ABE TUTORIALS

AREA 1 PROBLEM 37: MECHANICAL EFFICIENCY CALCULATION

THE INDICATED POWER OF AN ENGINE IS 69 HORSEPOWER. THE BRAKE HORSEPOWER IS 54. WHAT IS THE MECHANICAL OR ENGINE EFFICIENCY?

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a. 69%

b. 78%

c. 59%

d. none

Correct Answer: B

Detailed Solution:

Mechanical efficiency measures how much of the power generated inside the cylinder (Indicated Power) actually reaches the crankshaft (Brake Power) after overcoming internal friction.

Mechanical Efficiency (ηm) = (Brake Horsepower / Indicated Horsepower) × 100

Step 1: Identify the Given Values

• Indicated Horsepower (IHP) = 69 hp
• Brake Horsepower (BHP) = 54 hp

Step 2: Solve for Efficiency

ηm = (54 / 69) × 100
ηm = 0.7826 × 100
ηm = 78.26%

Result: b. 78% (Rounded)