30 June 2012
The 4th CTI International Conference: NOx Reduction was held on June 18-20, 2012 in Detroit, MI. The program started with two introductory seminars during the first day: “Basics of Exhaust Systems” (S. Carstens, EngineSens) and “SCR for Diesel Engine” (M. Khair, Watlow). Presentations during the following days—given by a number of fine speakers from the industry and academia—covered new developments in NOx aftertreatment, including urea-SCR and other technologies, as well as in-cylinder NOx control approaches in commercial and experimental, light- and heavy-duty engines.
The conference opened with an overview of worldwide NOx emission regulations for engines and vehicles (Joe Kubsch, MECA). California LEV III standards for light-duty vehicles, with a fleet average SULEV NOx+NMOG standard (0.030 g/mi) to be phased-in from 2015 through 2025 and 150,000 miles emission durability requirements, arguably present the biggest technical challenge. Federal Tier 3 standards—harmonized with LEV III—are anticipated from 2017, but the EPA proposal is unlikely before the US presidential elections (the expected Tier 3 fuel quality provisions would put some upward pressure on gasoline prices—an important election issue). Regardless of the time of adoption, the Tier 3 implementation schedule is expected to be harmonized with California (i.e., the federal standards would leap into the respective point on the LEV III fleet emission curve, skipping the initial years). For heavy-duty engines, standards of similar stringency to the US 2010 are being adopted by other countries. These include Euro VI and the proposed Japanese 2016 standards. However, contrary to US 2010, Euro VI standards additionally include a very stringent particle number limit which was introduced to ensure that particulate filters will continue to be used in the future. New, previously unregulated emissions are becoming regulated under the US GHG emission regulations—emission caps for nitrous oxide and methane put new demands on future emission systems.
Emission technologies for meeting regulatory requirements for criteria pollutants and greenhouse gases were reviewed by Tim Johnson (Corning). Some of the important trends include increasing BMEP, efficiency and reduced CO2 emissions in gasoline engines, which narrow the fuel economy difference between gasoline and diesel engines. Diesel engines, however, both light- and heavy-duty, also increase their efficiency. The BTE target of 50% for highway truck engines set by the US DOE is driving the development of a number of new technologies, such as exhaust heat recovery, turbo-compounding and hybrid powertrains. Highly efficient SCR systems are another important source of increased engine efficiency. SCR systems with NOx conversion efficiency on the order of 98% may become viable within a few years. The improvements in SCR technology include better catalyst formulations, higher cell density substrates (600 cpsi in post-DPF applications) and improved urea dosing strategies. With SCR systems of high NOx reduction efficiency, manufactures could optimize the diesel engine for efficiency and performance while the aftertreatment would ensure emission compliance—a scenario similar to that of the gasoline engine paired with highly efficient three-way catalyst.
Conference website: emission-control-systems.com