Conference report: 9th CTI Forum Exhaust Systems
14 February 2011
The 9th International CTI Forum: Exhaust Systems was held on January 24-27, 2011 in Stuttgart, Germany. The four-day program started with an introductory workshop on emission control from diesel and gasoline engines (S. Carstens, EngineSens). Forum presentations during the following days covered diesel exhaust aftertreatment and other engine emission control technologies, with the last day focusing on exhaust gas recirculation. The Forum also included a tour to the Mercedes-Benz V6 and V8 gasoline engine plant in Stuttgart-Untertürkheim.
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Regulatory Perspectives. The forum opened with an overview of emerging trends in emission regulations and emission control technology for diesel and gasoline engines (T. Johnson, Corning). California is developing LEV III emission standards for model year 2014-2022 light-duty vehicles, which are about to enter a formal proposal stage. The ultra-stringent emission limits considered for the LEV III stage include a fleet-average NMOG+NOx limit of 30 mg/mi—equivalent to the SULEV certification bin—a PM mass limit of 3 mg/mi (2017) and an optional SPN (solid particle number) limit of 6×1012 1/km. The PM limit could be further strengthened to 1 mg/mi from 2021. These PM limits may require the introduction of particulate filters on gasoline engines—R&D work on gasoline particulate filters (GPF) has already started.
In heavy-duty engine and vehicle technologies, new challenges will be brought by future fuel economy and greenhouse gas emission regulations. Regulations for heavy-duty onroad vehicles have been already adopted in Japan (fuel economy), have been proposed in the United States (GHG emissions) and are under development in the EU (CO2 emissions). While different regulatory approaches are being followed, all of the regulations will require significant improvements in engine and vehicle efficiency. For instance, under the US EPA proposal, engine efficiency would have to improve by about 6% and vehicle efficiency by 15% by 2019, with tougher requirements expected afterward.
Exhaust Gas Recirculation. EGR presentations covered both diesel and gasoline applications. EGR was once removed from gasoline engines, as the three-way catalyst could provide the required NOx reductions, but the technology is now re-introduced on turbocharged, DI gasoline engines (D. Styles, Ford). On gasoline engines, cooled EGR can improve fuel economy by reducing pumping work, improving combustion efficiency and decreasing enrichment used for catalyst protection. EGR can also improve knock tolerance. Manufacturers intend to extend the use of cooled EGR onto the entire engine map, but the increased heat rejection remains a challenge.
Future trends in diesel and gasoline EGR systems include the use of dual loop EGR systems, including a high- and a low-pressure EGR loop (A. Noble, Ricardo; M. Becker, BorgWarner). This strategy allows for increased EGR rates to meet diesel NOx emission standards (Euro 6, US Tier 2 Bin 5) and for CO2 reductions in gasoline engines. Combined with two-stage boosting systems, dual-loop EGR enables aggressive engine downsizing and further CO2 emission reductions. Several specific EGR topics were also discussed, including EGR control issues, EGR mass flow and temperature sensors (C. Ganseman, Sensor-Nite) and EGR cooler fouling (D. Styles, Ford).
Exhaust System Materials. ThyssenKrupp (K. Zimmermann) introduced tailored products for exhaust systems, including tailored blanks, coils and tubes. In the tailored products, materials of different thickness and grade are welded together, allowing for weight reductions. For instance, tailored blanks for an exhaust muffler can include heavier gauge material in the header regions—to enable the complex stamping and provide the required strength—while lower thickness material can be used in the center part of the muffler. Examples of commercial mufflers were shown (by Eberspacher and Tenneco) that achieved weight reductions of 22-27% through the use of tailored blanks. The technology can also bring overall material cost savings, especially when used for larger size components.
The next CTI conference on diesel emission control will be held in Detroit, USA, on May 16-20, 2011.
Conference website: www.exhaustsystems-forum.com