Power comparison (idealized): For engines of equal size and speed, how does the theoretical power of a four-stroke cycle engine compare with that of a two-stroke cycle engine?

Introduction / Context:
Cycle frequency directly influences indicated power in reciprocating engines. Two-stroke engines produce a power stroke every revolution, while four-stroke engines produce one every other revolution. The idealized comparison highlights why two-stroke engines can deliver more power density, all else being equal.

Given Data / Assumptions:

• Same displacement, same mean effective pressure, same rotational speed.
• No pumping/scavenging losses or timing penalties considered (idealized).
• Equal mechanical efficiency assumed for comparison.

Concept / Approach:
Indicated power ∝ number of power strokes per unit time. At the same rpm, a two-stroke fires once per revolution; a four-stroke fires once per two revolutions. Therefore, in the simplest theoretical sense, the four-stroke develops half the power of the two-stroke under identical mean effective pressure and displacement assumptions.

Step-by-Step Solution:

Verification / Alternative check:
Real-world factors (scavenging losses in two-strokes, valve timing in four-strokes) modify outcomes, but the baseline theoretical result is standard in textbooks and explains design trade-offs for power density versus emissions/efficiency.

Why Other Options Are Wrong:

• Same/Double/Four times: Contradict the direct proportionality to firing frequency given equal BMEP and displacement.

Common Pitfalls:
Ignoring that many high-output two-strokes suffer from scavenging and emissions issues, so real power advantage may be less than the ideal prediction; however, the theoretical comparison is correct.

Final Answer:
half