🔍 Key Concepts

• Diesel combustion quality is about how easily and smoothly fuel ignites under compression, not how it flows when cold • Different fuel properties (like viscosity, pour point, and sulfur content) affect engine wear, emissions, and handling, but not all directly measure ignition quality • There is a specific fuel rating scale for how readily diesel fuel ignites when injected into hot compressed air

💭 Think About

• Ask yourself: which property is specifically designed as a rating of ignition quality in diesel engines, instead of just describing physical characteristics of the fuel? • Consider what viscosity mainly affects in a fuel system — is it more about flow and injection, or about how quickly it starts to burn? • Think about which property engineers and engine manufacturers specify when they want good cold starting and smooth, knock‑free diesel operation

✅ Before You Answer

• Identify which option refers to a standardized scale or rating for diesel ignition quality • Eliminate any properties that are primarily about how thick the fuel is or how it behaves at low temperature, rather than about ignition • Verify which factor marine engineers look at when concerned about diesel knock, starting performance, and smooth combustion