Four-stroke cycle engines — working strokes per minute For a four-stroke reciprocating engine running at N revolutions per minute, the number of power (working) strokes per minute for one cylinder is:

Introduction / Context:
Engine performance calculations often require converting rotational speed to the number of working cycles. In a four-stroke engine, one thermodynamic cycle requires two full crankshaft revolutions, which directly determines the frequency of power strokes per cylinder.

Given Data / Assumptions:

• Four distinct strokes: intake, compression, power, and exhaust.
• Uniform speed N revolutions per minute.
• Single cylinder analysis for clarity.

Concept / Approach:
Each four-stroke cycle spans 720 crank angle degrees, or two complete revolutions. Therefore, each cylinder produces one power stroke every two revolutions. The number of power strokes per minute per cylinder is half the rotational speed.

Step-by-Step Solution:
Recognize cycle length: 2 revolutions per power event.Relate to speed: power strokes per minute = N / 2 per cylinder.For multi-cylinder engines, total power strokes per minute scale with the number of cylinders.

Verification / Alternative check:
Timing diagrams in engine textbooks show that only one of the four strokes is the power stroke, confirming the factor of one-half relative to crankshaft speed.

Why Other Options Are Wrong:
Equal to N, 2N, or 4N would imply a power stroke every revolution or more frequently, which contradicts the four-stroke mechanism.

Common Pitfalls:
Mixing up two-stroke and four-stroke conventions. A two-stroke engine produces one power stroke per revolution, whereas a four-stroke requires two revolutions.

Final Answer:
N / 2