"The rule that the EPA has put into effect effectively says that the nitrogen oxide emissions have to be reduced, but they don’t dictate how to achieve that," explains Elisabeth Torsner, vice president--market development for Outokumpu North America, Schaumburg, Ill. "About 65 percent of the large diesel truck companies have said they’ll use the urea method. It’s not a mandatory method, but it seems to be the most popular."
Urea is an organic compound that’s primarily used as a nitrogen fertilizer in crop production. Currently, 90 percent of its production is used in this manner, but urea is also used for highway deicing, cloud seeding, animal feed, and plastic and glue production. Surprisingly enough, it’s also used for teeth whitening.
The automotive-grade, urea-based solution DEF, which stands for diesel exhaust fluid, as it’s referred to in the United States, and AdBlue, as it’s been dubbed in Europe, is injected as a mist into the hot exhaust stream. The heat breaks down the urea into ammonia, the true cleaning agent. Through the catalytic converter, the nitrogen oxide is broken down into nitrogen and water, which are both harmless to the environment.
The implementation of DEF has been shown to reduce nitrogen oxide emissions by 90 percent, and when it’s used in conjunction with diesel particulate filters, nitrogen oxide emissions can be reduced to nearly zero. Some also claim a 3 percent increase in fuel efficiency.
Outfitting an engine
If urea SCRs become a primary technology for reducing diesel emissions, then stainless steel, particularly duplex stainless steels like LDX 2101 from Outokumpu, will be the material of choice. The stainless steel will be used in the DEF system tanks and the injection components leading from those tanks, for urea solution storage tanks, and the pumps and nozzles that will deliver the fluid at gas stations.
"There’s actually an ISO standard for this urea fluid," says Torsner, referring to ISO 22241-3. "Within the standard, they talk about recommended materials, as well as materials not recommended. They’re pretty clear on this when they say, ‘Materials forming compounds as a result of a reaction with ammonia, which may negatively interfere with the SCR converter system are, carbon steels; zinc-coated carbon steels; mild iron; nonferrous metals and alloys like copper, copper alloys, zinc and lead; solders containing zinc or copper; aluminum; aluminum alloys; magnesium and magnesium alloys; and plastics or metals coated with nickel.’"
Basically, that leaves stainless steel and a handful of polymers. Torsner says many of these polymers can also contain additives, "which can be detrimental. You have to select the polymer with care."
Therefore, LDX 2101 has a major advantage because of its corrosion resistance. The reason is because DEF is such a clean substance. It’s 32 percent urea, with distilled water as the remaining ingredient.
"It can’t take any contaminants whatsoever," says Torsner. "All of the lightweight metals that could come into play leach metal ions. Stainless steel is leaching so little that it’s difficult to measure. It doesn’t corrode or leach because it has a passive surface layer, which prevents material to move from the outside in and from beneath the surface layer into the fluid. Stainless steel, per its definition, doesn’t leach; the stainless steel prevents contamination."
Some trucking companies might not necessarily be happy about the extra money they have to spend on these new components and the additional weight it takes away from their payloads. Therefore, the lighter the components can be, the better.
LDX 2101 offers twice the mechanical strength of ASTM 304, one of the oldest and most widely used stainless steels, and its nominal 1.5 percent nickel content lends to increased price stability--304 contains 8.1 percent nickel. And it’s just as anti-corrosive as 304, with good stress-corrosion cracking resistance. Its high strength results in lightweight components.
"The most important thing to understand is that on a truck, this is an extra weight to carry," says Torsner. "Everyone wants a lightweight container for this fluid."
According to Torsner, a tank in LDX 2101 would weigh about half as much as one designed with 304. The same holds true for the storage tanks at service stations.
"If you can design a storage tank in lean duplex, you can utilize that strength," says Torsner. "There are a lot of industries that use the American Petroleum Institute’s standards for tank construction. There actually aren’t that many design standards to work off in the United States, so a number of people use the API 650 standard to construct tanks. In API 650 Appendix X, there’s a data sheet for using duplex grades, including LDX 2101. So you can utilize this much stronger material and reduce the weight while still following those guidelines."
Getting the emissions message out
For service centers stocking LDX 2101, the demand can come from a variety of sources. Companies adopting the technology on the consumer end include Audi, BMW, Hyundai, Jeep, Kia, Mini Cooper, Volkswagen and Mercedes-Benz. Freightliner, Kenworth, Mack, Peterbilt, Cummins, Detroit Diesel and Volvo round out the commercial end.
"Service centers just need to be reminded that they already have it in their inventory and need to market it appropriately," says Torsner. "For trucking companies, the urea tank will call for sheet material, and for the exhaust, pipe is needed for the tubing leading into it. For the storage at service stations and fleet management stations, the fuel will require larger storage tanks, which will need even more sheet, plate and pipe material.This is a big market that we’re trying to alert."
Outokumpu provides LDX 2101 in sheet, plate and pipe. Plate is provided through the New Castle, Ind., mill; pipe from the Wildwood, Fla., mill; and sheet from Outokumpu’s European operations.
The regulation, therefore, equates to big opportunities for Outokumpu and for service centers that carry the appropriate material. Most important, however, are the big improvements that it offers the environment. The goal the EPA set forth is to effectively reduce the carbon monoxide levels in the atmosphere. Achieving that initiative will minimize the greenhouse effect and maximize humans’ time on this planet. MM