Indicated power vs. brake power Choose the correct statement regarding the relationship between indicated power (IP) and brake power (BP) of an internal combustion engine.

Introduction / Context:Engine performance uses three related measures: indicated power (IP), brake power (BP), and friction power (FP). IP is the power developed in the cylinder based on pressure–volume work, BP is the useful shaft output, and FP accounts for mechanical and pumping losses. Understanding their relationship is essential for interpreting dynamometer tests and efficiency calculations.

Given Data / Assumptions:

• Well-defined IP from indicator diagrams or calculations.
• BP measured at the crankshaft via dynamometer.
• Mechanical efficiency eta_m = BP / IP is less than 1 due to losses.

Concept / Approach:

The fundamental relationship is IP = BP + FP. Friction power includes bearing friction, piston and ring friction, valve train losses, pumping work, and accessory loads. Therefore BP, being IP minus these losses, must be lower than IP. No practical condition yields BP > IP; at best, reductions in friction raise BP closer to IP, but never beyond it.

Step-by-Step Solution:

Verification / Alternative check:

Mechanical efficiency values (typically 0.75–0.90 for many engines) confirm BP/IP < 1. Morse tests and motoring tests independently demonstrate positive friction power, reinforcing IP > BP.

Why Other Options Are Wrong:

Equality (option c or d) would require zero losses, which is unrealistic. Option e adds an engine-type condition that does not alter the fundamental inequality.

Common Pitfalls:

Confusing brake mean effective pressure (BMEP) with indicated mean effective pressure (IMEP); BMEP is always lower than IMEP for the same engine and conditions because of mechanical and pumping losses.

Final Answer:

Disagree — indicated power is greater than brake power due to mechanical losses