What does the Reid vapor pressure test measure?

The Reid vapor pressure test specifically measures the volatility of a liquid fuel, which is primarily concerned with how readily it will vaporize at a given temperature. This property is crucial in aviation fuel contexts since high volatility fuels can lead to vapor lock, where fuel vaporizes in the fuel system and interrupts proper fuel flow to the engine. Vapor lock can cause engine performance issues, particularly in high-temperature conditions or at high altitudes where pressure drops.

The test involves placing a sample of gasoline in a closed container and subjecting it to a specific temperature, usually 100 degrees Fahrenheit (37.8 degrees Celsius). The pressure exerted by the vapor above the liquid is then measured, indicating how easily the fuel can vaporize under those conditions. A higher Reid vapor pressure correlates with a greater tendency for vapor lock and therefore becomes an essential characteristic to monitor in aviation fuels.

While other options relate to properties of fuel, they do not specifically pertain to vaporization behavior or vapor lock, making the correct answer centered on the importance of understanding fuel behavior under specific environmental conditions.