What is ultra-low sulfur diesel?

Ultra-low sulfur diesel (ULSD) is diesel fuel with 15 parts per million (ppm) or lower sulfur content. The U.S. Environmental Protection Agency requires 80% of the highway diesel fuel refined in or imported into the United States (100% in California) to be ULSD as of 2006. One hundred percent must be ULSD nationwide by 2010. Different requirements apply to non-highway diesel.

Currently, the vast majority of ULSD is produced from petroleum. However, biodiesel; biomass-to-liquids, coal-to-liquids, and gas-to-liquids diesel; and hydrogenation-derived renewable diesel are inherently ultra-low sulfur fuels and could help meet ULSD requirements in the future. Petroleum-based ULSD is not considered an alternative fuel under the Energy Policy Act of 1992 (EPAct), but most ULSD fuels produced from non-petroleum and renewable sources are considered EPAct alternative fuels.

Ultra-Low Sulfur Diesel as a Vehicle Fuel

Ultra-low sulfur content in diesel fuel is beneficial because it enables use of advanced emission control technologies on light-duty and heavy-duty diesel vehicles. The combination of ULSD with advanced emission control technologies is sometimes called Clean Diesel.

Nitrogen oxides (NOx) and particulate matter (PM) are the two most harmful diesel pollutant emissions. These emissions can be controlled with the use of catalytic converters (for NOx) and particulate traps (for PM). However, sulfur—in amounts that used to be allowable in diesel fuel—deactivates these devices and nullifies their emissions control benefits. Using ULSD enables these devices to work properly.

In general, ULSD should cause no noticeable impact on vehicle performance, although fuel economy might be slightly reduced because the process that produces ULSD can also reduce the fuel's energy content. Removing sulfur from diesel reduces lubricity. This issue can be resolved by the addition of additives prior to retail sale that increase lubricity. In addition, blending biodiesel with ULSD also increases lubricity.

Using ULSD in older diesel vehicles might affect fuel system components or loosen deposits in fuel tanks. These vehicles should be monitored closely for fuel system problems and premature fuel filter plugging during the transition to ULSD. New vehicles designed to use ULSD must never be fueled with a higher-sulfur fuel. If kerosene is blended with ULSD for improved cold-weather performance, it must be ultra-low sulfur (15 ppm or lower) kerosene. New engine oils have been developed for use with new diesel vehicles fueled with ULSD.

What is hydrogen?

Hydrogen is the simplest and most abundant element in the universe—it is number 1 on the periodic table of elements (this link takes you to Los Alamos National Laboratory's site). At Earth surface temperatures and pressures, it is a colorless, odorless gas (H2). However, hydrogen is rarely found alone in nature. It is usually bonded with other elements. See the AFDC Fuel Properties database for more details.

Very little hydrogen gas is present in Earth's atmosphere. Hydrogen is locked up in enormous quantities in water (H2O), hydrocarbons (such as methane, CH4), and other organic matter. Efficiently producing hydrogen from these compounds is one of the challenges of using hydrogen as a fuel.

Currently, steam reforming of methane (natural gas) accounts for about 95% of the hydrogen produced in the United States. Almost all of the approximately 9 million tons of hydrogen produced here each year are used for refining petroleum, treating metals, producing fertilizer, and processing foods. Hydrogen has been used for space flight since the 1950s; learn more on the NASA Web site.

Hydrogen also can be used to fuel internal combustion engines and fuel cells, both of which can power low- or zero-emissions vehicles such as fuel cell vehicles. Major research and development efforts are aimed at making hydrogen vehicles practical for widespread use.

Diesel Vehicles

Diesel vehicles may be making a comeback. Diesel engines are more powerful and fuel-efficient than similar-sized gasoline engines (about 30-35% more fuel efficient). Plus, today's diesel vehicles are much improved over diesels of the past.

Better Performance

Improved fuel injection and electronic engine control technologies have

• Increased power
• Improved acceleration
• Increased efficiency

New engine designs, along with noise- and vibration-damping technologies, have made them quieter and smoother. Cold-weather starting has been improved also.

Cleaner

Today's diesels must meet the same emissions standards as gasoline vehicles, and advances in engine technologies, ultra-low sulfur diesel fuel, and improved exhaust treatment have made this possible.

Although emissions of particulates and smog-forming nitrogen oxides (NOx) are still relatively high, new "clean" diesel fuels, such as ultra-low sulfur diesel and biodiesel, and advances in emission control technologies will reduce these pollutants also.