ASTM updates gasoline specification for winter efficiency

ASTM International’s Petroleum Products, Liquid Fuels, and Lubricants Committee (D02) has revised its specification for automotive spark-ignition engine fuel (gasoline). The revised standard is now available as ASTM D4814-24. The standard is used throughout the United States and many other countries and impacts how fuel suppliers make gasoline for different geographic regions and seasons.

The revision was driven by a review of multi-decade average seasonal temperatures used to develop the volatility classes for gasoline. The revision also revises wintertime 50% distillation limits based on vehicle testing.

According to Dr. James Simnick, ASTM member and owner of Simnick Consulting LLC based in Naperville, Illinois, U.S.A., the revision incorporates updates to the schedule for the proper volatility of gasoline in areas of the United States for every month of the year and adds clarifying language on how to interpret Table 4, which is the schedule of U.S. seasonal and geographical volatility classes.

“This standard and its latest revision will affect how well gasoline runs in vehicles and gasoline-equivalent equipment,” says Simnick.

Although the Table 4 revision is U.S. centric, the ballot that passed also allows for a more relaxed T50 distillation minimum limit in the winter time. The minimum is moved from 65.6°C (150°F) to 62.8°C (145°F) for gasoline blended with ethanol.

The T50 distillation minimum limit in the context of winter fuel specifications refers to the temperature at which 50% of a fuel sample has evaporated during a distillation test. This parameter is important for assessing the fuel’s volatility and its ability to vaporise efficiently, especially in cold weather conditions.

In winter, it is crucial for fuels, particularly gasoline, to have a lower T50 value to ensure that the fuel can vaporise easily in the engine for efficient combustion. If the T50 value is too high, the fuel may not vaporise properly in cold weather, leading to issues such as hard starting, poor engine performance, and increased emissions.

The minimum limit for T50 is set to ensure that the fuel has sufficient volatility to perform well in winter conditions. This limit may vary depending on regional specifications and the type of fuel.

This change in the ASTM gasoline specification will make it easier for refiners to make ethanol blended gasoline resulting in perhaps more supply and lower manufacturing cost, said Simnick, who retired from bp in 2020 after 41 years with the company.

The standard is used by many stakeholders including refiners, fuel importers, renewable fuel makers, pipelines, shipping companies, automakers and engine designers, state and federal regulators, test laboratories and others.