nox abatement - cleers€¦ · model vs brack (2016) urea decomposition urea mass decreases over...

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NOX ABATEMENT

—1D/3D simulation of urea dosing and

selective catalytic reduction

J. C. Wurzenberger, A. Nahtigal, T. Mitterfellner, K. Pachler, S. Kutschi

J.C. Wurzenberger | CDS | 14 September 2017 | 2Public

WHY SIMULATION

▪ Urea SCR is the technology to reduce NOx emissions in HD applications

▪ NOx aftertreatment needs to deal with strongly transient operating conditions

▪ Deposit formation is a key aspect in the design if DEF dosing systems

▪ 3D phenomenon influenced by geometry, flow, control Candidate for 3D CFD

▪ Transient phenomenon influenced by the course of the operating conditions Candidate for Real-time system level simulation

BACKGROUND


DEPOSITS DEPEND ON:

1. DESIGN

2. INJECTOR

3. BOUNDARY CONDITIONS

All physical phenomena can

be covered by 3D FIRE™

in detail - but long

simulation time is required.

SOLUTION: Provide CFD-

3D FIRE™ simulation

results to Real – Time

capable 1D BOOST™.


CONTENT

1. Model / Model Validation

i. DEF Dosing (CFD)

ii. Drive Cycle Performance (SysEng)

2. Tools and Workflows

3. Use Case

4. Summary


SPRAY PREPARATION MODELS

▪ Injection of urea-water solution▪ Urea-water properties: f(T,wi,g)

▪ Nozzle modeling

DEF DOSINGINJECTION OF UREA-WATER SOLUTION




▪ Nozzle modeling

▪ Spray/gas interaction▪ Multicomponent evaporation

▪ Thermolysis: (NH2)2CO NH3 + HNCO

▪ Hydrolysis: HNCO + H2O NH3 + CO2

DEF DOSINGSPRAY/GAS INTERACTION

H 0 (l)2

H 0 (g)2

H 0 (l)2

H 0 (g)2

(NH ) CO (s or l)2 2

(NH ) CO (g)2 2

NH (g) + HNCO (g)3

H 02 (NH ) CO2 2

I. II. III.



(NH ) CO (g)2 2

(NH ) CO (g)2 2

H 0 (l)2

H 0 (g)2

H 0 (l)2

H 0 (g)2


(NH ) CO (g)2 2

NH (g) + HNCO (g)3

H 02 (NH ) CO2 2

I. II. III.



(NH ) CO (g)2 2

(NH ) CO (g)2 2

H2O

(NH2)2CO NH3

HNCO

NH3

CO2




▪ Nozzle modeling




DEF DOSINGSPRAY/GAS INTERACTION

H2O

(NH2)2CO NH3

HNCO

NH3

CO2

VelocityNH3

Uni=0.84 =0.94




▪ Nozzle modeling




▪ Spray/wall interaction▪ Heat transfer between spray and wall

▪ Wallfilm formation

▪ Multicomponent film evaporation & thermolysis

DEF DOSINGSPRAY/WALL INTERACTION

H2O

(NH2)2CO NH3

HNCO

NH3

CO2


DEF DOSINGSPRAY/WALL INTERACTION -- VALIDATION

Nahtigal et al. “SCR recent development and method”, AVL International Simulation Conference, 2017

Test bench at Graz University of Technology




▪ Nozzle modeling







▪ Cooling of walls▪ Radial and lateral heat transfer (walls, mixers,…)

DEF DOSINGCOOLING OF WALLS




▪ Nozzle modeling







▪ Cooling of walls▪ Radial and lateral heat transfer (walls, mixers,…)

▪ Catalytic conversion▪ Ad- and desorption, fast, standard, slow SCR,…

DEF DOSINGCATALYTIC CONVERSION

H2O

(NH2)2CO NH3

HNCO

NH3

CO2


CONTENT


i. DEF Dosing (CFD)



3. Use Case

4. Summary


SYSTEM ENGINEERING MODELDRIVER, VEHICLE, DRIVELINE ENGINE, COOLING, CONTROL …

Multi-physics model

Multi-rate numeric

Diesel Exhaust System

Dedicated coupling technique for engine thermodynamics and EAS modeling


0D/1D DOSING MODEL

▪ Arbitrary liquid/gas mixtures

▪ Instantaneous evaporation gas phase▪ Break-up model (DEF2NH3+CO2+6H2O)

▪ Spraying liquid droplets

▪ Split is empirical parameterized or from CFD

▪ Droplets▪ Passive transport

▪ Deposition following “adsorption chemistry”

▪ Wall film▪ Heat-transfer: wall, wall film and gas phase

▪ Multi-component evaporation f(Tw, pi,g, Re)

▪ Arbitrary film reaction chemistry (i.e. decomposition of urea)

SYSTEM ENGINEERING MODELDOSING, EVAPORATION, WALL FILM …

Qz

vw

t

w

gpassi,gpassi,g

emptys,passi,depdep Zwkr

injection

surfaceu w

wutransport

wu

u b t c adecomposition

HNCO + NH3H2O

Instantaneous evaporation

transport

deposition

H2O, HNCO, NH3


MODEL BRACK (2014*, 2016†)

▪ Rates are parameterized using experimental data from TGA measurements

▪ Translated into open User-Coding models

▪ General rate:

▪ CYA decomp. rate:

▪ HNCO evap. rate:

▪ AR, VR: estimated to match published data

▪ Validated using published data

SYSTEM ENGINEERING MODELWALL FILM – UREA DECOMPOSITION MODEL

1) CYA(s) 3 HNCO(g)2) biuret(m) urea(m) +HNCO(l)3) urea(m) +HNCO(l) biuret(m)4) urea(m) HNCO(l) +NH3(g)5) 2 biuret(m) ammelide(s) +HNCO(l) +NH36) biuret(m) +HNCO(l) CYA(s) +NH3(g)7) biuret(m) +HNCO(l) triuret(s)8) triuret(s) CYA(s) +NH3(g)9) urea(m) +2HNCO(l) ammelide(s) +H2O(g)10) biuret(m) biuret(matrix)11) biuret(matrix) biuret(m)12) biuret(matrix) 2 HNCO(g) +NH313) urea(s) urea(m)14) ammelide(s) ammelide(g)15) HNCO(l) HNCO(g)

* Brack, W.; Heine, B.; Birkhold, F.; Kruse, M.; Schoch, G.; Tischer, S. & Deutschmann, O., Chemical Engineering Science, 2014, 106, 1-8

† Brack, W.; Heine, B.; Birkhold, F.; Kruse, M. & Deutschmann, O., Emission Control Science and Technology, 2016, 1-9

biuret

triuret

cyanuric acid ammelideurea


MODEL VS BRACK (2014)

▪ CYA decomposition▪ CYA(s) 3 HNCO(g) (0th order rate!)

▪ TGA Experiment: 6mg CYA heated at different heating rates

▪ End-of-decomposition temperature increases with increasing heating rate

▪ Good match with published data

▪ Biruet decomposition▪ All 15 reactions

▪ TGA Experiment: ~50mg biuret heated at 2K/min

▪ Initial decomposition to major amounts of CYA, minor amounts of ammelide, which, in turn decompose at higher temperatures

▪ Good match with published data

SYSTEM ENGINEERING MODELVALIDATION – CYA & BIURET DECOMPOSITION

CYA decomposition

Biuret decomposition



▪ Urea Decomposition

▪ All 15 reactions

▪ Simulation: initial urea decomposed at different constant temperatures for 180 min assuming two different film thicknesses

▪ Brack presents several contour plots gained from simulation data like the own shown here

▪ To compare them cuts at 5 temperatures were made to gather data points for comparison

SYSTEM ENGINEERING MODELVALIDATION – UREA DECOMPOSITION (SETUP)



▪ Urea Decomposition

▪ Urea mass decreases over time

▪ Fasted decomposition at highest temperature

▪ Incomplete decomposition for all temperatures, in the given time span, is in line with the reference data

▪ Effect of changing film thickness (model input parameter) is reflected accurately

▪ Reasonable qualitative agreement between simulated data from Brack and BOOST, for both cases

SYSTEM ENGINEERING MODELVALIDATION – UREA DECOMPOSITION (TOTAL MASS)

Total mass decrease

173 µm film thickness


Points: data from contour plots x-cutsLines: BOOST simulation



SYSTEM ENGINEERING MODELVALIDATION – UREA DECOMPOSITION (SPECIES F1)

Species mass fractions





SYSTEM ENGINEERING MODELVALIDATION – UREA DECOMPOSITION (SPECIES F2)

Species mass fractions




CONTENT


i. DEF Dosing (CFD)



3. Use Case

4. Summary


EAS TOOLS –REACTION MODELING

User Coding Interface

Reaction/Transfer/Diffusion

RT-Solver /1D, 2D, 1D+1D/ for catalysts, filters, pipes, dosers,… EAS systems

𝑉 ⋅𝜕𝜌

𝜕𝑡= −

𝜕 ሶ𝑚

𝜕𝑧⋅ d𝑧 +MG𝑖 ⋅𝜈𝑖,𝑗 ⋅ ሶ𝑟𝑗 | 0 =

d𝑝

d𝑧− 𝜁 ⋅

1

2⋅ 𝜌 ⋅ 𝑣2

𝑉 ⋅𝜕𝜌 ⋅ 𝑤𝑖𝜕𝑡

= −𝜕 ሶ𝑚 ⋅ 𝑤𝑖𝜕𝑧

⋅ d𝑧 + D ⋅ 𝜌 ⋅ AC ⋅𝜕2𝑤𝑖𝜕𝑧2

⋅ d𝑧 − 𝛽 ⋅ 𝜌 ⋅ AW ⋅ 𝑤𝑖 − 𝑤𝑖,L

𝑉 ⋅𝜕𝜌 ⋅ 𝑢

𝜕𝑡= −

𝜕 ሶ𝑚 ⋅ ℎ

𝜕𝑧⋅ d𝑧 + 𝜆 ⋅ AC ⋅

𝜕2𝑇

𝜕𝑧2⋅ d𝑧 − 𝛼 ⋅ AW ⋅ 𝑇 − 𝑇W

𝑚L ⋅𝜕𝑤𝑖,L𝜕𝑡

= 𝛽 ⋅ 𝜌 ⋅ AW ⋅ 𝑤𝑖 −𝑤𝑖,L +MG𝑖 ⋅𝜈𝑖,𝑗 ⋅ ሶ𝑟𝑗

𝑚W ⋅ 𝑐p,W ⋅𝜕𝑇W𝜕𝑡

= 𝜆W ⋅ AW ⋅𝜕2𝑇𝑊𝜕𝑧2

⋅ d𝑧 + AW ⋅ 𝛼 ⋅ 𝑇 − 𝑇W +Δℎ𝑗 ⋅ ሶ𝑟𝑗 | 𝑍𝑛d𝑤𝑘,𝑛,Sd𝑡

= MG𝑘 ⋅𝜈𝑘,𝑗 ⋅ ሶ𝑟𝑚

Execution Environments

MyReac.ucp

MyTrans.ucp

MyDiff.ucp

MyModel.fmu

MyModel.zip

Kinetics/Transfer

Library• ASC: Scheuer

• LNT: Olsson

• SCR: Olsson

• SCR: Ebrahimian/Brack

• TWC: Brinkmeier

• DPF: Konstandopoulos

• CSF: Premchand

• XXX: Surface Chemkin

• …

This

study


1D / 3D SIMULATION WORKFLOW

Tasks

Tools

Results

Component Design

3D CFD

EAS

Species uniformity, wall

film mass and

position,…

Concept Layout

Virtual Testing

1D EAS

Optimization

EAS Layout (drive cycle

emissions, component

performance,

durability….)

Reaction modeling/

parameterization

1D EAS

Coding Interface

Optimization

Model

(kinetic, transfer,

diffusion…)

Control Develepment

/Calibration

1D EAS

Control strategy

Control params.


CONTENT


i. DEF Dosing (CFD)



3. Use Case

4. Summary


▪ HD exhaust line

▪ Simplified Geometry

▪ Artificial mixer geometry

▪ Fame Poly Mesh

▪ 4.200.000 cells

▪ w/o wall film reactions

▪ w/ wall film evaporation

COMPONENT DESIGNDEF DOSING – MODEL SETUP

Mixer

Tg

(degC)

mg(kg/h)

mDEF(g/s)

Nr. pulses

(-)

Case 220 220 2000 2 10

Case 270 270 2000 2 10

Case 370 370 2000 2 10


COMPONENT DESIGNDEF DOSING – 3D SIMULATION RESULTS

Urea dosing – snapshot of animation

Wall FilmCase 370

Wall FilmCase 220

Wall FilmCase 270


DISCUSSION

▪ Most of the injected DEF vaporizes in the gas phase

▪ Wall film formation declines with increasing temperature

▪ Simulation of 10 pulse gives a trend, full steady-state is not reached

▪ Results for 1D▪ Deposition split ratio

▪ Film thickness

▪ Frozen flow field* technology enables a significant speed-up to conventional CFD

COMPONENT DESIGNDEF DOSING – 2D SIMULATION RESULTS

Wall Film Mass

0

5

10

15

20

Liq

uid

ma

ss in

jecte

d (

g)

0 2 4 6 8 10

Time (s)

9.95

20

3.8755

2.48917

0.741679

Transient_220 - Injected mass

Transient_220 - WF mass



Gas

temp.

(degC)

Mass

flow

(kg/h)

Dosing

rate

(g/s)

Nr.

pulses

Film

mass

(%)

CPU

time**

[h]

Case 220 220 2000 2 10 19.3 243

Case 270 270 2000 2 10 12.45 151

Case 370 370 2000 2 10 3.7 106

* Schellander D., Pachler K., Schmalhorst C., Nahtigal A., “Predictive Numerical Models and Methods for Selective Catalytic Reactor Applications in Diesel Powered Vehicles”, COMODIA 2017

** CPU time for 10s physical time on Linux cluster on 64 cores (less WF accumulation -> faster sim.)


SUMMARY

▪ AT Model: DOC, injector, pipes, SCR, AMOX

▪ Engine out data from test bed (measured drive cycle)

▪ Injection mass flux: Controlled =1.1▪ Injection shut off: TSD_SCR ≥ 180°C▪ DEF split is taken from CFD▪ ~75% instantaneous evaporation

▪ ~25% wall film

▪ Passive species are deposited(= converted to surface species) in dedicated pipe

CONCEPT SIMULATIONHD EXHAUST LINE – MODEL SETUP

Start of injection@Ts(SCR) = 180°C


SUMMARY

▪ SCR operating conditions are reached after ~120s

▪ Tailpipe NOx levels out after cold start and shows slight increase for the remaining simulation time

▪ NH3 conversion▪ SCR: 85%

▪ AMOX: 100%

▪ NOx conversation: 93%

CONCEPT SIMULATIONHD EXHAUST LINE – TAILPIPE EMISSIONS


SUMMARY

▪ Results depend on assumed wall film thickness60 µm: avg. film thickness from CFD173 µm: moving film (Brack2016)

▪ after 60 min:

▪ thin film: less deposits, formed CYA decomposes again fully

CONCEPT SIMULATIONHD EXHAUST LINE – DEPOSIT FORMATION

dfilm / µm CYA / mg ammelide / mg Total / mg

60 - 150 150

173 320 380 700


SUMMARY

▪ 1/3 pipe insulation lower decomposition temperatures (~25°C)

▪ after 60 min:

▪ higher total deposit mass

CONCEPT SIMULATIONHD EXHAUST LINE – DEPOSIT FORMATION

dfilm / µm CYA / mg ammelide / mg Total / mg

60 - 200 200

173 710 410 1120


▪ 3D DEF dosing model validated in various sub-models

▪ 1D real-time, system engineering model urea decomposition model from Brack

▪ 3D-1D workflow

▪ 3D simulations provide dosing split ratio and film thickness

▪ 1D simulations show strong impact of film thickness (film surface area) on urea decomposition

SUMMARY

nox abatement - cleers€¦ · model vs brack (2016) urea decomposition urea mass decreases over...

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