How to Make the Switch to Ultra Low Sulfur Diesel Fuel

Ultra low sulfur diesel (ULSD) is a diesel fuel with a maximum of 15-ppm sulfur content. Diesel engines equipped with advanced emissions after-treatment devices, such as catalyzed diesel particulate filters (DPF) or diesel oxidation catalysts (DOC), need to use ULSD in order to prevent damage because these devices are poisoned by exposure to higher levels of sulfur.

Most on-road 2007 engines are equipped with after-treatment to make it possible to meet the U.S. Environmental Protection Agency (EPA) emissions standards. Now most non-road Interim Tier 4 and Final Tier 4 vehicle engines will utilize sulfur-sensitive after-treatment technologies to meet the EPA emissions standards.

The following table outlines the schedule for non-road engines to meet Interim Tier 4 and Final Tier 4 emissions standards.

In California, diesel fuel made the transition to 15-ppm sulfur fuel for all on-road and non-road diesel fuel sold on September 1, 2006.

As required by the EPA, the transition to ULSD in the other 49 states for the on-road began on October 1, 2006, where at least 80 percent of the fuel sold must meet the 15-ppm sulfur maximum. The remaining 20 percent can be 500-ppm sulfur fuel (supplied from smaller oil refineries). On October 1, 2010, 100 percent of the diesel fuel sold at the retailer must meet the 15-ppm sulfur maximum.

There is an exception for rural areas of Alaska until 2010. A single grade of diesel fuel is generally distributed to rural Alaska, since carrying two grades could result in significant economic hardship for these rural communities. Alaska and the EPA have an agreement that rural areas will begin transitioning highway and non-road diesel fuel to ULSD beginning June 1, 2010, and ULSD fuel must be at retailers by December 1, 2010. However, if in these rural areas, an on-road vehicle has a 2007 or newer engine or if a non-road vehicle has an Interim Tier 4- or Final Tier 4-compliant engine equipped with catalyzed after-treatment devices, ULSD must be used in those vehicles.

The sulfur level of non-road diesel fuel will transition per the following schedule for all states except California and Alaska

Beginning June 1, 2006, when EPA required that at least 80 percent of the on-road diesel fuel be ULSD, many refineries switched completely to producing ULSD for both on- and off-road applications. With limited tankage for diesel fuel, it was not practical for refineries to carry two diesel fuels with different sulfur levels.

Non-road diesel fuel use accounts for about 18 percent of diesel fuel sales. Current estimates are that about 90 percent of the non-road diesel fuel sold is ULSD containing a red dye.

Watch for deposits

For older vehicles that have previously operated on high-sulfur diesel fuel (>500 ppm sulfur), ULSD may adversely affect fuel system components (mainly seals) and/or loosen deposits in the vehicle fuel tanks.

ULSD has greater solvency than diesel fuels with higher sulfur content. Because the fuel can loosen deposits on fuel storage tanks, inspect and remove any debris. In addition, owners and operators should monitor their current diesel-powered vehicles for potential fuel leaks or premature fuel filter plugging during the changeover to ULSD fuel.

Fuel consumption may change

Depending upon how the ULSD fuel was processed, there may be a slight increase in fuel consumption compared to higher sulfur fuel. Actual equipment measurements have shown fuel consumption increases to 3 percent.

Injector deposits and wear

The same oil refinery process that is used to remove sulfur also removes oxygen, nitrogen, aromatic compounds and other key characteristics in diesel fuel, which are considered natural lubricity agents and antioxidants. Some of the process methods used to make ULSD can produce fuels predisposed to forming injector deposits in high-pressure common rail (HPCR) fuel systems.

These deposits can result in rough running, misfires and power loss. If this occurs, contact your fuel supplier. There are also some detergent-containing fuel conditioners sold in the after-market that will help prevent the formation of these deposits. However, not all detergents work. Check with your dealer for products approved by your equipment manufacturer.

ULSD fuels must meet the same lubricity requirements as 500-ppm sulfur diesel fuels, which is up to 520-micron maximum wear scar diameter as measured on a High Frequency Reciprocating Rig (HFRR) test.

As necessary, additives are introduced prior to retail sale to restore lubricity removed during the sulfur removal process. The lubricity spec is important to older vehicles as many of the older vehicle's fuel injection systems are lubricated by the diesel fuel. Reduction in the lubricity value will affect the wear rate on the older injection systems. If you are concerned that your fuel may not be meeting this lubricity standard, contact your fuel supplier.

Cold-flow changes

ULSD fuel is a more paraffinic fuel than 500-ppm sulfur fuel and has a different wax distribution. Cold-flow improvers that worked in 500-ppm sulfur fuel may not provide the same performance in ULSD fuel.

When purchasing cold-flow improvement additives for cold-weather operation, be sure the product was formulated to work in ULSD; these products also work in 500-ppm sulfur fuel. The cold-flow performance is important to keep fuel filters from gelling and the vehicle operating in colder temperatures. Check with either your fuel supplier or dealer.

As with any after-market additive, be sure the product has been approved by your equipment/engine manufacturer.

Microbial growth

Due to its lower sulfur content, ULSD is more prone to microbial growth than 500-ppm sulfur fuel. Long periods of fuel storage can create an ideal environment for microbes to grow in fuel storage and vehicle tanks. These microbes can plug fuel filters resulting in increased replacement of fuel filters. Tanks are most vulnerable at seasonal changes, summer to fall and winter to spring.

Watch for dark, slimy growth at the interface area between the diesel fuel and the water-bottom or throughout the fuel. There may also be a “rotten egg” odor. Look for slime on the interior walls of the tanks and in the sump area—check water drawn from the sump area for slimy debris.

Microbial growth can multiply rapidly and may form into long strings, mats or globules. They can only be removed from the fuel system by a diesel-fuel biocide.

If you suspect microbial growth in your fuel tanks, contact your fuel supplier. Diesel-fuel biocide treatments are also available at many dealers. A regular fuel-tank biocide treatment schedule can prevent microbial growth.