preparation in the tailpipe: Spray/wall interaction and deposit formation M. Börnhorst, C. Kuntz, S. Tischer, O. Deutschmann

Cross-Cut Lean Exhaust Emissions Reduction Simulations (CLEERS) Workshop, Sept. 18-20, 2018, Ann Arbor

KIT - Institute for Chemical Technology and Polymer Chemistry (ITCP)

Courtesy of Bosch www.dieselforum.org

KIT – The Research University in the Helmholtz Association www.kit.edu Ammonia preparation in the tailpipe

AdBlue injection DOC & DPF SCR ASC

Diesel oxidation catalyst and Selective catalytic Ammonia slip Source: BMW particel filter reduction catalyst thermolysis & (NH2)2CO (l)  NH3 (g) + HNCO (g) hydrolysis HNCO (g) + H2O (g)  NH3 (g) + CO2 (g)

SCR reaction 2 NH3 + NO + NO2  2 N2 + 3 H2O

Robert Bosch GmbH

Injection of a 32.5 wt.-% urea solution (AdBlue®) used as precursor for ammonia Formation of liquid and solid deposits by incomplete evaporation and urea conversion

 Serious loss of NOx reduction efficiency Endoscopic records from a hot gas test rig [1] [1] Brack, W., Untersuchung der Ablagerungsbildung durch Harnstofffolgeprodukte im Abgasstrang, PhD thesis (2015), 1-175

2 Sept. 20, 2018 Marion Börnhorst Institute for Chemical Technology and Polymer Chemistry Liquid and solid deposits in SCR systems

Spray: Drops: pinj, Tinj, minj ud, dd, Td Thermolysis & Hydrolysis Gas:

Tg, pg, ug SCR Evaporation

Solid deposit

Wall: Liquid Film: Solid by-products: Θ, Ra, Tw Af, hf, Tf Triuret Ammelide Ammeline

3 Sept. 20, 2018 Marion Börnhorst Institute for Chemical Technology and Polymer Chemistry Outline

• Deposit formation at a hot gas test rig Urea • Deposit characterization decomposition

• Kinetic measurements on urea decomposition MPTR Kinetic • DETCHEM model modeling

• Coupling of kinetic model with StarCCM+ simulation Integration to CFD

4 Sept. 20, 2018 Marion Börnhorst Institute for Chemical Technology and Polymer Chemistry Laboratory test rig

Hot gas test rig with integrated urea dosing system

Injection/measurement cell designed for undisturbed flow and optical access Control unit

UWS tank

Flowmeter Measuring Diffusor Contraction section Vertical compressor

Parameter Unit Operating range Gas flow L/min 50 - 3000 Gas velocity m/s 0.5 - 25 ReynoldsTABELLE number - 1200 - 50000 Gas temperature °C 100 – 350 Injection mass flow kg/h 0.03 – 5.3

Injection pressure bar 5 Injection angle ° 33

5 Sept. 20, 2018 Marion Börnhorst Institute for Chemical Technology and Polymer Chemistry Deposit formation in lab test bench Injection Film formation during injection

Evaporation leaves solid deposits

Dissolution of existing deposits

Deposit build-up over time

OP: Tgas= 300°C, Vgas= 1200 L/min, ugas = 11 m/s, murea = 1 g/min, 3 x 40 min injection

6 Sept. 20, 2018 Marion Börnhorst Institute for Chemical Technology and Polymer Chemistry Deposit sampling

1 2

3 4

OP Tgas / °C Vgas / L/min ugas / m/s - Three injection periods of 40 min 1 150 866 8.0 - UWS mass flow of 1 g/min 2 190 916 8.5 3 280 1030 9.5 4 320 870 8.0

7 Sept. 20, 2018 Marion Börnhorst Institute for Chemical Technology and Polymer Chemistry Deposit Characterization

High Performance Liquid Chromatography (HPLC)

 Deposit composition

Thermogravimetric analysis (TGA)

 Decomposition kinetics

Keyence LJ-V7200 3D-Structure analysis Laser profile sensor

 Surface profile of deposits

8 Sept. 20, 2018 Marion Börnhorst Institute for Chemical Technology and Polymer Chemistry Deposit analysis by HPLC

Method development for qualitative and quantitative deposit analysis based on Koebel et al. (1995) and Bernhard et al. (2011) Separation and quantification of components by adsorption potential

Na2HPO4 buffer as solvent and eluent Anion exchange column Photodiode-array detector (UV/VIS)

Method validation and calibration by

standard solutions

Strong pH sensitivity affects

measurement accuracy acid

Urea

Biuret

Ammeline

Cyanuric Ammelid

9 Sept. 20, 2018 Marion Börnhorst Institute for Chemical Technology and Polymer Chemistry TGA procedure

Thermogravimetric analysis of decomposition kinetics

Sample crucible Grinded, representative sample of deposit

TG Setup: Netzsch STA 409, TASC 414/2

Initial sample mass of 15 – 20 mg

Gas flow of 100 ml/min synthetic air

Temperature programm: heating rate of 2K/min, from 40 to 700°C

10 Sept. 20, 2018 Marion Börnhorst Institute for Chemical Technology and Polymer Chemistry TGA of urea and by-product decomposition

100 Urea

80 2 60 40 1 3

20 sample mass[%] 0 50 100 150 200 250 300 350 400 450 500 550 600 Temperature [°C]

100 Biuret 80 Cyanuric acid Ammelide 60 40 20 samplemass [%] 0 50 100 150 200 250 300 350 400 450 500 550 600 Temperature [°C]

11 Sept. 20, 2018 Marion Börnhorst Institute for Chemical Technology and Polymer Chemistry Characterization of OP 1 deposit

OP Tgas / °C Vgas / L/min ugas / m/s Deposit volume cm³ 16.87 1 150 866 8.0 Max. height mm 19.25

Mean height mm 5.24

Substance Urea Biu Triu CyA Amd Amn Mel Rest

Portion 65.6 0.2 0 0 0 0 0 34.2 [wt.-%]

100 OP 1 urea 80

60 loss / / loss %

ass ass 40 M

20

0 0 100 200 300 400 500 600 700 Temperature / °C

Characterization of solid deposits from urea water solution injected into a hot gas test rig, Börnhorst et al. (2018)

12 Sept. 20, 2018 Marion Börnhorst Institute for Chemical Technology and Polymer Chemistry Characterization of OP 2 deposit

OP Tgas / °C Vgas / L/min ugas / m/s Deposit volume cm³ 0.13 2 190 916 8.5 Max. height mm 0.80

Mean height mm 0.47

Substance Urea Biu Triu CyA Amd Amn Mel Rest

Portion 57.0 9.7 2.2 0.4 0 0 0 30.7 [wt.-%]

100 OP 2 urea 80

60

40 Mass loss / Mass/ % loss

20

0 0 100 200 300 400 500 600 700 Temperature / °C Characterization of solid deposits from urea water solution injected into a hot gas test rig, Börnhorst et al. (2018)

13 Sept. 20, 2018 Marion Börnhorst Institute for Chemical Technology and Polymer Chemistry Characterization of OP 3 deposit

OP Tgas / °C Vgas / L/min ugas / m/s Deposit volume cm³ 0.83 3 280 1030 9.5 Max. height mm 2.55

Mean height mm 0.57

Substance Urea Biu Triu CyA Amd Amn Mel Rest

Portion 19.4 2.3 0 53.1 5.8 0.9 0 18.5 [wt.-%]

100 OP3 cyanuric acid 80

60 loss / / loss %

ass ass 40 M

20

0 0 100 200 300 400 500 600 700 Temperature / °C

Characterization of solid deposits from urea water solution injected into a hot gas test rig, Börnhorst et al. (2018)

14 Sept. 20, 2018 Marion Börnhorst Institute for Chemical Technology and Polymer Chemistry Characterization of OP 4 deposit

OP Tgas / °C Vgas / L/min ugas / m/s Deposit volume cm³ 0.35 4 320 870 8.0 Max. height mm 2.46

Mean height mm 0.99

Substance Urea Biu Triu CyA Amd Amn Mel Rest

Portion 1.6 0 0 68.1 5.9 1.2 0 23,2 [wt.-%]

100 OP4 cyanuric acid 80

60

40 mass mass loss % /

20

0 0 100 200 300 400 500 600 700 Temperature / °C

Characterization of solid deposits from urea water solution injected into a hot gas test rig, Börnhorst et al. (2018)

15 Sept. 20, 2018 Marion Börnhorst Institute for Chemical Technology and Polymer Chemistry Deposit composition

100 Urea

80 OP 1

60 OP 3 OP 2 40 OP 4

20 samplemass [%] 0 50 100 150 200 250 300 350 400 450 500 550 600 Temperature [°C]

Similar deposit composition for similar operating temperatures

Prediction of deposit composition by characteristic urea decomposition kinetics

16 Sept. 20, 2018 Marion Börnhorst Institute for Chemical Technology and Polymer Chemistry DETCHEMMPTR

Multiple Phase Tank Reactor 0D batch type reactor model Solves for species balances in multiple phases and heat balance Homogeneous and inter-phase reactions

ni,in

ni,g,Vg Inter-phase Reactions Homogeneous ni,aq,Vaq Reactions

Homogeneous ni,l,Vl Reactions Inter-phase Reactions Homogeneous ni,s,Vs Reactions

17 Sept. 20, 2018 Marion Börnhorst Institute for Chemical Technology and Polymer Chemistry Kinetic model

Consumption Production Water Carbon dioxide Isocyanic acid Ammonia Urea Biuret Triuret Melamine Ammeline Ammelide Cyanuric Acid

18 Sept. 20, 2018 Marion Börnhorst Institute for Chemical Technology and Polymer Chemistry Decomposition of urea in DETCHEMMPTR

10 total urea(l) urea(s) 8 biu(l) biu(s)

mg triu(l) 6 triu(s) cya(s)

Mass / % Mass 4 ammd(s)

2

0 100 200 300 400 500 600 700 Temperature / °C

Validation of overall mass loss by experimental data Evolution of different species in liquid and solid phase during decomposition

19 Sept. 20, 2018 Marion Börnhorst Institute for Chemical Technology and Polymer Chemistry Simulation of chemical decomposition

urea biuret

cyanuric acid triuret

20 Sept. 20, 2018 Marion Börnhorst Institute for Chemical Technology and Polymer Chemistry CFD-Simulation of thermogravimetric decomposition in StarCCM+

Mesh with ~30000 cells Timestep of 20 ms Segregated flow model k-ε-turbulence model Evaporation/condensation model Rohsenow boiling model Complex Chemistry CVODE model

MPTR algorithm  C-code  Implementation by user coding

21 Sept. 20, 2018 Marion Börnhorst Institute for Chemical Technology and Polymer Chemistry Coupling of DETCHEMMPTR with Star-CCM+

StarCCM+ Calculation of (g) concentrations in gas phase and liquid film, (l) gas-liquid equilibrium, heat balance

ri ci, film, Tfilm, t

User Code MPTR

(aq) Calculation of reaction rates in (l) different phases (aq, l, s) and at interfaces (s)

22 Sept. 20, 2018 Marion Börnhorst Institute for Chemical Technology and Polymer Chemistry Simulation of by-product decomposition

Excellent agreement with simulation in DETCHEMMPTR

cyanuric acid Continuous improvement of kinetic model for better agreement with experiments

biuret triuret

23 Sept. 20, 2018 Marion Börnhorst Institute for Chemical Technology and Polymer Chemistry Conclusion

Systematic study on deposit formation in a hot gas test rig Characterization of derived solid deposits Kinetic modeling of urea decomposition and simulation in DETCHEMMPTR Integration of DETCHEMMPTR algorithm into a CFD simulation by user coding

Outlook

Comprehensive simulation of entire test rig Flow field Spray injection Spray/wall interaction Wall heat transfer Liquid film formation and flow Urea decomposition and by-product formation

24 Sept. 20, 2018 Marion Börnhorst Institute for Chemical Technology and Polymer Chemistry We acknowledge financial support by

Thank you for your attention.

Research Association for Combustion Engines Contact: [email protected]

KIT - Institute for Chemical Technology and Polymer Chemistry (ITCP)

Courtesy of Bosch www.dieselforum.org

KIT – The Research University in the Helmholtz Association www.kit.edu