2-stroke cycle gasoline engine

TWO-STROKE

CYCLE

GASOLINE

ENGINE

Engine Construction, Design and Principle

of Operation

Laboratory Exercise No. 3

Diaz, Loieji

Lahom, Leslie Joy

Llena, Joemar

Vela, Ma. Lourdes Maureen

Andres,

Christian

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.

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

INTRODUCTION

INTRODUCTION

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.

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.

RESULTS & DISCUSSION

I. Basic parts of a typical two-stroke cycle gasoline

engine



engine

• Cylinder block ─

an integrated structure compri

sing the cylinder of

a reciprocating engine and

often some or all of their

associated surrounding

structures



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



engine

• Crankshaft ─ mechanical part able to perform a

conversion between reciprocating motion and rotational

motion



engine

• Connecting rod ─ connects the piston to

the crank or crankshaft



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.



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




engine

• Inlet port ─ supplies the fuel/air

mixture to the cylinder

─ primary function of the

intake manifold is

to evenly distribute the

combustion mixture



engine

• Transfer port ─ the simplest of the designs and the most

common in small two-stroke engines



engine

• Exhaust port ─

the opening, in the cylinder or valve, by which the exhau

st steam escapes.



engine

• Deflector ─ where the gas flow within the cylinder must

be carefully directed in order to provide

efficient scavenging


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.



As the piston moves up, it compresses the mixture above

and draws into the crankcase below a new air-fuel mixture.


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.



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.



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.



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.



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.


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.



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.



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.



Cycle Engines

5. It consumes more lubricating oil because of the greater

amount of heat generated.



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.

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.

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.

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.

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.

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.

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.

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.

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.

SUPPLEMENTAL

QUESTIONS



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.

SUPPLEMENTAL

QUESTIONS



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.

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.

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

2-stroke cycle gasoline engine

Engineering