Beyond Words: Clarifying the Baffling World of Diesel Terminology

Let’s not kid ourselves: with so many words used to describe the fuel most commonly known as diesel (we count upwards of 25 terms that mean different things), it’s pretty easy for a conversation about diesel to get lost in translation. With that in mind, this quick Q&A clarifies the similarities and differences between the various kinds of diesel in today’s motor fuel supply.

What’s the difference between diesel, biodiesel, biodiesel blends and renewable diesel?

Diesel, which is also called petroleum diesel, standard diesel, conventional diesel, fossil diesel and petrodiesel, is petroleum-based. It is available in two grades used as transportation fuel: Diesel No. 1 (1-D) and Diesel No. 2 (2-D). Diesel No. 2 is the most common grade of diesel used in the motor fuel supply.

Biodiesel, a biofuel known as B100, is made from biomass oils including plant oils, cooking oil, animal fat and even algae. Biodiesel is produced through a process called transesterification. It meets the ASTM D6751 specification. B100 is most often used as a blendstock, not as a transportation fuel.

Biodiesel blends are created by blending biodiesel into petroleum diesel or renewable diesel. Biodiesel blends comprise most of the diesel fuel sold as transportation fuel. Not unlike how most consumers use the word “gasoline” to describe ethanol blends such as E10, biodiesel blends are, at least colloquially, known to most people as just “diesel.” Biodiesel blends are classified based on the percentage of biodiesel content contained in the fuel:

B20: The most common biodiesel blend, which ranges from 6% to 20% biodiesel.
B5: Contains 5% biodiesel and is most commonly used in fleet vehicles.

Renewable diesel (also sometimes called green diesel) is a biofuel, but it is not the same as biodiesel. Renewable diesel is made from the same renewable resources as biodiesel, but it is created through a different process. In fact, renewable diesel is chemically identical to petroleum diesel and meets ASTM D975, the specification for petroleum diesel. As a result, renewable diesel can also be blended with biodiesel to create biodiesel blends such as B20 and B5.

What is highway diesel, non-road diesel and ultra low sulfur diesel?

Highway diesel (also called on-road and clear diesel) and off-road diesel (also called non-road diesel, non-highway diesel, ag diesel and red diesel) are classifications with legal implications.

Off-road diesel is approved for use in vehicles/machinery not driven on the road including farm equipment and heavy-duty earthmoving equipment. Chemically, off-road diesel and highway diesel (the diesel required for road vehicles) are the same. But because off-road diesel isn’t used for road transportation, a fuel tax isn’t included in its purchase price. Off-road diesel is dyed red so that authorities can easily distinguish it from highway diesel. Motorists caught driving a road vehicle containing off-road diesel on public roads may face tax evasion charges.

Ultra low sulfur diesel (ULSD) is a regulatory designation that mandates the amount of sulfur contained in diesel. Since 2010, the U.S. Environmental Protection Agency has required that all diesel fuel supplied for road transportation — and all highway diesel vehicles use — ULSD. ULSD contains just 15 parts per million of sulfur (prior to regulating sulfur content, diesel contained as much as 5,000 ppm of sulfur). This requirement was developed to reduce pollution. Because highway diesel and off-road diesel are essentially the same except for the dye and the taxes, they are both considered ULSD fuels.

What is the difference between auto diesel and truck diesel?

The terms auto diesel and truck diesel are used to describe flow rates (and the equipment used to dispense those flow rates) needed to pump fuel into different types of vehicles.

Auto diesel is pumped through fuel dispensers that serve light-duty road vehicles. Auto diesel fuel dispensers pump fuel at a rate of about 10 gallons per minute (gpm). Truck diesel is pumped through high-flow dispensers that serve heavy-duty road vehicles. Truck diesel dispensers are rated up to 50 gpm.

Dispenser Filter Selection for Diesel Fuels
Three lines of PetroClear filters are compatible with petroleum diesel, biodiesel, biodiesel blends and renewable diesel:

PetroClear green filters: Removes particulate, senses water and detects phase separation*
PetroClear brown filters: Removes particulate and senses water
PetroClear red filters: Removes particulate

A fuel dispenser filter’s micron rating is especially important for protecting diesel engines. According to a recent Diesel Fuel Quality Council (DFQC) report, diesel engines may be susceptible to damage from particulate as small as 4 microns. Watch this video to learn more.

For additional guidance selecting filters that are compatible with specific dispensers, please reference PetroClear’s Dispenser Filter Selection Tool.

*Phase separation only applies to ethanol blends. PetroClear’s green filters are designed to be compatible with the maximum number of fuels, including diesel, biodiesel, biodiesel blends,  renewable diesel, neat gasoline and ethanol blends to help operators simplify filter inventory.