Piston Engines Flashcards
1
Q
How do piston engines produce power?
A
By converting chemical energy —-> mechanical energy
2
Q
Principle of operation
A
- Petrol is mixed with air
- Mixture introduced to cylinder through INLET port
- This port is closed by the INLET valve
- Cylinder is sealed on the other end by a piston
- This mixture drawn in is called the CHARGE
- Charge is ignited by an electric spark plug
- Hot air expands, confined by cylinder
- Increases pressure, cylinder moves down
- Piston is connected to crankshaft
- Angular momentum of crankshaft push the piston back up
- Exhaust valve opens to allow products of combustion to exit
3
Q
Four stroke cycle (suck, squeeze, bang, blow)
A
- Induction - mixture drawn into cylinder
- Compression - Mixture compressed to maximise pressure
- Power - Piston is driven down to produce mechanical power
- Exhaust - Waste gases are expelled
4
Q
Stroke
A
Distance between top dead and bottom dead centre
5
Q
When does ignition (combustion) occur?
A
Between compression and power strokes
6
Q
Induction stroke (normally aspirated)
A
- Piston moves down, volume increases, less temp and pressure
- Air moves into cylinder
- Inlet valve is open, exhaust closed
7
Q
Compression stroke
A
- Inlet valve closes, exhaust still closed
- As pistons move up, volume decreases
- Pressure and temp increases
8
Q
Power stroke
A
- Rise in pressure = piston moves down
- Volume increases
- This is the only stroke that produces power
9
Q
Exhaust stroke
A
- Exhaust valve opens when piston is at BDC
- Volume decreases
- Products of combustion are expelled
10
Q
Why is the speed and rotation of the crankshaft important for pilots?
A
Helps the pilot to control the A/C speed and performance
11
Q
Ineffective crank angle
A
- Very little linear movement close to TDC and BDC
12
Q
Valve lead
A
- End of exhaust stroke
- Before piston reaches TDC, inlet valve opens
- Allows fresh mixture before repeating the cycle
13
Q
Inlet valve lag
A
- Inlet valve remains open when piston moves down
- Remains open beyond BDC
14
Q
What do inlet lead and inlet valve lag help in maximising?
A
Amount of mixture that enters the cylinder during the ineffective crank angle
15
Q
Exhaust lead
A
Opposite of inlet - allows remaining gases to clear
