AXI News Center


Ultra Low Sulfur Diesel (ULSD): The Good, the Bad, and the Rusty

Over the past three decades, the EPA has mandated an overall 99.7% reduction in diesel fuel sulfur content, compared to the high-sulfur diesel fuels used prior to the 1990s. How does this change in fuel chemistry affect your engine, tank, and bottom line? Let’s review ULSD regulations, the reasoning behind these regulations, and preventative maintenance solutions for your engine.

ULSD: A Timeline

In 1990, Congress amended the Clean Air Act to require stricter Hydrocarbon, SOx, CO, NOx, and particulate matter emission reductions. These amendments also included, among other things, stricter tailpipe emission standards and stricter emission testing procedures. During this time, the EPA also started imposing limits on diesel fuel sulfur content.

Fast forward to 2001, the EPA finalized a federally-mandated program called the 2007 Heavy-Duty Highway Diesel Program, which was created to lower emissions from highway diesel engines. This program, effective June 2006, decreased the maximum allowed diesel sulfur level from 500 to 15 parts per million (ppm), essentially mandating the switch from Low Sulfur Diesel to Ultra Low Sulfur Diesel.

Following shortly after the inception of the 2001 highway diesel program, the EPA issued the Clean Air Non-Road Diesel – Tier 4 Final Rule, which mandated sulfur reductions for non-road diesel engines, effective in 2007. This first lowered the maximum diesel fuel sulfur levels from 3,000 to 500 ppm in 2007, and then from 500 to 15 ppm in 2010.

ULSD: A Reduction in Emissions and a Change in Fuel Chemistry

Since the 1990s, the EPA has mandated an overall 99.7% reduction in fuel sulfur content. They have done so in order to reduce diesel fuel emissions and pollution. Sulfur oxides (SOx), specifically SO2, cause both health and environmental harm. Health concerns related to exposure from SOx include respiratory problems and lung damage. SOx causes environmental harm in the form of tree, plant, and stone damage; acid rain; and reduced visibility (haze).

The less sulfur content in fuel, the less SOx emissions that fuel will release. Therefore, a reduction in fuel sulfur content means less pollution.

Additionally, reducing sulfur content greatly alters the lubricating properties and overall chemical composition of diesel fuel. The refinery process that is used to remove sulfur from diesel fuel is called severe hydrotreating. Hydrotreating affects diesel fuel in the following ways:

  • Removes sulfur
  • Removes natural lubricity compounds
  • Lowers aromatic content
  • Lowers conductivity
  • Increases the cetane level
  • Lowers energy density
  • Lowers fuel economy
  • Increases fuel production costs

The estimated decrease in fuel economy is 1%. According to the EPA, severe hydrotreating increases fuel production costs by 5 to 7 cents per gallon. However, these costs may be significantly higher depending on market, distribution, and other production factors.

Biofuel, Ethanol, & ULSD: Same Tank, Different Fuels

In 2007, as emission and pollution awareness and prevention was on the rise, ethanol-gasoline mandates came into full effect. Since this time, fuel tank corrosion damage has hit an all-time high, not only in gasoline tanks, but in diesel fuel tanks, as well. This is due to the fact that fuel hauling tanker trucks participate in switch loading, which means that one day, a truck will haul ethanol-based gasoline, and the next day haul ULSD.

Storage tanks containing just ULSD can and do have corrosion problems when they are not maintained properly. However, as the EPA has confirmed, accelerated tank corrosion occurs when ULSD is exposed to small quantities of biofuel. When ULSD is exposed to ethanol, or other types of biofuel, even in small quantities, several problems occur, including increased microbial growth, and in turn, a decrease in pH, which is key to tank corrosion and rust.

ULSD Problem Prevention

To effectively combat the potential problems associated with ULSD, including decreased lubricity, energy density, and fuel economy, use a broad spectrum fuel additive. Whether it’s a car, truck, boat, yacht, or generator, a fuel additive, such as AXI International’s AFC 710, can clean and protect your engine. This Tier-4 compliant fuel additive will not only add lubricity to your fuel, it will clean out your fuel system and tank, increase fuel economy, increase filter life, and increase horsepower. By allowing fuel to combust more fully, AFC-710 aids in diesel fuel emission and pollution reduction. To read more about AXI International’s fuel additives, click here.