Fundamental Processes Controlling Ash Accumulation in Diesel Particulate Filters and Impacts on DPF Performance

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1 MIT Diesel Engine, Lubricant, & Aftertreatment Consortium Fundamental Processes Controlling Ash Accumulation in Diesel Particulate Filters and Impacts on DPF Performance 2012 DOE Crosscut Workshop on Lean Emissions Reduction Simulation May 2, 2012 Alexander Sappok V. Wong, C. Kamp, S. Munnis, I. Dimou, C. Chiou, Y. Wang, I Govani, M. Bahr, E. Cross, J. Kroll Massachusetts Institute of Technology Sloan Automotive Laboratory Cambridge, MA 1

2 Ash Accumulation Reduces DPF Life and Engine Efficiency Lube/ Fuel Engine-Out Emissions DPF Ash Accumulation DPF P Catalyst Efficiency & DPF Life Engine-Out Ash Emissions Source: K. Aravelli More Ash than Soot in DPF! DPF Lubricant Additives Ash Function Of: Incoming ash/soot particles Lubricant composition Exhaust conditions/regeneration Image: Adapted from ORNL DPF design parameters DPF operating history 2

3 Ash Accumulation and Deposit Formation Differs from PM! ~ 100 nm τ cr ~ 1 µm 3

Program Approach & Consortium Activities Holistic approach considering lubricant chemistry, engine operation, and aftertreatment design through combination of focused experiments and theoretical

4 Program Approach & Consortium Activities Holistic approach considering lubricant chemistry, engine operation, and aftertreatment design through combination of focused experiments and theoretical models. Models and Theory Build on Existing Framework Existing Knowledge Base Ash Properties Analysis Lab and Field Targeted Experiments Address Specific Knowledge Gaps Enhance fundamental understanding of key parameters controlling ash properties and impact on aftertreatment performance. 4

5 Experimental Facilities Cummins ISB 300 Variable geometry turbocharger Cooled EGR Common rail fuel injection Fully electronically controlled Gaseous and PM emissions measurement systems DPF Bench Reactors P, T Sensors FTIR DPF Core Accelerated Ash Loading 5

$X-Ray Diffraction Ash Exposed to$ and increasing use as part of DPF

6 Analytical Test Facilities Center for Materials Science (CMSE) Materials Analysis FTIR, Raman, XPS, Optical Microscopes Thermal Analysis TGA, ICP-OES Electron Microscopy SEM EDX, TEM, FIB Y X X-Ray Diffraction Ash Exposed to Elevated Temperatures Extensive and increasing use as part of DPF post-mortem analysis and ash characterization 6

7 Key Parameters Controlling Ash Deposits and DPF Impacts Engine-Out Ash Emissions and Transport Form of ash in exhaust/feed gas entering DPF; ash trapping efficiency Ash Deposit Accumulation and Build-Up in the DPF Agglomerate formation and ash mobility/distribution in DPF Ash Impact on DPF Pressure Drop Response Ash composition and properties relevant to DPF performance Sensitivity of DPF Design Parameters to Ash Accumulation Substrate materials, pore size & distribution, porosity Role of Engine Control Strategies and Exhaust Conditions Temperature, flow, and feed gas conditions affecting ash deposits Regeneration Processes Real-time optical studies of ash formation and mobility Ash Catalyst Interactions Chemical and physical interactions of ash and catalyst/washcoat 7

Lubricant-Derived Ash Precursors Bound to PM SAE 2007-01-0318 Counts 100 90 80 70 60 50 40 30 20 10 0 C Zn P S A2 A1 100 nm 10.4 10.0 9.6 9.2 8.8 8.4 8.0 7.6 7.2 6.8 6.4 6.0 5.6 5.2 4.8 4.4 4.0 3.6 3.

8 Lubricant-Derived Ash Precursors Bound to PM SAE Counts C Zn P S A2 A1 100 nm Energy [kev] Cu Zn Cu A1 A2 100 nm Lubricant-derived ash transported to DPF bound to carbonaceous PM Size of ash precursors of same order or smaller than PM agglomerates No lubricant-derived ash particles found separate from PM Cu peaks due to background from copper TEM grid 8

Nearly All Metallic Ash Components Trapped in DPF

trapping efficiency in DPF Trapping Efficiency Ca Fe

67% Elemental emission rates determined from ICP

9 Nearly All Metallic Ash Components Trapped in DPF 1682 rpm, 25% load (Steady-State) Measured elemental trapping efficiency in DPF Trapping Efficiency Ca Fe Mg P S Zn 99.87% 92.43% 98.01% 85.09% 64.89% 99.67% Elemental emission rates determined from ICP analysis Post-DPF PM sampling 20 hours for sample size of 2-3 mg 9

10 Particle Mass Spectrometer for Ash Measurements ASME ICEF Time-Resolved Mass-Spec Coating Evaporating Core Evaporating 10

11 Real-Time Measurement of Exhaust Ash Emissions (I) ASME ICEF Hz (ions/s) inject_rate SMPS Mass Boron Oil Injection Rate (ml/min) diameter (nm) :30 PM 10/11/10 40x :00 PM 6:30 PM 7:00 PM 7:30 PM 8:00 PM Date and Time Total SMPS Mass (ug/m3) 11

12 Real-Time Measurement of Exhaust Ash Emissions (II) ASME ICEF x Hz (ions/s) inject_rate SMPS Mass Zn Boron S K Na P Ca Oil Injection Rate (ml/min) signal, Hz 100 diameter (nm) :30 PM 10/11/10 40x :00 PM 6:30 PM 7:00 PM 7:30 PM 8:00 PM Date and Time Total SMPS Mass (ug/m3) 12

13 Key Parameters Controlling Ash Deposits and DPF Impacts Engine-Out Ash Emissions and Transport Form of ash in exhaust/feed gas entering DPF; ash trapping efficiency Ash Deposit Accumulation and Build-Up in the DPF Agglomerate formation and ash mobility/distribution in DPF Ash Impact on DPF Pressure Drop Response Ash composition and properties relevant to DPF performance Sensitivity of DPF Design Parameters to Ash Accumulation Substrate materials, pore size & distribution, porosity Role of Engine Control Strategies and Exhaust Conditions Temperature, flow, and feed gas conditions affecting ash deposits Regeneration Processes Real-time optical studies of ash formation and mobility Ash Catalyst Interactions Chemical and physical interactions of ash and catalyst/washcoat 13

Ash First Accumulates Along DPF Channel Walls ASME ICEF2009-14080 Channel Width [mm] Center Center - 18 mm

0 0 25 50 75 100 125 150 1.5 1.3 1.0 42 g/l Ash 0.8 (240K mile equiv.) Plug 0.5 0.

14 Ash First Accumulates Along DPF Channel Walls ASME ICEF Channel Width [mm] Center Center - 18 mm Center -36 mm Center Center - 18 mm Center -36 mm g/l Ash 0.8 (70K mile equiv.) g/l Ash 0.8 (240K mile equiv.) Plug mm 133 mm 57 mm 133 mm Axial Distance [mm] Ash accumulation reduces DPF volume and affects pressure drop 14

Initial Ash Deposition and Layer Formation Ash layer build-up evident by changing P profiles. Pressure Drop [Kpa] Benefit from ash layer formation 10.7 g/l Ash 0 g/l Ash 6.9 g/l Ash 3.

15 Initial Ash Deposition and Layer Formation Ash layer build-up evident by changing P profiles. Pressure Drop [Kpa] Benefit from ash layer formation 10.7 g/l Ash 0 g/l Ash 6.9 g/l Ash 3.0 g/l Ash DPF Ash PM Ash layer not fully established until 10 g/l or ~ 50,000 miles Pressure Drop [Kpa] 10.7 g/l Ash Soot Load 6.9 g/l [g/l] Ash 3.0 g/l Ash 0 g/l Ash Soot Load [g/l] 15

Application of Tracer Produces Stratified Ash Layers ASME ICEF2011-60072 Ash Thickness and Distribution 1400 Ca Ash Zn Ash Mg Ash Channel Width [µm] 1200 1000 800 600 400 200 0

16 Application of Tracer Produces Stratified Ash Layers ASME ICEF Ash Thickness and Distribution 1400 Ca Ash Zn Ash Mg Ash Channel Width [µm] Periphery Centerline Ash Plug Axial Distance [mm] 700 Ca Zn Mg Ash Layer Thickness [µm] DPF Substrate Axial Distance [mm] 16

Voids in Ash Plug Opportunities to Improve Packing ASME ICEF2011-60072 Voids may explain low ash

17 Voids in Ash Plug Opportunities to Improve Packing ASME ICEF Voids may explain low ash packing density Large voids throughout ash layer Start of plug and ash layer Si Ca Zn O Mg Al 17

18 Key Parameters Controlling Ash Deposits and DPF Impacts Engine-Out Ash Emissions and Transport Form of ash in exhaust/feed gas entering DPF; ash trapping efficiency Ash Deposit Accumulation and Build-Up in the DPF Agglomerate formation and ash mobility/distribution in DPF Ash Impact on DPF Pressure Drop Response Ash composition and properties relevant to DPF performance Sensitivity of DPF Design Parameters to Ash Accumulation Substrate materials, pore size & distribution, porosity Role of Engine Control Strategies and Exhaust Conditions Temperature, flow, and feed gas conditions affecting ash deposits Regeneration Processes Real-time optical studies of ash formation and mobility Ash Catalyst Interactions Chemical and physical interactions of ash and catalyst/washcoat 18

19 Additive Chemistry Impact on Ash Properties Lubricant matrix all formulated to 1% sulfated ash, except base oil. Lubricant Ca Mg Zn P S B Mo ppm ppm ppm ppm ppm ppm ppm Base <1 <1 < <1 Base + Ca 2,928 5 < <1 Base + Mg* <1 2,070 <1 <1 460 <1 Base + ZDDP <1 < ,530 6,901 1 <1 Base, Ca+ZDDP* 2480 < ,180 2,750 <1 Base, Mg+ZDDP* < ,180 2,840 <1 Commercial CJ-4 1, , ,200* Composition of ash directly related to lubricant additive chemistry. Major Ash Components Density Melting Point Description g/cm 3 C CaSO 4 Calcium Sulfate ,460 Sinters/Decomposes ~1,250 C CaZn 2 (PO 4 ) 2 Calcium Zinc Phosphate 3.65 Zn 2 (P 2 O 7 ) Zinc Pyrophosphate 3.75 Sintering begins ~ 800 C Zn 3 (PO 4 ) 2 Zinc Phosphate Sintering begins ~ 800 C Zn 2 Mg(PO 4 ) 2 Zinc Magnesium Phosphate 3.60 MgO Magnesium Oxide ,832 MgSO4 Magnesium Sulfate ,124 Decompostion 900-1,100 C 19

20 Ca Ash Shows 2X Increase in P Over Zn & Mg Ash Flow 25 C, Space Velocity: 20,000 hr -1 Pressure Drop [kpa] ASME ICES Ash: Ca Mg ρ Pack = 0.19 g/cm 3 Ca Zn ρ Pack = 0.25 g/cm 3 ε = 91% ρ Pack = 0.19 g/cm 3 ε = 95% CJ-4 ρ Pack = 0.30 g/cm 3 ε = 91% Ash: Zn ε = 95% Total Ash Load [g/l] Equivalent Hours* 2,840 4,260 5,670 Equivalent Miles* 110 K 160 K 220 K Lubricant additive chemistry affects ash properties and pressure drop Ca-based ash shows much larger effect on pressure drop than Zn ash * Assumes: 15 g/hr avg. oil consumption, avg. speed of 40 mph, and full size DPF of 12 L volume 20

Ash Chemistry Impacts Ash Properties and DPF P ASME ICES2012-81237 Pressure Drop [kpa] 9 6 3 0 1.

21 Ash Chemistry Impacts Ash Properties and DPF P ASME ICES Pressure Drop [kpa] Ca - Ash Ca + ZDDP 25 g/l Ca 29 g/l CJ-4 33 g/l No Ash Mg + ZDDP 23 g/l Cummumlative PM Load [g/l] 1.5 Mg 28 g/l Ash Distribution Profiles ZDDP 28 g/l Cordierite 200/12 Differences in DPF P due to ash properties (ρ, ε, D p ) Channel Width [mm] Axial Distance [mm] Channel Width [mm] Axial Distance [mm] 21

differences in P o Complex mixture of metal oxides, sulfates, phosphates o Characterization of particle

22 Detailed Understanding of Ash Properties Required P Wall / Ash / Soot K = = ( ε ) f, D P µ v K P w ε = 1 w ρ ρ Packing Theoretical Ash Properties o Provide critical information to explain fundamental differences in P o Complex mixture of metal oxides, sulfates, phosphates o Characterization of particle morphology, physical, chemical properties challenge New Techniques and Diagnostics o C. Kamp Presentation (12/2010) 22

CJ-4 Ash Composition and Porosity SAE 2010-01-1213 CaSO 4 Ash Wall Density Theoretical Density Ash Porosity Zn 2 Mg(PO 4 ) 2 [g/l]

23 CJ-4 Ash Composition and Porosity SAE CaSO 4 Ash Wall Density Theoretical Density Ash Porosity Zn 2 Mg(PO 4 ) 2 [g/l] [g/cm 3 ] [g/cm 3 ] [%] ε = 1 ρ ρ Packing Theoretical Zn 2 Mg(PO 4 ) 2 Zn 2 Mg(PO 4 ) 2 CaSO 4 23

Ash PM Layer Interface Clearly Defined SAE 2012-01-0836 Focused Ion Beam (FIB) Milling Coupled with

24 Ash PM Layer Interface Clearly Defined SAE Focused Ion Beam (FIB) Milling Coupled with SEM Unlike PM depth filtration in DPF surface pores, very little soot penetrates into ash layer. 24

Individual Ash Particles Also Porous SAE 2012-01-0836 Focused Ion Beam (FIB) Milling

25 Individual Ash Particles Also Porous SAE Focused Ion Beam (FIB) Milling Coupled with SEM Particle most likely formed from sintering/agglomeration of ash precursors. 25

26 Ash Particles and Agglomerates Porous Shells! SAE Ash agglomerates consist of porous particles Images: C. Kamp Consistent with low packing density and high porosity measurements 26

27 Ash Accumulation Also Influences Soot Properties SAE No Ash 42 g/l Ash 42 g/l Ash (Adjusted) 10 Pressure Drop [kpa] RPS P = PM Ash, i Adjust specific soot load to account for actual available trap volume P PM Clean, i Cummumlative PM Load [g/l] Ash deposits displace soot in DPF higher local soot loads 27

28 Variation in PM Layer Properties with DPF Flow Well-Known K soot x10-14 [m 2 ] Source: SAE Image: Menelaos, T., Ph.D. Thesis, Yale, U d Pe = D Inertia Pe = Diffusion w Pr imary Porosity SAE Source: SAE Image: Menelaos, T., Ph.D. Thesis, Yale,

29 Variation of Soot Properties Due to Ash Deposits SAE Packing Density Permeability Relative Chnage [ 200% 150% 100% 50% 0% -50% -100% 25K GHSV Soot Properties Estimated from empirical Pe number correlations for constant flow rate Low space velocity conditions most strongly affected by ash loading Ash Load [g/l] 20% 15% 50K GHSV Relative Chnage [ 10% 5% 0% -5% -10% 75K GHSV 75K GHSV Soot deposited at flows > 75K 1/hr insensitive to ash loading -15% -20% 50K GHSV Ash Load [g/l] 29

30 Key Parameters Controlling Ash Deposits and DPF Impacts Engine-Out Ash Emissions and Transport Form of ash in exhaust/feed gas entering DPF; ash trapping efficiency Ash Deposit Accumulation and Build-Up in the DPF Agglomerate formation and ash mobility/distribution in DPF Ash Impact on DPF Pressure Drop Response Ash composition and properties relevant to DPF performance Sensitivity of DPF Design Parameters to Ash Substrate materials, pore size & distribution, porosity Role of Engine Control Strategies and Exhaust Conditions Temperature, flow, and feed gas conditions affecting ash deposits Regeneration Processes Real-time optical studies of ash formation and mobility Ash Catalyst Interactions Chemical and physical interactions of ash and catalyst/washcoat 30

Parameters Filter/substrate materials DPF coatings and catalysts Filter geometry

31 Sensitivity of DPF Design Parameters to Ash Matrix 1 st Trial Porosity Low High 2 nd Trial High Mean Pore Size Low Low High 3 rd Trial Moderate Low Additional DPF Parameters Filter/substrate materials DPF coatings and catalysts Filter geometry and cell configuration Multi-Cartridge Filter Holder 12 DPF Segments Ash Loading 31

32 DPFs Experience Even Ash Loading and Temperatures Average Ash Deposition after 60 hrs of operation: 20 g/l % 9.1 % 4.8 % 0.0 % 4.3 % 9.1 % Ash evenly distributed in core samples Little P variation between duplicate samples Ash [g/l] Inlet Temperature (before the cone) Pressure Drop Variation 20 g/l ash 14 g/l ash 610 C (±25) 7 g/l ash 0 g/l ash (Space Velocity range: 6,500 55,000 [1/hr]) 32

33 Similar P Response to PM Accumulation for All DPFs DPF Pressure Drop Response 0 g/l Ash SiC (40%,15*µm) with 0 g/l ash Cd (50%,15*µm) with 0 g/l ash SiC (50%,15*µm) with 0 g/l ash SiC (60%,15*µm) with 0 g/l ash SiC (60%,25*µm) with 0 g/l ash * Indicates pore and porosity size class 33

34 Sensitivity of DPF Porosity to Ash Accumulation Varies Low Ash Load (5 g/l) High porosity DPFs reduce ash P sensitivity 0 g/l 5 g/l Moderate Ash Load (20 g/l) P Insensitive to DPF Porosity at Elevated Ash Levels. (40%) Pressure Drop [kpa] 3 % (60%) 15 % (50%) 23 % (40%) (60%) (50%) Sensitivity of P to ash accumulation increases with decreasing DPF porosity at low filter ash levels At high ash loads, ash dominates P, which is insensitive to initial DPF porosity of filter, over range tested 34

35 Key Parameters Controlling Ash Deposits and DPF Impacts Engine-Out Ash Emissions and Transport Form of ash in exhaust/feed gas entering DPF; ash trapping efficiency Ash Deposit Accumulation and Build-Up in the DPF Agglomerate formation and ash mobility/distribution in DPF Ash Impact on DPF Pressure Drop Response Ash composition and properties relevant to DPF performance Sensitivity of DPF Design Parameters to Ash Accumulation Substrate materials, pore size & distribution, porosity Engine Control Strategies and Exhaust Conditions Temperature, flow, and feed gas conditions affecting ash deposits Regeneration Processes Real-time optical studies of ash formation and mobility Ash Catalyst Interactions Chemical and physical interactions of ash and catalyst/washcoat 35

Exhaust Conditions Are Continually Changing DPF Temperature Distribution (300-420K

Deer 2006 SAE 2009-01-1262 Potential for short excursions above 700 C over DPF

36 Exhaust Conditions Are Continually Changing DPF Temperature Distribution ( K Miles, HD Diesel) Typical Highway Drive Cycle DPF Inlet Temp Speed Air Flow Corning Deer 2006 SAE Potential for short excursions above 700 C over DPF operating history Exhaust flow rates also vary considerably, even over highway drive cycle 36

Exhaust Temperature Significantly Affects Ash Volume SAE 2012-01-1093 5 0 Lab Zn: *800 C Lab CJ-4: *940 C Lab Ca: *1,260 C Competing Effects on P Based on Ash Distribution Change in Length [%] -5-10

37 Exhaust Temperature Significantly Affects Ash Volume SAE Lab Zn: *800 C Lab CJ-4: *940 C Lab Ca: *1,260 C Competing Effects on P Based on Ash Distribution Change in Length [%] Field CJ-4: *705 C Change in Length = dl/l o *Sintering Onset Temperature [C] Lost contact with probes Large decrease in ash volume for temperatures over 700 C Reduction in ash weight over temperature ranges less than 10% Typical ash porosities 85% - 95% means large potential to reduce volume 37

38 Elevated Temperatures Exert Large Effect on Ash Packing SAE Change in P 6.0% 4.0% 2.0% 0.0% -2.0% -4.0% -6.0% 650 C High Flow Exposure to 200,000 hr -1 Ca (28 g/l, Per) Zn (28 g/, Per) CJ-4 (13 g/l, Per) CJ-4 (33 g/l, Con) CJ-4 (42 g/l, Per) 2.4% 1.7% -2.2%-2.4% -5.3% Lab Ca Field Lab CJ4 Field Normalized P High Temperature Exposure 13 g/l CJ-4 Ash Control (No Ash) 28 g/lca Ash 28 g/l ZDDP Ash 42 g/l CJ-4 Ash Ash Volume Reduction Fast DPF core heated to 880 C in 5 min, then quenched. 800 C 1,000 C CJ-4 Lab Ash 0 min 5 min 38

39 Large Reduction in Ash Volume at Elevated Temperatures SAE C 700 C 800 C 900 C 1,000 C 1,100 C 28 g/l ZDDP 28 g/l Calcium 42 g/l CJ-4 (P) 33 g/l CJ-4 (C) 39

40 High Temperatures Cause Ash Layer Cracking/Shrinking SAE g/l CJ-4 Ash (Periodic) 33 g/l CJ-4 Ash (Continuous) 650 C 700 C 800 C 900 C 1,000 C 1,100 C Despite large volume reduction, ash weigh change < 7% 40

41 Similar Behavior in Lab/Field Ash May Be Due to Chemistry SAE C 700 C 800 C 900 C 1,000 C 1,100 C Lab Calcium Field A Lab Field D CJ-4 (P) 41

42 Chemical and Physical Changes in Ash at High Temps. SAE Ash Composition Changes Irreversibly Temperature Equilibrium Crystal Structures formed at High Temperatures min( γ S das ) Ca Zn 42

43 Applications to Understand Field DPF History Normal Field Ash SAE Field Ash Exposed to Thermal Event Prior High Temperature Exposure Ash Necking & Agglomeration Wetting on Substrate 43

44 Conceptual Description of Temperature Effects on Ash Possible Effect of Temperature on Ash Deposits Ash Deposits in Typical DPF DPF Pores Exposed! Ash Deposits After High Temp. Competing Processes Require Detailed Understanding Elevated temperatures result in significant ash volume reduction Location of ash deposits (channel vs. wall) plays a large role in impact on P Deterioration of ash cake layer could result in increased P with soot 44

45 Key Parameters Controlling Ash Deposits and DPF Impacts Engine-Out Ash Emissions and Transport Form of ash in exhaust/feed gas entering DPF; ash trapping efficiency Ash Deposit Accumulation and Build-Up in the DPF Agglomerate formation and ash mobility/distribution in DPF Ash Impact on DPF Pressure Drop Response Ash composition and properties relevant to DPF performance Sensitivity of DPF Design Parameters to Ash Accumulation Substrate materials, pore size & distribution, porosity Role of Engine Control Strategies and Exhaust Conditions Temperature, flow, and feed gas conditions affecting ash deposits Regeneration Processes Real-time optical studies of ash formation and mobility Ash Catalyst Interactions Chemical and physical interactions of ash and catalyst/washcoat 45

Optical Access System for DPF Regeneration Studies Understand

strategies may impact ash agglomeration and mobility Role of soot

Regeneration Parameters Thickness of PM Layer Role of NO 2 from DOC

46 Optical Access System for DPF Regeneration Studies Understand Influence of Regeneration on Ash Properties Active/Passive strategies may impact ash agglomeration and mobility Role of soot interactions with ash during regeneration important DPF Substrate Regeneration Parameters Thickness of PM Layer Role of NO 2 from DOC vs. CDPF Temperature and flow conditions Catalysts interactions 2 nd Generation Air 46

47 Video: PM Oxidation on Clean DPF Surface (Heavy PM) 47

48 Video: PM Oxidation with Ash (DPF Cross Section) 48

49 Current Optical Setup for Flow Reactor Testing Gasket Quartz Glass 27mm by 1.44mm Slit in Matting and One Channel of the DPF Channel View 49

50 Video: PM Oxidation on Clean DPF Surface (Heavy PM) 50

51 Ash Deposition on Top of PM Layer: Regeneration Coat surface of soot cake with thin layer of ash Allows for visualization of ash/pm mobility during regeneration Enables visualization of ash agglomerate formation Ash PM (Genset) Substrate Thin ash layer not fully-established Ash applied via accelerated loading system Thick, fullyestablished PM layer PM loading accomplished using genset 51

52 Ash Deposition on Top of PM Layer: Regeneration Regeneration with thin ash layer covering PM surface

53 Video: Ash Deposited on Top of PM Layer Substrate 53

54 Ash Agglomeration Process During Soot Oxidation ~ 100 nm ~ 1 µm Ash residence time in DPF is long ~ 100,000 + Miles Internal void shows walls composed of ~nm scale particles 54

55 Key Parameters Controlling Ash Deposits and DPF Impacts Engine-Out Ash Emissions and Transport Form of ash in exhaust/feed gas entering DPF; ash trapping efficiency Ash Deposit Accumulation and Build-Up in the DPF Agglomerate formation and ash mobility/distribution in DPF Ash Impact on DPF Pressure Drop Response Ash composition and properties relevant to DPF performance Sensitivity of DPF Design Parameters to Ash Accumulation Substrate materials, pore size & distribution, porosity Role of Engine Control Strategies and Exhaust Conditions Temperature, flow, and feed gas conditions affecting ash deposits Regeneration Processes Real-time optical studies of ash formation and mobility Ash Catalyst Interactions Chemical and physical interactions of ash and catalyst/washcoat 55

56 Summary and Conclusions Detailed understanding of all system parameters important to reduce impact of ash on DPF degradation and fuel efficiency. I. Ash Build-Up: Ash loading of ~ 10 g/l or around 50,000 miles required to form fully-established ash layer. II. Ash Morphology: Two porosity scales identified in ash layer and ash primary particles, which are themselves hollow. III. Lube Chemistry: Ash properties and DPF pressure drop strong function of additive composition. IV. Exhaust Conditions: Transient changes in temperature induce much larger variations in ash packing than high flow rates. V. DPF Parameters: DPF pressure drop relatively insensitive to original substrate porosity following ash layer build-up. VI. Regeneration Effects: Preliminary optical studies highlight importance of regeneration parameters but requires further study. 56

57 Acknowledgements Research supported by: MIT Consortium to Optimize Lubricant and Diesel Engines for Robust Emission Aftertreatment Systems We thank the following organizations for their support: - Caterpillar - Chevron/Oronite - Cummins - Detroit Diesel - Infineum - Komatsu - NGK - Oak Ridge National Lab - Süd-Chemie - Valvoline - US Department of Energy - Ciba - Ford - Lutek MIT Center for Materials Science and Engineering 57

Recent Trends for Filter Development for Diesel Particulate Aftertreatment

7 th International ETH-Conference on Combustion Generated Particles August 18 2, 23 Recent Trends for Filter Development for Diesel Particulate Aftertreatment A. Schäfer-Sindlinger, C.D. Vogt NGK Europe