Vapor lock index

Also known as: VLI

The vapor lock index is the measure used to control the tendency of gasoline to form vapor lock in most markets outside of US. The measurement for VLI is calculated:

VLI = 10x(Vapor pressure in kPa) +7x(% evaporated at 70C)

Typical values range from 800 to 1,250, and lower VLI is better.

In the US, vapor lock is controlled by the vapor-liquid ratio rather than VLI. Vapor-liquid ratio is the temperature at which gasoline forms a ratio of vapor volume to liquid volume that is equal to 20.

The normal range for vapor-liquid ratio is 35 to 60 C (95 to 140 F). Higher vapor-liquid ratio is better.

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