DEPARTMENT OF MECHANICAL ENGINEERINGDEPARTMENT OF MECHANICAL ENGINEERING
MUTHAYAMMAL ENGINEERINGMUTHAYAMMAL ENGINEERING
Presented byPresented by
Assistant Professor ,MEC –RasipuramAssistant Professor ,MEC –Rasipuram
Four Stroke Gas EnginesFour Stroke Gas Engines
The four strokes of a internal combustion engine are:
Each cycle requires two revolutions
of the crankshaft (720˚ rotation), and
one revolution of the camshaft to complete
Each stroke = 180˚ of
Intake StrokeIntake 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
Intake valve stays open and the
Exhaust valve stays closed during
Compression strokeCompression 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
Power strokePower stroke
At the end of compression stroke
the sparkplug fires, igniting the air/fuel
Both the valves stay closed in
The expanding gases from the
combustion in the cylinder
(with no escape) push the piston
The piston travels from TDC to BDC.
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
Intake valve remains closed.
Valve TimingValve Timing
The ratio of cam to crank sprocket is 2:1
For every two revolutions of
Crankshaft, the Camshaft turns once.
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
Ignition systemIgnition system
Provides high voltage surges – as high as 47,000 volts to the spark plug
• permanent magnet.
• armature assembly.
• breaker points.
• spark plug.
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)
Fins are used to dissipate heat
Coolant is used to dissipate heat.