Throat Unit Collector Modeling for Gasoline Particulate Filter Performance

Transcription

1 Throat Unit Collector Modeling for Gasoline Particulate Filter Performance Pengze Yang Texas A&M University Andrea Strzelec Mississippi State University

2 Outline Motivation & Background Approach Results Single throat unit collector efficiency and derivation of total wall efficiency Throat unit collectors with sequence of diameter ratio and their efficiency Compare transient GPF wall loading simulation with experimental data Model Improvement Work in Progress GPF wall heterogeneity effects on GPF performance Summary Acknowledgement Appendix 2

3 GPFs are Needed to Meet the Particulate Emissions Standards GDI has higher particulate matter (PM) and particle number (PN) emissions than port fuel injection (PFI). [1] There is need for high filtration efficiency GPFs to meet the EURO 6 or similar PN regulations.[2] [3] [1] Maricq, M. How are emissions of nuclei mode particles affected by emission control. in HEI-conference May [2] Badshah, H., Kittelson, D., and Northrop, W., Particle Emissions from Light-Duty Vehicles during Cold-Cold Start, SAE Int. J. Engines 9(3): , 2016, doi: / [3] Johnson, T. and A. Joshi, Review of Vehicle Engine Efficiency and Emissions. 2018, SAE International. 3

4 GPF Modeling Backgrounds The analytical method with unit collector model [5] 3D CT-scanned model + CFD Throat unit collector model Analytical Method + CFD Cavity D Pore d p + Simple, efficient & robust Clean and loading state simulation - Single degree of freedom(unit collector size) + More degrees of freedom to feature cavity, pore size and their connectivity Time & Cost efficient Enable clean and loading state simulation [4] + Resolve detailed microstructure of GPF - Time & Cost consuming Only reconstruct limited fraction of porous medium each time [4] Kočí, P., et al., 3D reconstruction and pore-scale modeling of coated catalytic filters for automotive exhaust gas aftertreatment. Catalysis Today, [5] Konstandopoulos, A.G. and J.H. Johnson, Wall-flow diesel particulate filters their pressure drop and collection efficiency. 1989, SAE Technical Paper. 4

5 Approach Objective: Create the throat unit collector model to better represent the microstructure of GPFs and search for approaches to increase the filtration efficiency of GPFs Approaches: Create the throat unit collector and predict the single collector efficiency using CFD Derive the equation for predicting the total GPF filtration efficiency Create throat unit collectors with sequence of diameter ratios and investigate their effects on the filtration efficiency Use the throat unit collector model to predict the sample GPF filtration behavior while loading 5

6 Validation Experiments Sample Description GPF_300/12 Diameter [mm] 25.5 Length [mm] 75.4 Channel Depth [mm] 67 Plug Length [mm] 8.4 Cell Width [mm] 1.2 Wall Thickness [mm] 0.3 Cell Density [CPSI] 300 Porosity 0.65 Experimental data based on the sample GPFs are pending for publication (SAE draft 19FFL-0155) [6] [6] Porosimetry test results provided by Dinex. Average Pore Size [um] 15 6

7 Throat Unit Collector Creation Real GPF wall microstructure [8] Cavity D GPF wall model with circular obstacles Pore d p [8] The GPF wall SEM image is provided by Ford Motor Company. Throat unit collector model 7

8 Single Throat Unit Collector and Its Aggregation Void Volume Throat Collector Volume ' 2 Total Volume a ' b D d p Inflow 30,000/60,000 hr -1 S.V. Particle Injection b 12 mil a Single collector efficiency predicated by CFD Total efficiency across the wall E 8

9 50 nm particles Determine single h = collector efficiency Numberof Particles Trapped Number of Particles Injected 100 nm particles 150 nm particles 9

10 Derivation of Total Efficiency E E 1 C e C 3 2 t 2 2 D 4Dsin cos D Where, t is the thickness of GPF wall; is porosity; is the angle shown below; D is the cavity diameter Cavity D Pore dp 10

11 Diameter Ratio D/dp Cavity D b Pore dp Diameter ratio D/dp dp [um] D [um] 2: : : : : Baseline 30 um 15 um um 15 um 22.5 um Baseline 19.2 um 15 um 15 um 15 um 2:1 1.75:1 1.5:1 1.3:1 1:1 11

12 Single Collector Efficiency Single Unit Collector Efficiency Changes Nonlinearly_75nm_30,000 hr Diameter ratio with minimum efficiency 0.1 2:1 1.75:1 1.5:1 1.3:1 1:1 Diameter Ratio 75nm single efficiency_fixed dp Simulation results show that as throat unit collector diameter ratio decreases, single collector efficiency for 75nm particles first decreases and then increases. Diameter ratio of 1.5:1 shows the minimum single efficiency. 12

13 Total Filtration Efficiency Throat Unit Collector Model Validation ~5% difference :1 ratio (baseline), hr-1 Experiment, hr Particle Size [nm] 13

14 Total Filtration Efficiency Size Dependent Filtration Efficiency Increases as Diameter Ratio Decreases :1 ratio, hr-1 1.5:1 ratio, hr-1 1.3:1 ratio (baseline), hr-1 1:1 ratio, hr-1 2:1 ratio, hr-1 1.5:1 ratio, hr-1 1.3:1 ratio (baseline), hr-1 1:1 ratio, hr Particle Size [nm] Despite the nonlinear change of single unit collector efficiency with diameter ratio, the overall GPF wall efficiency shows a relatively linear trend. With diameter ratio decreases, the overall efficiency increases. GPF wall design with whole 1:1 throat unit collectors might potentially produce a higher filtration efficiency than sample GPFs. 14

15 Pore Size Shrinks During Particulates Diameter ratio increases when loading, due to the blockage of pore Loading Cavity D D d Initial p0 p0 1.3, D 19.2 m, d 15 m D Final 2, D m, d p 9.3 m d p Pore dp D/ dp Assumptions: (1) Particulates only load on upstream collector wall. (2) The loading only influents the pore size. The cavity size stays fixed. (3) The newly formed bridging at the collector throat has a thickness of 1um. (4) Particle laden flow through the bridging region has a filtration efficiency close to 100%. 1 20, 30,000.., 75 C hr S V nm Particles Upstream and throat deposition Downstream deposition 1.3:1 95% 5% 1.5:1 83% 17% 2:1 85% 15% 15

16 Single Collector Efficiency Single Collector Efficiency Single unit collector efficiency and ' _75nm_30,000 hr is the single unit collector efficiency excluding the bridging region. ' is the total single unit collector efficiency counting the bridging region nm single efficiency_fixed D_eta 75nm single efficiency_fixed dp_eta 2:1 1.75:1 1.5:1 1.3:1 1:1 Diameter Ratio 75nm single efficiency_fixed D_eta 75nm single efficiency_fixed D_eta' 0.1 2:1 1.75:1 1.5:1 1.25:1 Diameter Ratio 16

17 Filtration Efficiency Pore Size [um] Total Wall Efficiency Changes with Time_75nm_30,000 hr Predicted total efficiency matches experiment TIme [hr] Pore Size Total efficiency_75nm_transient Experiment_75nm_transient Single top collector efficiency_eta_75nm_transient Single top collector efficiency_eta'_75nm_transient Actively working on the pressure drop modeling using the throat unit collector model 0 17

18 Work in Progress: GPF Wall Heterogeneity Effects on its Performance GPF_300/12 Channel Depth [mm] 67 Plug Length [mm] 8.4 Cell Width [mm] 1.2 Wall Thickness [mm] 0.3 Cell Density [CPSI] 300 Inlet Channel Outlet Channel Porous Wall Inlet Zone Outlet Zone Porosity 0.65 Average Pore Size [um] 15 18

19 The Disparity between Particle Deposition Distributions and Wall Velocity Distribution Shows the Necessity of CFD Simulation Inlet Channel Outlet Channel Porous Wall Inlet Zone Outlet Zone Normalized Wall Velocity u wi /u wmax & Particle Deposition N i /N max N N i u u max wi wmax Wall Velocity Particle Deposition_25nm Particle Deposition_50nm Particle Deposition_75nm Particle Deposition_150nm Normalized particle deposition for each zone. i is the zone # Normalized wall velocity along channel Channel Zone 19

20 User Defined Function to Configure Wall Permeability Profile and Determine Filtration Efficiency By using User Defined Function (UDF), filtration efficiency can be resolved to every single particle injected in the system, in accordance to their property and local fluid velocity. Inlet Channel #1 Porous Wall Inlet Channel #2 20

21 Permeability [um2] Permeability [um2] Permeability Changing Axially Uniform Low permeability in the middle GPF Length [inch] GPF Length [inch] 21

22 Permeability [um2] Permeabiltiy [um2] Permeability Changing Axially Linearly increasing Linearly decreasing GPF Length [inch] GPF Length [inch] For the purpose of higher resolution, we are also considering to split the GPF wall into 8 or more zones. 22

23 Permeability Changing Verticaly_Artificial Ash Membrane Add a layer of ash, with different possible distribution along the channel [9] Compare to the results of blank GPF Ash Membrane Porous wall [9] Lambert, C.K., et al., Analysis of Ash in Low Mileage, Rapid Aged, and High Mileage Gasoline Exhaust Particle Filters. SAE International Journal of Engines, ( ). 23

24 Porosity Transient GPF Wall Porosity Profile dt=10min_0 min dt=10min_10 min dt=10min_20 min dt=10min_30 min dt=10min_40 min dt=10min_50 min dt=10min_60 min Channel Zone 24

25 Summary 1. Throat unit collector modeling Using the throat unit collector model, total wall filtration efficiency increases with decreasing collector diameter ratio. Throat unit collector model is able to simulate the pore bridging behavior during loading process and matches the GPF transient filtration efficiency data well. 2. GPF wall heterogeneity effects on its performance (work in progress) 3D GPF geometry is created that is capable of predicting pressure drop. UDF is developed to configure GPF wall permeability profile and predict filtration efficiency at both initial and loading states. 25

26 Acknowledgements My sincere gratitude goes to Christine Lambert s team at Ford Motor Company for their support and inspiration. I would like to thank the catalyst modeling team at Cummins for supporting me and offering priceless advices to this research. I would also like to acknowledge Quinton Porter for providing the experiment data to validate the model. Thank you! Questions? 26

27 Technical Backups 27

28 Throat Unit Collector Transient Modeling Assumption 28

29 Experiment Setup (1)Building air, (2)Atomizers, (3)Dryers, (4)MFC, (5)Filter chamber, (6)Classifier, (7)Differential mobility analyzer, (8)Cleanroom particle counter, (9)DPT (6-8)Scanning Mobility Particle Sizer 29