Diesel Applications Multiphase Multicomponent Modeling using Star-CD - - PowerPoint PPT Presentation

Institute for Powertrains & Automotive Technology

Institute for Powertrains & Automotive Technology

Urea Injection and Preparation in Diesel Applications

Multiphase Multicomponent Modeling using Star-CD

STAR European Conference 2010, London Dipl.-Phys. Simon Fischer

• Dr. Thomas Lauer

STAR European Conference 2010 Urea Injection and Preparation in Diesel Applications March 23rd 2010 | London | Simon Fischer | Slide 2

Contents

 The SCR-Process: Problem Introduction  Methodology and Analysis Setup  Thermodynamic Multicomponent Model of a Urea-Water-Solution  Droplet-Wall-Interaction and Liquid Film Dynamics  Conjugate Heat Transfer and Liquid Film Boiling  Ammonia Homogenization  Conclusion and Outlook

STAR European Conference 2010 Urea Injection and Preparation in Diesel Applications March 23rd 2010 | London | Simon Fischer | Slide 3

Contents

 The SCR-Process: Problem Introduction  Methodology and Analysis Setup  Thermodynamic Multicomponent Model of a Urea-Water-Solution  Droplet-Wall-Interaction and Liquid Film Dynamics  Conjugate Heat Transfer and Liquid Film Boiling  Ammonia Homogenization  Conclusion and Outlook

STAR European Conference 2010 Urea Injection and Preparation in Diesel Applications March 23rd 2010 | London | Simon Fischer | Slide 4

Problem Introduction: Future Diesel Emission Limits

exhaust aftertreatment of NOx is a major requirement for future Diesel engines

[1]

NOx- Emissions [g/km] Particle Emissions [g/km]

SCR source: Auto News

STAR European Conference 2010 Urea Injection and Preparation in Diesel Applications March 23rd 2010 | London | Simon Fischer | Slide 5

Principle of Selective Catalytic Reduction (SCR)

exhaust gas flow (NOx)

injection of a water-urea mixture 32.5 mass-% urea 67.5 mass-% water

timescales of ammonia preparation ammonia uniformity at catalyst frontal area exhaust pipe

impingement film transport heat transfer ammonia (NH3) vapour homogenization preparation process 1) water evaporation 2) chemo-physical urea decomposition to ammonia (thermo-/hydrolysis)

CFD-simulation for efficient SCR-system design

SCR-catalyst:

„NOx+NH3 →N2 + H2O“

STAR European Conference 2010 Urea Injection and Preparation in Diesel Applications March 23rd 2010 | London | Simon Fischer | Slide 6

Contents

 The SCR-Process: Problem Introduction  Methodology and Analysis Setup  Thermodynamic Multicomponent Model of a Urea-Water-Solution  Droplet-Wall-Interaction and Liquid Film Dynamics  Conjugate Heat Transfer and Liquid Film Boiling  Ammonia Homogenization  Conclusion and Outlook

STAR European Conference 2010 Urea Injection and Preparation in Diesel Applications March 23rd 2010 | London | Simon Fischer | Slide 7

Methodology and Validation Setup

straight exhaust pipe urea-water- solution-injection from engine exhaust gas flow SCR-Catalyst CFD mesh according to experimental setup

OP 3 - high temperature / mass flow / NOx raw emission OP2 - intermediate temperature / mass flow / NOx raw emission OP1 - low temperature / mass flow / NOx raw emission

Analysis of Representative Operating Points (OP):

STAR European Conference 2010 Urea Injection and Preparation in Diesel Applications March 23rd 2010 | London | Simon Fischer | Slide 8

Contents

 The SCR-Process: Problem Introduction  Methodology and Analysis Setup  Thermodynamic Multicomponent Model of a Urea-Water-Solution  Droplet-Wall-Interaction and Liquid Film Dynamics  Conjugate Heat Transfer and Liquid Film Boiling  Ammonia Homogenization  Conclusion and Outlook

STAR European Conference 2010 Urea Injection and Preparation in Diesel Applications March 23rd 2010 | London | Simon Fischer | Slide 9

Thermodynamic Multicomponent Model (Liquid Film, Droplets)

TBoil(Yurea) Partial Pressures (Raoult`s law):

AdBlue: 32.5 Mass.-% Urea, 67.5 Mass.-% Water

pure water: Antoine equation implemented in dropro.f, lqfpro.f pure urea: saturation pressure curve implemented in dropro.f, lqfpro.f

) ( ) (

, T

p x T p

i pure s i i s i i s tot

T p T p ) ( ) (

Total Pressure (Dalton`s law):

STAR European Conference 2010 Urea Injection and Preparation in Diesel Applications March 23rd 2010 | London | Simon Fischer | Slide 10

Decomposition of a Single Urea-Water-Solution-Droplet

water evaporation urea thermolysis

two-step preparation process modeled

[1] [1] Wang, Baek,Lee: Experimental Investigation on Evaporation of Urea-Water-Solution Droplet for SCR Applications, AICE 2009

heat flux through fibre, fine tuning of urea-psat-curve

STAR European Conference 2010 Urea Injection and Preparation in Diesel Applications March 23rd 2010 | London | Simon Fischer | Slide 11

Contents

 The SCR-Process: Problem Introduction  Methodology and Analysis Setup  Thermodynamic Multicomponent Model of a Urea-Water-Solution  Droplet-Wall-Interaction and Liquid Film Dynamics  Conjugate Heat Transfer and Liquid Film Boiling  Ammonia Homogenization  Conclusion and Outlook

STAR European Conference 2010 Urea Injection and Preparation in Diesel Applications March 23rd 2010 | London | Simon Fischer | Slide 12

Multiphase Modeling: Challenge Of Timescales

Small Time Scales:

 turbulent flow field  droplet dynamics  species (ammonia) transport

Steady-State Calculation (PISO)

 fluid flow field  temperature field  no spray injection (liquid phase)

Large Time Scales:

 liquid film formation and -dynamics  ammonia formation from film  wall cooling (CHT)

Transient Calculation (Simple)

 thermodynamics (enthalpy)  droplets and liquid film  species (ammonia, water vap.)  time steps: 0.1 ms (droplets present) 1 ms (otherwise)

Solution Strategy: Restart with flow field solvers switched off simulated interval of several minutes incl. spray dynamics and species transport

STAR European Conference 2010 Urea Injection and Preparation in Diesel Applications March 23rd 2010 | London | Simon Fischer | Slide 13

Droplet Dynamics: Injection

three hole nozzle

diameter distribution from measurement

timescale miliseconds droico.f

no primary break-up modelled

STAR European Conference 2010 Urea Injection and Preparation in Diesel Applications March 23rd 2010 | London | Simon Fischer | Slide 14

Droplet Impingement Regimes

depending on liquid properties, droplet dynamics, wall temperature,…

OP 3 – high temp. OP2- medium temp. OP1 - low temp

…complex behaviour Bai-Model (Sw30) Spread-Model

STAR European Conference 2010 Urea Injection and Preparation in Diesel Applications March 23rd 2010 | London | Simon Fischer | Slide 15

Liquid Film Formation: Validation

Experiment (Videoanalysis) Simulation Spread- Model Simulation Bai- Model- Switch 30 OP 1 („cold“) extensive liquid film, flow to pipe bottom

 x

OP 2 („medium“) thin film after some delay, no remarkable flow

x 

OP 3 („hot“) no permanent film

x 

impingement model not yet predictive across whole temperature range

not observed in simulation

STAR European Conference 2010 Urea Injection and Preparation in Diesel Applications March 23rd 2010 | London | Simon Fischer | Slide 16

Simulated Liquid Film Formation

OP3-Bai-Sw30 OP2-BaiSw30 OP1- Spread

…

OP1-BaiSw30

massive liquid film with spread model in OP1 small extent liquid film with Bai model in OP1 no permanent film in OP3 transient behaviour in OP2

STAR European Conference 2010 Urea Injection and Preparation in Diesel Applications March 23rd 2010 | London | Simon Fischer | Slide 17

Droplet Impingement and Liquid Film Dynamics

timescale milliseconds timescale minutes liquid film spread after 120 s

high Droplet Diameter low Film Thickness

STAR European Conference 2010 Urea Injection and Preparation in Diesel Applications March 23rd 2010 | London | Simon Fischer | Slide 18

Liquid Film Dynamics Validation

180° 90° 180° 90°

Experiment Simulation

Video-Analysis [2] Simulation Distribution of Liquid Film after 120 Seconds

OP1- Spread

excellent description of film dynamics

STAR European Conference 2010 Urea Injection and Preparation in Diesel Applications March 23rd 2010 | London | Simon Fischer | Slide 19

Contents

 The SCR-Process: Problem Introduction  Methodology and Analysis Setup  Thermodynamic Multicomponent Model of a Urea-Water-Solution  Droplet-Wall-Interaction and Liquid Film Dynamics  Conjugate Heat Transfer and Liquid Film Boiling  Ammonia Homogenization  Conclusion and Outlook

STAR European Conference 2010 Urea Injection and Preparation in Diesel Applications March 23rd 2010 | London | Simon Fischer | Slide 20

Thermal Wall Boundary Conditions In Star-CD

Adiabatic Fixed Temperature Fixed with Resistance Conjugate Heat Transfer Relevance in SCR-Modeling wall as a heat source

   !!!

cooling of wall due to evaporation

  !!!

thermal inertia of wall

 !!

wall parallel heat conduction

 !!

STAR European Conference 2010 Urea Injection and Preparation in Diesel Applications March 23rd 2010 | London | Simon Fischer | Slide 21

Meshing For Conjugate Heat Transfer Approach

boundary Layer extruded solid cells for CHT single layer approach fluid cells trimmed from custom-grid

STAR European Conference 2010 Urea Injection and Preparation in Diesel Applications March 23rd 2010 | London | Simon Fischer | Slide 22

The Nukiyama Film Boiling Model (Star-CD 4.10)

OP 3 OP2 OP1

regime positions from experiment (IR-thermography)

Burnout Point Leidenfrost Point Film-boiling Transition- Nucleate- Convection

STAR European Conference 2010 Urea Injection and Preparation in Diesel Applications March 23rd 2010 | London | Simon Fischer | Slide 23

Local Wall Spray Cooling

OP 1-Spread

Temperature T[ C] primary impingement position (water evaporation)

Flow direction

IR-Thermography Star-CD 4.10

good qualitative representation

STAR European Conference 2010 Urea Injection and Preparation in Diesel Applications March 23rd 2010 | London | Simon Fischer | Slide 24

Wall Spray Cooling

OP3-Bai Sw30 OP2-BaiSw30

Steady State Wall Cooling Dynamics of Cooling Process

OP1-Spread

IR-Themography Star-CD 4.06 Star-CD 4.10

numerical instability in v4.10 Bai model for thermal break- up-regime (currently fixed by Switch 30 and NOTHBREAK in *.prob)

STAR European Conference 2010 Urea Injection and Preparation in Diesel Applications March 23rd 2010 | London | Simon Fischer | Slide 25

Contents

 The SCR-Process: Problem Introduction  Methodology and Analysis Setup  Thermodynamic Multicomponent Model of a Urea-Water-Solution  Droplet-Wall-Interaction and Liquid Film Dynamics  Conjugate Heat Transfer and Liquid Film Boiling  Ammonia Homogenization  Conclusion and Outlook

STAR European Conference 2010 Urea Injection and Preparation in Diesel Applications March 23rd 2010 | London | Simon Fischer | Slide 26

Film Thickness

OP 1

Ammonia Vapour Homogenization

Ammonia- Concentration high low

STAR European Conference 2010 Urea Injection and Preparation in Diesel Applications March 23rd 2010 | London | Simon Fischer | Slide 27

Ammonia Vapour Homogenization: Validation

FTIR- measurement [2] Ammonia- Concentration

OP 1

Simulation high low

concentrations scaled by mean value

STAR European Conference 2010 Urea Injection and Preparation in Diesel Applications March 23rd 2010 | London | Simon Fischer | Slide 28

Contents

 The SCR-Process: Problem Introduction  Methodology and Analysis Setup  Thermodynamic Multicomponent Model of a Urea-Water-Solution  Droplet-Wall-Interaction and Liquid Film Dynamics  Conjugate Heat Transfer and Liquid Film Boiling  Ammonia Homogenization  Conclusion and Outlook

STAR European Conference 2010 Urea-injection and -preparation in Diesel applications March 23rd 2010 | London | Simon Fischer | Slide 29

Conclusion

 validated Star-CD-Model of the urea-water-solution preparation process:  simulation of several injection events and long time liquid film behaviour via separated (steady) flow field and liquid-phase/thermodynamic calc.  two step ammonia preparation process modeled properly with Raoults` law  predictive impingement model for whole temperature range missing → massive film formation (OP1) currently forced by spread-model → break-up model in v4.10 (for high temp. impingement) not stable  liquid film dynamics well represented in simulation  implementation of Conjugate Heat Transfer for a correct prediction of liquid film formation and preparation timescales (validated by IR-themography)  promising liquid film boiling model improvements from v4.06 to v4.10

STAR European Conference 2010 Urea-injection and -preparation in Diesel applications March 23rd 2010 | London | Simon Fischer | Slide 30

Outlook

• check and adaption of improved Star-CDs` physical models (4.10/4.12)
• NIST approach (internal calculation) for multicomp. thermodynamics properties
• fix of Break-Up regime numerical instabilities of extended Bai-model (v4.10)

(currently NOTHBREAK in *.prob and Switch 30 → support)

• underestimation of liquid film at low temperatures (OP1): tuning of critical

Regime Weber-Numbers to realize „one-fits-all“ Bai-impingement-model

• adaption of liquid film boiling model (Nukiyama-curve) for urea-water solution

(currently standard Star-CD parameter set for pure water) (thermography data available)

• evaluation of post impingement droplet properties (e.g. size distribution)

laser-diffraction data available

• towards a fully predictive SCR-process Star-CD-model

Institute for Powertrains & Automotive Technology

Institute for Powertrains & Automotive Technology

Thank you for your attention!

Dipl.-Phys. Simon Fischer simon.fischer@ifa.tuwien.ac.at