Subtopic: Thermodynamic principles of I.C. engines
Question Statement:
An oil engine works on the ideal diesel cycle with a compression ratio of 18:1. The constant pressure energy addition ceases at 10% of the stroke. The intake pressure and temperature are 100 kPa and 300 K respectively. The hourly air consumption is 100 m³. If the ratio of specific heats is 1.4, the maximum temperature in the cycle is
Options:
(A) 953.3 K
(B) 1334.6 K
(C) 2154.5 K
(D) 2573.9 K
Official Answer Key:
D
Step-by-Step Solution & Explanation
Compression (isentropic): T₂ = T₁·r^(k−1) = 300×18^0.4 = 953.3 K. Cut-off ratio ρ: V₃ = V₂ + 0.10(V₁−V₂); with V₁ = r·V₂, ρ = V₃/V₂ = 1 + 0.10(r−1) = 1+0.1(17) = 2.7. Constant-pressure heat addition: T₃ = T₂·ρ = 953.3 × 2.7 = 2573.9 K (maximum cycle temperature). (A) is only T₂, mistaken for the maximum; (C) uses an incorrect cut-off ratio.
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