Vapor pressure
Vapor pressure is a common measure of gasoline volatility. It indicates how it will perform under different operating conditions.
Gasoline with high vapor pressure is preferred for easy engine starting. However, it also influences an engine’s evaporative emissions. Volatile organic compounds, which are emitted when gasoline vaporizes, will create ozone when they react with nitrogen oxides.
Thus, a maximum vapor pressure limit is set in gasoline specifications to help reduce evaporative emissions and thereby reduce the formation of ozone. The specifications also set a minimum limit to ensure that engines start easily.
Sudan’s gasoline specifications set minimum and maximum limits for vapor pressure for summer and winter. Summer regulatory limits are 45–60 kPa, while winter limits are 55–70 kPa.
SGS Worldwide Fuel Survey results on gasoline samples taken in 2017-2019 showed that all winter samples taken had vapor pressure values within the upper limit but not within the lower limit. No summer samples were taken.
Average vapor pressure of gasoline samples in the winter season, 2017-2019
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Source: SGS Worldwide Fuel Survey, 2022