D2 is a refinery abbreviation for Gasoil. It is the second distillate from crude oil and can be used without reformers and additives. The first engines used D2 as fuel—before petrol cars as we know them today were invented.
This is because the engine, invented by a German named Diesel, requires no spark plugs. The diesel engine ignites and combusts when pressure increases, causing the heated “plug” to trigger combustion. This is where the name “Diesel” originates, as the same principles are still used in diesel engines today.
However, the automotive diesel you fill today contains additives added by the refinery to make the engine more efficient and easier to start in winter. Diesel changes its flash point in winter and also includes additives to absorb water from condensation.
Using summer diesel in winter may offer better mileage, but your fuel pipes may freeze or burst, and the wax content makes diesel flow thicker
The principal difference between Gasoil and D2 is the sulphur content. Just 10 years ago, the US EPA introduced a limit of 4% sulphur in Gasoil, whereas Europe and the rest of the world followed later.
As often happens, once sulphur removal was required, more efficient methods for extraction were developed. It was also discovered that sulphur, in the form of sulphuric acid, could be traded profitably, which became a strong incentive for extracting as much as possible.
Today, Low Sulphur Gasoil no longer means 4% sulphur—it is now below 0.2%. There is also a newer category, Ultra Low Sulphur, with a maximum content of 0.02%. The limits here are:
- (a) Mass spectrographs require extensive calibration to measure below 1000 ppm,
- (b) Sulphur tends to form clogs—its molecules bind with free hydrogen to form clusters that can be broken if “cracked” by the refinery.
However, since D2 is a distillate and has not been cracked, this natural clustering remains a relevant consideration.
ISO has a standard for D2 that most oil companies use as a reference.
In the U.S., it is ANSI that defines the national standard for D2, based on proposals from ASTM, API, and EPA.
In Europe, there are similar national variants, such as those set by DIN in Germany.
The GOST variant for D2/Gasoil is GOST 305–82, which now specifies a sulphur content of 0.02% MAX, aligning with the ISO standard. However, the ANSI standard refers to this level as “Ultra Low Sulphur” and retains 0.2% (2000 ppm) as the definition for “Low Sulphur.” The reduction of sulphur in Gasoil used for heating has contributed to lower pollution levels in many cities.
Automotive diesel also has national variants, but the most commonly traded are EN590 and EN560, both specified by ISO in Paris. These diesel grades may also be sold in the U.S. and remain compliant with EPA regulations.
Automotive diesel is now being tested in aircraft with promising results, offering up to 40% greater mileage per unit of weight compared to kerosene. In the effort to reduce emissions, one possible outcome is that planes may eventually fly on Gasoil instead of kerosene. The primary challenge is condensate, ice particles, and wax, which can damage jet engines (turbines). A preliminary solution involves heating the Gasoil before injection and passing it through an electrostatic filter.
