Compare compression ratios: Is the compression ratio in Diesel engines lower or higher than in petrol (spark-ignition) engines?

Introduction / Context:
Compression ratio (CR) strongly influences efficiency, power characteristics, and combustion. Diesel engines use compression ignition, requiring high temperature from compression alone, whereas petrol engines use spark ignition and are limited by knock resistance of the fuel.

Given Data / Assumptions:

• Typical petrol engine CR ≈ 8 to 12 (modern high-efficiency designs may be slightly higher).
• Typical Diesel engine CR ≈ 14 to 22 (some heavy-duty higher).

Concept / Approach:
Diesel relies on heat of compression to ignite fuel; thus CR must be higher than petrol. This directly contradicts the statement that Diesel CR is less than petrol CR.

Step-by-Step Solution:

Verification / Alternative check:
Thermal efficiency trends show higher CR increases theoretical efficiency (per ideal cycles), consistent with Diesel engines having higher CR to achieve self-ignition and high efficiency.

Why Other Options Are Wrong:
Choosing “Agree” would misstate fundamental engine design differences and fuel ignition methods.

Common Pitfalls:

• Confusing boost pressure in turbocharged petrol engines with static CR.
• Overgeneralizing from specific models; the general rule remains Diesel CR > petrol CR.

Final Answer:
Disagree