Nanoscaled Particle Size Distributions and Gas Temperatures from Time-resolved LII Measurements

Institut für Chemische TechnikEngler-Bunte-Institut/VerbrennungstechnikUniversität Karlsruhe (TH)

Prof. Dr.-Ing. H. Bockhorn

Dipl.-Ing. Thilo Lehre

Institut für Chemische Technik and Engler-Bunte Institut

Universität Karlsruhe

H.Bockhorn, B.Jungfleisch, T. Lehre, R. Suntz

Nanoscaled Particle Size Distributions and Gas Temperatures from

Time-resolved LII Measurements




Motivation• Environmental: Soot emission regulations

• Modelling: Data for gas-to-particle conversion models

• Nanotechnology: Properties depend on p(r)

• Product Design: Control p(r) by varying process parameters

Experimental approach : Optical method

Non-intrusive temporally and spatially resolved in-situ characterization of particle sizes




Diameter D63 based on

2

2

2

lnlnexp

2

1)(

mrr

rrP =

0.34

Rayleigh-Scattering: 6th Moment M6

LII: 3th Moment M3

Present Particle Sizing Technique: RAYLIX




• Solving mass and engergy balance yields TP(t)

• Accurate description of heat / mass transport kinetics is essential

Modelling LII: Mass and Energy Balances




Planck‘s law for a single particle:

Signal decay for particle size distribution p(r):

Assessment of p(r) and Tg: Multidimensional Nonlinear Regression

M

N

i i

Mii aavaluesfitMinaatyy

........,

1

!2

1

12

gPemem

emgP TCT

Cr

CTTrtR 3

123

61

, 1exp,,,

drTTrtRrpNtJ emgPTem ,,,,)(),(

Modelling LII: Signal Decays

yi: measured datay: model functioni: weight




Detection of Time-Resolved LII- Signals in laminar premixed flat flame (12kPa / 1 atm)




TEM analysis yields:

p(r) log-normal, =0.34

2,6 nm < rm < 16 nm

Na-D inversion method:

gas temperatures Tg

LII Model validation




• Calculations agree with experiments (moderate laser fluxes)

• Assessment of p(r) and Tg from LII signals seems possible

Comparison of measured and calculated LII-signals




Non-linear Regression: P(r) log-normal, = 0.34; rm=8.3 nm; Tg=1724 K




Model Uncertainties during LASER pulse due to Absorption kinetics Heat/mass transfer kinetics ???

Excitation curves in atmospheric laminar premixed flat flame:

Model and Measurements




Particle Temperature Measurements : 2 colour LII

12

215

2

1

12

ln

11

I

IK

khc

T

cal




1D + time resolved 2 colour LII in laminar atmospheric premixed flat flame




Additional Measurements in atmospheric laminar premixed flat flame

Particle diameter:

RAYLIX

Flame temperature:

2 colour pyrometry




Input to calculated T(t): measured TP(15ns after pulse); no absorption model

p(r) and Tg from independant measurements

Validation of heat/mass transfer kinetics




Advantages of 2 colour LII

• Modelling LII during Laser pulse not required

• Modelling superheating not required

• Independance of refractive index (grey bodies)

• Experimental value for laser fluence not required




rt

tTtT

exp0

iri

tptTtT

exp0

monodisperse size distribution

lognormal size distribution

Nonlinear Regression

Fit parameters: rm ,

Fit function: TP(t)

Result: Flat minimum

region = a rm + b




Low time resolution has no effect on measured particle temperatures ( 2 colour LII ) for t > 20ns




Nonlinear Regression: Fit parameters: rm , Fit function: TP(20ns) –TP ( 1000ns)

Unique minimum along = a rm + bexists




lognormal =0.34:rm = 5nm

monodisperse: rm = 10nm

Sensitivity to rm for a given shape of p(r)




Sensitivity of 2 colour LII to p(r)




23

3

6

2

27exp

)(

)(barr

drrpr

drrprKS mmR

barrf mm )(

Time-resolved LII:

RAYLIX:

Particle Size Distributions from Scattering + LII




Summary• LII model validation in sooting laminar premixed

flames (1 bar; 0.12bar)

• Heat/mass transfer kinetics validation based on

particle temperature measurements

• Assessment of p(r) and Tg from LII / 2 colour LII

using Multi - D- nonlinear regression

• Time range>1us gives good sensitivity to p(r)

• Simultaneous detection of scattering increases

sensitivity to p(r)

• Outlook: P(r) in laminar diffusion flame

space

time

Nanoscaled Particle Size Distributions and Gas Temperatures from Time-resolved LII Measurements

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