Reid vapour pressure (RVP) significance for gasoline: identify which performance or operability issue RVP is most directly used to assess among pour point, cloud point, vapour-lock tendency, and carbon residue.

Introduction / Context:
Reid vapour pressure (RVP) is a standardized measure of gasoline volatility at a specified temperature. Regulators and refiners control RVP seasonally to balance startability in cold weather with hot-fuel handling issues in warm weather.

Given Data / Assumptions:

• Fuel: conventional gasoline.
• RVP measured at standard conditions (Reid method).
• Engine/fuel system exposed to varying ambient temperatures.

Concept / Approach:
Higher RVP implies more volatile fuel, which aids cold starting but increases the risk of vapour lock and evaporation losses in hot conditions. Vapour lock occurs when gasoline vaporizes in the fuel pump or lines, interrupting liquid flow and causing stalling. Therefore, RVP is directly connected to vapour-lock tendency rather than low-temperature pour/cloud points (relevant to diesel) or carbon residue (a heavy-fuel property).

Step-by-Step Solution:

Verification / Alternative check:
Seasonal gasoline specifications set upper RVP limits for summer to mitigate vapour lock and evaporative emissions while still meeting startability targets.

Why Other Options Are Wrong:

Common Pitfalls:
Assuming higher RVP is always better; it must be optimized for climate and engine design.

Final Answer:
Vapour-locking tendency