🔍 Key Concepts

• ignition quality of diesel fuel vs. its energy content • what the cetane scale is used to measure in diesel engines • difference between properties: specific gravity, viscosity, and calorific value

💭 Think About

• Which property tells you how EASILY and SMOOTHLY diesel fuel starts to burn when injected into a hot cylinder? • Which of these terms is specifically defined for diesel engine performance, similar to how octane is used for gasoline? • Do properties like specific gravity, viscosity, or calorific value directly measure how quickly fuel auto‑ignites, or do they describe something else?

✅ Before You Answer

• Identify which option is a standardized rating scale used only for diesel ignition performance. • Confirm that specific gravity and viscosity mainly describe physical characteristics, not ignition quality. • Check whether calorific value refers to total heat energy released, not how readily the fuel ignites.