Alternatives to Conventional Number 2 Diesel Fuel

The five most common alternatives to conventional number 2 diesel fuel include ultra-low sulfur diesel fuel (ULSD), biodiesel (B20), number 1 diesel fuel, compressed natural gas (CNG), and propane. Below is a description of these five fuels and the costs and benefits to fleet operators. These fuels show great promise, but if you have any questions about the viability of using an alternative to conventional diesel in your fleet, you should contact your Original Engine Manufacturer (OEM).

Ultra-Low Sulfur Diesel (ULSD)

Ultra-low sulfur diesel (ULSD) is diesel fuel that has had the sulfur content reduced from approximately 500 parts per million (ppm) sulfur to 15 ppm sulfur. This cleaner diesel fuel will be available nationwide in 2006 before new diesel vehicles are introduced to meet the U.S. Environmental Protection Agency’s (EPA) 2007 emissions standards. These 2007 standards require significant emissions reductions in heavy-duty diesel trucks and buses, which will be accomplished through the use of after-market equipment, such as particulate filters and oxidation catalysts. In order to achieve the greatest emissions reductions, ULSD must be utilized. This fuel can be used in all diesel engines with little or no modification to the engine or fuel system.

The primary benefit of using ULSD is emissions reductions. Using ULSD fuel without particulate filters or oxidation catalysts could provide up to a 13 percent reduction in particulate matter (PM), a 13 percent reduction in hydrocarbons (HC), a 6 percent reduction in carbon monoxide (CO), and a 3 percent reduction in nitrogen oxide (NOx). If ULSD is used with particulate filters or oxidation catalysts, the reductions are 20 – 80 percent in PM, 90 percent in HC, 90 percent in CO, and 15 – 20 percent in NOx.

There are some potential drawbacks to using ULSD fuel. These drawbacks include cost, availability, lubricity, and cold flow properties. At this time, the cost of ULSD is difficult to estimate due to the fact it is not available in Colorado. EPA estimates “that when fully implemented the sulfur reduction requirement will increase the cost of producing and distributing diesel fuel by about five cents per gallon.” Other sources indicate this cost per gallon will be higher. This increased cost is due to additional refining costs to remove the sulfur from the fuel. Another issue hindering the widespread use of ULSD at this time is the availability of the fuel. Currently the fuel is available in limited parts of the country, primarily on the east coast. At this time, the fuel is not available in Colorado.

The process used to refine ULSD also results in a loss of lubricity, which could potentially result fuel system component wear. However, additives or blending ULSD with biodiesel increases the lubricity of ULSD. Puget Sound Clean Cities reports that they have not encountered any problems with ULSD when properly formulated with additives or biodiesel. Other potential issues with ULSD are the cold flow properties. In cold weather, the cloud point of ULSD is higher than conventional diesel. Therefore, ULSD may require added precautions, such as additives or heated storage tanks, when the ambient temperature gets very low.

Biodiesel (B20)

“Biodiesel” is a clean-burning fuel containing no sulfur or aromatic compounds. It is produced from a number of renewable sources including soybean oil, rapeseed oil, and animal fats. These sources can be obtained from agricultural feedstocks or by recycling used oil, such as cooking grease. The most common form of biodiesel found in the United States is derived from soybean oil.

Biodiesel can be used in its pure form, B100 or “neat biodiesel,” or blended with conventional diesel. The most common blend is B20, which contains 20 percent biodiesel blended with 80 percent conventional diesel. The major advantage of B20 when compared to other alternative fuels is that it can be used in any diesel engine with little or no modification to the engine or fuel system.

Most Original Engine Manufacturers (OEM) have issued statements that support the use of biodiesel in certain percentages. However, biodiesel could impact certain elastomers and natural rubber compounds in the fuel system. When biodiesel fuels are used, the condition of seals, hoses, gaskets, and wire coatings should be monitored regularly. According to the National Biodiesel Board’s experience, there is no impact on these components when using B20 and lower. Currently, OEMs are switching to components suitable for use with low-sulfur and biodiesel fuel.

The benefits of B20 include enhanced lubricity, fuel system cleaning properties, and environmental benefits. Changes in diesel fuel, primarily the reduction of sulfur and aromatic levels, and the process used to reduce these pollutants have reduced the lubricity of diesel fuel. However, the addition of biodiesel, even in smaller quantities than B20, increases fuel lubricity. This increased lubricity can increase the life of heavy-duty engines. In addition to enhanced lubricity, biodiesel acts as a solvent and cleans engine systems. This can cause fuel filter clogs when biodiesel is first used so fuel filters should be monitored.

A final advantage of using biodiesel is the environmental benefit. EPA’s draft report, “A Comprehensive Analysis of Biodiesel Impacts on Exhaust Emissions” from October of 2002 indicates that soybean-based B20 reduces particulate matter by 10 percent, hydrocarbons by 21 percent, and carbon monoxide by 11 percent. Nitrogen oxide is increased by 2 percent.

Potential drawbacks with biodiesel use include cost, cold flow properties, fuel economy, and shelf life. The cost to add a percentage point of biodiesel to conventional diesel is $0.01. Therefore, the additional cost to add up to 20 percent biodiesel, B20, to conventional diesel fuel is approximately $0.20. As more refiners of this fuel enter the market, fuel prices should decrease.

Other potential drawbacks of B20 are cold flow properties. These cold flow properties arise when diesel fuel, including both biodiesel and conventional diesel fuels, are used in very cold temperatures. According to the United States Department of Agriculture, the cold filter plugging point of B20 is approximately 7 degrees warmer than with conventional diesel. However, this small increase in the temperature at which B20 starts to freeze compared to conventional diesel does not present problems for most users. In Cedar Rapids, Iowa, Five Seasons Transportation began using B20 during one of the coldest winters on record with temperatures at -20 degrees Fahrenheit. They made no changes to their operation, other than incorporating 20 percent biodiesel into their existing fleet, and had no significant problems for 1.4 million miles of operation.

Another drawback of using biodiesel is fuel economy. Overall, conventional diesel contains more energy content, and therefore provides higher fuel economy than biodiesel. According to EPA, plant-based B20 contains more energy content than animal-based B20. This energy content has a direct relation on fuel economy with plant-based biodiesel providing better fuel economy than animal-based biodiesel. EPA estimates that the fuel economy penalty for B20 is between 1.6 percent (plant-based biodiesel) - 2.15 percent (animal-based biodiesel). However, B20 has a higher cetane number than conventional diesel, which increases the engine’s performance to balance some of the energy loss.

A final potential issue with B20 is shelf life. The current industry standard is that biodiesel should be used within six months. Most fuel is used long before six months so this should not present a problem unless an operator is storing fuel for a long period of time. If this is the case, fleet operators should test the fuel prior to use.

If you have any questions about the use of biodiesel fuel in a specific engine, contact your OEM and/or the National Biodiesel Board at (800) 841-5849.

Number 1 Diesel Fuel

Number 1 diesel fuel is an alternative to conventional diesel fuel. This fuel has lower sulfur than conventional diesel and, therefore, provides some emissions benefits. In addition to lower sulfur, the fuel has better cold flow properties than conventional diesel, making it a good alternative for cold weather operations.

Some potential drawbacks of number 1 diesel fuel include reduced lubricity, which can be addressed with additives, and reduced fuel economy. More research is pending on this fuel. Please visit the Clean Air Fleets web site at www.cleanairfleets.org for developing information.

Compressed Natural Gas (CNG)

Natural gas is one of the most common forms of energy used today. Compressed natural gas (CNG) is used in thousands of vehicles worldwide primarily due to its lower cost and the fact it generates fewer exhaust and greenhouse gas emissions than gasoline- or diesel-powered vehicles.

Overall, the benefits of using CNG include lower fuel costs, increased performance, and emissions reductions. Generally, CNG costs 15 – 40 percent less than gasoline or diesel fuel. In conjunction with the increased performance experienced by CNG vehicles, operators get a longer lasting, lower-operating cost vehicle. Emissions reductions are significant for CNG fueled vehicles at approximately 90 percent for CO, 35 – 60 percent for NOx, and 50 – 75 percent for HC.

Two drawbacks exist for CNG vehicles; vehicle cost and fuel economy. The increased vehicle cost of $3,500 to $6,000 is primarily due to the higher cost of fuel cylinders. Additionally, more frequent fueling of CNG vehicles is required due to the lower energy content of CNG.

Propane

Propane, or liquefied petroleum gas (LPG), has been used as a transportation fuel since the 1940s. Most vehicles that use this fuel are dual-use vehicles in that they can switch between gasoline or propane fuel. The benefits of propane-fueled vehicles include cost and emissions reductions. The cost of propane, depending on market factors, is usually comparable to gasoline. Depending upon vehicle calibration, propane provides carbon monoxide and hydrocarbon emissions reductions.

The primary drawbacks with propane vehicles are the cost of the vehicle and reduced fuel economy. Overall, the cost of propane-fueled vehicles is $3,000 to $5,000 higher than gasoline-fueled vehicles. Additionally, these vehicles get reduced fuel economy compared to gasoline-powered vehicles.

Sources

National Biodiesel Board – www.biodiesel.org
Puget Sound Clean Cities Coalition – www.cityofseattle.net/cleancities
U.S EPA Office of Transportation and Air Quality – www.epa.gov/otaq