What can cause fuel flow blockage in aircraft fuel systems?

Fuel vaporization can lead to fuel flow blockage in aircraft fuel systems due to the conditions under which the fuel is maintained at lower pressure and higher temperatures within the fuel lines and components. When fuel vaporizes, it creates gas bubbles that can impede the continuous flow of liquid fuel to the engine. This phenomenon, often referred to as fuel vapor lock, occurs particularly when the temperature of the fuel rises above its boiling point at a given pressure, causing the liquid fuel to convert to vapor and disrupt the flow necessary for proper engine operation.

In the context of the other options, low fuel temperatures typically ensure that fuel remains in a liquid state and flows effectively. Improper fuel mixing can lead to fuel quality issues but does not directly block fuel flow in the same way vaporization does. High engine RPMs generally increase fuel flow demand but do not inherently block flow; they may actually exacerbate fuel vaporization if the system is not adequately designed to handle such conditions. Therefore, fuel vaporization stands out as a clear cause of flow blockage due to its direct impact on the fuel's state and continuity within the system.