“A 4-stroke engine is a type of internal combustion engine that completes a power cycle with four strokes of the piston during only two crankshaft revolution.” Two Stroke engine are classified as- 4-stroke petrol engine 4-stroke diesel engine

1. Fundamentals of Mechanical
Engineering (BME-101/201)
UNIT-2
4-STROKE ENGINE
PREPARED BY
ER. PEEYUSH CHAUHAN
ASSISTANT PROFESSOR
DEPARTMENT OF MECHANICAL ENGINEERING

2. “A 4-stroke engine is a type of internal combustion engine that
completes a power cycle with four strokes of the piston during only two
crankshaft revolution.”
Two Stroke engine are classified as-
1. 4-stroke petrol engine
2. 4-stroke diesel engine
INTRODUCTION

3. • There are following strokes in 4-stroke engine
1. Suction Stroke
2. Compression Stroke
3. Working/Power/ Expansion Stroke
4. Exhaust Stroke
• In 4-stroke engines valves are use instead of ports.

7. 1. Piston- The piston transfers the expanding force of gases to the
mechanical rotation of the crankshaft through a connecting rod.
2. Connecting Rod- It transfers motion from a piston to the crankshaft
and acts as a lever arm.
3. Crankshaft- It converts the reciprocating motion to rotational
motion.
4. Flywheel – It is a mechanical device that is used to store energy.
Construction of A Two-Stroke Engine

8. 5. Spark Plug – It delivers electric current to the combustion chamber
and in turn ignites the air-fuel mixture leading to abrupt expansion of
gases.
6. Counter Weight – Counterweight on the crankshaft is used to
reduce the vibrations due to imbalances in the rotating assembly.
7. Inlet and Outlet valves – These Valves allow fresh air with fuel to
enter and exit from the cylinder.
8. Fuel Injector: It’s used for injecting the fuel.

9. 4-Stroke
Petrol Engine

10. 1. Intake Stroke (Suction Stroke)
• Piston move from top dead center (TDC) to bottom dead center
(BDC).
• Intake valve is open and the exhaust valve is shut.
• Downward motion of the piston creates a vacuum (i.e., negative air
pressure), which draws the air-fuel mixture into the engine through
the open intake valve.
• Crankshaft rotate 00
to 1800
.
Working of A 4-Stroke Petrol Engine

12. 2. Compression Stroke-
• Piston moves up the cylinder bore from BDC to TDC.
• Both Intake and exhaust valves are closed.
• Upward motion of the piston compresses the air-fuel mixture in the
combustion chamber.
• Crankshaft rotate 1800
to 3600
.
3. Power/Expansion/working Stroke-
• Spark plug fires and ignites the compressed air-fuel mixture just
before the end of the compression (i.e., previous) stroke.
• This ignition/combustion forces the piston down the cylinder bore
and rotates the crankshaft, propelling the vehicle forward.

13. • Piston moves down the cylinder bore from TDC to BDC.
• Intake and exhaust valves are both closed.
• Crankshaft rotate 3600
to 5400
.
4. Exhaust Stroke-
• Piston moves up the cylinder bore from BDC to TDC. The
momentum created by the power stroke keeps the crankshaft moving
and the other three strokes going in sequence.
• Intake valve is closed and the exhaust valve is open.
• Final stroke pushes the spent gases and exhausts out of the cylinder.
The cycle is now complete and the piston is ready to begin the intake
stroke.

14. 4-Stroke
Diesel Engine

15. 1. Intake Stroke (Suction Stroke)
• Piston move from top dead center (TDC) to bottom dead center
(BDC).
• Intake valve is open and the exhaust valve is shut (Close).
• Downward motion of the piston creates a vacuum (i.e., negative air
pressure), which draws the air into the engine through the open intake
valve.
• Crankshaft rotate 00
to 1800
.
Working of A 4-Stroke Diesel Engine

18. 2. Compression Stroke-
• Piston moves up the cylinder bore from BDC to TDC.
• Both Intake and exhaust valves are closed.
• Upward motion of the piston compresses the air in the combustion
chamber.
• Crankshaft rotate 1800
to 3600
.
3. Power/Expansion/working Stroke-
• Fuel is injected by fuel injector and burn the compressed air just
before the end of the compression (i.e., previous) stroke.
• This combustion forces the piston down the cylinder bore and rotates
the crankshaft, propelling the vehicle forward.

19. • Piston moves down the cylinder bore from TDC to BDC.
• Intake and exhaust valves are both closed.
• Crankshaft rotate 3600
to 5400
.
4. Exhaust Stroke-
• Piston moves up the cylinder bore from BDC to TDC. The
momentum created by the power stroke keeps the crankshaft moving
and the other three strokes going in sequence.
• Intake valve is closed and the exhaust valve is open.
• Final stroke pushes the spent gases and exhausts out of the cylinder.
The cycle is now complete and the piston is ready to begin the intake
stroke.

20. 1. 4-stroke engines always make extra torque than 2-stroke engine at
low RPM.
2. 4-stroke engines have greater fuel efficiency than 2-stroke ones
because fuel is consumed once every 4-strokes.
3. 4-stroke engine produces less pollution.
4. Only the moving parts need lubrication intermediately. No extra oil
or lubricant is added to fuel.
5. More durable.
6. Produce less vibration & noise.
7. Less wear & tear due to good lubricating system.
Advantages of 4-Stroke Engine

21. 1. A 4-stroke engine has complex valve mechanisms operated &
controlled by gears & chain.
2. As power gets delivered once every 2 rotations of crankshaft (4
strokes), hence 4-stroke is less powerful.
3. A four stroke engine has much more parts than 2-stroke engine. So
they often require repairs which leads to greater expense.
Disadvantages of 4-Stroke Engine

22. 4-stroke engines are still found in a variety of applications, such as-
• Automobile industries.
• Bus, trucks and other transportation vehicles.
• Pumping system.
• Mobile electric generators.
• Aircraft and marine engines.
• Diesel engines find application in pump sets, construction machinery,
air compressor, drilling rigs, etc.
Applications of 4-Stroke Engine