Engine and Systems Flashcards
What are the 4 strokes to a four stroke reciprocation engine cycle?
4-stroke Cycle
- Intake(suck)
- Compression (squeeze)
- Combustion (bang)
- exhaust (blow)
What happens during each stroke of a four-stroke engine cycle? (What is the piston doing, Spark plugs, Valves?)
Intake Stroke
Intake stroke (1st stroke)
- Piston is pulled down in the cylinder by the crankshaft
- This lowers the pressure in the cylinder and allows the air/fuel mixture to be sucked into the cylinder from the carburator through the intake valve
- Intake Valve is open
What happens during each stroke of a four-stroke engine cycle? (What is the piston doing, Spark plugs, Valves?)
Compression Stroke
Compression Stroke(2nd stroke)
- Intake valve is closed
- Piston is driven up, and compresses fuel/air mixture increasing its temperature
- As piston reaches top of cylinder, spark plugs ignite the fuel/air mixture
- This ignition begins a controlled burn and the start of the power stroke
How is power increased?
Power is increased by increasing the amount of air/fuel mixture that enters the Cylinder during the intake stroke,
What happens during each stroke of a four-stroke engine cycle? (What is the piston doing, Spark plugs, Valves?)
Power Stroke
Power Stroke(3rd stroke)
- Fuel/air mixture expands as it burns, forcing the piston to the bottom of the cylinder.
- Just prior to the end of the power stroke, the exhaust valve opens.
What happens during each stroke of a four-stroke engine cycle? (What is the piston doing, Spark plugs, Valves?)
Exhaust stroke
- Piston is driven back up to the top of the cylinder, driving the exhaust gases out the exhaust valve
- Exhaust valve is open
The power strokes of the cylinders are spaced so that they occur …
The power strokes of the cylinders are spaced so that they occur “at different positions during the revolution of the crankshaft.”
Each cylinder provides a power stroke per __ revolutions of the crankshaft, whether it’s a 4 or 6 cylinder engine.
Each cylinder provides a power stroke per 2 revolutions of the crankshaft, whether it’s a 4 or 6 cylinder engine.
Exhaust System
Burned gases leave cylinders, then exit the aircraft through the exhaust pipe on the underside of the cowling
How is cabin heat and defrost provided on most GA airplanes
- Via the exhaust system
- A shroud around muffler provides heated air for use in cabin heating/defrosting and carburetor heat
How is carburetor heat created for use?
A shroud around muffler provides heated air for use in cabin heating/defrosting and carburetor heat
What’s a Magneto?
- A magneto is a self-contained generator of electricity used to provide electricity to the spark plugs.
- Mechanically driven by the engine.
- Consists of a magnet that is rotated near a conductor which has a coil of wire around it.
- The rotation induces electrical current to flow in the coil.
What do the coils of wire of the Magneto do?
Around this primary coil of wire are many more coils of thinner wire which amplify, or transform, the primary voltage into the higher voltage needed for the spark plugs.
What is the arrangement of primary & secondary coils in the magneto called?
- The arrangement of primary & secondary coils in the magneto is called a transformer.
- The higher voltage is what is fed to the spark plugs which ignites the fuel/air mixture
What do spark plugs do?
The higher voltage from the magneto is what is fed to the spark plugs which ignites the fuel/air mixture
What makes sure the magneto delivers the higher voltage to each spark plug properly?
- a distributor in the magneto delivers the higher voltage to each spark plug at different times
- The distributor has a finger which is geared to crankshaft so it turns only once for every two turns of crankshaft
- .This finger turns once for each 4-stroke cycle
Because of this, the magneto distributes the current to each cylinder in the correct order.
Magnetos run __________ of all other electrical sources of power…they only need _____ to rotate the magnet
Magnetos run independently of all other electrical sources of power…they only need engine to rotate the magnet = engine driven.
If a lower grade of fuel is used what can happen?
It’s important to use the correct grade of aviation fuel:
If a lower grade is used than needed, it will cause high engine temperatures and detonation.
If a higher grade of fuel is used, what can happen?
It’s important to use the correct grade of aviation fuel:
If a higher grade is used than needed, spark plugs can be fouled by lead deposits.
What is detonation?
- Detonation is explosive combustion
- When gas is compressed it’s temperature and pressure rises.
- If it rises too high the air/fuel mixture in the cylinder will explode rather than burn evenly.
- Detonation can be very damaging to pistons, valves, & spark plugs
What is a sign of detonation?
Excessively high cylinder head temperature is a sign of detonation
What causes detonation?
- Lower fuel grade than recommended
- Old fuel (additives evaporate lowering the octane rating)
- Too lean of a mixture = too little fuel mixed with the air for burning in the cylinders.
- Over-heated engine.
- Excessive temperature of air passing through the carburetor
What do you do if detonation occurs in flight?
If detonation occurs in flight:
- Richen the fuel/air mixture
- Reduce thrust by pulling back on the throttle (less pressure in the cylinders with less power).
- Increase airspeed to increase airflow to the engine (to cool the cylinders).
- Increasing airspeed without increasing thrust requires a descent.
What is pre-ignition?
Ignition of fuel/air mixture before spark plug fires (before the piston reaches TDC)
The results of pre-ignition include:
The results of pre-ignition include:
- A rough running engine
- A sudden rise in cylinder head temperature
- Possible backfiring of the engine
- Possible engine damage
Pre-Ignition can be caused by:
Pre-Ignition can be caused by:
- Carbon or lead deposits (hot-spots in cylinder)
- Using high power with the fuel/air mixture too lean (no extra fuel available for cooling).
- Overheated spark plugs ( possibly due to detonation).
What is the carburetor ?
The carburetor mixes the fuel with the air prior to sending this mixture to the cylinders for combustion
What is the correct ratio of fuel/air?
The correct ratio of fuel/air is approximately 1 part fuel to 12 parts air by weight
What is a rich mixture?
A rich mixture means that the fuel/ air ratio is larger
(1:8 maximum).
What is a lean mixture?
A lean mixture means that the fuel/air ratio is smaller
(1:20 minimum).
What is latent heat of vaporization?
I think based on the Jep book…
The vaporization of fuel contributes to a temperature decrease in the carburetor
What is the first indication of Carb Ice
- A decrease in RPM
- Rough running engine
What conditions are favorable to the formation of carburetor Ice?
- Tempurature below 70 F
- High humidity
What’s the differnence between rich fuel/air mixture and lean fuel/air mixture?
rich fuel/air mixture
With a rich fuel air mixture there will be excess fuel after burning. This can cause
- loss of power
- rough running engine
- high fuel consumption
- fouling of spark plufs
- formation of lead deposits
On a good note, the cylinder head temperatures are cooler
What’s the differnence between rich fuel/air mixture and lean fuel/air mixture?
lean fuel/air mixture
A lean mixture means there is a relative shortage of fuel compared to the air in the fuel/air mixture, so after burning, there will be some oxygen left over.
This causes excessively high cylinder head temperatures possibly leading to detonation or pre-ignition
Is it better to have a too rich or too lean fuel/air mixture?
A little “too rich” mixture is preferable to a “too lean” mixture
When starting a C-172 engine, do both magnetos provide electrical current to all of the spark plugs?
No, the left magneto provides electrical current to 1 spark plug in each cylinder
What are the causes of a temperature drop in the carburetor venturi?
- pressure drop
- latent heat of vaporization
Does application of carburetor heat affect engine performance?
Yes. Causes a reduction of RPM. Heated air is less dense ?
To ask Bill: Why would an rich mixture cause a reduction in RPM?
What does the throttle do?
The throttle lever in the cockpit allows the pilot to vary the airflow into the carburetor throat by positioning the throttle plate (butterfly valve).
Why does that matter?
The greater the amount of airflow, the greater the pressure differential between the carburetor throat and the float chamber, and the more fuel/air mixture provided to the cylinders.
The more fuel/air mixture to the cylinders = more power = more thrust
The greater the amount of airflow to the carburetor means what?
The greater the amount of airflow, the greater the pressure differential between the carburetor throat and the float chamber, and the more fuel/air mixture provided to the cylinders.
The more fuel/air mixture to the cylinders = more power = more thrust
Engine Controls in the cockpit
Mixture
Mixture: used to adjust the metered weight of fuel to be mixed with air in the carburetor
Engine Controls in the cockpit
Throttle
Throttle: used to adjust the amount of fuel/air mixture to be delivered to the cylinders = increases/decreases power = adjusts thrust
Engine Controls in the cockpit
Tachometer
Tachometer: engine instrument used to adjust/monitor engine rpm.
What type of fuel systems are typical on high wing, small aircraft and why?
Gravity fed systems are typical on high wing, small aircraft, because they are simple!
Fuel Systems
What are located under each wing and are used to check for fuel contamination during pre-flight
Sumps located under each wing are used to check for contamination during the preflight
What provides power to turn the propeller?
The engine provides power to turn the propeller
Where is a Reciprocating Engines mounted?
Mounted to firewall, which protects
occupants, and turns the propeller
What does a Reciprocating Engine power?
Powers Accessories:
- alternator,
- vacuum pump (for instruments), and
- provides heat
Where is the power generated in a reciprocating engine?
Cylinders are where the power is generated
What makes sure the intake and exhause valves open/close at the correct times?
Intake & exhaust valves must open/close at correct times.
Regulated by a camshaft
Camshaft rotates at ??? the rate of the crankshaft
Camshaft rotates 1/2 the rate of the crankshaft
Intake/exhaust valves open/close??? per complete cylinder cycle = once per ?? crankshaft revolutions = ?? per camshaft revolution
Intake/exhaust valves open/close 1 time per complete cylinder cycle = once per 2 crankshaft revolutions = once per camshaft revolution
An dual ignition system in a small airplane includes
For small airplanes, this system includes:
- Two magnetos which send electric current to the spark plugs.
Two spark plugs per cylinder.
Each magneto sends current to one spark plug in each cylinder
Having a ____ ignition system results in more ___ burning of the fuel/air mixture, and is more _______
Having a dual ignition system results in more even burning of the fuel/air mixture, and is more fuel efficient
The starter is powered by the _______
Starter is powered by the battery
When starter is engaged, it _______
When starter is engaged, it rotates the crankshaft
