This document discusses the four strokes of a four-stroke internal combustion engine: intake, compression, power, and exhaust. It explains that each stroke involves a 180-degree rotation of the crankshaft. The intake stroke draws in air and fuel, compression stroke compresses the mixture, power stroke ignites the mixture to push the piston, and exhaust stroke pushes out the burned gases. It also briefly describes the valve timing, carburetor, ignition system, lubrication via oil splash, and air or liquid cooling systems in a four-stroke engine.

1. DEPARTMENT OF MECHANICAL ENGINEERINGDEPARTMENT OF MECHANICAL ENGINEERING
MUTHAYAMMAL ENGINEERINGMUTHAYAMMAL ENGINEERING
COLLEGE,RASIPURAM.COLLEGE,RASIPURAM.
Presented byPresented by
A.KALAIYARASANA.KALAIYARASAN
Assistant Professor ,MEC –RasipuramAssistant Professor ,MEC –Rasipuram

2. Four Stroke Gas EnginesFour Stroke Gas Engines
The four strokes of a internal combustion engine are:
•Intake
•Compression
•Power
•Exhaust
Each cycle requires two revolutions
of the crankshaft (720˚ rotation), and
one revolution of the camshaft to complete
(360˚ rotation).
Each stroke = 180˚ of
crankshaft revolution.

3. Intake StrokeIntake Stroke
First Stroke
The piston moves down the cylinder
from TDC (Top Dead Center) to BDC
(Bottom Dead Center).
This movement of piston causes low
air pressure in the cylinder (vacuum)
Mixture of Air and Fuel in the ratio
of 14.7 : 1 (air : fuel) is drawn into
the cylinder.
Intake valve stays open and the
Exhaust valve stays closed during
this stroke.

4. Compression strokeCompression stroke
Second stroke
The piston moves from BDC to TDC
Intake and exhaust valves stay closed
Air and fuel mixture is compressed
8:1 to 12:1
The pressure in the cylinder is raised

5. Power strokePower stroke
Third stroke
At the end of compression stroke
the sparkplug fires, igniting the air/fuel
mixture.
Both the valves stay closed in
this stroke.
The expanding gases from the
combustion in the cylinder
(with no escape) push the piston
down.
The piston travels from TDC to BDC.

6. Exhaust strokeExhaust stroke
Fourth and last stroke
The momentum created by the
Counter-weights on the crankshaft,
move the piston from BDC to TDC.
The exhaust valve opens and
the burned gases escape into the
exhaust system.
Intake valve remains closed.

7. Four strokesFour strokes
All four strokes

8. Four Cylinder EngineFour Cylinder Engine

9. Valve TimingValve Timing
The ratio of cam to crank sprocket is 2:1
For every two revolutions of
Crankshaft, the Camshaft turns once.
Belt driven
Chain driven
Gear driven

10. CarburetorCarburetor
The job of the carburetor is to
accurately meter extremely tiny
quantities of fuel and mix it with
the air entering the engine, so that
the engine runs properly.
It works on the principle of
High and low pressure
High and low pressure is created
with the help of Venture

11. Ignition systemIgnition system
Provides high voltage surges – as high as 47,000 volts to the spark plug
Parts
• permanent magnet.
• armature assembly.
• breaker points.
• condenser.
• spark plug.

12. LubricationLubrication
In the engine, dippers on the connecting-rod bearing caps enter
the oil pan with each crankshaft revolution to produce the oil splash.
A passage is drilled in each connecting rod from the dipper to the
bearing to ensure lubrication.(used only on 4-stroke small engines)

13. CoolingCooling
Air cooled
Fins are used to dissipate heat
Liquid cooled
Coolant is used to dissipate heat.