GATE 2025 ME – Question 32
The thermal efficiency of an ideal air-standard Otto cycle is 0.5. The value of specific heat ratio of air is 1.4. The compression ratio of the cycle is ______________ (rounded off to 1 decimal place).
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Correct answer: 5.67 to 5.73
Explanation
The efficiency of the Otto cycle is $\eta = 1 - r^{1 - \gamma}$. So $0.5 = 1 - r^{-0.4}$, which gives $r^{0.4} = 2$ and $r = 2^{2.5} = 5.66$, which is 5.7 to one decimal place.