Diesel Engine Design — Typical Compression Ratio Range Select the usual compression ratio range adopted in compression-ignition (diesel) engines for road vehicles and stationary power.

Introduction / Context:
Compression ratio is the key parameter distinguishing diesel engines from spark-ignition engines. Higher ratios increase air temperature during compression, enabling auto-ignition of injected fuel. Knowing the normal range is essential for understanding efficiency, emissions, and starting performance.

Given Data / Assumptions:

• Conventional four-stroke automotive and industrial diesels.
• Turbocharging/aftercooling may slightly influence chosen ratios but not the general range.
• Not considering extreme experimental engines.

Concept / Approach:
CI engines typically employ compression ratios from about 15:1 to 25:1. This range provides sufficient end-of-compression temperatures for reliable ignition across operating conditions, while balancing mechanical stress and NOx formation.

Step-by-Step Solution:
Recall: SI engines use ~8–12; CI engines much higher.Standard practice: light-duty ~16–18; heavy-duty may approach ~20–22.Therefore, the correct broad range is 15–25.

Verification / Alternative check:
Manufacturer datasheets for common diesels list CR within this band, confirming the norm.

Why Other Options Are Wrong:
6–10 and 10–15 are typical of SI engines, insufficient for CI ignition.25–40 and higher are uncommon due to stress, noise, and diminishing returns.

Common Pitfalls:
Assuming turbocharged diesels always use lower CR; while sometimes reduced, they still sit within the 15–25 range.

Final Answer:
15–25