THE FOUR STROKE CYCLE

1
THE FOUR STROKE CYCLE
BUT HOW DOES IT WORK EXACTLY?
WE KNOW ABOUT-
WHICH WE KNOW AS-
1. INDUCTION
SUCK
2. COMPRESSION
SQUEEZE
3. COMBUSTION
BANG
4. EXHAUST
BLOW
2
WELL SEE A STEP BY STEP EXPLAINATION OF THIS
DIAGRAM
Operating Cycle
3
AND THIS DIAGRAM
Down
Up
Up
Down
1 Stroke the piston sliding either up or down
the cylinder
Therefore a Four Stroke engine is 2 revs of the
crankshaft
Operating Cycle
4
TDC
STROKE 1
BDC
Operating Cycle
5
TDC
STROKE 2
BDC
Operating Cycle
6
TDC
STROKE 3
BDC
Operating Cycle
7
TDC
STROKE 4
BDC
Operating Cycle
8
And the whole process starts again
Operating Cycle
9
But -
Because valves dont open and close instantly,
and
the air/fuel mixture doesnt explode instantly
(its a rapid burning process)
valve operation and air/fuel ignition isnt 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.
Operating Cycle
10
The start of Induction Stroke 1
Well start the process at 30 degrees before TDC
TDC
BDC
Operating Cycle
11
The start of Compression Stroke 2
The induction stroke ends at 15 degrees after BDC.
TDC
Inlet valve opens
1. Induction
Trapping the air/fuel mixture in the cylinder
BDC
Inlet valve closes
Operating Cycle
Called Valve Lag because it is after BDC
12
The start of Power Stroke 3
Ignition occurs at 30 degrees before TDC.
TDC
Inlet valve opens
1. Induction
2. Compression
And is the start of the Power stroke
BDC
Inlet valve closes
Operating Cycle
13
The start of Exhaust Stroke 4
Burning air/fuel mixture reaches maximum expansion
TDC
Inlet valve opens
And is the end of the Power stroke and start of
the Exhaust stroke
Ignition
1. Induction
3. Power
2. Compression
Called Valve Lead because it is before BDC
BDC
Inlet valve closes
Operating Cycle
14
The end of Exhaust Stroke 4
This position is towards the end of the Exhaust
stroke
TDC
Inlet valve opens
Ignition
1. Induction
2. Compression
3. Power
4. Exhaust
And is ALSO the beginning of the Induction stroke
Exhaust valve opens
BDC
Inlet valve closes
Operating Cycle
15
Valve Overlap - Stroke 4 to 1
This is called Valve Overlap
TDC
Exhaust valve closes
Inlet valve opens
Ignition
1. Induction
2. Compression
3. Power
4. Exhaust
Therefore the Induction stroke starts 45 degrees
before the end of the Exhaust stroke
Exhaust valve opens
BDC
Inlet valve closes
Operating Cycle
16
The start of Induction Stroke 1
This position is at the end of the exhaust stroke
TDC
Exhaust valve closes
Inlet valve opens
Ignition
1. Induction
2. Compression
3. Power
4. Exhaust
And is 45 degrees into the induction stroke
Exhaust valve opens
BDC
Inlet valve closes
Operating Cycle
17
Simple isnt it!
Suck
Squeeze
Bang
Blow
Operating Cycle
18
But, this is happening in every cylinder
in all 4 stroke engines
no matter how many cylinders there are.
Lets look at the most typical vehicle engine,
the Inline 4
Operating Cycle
19
The cylinders are numbered from
1 3 4 - 2
to the rear
the front
Operating Cycle
20
Operating Cycle
21
Operating Cycle
22
Operating Cycle
23
Operating Cycle