piston engine propulsion chapter 2 the four stroke cycle 1933 alvis engine 2014 hyundai engine
TRANSCRIPT
PISTON ENGINE PROPULSION
Chapter 2
The Four Stroke Cycle
1933 Alvis Engine
2014HyundaiEngine
BUT HOW DOES IT WORK EXACTLY?
The Four Stroke Cycle
LET’S LOOK IN MORE DETAIL
The Four Stroke Cycle Operating Cycle
1. INDUCTION
4. EXHAUST
3. COMBUSTION
2. COMPRESSION
Known as SUCK
Known as BLOW
Known as BANG
Known as SQUEEZE
Air and fuel mixture is sucked into the cylinder.
Air and fuel mixture is compressed by the piston.
Air and fuel mixture is ignited and the piston is pushed down.
Burnt gas is pushed out by piston.
Which gives: SUCK, SQUEEZE, BANG, BLOW
The Four Stroke Cycle
1 2 3 4
BANG SQUEEZE SUCKBLOW
Operating Cycle
The Four Stroke Cycle
1
2
3
4
INDUCTION (first downstroke)
COMBUSTIO N (second downstroke)
EXHAUST (second upstroke)- Exhaust valve open- P iston moves back up the cylinder (from BDC to TDC)-The burnt (exhaust) gases, having now performed their useful work on the Power Stroke, escape in to the atmosphere via the exhaust pipe.
- Inle t valve open- P iston moves down the cylinder (from TDC to BDC)- Fuel air m ixture (the charge) is drawn into the cylinder
- - Spark occurs, igniting the compressed fuel/air m ixture- R apid expansion of the burning m ixture forces the p iston back down the cylinder (from TD C to BDC).
Both valves are closed
COMPRESSIO N(first upstroke)- Both valves are closed- P iston moves back up the cylinder (from BDC to TDC)- Fuel air m ixture is com pressed in to the top of the cylinder (the combustion cham ber).
Operating Cycle
1 ‘Stroke’ = the piston sliding either up or down the cylinder
Therefore a ‘Four’ Stroke engine
is 2 revs of the crankshaft
Down
Down
UpUp
The Four Stroke Cycle
TDC
BDC STROKE 1
PISTON MOVES DOWN CYLINDER
CRANK ROTATES
AIR/FUEL DRAWN (INDUCED - SUCKED) INTO CYLINDER
Operating Cycle
The Four Stroke Cycle Operating Cycle
TDC
BDCSTROKE 2
CRANK CONTINUES TO
ROTATE
PISTON MOVES BACK UP CYLINDERAIR/FUEL TRAPPED (COMPRESSED - SQUEEZED) IN CYLINDER
The Four Stroke Cycle Operating Cycle
TDC
BDCSTROKE 3
CRANK STARTS 2ND ROTATION
PISTON FORCED DOWN CYLINDERAIR/FUEL IGNITED AND BURNS (COMBUSTION - BLOW) IN CYLINDER
The Four Stroke Cycle Operating Cycle
TDC
BDCSTROKE 4
CRANK CONTINUES 2ND
ROTATION
PISTON MOVES BACK UP CYLINDER AGAINBURNT AIR/FUEL PUSHED OUT OF CYLINDER (EXHAUST – BLOW)
The Four Stroke Cycle Operating Cycle
When the end of the exhaust stroke is reached
It is of course the start of the induction stroke And the whole process
starts again
The Four Stroke Cycle Operating Cycle
But :-
Because valves don’t open and close instantly, and
The air/fuel mixture doesn’t explode instantly
(it’s a rapid burning process)
Valve operation and air/fuel ignition are’nt set at the TDC and BDC positions.
These events are set to occur at the following positions, designated as angular positions of the crank shaft.
The Four Stroke Cycle Operating CycleThe start of Induction – Stroke 1
TDC
BDC
We’ll start the process at 30 degrees before TDC At which point, the Inlet valve
begins to open
The Four Stroke Cycle Operating CycleThe start of Compression – Stroke 2
TDC
BDC
1.
Ind
uc
tion
Inlet valve opens
The induction stroke ends at 15 degrees after BDC. When the Inlet valve closes
Inlet valve closes
Called Valve Lag because it is after BDC
Trapping the air/fuel mixture in the cylinder
The Four Stroke Cycle Operating CycleThe start of Power – Stroke 3
TDC
BDCInlet valve
closes
1.
Ind
uc
tion
2.
Co
mp
res
sio
n
Inlet valve opens
Ignition occurs at 30 degrees before TDC.
Ignition
At this point, both valves are closed
And is the start of the Power stroke
The Four Stroke Cycle Operating CycleThe start of Exhaust – Stroke 4
TDC
BDCInlet valve
closes
1.
Ind
uc
tion
2.
Co
mp
res
sio
n
Inlet valve opens
Ignition
3. P
ow
er
Exhaust valve opens
Burning air/fuel mixture reaches maximum expansion
15 degrees before BDC, the exhaust valve opens
Called Valve Lead because it is before BDC
And is the end of the Power stroke and
start of the Exhaust stroke
TDC
BDCInlet valve
closes
1.
Ind
uc
tion
2.
Co
mp
res
sio
n
Ignition
3. P
ow
er
Exhaust valve opens
4.
Ex
ha
us
t
The Four Stroke Cycle Operating CycleThe end of Exhaust – Stroke 4
This position is towards the end of the Exhaust stroke
And is ALSO the beginning of the Induction stroke
So as the exhaust valve starts to
close, the inlet valve starts to open
Inlet valve opens
The Four Stroke Cycle Operating CycleValve Overlap - Stroke 4 to 1
TDC
BDCInlet valve
closes
1.
Ind
uc
tion
2.
Co
mp
res
sio
nInlet valve opens
Ignition
3. P
ow
er
4.
Ex
ha
us
t
Exhaust valve
closes
Exhaust valve opens
This is called ‘Valve Overlap’‘Valve Overlap’
Therefore the Induction stroke starts 45 degrees45 degrees beforebefore the end
of the Exhaust stroke
Both the inlet and exhaust valves are partially open
The start of Induction – Stroke 1The Four Stroke Cycle Operating Cycle
TDC
BDCInlet valve
closes
1.
Ind
uc
tion
2.
Co
mp
res
sio
n
Inlet valve opens
Ignition
3. P
ow
er
4.
Ex
ha
us
t
Exhaust valve
closes
Exhaust valve opens
This position is at the end of the exhaust stroke
And is 45 degrees into the induction
stroke
The inlet valve is now open
The exhaust valve is now closed
The Four Stroke Cycle Operating Cycle
PROPULSION 33-11
In le tva lve
closes
In letva lveopens
Charge ign ited
BDC
TDC
Exhaustvalveopens
Exhaustvalve
closes
1Ind
uctio
n
Pow
er3
Exh
aust
42co
mp
ress
ion
Lead
LeadLag
Lag
Lag
30
Valve overlap
Simple isn’t it!
Suck
Squeeze
Bang
Blow
The Four Stroke Cycle Operating Cycle
in all 4 stroke engines
no matter how many cylinders there are.
Lets look at the most typical vehicle engine,
the ‘Inline 4’
But, this is happening in every cylinder
The Four Stroke Cycle Operating Cycle
The cylinders are numbered from
the front
to the rear
The Four Stroke Cycle Operating Cycle
And the firing order is:- 1 – 3 – 4 - 2
The Four Stroke Cycle Operating Cycle
The Four Stroke Cycle Operating Cycle
The Four Stroke Cycle Operating Cycle
The Four Stroke Cycle Operating Cycle