Diesel is one of the higher-valued light products (along with jet fuel and gasoline). It is used primarily in the transportation sector, and it is the primary fuel used in heavy-duty trucks and locomotives. Also, in some markets, it is used in light-duty cars and trucks.
Diesel-range material also has a number of off-road uses, as a fuel for construction and farm equipment and as a heating fuel (home heating oil). However, this is a much smaller share of use than the transport sector uses.
Generally, refiners will try to maximize their yield of diesel, along with gasoline, to maximize profit. Since the two products draw from different boiling range material, they are largely complementary. However, there are a few conversion units that favor one over the other, forcing refiners to make a call on which will be more value-creating. Most notably, FCCs will tend to upgrade VGO more toward gasoline, and hydrocrackers will upgrade VGO more toward diesel.
Diesel tends to compete with jet fuel for some of the same blendstocks, specifically kerosene, which makes up most of jet fuel and is a good blendstock into diesel. As a result, maximizing jet fuel production can come at the cost of diesel yield, and vice versa.
Diesel is typically a complex blend of many different refinery streams. The most common components are:
- Hydrotreated distillate from the distillate hydrotreater
- Hydrocracker distillate from the hydrocracker
- Straight run gasoil from the atmospheric crude tower
- Hydrotreated kerosene from the kerosene hydrotreater
- Hydrocracker kerosene from the hydrocracker
- Straight run kerosene from the atmospheric crude tower
Diesel can also include some blendstocks that do not come from refining. These include:
- Biodiesel - Produced through processing a vegetable oil or animal fat using a transesterification process
- Renewable diesel - Produced through hydroprocessing a vegetable oil or animal fat
- GTL diesel - Produced from natural gas using a Fischer-Tropsch process
Diesel product qualities
Diesel-powered vehicles use diesel cycle engines, which rely on the heat of compression to ignite the fuel. To perform well, this requires diesel to have specific product qualities. Some of the more important ones are:
- Cetane - Measure of the tendency of diesel fuel to auto-ignite when injected into the combustion chamber of a diesel engine
- Sulfur content - Measure of the sulfur remaining in the fuel. Lower sulfur is more desirable. Sulfur content is measured as ppm wt
- Cloud point - Indicator of the tendency of a fuel to form wax crystals when cold. Lower cloud point is more desirable
- Pour point - Measure of the tendency of a fuel to become more viscous and resist flowing when cold. Lower pour point is more desirable
- Flash point - Temperature at which a fuel emits enough vapor to form a combustible mixture of hydrocarbon and air. Higher flash point is more desirable