Division of Combustion Physics, Lund University P. O. Box 118, S-221 00 Lund, Sweden Tolvan...

Division of Combustion Physics, Lund UniversityP. O. Box 118, S-221 00 Lund, Sweden

Tolvan Tolvansson, 2007Tolvan Tolvansson, 2007

Presentation at CAST meeting February 7, 2008

Per-Erik Bengtsson, Division of Combustion Physics, Lund University

Activities at Combustion Physics Department of Physics

within the area of soot diagnostics

Per-Erik Bengtsson, Henrik Bladh, Jonathan Johnsson




Enoch Thulin-laboratory inaugurated in 2001, belonging to Lund Combustion Centre.

Combustion Physics(at Physics Dep., TF)~35 people

Soot diagnostic group Per-Erik Bengtsson Henrik Bladh Jonathan Johnsson

Facilities12 modern laser laboratories(1 soot diagnostic lab.)1 engine laboratory1 fire laboratory1 high-pressure combustion rig

Combustion Centre in Lund!Large Scale Facility in Europe!




Main activities at Combustion Physics

• Development of optical diagnostic techniques (often laser-based) for combustion processes for measurements of e.g. temperature species concentrations velocities particle characteristics

• Application of these techniques to different flame systems for phenomenological studies and model validation

• Measurements in practical devices such as internal combustion engines, gas turbines, etc.

Laser techniques have unique features such as non-intrusivity, and high spatial as well as temporal resolution!




Brief historical background

• Combustion Physics has long tradition in soot diagnostics in flames.

• Elastic scattering measurements in combination with extinction measurements absorption were developed at the end of 1980´s for soot concentration and size measurements in flames.

• A soot diagnostic technique (for soot volume fractions) was developed in Lund during the 1990´s based on soot vaporization and subsequent excitation of produced C2-fragments.

• More focus is now put on soot measurements using laser-induced incandescence (LII), which is the dominating technique nowadays for non-intrusive soot volume fraction and soot particle size measurements.

• 2003-2007 we were partners in a European programme, AEROTEST, developing an LII-system that remotely and non-intrusively can measure soot volume fraction in aerocraft engine exhausts (on ground). Discussions on a follow-up programme has started.




• Project Development of a laser-diagnostic tool for characterization of nanoparticles from combustion.Time period 2008 – 2010Financed by Swedish Research Council

• Project Soot diagnostics within a project ”Transient spray combustion”. To develop laser-induced incandescence (LII) as a tool for soot measurements, especially for soot particle sizing.

The project involves experimental laboratory studies, theoretical development and applied measurements in IC engines.

Time period 2006 – 2009

Financed by Strategic Science Foundation through the Centre of Combustion Science and Technology

Present projects




Laser-induced incandescence (LII)• Soot particles are exposed to a

laser pulse.• The particles are heated by the

laser light to temperatures around 4000 K.

• The resulting temperature radiation from this process is the LII signal.

• The LII signal can be used for soot particle measurements (volume fraction and size)

Absorption

Radiation(LII signal)

Heat conduction

Sublimation

Flat flame burning ethylene and air on a McKenna flat flame burner

Time in soot formation process

Schematic illustration of the LII process




Basic LII setup for particle sizing

Beam dump

Lens combination

Burner

Time

Photomultiplier

Lens

Sig

nal s

tren

gth

Optical filter transmittingat visible wavelengths




Evaluation of soot particle size distributions

• The time decay of the LII signal can be used to evaluate the soot particle size and the width of the distribution.

• This is done using a heat and mass transfer model for laser-heated particles.

• Best-fit data is found of particle size and size distribution in numerical comparison between model and experiment.

0 50 100 150 200 250 3000

1

Time (ns)

No

rmal

ised

sig

nal Time-resolved

LII signal

d=50 nm

d=10 nm

Laser pulse

06

12 32

232

dt

dTcDd),T(M),D(D

dt

dM

M

H

GD

D)TT(k)t(q

)m(EDss

b

v

v

MFP

ga

Absorption Heat conduction Sublimation Radiation Internal energy change

Heat transfer model




Example of results from size distribution evaluation

• Experimental time-resolved LII signal from a sooting flame has been evaluated using the Lund heat and mass

transfer model a fitting procedure

developed within this project.

• As a result a best-fit lognormal size distribution was obtained

0 200 400 600 800 1000 1200 1400 1600 18000

20

40

60

80

100

Time (ns)

LII s

igna

l

Model signalExperiment

10 15 20 25 30 35 40 45 500

1

2

3

4

5

6

7

8

9

10

Particle size (nm)

Best-fit lognormal size distribution

Inte

nsity




Present and future work

• Installation of new laser Nd:YAG laser system• Characterization of measurement system (experimental

equipment, theoretical model, fitting procedure)• Apply the measurement system to simple sooting

laboratory flames, such as the McKenna burner.• Continue the discussion with other groups in the transient

spray project about common tasks, especially the chemical kinetic sub-project and the engine experiment sub-project.

• Identify projects that can be performed together with partners working with aerosols in Lund. Development of soot generator and characterization of

exhausts Comparisons of different aerosol measurement techniques

• LII can be used for non-intrusive transient particle measurements




Drawing: Jonathan Johnsson




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