Engine Power Accounting If the indicated power (I.P.) and the frictional power (F.P.) of an engine are known, which quantity can be directly computed?

Introduction / Context:
Engine performance analysis separates the power produced inside the cylinder from what is actually delivered at the crankshaft. Understanding the simple relationship among indicated power, brake power, and frictional power is vital for test-cell calculations and coursework problems.

Given Data / Assumptions:

• I.P. = power developed by gas pressure on the piston.
• F.P. = mechanical losses due to friction, pumping, and auxiliaries.
• All values at the same operating point (speed and load).

Concept / Approach:
The power balance is linear: brake power is what remains after mechanical losses are subtracted from the gross indicated power. This is often written as B.P. = I.P. − F.P. The relationship underpins definitions of mechanical efficiency and is used when deriving other performance metrics.

Step-by-Step Solution:
Start with the power balance: B.P. + F.P. = I.P.Rearrange: B.P. = I.P. − F.P.Since I.P. and F.P. are known, compute B.P. directly by subtraction.

Verification / Alternative check:
Mechanical efficiency can be checked as eta_m = B.P. / I.P. If eta_m is within a plausible range (say 0.75–0.9 for many engines), the calculation is consistent.

Why Other Options Are Wrong:
Compression ratio: depends on geometry, not power figures.Specific air consumption and mean effective pressure: require mass-flow or pressure–volume data, not just I.P. and F.P.Volumetric efficiency: needs airflow and displacement information.

Common Pitfalls:
Mixing units or using kilowatts and horsepower inconsistently.

Final Answer:
brake power