1. The document discusses the two-stroke cycle gasoline engine, describing its basic parts and principle of operation. It has several key advantages over the four-stroke engine, including higher power density and simpler design. 2. The basic parts are the piston, cylinder block, crankshaft, connecting rod, flywheel, spark plug, inlet port, exhaust port, and transfer port. Each downward piston stroke is a power stroke, and each upward stroke is a compression stroke. 3. It intakes and exhausts on the same stroke, achieving two cycles per revolution compared to one cycle per two revolutions for a four-stroke. However, its scavenging is less efficient, resulting in lower thermal

1. TWO-STROKE
CYCLE
GASOLINE
ENGINE
Engine Construction,
Design and Principle
of Operation
Laboratory Exercise No. 3

2. Diaz, Loieji
Lahom, Leslie Joy
Llena, Joemar
Vela, Ma. Lourdes Maureen
Andres,
Christian

3. INTRODUCTION
Two-stroke cycle engine
The gasoline two stroke engine, and the cylinder
ports on which it depends, were invented by Joseph Day
in 1889. These cylinder ports were subsequently
incorporated into diesel two-stroke engines, replacing
either just the inlet valves or both inlet and exhaust
valves.

4. INTRODUCTION
Two-stroke cycle engine
― performs the same cycle of events as the four-
cycle engine
― intake, compression, power, and exhaust functions
take place during only two strokes of the piston ― up
& down
― takes only one revolution of the shaft to complete
a two-stroke cycle

5. INTRODUCTION

6. INTRODUCTION

7. OBJECTIVES
1. To discuss the principle of operation of a two-stroke
cycle gasoline engine.
2. To enumerate the principal engine parts and functions
of a two-stroke cycle engine.

8. PROCEDURE
1. Enumeration of the basic parts of a typical two cycle
gasoline engine.
2. Discussion of the function of each part.
3. With the aid of illustration, step by step principle of
operation of a two cycle gasoline engine is discussed.
4. the advantages and disadvantages of a two-cycle
gasoline engine are enumerated.

9. RESULTS & DISCUSSION
I. Basic parts of a typical two-stroke cycle gasoline
engine

10. RESULTS & DISCUSSION
I. Basic parts of a typical two-stroke cycle gasoline
engine
• Cylinder block ─
an integrated structure compri
sing the cylinder of
a reciprocating engine and
often some or all of their
associated surrounding
structures

11. RESULTS & DISCUSSION
I. Basic parts of a typical two-stroke cycle gasoline
engine
• Piston ─ component of
reciprocating engines. It is the
moving component that is
contained by a cylinder and is
made gas-tight by piston rings

12. RESULTS & DISCUSSION
I. Basic parts of a typical two-stroke cycle gasoline
engine
• Crankshaft ─ mechanical part able to perform a
conversion between reciprocating motion and rotational
motion

13. RESULTS & DISCUSSION
I. Basic parts of a typical two-stroke cycle gasoline
engine
• Connecting rod ─ connects the piston to
the crank or crankshaft

14. RESULTS & DISCUSSION
I. Basic parts of a typical two-stroke cycle gasoline
engine
Flywheel ─ This is usually made of cast iron and its primary
function is to maintain uniform engine speed by carrying
the crankshaft through the
intervals when it is not
receiving power from a
piston.

15. RESULTS & DISCUSSION
I. Basic parts of a typical two-stroke cycle gasoline
engine
• Sparkplug ─ device for delivering electric
current from an ignition system to
the combustion chamber of a spark-ignition
engine to ignite the compressed fuel/air
mixture by an electric spark

16. RESULTS & DISCUSSION

17. RESULTS & DISCUSSION
I. Basic parts of a typical two-stroke cycle gasoline
engine
• Inlet port ─ supplies the fuel/air
mixture to the cylinder
─ primary function of the
intake manifold is
to evenly distribute the
combustion mixture

18. RESULTS & DISCUSSION
I. Basic parts of a typical two-stroke cycle gasoline
engine
• Transfer port ─ the simplest of the designs and the most
common in small two-stroke engines

19. RESULTS & DISCUSSION
I. Basic parts of a typical two-stroke cycle gasoline
engine
• Exhaust port ─
the opening, in the cylinder or valve, by which the exhau
st steam escapes.

20. RESULTS & DISCUSSION
I. Basic parts of a typical two-stroke cycle gasoline
engine
• Deflector ─ where the gas flow within the cylinder must
be carefully directed in order to provide
efficient scavenging

21. RESULTS & DISCUSSION
II. Principle of a two cycle gasoline engine

22. RESULTS & DISCUSSION
II. Principle of a two cycle gasoline engine
As the piston travels down, the mixture previously drawn
into the crankcase is partially compressed. As the piston nears
the bottom of the stroke, it uncovers the exhaust and intake ports.
The exhaust flows out, reducing the pressure in the cylinder.
When the pressure in the combustion chamber is lower than the
pressure in the crankcase through the port openings to the
combustion chamber, the incoming mixture is deflected upward
by a baffle on the piston.

23. RESULTS & DISCUSSION
II. Principle of a two cycle gasoline engine
As the piston moves up, it compresses the mixture above
and draws into the crankcase below a new air-fuel mixture.

24. RESULTS & DISCUSSION
II. Advantages of two-stroke Cycle Over Four-stroke
Cycle Engines
1) The two-stroke cycle engine gives one working stroke for
each revolution of the crankshaft. Hence theoretically the power
developed for the same engine speed and cylinder volume is
twice that of the four-stroke cycle engine, which gives only one
working stroke for every two revolutions of the crankshaft.
However, in practice, because of poor scavenging, only 50-60%
extra power is developed.

25. RESULTS & DISCUSSION
II. Advantages of two-stroke Cycle Over Four-stroke
Cycle Engines
2) Due to one working stroke for each revolution of the
crankshaft, the turning moment on the crankshaft is more
uniform. Therefore, a two-stroke engine requires a lighter
flywheel.
3) The two-stroke engine is simpler in construction. The design
of its ports is much simpler and their maintenance easier than
that of the valve mechanism.

26. RESULTS & DISCUSSION
II. Advantages of two-stroke Cycle Over Four-stroke
Cycle Engines
4) The power required to overcome frictional resistance of the
suction and exhaust strokes is saved, resulting in some economy
of fuel.
5) Owing to the absence of the cam, camshaft, rockers, etc. of
the valve mechanism, the mechanical efficiency is higher.
6) The two-stroke engine gives fewer oscillations.

27. RESULTS & DISCUSSION
II. Advantages of two-stroke Cycle Over Four-stroke
Cycle Engines
7) For the same power, a two-stroke engine is more compact and
requires less space than a four-stroke cycle engine. This makes it
more suitable for use in small machines and motorcycles.
8) A two-stroke engine is lighter in weight for the same power
and speed especially when the crankcase compression is used.

28. RESULTS & DISCUSSION
II. Advantages of two-stroke Cycle Over Four-stroke
Cycle Engines
9) Due to its simpler design, it requires fewer spare parts. 10) A
two-stroke cycle engine can be easily reversed if it is of the valve
less type.

29. RESULTS & DISCUSSION
II. Disadvantages of two-stroke Cycle Over Four-stroke
Cycle Engines
1. The scavenging being not very efficient in a two-stroke
engine, the dilution of the charges takes place which results in
poor thermal efficiency.

30. RESULTS & DISCUSSION
II. Disadvantages of two-stroke Cycle Over Four-stroke
Cycle Engines
2. The two-stroke spark ignition engines do not have a separate
lubrication system and normally, lubricating oil is mixed with the
fuel. This is not as effective as the lubrication of a four-stroke
engine. Therefore, the parts of the two-stroke engine are
subjected to greater wear and tear.

31. RESULTS & DISCUSSION
II. Disadvantages of two-stroke Cycle Over Four-stroke
Cycle Engines
3. In a spark ignition two-stroke engine, some of the fuel passes
directly to the exhaust. Hence, the fuel consumption per
horsepower is comparatively higher.
4. With heavy loads a two-stroke engine gets heated up due to
the excessive heat produced. At the same time the running of the
engine is riot very smooth at light loads.

32. RESULTS & DISCUSSION
II. Disadvantages of two-stroke Cycle Over Four-stroke
Cycle Engines
5. It consumes more lubricating oil because of the greater
amount of heat generated.

33. RESULTS & DISCUSSION
II. Disadvantages of two-stroke Cycle Over Four-stroke
Cycle Engines
6. Since the ports remain open during the upward stroke, the actual
compression starts only after both the inlet and exhaust ports have
been closed. Hence, the compression ratio of this engine is lower
than that of a four-stroke engine of the same dimensions. As the
efficiency of an engine is directly proportional to its compression
ratio, the efficiency of a two-stroke cycle engine is lower than that
of a four-stroke cycle engine of the same size.

34. CONCLUSION
‰ The basic parts of a two stroke cycle
gasoline engine are: piston, cylinder block, crankshaft, piston rod,
flywheel, sparkplug,
inlet port, exhaust port, transfer port and
deflector .
Each downward stroke of the piston is a
power stroke and each upward stroke of the
piston is a compression stroke.

35. CONCLUSION
‰ The intake and exhaust cycle may be considered a part of
the power and compression stroke and begins after completion of
the power stroke as the exhaust valves open. The intake
and exhaust cycle ends after the piston closes off
the intake ports of the cylinder liner on the
compression stroke.

36. SUPPLEMENTAL
QUESTIONS
1. What is more powerful, two-stroke or four-stroke
cycle engine? Why?
Two-stroke cycle engine is more powerful than four-stroke
cycle engine. It is capable of producing quick and sudden bursts of
power that are not sustained for a long period of time. It produces
high power for a relatively short period while four-stroke cycle
engine produces low power for a long period of time.

37. SUPPLEMENTAL
QUESTIONS
1. What is more powerful, two-stroke or four-stroke
cycle engine? Why?
In 2 stroke engine, every alternate stroke is power stroke,
unlike in a 4 stroke engine in which power gets delivered only once
in every 4 strokes. This gives a significant power boost. Also, the
acceleration will be higher & power delivery will be uniform due to
same reason.

38. SUPPLEMENTAL
QUESTIONS
2. Explain why two-stroke cycle engines produces more
smoke compared to four-stroke cycle engine.
2-stroke cycle engines are not efficient in burning fuel. The
burning of lubricating oil that is being mixed and the exhaust of un-
burnt fuel makes them a lot more polluting than 4-stroke engines of
same power. The combustion of oil added in the mixture creates a
lot of smoke which leads to air pollution.

39. SUPPLEMENTAL
QUESTIONS
3. What are the distinguishing features of a two-stroke
cycle gasoline engine?
• Two-stroke engines do not have valves, which simplifies
their construction and lowers their weight.
• Two-stroke engines fire once every revolution, while four-
stroke engines fire once every other revolution. This gives two-
stroke engines a significant power boost.

40. SUPPLEMENTAL
QUESTIONS
3. What are the distinguishing features of a two-stroke
cycle gasoline engine?
• Two-stroke engines can work in any orientation, which can
be important in something like a chainsaw. A standard four-stroke
engine may have problems with oil flow unless it is upright, and
solving this problem can add complexity to the engine.

41. SUPPLEMENTAL
QUESTIONS
4. What is the reason why oil is being mixed to the fuel
of a two-stroke cycle engine?
Oil is being mixed to the fuel of a two-stroke cycle engine
because the crankcase is part of the intake process, it cannot act as
an oil sump as is found on four-cycle engines. In 2-stroke,
lubricating oil is mixed with fuel so it burns as fuel burns and
consumed more, while in 4-stroke, lubricating oil is contained in
the crankcase.

42. SUPPLEMENTAL
QUESTIONS
4. What is the reason why oil is being mixed to the fuel
of a two-stroke cycle engine?
Two-stroke engines employ a total-loss lubrication system
that combines oil and fuel to provide both energy and engine
lubrication. The oil and fuel are combined in the cylinder’s intake
tract and lubricate critical components such as the crankshaft,
connecting rods and cylinder walls.

43. SUPPLEMENTAL
QUESTIONS
4. What is the reason why oil is being mixed to the fuel
of a two-stroke cycle engine?
In general, two-stroke engines are known to wear more
quickly than four-stroke engines because they don’t have a
dedicated lubricant source; however, high-quality two-stroke oil
significantly reduces engine wear.

44. SUPPLEMENTAL
QUESTIONS
5. What specific job applications do two-cycle gasoline
engine find itself most suitable?
Two-strok engines are ideal in applications such as
chainsaws, weed trimmers, outbourd motors, off-road
motorcycles and racing applications.
Two-stroke engines are also easier to start in cold
temperatures, making them ideal for use in snowmobiles.

45. REFERENCES
Print-outs
• Internal Combustion Engine Fundamentals. John B. Heywood. McGraw-Hill, Inc. USA.
1988
• Basic of Engine Operations. The Goodheart Willcox Co.,Inc
• AENGR411lecture handout. Emmnuel Sicat.2016
Online
• http://www.slideshare.net/amanina_mal/agriculture-engineeringchptr15
• http://en.wikipedia.org/wiki/
Others
• Microsoft Student 2008 Encarta Encyclopedia