Which term describes a fuel's resistance to flow?

• A. Viscosity
• B. Cloud Point
• C. Demulsification
• D. Storage Stability

Answer: (A)

Viscosity is the measure of a fuel's resistance to flow, reflecting how thick or thin the liquid is. This property changes with temperature—fuels flow more easily when warm and resist flow more as they cool—which directly affects how fuel moves through pumps, filters, and injectors, and how well it atomizes for combustion. That makes viscosity the term that describes a fuel's resistance to flow.

Cloud point describes the temperature at which wax crystals form in some fuels, which can clog flow pathways in cold conditions, but it is about crystallization, not the general resistance to flow. Demulsification is about separating water from fuel, not flow resistance. Storage stability refers to how fuel holds up over time against degradation, not its flow characteristics.