Some SCR Systems Not Controlling NOx, Navistar Says

During a California Air Resources Board (ARB) workshop, Navistar International Corporation said it identified compliance loopholes found in current liquid-based selective catalytic reducation (SCR) systems.

The ARB workshop on July 20 invited stakeholders to discuss the SCR system attributes that will be evaluated during staff review of an application for certification. The U.S. Environmental Protection Agency participated in the workshop, which was held at an ARB office in El Monte, Calif.

SCR is the primary control strategy for nitrogen oxides (NOx) for most heavy-duty on-road diesel engines. Because SCR systems involve operator intervention, SCR systems should be designed to ensure compliance and continued safe vehicle operation, an ARB press release said.

Navistar’s concerns were supported by independent test findings that show new commercial vehicles that must contain liquid urea to meet federal NOx emissions standards continue to operate effectively when urea is not present. At such times, Navistar said, the vehicles emit levels of NOx as much as 10 times higher or more than when urea is present.

The research was conducted by EnSIGHT, an independent environmental consulting firm, using two long-haul vehicles and one heavy-duty pickup, all of which use SCR technology that relies on liquid urea to clean up NOx emissions after they leave the engine.

EnSIGHT’s research showed that when liquid urea was not present, there was little or no effect on the vehicles’ operations. This included long periods of time when the vehicles’ urea tanks were empty or were refilled with water instead of urea. One truck tested appears to operate indefinitely with water and, as a result, without any functioning SCR NOx control. That truck has accumulated more than 13,000 miles with its SCR NOx emission control turned off.

European research also has shown that even with a full tank of liquid urea, the SCR NOx emission control system does not turn on when exhaust temperatures are not hot enough. This occurs during stop-and-go traffic. That means that there is frequently no SCR NOx control when these trucks are operating in urban areas as well as in any other congested traffic situation.

Navistar, which commissioned EnSIGHT’s work, joined two the Coalition for Clean Air and Environment Now in calling on the EPA and CARB to eliminate the loopholes and the resulting excessive NOx emissions. Jack Allen, president of Navistar’s North American truck group, said, “We will be working with the EPA and CARB to ensure full environmental compliance.”

“Truck owners are paying a substantial price to comply with 2010 NOx requirements,” said Allen. “They, and the public, deserve to know that the new equipment they are purchasing actually works as promised to curb pollution. It’s obvious, however, that these trucks can operate effectively without liquid urea, and that under these and other conditions, SCR NOx emission control is turned off. We’re calling on the EPA and CARB to assure that all vehicles, not just ours, work when they are supposed to be working.”

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