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

STAR European Conference 2010, 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 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

Problem Introduction: Future Diesel Emission Limits Particle Emissions [g/km] [1] SCR NO x - Emissions [g/km] source: Auto News exhaust aftertreatment of NO x is a major requirement for future Diesel engines STAR European Conference 2010 Urea Injection and Preparation in Diesel Applications 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 heat transfer impingement film transport injection of a preparation process water-urea mixture 1) water evaporation 32.5 mass-% urea 2) chemo-physical urea 67.5 mass-% water decomposition to ammonia (thermo-/hydrolysis) CFD-simulation for efficient SCR-system design SCR-catalyst: „NO x +NH 3 →N 2 + H 2 O“ timescales of ammonia preparation ammonia uniformity at catalyst frontal area STAR European Conference 2010 Urea Injection and Preparation in Diesel Applications 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 STAR European Conference 2010 Urea Injection and Preparation in Diesel Applications March 23rd 2010 | London | Simon Fischer | Slide 6

Methodology and Validation Setup CFD mesh according to urea-water- experimental setup solution-injection SCR-Catalyst 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 STAR European Conference 2010 Urea Injection and Preparation in Diesel Applications 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 STAR European Conference 2010 Urea Injection and Preparation in Diesel Applications March 23rd 2010 | London | Simon Fischer | Slide 8

Thermodynamic Multicomponent Model (Liquid Film, Droplets) Partial Pressures (Raoult`s law): , T i pure i ( ) ( ) p T x p T Boil (Y urea ) s i s Total Pressure (Dalton`s law): i p ( T ) p ( T ) tot s i pure water: pure urea: Antoine saturation equation pressure curve AdBlue: implemented in implemented in 32.5 Mass.-% Urea, dropro.f, lqfpro.f dropro.f, lqfpro.f 67.5 Mass.-% Water STAR European Conference 2010 Urea Injection and Preparation in Diesel Applications 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 STAR European Conference 2010 Urea Injection and Preparation in Diesel Applications 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 STAR European Conference 2010 Urea Injection and Preparation in Diesel Applications 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: Transient Calculation (Simple) Steady-State Calculation (PISO)  thermodynamics (enthalpy)  fluid flow field  droplets and liquid film  temperature field Restart with  species (ammonia, water vap.)  no spray injection (liquid phase) flow field solvers  time steps: 0.1 ms (droplets present) switched off 1 ms (otherwise) 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 12

Droplet Dynamics: Injection three hole nozzle no primary break-up modelled diameter distribution from droico.f measurement timescale miliseconds STAR European Conference 2010 Urea Injection and Preparation in Diesel Applications March 23rd 2010 | London | Simon Fischer | Slide 13

Droplet Impingement Regimes depending on liquid properties, droplet dynamics, wall temperature ,… Bai-Model (Sw30) Spread-Model OP1 - low temp OP2- medium temp. OP 3 – high temp. … complex behaviour STAR European Conference 2010 Urea Injection and Preparation in Diesel Applications March 23rd 2010 | London | Simon Fischer | Slide 14

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

Simulated Liquid Film Formation OP1- Spread massive liquid film with spread model in OP1 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 … STAR European Conference 2010 Urea Injection and Preparation in Diesel Applications March 23rd 2010 | London | Simon Fischer | Slide 16

Droplet Impingement and Liquid Film Dynamics high Film Droplet Diameter Thickness liquid film spread after 120 s timescale milliseconds timescale minutes low STAR European Conference 2010 Urea Injection and Preparation in Diesel Applications March 23rd 2010 | London | Simon Fischer | Slide 17

Liquid Film Dynamics Validation Distribution of Liquid Film after 120 Seconds excellent description of film dynamics Video-Analysis [2] Experiment 90° 180° Simulation Simulation 90° 180° OP1- Spread STAR European Conference 2010 Urea Injection and Preparation in Diesel Applications 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 STAR European Conference 2010 Urea Injection and Preparation in Diesel Applications March 23rd 2010 | London | Simon Fischer | Slide 19

Thermal Wall Boundary Conditions In Star-CD SCR-Modeling Heat Transfer Relevance in Temperature Resistance Conjugate Fixed with Adiabatic Fixed    !!! 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 20

Meshing For Conjugate Heat Transfer Approach extruded solid cells for CHT single layer approach fluid cells boundary Layer trimmed from custom-grid STAR European Conference 2010 Urea Injection and Preparation in Diesel Applications March 23rd 2010 | London | Simon Fischer | Slide 21