The bureaucrats in Washington, DC, and California are working on new emissions rules that will impact the heavy-duty trucking industry in just a few years. As expected, suppliers are already developing and soon will be marketing cleaner diesel fuels. No matter how much hype is given to alternative fuels like natural gas and propane, hybrid-electric vehicles, and even fuel cells, diesel engines will be around for a long, long time.
New emissions standards
The Environmental Protection Agency (EPA) and the California Air Resources Board (CARB) are both planning more stringent emissions requirements for heavy-duty diesel engines. These new standards, expected to go into effect in 2007, are in response to concerns about health hazards from particulate matter (PM) emissions. These tiny, soot-like particles in diesel exhaust are thought to cause cancer and respiratory diseases.
New CARB standards will probably include emissions levels of about 0.5 grams per brake/horsepower-hour for oxides of nitrogen (NOx) and 0.01 g/bhp-hr for PM. The current requirement is for 4 g/bhp-hr (dropping to 2 g/bhp-hr in 2004) for NOx and 0.1 g/bhp-hr for PM. The EPA has not yet released the details of their new standards. However, they will undoubtedly follow those of CARB.
The new EPA standards are expected to include requirements for exhaust treatment techniques including diesel particulate traps and NOx trap/catalyst systems. These devices in turn will dictate the use of ultra low sulfur diesel fuel, as the high sulfur content in most current diesel fuel would clog them. While the EPA is considering sulfur levels of 5 to 40 parts-per-million, the CARB is looking at levels of 30 ppm. Current standards allow for up to 500 ppm of sulfur in highway diesel fuel.
Two suppliers have recently announced new products designed to significantly lower NOx and particulate matter emissions.
ARCO Emission Control Diesel
ARCO has developed a reformulated diesel fuel, Emission Control (EC) Diesel, containing much less sulfur than current products. EC Diesel also has a higher cetane rating and less aromatics, which helps lower emissions while improving performance. Initial testing of EC Diesel showed up to a 15 percent reduction in particulates and a five percent reduction in NOx emissions, with no apparent loss in fuel economy. This is in comparison with today's California diesel, considered one of the nation's cleanest diesel fuels.
ARCO plans to confirm that its new EC Diesel fuel can make dramatic reductions in soot emissions from diesel-powered vehicles through an extensive demonstration program in Southern California. More than 160 vehicles from seven fleets will participate in this year-long demonstration. These include school and transit buses, pickups, refuse trucks and tractor-trailer rigs. A key goal is to show that existing diesel trucks and buses, fitted with catalytic converters and running on EC Diesel can match or exceed the performance of vehicles powered by alternative fuels. ARCO plans to initially market EC Diesel in California, and later it could be distributed nationwide.
PuriNOxT Performance Systems
Lubrizol and Caterpillar are developing a low-emission diesel called PuriNOxT Performance System, a blend of additives, water and commercial diesel fuel. Compared to current diesel fuels, testing to date shows that PuriNOx reduces NOx emissions by 5 to 30 percent and PM emissions by 20 to 50 percent. PuriNOx can be used in any older or newer diesel engines without modification to fuel systems or engine hardware. PuriNOx fuel would be blended in the field using portable and automated PuriNOx blending units that combine the PuriNOx additive package, water, diesel fuel and, when necessary, seasonal components like freeze depressants. The blending unit could be purchased or leased.
How does PuriNOx reduce NOx and PM? Water blended into the PuriNOx fuel lowers peak combustion temperatures so less NOx is produced. PuriNOx also delays combustion slightly so fewer particulates are produced.
In contrast to aqueous (fuel-in-water) blends that also reduce emissions, PuriNOx fuel is a water-in-fuel emulsion. According to Lubrizol, when water droplets are dispersed homogeneously throughout the fuel, the blend takes on the characteristics of the fuel. Consequently, PuriNOx fuel behaves similarly to ordinary diesel fuel with regard to corrosion, lubricity and viscosity. In contrast, aqueous fuels take on the characteristics of the water. Thus, they are more prone to inefficient combustion. They also have higher viscosity and are more corrosive. Such blends also tend to be deficient in lubricity and are susceptible to mixing with water already present in the system.
The benefits of adding water to diesel fuel have been known for some time. However, the biggest obstacle has been keeping the mixture stable in storage. Lubrizol solved this problem by using specialized chemistry to encapsulate the water droplets. At room temperature, PuriNOx fuel remains a completely homogeneous emulsion for a minimum of two months. Beyond two months, gravity causes the larger emulsion droplets to gradually settle, resulting in slightly higher concentrations of water at the bottom of a storage container. However, the fuel is still considered to be stable, and with any agitation, the larger droplets will re-disperse. With the slightest movement or agitation, PuriNOx fuel remains stable for a minimum of three months in fuel tanks and storage tanks.
Because water supplies no energy, there may be a reduction in peak horsepower and torque when using PuriNOx, which is partially compensated for by the fuel's increased thermal efficiency.
The PuriNOx additive package does add several cents to the price per gallon. However, when the fuel and water is blended, some fuel is displaced. This means less diesel fuel is actually contained in each gallon. The bottom line is that users may experience increased operating costs because larger quantities of more expensive PuriNOx fuel will be consumed to provide equal horsepower. These cost increases may be compensated by tax incentives and/or air pollution credits.
PuriNOx fuel is being tested in Ohio and California at multiple locations in a variety of engines. Once testing is complete, marketing should start in California, New England, the Midwest, Mid-South, Texas and Arizona. Initially, the PuriNOx Performance System will be sold to fleets, distributors and suppliers that do their own fueling.
Bill Siuru, PhD, PE, is a technology journalist who resides in Colorado Springs, CO.