Date post: | 15-Dec-2015 |
Category: |
Documents |
Upload: | cara-langdon |
View: | 212 times |
Download: | 0 times |
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
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
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
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
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
𝜆𝑓 𝑣𝑑𝑙
Masssoot= pixel area𝜌 𝐾𝐿𝜆𝑘𝑒
=𝜌∫ 𝑓 𝑣𝑑𝑙 [𝑔/𝑐𝑚2¿ ]¿
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
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
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
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
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
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
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.
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
ECN 3 14Apr 2014
ECN Ensemble Averaged SVF (IFPEN/Sandia)
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
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
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
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)
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
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
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)
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.
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)
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
Conclusions
Outlook
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
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)
FUEL
Chemicalmechanism (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
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)
FUEL
Chemicalmechanism (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:
Modeling Approach
Temp [K] 800 850 900 1000 1100 1200
O2 [vol%] 15 13/15/17/21 13/15/17/21 13/15/17/21 13/15/17/21 13/15/17/21
Density [kg/m3]
22.87.6/15.2/22.8/30.4
7.6/15.2/22.8/30.4
7.6/15.2/22.8/30.4
7.6/15.2/22.8/30.4
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 length
Onset of the averaged OH concentration
Ignition delay
Maxmium 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
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
0
10
20
30
40
50
60
120011001000900
Tot
al S
oot m
ass
[ug]
Ambient Temperature [K]
7.6 15.2 22.8 30.4
850
ECN Spray-AO
2 15%
Density [kg/m3]
0
15
30
45
60
75
120011001000900
Tot
al S
oot m
ass
[ug]
Ambient Temperature [K]
50 100 150
850
ECN Spray-AO
2 15%
Pressure [MPa]
0
10
20
30
40
50
60
120011001000900
Lif
t-of
f le
ngth
[m
m]
Ambient Temperature [K]
13% 15% 17% 21%
850
ECN Spray-A
Density 22.8 kg/m3 O2
0
10
20
30
40
50
60
120011001000900
Lif
t-of
f le
ngth
[m
m]
Ambient Temperature [K]
7.6 15.2 22.8 30.4
850
ECN Spray-AO
2 15%
Density [kg/m3]
0
15
30
45
120011001000900
Lif
t-of
f le
ngth
[m
m]
Ambient Temperature [K]
50 100 150
850
ECN Spray-AO
2 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-reactingT
amb=900K
Density=22.8kg/m3
Inj Dur=6.0 ms
0 1 2 3 4 50
5
10
15
20
25
30
Liq
uid
Pen
etra
tion
[mm
]
Time ASI [ms]
Expt. Simulation
ECN Spray-An-C12 non-reactingT
amb=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-reactingT
amb=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-reactingT
amb=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-reactingT
amb=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
Tot
al S
oot m
ass
[ug]
Ambient Temperature [K]
13% 15% 17% 21%
850
ECN Spray-A
Density 22.8 kg/m3
O2
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
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
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
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
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]
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
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)
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)
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
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
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
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?
ECN
ECN 3 Topic 2.3 – Soot fields 43April 4th 2014
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
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)
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
sootO2
C2H2
soot
DI DICMC CMC
Source: Bolla et al., Comb. Theory Modelling (2014)
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)
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
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
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
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
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
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
𝜆𝑓 𝑣𝑑𝑙
Masssoot= pixel area𝜌 𝐾𝐿𝜆𝑘𝑒
=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