27 April 2010
This year’s SAE Congress, held from April 13-15, had a number of significant changes from previous years. The most notable change was the condensed schedule over 3 days instead of 4 days as in the past. To partly make up for the lost day, sessions started at 8am and presentations were held every 20 minutes. This left little time for questions and discussion. This year also saw members paying if they wanted to attend for more than one day. SAE’s member benefit of $99 was only good for one day’s attendance which meant that SAE members wanting to attend the entire three days had to pay as much as $500. In addition to the technical paper presentations, this year’s meeting had numerous oral only open forums, keynote talks and various “chats with experts”.
The Diesel Exhaust Emission Control sessions started with a keynote talk by Tim Johnson of Corning [2010-01-0301] that reviewed changes affecting diesel exhaust emissions control. Topics covered included regulatory developments, engine developments, NOx control, PM control and hydrocarbon and CO control.
NOx Control. Technical papers related to NOx control mainly covered urea SCR systems and systems that combine lean NOx traps (LNT) and SCR catalysts. There were also a few papers on LNTs and lean NOx catalysts.
Urea SCR. An important keynote address by Christopher Laroo of the US EPA discussed progress on a test program looking at dioxin, furan, PCB and PAH emissions from diesel engines that use Cu/Z SCR catalysts. To-date, steady state testing revealed no sign of elevated dioxin and furan emissions over Cu/Z SCR catalysts with typical fuel, engine oil and urea chlorine levels. The effect of chlorine in the intake air was not considered. The program will continue with transient tests planned for later this year.
A urea SCR paper by Ford [2010-01-1183] covered a system for achieving EPA Tier 2 Bin 5 NOx emissions using a Euro 4 compliant 2007 2.7L V6 Land Rover. In order to achieve these emissions with this vehicle, the SCR system has to provide high NOx conversion soon after a cold start. To this end, the aftertreatment system included a DOC close coupled to the engine, a stand-alone Cu/Z SCR catalyst and a DPF that also included a Cu/Z SCR coating. This effectively provided two SCR catalysts arranged in series. Maximum NOx conversions are achieved when an SCR catalyst is loaded with ammonia to as close to its Threshold Storage Capacity as possible. This however creates the risk that significant ammonia will be released if the SCR catalyst temperature rises. With this system, the first SCR catalyst is loaded with ammonia as soon as possible after a cold start and the SCR coating on the DPF is intended to capture any ammonia released from the first SCR catalyst. To meet the design objective of Tier 2 Bin 5 NOx and NMHC emissions, engine out NOx also needed to be adjusted with the EGR calibration and an SCR warm-up strategy using post injection of fuel was required.
Daimler provided some details of the BlueTec system for 2010 NAFTA Sprinter vans [2010-01-1172]. The aftertreatment includes a DOC followed by a DPF and 2 urea-SCR catalysts. Daimler chose the vehicle certification option. Over an aging period of 120,000 miles, NO2/NOx ratios remained in the 35-52% and ammonia slip less than 10 ppm. Overall NOx reduction is above 90%. A comparison of Daimler’s NAFTA 2007 and NAFTA 2010 Sprinter vans in the 8,501-10,000 lb GVW category are summarized below:
|Power||154 hp (115 kW)||188 hp (140 kW)|
|Torque||280 ft-lb (380 Nm)||325 ft-lb (440 Nm)|
|FTP75 NOx||1.41 g/mi||0.16 g/mi|
|FTP75 fuel economy||17.9 mpg||17.7 mpg|
|HWFET NOx||0.83 g/mi||0.34 g/mi|
|HWFET fuel economy||24.3 mpg||24.7 mpg|
Urea (AdBlue or DEF) consumption in this weight class vehicle is estimated at 1.5-2.0 L/1000 miles while for the 10,000 lb and over weight class, it is estimated at 1.7-2.5 L/1000 miles.