US EPA and California ARB examine urea-SCR engine certification requirements

22 July 2010

In a joint workshop held earlier this week, the US Environmental Protection Agency (EPA) and the California Air Resources Board (ARB) discussed certification of diesel truck engines equipped with urea-SCR NOx reduction technology. The EPA and ARB agreed to hold the workshop under the court settlements the two agencies reached with Navistar, who was challenging the legality of the SCR certification guidance adopted by the EPA and used in the process of emission certification of 2010 SCR truck engines by Navistar competitors.

Navistar, supported by the environmental groups Coalition for Clean Air and Environment Now, called on the EPA and ARB to eliminate regulatory ‘loopholes’ that can result in excessive NOx emissions from vehicles using urea-SCR technology.

Navistar quoted results from a study it commissioned from EnSIGHT, an environmental research consulting company. The study examined the operation of SCR trucks when urea was not present—including operation with empty urea tanks and with urea tanks filled with water—to conclude that there was little or no effect on the vehicles’ operations. One truck tested appeared 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.

These observations seem to indicate that some SCR trucks do not comply with the SCR certification requirements. The existing EPA guidance does require that vehicles with SCR technology include a ‘driver inducement’ functionality that makes it impossible to operate the vehicle without urea.

Navistar also indicated that SCR systems remain inactive when exhaust temperatures are low, such as during stop-and-go urban driving—an issue that has been identified by European research.

Navistar is the only major engine manufacturer who does not use the SCR technology in their 2010 truck engines, but the company is considering the use of ‘solid SCR’ technology in future engines.

Source: California ARB | Navistar