A number of agencies regulate diesel fuel to ensure quality and environmental cleanliness. Diesel fuel is graded according to its chemical properties. All diesel oil must be properly labelled by its grade level. The grade level informs the consumer on what vehicles he may use the diesel fuel and how it impacts the environment.
The American Society for Testing and Materials established seven grade levels for diesel fuel oil. The lowest levels are lighter and contain less sulphur. Sulphur is a key aspect to diesel fuel combustion. Sulphur is also regulated by the Environmental Protection Agency. The EPA makes sure that the levels of sulphur in diesel fuel are maintained within a sustainable level. The highest level grades contain more sulphur and are used primarily for heating purposes.
1-D is a subcategory of three diesel fuel oil grades. The grades in this category are 1-D S15, 1-D S500, and 1-D S5000. S15 is the lightest while S5000 is the heaviest. The numbers for these grades indicate the level of sulphur in the diesel fuels. These 1-D fuels are for diesel engines that do not burn at high temperatures and require shifting between various speeds. A motor vehicle that needs to go between speeds uses 1-D fuels. 1-D is also one of the newest diesel fuel levels to be produced. The fuel has been made since the arrival of increased environmental regulations for better fuel standards and lower sulphur levels in diesel fuel. Consumers are able to tell if a diesel fuel is a 1-D if it is advertised as ultra low sulphur diesel.
2-D is another subcategory of three higher grade diesel fuel oil grades. These fuels also contain sulphur levels noted as 2-D S15, 2-D S500, and 2-D S5000. These fuels are meant for heavier motor vehicles that require higher burning fuels. Many trucks with large loads require using these fuels to burn at high speeds. Non-motor vehicles like trains often use 2-D fuels.
4-D is a single diesel fuel grade and the heaviest one of the seven. This fuel is required for large vehicles that need to maintain a constant speed, such as a cruise ship.