Question Bank • QB_FP_029 MCQ • 2 Marks

Section 3: Farm Power

Farm Power

Subtopic: I.C. engine cycles

Question Statement:

For the same maximum cylinder peak pressure ($P_{\max}$) and same maximum cylinder peak temperature ($T_{\max}$), the thermal efficiencies of ideal air-standard cycles compare as follows:

Options:

  • (A) $\eta_{\text{Diesel}} > \eta_{\text{Dual}} > \eta_{\text{Otto}}$
  • (B) $\eta_{\text{Otto}} > \eta_{\text{Dual}} > \eta_{\text{Diesel}}$
  • (C) $\eta_{\text{Otto}} = \eta_{\text{Diesel}} = \eta_{\text{Dual}}$
  • (D) $\eta_{\text{Dual}} > \eta_{\text{Otto}} > \eta_{\text{Diesel}}$

Answer Key:

A

Step-by-Step Solution & Explanation

When constrained to the same peak pressure and peak temperature, heat rejection in the Otto cycle is larger than that in the Diesel cycle because the Otto cycle must operate at a much lower compression ratio to avoid exceeding the peak pressure. Thus: $\eta_{\text{Diesel}} > \eta_{\text{Dual}} > \eta_{\text{Otto}}$.
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