Today, millions of trucks undergo road-bound treks to transport goods. The diesel engines that power these vehicles support this system. These engines, which also are found in buses and some smaller automobiles, require diesel fuel, which needs to adhere to certain specifications.
Various grades of diesel fuel oils are established in ASTM D975-21: Standard Specification for Diesel Fuel.
Diesel Fuel Background
Rudolf Diesel invented the diesel engine in 1893. Powered by a fuel that was considered an unwanted byproduct or distillate of crude oil refining for decades prior, the new engine burned fuel at a lower rate, making better use of the heat generated. It was also was, and still is, safer than gasoline because its vapors did not explode or ignite as easily.
Despite its efficiency—diesel contains ten percent more energy per gallon than gasoline—diesel engines did not take off for some time. However, by 1913, the same year as Diesel’s mysterious death, the diesel engine was in large freight trucks, tractors, trains, and ships.
Due to issues with environmental and public health, standard forms of diesel fuel have adapted over the years. One of the more recent progressions is the limitation of sulfur content in diesel fuels. As of 2007, a maximum of 15 ppm sulfur in diesel has been the norm for on-road vehicles. It has since been set at that limit for non-road vehicles, locomotives, and marine vessels.
Diesel Grades in ASTM D975-21
In general, there are two primary grades of standard diesel fuel: Diesel #1 and Diesel #2.
Diesel #2 is general purpose, being able to sustain heavy loads and providing better fuel economy. In fact, No. 2-D (when following ASTM D975-21 nomenclature) is specified by diesel automakers for normal driving conditions. #1 is more volatile and special-purpose, being used for cold conditions, for example. The two types of oil can be blended.
According to ASTM D975-21: Standard Specification for Diesel Fuel Oils, there are seven diesel fuel grades:
- Grade No. 1-D S15
- Grade No. 1-D S500
- Grade No. 1-D S5000
- Grade No. 2-D S15
- Grade No. 2-D S500
- Grade No. 2-D S5000
- Grade No. 4-D
Please note that three of these are variants of Diesel #1, and three are of Diesel #2. The distinction here is sulfur content, meaning that Grade No. 1-D S15 is a special-purpose, light middle distillate fuel at a maximum of 15 ppm sulfur.
Grade No. 4-D includes more viscous middle distillates and blends with residual fuel oils.
To combat fossil fuel emissions, many trucks now use biodiesel or a biodiesel blend—an update to the definition for this was actually the main change made to ASTM D975-21. Biodiesel, which ASTM D975-21 designates B100, produces 75 percent fewer emissions than conventional diesel.
In the United States, the Renewable Fuel Standard (RFS) requires transportation fuel sold in the U.S. to contain a minimum volume of renewable fuels. This means that diesel importers are required to use a specific volume of biodiesel based on a percentage of its petroleum product sales.
Some economists are weary of the high costs of biodiesel. In fact, due to government policies aimed at finding alternatives to fossil fuels, biodiesel prices grew from 35 cents per pound to around 1 dollar per pound between 2020-2021. The emerging version of the fuel, known as renewable diesel, can be made in large refineries and is not limited by the cold weather, unlike the earlier version of biodiesel. With this, the production capacity for renewable diesel is projected to grow to around 5 billion gallons by 2024. While the usage of biodiesel directly emits less greenhouse gases, many environmentalists are concerned that its growing consumption might contribute to greenhouse gas releases resulting from land clearing for new soybean fields.
Other than detailing the grades of diesel fuel, ASTM D975-21 offers test methods. It covers additional information in its annexes.
ASTM D975-21: Standard Specification for Diesel Fuel is available on the ANSI Webstore.