provides the basic information about engines...

1. Government
Engineering
College Bhavnagar
Assignment on Elements Of
Mechanical Engineering

2. Prepared by:
Name Enrollment no.
Bhavika Chavda 140210107008
Sagar Harsora 140210107018
Kuldip vasghsya 140210107029
Bhavya Sheth 140210107056
Keval vora 140210107062
Topic: Four Stroke Engine

3. A four-stroke engine (also known as four-cycle) is
an internal combustion engine in which the piston
completes four separate strokes which constitute a single
thermodynamic cycle

4. TYPES OF STROKES

5. FOUR STROKE ENGINE

6. FOUR STROKE CYCLE ENGINES
• In a four-stroke engine the cycle of the operation of engine is completed by four
strokes of the piston inside the cylinder.
• During these four strokes fuel is once injected and burnt inside the engine and
two revolutions of the crankshaft are obtained.
• In a four-stroke spark ignition (SI) engine the burning of the fuel occurs by the
spark generated from the spark plug.
Crankshaft- a round shaft with lobes, that rotates to open
and close the fuel and exhaust valves.

7. BASIC
COMPO-
NENTS
OF
FOUR-
STROKE
ENGINE
S
Intake Valve
Valve Cover
Intake Port
Head
Coolant
Engine Block
Oil Pan
Oil Sump
Crankshaft
Camshaft
Exhaust Valve
Spark Plug
Exhaust Port
Piston
Connecting Rod
Rod Bearings

8. TYPES OF STROKES USED IN
FOUR STROKES ENGINE
1. Suction stroke
2. Compression stroke
3. Expansion stroke or Power Stroke
4. Exhaust stroke

9. TYPES OF FOUR STROKES
ENGINE
1. Spark ignition engines ( Petrol Engine ) S.I
2. Compression engine (Diesel Engine ) C.I

10. WORKING OF FOUR STROKE S.I
ENGINE
• Mostly working fuel of these engine is Petrol or Gas
• Compression ratio used in these engines varies from 5 to 10

11. 1) SUCTION (INTAKE)STROKE
• At the beginning of this stroke the piston is at the top dead center or near the cylinder
head and is about to move down.
• At this instance the inlet valve fitted in the cylinder head is opened and the exhaust
valve remains closed due to the pressure difference.
• As the piston moves down the suction pressure is created inside the cylinder, drawing an
air-fuel mixture into the cylinder.
• When the piston reaches the bottom most position or bottom dead center, the suction
stroke ends and the inlet valve is closed.

12. 2) COMPRESSION STROKE:
• During this stroke the piston starts moving from bottom dead center to top dead
center.
• As the piston moves up, the air-fuel mixture gets compressed into the clearance
volume of the cylinder.
• At the end of the stroke the spark is generated by the spark plug, which causes
the burning of the fuel and the release of large amounts of thermal energy.
• Due to this heat, high pressures are generated.

13. 3) EXPANSION OR POWER
STROKE:
• he large amount of pressure generated at the end of the compression stroke
pushes the piston towards the bottom dead center.
• It is during this stroke that the actual power is produced by the engine, hence
this stroke is called the power stroke and since the expansion of gases occurs
during this process, it is also called the expansion stroke.
• During this stroke, both the inlet and exhaust valves remain closed.

14. 4) EXHAUST STROKE
• Towards the end of the expansion stroke the inlet valve remains closed while the exhaust
valve opens due to the internal and external pressure difference.
• The piston starts moving in an upward direction and all the residual gases that are left
after the expansion stroke are swept outside the cylinder and escape through the exhaust
chamber.
• At the end of the exhaust stroke, the piston reaches top dead center position and then
starts moving in the downward direction to suck the air-fuel mixture and complete the
suction stroke.

15. WORKING OF FOUR STROKE C.I
ENGINE
• The cycle of operations of the four-stroke compression ignition (CI) engine
are completed in four strokes of the piston inside the cylinder.
• During these four strokes two revolutions of the crankshaft are produced.
• In compression ignition (CI) engines, burning of fuel occurs due to
compression of the fuel to very high pressures. At very high pressures the fuel,
i.e. diesel, starts burning automatically without the need of any external
flame.

16. 1) SUCTION STROKE
• At the start of the suction stroke the piston is located at top dead center position.
As it moves down,
• the inlet valve located in the cylinder head opens, while the exhaust valve remains
closed.
• From the inlet valve, air is drawn into the cylinder which continues until the
piston reaches bottom dead center or the bottom most position inside the cylinder.
• At this point the suction stroke completes and the suction or inlet valve closes.

17. 2) COMPRESSION STROKE
• During the compression stroke the piston starts moving in upward and
compresses the air in the clearance volume.
• While in the case of spark ignition (SI) engines, the compression ratio is
about 6-10, the CI engine this ratio is about 16-20.
• This clearly indicates that the compression pressure exerted in the CI engines
is much more than in SI engines.

18. 3) EXPANSION STROKE
• Towards the end of the compression stroke, the fuel is injected into the clearance volume.
• Due to excessively high pressures, the fuel starts burning instantly, creating large amounts of
thermal energy, which further raises the pressure.
• Because of this pressure the piston starts moving down.
• The fuel injection rate is such that the pressure inside the cylinder is maintained constant even
though the piston moves down.
• The expansion stroke ends when the piston reaches the bottom position. During this stroke the
inlet and exhaust valves remain closed.

19. 4) EXHAUST STROKE
• After the expansion stroke a number of residual gases are left in the cylinder and need to be
cleared from of the cylinder.
• During the exhaust stroke the exhaust valve opens due to the difference between the atmospheric
pressure and the pressure of exhaust gases inside the cylinder.
• As the piston moves from the bottom to the top position the exhaust gases are swept out of the
cylinder.
• When the piston reaches the topmost position all the exhaust gases are released.
• As the piston starts moving down, the inlet valves open and fresh air is drawn into the cylinder.