Comparison of Two-Stroke and Four-Stroke Engines - week 5

S/N

Two stroke cycle engine

Four stroke cycle engine

Advantages

Disadvantages

1

A cycle is completed in 2 strokes or one revolution of the crankshaft.

A cycle is completed in 4 strokes or two revolution of the crank shaft.

2

It develops twice the number of power strokes than the four stroke engines.

It develops half the number of power stroke than two stroke engine.

3

For the same power developed, the two stroke engine is much lighter, less bulky and it occupies less floor area.

For the same power developed, the four stroke engine is bulky, heavier and it occupies more floor area.

4

Turning moment is more uniform and hence, lighter flywheel is required.

Turning moment is not uniform and hence, heavier flywheel is required.

5

It contains ports which are operated by the piston itself therefore, no separate mechanisms are required

It contains valves which are operated by separate mechanisms.

6

Initial cost is low due to less complexity in mechanism.

Initial cost is high because of heavier and complicated mechanisms.

7

Mechanical efficiency is more.

Mechanical efficiency is low.

8

It is easy to start.

It requires separate starting motor.

9

It can be run in either direction which is useful in marine engines.

It can be run in only one direction.

S/N

Two stroke cycle engine

Four stroke cycle engine

Disadvantages

Advantages

1

Thermal efficiency is low.

Thermal efficiency is high.

2

Volumetric efficiency is low.

Volumetric efficiency is more.

3

Greater cooling and lubrication are required.

Lesser cooling and lubrication are required

4

Overall efficiency is less.

Overall efficiency is more

5

Greater rate of wear and tear.

Lesser rate of wear and tear.

6

It is used in light vehicles only(e.g.) scooters, motor cycles etc.

Used in heavy vehicles such as cars, buses, trucks etc.

7

Sudden release of exhaust gases makes the exhaust noisier.

Release of exhaust gas is more uniform and hence noiseless operation.

8

Specific fuel consumption is more because of escaping of the fresh charge with exhaust gases.

Specific fuel consumption is less because of separate exhaust stroke.

9

Less compression ratio.

More compression ratio.