🔍 Key Concepts

• Difference between ignition quality and other fuel properties like viscosity and acidity/neutralization number • What diesel engines need from fuel at the moment of injection for proper combustion • Standard scale used in industry to rate how easily diesel fuel auto‑ignites under compression

💭 Think About

• Which of these choices refers specifically to how readily a diesel fuel will ignite under compression, not how thick it is or how much air is mixed with it? • Think about gasoline vs diesel: gasoline uses an octane rating for knock resistance; what is the roughly equivalent rating term used for diesel fuels? • Which properties listed are more about handling/flow (thickness), chemical contamination/acidity, or mixture control—rather than ignition behavior?

✅ Before You Answer

• Eliminate any option that measures thickness/flow characteristics rather than ignition behavior. • Eliminate any option that is about the fuel–air mixture in the engine, which is an operating condition, not an inherent fuel rating. • Focus on the option that is an industry-standard rating scale for how quickly and easily diesel fuel ignites in a compression-ignition engine.