Low Temperature Aftertreatment for Future Engines Challenges and Opportunities

Transcription

1 Low Temperature Aftertreatment for Future Engines Challenges and Opportunities Is it needed? Is high possible?? Is it affordable??? Kushal Narayanaswamy Propulsion Systems Research Lab General Motors Global R&D, Warren, MI Acknowledgements Paul Najt & Chang Kim 1

2 Drivers for Next Generation High-Efficiency Low-Temperature Aftertreatment US 54.5mpg in 2025 EU 58mpg in 2020 CN 56mpg in 2020 Global Fuel Economy Requirements Criteria Emission Regulations 2

3 Challenges Exhaust Temperature Thermal Durability (Robust Aging) PGM Management Fuel Economy Improvement Enabling Cost-Effective Aftertreatment Technology Particulates Exhaust Oxygen N 2 O, Sulfur Content 3

4 1. The Exhaust Temperature Challenge* Downsize Boost Lean: The use of lean-burn enhances efficiency, but dramatically reduces exhaust temperatures, impeding catalyst performance at light loads Downsize Boost: Energy extracted by turbocharger lowers exhaust temperature Downsize Boost w/egr: Addition of high levels of EGR lower exhaust temperatures degrading catalyst performance at light loads REDUCED EXHAUST TEMPERATURE 2. Manage peak temperature to minimize catalyst performance loss & thermal degradation * Excluding cold start 4

5 Exhaust Temperature ( C) Downsize Boosted Lean Exhaust Temperatures (max efficiency calibration) Min. T for HC Exhaust Port Turbo Out Under Floor NMEP (kpa) RPM FTP Points

6 Fuel Penalty (%) Fuel Penalty for Raising Exhaust Temperature With Incidental Heat Loss of 20% Without Heat Loss T after Cold Start ( C) ~ 2-3% fuel penalty is estimated to raise the exhaust temperature by 50 C 6

7 Exhaust Thermal Management. Strategy Catalyst Temperature > 300 C Fuel Penalty Stop/Start + - CAT 1 CAT 2 CAT 3. Stop/Start with Aggressive DFCO CAT 1 CAT2 CAT 3 Lambda/split ++ + CAT 3. EHC during idle EHC during deceleration CAT 1 CAT 2 CAT 3 EHC during deceleration + Stop-Start CAT 2 CAT 3 EHC = Electrically Heated Catalyst CAT 1 CAT 2 CAT 3 6/6/2013 7

8 Limitation of Low Temperature Performance Activity NOx & Temp NOx & Temp Oxidation Efficiency Limit over Conventional PGM-based TWC Temperature Sensitivity of Ammonia-SCR for NO x Efficiency Tail Pipe NOx SCR In Temp Optimal Temperature for SCR FTP75 Optimal Temperature for SCR T ~ 50 C (GM-POSTECH, Chemical Engineering Journal 2012) Time (sec) Can models help address the low temperature challenge? 8

9 PGM Content and Thermal Durability For Lean-Burn Exhaust Condition NO to NH 3 conversion Conversion C 3 H 6 TWC formulation: 100% 80% 60% 40% % t Temperature ( C) Pd Pd/Pd+Ce Pd+Ce LNT LNT-only Pd-only 0% TWC inlet T ( C) (ORNL, DEER 2012) Inlet Temperature ( C) (GM-PNNL, Catal. Today 2012) 9

10 The Exhaust Oxygen Challenge Passive Ammonia SCR System Lean NO x Trap - High PGM Cost - Sulfur Poisoning - Desulfation Required Conventional TWC - Poor NO x efficiency with DFCO / Lean Urea-SCR - Secondary urea tank with injection system; high urea consumption for gasoline - Urea Solution Freezing EXHAUST OXYGEN CONTENT

11 PASS - How Does It Work? Urea-Free SCR System RICH NH 3 H 2 O TWC LEAN NO x SCR N 2 DURING RICH: NO x + H 2 /CO NH 3 + CO 2 Use H 2 and CO to generate NH 3 over TWC and store NH 3 in multiple SCRs DURING LEAN: NO x + NH 3 N 2 + H 2 O Use the stored NH 3 for lean NO x conversion

12 FTP Cycle Results from Homogeneous Charge Application with DFCO & Lean Idle WRAF DFCO / Lean-idle NO x Post-TWC NO x TWC Converter TWC AFR Toggling SCR Converter NH 3 SCR Tailpipe NO x Tier2 Bin3 NH 3 produced over TWC with simple AFR toggling allowed SCR to remove NO x effectively

13 Vehicle Speed (km/h) NEDC Results from Stratified Charge Application Extended Lean Operation Post-TWC NO x TWC Converter SCR Converter WRAF TWC Multiple SCRs Tailpipe NO x Euro VI 100 NH 3 /NO x ratio is always greater than 1 over SCR for maximum conversion efficiency

14 Cum N2O (mg/km) Vehicle Speed (km) Cumulative N 2 O Comparison: TWC vs LNT TP N2O with TWC only TP N2O with TWC+LNT Vehicle Speed (km) Test Time (s) ~40% lower N 2 O was produced over TWC only aftertreatment architecture (e.g. PASS) 14

15 Particle Size Distribution Gasoline vs Diesel UW-PNNL-GM, 2012 DEER SIDI particle size distributions are shifted to the smaller end compared to diesel SIDI soot aggregates tend to be less compact than diesel particles (relevant to filtration) SIDI soot resulting from all fuels tested had very high organic content which was tightly integrated with the inorganic carbon (relevant to regeneration)

16 Vehicle Telematics and Aftertreatment 6/6/

17 Summary and Future Research Needs Available exhaust energy is going down as engine efficiency improves Increased constraints on aftertreatment system Engineering solutions can take you only so far Fundamental experiments and modeling needed to address key knowledge gaps pertaining to low temperature aftertreatment Key areas of research include Surface chemistry and physics for high-efficiency, low-temperature catalysis and filtration Interactions between reaction and diffusive transport phenomena to enable low back-pressure, high filtration, and reduced gaseous emissions in a single device Robust models providing insights on performance and methods of optimizing configurations 6/6/

18 Thank You! 18