Question Bank • QB_FP_146 NAT • 2 Marks

Section 3: Farm Power

Farm Power

Subtopic: Thermodynamic principles of I.C. engines

Question Statement:

An air-standard Otto cycle operates with a compression ratio $r = 8$. Taking the ratio of specific heats $\gamma = 1.40$, calculate the air-standard thermal efficiency as a percentage (round off to 2 decimal places).

Answer Key:

56.47

Step-by-Step Solution & Explanation

Air-standard efficiency of Otto cycle: $\eta = 1 - \frac{1}{r^{\gamma - 1}} = 1 - \frac{1}{8^{1.4 - 1}} = 1 - \frac{1}{8^{0.4}}$ $8^{0.4} = 2.2974$ $\eta = 1 - \frac{1}{2.2974} = 1 - 0.43528 = 0.56472 \implies 56.47\%$ Acceptable range: $56.3 - 56.7\%$.
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