In recent years, environmental regulations have significantly affected diesel fuel formulation and specification limits. The introduction of tighter limits, coupled with rapid changes in engine design to meet new emission regulations, created the need to address several fuel properties to ensure proper performance while minimizing engine maintenance problems.
Some fuel users believe that, under certain circumstances, they can benefit from diesel fuel with properties modified beyond the minimum ASTM D 975 specifications. A number of fuel suppliers offer these specially formulated fuels in addition to normal diesel fuel. Diesel fuel with these modifications is often called premium diesel, although other names are also used.
The premium diesel concept differs from that of premium gasoline. Gasoline engines of certain types and compression ratios require a higher octane number fuel to avoid knocking.Therefore, all fuel suppliers offer a higher octane level of premium gasoline for these vehicles.
Conversely, premium diesel is typically related to varying multiple fuel properties. Some of the more commonly modified fuel properties are: cetane number, low-temperature operability, stability, lubricity, detergency, and heating value. The premium diesel fuel suppliers tailor the specific properties of their premium diesel to match the various performance demands in different marketing regions. The level of improvement in each property usually varies from one supplier to another and may also vary from region to region.
Several organizations have proposed meaningful standards for premium diesel. The intent of these standards is to ensure that all diesel fuel carrying the “premium” classification provides significant functional benefits when compared to normal diesel fuel. Currently,the National Conference on Weights and Measures (NCWM), the Engine Manufacturers’ Association (EMA), and the Alliance of Automobile Manufacturers (AAM) have made the three most complete proposals. The NCWM’s premium diesel proposal has received the most widespread support to date.