23 April 2011
This year’s SAE Congress, held on April 12-14 in Detroit, continued to use the new format adopted last year, with a three-day condensed schedule and 20-minute presentations. In addition to the technical paper presentations, there were numerous oral-only open forums, keynote talks and various “chats with experts”. While the technical level of the conference was high and the meeting rooms were full during several of the engine and emission sessions, the exhibition accompanying the Congress remained downsized, not yet recovered from the economic recession.
The diesel exhaust emission control sessions started with a keynote talk by Tim Johnson of Corning [2011-01-0304] that reviewed changes affecting diesel exhaust emissions control. The major regulatory challenges that will drive engine development in the coming years include the LEV III emission standards for light-duty vehicles being developed in California (it is believed that these will be followed by US federal Tier 3 standards) and CO2/fuel economy regulations for light- and heavy-duty vehicles worldwide. The technical topics covered included engine developments, NOx control, PM control and hydrocarbon and CO control. Manufacturers are focusing on optimization and cost reduction of their emission systems. This includes a growing effort to downsize or eliminate aftertreatment. For example, the Skyactive-D engine under development by Mazda targets Tier 2 Bin 5 emissions without NOx aftertreatment and several nonroad manufacturers intend to meet Tier 4 standards without the use of diesel particulate filters (DPF).
The LEV III standards are believed to eventually require an NMOG+NOx fleet average equivalent to the SULEV or the federal Tier 2 Bin 2 certification level. This presents a challenge for both gasoline and diesel emission control systems, especially during the cold start phase. In developing their diesel engines marketed under the BlueTec badge, Daimler considers three LEV III approaches: (1) a passive NOx adsorber + DPF + SCR, (2) a close-coupled SCR-on-DPF device or (3) a system utilizing an electrically heated catalyst + DPF + SCR [2011-01-0294].
NOx Aftertreatment. Most papers on NOx aftertreatment focused on urea-SCR—a technology that allows for a fuel efficient engine calibration to provide simultaneous reductions of NOx, PM and CO2 emissions. Some of the highlights in urea-SCR sessions included:
- Hino Motors [2011-01-1309] presented a summary of their US 2010 SCR system. The system uses a muffler mounted burner not only for active DPF regeneration but for SCR catalyst heat-up. By using the burner, urea injection can start about 100 s after engine start while without, the time is extended to 600 s. The faster warm up time is reflected in FTP NOx emissions: 0.25 g/bhp-hr without the burner and 0.18 g/bhp-hr with the burner.
- Johnson Matthey [2011-01-1312] provided a glimpse of what they are proposing for heavy-duty applications subject to fuel economy requirements. By replacing the diesel particulate filter with a diesel particulate filter coated with an SCR catalysts (SCR-DPF) and keeping the flow-through SCR elements downstream, the SCR volume in the after-treatment assembly can be increased substantially without affecting the overall packaging. This can allow much higher NOx conversion efficiencies and allow engines to be calibrated to higher engine-out NOx levels such as 4.5 g/bhp-hr or even higher and operate at higher thermal efficiencies.
- Ecocat [2011-01-1316] presented their approach to EU Stage IIIB and Stage IV DPF-free aftertreatment systems based on vanadium SCR catalysts. The SCR system is required to provide 50% NOx reductions for Stage 3A and 80-95% for Stage 4. the high conversion target will affect the required catalyst amount and dosing strategy margins, particularly after aging. No significant vanadium loss was observed from the SCR catalyst but some activity loss due to sintering was noted.
Conference website: www.sae.org/congress