Effect of engine speed on indicated power For a given reciprocating engine operating near its efficient range, how does indicated power generally change as the rotational speed increases (other conditions reasonably similar)?

Introduction / Context:
Indicated power reflects the rate of doing work inside the cylinder. Speed determines how many cycles occur per unit time, which directly affects indicated power when mean effective pressure is maintained. This is a foundational relation used in engine performance mapping.

Given Data / Assumptions:

• Engine is operated within a range where volumetric efficiency and combustion remain acceptable.
• Mean effective pressure does not collapse drastically as speed increases.
• No knock or severe pumping losses limiting output.

Concept / Approach:
For reciprocating engines, indicated power is proportional to indicated mean effective pressure multiplied by displacement per cycle and cycles per second. If pmi remains approximately steady, increasing speed increases the number of power events per minute, so indicated power rises. At very high speed, pmi may fall due to breathing limits, but the general relationship over a moderate range is increasing indicated power with speed.

Step-by-Step Solution:
Use proportionality: IP ∝ pmi * displacement per cycle * cycles per minute.As speed N increases, cycles per minute increase in direct proportion.Therefore, provided pmi does not drop excessively, IP increases with N.

Verification / Alternative check:
Manufacturer performance curves commonly show rising indicated and brake power with speed up to a rated point, after which power plateaus or declines as pmi falls.

Why Other Options Are Wrong:
Power remaining constant or decreasing would only apply where pmi falls enough to offset the increase in cycles; that is not the general case in the efficient operating band.

Common Pitfalls:
Extrapolating beyond the efficient range and assuming the same trend continues without accounting for breathing and combustion limits.

Final Answer:
Increase