Question

In a two-stroke engine, the power stroke occurs compared to a four-stroke engine -

• A. Double
• B. Same
• C. Triple
• D. Four times Correct Answer: (A) Double

Hint:

Engine Comparison Rule: - Two-stroke engine: $1$ Power Stroke = $1$ Revolution of Crankshaft ($360^\circ$). - Four-stroke engine: $1$ Power Stroke = $2$ Revolutions of Crankshaft ($720^\circ$). Therefore, at any given RPM, a two-stroke engine fires twice (double) as frequently.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
In internal combustion engines, the term "power stroke" refers to the specific stage of the engine cycle where the ignited fuel-air mixture expands, forcing the piston downward and generating mechanical power. The frequency of this power stroke relative to crankshaft rotations distinguishes two-stroke engines from four-stroke engines.

Step 2: Detailed Explanation:
An internal combustion engine requires four distinct operations to complete one full thermodynamic cycle: Intake, Compression, Power, and Exhaust.

• In a four-stroke engine, these four operations require four separate piston movements (strokes), which correspond to two full rotations ($720^\circ$) of the crankshaft. Thus, it produces $1$ power stroke for every $2$ crankshaft revolutions.

• In a two-stroke engine, these four functions are compressed into just two piston movements (strokes) by combining intake/exhaust and compression/power stages. This happens during one full rotation ($360^\circ$) of the crankshaft. Thus, it produces $1$ power stroke for every $1$ crankshaft revolution.
When compared over an equal number of crankshaft revolutions, a two-stroke engine delivers a power stroke twice as often as a four-stroke engine, which means the power stroke occurs double the number of times.

Step 3: Final Answer
The power stroke in a two-stroke engine occurs double the number of times compared to a four-stroke engine for the same number of crankshaft revolutions.