Changes Coming to SCR for Model Year 2011 Vehicles?


The EPA and California Air Resources Board held a joint workshop that presented preliminary proposals to reconsider 2010 engine certification requirements when it comes to Selective Catalyst Reduction systems in heavy-duty trucks, especially when those systems run low or completely out of diesel exhaust fluid.

The workshop was announced on July 8 on the Federal Register to look into the possible issue, first raised by Navistar, the chief opponent of SCR in favor of its Exhaust Gas Re-circulation system to meet 2010 NOx emissions standards. EGR addresses the pollutants directly in the engine while SCR uses aqueous urea, or DEF, to treat NOx emissions downstream in the tailpipe. The issue is a relevant one for school bus operators interested in purchasing either system for medium-duty engines and has sparked much controversy and sales competition over the past two years.

EPA currently addresses the potential of operators running SCR on an empty or low tank of DEF with existing regulations regarding allowable and necessary maintenance and adjustable parameters, including a reserve tank of DEF than can supply the vehicle for several hundred miles even after the driver gauge reads empty. These also apply in the case where the SCR system may have been tampered with, such as an operator filling the DEF tank with water. Certified engine configurations include provisions and inducements designed to address these regulatory concerns. EPA previously provided guidance to heavy-duty diesel engine manufacturers in March 2007 and December 2009 to facilitate manufacturer planning in advance of certification. Then, last November, EPA published its approval of specific maintenance intervals for DEF refills for certain manufacturers.

The July 20 workshop reviewed EPA’s current policies for 2011 and later model year engines to ensure that the SCR systems correctly limit levels of NOx. A CARB representative later said that hardware changes could be made for 2011 model years but that there remained a lot of work to be done to determine what, if any, updates are necessary. She did not rule out the possibility that any changes would need to be delayed until the 2012 model year.

Navistar presented a study it commissioned from EnSight LLC, an environmental consulting company based in Walnut Creek, Calif., that found that a lack of DEF can lead to a spike in NOx emissions. When liquid urea was not present, the research showed little or no effect on the vehicles’ operations. This could mean that the engines could go no longer comply with the federal regulations. 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.

Meanwhile, Cummins representatives told the EPA and CARB that the DEF gauge located on the driver’s dash and warning lamps indicated when the tank needs to be refilled. In the August issue of School Transportation News, a representative of a Thomas Bus Dealer in Wisconsin that has been testing a 2010 SCR school bus since February likened running out of DEF to running out of fuel. Cummins added during the workshop that “[t]hese vehicles are driven by the most professional operators on the road, with daily maintenance checks required for the vehicles. They have a job to do, and when doing a single new fluid check will avert a significant speed limitation and torque de-rate during that job, we are confident that they will do it.” It also pointed out that DEF is readily available at dealers, truck stops and retail outlets nationwide.

Cummins also cautioned that any “inducement strategy applied by EPA and CARB to prevent SCR operators from running low or completely out of DEF “should not [sic] prevent an emergency vehicle from getting to a rescue site, nor should we create a hazardous road condition.” Cummins said that, with 2011 only six months away, “it is not feasible to make changes to these already-developed products without compromising quality.”