For the same rated power and same engine speed of a two stroke engine and a four stroke engine. Which of the following statement is correct

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NPCIL Stipendiary Trainee ME 2018

Answer 1

Concept:

Four-stroke engines: In this type of engine, one power stroke is obtained in two revolutions of the crankshaft.

Two-stroke engines: In this engine, one power stroke is obtained in each revolution of the crankshaft.

Four Stroke Engine	Two-stroke Engine
Four operations (suction, compression, power, and exhaust) take place in the four strokes of the piston	The four operations take place in two strokes of the piston
In gives one power stroke in the four strokes, i.e. in two revolutions of the crankshaft. As such three strokes are idle strokes	The power stroke takes place in every two strokes i.e. one power stroke for one revolution of the crankshaft
Due to more idle strokes and non-uniform load on the crankshaft, a heavier flywheel is required	The engine has a more uniform load as every time the piston comes down it is the power stroke. As such a lighter flywheel is used
The engine has more parts such as valves and its operating mechanism. Therefore, the engine is heavier	The engine has no valves and valve operating mechanism; Therefore, it is lighter in weight.
The engine is costlier as it has more parts	The engine is less expensive as it has a lesser number of parts
The engine efficiency is more as the charge gets completely burnt out. Consequently, fuel efficiency is more	The efficiency is less. A portion of the charge escapes through the exhaust port, and because of this, the fuel efficiency is less.