GATE 2018 ME (ME2) – Question 65
A spark-ignition vehicle engine follows an air-standard Otto cycle with γ = 1.4. It produces 70 kW while consuming 10.3 kg fuel/hour of calorific value 44000 kJ/kg. Find compression ratio, to two decimal places.
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Correct answer: 7.40 to 7.80
Explanation
Fuel heat-input rate is $10.3(44000)/3600=125.8889$ kW, so $\eta=70/125.8889=0.556046$. For an Otto cycle, $\eta=1-r^{1-\gamma}$. Thus $r=(1-\eta)^{-1/0.4}=7.614735$: **7.61**.