ignition has been shut off
Pre-ignition
In carburetors in which a single venturi is insufficient to provide an adequate pressure drop, a(an) ________ is installed
Boost venturi
The property that prevents a liquid from readily breaking apart based on molecular cohesiveness
surface tension
The two methods of fuel metering in reciprocating engines
Carburetion, fuel injection
The type of valve inside the float chamber
Needle valve
As a general rule for AVGAS, a ratio of _______ to _______ will support combustion
8:1 to 16:1
Condition in which an excessively rich fuel/air mixture causes a slow combustion and un-burned fuel leaves the cylinder and mixes with the air in the exhaust system and ignites
Afterfire
The condition in which an extremely lean fuel/air mixture burns slowly which will remain burning when the intake valve opens for the next cycle, which ignites the intake air before the intake valve closes and burns in the induction manifold
Backfiring
The theoretical perfect air/fuel mixture for a piston engine in 0:0 format
15:1
Burning of the fuel/air mixture prior to the spark plug firing
Pre-ignition
The three types of fuel injection
Direct, continuous-flow, electronically controlled
The only accurate way to measure a fuel/ air ratio
By weight
The tube that connects the float chamber to the throat of the venturi
U-tube
Detonation will cause: 4 things
- High cylnder head temperatures 2. Rough running engine 3. Higher pressure 4. Loss of power
The 5 sytems of a carburator
- Main metering 2. Idling 3. Mixture control 4. Accelerating 5. Economizer
The amount of work done by the engine compared to the amount of heat supplied to it
Thermal efficiency
All float chambers are vented to_______
atmosphere
What needs to happen to the fuel for complete and even burning
Atomized
Best economy mixture setting refers to the ratio which provides
The greatest amount of power for the least amount of fuel
A decrease in air density for a given air/fuel mixture yields a _____ mixture
richer
The number of pounds burned per hour to produce 1 horsepower
Specific fuel consumption
The stoichiometric mixture describes
A mixture in which all oxygen is used during combustion
Aircraft with fixed pitch propellers can use the ______gauge to adjust fuel mixture
Tachometer
An increase in humidity _______ engine performance
Degrades
A increase in air density for a given air/fuel mixture yields a _____ mixture
leaner
The uncontrolled, explosive ignition of a fuel/air mixture in a cylinder
detonation
The most accurate parameter for gauging/ setting fuel mixture
EGT
The condition of the EGT in lean mixture condition
Higher
The condition of the EGT in rich mixture
Cooler
What he size of the pressure differential between the float chamber and the venturi will determine
The amount of fuel transferred from the float chamber to the main metering jet
In a simple float type carburetor, the maximum amount of fuel flowing through the discharge nozzle is limited by
Size of the main metering jet
The term for the 1/8” difference between the height level fuel in the float chamber and the height level of fuel at the discharge nozzle
Fuel metering head
The function of the fuel metering head distance
The prevention of fuel leaking from the carburetor into the venturi
The function of idle jets in a float type carburetor
Ensure consistent engine operation at idle speed
The term for a system which uses sealed bellows to move a variable orifice, so that during a climb, when atmospheric pressure decreases, the bellows expand which leans the fuel/air mixture
AMC (automatic mixture control)
When the throttle valve is opened rapidly, the condition of the fuel/air mixture______ due to _________
leans, due to fuel discharge nozzle lagging
The typical method of preventing problem of the mixture momentarily leaning out during rapid opening of the throttle/ butterfly valve
Using of the accelerator pump
Heat generated by operating at maximum power, which can be more than air cooling can dissipate, can be dissipated by power enrichment. Another term for power enrichment can be Economizer. Why
It also permits the pilot to use a leaner mixture at cruise
2 cons of using a float type carburetor
- Ice formation 2. Unusual body attitudes
the 2 types of carburetor icing
- Fuel evaporation ice 2. Throttle ice
The first place on a piston engine aircraft (non fuel injection) to start accumulating ice during flight
Carburetor
The process of fuel evaporation ice
Fuel vapor inside the venturi absorbs heat which drops the overall temperature
Typical temperature range and humidity percentage which carburetor ice will start to form
40-50 F, 60%
The very specific area in a (non fuel injection) piston engine where throttle icing first accumulates
Behind the partially closed throttle valve
The description of a pressure balance duct in a carburetor system
A duct which balances pressure between the float chamber and the venturi
The type of system, also named by anti-detonation injection system, used on piston engines with pressure injection, that produce
Water Injection system
The composition of the fluid injected into a pressure injection carburetor system
Water and alcohol
The term given for a fuel injection system which has the fuel directly injected into the combustion chamber
Direct fuel injection
The most commonly used type of fuel injection system used on piston engines
Continuous-flow fuel injection system use in piston engines
The fuel system in which fuel is delivered to the outside of the intake valves of the cylinder before being sucked into the cyilinder for combustion
Continuous-flow fuel injection
The 2 types of continuous-flow fuel injection systems used in the US
- Precision Airmotive RSA 2. Teledyne Continental Motors
The 5 components of the RSA Fuel metering system
- Venturi housing 2. Fuel metering unit 3. Fuel regulator 4. Fuel divider 5. Fuel Nozzle
The system in a carburetor which increases fuel flow at high power settings
Power enrichment/ Economizer
The 2 types of Economizers found on piston engines
- Needle type 2. Air bleed type
Identify
Economizer needle
The measure of the vacuum pressure between the throttle and the cylinders
MAP pressure
The more the throttle is opened, the ________ that manifold pressure _______to atmospheric pressure.
closer, returns
Desribe what is happening
Manifold pressure is lower because there is not a large amount mass flow into the engine
Desribe what is happening
Since the throttle is being opened and there is more mass flow entering the intake, there is a greater density of fuel/air mxiture per same volume so there is an incrase in pressure
The 3 types of mixture control in float type carburetors
- Variable Orifice
- Back suction
- Automatic mixture control (AMC)
With the Back-suction mixture control, describe operation during idle/ cutoff position
The float chamber is vented to the low pressure side of the venturi to elimiate any potential pressure gradient between the float chamber and the discharge nozzle
For idle mizture adjustment in a float carburetor, the engine should be run until the cylinder head
Cylinder head temperature is within normal range
The required action in order to check the idle mixture control on a float carbureator and what to watch for (3 conditions- too lean, too rich, just right)
Pull mixture aft and watch tachometer
- RPM will increase slightly before dropping rapidly (just right)
- Immediate drop in RPM (Too lean)
- Momemtary increase of more than 50 RPM (too rich)
Typical idle speed for float type carburetors engines
600- 800 RPM
The checmical used to clean a carburetor of grease, oil and varnish from gasoline additives
Stoddard Solvent
What not to use to dry carburetors with after cleaning with Stodard Solvent and why
Shop rags, lint can clog up metering jets
How to float clearance between the gasket and float on some carburetors is measured
With the shank of a drill bit
Most carburetor bodies are constructed out of
cast aluminium
Since carburetor bodies are very soft (cast aluminium) the method for protecting any threaded openings from damage upon insertion
Insert the first thread, followed by application of thread lubricant to the threads
The mechanical control stops on a carburetor should be reached before
The controls reach their stops in the cockpit
The amount of control travel possible between the engine component’s stop and the cockpit stop is termed
Spring back
