subtopic 2.3: soot field

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ECN 3 1 Apr 2014 ECN Subtopic 2.3: Soot Field Topic 2.0 Organizer Jose M. Garcia-Oliver Subtopic 2.3 Coordinators Michele Bolla, ETH Dan Haworth, PSU Scott Skeen, Sandia Subtopic 2.3 Contributors Experimental IFP Energy nouvelles Sandia Meiji University Modeling University of Wisconsin Politecnico di Milano ETH Zurich POLI MI Wisconsi n Sand ia

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Subtopic 2.3: Soot Field. POLIMI. Topic 2.0 Organizer Jose M. Garcia-Oliver Subtopic 2.3 Coordinators Michele Bolla, ETH Dan Haworth, PSU Scott Skeen, Sandia Subtopic 2.3 Contributors Experimental IFP Energy nouvelles Sandia Meiji University Modeling - PowerPoint PPT Presentation

TRANSCRIPT

Page 1: Subtopic 2.3: Soot Field

ECN 3 1Apr 2014

ECN Subtopic 2.3: Soot Field

Topic 2.0 OrganizerJose M. Garcia-Oliver

Subtopic 2.3 CoordinatorsMichele Bolla, ETHDan Haworth, PSUScott Skeen, Sandia

Subtopic 2.3 Contributors Experimental

IFP Energy nouvellesSandiaMeiji University

ModelingUniversity of Wisconsin Politecnico di MilanoETH Zurich

POLIMI

Wisconsin

Sandia

Page 2: Subtopic 2.3: Soot Field

ECN 3 2Apr 2014

ECN Review of ECN 2 Soot Session

• Dan Haworth provided discussed the physics of soot formation and CFD-based soot modeling, emphasizing the importance of radiation heat transfer (see Webex recording)

• Emre Cenker presented LII/LEM experiments for Spray A and a few parametric variants– Peak SVF of 2-4 ppm for Spray A (930 K, 21.8 kg/m3)– Peak SVF of 12 ppm at 1030 K– Signal trapping considered to be negligible

• Two groups (ETH and U Wisconsin) submitted mean soot volume fraction data for Spray H– Models reproduced measured soot levels and trends with variations in ambient O2 and density– No definitive conclusions were drawn regarding the merits of the different modeling approaches

• Recommendations from ECN 2:– Ambient temperature of ECN pre-combustion vessels should be well characterized– LII measurements exhibited significant statistical error due to jitter between the laser and camera. Future LII

experiments must minimize jitter and account for it in the LII calibration– Long injection duration for measurements examining quasi-steady behavior– Begin looking at Spray A (n-dodecane)– Modelers should perform systematic parametric studies to isolate and quantify the effects of individual

physical processes• Turbulence-Chemistry Interaction• Turbulence-Radiation Interaction• Nucleation, surface growth, agglomeration

Page 3: Subtopic 2.3: Soot Field

ECN 3 3Apr 2014

ECN Subtopic 2.3: Objectives

• Soot Onset (Timing and Location)– How to quantify for consistency between experiments and modeling– Parametric variation (850 K, 900 K, 1000 K) (13%, 15%, 21% O2)

• 2-D Soot Field– Transient progression (1.5, 2.0, 2.5, 4.5 ms ASOI)– Compare IFPEN LII with extinction imaging from Sandia at available timings– Evaluation of signal-trapping– Standardization of soot non-dimensional extinction coefficient

• Soot Temperature– Comparison of 2-Color pyrometry (IFPEN) with Imaging Spectrometer (Sandia)

• Soot Particle Size– What is the primary particle size at the location of peak SVF?– How does particle size change as a function of distance from the injector?

“To improve the understanding of the physical/chemical processes of soot formation and oxidation under engine-relevant conditions and to distill this improved understanding into predictive CFD-based models.”

-ECN3 Guidelines

Page 4: Subtopic 2.3: Soot Field

ECN 3 4Apr 2014

ECN Sandia Extinction Imaging Setup

• Simultaneous ignition delay, quasi-steady lift-off length, and soot extinction measurements

• Two incident wavelengths has proven useful for understanding optical properties of soot

• Soot Measurement Resolution– 85 kHz 35 µs (2 wavelength) 23 µs (1 wavelength)– 100 µm per pixel

• Lower Detection Limit (Beam-steering)– < 0.5 ppm

Page 5: Subtopic 2.3: Soot Field

ECN 3 5Apr 2014

ECN Extinction Imaging

Spray A

• Soot mass is proportional to measured optical thickness (KL) • High-speed extinction imaging measurements provide time-resolved KL maps• Total mass and axial resolved soot mass do not require tomography for comparison to

modeled SVF results• Mass-based soot onset timing and location provide targets for modeling efforts• Inception of soot in spray head and its progression downstream provide a difficult

modeling target

𝐾𝐿=∫ 𝑘𝑒

𝜆 𝑓 𝑣𝑑𝑙 Masssoot= pixel area𝜌 𝐾𝐿 𝜆𝑘𝑒

=𝜌∫ 𝑓 𝑣𝑑𝑙 [𝑔/𝑐𝑚2¿ ]¿

Page 6: Subtopic 2.3: Soot Field

ECN 3 6Apr 2014

ECN Time Sequence of LII vs. Time-Resolved Extinction

*Tamb: 930 K *ρamb: 21.8 kg/m3

• Can compare progression of total soot mass as an indicator of soot onset• Appears to be a mismatch in reacting vapor penetration

Page 7: Subtopic 2.3: Soot Field

ECN 3 7Apr 2014

ECN Soot Onset: Timing and Location

• Mass-based soot onset timing and location provide targets for modeling efforts– Based on a soot mass threshold of 0.5 µg for total mass– Based on a soot mass threshold of 10 ng for axial resolved mass

• Rate of total soot mass increase is very similar for IFPEN LII data and Sandia Extinction Imaging Data

• 200 µs difference in soot onset potentially explained by uncertainty in IFPEN vapor penetration

Page 8: Subtopic 2.3: Soot Field

ECN 3 8Apr 2014

ECN Soot Onset: Timing and Location

15%850 K

15%1000 K

Tamb [K] 850 900 1000

Mean Soot Mass [µg](quasi-steady) 2 14 42

Page 9: Subtopic 2.3: Soot Field

ECN 3 9Apr 2014

ECN Soot Onset: Timing and Location

15%850 K

15%1000 K

Tamb [K] 850 900 1000

Mean Soot Mass [µg](quasi-steady) 2 14 42

Full soot field was not captured, so numbers are considered low relative to reality

Page 10: Subtopic 2.3: Soot Field

ECN 3 10Apr 2014

ECN Soot Onset: Timing and Location

13%900 K

21%900 K

O2,amb [%] 13 15 21

Mean Soot Mass [µg](quasi-steady) 10 14 11

Page 11: Subtopic 2.3: Soot Field

ECN 3 11Apr 2014

ECN Soot Onset: Timing and Location

13%900 K

21%900 K

O2,amb [%] 13 15 21

Mean Soot Mass [µg](quasi-steady) 10 14 11

Full soot field was not captured, so numbers are considered low relative to reality

Page 12: Subtopic 2.3: Soot Field

ECN 3 12Apr 2014

ECN Soot Timing and Location Relative to Ignition• Parametric variation around Spray A in temperature and O2 concentration show a

predictable trend in the time between high-temperature ignition and soot onset and the location of high-temperature ignition and soot onset.

Page 13: Subtopic 2.3: Soot Field

ECN 3 13Apr 2014

ECN Time-Resolved Total Soot Mass

• Higher ambient temperature and O2 lead to better performance of UW model

• UW model scales similarly later during quasi-steady period for AR and O3 cases

• Between 1 and 2 ms ASOI, POLIMI model scales similarly for all but the 21% O2 case

Wisconsin

Page 14: Subtopic 2.3: Soot Field

ECN 3 14Apr 2014

ECN Ensemble Averaged SVF (IFPEN/Sandia)

Page 15: Subtopic 2.3: Soot Field

ECN 3 15Apr 2014

ECN Ensemble Averaged SVF

sdf

LII n-heptane: 15% O2, 1000 K, 1500 bar, 30 kg/m3, 100 µm orifice

With sufficient statistics, ensemble average of single-shot LII yields axisymmetric images similar to time- and ensemble-averaged extinction imaging data

Page 16: Subtopic 2.3: Soot Field

ECN 3 16Apr 2014

ECN Radial Profiles of fv

• Signal trapping may cause plateau in LII data

• Correction must be applied to raw LII signal before integration and calculation of fv

• IFPEN used a 425 nm +/- 15 nm bandpass filter for collection of LII signal

• Extinction measurements at Sandia using 406 nm incident light showed a mean KL of ~0.9 between 55 and 60 mm (KL = 0.45 for half the path length)

• Signal trapping could result in 36% of the signal blocked along the centerline

• Must also consider the effect of ke

Sandia KL using406 nm incident light

Page 17: Subtopic 2.3: Soot Field

ECN 3 17Apr 2014

ECN Non-dimensional Extinction Coeff., ke

Primary Particle

Diameter, dp

ke (N=5)

ke (N=75)

ke (N=150)

[nm] unitless unitless unitless

10 7.03 7.08 7.12

16 7.04 7.21 7.28

20 7.06 7.33 7.47

30 7.12 7.77 8.04

40 7.25 8.37 8.77

50 7.45 9.08 9.62

60 7.72 9.90 10.6

• Standard ke was updated from 4.9 to 8.7 for 632.8 nm extinction measurements• ke computed from Rayleigh-Debye-Gans theory for fractal aggregates is different• Refractive index 1.75-1.03i from Williams et al. Int. J. Heat and Mass Transfer (2007) • Np primary particles per aggregate, dp primary particle diameter• Incident wavelength of 632.8 nm• Greater effect of Np for larger primary particle size• Small particles sizes in Spray A measured by TEM means uncertainty in assumption

of constant Np is reduced• Greatest uncertainty remains in the refractive index of soot

Page 18: Subtopic 2.3: Soot Field

ECN 3 18Apr 2014

ECN Non-dimensional Extinction Coeff., ke

Primary Particle

Diameter, dp

ke (N=5)

ke (N=75)

ke (N=150)

[nm] unitless unitless unitless

10 7.03 7.08 7.12

16 7.04 7.21 7.28

20 7.06 7.33 7.47

30 7.12 7.77 8.04

40 7.25 8.37 8.77

50 7.45 9.08 9.62

60 7.72 9.90 10.6

• Standard ke was updated from 4.9 to 8.7 for 632.8 nm extinction measurements• ke computed from Rayleigh-Debye-Gans theory for fractal aggregates is different• Refractive index 1.75-1.03i from Williams et al. Int. J. Heat and Mass Transfer (2007) • Np primary particles per aggregate, dp primary particle diameter• Incident wavelength of 632.8 nm• Greater effect of Np for larger primary particle size• Small particles sizes in Spray A measured by TEM means uncertainty in assumption

of constant Np is reduced• Greatest uncertainty remains in the refractive index of soot

O3 (21% O2)

Page 19: Subtopic 2.3: Soot Field

ECN 3 19Apr 2014

ECN Signal Trapping

• Correction based on Sandia extinction data improves plateau somewhat

• Correction actually decreases mass along chosen cross section by 4%

• Use uncorrected fv as ILII(x,y), make correction based on Gaussian KL from Sandia data, re-integrate new KLLII

• Correction increases mass by a factor of 1.8

Page 20: Subtopic 2.3: Soot Field

ECN 3 20Apr 2014

ECN Total Soot Mass

• IFPEN calibrated with 632.8 HeNe laser extinction– ke = 8.7 was standard at the time of publication

• Sandia extinction imaging with 406 nm LED– ke = 7.76 based on RDG theory with dp = 16 nm and Np = 150

Page 21: Subtopic 2.3: Soot Field

ECN 3 21Apr 2014

ECN Total Soot Mass

• IFPEN calibrated with 632.8 HeNe laser extinction– ke = 8.7 was standard at the time of publication– ke = 7.28 from RDG theory with dp = 16 nm, Np=150 as in Imaging

Extinction work (20% increase in fv and soot mass)

Page 22: Subtopic 2.3: Soot Field

ECN 3 22Apr 2014

ECN Summary

• Extinction imaging measurements have provided useful targets for modeling efforts including:

– Soot onset time– Soot onset location– Soot mass and/or soot volume fraction– Transient progression of the 2D soot field with high temporal resolution (35 µs)

• Need to increase field of view and further reduce effects of beam steering

• Comparison of LII/LEM measurements from IFPEN and Sandia’s Extinction Imaging measurements

– Similar rate of soot mass increase for Spray A– Differences in reacting penetration may explain difference in soot onset time– Differences in SVF lessened by accounting for signal trapping (~400 nm)– Differences in SVF lessened further by considering ke derived from Rayleigh-Debye-

Gans theory

• Primary particle size as measured by IFPEN/Meiji ranges from 10-20 nm

– Small primary particle sizes reduce the error associated with our assumption of constant Np throughout the soot field.

Page 23: Subtopic 2.3: Soot Field

ECN 3 23Apr 2014

ECN Dirty Laundry-Nozzle Aging (injector 370)

• Similar lift-off lengths and total soot mass, slightly short ignition delay time for later data, significantly shorter soot onset time

• Mass measurements and pressure traces indicate change in discharge coefficient (more mass in later experiments)

Tamb = 905 KLift-off: 16.09

τig = 404 µs (chemi)τig = 400 µs (press)

Tamb = 902.5 KLift-off: 16.23

τig = 344 µs (chemi) faster cameraτig = 370 µs (press)

Page 24: Subtopic 2.3: Soot Field

ECN

ECN 3 Topic 2.3 – Soot fields 24April 4th 2014

Outline: Soot modeling

Presentation soot models used (3 contributors)– UW, POLIMI and ETH

Analysis C2H2 as soot „initial condition“ – C2H2 total mass in time (UW, ETH, POLIMI and UNSW)– Spatial distribution at 1.5 ms and 4 ms (UW, ETH, POLIMI, UNSW and ANL)

Analysis soot results for reference case– Total soot mass in time– Soot spatial extent at 1.5/2.0/2.5 ms compared to KL (qualitative)– SVF comparison at 4 ms (quantitative)– Mean particle size at 4ms

Analysis Soot onset– Evolution of soot mass and location

Sensitivity analysis soot model– Surface growth rate

ConclusionsOutlook

Page 25: Subtopic 2.3: Soot Field

ECN

ECN 3 Topic 2.3 – Soot fields 25April 4th 2014

Overview ECN Soot modeling

ECN 1: No soot results presented ECN 2: Only Spray H (n-heptane) considered

Two contributors: UW and ETH Both used two-equation soot model

UW: G. Vishwanathan et al., Comb. Sci. and Tech. 182 (2010)

ETH: M. Bolla et al., Comb. Sci. and Tech. 185 (2013) Comparison of quasi-steady soot only

ECN 3: Spray A (n-dodecane) considered Three contributors: UW, ETH and POLIMI All used two-equation soot model

UW and ETH used the same soot model as ECN 2 Soot modeling for Spray A at early stage (to-date no

publication) Comparison of soot temporal and spatial evolution

Focus on soot onset evolution

Page 26: Subtopic 2.3: Soot Field

ECN

ECN 3 Topic 2.3 – Soot fields 26April 4th 2014

Two-equation soot model

ACETYLENE / PAH

PRODUCTS

Inception (1)

Coagulation (5)SurfaceGrowth

(2)

Surface oxidation (3-4)

FUELChemicalmechanism (0)

Solve transport equation for soot mass fraction and number density

Accounts for inception, surface growth, coagulation and surface oxidation

Calibrated reaction rates (semi-empirical) Mono-disperse spherical soot particles

assumed Agglomeration neglected

[-]SY

3

#SN m

, , . ,S S S SY Y INCEPTION Y SUR GROWTH Y OXIDATIONw w w w

, ,S S SN N INCEPTION N COAGULATIONw w w

Page 27: Subtopic 2.3: Soot Field

ECN

ECN 3 Topic 2.3 – Soot fields 27April 4th 2014

Two-equation soot model

ACETYLENE / PAH

PRODUCTS

Inception (1)

Coagulation (5)SurfaceGrowth

(2)

Surface oxidation (3-4)

FUELChemicalmechanism (0)

[-]SY

3

#SN m

, , . ,S S S SY Y INCEPTION Y SUR GROWTH Y OXIDATIONw w w w

, ,S S SN N INCEPTION N COAGULATIONw w w

2 2 22 SC H C H

2 2 22S SC H nC n C H

21

2SC O CO

SC OH CO H

nnP P

(1) Particle Inception

(5) Particle Coagulation

(2) Particle Surface Growth

(3) Particle Oxidation by O2

(4) Particle Oxidation by OH

ETH and POLIMI: 16 16 4 2( ) 16 5SC H A C H UW:

Page 28: Subtopic 2.3: Soot Field

Modeling Approach

Temp [K] 800 850 900 1000 1100 1200O2 [vol%] 15 13/15/17/21 13/15/17/21 13/15/17/21 13/15/17/21 13/15/17/21Density [kg/m3] 22.8 7.6/15.2/

22.8/30.47.6/15.2/22.8/30.4

7.6/15.2/22.8/30.4

7.6/15.2/22.8/30.4

7.6/15.2/22.8/30.4

Pinj [MPa] 150 50/100/150 50/100/150 50/100/150 50/100/150 50/100/150

Computational grid Related sub-models

Lift-off lengthOnset of the averaged OH concentrationIgnition delayMaxmium dT/dt Maxmium dOH/dt

Phenomenon Model

Spray breakup KH-RT instability

Evaporation Discrete multicomponent (DMC)

Turbulence Generalized RNG k−ε model

Combustion SpeedChem

Droplet collision ROI model

Near nozzle flow Gas-jet model

Soot formation Multi-step phenomenological

Page 29: Subtopic 2.3: Soot Field

Physical process Expression

Inception:A4soot

C2H2 surface growth

Coagulation

O2 oxidation

OH oxidation

PAH condensation

Transport equations

G. Vishwanathan et al., Combustion Science and Technology, 2010, 182(8):1050-1082.

Soot Modeling Approach

Page 30: Subtopic 2.3: Soot Field

0

10

20

30

40

50

60

120011001000900

Tota

l Soo

t mas

s [u

g]

Ambient Temperature [K]

7.6 15.2 22.8 30.4

850

ECN Spray-AO2 15%

Density [kg/m3]

0

15

30

45

60

75

120011001000900

Tota

l Soo

t mas

s [ug

]

Ambient Temperature [K]

50 100 150

850

ECN Spray-AO2 15%

Pressure [MPa]

0

10

20

30

40

50

60

120011001000900

Lift-

off l

engt

h [m

m]

Ambient Temperature [K]

13% 15% 17% 21%

850

ECN Spray-ADensity 22.8 kg/m3 O2

0

10

20

30

40

50

60

120011001000900

Lift-

off l

engt

h [m

m]

Ambient Temperature [K]

7.6 15.2 22.8 30.4

850

ECN Spray-AO2 15% Density [kg/m3]

0

15

30

45

120011001000900

Lift-

off l

engt

h [m

m]

Ambient Temperature [K]

50 100 150

850

ECN Spray-AO2 15%

Pressure [MPa]

Non-reacting mixing

Soot modeling results

0 1 2 3 40

20

40

60

80

100

Vap

or P

enet

ratio

n [m

m]

Time ASI [ms]

Expt. Simulation

ECN Spray-An-C12 non-reactingTamb=900K

Density=22.8kg/m3

Inj Dur=6.0 ms

0 1 2 3 4 50

5

10

15

20

25

30

Liqu

id P

enet

ratio

n [m

m]

Time ASI [ms]

Expt. Simulation

ECN Spray-An-C12 non-reactingTamb=900K

Density=22.8kg/m3

Inj Dur=6.0 ms

0.0 1.5 3.0 4.5 6.00.00

0.04

0.08

0.12

0.16

0.20ECN Spray-An-C12 non-reactingTamb=900K

Density=22.8kg/m3

Inj Dur=6.0 ms

Mix

ture

Fra

ctio

n [-

]

Radial distance [mm]

Expt. Simulation

Z=20mm

0.0 2.5 5.0 7.5 10.00.00

0.03

0.06

0.09

0.12

0.15ECN Spray-An-C12 non-reactingTamb=900K

Density=22.8kg/m3

Inj Dur=6.0 ms

Mix

ture

Fra

ctio

n [-

]

Radial distance [mm]

Expt. Simulation

Z=40mm

20 25 30 35 40 45 50 55

0.05

0.10

0.15

0.20

0.25ECN Spray-An-C12 non-reactingTamb=900K

Density=22.8kg/m3

Inj Dur=6.0 ms

Mix

ture

Fra

ctio

n [-

]

Axial distance [mm]

Expt. Simulation

Axial

Reacting conditions

0

10

20

30

40

50

60

120011001000900

Tota

l Soo

t mas

s [ug

]

Ambient Temperature [K]

13% 15% 17% 21%

850

ECN Spray-ADensity 22.8 kg/m3

O2

Page 31: Subtopic 2.3: Soot Field

ECN

ECN 3 Topic 2.3 – Soot fields 31April 4th 2014

Total C2H2 mass

Large differences in peak C2H2 mass (factor 4)All simulation predict a plateau after approx. 3 msDelays in start of C2H2 production coincides with differences in ID

Different ID:UW 0.82 msETH 0.48 ms

POLIMI 0.62 msUNSW 0.70 ms

EXPERIMENT 0.41 ms

ID

Page 32: Subtopic 2.3: Soot Field

ECN

ECN 3 Topic 2.3 – Soot fields 32April 4th 2014

C2H2 comparison at 1.5 and 4 ms

1.5 ms

4 ms

r=0mm

r=0mm

LOL

Page 33: Subtopic 2.3: Soot Field

ECN

ECN 3 Topic 2.3 – Soot fields 33April 4th 2014

Total soot mass

Comparison total soot massOnset of soot formation

UW and ETH show a comparable magnitude and shape Experimental first soot bump not captured by the models Delays in start of soot formation coincides with differences

in ID

ID

Page 34: Subtopic 2.3: Soot Field

ECN

ECN 3 Topic 2.3 – Soot fields 34April 4th 2014

Temporal evolution soot region: 1.5/2.0/2.5 ms

1.5 ms 2 ms 2.5 ms

Qualitative

Soot region in qualitative agreement Differences in soot spread and tip penetration

Simulation has shorter penetration at 2/2.5 ms

Experiment: KL signalSimulation: normalized SVF

Page 35: Subtopic 2.3: Soot Field

ECN

ECN 3 Topic 2.3 – Soot fields 35April 4th 2014

Soot volume fraction at 4 ms

r=0mm

z=60mm

Quantitative

Soot region in qualitative agreement Different axial offsets LOL-soot UW and ETH show comparable results UW tighter in radius ->less soot volume

LOL

[ppmv]

Page 36: Subtopic 2.3: Soot Field

ECN

ECN 3 Topic 2.3 – Soot fields 36April 4th 2014

Computed mean particle size at 4 ms

[nm]

UW and ETH models predict largest particles of 17-18 nm Largest mean particle size at peak soot

Page 37: Subtopic 2.3: Soot Field

ECN

ECN 3 Topic 2.3 – Soot fields 37April 4th 2014

Soot onset: Evolution axial soot massUW ETH EXP

ID=0.82 ms ID=0.48 ms ID=0.41 ms

For soot onset analysis „reset processes“-> Consider time after ID

ETH shows a good shape, soot 2 times lower

UW is 2 times lower than ETH-> Comparable SVF but lower spread

of the soot region UW overpredicts location of soot onset

-> due to larger ID (0.82 vs. 0.41 ms)

Page 38: Subtopic 2.3: Soot Field

ECN

ECN 3 Topic 2.3 – Soot fields 38April 4th 2014

Soot onset: Evolution SVF simulationUW ETHID=0.82 ms ID=0.48 ms

Evolution of SVF is comparable UW reaches half SVF max after

ID+0.7ms and ETH takes 0.8 ms (quasi-steady SVF max is 6 ppmv)

Page 39: Subtopic 2.3: Soot Field

ECN

ECN 3 Topic 2.3 – Soot fields 39April 4th 2014

Soot onset: Mean particle size evolutionUW ETHID=0.82 ms ID=0.48 ms

UW shows a strong particle size peak at ID+0.1 ms

ETH shows a more smooth increase at the beginning (ID+0.1-0.2 ms)

Fast stabilization of particle size upstream

Spray A TEM60 mmIFPEN/Meiji

Page 40: Subtopic 2.3: Soot Field

ECN

ECN 3 Topic 2.3 – Soot fields 40April 4th 2014

Sensitivity analysis: Surface growth -33%

Soot mass is most sensitive w.r.t. surface growth (cf. e.g. Bolla et al., CST 2013)

-> most illustrative sensitivity study A 33% reduction in surface growth decreases total soot mass but not

the shape Both UW and ETH react analogously: reduction of soot mass by 40-

50% Radial SVF profiles are nearly down-scaled ->Soot region remains the

same

Page 41: Subtopic 2.3: Soot Field

ECN

ECN 3 Topic 2.3 – Soot fields 41April 4th 2014

Summary and conclusions

Detailed analysis of soot formation performed for reference case Large differences in C2H2 and soot onset -> DIFFERENT ID Soot onset: first soot peak not reproduced

Probably mixing related (Tip vortex dynamics) -> LES needed? Quasi-steady soot fairly well captured (same as ECN 2) Sensitivity analysis on surface growth assessed

Consistent results with and without TCI Soot spatial extent remains unchanged

-> Mostly mixture fraction determines where soot is Before looking at TCI and more complex soot models one should:

Assure accurate tip penetration and mixture fraction distribution

Improve ID

Page 42: Subtopic 2.3: Soot Field

ECN

ECN 3 Topic 2.3 – Soot fields 42April 4th 2014

Outlook - Topic 2.3 Soot field

Experimental Soot: Extinction Imaging in constant flow vessel (build up statistics for time-

resolved tomographic reconstruction) Gas sampling (can we measure acetylene axial profile?) Combined laser-induced incandescence with extinction imaging Spectrally resolved laser-induced fluorescence (progression of PAH

growth) Quantify soot in Spray A with other injectors Multiple injections Spray B

Soot modeling: Keyword for future: TRANSIENT

Short injection, multiple injection Understanding the first soot bump

Need for more accurate chemical mechanisms – ID must be improved Alternatively: re-visit n-heptane sprays in more detail?

Page 43: Subtopic 2.3: Soot Field

ECN

ECN 3 Topic 2.3 – Soot fields 43April 4th 2014

Page 44: Subtopic 2.3: Soot Field

ECN

ECN 3 Topic 2.3 – Soot fields 44April 4th 2014

LIF 355: consideration CH2O and PAH (first impression)

First impression of simulation compared to LIF 355 CH2O is more upstream and PAH(A4) is more downstream than

exp. LIF 355 coincides approx. with UW simulated C2H2

Simulation UW at 4 ms

Experiment IFPENLIF 355 at 4.7 ms

Page 45: Subtopic 2.3: Soot Field

Sandia constant-volumeSteady soot

Comparable soot volume fraction DI tight, CMC broad distribution

Experiment is in between

DI CMC Exp. 42 bar

85 bar

Source: Bolla et al., Comb. Theory Modelling (2014)

Page 46: Subtopic 2.3: Soot Field

Sandia constant-volumeQuasi-steady soot

Soot formation rate is comparable DI predicts 500 times larger soot oxidation rate

Caused by limited mixture fraction co-existance range

Formation Oxidation

PDF

sootO2

C2H2

soot

PDF

DI DICMC CMC

Source: Bolla et al., Comb. Theory Modelling (2014)

Page 47: Subtopic 2.3: Soot Field

Sandia constant-volumeTransient soot

DI overpredicts soot oxidation after end of injection

1

2

3

4

1 2 3 4

12% O2, 14.8 kg/m3, 1000 K DOI=1.8 ms

Source Exp.: Idicheria and Pickett, IJER (2011)

Page 48: Subtopic 2.3: Soot Field

ECN 3 48Apr 2014

ECN Pyrometry

• IFPEN 2-Color Setup– Collected 425 +/- 15 nm and 676 +/- 14.5 nm– Calibrated with Santoro burner inside vessel at 1 atm

• Eliminates uncertainties associated with soot emissivity– 15 images at 3.5 ms ASOI, ensemble averaged

Spray A, Tsoot

Page 49: Subtopic 2.3: Soot Field

ECN 3 49Apr 2014

ECN Pyrometry

• Sandia Imaging Spectrometer Setup– System images only the central 1.4 mm along spray axis– Collects emission from entire spray event– Exposure derived from high-speed imaging– Spectra quantified using a calibrated integrating sphere

Page 50: Subtopic 2.3: Soot Field

ECN 3 50Apr 2014

ECN Pyrometry

• Two very different pyrometry approaches– IFPEN: 2-color, 2 camera pyrometry– Sandia: Imaging Spectrometer, long exposure, center 1.4 mm

along spray axis

Page 51: Subtopic 2.3: Soot Field

ECN 3 51Apr 2014

ECN Soot Subtopic 2.3 Contributors

• Experimental– Sandia

• extinction imaging: Time-resolved KL maps, soot mass, and fv maps during quasi-steady period

• Soot pyrometry (Imaging Spectrometer): Spatially resolved soot particle temperature and KL along central axis of spray flame + total radiation from broadband soot emission

– IFPEN• Laser-induced Incandescence & Laser Extinction: Time sequence of fv along central

plane of spray flame, ensemble averaged fv during quasi-steady period• Two-camera, Two-color pyrometry: 2-D map of soot particle temperature

– IFPEN/Meiji• Soot sampling/TEM analysis: Soot particle sizing

Page 52: Subtopic 2.3: Soot Field

ECN 3 52Apr 2014

ECN Subtopic 2.3: Overall Objectives

• What is the soot distribution for Spray A?– How is it modified with different parametric variables?– How do different measurement techniques compare?– How accurate do different modeling approaches predict the soot field?

“To improve the understanding of the physical/chemical processes of soot formation and oxidation under engine-relevant conditions and to distill this improved understanding into predictive CFD-based models.”

-ECN3 Guidelines

High-speed Extinction Imaging, Spray A, n-dodecane

Page 53: Subtopic 2.3: Soot Field

ECN 3 53Apr 2014

ECN Soot Onset: Timing and Location

• Soot mass is proportional to measured optical thickness (KL) • High-speed extinction imaging measurements provide time-resolved KL maps• Total mass and axial resolved soot mass do not require tomography for comparison to model results• Mass-based soot onset timing and location provide targets for modeling efforts

– Based on a soot mass threshold of 0.5 µg for total mass– Based on a soot mass threshold of 10 ng for axial resolved mass

𝐾𝐿=∫ 𝑘𝑒

𝜆 𝑓 𝑣𝑑𝑙 Masssoot= pixel area𝜌 𝐾𝐿 𝜆𝑘𝑒

=𝜌∫ 𝑓 𝑣𝑑𝑙 [𝑔/𝑐𝑚2¿ ]¿

T1 (800 K)

Extinction due to beam steering helps define threshold. Soot extinction not detected for 800 K case. Soot mass attributed to beam steering equivalent to approx. 0.25 µg