Urea Injection and Preparation in Diesel Applications Multiphase Multicomponent Modeling using Star-CD

, London Urea Injection and Preparation in Diesel Applications Multiphase Multicomponent Modeling using Star-CD Institute for Powertrains & Automotive Technology Dipl.-Phys. Simon Fischer Dr. Thomas Lauer Institute for Powertrains & Automotive Technology

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 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 March 23rd 2010 London Simon Fischer Slide 3

Particle Emissions [g/km] SCR Problem Introduction: Future Diesel Emission Limits [1] NO x - Emissions [g/km] source: Auto News exhaust aftertreatment of NO x is a major requirement for future Diesel engines March 23rd 2010 London Simon Fischer Slide 4

Principle of Selective Catalytic Reduction (SCR) exhaust gas flow (NO x ) exhaust pipe ammonia (NH 3 ) vapour homogenization impingement heat transfer film transport injection of a water-urea mixture 32.5 mass-% urea 67.5 mass-% water preparation process 1) water evaporation 2) chemo-physical urea decomposition to ammonia (thermo-/hydrolysis) CFD-simulation for efficient SCR-system design timescales of ammonia preparation ammonia uniformity at catalyst frontal area SCR-catalyst: NO x +NH 3 N 2 + H 2 O March 23rd 2010 London Simon Fischer Slide 5

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 March 23rd 2010 London Simon Fischer Slide 6

SCR-Catalyst Methodology and Validation Setup urea-watersolution-injection CFD mesh according to experimental setup exhaust gas flow straight exhaust pipe from engine Analysis of Representative Operating Points (OP): OP1 - low temperature / mass flow / NO x raw emission OP2 - intermediate temperature / mass flow / NO x raw emission OP 3 - high temperature / mass flow / NO x raw emission March 23rd 2010 London Simon Fischer Slide 7

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 March 23rd 2010 London Simon Fischer Slide 8

Thermodynamic Multicomponent Model (Liquid Film, Droplets) Partial Pressures (Raoult`s law): p i s ( T) x i p pure, i s ( T) T Boil (Y urea ) Total Pressure (Dalton`s law): p ( T) p ( T) tot i i s pure water: Antoine equation implemented in dropro.f, lqfpro.f AdBlue: 32.5 Mass.-% Urea, 67.5 Mass.-% Water pure urea: saturation pressure curve implemented in dropro.f, lqfpro.f March 23rd 2010 London Simon Fischer Slide 9

Decomposition of a Single Urea-Water-Solution-Droplet water evaporation urea thermolysis [1] heat flux through fibre, fine tuning of urea-p sat -curve two-step preparation process modeled [1] Wang, Baek,Lee: Experimental Investigation on Evaporation of Urea-Water-Solution Droplet for SCR Applications, AICE 2009 March 23rd 2010 London Simon Fischer Slide 10

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 March 23rd 2010 London Simon Fischer Slide 11

Multiphase Modeling: Challenge Of Timescales Small Time Scales: Large Time Scales: turbulent flow field liquid film formation and -dynamics droplet dynamics ammonia formation from film species (ammonia) transport wall cooling (CHT) Solution Strategy: Steady-State Calculation (PISO) fluid flow field temperature field no spray injection (liquid phase) Restart with flow field solvers switched off Transient Calculation (Simple) thermodynamics (enthalpy) droplets and liquid film species (ammonia, water vap.) time steps: 0.1 ms (droplets present) 1 ms (otherwise) simulated interval of several minutes incl. spray dynamics and species transport March 23rd 2010 London Simon Fischer Slide 12

Droplet Dynamics: Injection three hole nozzle no primary break-up modelled diameter distribution from measurement droico.f timescale miliseconds March 23rd 2010 London Simon Fischer Slide 13

Bai-Model (Sw30) Spread-Model Droplet Impingement Regimes depending on liquid properties, droplet dynamics, wall temperature, OP1 - low temp OP2- medium temp. complex behaviour OP 3 high temp. March 23rd 2010 London Simon Fischer Slide 14

Liquid Film Formation: Validation Experiment (Videoanalysis) Simulation Spread- Model Simulation Bai- Model- Switch 30 OP 1 ( cold ) OP 2 ( medium ) extensive liquid film, flow to pipe bottom x thin film after some delay, no remarkable flow x not observed in simulation OP 3 ( hot ) no permanent film x impingement model not yet predictive across whole temperature range March 23rd 2010 London Simon Fischer Slide 15

Simulated Liquid Film Formation massive liquid film with spread model in OP1 OP1- Spread OP1-BaiSw30 OP2-BaiSw30 OP3-Bai-Sw30 no permanent film in OP3 transient behaviour in OP2 small extent liquid film with Bai model in OP1 March 23rd 2010 London Simon Fischer Slide 16

Droplet Impingement and Liquid Film Dynamics high low Droplet Film Diameter Thickness liquid timescale film spread milliseconds minutesafter 120 s March 23rd 2010 London Simon Fischer Slide 17

excellent description of film dynamics Simulation Video-Analysis [2] Simulation Experiment Liquid Film Dynamics Validation Distribution of Liquid Film after 120 Seconds 90 180 90 180 OP1- Spread March 23rd 2010 London Simon Fischer Slide 18

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 March 23rd 2010 London Simon Fischer Slide 19

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!! March 23rd 2010 London Simon Fischer Slide 20

Meshing For Conjugate Heat Transfer Approach extruded solid cells for CHT single layer approach fluid cells boundary Layer trimmed from custom-grid March 23rd 2010 London Simon Fischer Slide 21

The Nukiyama Film Boiling Model (Star-CD 4.10) Convection Transition- Nucleate- Film-boiling OP1 Burnout Point OP2 OP 3 regime positions from experiment (IR-thermography) Leidenfrost Point March 23rd 2010 London Simon Fischer Slide 22

Local Wall Spray Cooling OP 1-Spread IR-Thermography Temperature T[ C] Flow direction primary impingement position (water evaporation) Star-CD 4.10 good qualitative representation March 23rd 2010 London Simon Fischer Slide 23

Wall Spray Cooling Dynamics of Cooling Process Steady State Wall Cooling OP1-Spread OP2-BaiSw30 OP3-Bai Sw30 numerical instability in v4.10 Bai model for thermal breakup-regime (currently fixed by Switch 30 and NOTHBREAK in *.prob) IR-Themography Star-CD 4.06 Star-CD 4.10 March 23rd 2010 London Simon Fischer Slide 24

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 March 23rd 2010 London Simon Fischer Slide 25

Ammonia Vapour Homogenization OP 1 high Ammonia- Film Concentration Thickness low March 23rd 2010 London Simon Fischer Slide 26

Ammonia Vapour Homogenization: Validation OP 1 Simulation concentrations scaled by mean value high Ammonia- Concentration FTIR- measurement [2] low March 23rd 2010 London Simon Fischer Slide 27

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 March 23rd 2010 London Simon Fischer Slide 28

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

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

Thank you for your attention! Institute for Powertrains & Automotive Technology Dipl.-Phys. Simon Fischer simon.fischer@ifa.tuwien.ac.at Institute for Powertrains & Automotive Technology