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Typical pressure at the end of compression in diesel (CI) engines: choose the nearest value. Select the approximate end-of-compression pressure in a conventional automotive diesel engine.

Difficulty: Easy

Correct Answer: 35 bar

Explanation:

Concept/Approach
Diesel engines have high compression ratios (≈ 14–22). With intake pressure near 1 bar and polytropic compression (n ≈ 1.35–1.4), the end-of-compression pressure typically lies around 30–45 bar.


Back-of-envelope check
P₂ ≈ P₁ × rⁿ. Taking r = 16 and n = 1.35 → P₂ ≈ 1 × 161.35 ≈ 40 bar (order of magnitude), consistent with 30–45 bar.


Final Answer
35 bar (closest option).

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