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The thermal efficiency of a 2-stroke engine is __________ with respect to a 4-stroke engine.
1. more
2. less
3. same
4. None of these

1 Answer

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Best answer
Correct Answer - Option 2 : less

Explanation:

Following are the differences in 4-stroke and 2-stroke engines.

S.No.

Four-stroke engine

Two-stroke engine

1. 

It has one power stroke for every two revolutions of the crankshaft.

It has one power stroke for each revolution of the crankshaft.

2.

A heavy flywheel is required and the engine runs unbalanced because turning moment on the crankshaft is not even due to one power stroke for every two revolutions of the crankshaft.

The lighter flywheel is required and the engine runs balanced because the turning moment is more even due to one power stroke for each revolution of the crankshaft.

3.

Engine is heavy

Engine is light

4. 

Engine design is complicated due to the valve mechanism.

Engine design is simple due to the absence of the valve mechanism.

5. 

More cost.

Less cost than 4 stroke.


 

6.

Less mechanical efficiency due to more friction in many parts.

More mechanical efficiency due to less friction on a few parts.

7.

More output due to full fresh charge intake and full burnt gases exhaust.

Less output due to the mixing of fresh charge with the hot burnt gases.

8.

Engine runs cooler.

Engine runs hotter.

9.

These engines are water-cooled.

These engines are air-cooled.

10. 

Less fuel consumption and complete burning of fuel. Hence more thermal efficiency.

More fuel consumption and the fresh charge is mixed with exhaust gases. Hence less thermal efficiency.

11.

The engine requires more space.

The engine requires less space.

12. 

Complicated lubricating system.

Simple lubricating system.

13. 

Less noise is created by the engine.

More noise is created by the engine.

14. 

The engine consists of an inlet and exhaust valve.

The engine consists of inlet and exhaust ports.

15.

It consumes less lubricating oil.

It consumes more lubricating oil.

16.

Less wear and tear of moving parts.

More wear and tear of moving parts.

17.

Used in cars, buses, trucks etc.

Used in mopeds, scooters, motorcycles etc.

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