Future Directions in Diesel SCR Systems

Transcription

1 Future Directions in Diesel SCR Systems 2012 CLEERS Workshop Christine Lambert Ford Research and Advanced Engineering Dearborn, MI May 1,

2 Outline Background of a 2010 U.S. SCR system Catalyst development challenges Catalyst and filter structures LEVIII catalyst system predictions Greenhouse gases (N 2 O) Summary / Next steps Acknowledgements May 1,

3 2010 U.S. Super Duty Diesel Aftertreatment aqueous urea 2011 model year trucks >8500 lbs (MDV) Certified as complete vehicle on LD FTP-75 LEVII emissions (0.2 g/mi NOx) 120,000 mi durability media.ford.com, 2011 May 1,

4 Diesel Fraction of New U.S. Vehicle Sales % Diesel Market Share Cars Class 1 + Class 2 trucks Class 2b + Class 3 trucks Class 2b trucks Class 2b trucks (Ford+GM+Chrysler) Class 3 trucks (Ford+GM+Chrysler) Trucks Class 3: 10,001-14,000 lbs Class 2b: 8,501-10,000 lbs Trucks Class 1: < 6,000 lbs Class 2: 6,001-10,000 lbs Cars Year Wallington et al., Energy Policy, in press May 1,

5 A Brief History of U.S. Diesel Aftertreatment Evolution of emissions standards for NOx and PM. Emission standards applicable for medium-duty diesels (g/[bhp hr]) NOx PM Model Year mid-1990s: Diesel oxidation catalysts (DOCs) with ceria and alumina for PM oxidation 2007: 2010: ultra-low sulfur diesel, particulate filters for PM control high precious metal DOCs lean NOx control (NOx traps) lean NOx control (urea SCR) Wallington et al., Energy Policy, in press. May 1,

6 Timeline for 2010 Diesel Aftertreatment 7/01 Ford s DOE Contract starts Research 12/05 Ford s DOE Contract ends Advanced Forward Model Ford research on SCR ~ Parallel Research on SCR and LNTs 1Q05 Ford s 2010 Diesel Program starts 4Q05 Urea SCR selected for 2010 Diesel 2Q06 Enhanced Cu/zeolite durability achieved 3Q07 Diesel Catalyst RFQ to Suppliers 4/10 Super Duty J1 11/10 Super Duty J2 Decision to chassis certify K lbs not exactly to scale May 1,

7 Diesel Aftertreatment Layout DOE Program Truck 6000 lbs LDDT Pt DOC Cu/beta SCR Pt CDPF exhaust flow NOx sensor PM CO 2 CO CO 2 NO + NH 3 N NH 2 3 N 2 DOC* HC CO 2 HC,CO CO DOC* 2 Pt DOC Spray Target urea SCR CDPF Cu/beta Pt to engine intake 2011MY Super Duty 8,500 14,000 lbs Pd-rich DOC Cu/CHA SCR Pt/Pd CDPF Pd-rich Cu/CHA Pt/Pd May 1,

8 A Few Challenges Faced During Commercial Urea SCR System Development Low exhaust gas temperatures Catalyst thermal stability HC poisoning/coking of SCR Precious metal poisoning of SCR Catalyst deterioration by sulfur Catalyst system cost May 1,

9 Temperature (C) Temperature Operating Windows SCR Inlet Temperature on FTP Test Time (s) Ford 3.5L GTDI (5250 lbs) Ford 2011MY Diesel (9500 lbs) Diesel truck has very low exhaust gas temperatures Vehicle speed (mph) May 1,

10 Conversion Efficiency Thermal Stability of DOC HC Light-Off Conversion 2-Mode 100 hrs / 300 ppm S + 20 mgp/gal 2:1 1:4 20:1 Pt only Addition of Pd to Pt has a stabilizing effect for HC oxidation during cold-start Temperature (Deg C) 50% NO 2 :NO x 40% 2:1 Pd also stabilizes Pt for NO oxidation but has no inherent activity itself % NO 2 of Total NO x 30% 20% 10% 20:1 1:4 Pt only 0% Temperature (C) May 1,

11 Thermal Stability of SCR Catalyst Thermal stability of Cu/zeolite recently improved from 750 to 900 C (Cu/beta Cu/CHA) NO 2 no longer needed for low temp conversion Lower cost aftertreatment now possible 4NH 3 + 4NO + O 2 4N 2 + 6H 2 O Cavataio May 1,

12 HC Poisoning/Coking of Zeolitic SCR SCR HC/coking issue resolved by transition from Beta to CHA. DEER 2004 May 1,

13 Precious Metal Poisoning of SCR EVALUATION of DYNAMOMETER AGED FeSCR CATALYST Lab flow reactor Pt poisoning of Cu SCR by upstream DOC NOx Conversion (%) st Inch (Inlet) 2nd Inch 3rd I nch 4th Inch 5th Inch 6th Inch (Outlet) NOx Conversion (%) Non - Contaminated Contaminated C atalyst Temperature (ºC) Inlet Gas Temperature (ºC) Pt from upstream DOC can volatilize and interfere with SCR function Prime indicators are increased NH 3 oxidation and N 2 O make Front section of catalyst most affected and can be regenerated Pt DOC may be stabilized with addition of Pd and lower exotherm Ts SAE SAE May 1,

14 Sulfur Effects on Cu/zeolite NOx conversion (%) Effect of 120K mi at 15ppm fuel sulfur degreened 120k mi sulfated 10 after regen at 650 C Catalyst Temperature ( C) % NOx Conversion Effect of 20ppm SO2 at 200 C (Calculated miles based on 15ppm fuel sulfur) Temperature( C) 0 miles 500 miles Sulfur affects NOx activity below 300C Sulfur can be removed by lean filter regeneration conditions (>650C) Amount adsorbed between regens can be tolerated based on 15 ppmwt S in diesel fuel DEER 2004 May 1,

15 140 Catalyst Cost Impact Precious Metal Usage in Super Duty DOCs MY J1 DOC+SCR+CDPF DOC +CDPF Pt rich Pd rich 2011MY J2 DOC+SCR+CDPF 20 DOC only PGM Content Pt Equivalence May 1,

16 2012 MDV Cert Data 0.45 Ford, GM, Daimler, Isuzu use Urea SCR Dodge uses LNT TP NOx (g/mi) TP NMHC (g/mi) lbs GVW lbs GVW May 1,

17 Future Implications for Chassis Certified Diesel MDV All 8501 to 10K lbs must chassis certify (~2016MY) FUL increased to 150,000 mi (2016MY start) SFTP at FUL (all emissions level lower than ULEV340 or ULEV570 require SFTP) K lbs US06 + SC03 10,001 14K lbs: LA92 + SC03 CO 2 reporting (2012MY) Greenhouse gases (CH 4, N 2 O - reporting in 2012MY, regulated in 2013MY) May 1,

18 Accelerated Aging Conditions Equivalent to 150K mi Hydrothermal Oven: DOCs 900 C, 80hrs SCR catalysts 800 C, 80hrs SCR filter 800 C, 80hrs Slip catalyst 750 C, 80hrs May 1,

19 Chassis Cert Data ( ,000 lbs GVW) 0.35 TP NOx (g/mi) ~75% less NOx SULEV150 SULEV170 ULEV200 ULEV340 LEV TP NMHC (g/mi) May 1,

20 Chassis Cert Data (10,001-14,000 lbs GVW) 0.6 TP NOx (g/mi) ~75% less NOx SULEV200 ULEV270 ULEV570 SULEV230 ULEV400 LEV TP NMHC (g/mi) May 1,

21 Potential SCR Technologies: SCR Filter From Engine To Tailpipe DOC SCR DPF From Engine Urea To Tailpipe Engine DOC Urea SCR Filter Simplified Tailpipe DOC SCR SCR Filter Urea Higher Performance May 1,

22 Modeling Implications of SCR Filter Technology Low Porosity Flow Through High Porosity Flow Through High Porosity Wall Flow Low Pore Volume Small Pore Size High Pore Volume Larger Pore Size High Pore Volume Larger Pore Size Wall flow vs channel flow Lower washcoat loading per volume Backpressure sensitive May 1,

23 4.4LPrototype Light Duty Diesel Test Cycle: US FTP-75 Turbo DOC urea Mixer SCR SCR SCR Filter Slip 0.10 case 1 Engine calibration changes Urea calibration changes Heating strategies ~1.8% FE Increased PGM SCR filter helps at higher SV TP NOx (g/mi) case 4 case 5 case 3 case SULEV TP NMHC (g/mi) (b) SAE May 1,

24 Future SCR Technologies Extruded zeolite offers higher density of active material Replace one or more bricks for higher performance Downsize the SCR System From Engine To Tailpipe DOC SCR DPF From Engine Urea To Tailpipe DOC exscr escr DPF Urea May 1,

25 Modeling Implications of Extruded SCR Technology Higher backpressure due to thicker walls Slower warmup due to greater mass Higher SV if downsizing Different cell geometry Washcoated Washcoat collects in corners, resulting in circular flow channels. Extruded Flow channels are assumed to be square. w s α w s α May 1,

26 NOx Conversion vs. CuZ Content NO conversion (%) SCR Filter 1xSCR 2xSCR or 1x exscr 2xexSCR % NO conv at 200C % NO conv at 300C Normalized CuZ content May 1,

27 Predicted FTP-75 NOx Efficiency FTP-75 NOx conversion (%) (9500 lbs diesel truck at 150K mi) SULEV150 NOx conversion with an avg 2012 TP NMHC 75 ExSCR SCR+SCR Filter 2xSCR ExSCR+SCR ExSCR+SCR Filter 2xExSCR + SCR Filter System SCR Content May 1,

28 Passive and Active Heat Management: FTP-75 prescr T 250 Temperature Pre-SCR Bag Temperature (deg C) Green Line - Baseline Blue Lines - Double Wall/Heat Wrap Through DPF Red Line - Strategy changes for Heat Management Time (sec) Goal: manage heat while not impacting fuel economy or HC May 1,

29 Greenhouse Gases (2013+) MDV standards 50 mg/mi CH 4 50 mg/mi N 2 O Composite of FTP-75 (55%) and HWFET (45%) N 2 O factor =298 for CO 2 equivalence May 1,

30 N 2 O from Diesel SCR Systems on FTP FTP-75 N 2 O as measured (mg/mi) engine out post DOC post SCR post DPF Test number Half of N 2 O from HC + NOx on DOC Other half of N 2 O from Urea SCR Submitted to IJPT May 1,

31 N 2 O from Diesel SCR Systems During Filter Regeneration on FTP Exhaust temperature (C) & postscr NH 3 (ppm) N 2 O (ppm) Test time (s) postdoc N2O postscr N2O postscr NH3 postdoc temperature postscr temperature postdpf temperature Submitted to IJPT May 1,

32 Composite N 2 O for 9500 lbs diesel truck FTP-75 FTP-75 w/regen HWFET Composite Weighted CO 2 equivalence N 2 O (mg/mi) % N 2 O formation pathways found: Engine out HC +NOx --> DOC N 2 O DOC NO --> SCR NO 2 --> SCR N 2 O N 2 O minimized by: - low loaded, Pd-rich DOCs - Cu/CHA SCR Submitted to IJPT May 1,

33 Summary Diesel catalyst system development has unique challenges that were overcome Potential SCR technologies such as extruded SCR and SCR filter may help meet future standards Calibration and heat management will also play an important role The sources of N 2 O within the diesel SCR system are understood May 1,

34 Next Steps for Diesel MDV Materials cost reductions continue PGM reductions substitution of Pt with Pd Assess future emission impacts FTP-75 filter regen penalty SFTP PM GHG May 1,

35 Acknowledgments DOE: DE-FC26-01NT41103 ( ) Ford: VERL team, Jeff Hepburn, Douglas Dobson, James Warner, Jeong Kim, Giovanni Cavataio, Kevin Guo, Yisun Cheng, Cliff Montreuil, James Girard, Hungwen Jen, Scott Williams, Dave Kubinski, Brendan Carberry, Rick Soltis, Devesh Upadhyay, Michiel van Nieuwstadt, Mike Levin and many others Catalyst Suppliers: BASF, JMI, Umicore And many, many more May 1,