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Towards predictive ash accumulation and transport modeling
G. Koltsakis, M. Mitsouridis, I. MylonidisExothermia SA
K. Baumgard, R. Duddukuri, W. ZhouJohn Deere Power Systems
S. George, S. Viswanathan, A. HeibelCorning Incorporated
CLEERS 2020
Effect of ash on pressure drop & filtration
15-Sep-2020
• Kamp, C., et al. Soot and Ash Deposition Characteristics at the Catalyst-Substrate Interface and Intra-Layer Interactions in Aged Diesel Particulate Filters Illustrated using Focused Ion Beam (FIB) Milling, SAE Int. J. Fuels Lub, 2012
• Sappok A., et al. Individual and Synergistic Effects of Lubricant Additive Components on Diesel Particulate Filter Ash Accumulation and Performance, ASME ICES2012-81237, 2012
• Custer, N., et al. Lubricant-Derived Ash Impact on Gasoline Particulate Filter Performance, SAE International, 2016
• Boger, T. and Cutler, W. System integration and application for a three way catalyst coated gasoline particulate filter, SAE International, 2019
Filtration efficiency increases with ash
Impact of ash on Pressure drop depends (at least) on soot loading
Motivation
15-Sep-2020
Develop predictive model for ash accumulation/migration and deltaP impact
Use model for system design and controls optimization at early design phase
Data from ~ 500 h transient engine tests
Earlier modeling works
15-Sep-2020
Conceptual particulate transport mechanisms
• Sappok A., et al. Theoretical and Experimental Analysis of Ash Accumulation and Mobility in Ceramic Exhaust Particulate Filters and Potential for Improved Ash Management, SAE Int. J. Fuels Lubr, 2014
Literature models aim to describe discreet ash migration events of pre-accumulated ash under steady flow.
The present work aims at ‘life cycle’ transient analysis.
Ash agglomerate
Ash precursors
• 𝐹: laminar channel flow friction factor• 𝜂: gas viscosity• 𝑢 𝑧 : inlet channel local mean axial velocity• 𝑏𝑙𝑜: open width of the inlet channel
considering the ash deposit profile
1-D approach1-D model based on a simple force balance on the soot/ash particle and an empirical parameter to describe the critical particle removal/detachment stress:
3-D approach3-D CFD model estimating the drag and lift forces imposed on the particle by the exhaust flow under steady state conditions.
Modeling
15-Sep-2020
Modeling framework and requirements
15-Sep-2020
Channel and wall flow distribution
Filtration of soot and ash particles (in-wall and cake)
Pressure drop incl impact of ash layer and plug
Heat transfer
Soot reactions and exothermic effects
Species transfer
Wall catalytic reactions
Soot-borne & agglomerated ash particles
Soot migration
Ash agglomeration
Ash agglomerate migration
Well described in the literature
Focus of present study
Modeling and simulation platform used here: exothermia suite (former axisuite)
Soot- & gas-borne ash precursors
15-Sep-2020
• Wang, Y., et al. The Origin, Transport, and Evolution of Ash in Engine Particulate Filters, Applied Energy, 2020• Lambert C., et al. Analysis of High Mileage Gasoline Exhaust Particle Filters, SAE International, 2016• McGeehan, J., et al. Extending the Boundaries of Diesel Particulate Filter Maintenance With Ultra-Low Ash - Zero-Phosphorus Oil, SAE International, 2012• Pirjola, L., et al. Effects of Fresh Lubricant Oils on Particle Emissions Emitted by a Modern Gasoline Direct Injection Passenger Car, Environ. Sci. Technol., 2015• Morcos, M., et al. Characterization of DPF Ash for Development of DPF Regeneration Control and Ash Cleaning Requirements, SAE International, 2011• Fang, H., et al. Spectroscopic Study of Biodiesel Degradation Pathways, SAE International, 2006
Low ash/soot ratio High ash/soot ratio
Ash particles on carbon particles Formation of solid ash nanoparticles
Model assumptions– Soot-borne ash is filtered together with
soot and remains in the deposit after soot oxidation
– Gas-borne ash is introduced as ‘filterable’ multi-disperse aerosol
Flow-induced soot migration submodel
15-Sep-2020
Detachment condition:
• 𝜏𝑖 > 𝜏𝑑𝑒𝑡𝑎𝑐ℎ, 𝜏𝑖 =𝑓∙𝜌∙𝑣𝑖
2
8
𝑁
𝑚2
Reattachment condition:
• 𝜏𝑖 < 𝜏𝑟𝑒𝑑𝑒𝑝𝑜𝑠𝑖𝑡𝑁
𝑚2
The model simulates the migration of pre-deposited ash-containing soot based on a simple shear stress submodel
Soot-borne ash is indirectly migrated
• Sappok A., et al. Theoretical and Experimental Analysis of Ash Accumulation and Mobility in Ceramic Exhaust Particulate Filters and Potential for Improved Ash Management, SAE Int. J. Fuels Lubr, 2014
• Sappok, A., et all. In-Situ Optical Analysis of Ash Formation and Transport in Diesel Particulate Filters During Active and Passive DPF Regeneration Processes, SAE Int. J. Fuels Lubr, 2013
• Dittler A. Ash Transport in Diesel Particle Filters, SAE Technical Paper 2012-01-1732, 2012
Ash accumulation & agglomeration
15-Sep-2020
Localized oxidation of the soot cake on the filter surface, characterized by the inward shrinking islands of soot, which serve to concentrate and agglomerate the ash
Soot with elevated ash content
• Sappok, A., et all. In-Situ Optical Analysis of Ash Formation and Transport in Diesel Particulate Filters During Active and Passive DPF Regeneration Processes, SAE Int. J. Fuels Lubr, 2013
• Ishizawa, T., et al. Investigation into Ash Loading and Its Relationship to DPF Regeneration Method, SAE International, 2009
• Custer, N., et al. Lubricant-Derived Ash Impact on Gasoline Particulate Filter Performance, SAE International, 2016
Temperature induced ash agglomeration submodel
15-Sep-2020
𝑅𝑎 𝑇 = 𝐴 ∗ 𝑒−𝐵
𝑇∗ 𝑓𝑎𝑠ℎ𝐶 , 𝑓𝑎𝑠ℎ =
Vash
Vcake
Thermal agglomeration mechanism:
The filtered deposit consists of:• Soot agglomerates• Soot-borne ash• Filtered ash primary particles
Soot oxidation exposes further primary ash particlesAsh primary particles form ash agglomerates. The rate depends on local temperature and ash/soot ratio
Flow-induced agglomerated ash migration submodel
15-Sep-2020
Ash detachment conditions:(1) Local soot cake inhibits ash detachment
𝑚𝑠𝑐𝑖 < 𝑚𝑠𝑐𝑑𝑒𝑡𝑎𝑐ℎ
𝑘𝑔
𝑚2
(2) Detachment depends on local velocity and local ash agglomerate size
𝑊𝑖 > 𝑊𝑑𝑒𝑡𝑎𝑐ℎ, 𝑊𝑖~𝑣𝑖 ∙ 𝐷𝑎
Ash redeposition condition:
• 𝑊𝑖 < 𝑊𝑟𝑒𝑑𝑒𝑝𝑜𝑠𝑖𝑡𝑚2
𝑠
Triggered by flow rate increase➔ Shear stresses increase, gradually overcoming the adhesion forces between ash agglomerates and substrate➔ Ash agglomerates detach
Testing campaign
15-Sep-2020
Burner rig
15-Sep-2020
• Separate flow paths for combustion & cooling air
• Ability to independently control soot, ash, NOx, exhaust flow & temperature etc.
• Instrumented for Δp, temperature, gaseous emissions, PM & PN measurements
Testing protocol• Part loaded to target ash load at desired
conditions• Periodic high flow routine for ash compaction
and transport• Periodic filter weights for monitoring ash
accumulation
• Periodic checks• 700ºC regeneration• Pressure drop evaluation: Flow scan
• Ash plug depth measurements: Borescope• 9 different locations spread across the cross
section of the filter• 3 channels at each location
Ash loads
High flows
Weights
Test protocol variationsCT-scans with ~ 30 g/l ash
15-Sep-2020
Low flow rate
Filter Aw/o HFs
w/o soot
Ash
on
lySo
ot
and
ash
Low flow rate with high flow events
Formation of ‘stochastic’ ash bridges
Ash accumulates mostly in the wall and as a layer
Substantial plug ash formation
High flow events affect plug length and/or density
Ash loading without soot @ low flow rate
15-Sep-2020
Initial in-wall ash accumulation followed by layer ash
Pressure drop model tuning to identify ash loaded wall & ash layer permeability
Non-destructive analysis of ash loaded filter (CT scan and borescope based ash plug measurements) at 30 g/l ash
Ash loading with soot and high flow events
15-Sep-2020
Pressure drop information and measurements of plug length were used to tune the ash model migration parameters
Predicted layer to plug ash migration during
high flow event
Soot loading
Soot oxidation
Ash loading
Ash loading with soot and high flow events
15-Sep-2020
Soot accumulation Soot oxidation Ash accumulation Ash migrationAsh accumulation
Transient engine dyno
15-Sep-2020
Ash plug formation & model validation
15-Sep-2020
The target of predictivity in terms of lifecycle pressure drop prediction is met
Encouraging results about model predictivity in terms of ash migration
~ 500 hours of transient engine operation
Predicting the effect of cell-structure
15-Sep-2020
The 300/7 asymmetric cell structure offers large deltaP advantage at soot loaded condition.
Simulation of 500 h of consecutive NRTCs with 2 different cell densities
Predicting the effect of forced regeneration frequency
15-Sep-2020
wal
l so
ot
effe
ct
Wall soot accumulation prevented by the ash layer
Simulation of 500 h of consecutive NRTCs with 2 different regen frequencies
Baseline vs 2 times more frequent activation of forced regeneration
Higher regen frequency associated with lower average soot loadings and deltaP
Plug ash pattern is fairly similar
Predicting the effect of regeneration strategy
15-Sep-2020
For the purely passive regeneration case, the model predicts virtually no plug ash.
wal
l so
ot
effe
ct
Wall soot accumulation prevented by the ash layer
Simulation of 500 h of consecutive NRTCs with 2 different regen strategies
Passive regeneration predicted assuming 20% higher inlet temperature
Conclusions
15-Sep-2020
A ‘mostly physical’ ash formation and migration model was developed accounting for:
– Soot layer detachment
– Thermally induced ash agglomeration
– Ash layer detachment
The model was calibrated vs burner test rig and applied in transient engine data.
The results are viewed as a first step towards life-cycle filter analysis supporting design and control optimization at early stage.
Further research topics identified with respect to– ash fate in the wall pores, intra pore migration and impact of coatings
– plug ash density as function of ash agglomerate size
– ash bridging
Thank you!
15-Sep-2020