two stroke engine

1. ABASYN UNIVERSITY ISLAMABAD CAMPUS
Department Of Electrical Engineering
Two stroke cycle with Timing Diagrams
BY
Abid Kamal
Waheed Alam Khan
Hijab Khan
Submitted To: Ma’am Rashida Khalid

2. Two stroke engine
• A two-stroke engine is a type of internal combustion
engine that completes a power cycle with two strokes
(up and down movements) of the piston during only
one crankshaft revolution.
• This is in contrast to a four-stroke engine, which
requires four strokes of the piston to complete a
power cycle during two crankshaft revolutions.
• Two-stroke engines are generally smaller and lighter
than four-stroke engines, and they have a higher
power-to-weight ratio.

3. History of 2 stroke engine
• The first practical two-stroke engine was developed
by the German engineer Karl Benz in 1879.
• One of the main advantages of the two-stroke engine
was its simplicity and compact size, which made it
suitable for use in a variety of applications, including
motorcycles, scooters, outboard motors, and portable
generators.
• During World War II, the two-stroke engine became
very popular due to its simplicity and light weight,
which made it suitable for use in military vehicles and
aircraft.

4. 2- stroke cycle explanation
• In a two-stroke cycle engine, the four strokes of a
typical four-stroke cycle engine (intake,
compression, power, and exhaust) occur in only
two strokes of the piston, resulting in a more
compact and lightweight engine.

5. Diagram

6. 2-stroke diagram steps
• Here is a timing diagram for a two-stroke cycle engine:
• Intake stroke: The intake valve opens and the piston moves
downward, drawing a fresh charge of fuel and air into the
combustion chamber.
• Compression stroke: The intake valve closes and the piston moves
upward, compressing the fuel and air mixture in the combustion
chamber.
• Power stroke: The spark plug fires, igniting the fuel and air
mixture and causing the piston to move downward, producing
power.
• Exhaust stroke: The exhaust valve opens and the piston moves
upward, pushing the exhaust gases out of the engine.
• Repeat: The cycle then repeats, with the intake valve opening and
the process starting over again.

7. 2-Stroke Petrol & Diesel Engine
Their are mainly two stroke in 2-stroke
engine:
1. Expansion Stroke
2. Compression Stroke

8. Expansion stroke
• In a two-stroke cycle engine, the expansion stroke is also
known as the power stroke, because it is during this stroke
that the fuel and air mixture in the combustion chamber is
ignited, causing the piston to move downward and produce
power.
• The expansion stroke begins when the spark plug fires,
igniting the fuel and air mixture in the combustion chamber.
As the mixture burns, it expands, pushing the piston
downward and producing power. The expansion stroke ends
when the exhaust valve opens, allowing the burned gases to
be expelled from the engine.

9. Compression Stroke
• During the compression stroke, the intake valve closes and
the piston moves upward, compressing the fuel and air
mixture in the combustion chamber.
• The purpose of the compression stroke is to increase the
pressure and temperature of the fuel and air mixture, which
allows it to burn more efficiently when ignited. A higher
compression ratio (the ratio of the volume of the
combustion chamber when the piston is at the bottom of its
stroke to the volume when the piston is at the top of its
stroke) results in a higher temperature and pressure in the
combustion chamber, which can lead to increased power
output.

10. At the beginning of the first stroke piston is at the TDC as shown in fig. A. Piston moves
from TDC to BDC.
The electric spark ignites the compressed charge in petrol engine & Diesel spray in diesel
engine when compression stroke is about complete . The combustion of the charge will
release the hot gases which increase the temperature and pressure in cylinder. The high
pressure combustion engine to force piston downward .
The piston perform power stroke till it uncovers the exhaust port As shown in fig. B. The
combustion gases which are at the pressure slightly higher than atmosphere pressure
escape through exhaust port.
The piston uncovers the transfer port the fresh charge flow from the crankcase into
cylinder through transfer port as shown in fig. B.
Which enters the cylinder pushes the burnt gases , so more amount of exhaust gases
come out through exhaust port as shown in fig. B.
This swiping out of exhaust gases by incoming fresh charge is called scavenging.
This will continue till the piston covers both the transfer and exhaust port during next
upward stroke.
First stroke

11. Second Stroke
In this stroke piston moves from BDC to TDC.
When it covers the transfer port in fig. C. , the supply of charge is
stopped and then when it moves further up it covers the exhaust port
completely in fig. D stop the scavenging.
Further upward motion of the piston will compressed the charge in the
cylinder.
After the piston reaches TDC the first stroke repeats again.

12. Second
Stroke
Fig.
C.
Transfer port
covered
Fig.
D.
Compression
commenced

13. Theoretical & Actual Valve Timing Diagram For 2-
Stroke Petrol Engine

14. Actual Valve Timing For 2-Stroke Petrol
Engine
• →70°After B.D.C.
• →60°Before B.D.C.
• →60°After B.D.C.
• →50°Before T.D.C.
• →50°After T.D.C.
.

15. Theoretical & Actual Valve Timing Diagram for 2-
Stroke Diesel Engine

16. Actual Valve Timing For 2-Stroke Diesel
Engine
E.P
.O. →80° Before B.D.C.
E.P
.C. →80°After B.D.C.
T
.P
.O. →60° Before B.D.C.
T
.P
.C. →60°After B.D.C.