GATE 2020 ME (ME2) – Question 65
Keeping all other parameters identical, an air-standard Diesel-cycle compression ratio increases from 15 to 21. Specific-heat ratio is 1.3 and cutoff ratio 2. Find (η_new − η_old) × 100, to one decimal.
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Correct answer: 4.6 to 4.9
Explanation
Diesel efficiency is $\eta=1-[r_c^\gamma-1]/[r^{\gamma-1}\gamma(r_c-1)]$. Evaluate withrc=2,γ=1.3 at r15 and21. Their difference multiplied by100 is **4.7 percentage points**. This is an absolute efficiency difference, not percentage increase relative to the old efficiency.