The 5th International LII Workshop provides a forum for open high-level discussion on the understanding of LII diagnostics and to foster relationships in joint research. Laser-induced incandescence (LII) has proven to be a powerful tool for particle concentration and particle size measurements in combustion, particle synthesis, as well as in environmental applications. However, different experimental approaches and data evaluation techniques exist which, while demonstrating the complexity of the physical processes involved in LII and the need for further research, has also somewhat hampered the acceptance by industry of LII as a measurement standard. In order to strengthen the community and to explore the development of a series of best practices for LII modeling, experiments, and data interpretation, a series of workshops was initiated in Duisburg, Germany (2005), followed by workshops in Bad Herrenalb, Germany (2006), Ottawa, Canada (2008) and Varenna, Italy (2010).
The 5th International LII Workshop will be held May 9–11, 2012 in Le Touquet, France
Zeyad Alwahabi (Adelaide University); Per-Erik Bengtsson (Lund Institute of Technology); Henning Bockhorn (Karlsruhe Institute of Technology); Silvana De Iuliis (CNR-IENI, Milano); Pascale Desgroux (PC2A, Université Lille 1, Lille); Klaus-Peter Geigle (DLR, Stuttgart); Douglas A. Greenhalgh (Glasgow Caledonian); Fengshan Liu (NRC Canada, Ottawa); Hope Michelsen (Sandia National Laboratories); Christof Schulz (IVG, University of Duisburg Essen); Greg Smallwood (NRC Canada, Ottawa); Rainer Suntz (Karlsruhe Institute of Technology); Kevin Thomson (NRC Canada, Ottawa); Stefan Will (Universität Erlangen); He Xu (Beijing Institute of Technology) We acknowledge the financial support of :
Nils-Erik Olofsson, Jonathan Johnsson, Henrik Bladh, Per-Erik Bengtsson
Klaus Peter Geigle, Gregor Gebel, Markus Köhler
Jonathan Johnsson, Henrik Bladh, Nils-Erik Olofsson, Per-Erik Bengtsson
Coffee break: 10:20-11:00 (registration continuation)
Jérôme Yon, Chloé Caumont-Prim, Alexis Coppalle, Kuan Fang Ren
14:00 Soot primary particle sizing in turbulent flames via combined LII and Elastic Light Scattering Brian Crosland, Matthew Johnson, Kevin Thomson
Emre Cenker, Gilles Bruneaux, Thomas Dreier, Christof Schulz
14:40 Poster advertising II (follow up) Free afternoon around 15:00
Damien Hebert, Alexis Coppalle, Jérôme Yon and Martine Talbaut
11:40 A combined laser induced incandescence, aerosol mass spectrometry, and scanning mobility particle sizing study of non-premixed ethylene flames Scott Skeen, Paul Schrader, Kevin Wilson, Nils Hansen, Hope Michelsen
Francesca Migliorini, Silvia Maffi, Silvana De Iuliis, Giorgio Zizak
12:30-14:00: lunch 8:50 9:00 11:20
Discussion on LII modelling 10:30-11:00: coffee break
11:00 Effects of particle coatings on laser induced incandescence Ray Bambha, Paul Schrader, Mark Dansson, Hope Michelsen
Discussion about the LII workshop follow up
19:00 banquet
Jun Hayashi, Nozomu Hashimoto, Noriaki Nakatsuka, Hirofumi Tsuji, Hiroaki Watanabe, Hisao Makino, Fumiteru Akamatsu
9:15
Discussion on combined and emerging approaches 10:45-11:15: Coffee break 12:15 buffet 11:15 Summary and conclusion of the workshop, hot topics, discussion about a next workshop
List of oral presentations (alphabetic order first author) Effects of particle coatings on laser induced incandescence Ray Bambha, Paul Schrader, Mark Dansson, Hope Michelsen SANDIA Defining a measurement strategy for 2D soot particle size imaging through detailed LII signal-decay analysis Emre. Cenker, Gilles Bruneaux, Thomas Dreier, Christof Schulz IFP En, Rueil-Malmaison, IVG and CENIDE, University of Duisburg-Essen Soot primary particle sizing in turbulent flames via combined LII and Elastic Light Scattering Brian Crosland, Matthew Johnson, Kevin Thomson Carleton University, NRC Ottawa LII and one-wavelength Aethalometer measurements of particulate matter in different environments Silvana De Iuliis, Silvia Maffi, Francesca Migliorini, Giorgio Zizak CNR-IENI, Milano An experimental setup to study soot sublimation as typically occurring in high fluence LII Klaus Peter Geigle, Gregor Gebel, Markus Köhler German Aerospace Centre (DLR), Stuttgart Time-resolved Laser induced incandescence measurement for a combustion field of the 0.5 kg-coal/h pulverized coal jet burner Jun Hayashi, Nozomu Hashimoto, Noriaki Nakatsuka, Hirofumi Tsuji, Hiroaki Watanabe, Hisao Makino, Fumiteru Akamatsu Osaka University Determination of the dimensionless extinction coefficient for soot generated by a PMMA flame Damien Hebert, Alexis Coppalle, Jérôme Yon and Martine Talbaut CORIA, University and INSA Rouen Influence of soot aggregate structure on particle sizing using laser-induced incandescence Jonathan Johnsson, Henrik Bladh, Nils-Erik Olofsson, Per-Erik Bengtsson University of LUND Soot particles detection by LIBS and LII analysis Francesca Migliorini, Silvia Maffi, Silvana De Iuliis, Giorgio Zizak CNR-IENI, Milano Pulsed laser heating of differently aged soot probed using LII and LES Nils-Erik Olofsson, Jonathan Johnsson, Henrik Bladh, Per-Erik Bengtsson Lund University A combined laser induced incandescence, aerosol mass spectrometry, and scanning mobility particle sizing study of non-premixed ethylene flames Scott Skeen, Paul Schrader, Kevin Wilson, Nils Hansen, Hope Michelsen SANDIA, Lawrence Berkeley National Lab.
Effects of particle coatings on laser induced incandescence Sandia National Laboratories, Combustion Research Facility, Livermore, CA 94551 U.S.A.
Primary author email: rpbambh@sandia.gov
In exhaust plumes and under some combustor conditions soot particles are often coated with unburned fuel, sulfuric acid, water, ash, and other combustion by-products.1,2 Diesel particles, for example, can be comprised of as much as 50% volatile compounds.3 These coatings can have an effect on particle optical properties and can thus have an influence on optical diagnostics applied to coated particles. The effects of particle coatings therefore need to be fully understood in order to apply optical diagnostics under a wide range of conditions.
We have compared time-resolved laser induced incandescence (LII) measurements on uncoated soot generated in a coflow diffusion flame with LII measurements on heavily coated soot generated in a fuel-rich premixed flame. Soot was extracted and cooled from both flames, and a thermodenuder was used to vary the coating on the particles extracted from the premixed flame. A scanning mobility particle sizer (SMPS) was used to monitor aggregate sizes from the two flames, and transmission electron micrography (TEM) was used to characterize particle morphologies. The results demonstrate striking differences in LII temporal evolution and dependence on laser fluence between coated and uncoated particles. These results can be understood in the context of particle energy balance during heating and cooling and are consistent with predictions based on an LII model that includes a heavy organic coating. (1) (2) (3)
Kittelson, D. B. J. Aerosol Sci. 1998, 29, 575-588.
Lighty, J. S.; Veranth, J. M.; Sarofim, A. F. J. Air Waste Manage. Assoc. 2000, 50, 15651618.
Witze, P. O.; Gershenzon, M.; Michelsen, H. A. Proc. SAE 2005, SAE Paper no. 200501-3791. Defining a measurement strategy for 2D soot particle size imaging through detailed LII signal-decay analysis
E. Cenker1,2, G. Bruneaux1, T. Dreier2, C. Schulz2 A combination of two-color soot pyrometry imaging, two-color time-resolved LII (TiRe-LII), Laser Extinction Method (LEM) and Transmission Electron Microscopy (TEM) of soot samples is used to define a strategy for two-dimensional imaging of soot particle size distributions. TiRe-LII is carried out both by single point measurements and 2D imaging, where LII signal-decay is determined for each pixel through time-gate-sweeping of the camera gate relative to the laser pulse. Experiments are carried out on an atmospheric laminar ethylene/air diffusion flame from a Santoro burner with a 1064-nm laser sheet operated in the low-fluence regime. For flame temperature measurements, two-color pyrometry images are tomographically inverted. The resulting temperature fields are used as input for the evaluation of the primary particle size from the local LII decay curves using the LIISim model.
It was found that the LII signal shows different decay properties at different delays after laser heating. As the particles cool down towards ambient temperature, calculated decay constants increase. For closer inspection, the TiRe-LII signal is divided into several 100-ns long segments and individual particle sizes are calculated for each segment by two-color LIISim curve-fitting. As the time-window is shifted further away from the laser, larger particle sizes are calculated. For a delay of 700 ns between two segments, the calculated particle size difference is greater than 12 nm. This variation is attributed to the polydisperse nature of the particle size distribution in the region of interest where small particles cool down to ambient temperature within a few hundred nanoseconds and their contribution to the detected LII signal fades out.
The dependence of the predicted particle sizes on the boundary conditions imposed for the simulation, such as ambient temperature, agglomeration, and accommodation coefficients are also quantitatively investigated. For validation of the evaluated particle sizes and uncertainty analysis, particles are sampled at different locations in the flame above the burner head via thermophoretic sampling on TEM grids. Primary particle sizes and dispersion are derived from TEM micrographs.
For the next step, these techniques will be applied in a high-pressure burner and a high-pressure spray vessel. In light of the time-segmented decay analysis, an optimized gate positioning for 2D-LII and a comprehensive simulation model strategy will be determined. 0 12
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K. J. Dauna*, J. T. Titantahb, M. Karttunena and T. A. Sipkensa
aUniversity of Waterloo, Waterloo ON Canada bUniversity of Western Ontario, London ON Canada
*Corresponding Author, kjdaun@uwaterloo.ca
There is growing interest in adapting time-resolved laser-induced incandescence
(TiRe-LII) to size metal nanoparticles, owing to their emerging applications in
materials science. Extending TiRe-LII to new aerosols requires a model for the heat
transfer between the laser-energized nanoparticles and the surrounding gas.
Unfortunately, the thermal accommodation coefficient, α, which defines the energy
transferred when a gas molecule scatters from the particle surface, is rarely
available. This parameter can sometimes be obtained from LII measurements made
on a reference aerosol sized using electron micrography, but this process is
notoriously time-consuming, and thermophoretic sampling of metal nanoparticles is
often problematic. These challenges have precluded interpretation of data from
several pioneering TiRe-LII studies on metal nanoparticles, including one by
Murakami et al. [
In this technique, a pairwise potential between the gas molecule and metal atoms is derived from ab initio (generalized gradient approximations of density functional theory, GGA-DFT) calculations of the gas/surface potential. The potentials then differentiated to obtain forces, and Newton’s equations of motion are timeintegrated to obtain atomic trajectories during a gas/surface scattering event. Finally, α is found through Monte Carlo integration over all incident gas molecular
This approach was initially used to characterize α between
soot and various gases, and is presently being extended to metal nanoparticles.
Preliminary results show that MD-derived Preliminary thermal accommodation coefficients for
accommodation coefficients are highly metal nanoparticles
sensitive to the potential well depth. αMD αexp
Unfortunately, a well-known limitation of Ni/Ar 0.20±0.02
GGA-DFT is that they cannot describe the Fe/He 0.07±0.01 0.01 [
Silvana De Iuliis, Silvia Maffi, Francesca Migliorini, Giorgio Zizak
Laser-Induced Incandescence (LII) technique is a powerful tool to measure concentration and size of soot particulate. In this work LII measurements are performed in different experimental conditions and compared with the ones derived by using a commercial aethalometer. This instrument allows to obtain the on-time concentration of optically absorbing aerosol particles by measuring the attenuation of 800 nm wavelength light through a quartz fiber filter. The filter is blackened over time with the aerosol picked up inside the instrument at controlled flows. Measurements are carried out with one second time-resolution. Absolute measurements in the ng/m3 range are derived for the particulate concentration. As for Laser-Induced Incandescence, soot particles are sampled in a test cell, consisting of a pyrex tube. The IR beam of a Nd:YAG laser (6 Hz, 200 mJ/cm2) is properly aligned within the tube. The LII signal is detected at two wavelengths (530 nm and 700 nm) with PMT modules coupled with interference filters. A fast digital oscilloscope, triggered by the laser Q-switch pulse, is used for data acquisition and storage.
The two sets of measurements are carried out at the exhaust of a soot generator (fuelled by methane) and of a diesel engine as well as in ambient air conditions (office and laboratories). In this way, a wide range of soot load and particulate of different nature are investigated.
As an example, in Fig. 1 measurements carried out in ambient air are shown versus time. Open symbols refer to the values of the LII peak at 500 nm wavelength collected about every 10 minutes. The concentration values obtained with the aethalometer are reported in closed symbols. The two sets of measurements are quite well overlapped confirming that the two techniques are sensitive to the same soot particulate and that the developed LII apparatus exhibits the high sensitivity necessary for environmental measurements. An experimental setup to study soot sublimation as typically occurring in high fluence LII
Klaus Peter Geigle, Gregor Gebel, Markus Köhler Institute of Combustion Technology, German Aerospace Centre (DLR),
Pfaffenwaldring 38-40, Stuttgart, Germany, klauspeter.geigle@dlr.de
Particle sizing with LII requires modeling of the temporal behavior of the
laserinduced emission. While most models are well validated in the low fluence regime,
agreement for high fluences is identified to be insufficient, specifically when
comparing different models for the short time window of soot sublimation (see Fig. 15 in [
As a consequence, particle sizes are typically deduced in a low fluence timeresolved LII experiment, with the temporal fit window starting after sublimation is assumed negligible. This approach becomes inconvenient with increasing pressure when the decay rates decrease significantly towards the duration of the exciting laser pulse. Modeling of the full LII profile is then desirable requiring best possible modeling of all sub-processes involved.
Sublimation of the soot surface due to a rapid temperature increase causes a
rapid vapor expansion of approximately 3-4 orders of magnitude within few
nanoseconds. This correlates with the assumption of a supersonic expansion once
vaporization becomes effective (see eq. 70 in [
Our experiment makes use of an experimental setup used to study plasma ignition of sprays [4,5]. A green laser pulse is focused into a premixed sooting flame and the resulting effect is monitored with a Schlieren setup involving an intensified CCD camera for detection. Because the expansion of the created wave produces a very weak gradient in our current setup, we had to use very high laser fluences, clearly beyond typical LII applications. However, the expansion occurring at LII employing “high fluences” is expected to follow a similar behavior as that detected for fluences close to plasma generation in flames. The wave expansion in the flame is somewhat faster than speed of sound at the respective flame temperatures while extrapolation to the wave origin is not possible at the required accuracy.
Based on this first approach we present ideas to optimize the experimental setup for future experiments then suited to validate the assumptions currently employed in calculating the sublimation term in LII models.
Fig. 1: Exemplary picture from time series visualizing an expansion wave generated by a high fluence laser pulse, detection delayed by 1.25 µs. & "
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Determination of the dimensionless extinction coefficient for soot generated by a PMMA flame Damien Hebert 1, Alexis Coppalle 1, Jérôme Yon 1 and Martine Talbaut 1 1 Laboratoire CORIA - UMR 6614, CNRS - Université et INSA de Rouen, France
hebert@coria.fr Influence of soot aggregate structure on particle sizing using laser-induced incandescence Jonathan Johnsson1, Henrik Bladh2, Nils-Erik Olofsson3, Per-Erik Bengtsson4
Soot aggregates formed in combustion processes can be described as random fractal structures. For theoretical studies of the physical properties of such aggregates, they have often been modelled as spherical primary particles in point contact. However, transmission electron microscopy (TEM) images show that the primary particles in general are more connected than in a single point; there is a certain amount of bridging between the primary particles. The results of particle sizing using laser-induced incandescence (LII) is crucially dependent on the heat conduction rate from the aggregate, which, in turn, depends on the amount of bridging.
In this work, aggregates with bridging are modelled using overlapping spheres, see Fig. 1, and it is shown how such aggregates can be built with specific fractal parameters. Aggregates with and without bridging are constructed, and it is investigated how the bridging influences the heat conduction rate in the freemolecular regime. It is shown that bridging has a significant influence on the shielding parameters that are inferred from the heat conduction results, Fig. 2. These results are used together with an LII model to show how LII particle sizing is affected by the difference in bridging.
Soot particles detection by LIBS and LII analysis
Francesca Migliorini, Silvia Maffi, Silvana De Iuliis, Giorgio Zizak " 345 % 9 ' # "
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Hergen Oltmann1, Stefan Will2
Nanoparticles produced in combustion processes often exhibit complex fractal
structures. While laser-induced incandescence (LII) is a proven technique for the
determination of primary particle size no information about aggregate sizes can be
obtained. To gather information about aggregate size and fractal dimension elastic
light scattering (ELS) [
The wide-angle light scattering (WALS) approach [
The basic performance of the approach was demonstrated previously by
measurements on soot particles in laminar premixed flames [
Fig. 1: Experimental setup
Fig. 2: Measurement on silica particles in a diffusion flame
C. M. Sorensen, Aerosol Sci. Technol. 35, 648-687 (2001) H. Oltmann, J. Reimann, S. Will, Combust. Flame 157, 516-522 (2010) H. Oltmann, J. Reimann, S. Will, Appl. Phys. B 106, 171-183 (2012)
A combined laser induced incandescence, aerosol mass spectrometry, and scanning mobility particle sizing study of non-premixed ethylene flames Scott Skeen1, Paul Schrader1, Kevin Wilson2, Nils Hansen1, Hope Michelsen1 1Sandia National Laboratories, Combustion Research Facility, Livermore, CA 94551 U.S.A. 2Lawrence Berkeley National Laboratory, Berkeley, CA 94720 U.S.A.
Primary author email: hamiche@sandia.gov
Investigations into the chemical composition of soot particles often rely on samples extracted from the flame environment for subsequent analysis by mass spectrometry. These mass spectra have contributed to the general consensus that polycyclic aromatic hydrocarbons (PAHs) are involved in soot nucleation and surface growth processes. In the pioneering work of Dobbins et al.,1,2 soot and soot precursor particles were extracted along the centerline of a non-premixed coflow flame by rapid-insertion thermophoretic sampling and subsequently analyzed by laser microprobe mass spectrometry (LMMS). Low in the flame, where TEM images suggested the particles were liquid-like, the mass spectrum was dominated by species between 200 and 300 amu in size. Higher in the flame, where TEM images indicated that carbonaceous aggregates were being formed, PAHs were no longer observed in the mass spectra. The laser-desorption ionization experiments of Bouvier et al.,3 Lemaire et al.,4 and Faccinetto et al.5 complemented and expanded the findings of Dobbins et al.1,2 Lemaire et al.4 showed that the fuel composition strongly influences the soot composition. Faccenetto et al.5 developed a new sampling method enabling some distinction between PAHs in the gas phase and those adsorbed onto the soot particles. Intrusive sampling techniques such as those used in the studies referenced above perturb the flame. In some instances such techniques may permit the agglomeration of existing particulates, condensation of low vapor pressure species onto the surface of soot nuclei, and nucleation of new clusters that could later be erroneously associated with nascent soot. Recently, we have coupled a nonpremixed, opposed-flow flame system to an aerosol mass spectrometer to investigate the chemical composition of soot particles extracted from different regions of the flame. The present work provides insight into the effects of our intrusive sampling method on the observed soot composition and size distributions by combining laser-induced incandescence (LII) measurements with intrusive particle diagnostics.
In this work, we performed time-resolved LII measurements in conjunction with flame-sampling aerosol mass spectrometry (AMS) and scanning mobility particle sizing (SMPS) measurements to (1) investigate differences in particle size and composition as a function of temperature and position in the flame and (2) investigate processes occurring within the sampling system during sample extraction. We probed three non-premixed, opposed-flow, ethylene flames at conditions ranging from nearly sooting to moderately sooting. In situ time-resolved LII measurements revealed differences in the temporal response as a function of laser fluence and position in the flame. These differences may result from varying absorption coefficients due to particle composition and/or differences in the extent of particle surface coatings. Particles extracted from different regions of the flame also yielded varying temporal LII profiles, size distributions (as determined by SMPS), and chemical compositions (as determined by AMS). The use of a thermal denuder prior to the ex situ LII, SMPS, and AMS instruments also provided information on the extent of PAH condensation onto existing particles and the propensity for liquid- or tarlike droplet nucleation within the sampling system.
List of posters (alphabetic order first author) Sizing of soot aggregates by two-dimensional multi-angle light scattering (2D-MALS) Michael Altenhoff, Jannis Reisky, Stefan Will Universität Erlangen-Nürnberg, Germany Universität Bremen Study of the wavelength dependence of the soot absorption function using the two-excitation wavelength Laser Induced Incandescence: application to fluorescent species detection. S. Bejaoui, R. Lemaire, E. Therssen, P. Desgroux PC2A, University of Lille 1, Ecole des Mines de Douai Comparison between Modeled and Measured Time-Resolved LII Signals and Soot Temperatures in a Laminar Premixed Flame S. Bejaoui, S. Batut, E. Therssen, P. Desgroux, F. Liu, K. A. Thomson, G. J. Smallwood PC2A, University of Lille 1 NRC Ottawa, Continuous Wave LII in an Atmospheric Pressure Kerosene Flame John D. Black and Paul Wright University of Manchester Applicability of Wright’s correction to Fuchs boundary sphere method for TiRe-LII calculations K.J. Daun, S.C. Huberman University of Waterloo Influence of temporal laser pulse length and shape on the time resolved laser induced incandescence signal M. Ditaranto, N.E. Haugen, C. Meraner, I. Saanum SINTEF, Trondheim Combined LII and LIF with multiple excitation wavelengths for diagnostics of soot and PAHs in laminar flames J. Dunn, I.S. Burns University of Strathclyde Experimental study of particle vaporization under pulse laser heating by LII and laser light extinction Alexander Eremin, Evgeny Gurentsov, Ekaterina Mikheyeva, Konstantin Priemchenko Joint Institute for High Temperature, Russian Academy of Sciences Experimental investigation of the influence of inert gas on soot formation A.Flügel, S. Beer, S. Will, J. Kiefer, A. Leipertz University of Erlangen-Nürnberg, SAOT Erlangen, University of Aberdeen Combination of high spatial resolution LII and LOSA measurements for determination of soot volume fraction and PAH concentration in laminar diffusion flames M. Leschowski, K. Thomson, D. Clavel, D. Snelling, C. Schulz, G. Smallwood IVG and CENIDE, University Duisburg-Essen, NRC Ottawa Combination of various particles measurement techniques for validation in laminar high pressure flames M. Leschowski, T. Dreier, C. Schulz IVG and CENIDE, University Duisburg-Essen Effect of laser pulse duration on laser-induced incandescence soot F. Liu, G.J. Smallwood NRC Ottawa Measurements of Soot Volume Fraction under Conditions Relevant to Engine Exhaust Using FourColour LII and Different Laser Energies Fengshan Liu, Xu He, Hongmei Li, Fushui Liu, Gregory J. Smallwood NRC Ottawa, Beijing Institute of Technology Relationship between LII Signal and Soot Volume Fraction – Effect of Primary Particle Diameter Polydispersity Fengshan Liu, Gregory J. Smallwood NRC Ottawa Novel soot volume fraction measurement through ratio-pyrometry and absolute light calibration Bin Ma and Marshall B. Long Yale University Modeling laser-induced incandescence of soot integrating spatial and temporal dependences of parameters involved in energy and mass balances Mohammed Mobtil, Romain Lemaire Ecole des Mines de Douai Evolution of the LII signals of soot particles measured in low pressure methane flames T. Mouton, P. Desgroux, X. Mercier PC2A, University of Lille1 Influence of LII on Soot Optical Properties in Reference Flames K. Thomson, K-.P. Geigle, D. Snelling, F.Liu, M. Köhler, G. Smallwood NRC Ottawa, DLR Stuttgart Evaluation of particle sizes of iron-oxide nano-particles in a low-pressure flame-synthesis reactor by simultaneous application of TiRe-LII and PMS B. Tribalet, A. Faccinetto, T. Dreier, C. Schulz IVG and CENIDE, University Duisburg-Essen Comparison of different techniques for measurement of soot and PM emission from Diesel engine Richard Viskup Institute for Design and Control of Mechatronical Systems,Johannes Kepler University
Sizing of soot aggregates by two-dimensional multi-angle light scattering (2D-MALS)
Michael Altenhoff1, Jannis Reisky2, Stefan Will1
For the understanding of soot formation in combustion processes
comprehensive information about local size properties of complex soot aggregates is
desired. Elastic light scattering (ELS) is a well-established optical technique which
allows for the in situ determination of aggregate size and fractal dimension of soot
particles in flames [
In continuation and extension of this approach we performed two-dimensional ELS-measurements under various scattering angles thus allowing for a simultaneous acquisition of particle parameters at various heights above burner (HAB). Measurements on a premixed ethene flame from a McKenna type burner with an equivalence ratio of 2.7 were carried out by irradiating a laser-light-section and detecting the scattered light using an intensified CCD camera (cf. Fig 1). The detection angle varied equidistantly in the scattering vector q from 17° to 163°, and the evaluation of obtained data was carried out for each pixel line from 10 mm to 20 mm HAB for three different areas: the flame axis only, the area determined by the depth of field and the maximum evaluable region. The obtained radii of gyration show good agreement with former results.
Fig. 1: Experimental setup
C.M. Sorensen, Aerosol Sci. Technol. 35: 648-687 (2001) J. Reimann, S.-A. Kuhlmann, S. Will, Appl. Phys. B 96: 583-592 (2009)
Study of the wavelength dependence of the soot absorption function using the two-excitation wavelength Laser Induced Incandescence: application to fluorescent species detection.
S. Bejaoui1, R. Lemaire2, E. Therssen1, P. Desgroux1 1Laboratoire PC2A, UMR CNRS 8522, F-59655 Villeneuve d’Ascq, France 2EMDouai, EI, F-59500 Douai, France
salma.bejaoui@ed.univ-lille1.fr
In this work, wavelength dependence of the absorption function of soot was
experimentally studied. We used a technique developed in our team which consists to heat
similarly the soot particles using two different laser excitation wavelengths. Thus, using two
lasers with the same temporal and spatial irradiance profiles, it is possible to find
combinations of the both lasers energies, below sublimation regime activation, insuring that
soot particles absorb the same energies, reach the same temperature and emit the same
Laser Induced Incandescence (LII) radiation [
Experiments are investigated in a turbulent diffusion flame of pulverised diesel and in a premixed methane flame stabilized on a McKenna burner. It is found that up to 700 nm the emission signal due to PAH /soot precursor LIF interferes with the LII one. Interestingly no LIF emission could be identified above 700 nm. Therefore this spectral region appears very attractive to collect soot incandescence in flames containing PAH.
The two-excitation wavelength LII method has been checked for the first time using a narrow
spectral detection set above 700 nm, by using several combinations of UV-visible and IR
radiations. Soot particles heating was controlled either looking at the Planck function above
700 nm or controlling the decay rate of the LII temporal signals. Once similar heating is
reached using any UV-vis radiation and the 1064 nm one, the method is used to get either
the ratio of soot absorption functions, or the LIF spectra of soot precursors even in the
presence of soot.
[
Flame
S. Bejaoui, S. Batut, E. Therssen, P. Desgroux Laboratoire PC2A, UMR CNRS 8522, F-59655 Villeneuve d’Ascq, France
salma.bejaoui@ed.univ-lille1.fr
F. Liu, K. A. Thomson, G. J. Smallwood National Research Council, Building M-9, 1200 Montreal Road, Ottawa, ON., Canada
LII experiments were conducted in a laminar premixed flame established with a McKenna burner at atmospheric pressure burning a mixture of methane, oxygen, and nitrogen with an equivalence ratio of 2.15 and with a flame stabilizer of stainless steel plate placed at 20 mm above the burner. A Nd:YAG laser at 1064 nm with a repetition rate of 10 Hz was used to produce a top-hat laser beam with a 6 ns pulse duration (FWHM) as the excitation source. Time-resolved LII signals were measured at 610 nm (20 nm FWHM) using a PMT at different locations in the flame and at different laser fluences. Soot temperature measurements were also conducted through recording LII spectra with a spectrograph at different locations along the flame centerline and different laser fluences. TEM analyses of soot sampled at HAB = 12 and 15 mm were also carried out to provide primary particle diameter distribution and average number of primary particles in an aggregate for LII model calculations.
Preliminary model calculations suggest that the base model LII developed at NRC was able to reproduce the experimental resolved LII signals accurately in the low-fluence regime; however, large discrepancies between the model and the experimental results occur at high fluences. To understand the role of physical and chemical processes that were not incorporated into the NRC LII model, annealing and photodesorption were implemented and their effects on the LII model results were investigated. This study is aimed at improving the NRC LII model at high laser fluences through a detailed comparison between the experimental LII results and the modeled LII results. Continuous Wave LII in an Atmospheric Pressure
Kerosene Flame
John D. Black and Paul Wright School of Electrical and Electronic Engineering, University of Manchester, UK
John.black-2@manchester.ac.uk
Fibre and diode lasers with sufficient power to heat soot particles to incandescent temperatures are readily available at lower cost than the nanosecond pulsed lasers traditionally used in LII. There are less stringent safety restrictions on the use of CW lasers and they can be delivered with excellent beam quality through standard optical fibres, making them more suitable for LII in practical environments. Using the collimated beam from a diode laser at 803 nm in the power range 5 – 30 W, LII was easily observable in a highly sooting kerosene flame (Fv ~10-5). However, the laser causes major changes in the combustion, increasing soot burn out rates and transferring heat to other regions of the flame.
In contrast to short pulse LII, soot particles experience laser heating and cooling by heat transfer at rates comparable with their reaction rate. Their residence time in the beam and other processes such as photophoresis and optical trapping also have to be considered.
Hence, modeling is much more complicated than for short pulse LII, and the processes are not well understood.
Visible emission spectra were collected using a traversable fibre optic probe from a magnified projected image of the flame shown in Figure 1. There is a good match between predicted emission spectra based on the Figure 1: LII in a quasi-2-D blackbody curve and observed spectra from the kerosene lamp flame with 28 W flame in the wavelength range 590 – 790 nm. 1phmotmogdriaapmheetderthcrwoulagshear bBeGa3mfilter From these spectra estimated soot temperature in the absence of the laser is 2150 K, rising to 2600 K in the region of a 28.5 W laser beam. Temperature rise is linear in laser power. Local soot temperature is increased both above and below the beam when the laser is present. Above the laser beam, light emitted at 700 nm decreases quadratically with distance from the height of the centre of the laser beam to the edge of the visible flame, although the soot particle surface temperature remains at ~2350 K in this upper part of the flame. The intensity of light emitted at 700 nm at the centre of the laser beam at varying laser power is in good agreement with a prediction based on blackbody radiation. This indicates that the mechanism of increased light emission is particle heating (LII) and not creation of additional soot by laser stimulated reactions in the flame.
Although cw LII is at a very early stage of development, the potential for combustion diagnostics – soot concentration, temperature, velocity by flow tagging, etc. – is obvious. The observations described here should provide a basis for future investigation of the processes involved. Applicability of Wright’s Correction to Fuchs’ Boundary
Sphere Method for TiRe-LII Calculations
K. J. Daun*, and S. C. Huberman
University of Waterloo, Waterloo ON Canada *Corresponding Author, kjdaun@uwaterloo.ca When LII experiments are performed on high pressure aerosols, transition-regime heat conduction from the laser-energized particles is usually calculated using Fuchs’ boundary sphere method. In this technique the Knudsen layer is represented by a collisionless boundary sphere enveloping the particle, which in turn is surrounded by a continuum gas. The analysis proceeds by equating the $(#)" Q heat transfer through the two domains and then solving
l for the unknown boundary sphere temperature, T . =E[$&l3#']" #" This calculation requires specification of the spherical
P shell thickness, , which is usually chosen as the mean
free path at T , ! "="!(T ). Filippov and Rosner [
( 2 a3 ),&1+ l a'5 &1+ l2 a2 '&1+ l2 a'3
$&l' . 1 $&l,#'P# &#'d# . l2 , % + 2 &1+ l2 a2 '5 2 % al22 *-- (1)
0 5 3 15
/
0
where P#(#) = 2cos#sin#. Filippov and Rosner [
2 2 . 1 $&l'Pl &l'dl . 1 $&l' 1 exp&% l ! 'dl (2)
0 0 ! which can be solved numerically.
We use Direct Simulation Monte Carlo to investigate this phenomenon under
typical LII conditions. The Knudsen layer thickness is found by sampling the radial
distance that incident gas molecules travel
before they collide with the surface. The 0.90
DSMC results reveal that particle curvature Wright [3]
increases the Knudsen layer thickness 0.85 Filippov and Rosner [
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! " # Combined LII and LIF with multiple excitation wavelengths for diagnostics of soot and PAH in laminar flames
Jaclyn Dunn 1, Iain Burns 1
Through the use of two complimentary laser techniques, laser induced incandescence and laser induced fluorescence, the formation of soot from polycyclic aromatic hydrocarbons (PAH) has been studied. Information on soot volume fraction (from signal peak intensity) and particle cooling rate (from the signal decay time) is obtained from incandescence signal, while fluorescence measurements offer information on PAH present. These techniques were used to study a premixed flat flame of ethylene and air at a range of equivalence ratios. This project involves the use of three different excitation wavelengths (1064 nm, 532 nm, 290 nm). The fluences were adjusted so that the soot particles are heated to the same temperature by each excitation wavelength, resulting in equal incandescence intensity. Since no fluorescence is detected for 1064 nm excitation the contributions from incandescence and fluorescence can be separated. This is achieved by subtracting any signal obtained for 1064 nm excitation from the signals obtained for excitation at shorter wavelengths, leaving the remaining signal to be attributed to fluorescence. A monochromator has been used to resolve the signals, thus generating a timesequence of emission spectra. This approach is helpful in identifying the contributions of LII and LIF to the signals detected. Experimental study of particle vaporization under pulse laser heating by LII and laser light extinction Alexander Eremin, Evgeny Gurentsov, Ekaterina Mikheyeva, Konstantin
Priemchenko Joint Institute for High Temperature Russian Academy of Sciences, 125412 Izorskaya st.13(2), Moscow, Russia, e-mail: gurentsov@ihed.ras.ru
Particle vaporization is one of the uncertainties in LII measurements of
particle size or volume fraction. The common recommended threshold of energy
fluence for soot vaporization is in the range of 0.1-0.2 J/cm2. However, for non-soot
particles or for carbonaceous particles different from soot, the vaporization threshold
might be unknown. One of the reasons is the decreasing of the particle refractive
index function E(m) with particle size [
The carbon particles were formed in pyrolisis of 1% C6H6+Ar behind reflected shock wave. Two-color Ti-Re LII technique was applied for particle heat up 2 temperature and size measurements at fluencies around 0.4 J/cm . He-Ne laser beam was adjusted coaxially to the YAG (1064 nm) laser beam and allowed to observe the decreasing of a volume of condensed phase due to vaporization. Additionally, the real particle temperature equilibrated with bath gas during pyrolisis process was measured by emission-absorption spectroscopy in visible range of spectra. The measured gas-particle temperature was less than frozen temperature behind shock wave due to endothermic effect of C6H6 decomposition. The vaporization temperature of small growing carbon particles with mean diameters of 214 nm was found to be in the range of 2900-3100 K in contrast to soot vaporization temperature 4000 K [6].
Growing iron particles of different sizes (2-11 nm), synthesized in the laser
photolysis reactor [
The dispersion of vaporization temperature observed in both experiments is probably caused by with the variation of particle properties formed at different conditions. The related value of evaporated fraction of condensed phase and particle vaporization temperature are analyzed in dependence on experimental conditions. " % & '(* * 1+ $ $ $ ! 0 ! 4
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A A ! !' ! " # Measurements of Soot Volume Fraction under Conditions Relevant to Engine Exhaust Using Four-Colour LII and
Different Laser Energies Fengshan Liu1, Xu He2, Hongmei Li2, Fushui Liu2, Gregory J. Smallwood1 1National Research Council, Building M-9, 1200 Montreal Road, Ottawa, ON., Canada 2Beijing Institute of Technology, Beijing 100081, China
e-mail: Fengshan.Liu@nrc-cnrc.gc.ca
Available experimental evidence shows that the apparent soot volume fraction (SVF) determined from two-colour LII (at 450 and 780 nm) for soot initially at near ambient room temperature displays a laser fluence dependence: it first increases with increasing the laser fluence until it reaches a maximum, after which it decreases with further increasing in laser fluence, due to sublimation. It is suggested that the low-fluence SVF anomaly is attributed to changes in soot emissivity in the 350 to 500 nm spectral range as a result of evaporation of condensed volatile organic compounds from soot particle surfaces due to laser heating. However, there is currently a lack of direct evidence to confirm the cause of the low fluence anomaly and a lack of detection strategy on how to avoid the low fluence SVF anomaly. The current approach using the two-colour LII technique is to operate the laser fluence around 2.1 mJ/mm2 with a 1064 nm laser, see Fig. 1.
In an attempt to address these two questions experimental measurements of SVF were conducted in a soot aerosol at near room temperatures at different laser fluence. A Nd:YAG laser of 6 ns FWHM operated at 532 nm was used to excite the soot particles. The resultant LII signals were detected at four spectral bands (with spectral widths varying between 12 to 40 nm) centered at 400, 631, 780, and 840 nm. The experimental results from this work provide useful insights into the cause of the low fluence SVF anomaly and an effective strategy to avoid this anomaly through detection of LII signals at longer wavelengths.
"!# $
% & ! " #$ % Fig. 1 Variation of soot concentration and temperature with laser fluence. Effect of Laser Pulse Duration on Laser-Induced
Incandescence of Soot
Fengshan Liu, Gregory J. Smallwood
The phenomenon of laser-induced incandescence (LII) has been utilized to develop versatile diagnostic techniques for measurements of combustion-generated soot concentration and primary particle size in many combustion applications. Many aspects in the implementation of LII have been investigated, such as the excitation laser wavelength and spatial profile, signal detection timing (prompt or delayed) and temporal width, and signal detection wavelengths. One potentially important parameter in LII practice that has received little attention in the LII community is the laser pulse duration. This is perhaps due to the fact that almost all the LII experiments conducted in the last two decades employed Q-switched, flashlamp pumped Nd:YAG lasers as the light source, which all provide a similar pulse duration in a narrow range between 5 and 10 ns FWHM. Few LII experiments were conducted using a much long laser pulse (microsecond) or much a shorter one (picoseconds). Picosecond laser pulses were shown theoretically to provide advantages over nanosecond ones in the determination of primary particle size distribution using lowfluence LII in flames at elevated pressures.
In this study the effect of laser pulse duration on the temperature histories of primary soot particle of different sizes was numerically investigated in both low- and high-fluence regimes under conditions of a typical atmospheric pressure laminar diffusion flame. The laser pulse durations considered in this study vary from 100 ps to 6 ns FWHM. Such laser pulse durations correspond to those of a typical Ti:Sapphire pulsed laser operated at 780 nm. Such laser is capable of generating laser pulses with duration from picoseconds to nanoseconds, depending on if the regenerative amplifier is seeded by the femtosecond oscillator.
Numerical results show that at a fixed laser fluence in the low-fluence regime with decreasing the laser pulse duration the effect of heat conduction on the peak soot temperature is suppressed. Under the conditions considered here heat conduction lowers the peak soot temperature of a 30 nm soot particle by about 70 K when the laser pulse is 6 ns FWHM. As the laser pulse duration decreases, the differences in the peak temperatures reached by particles of different sizes become smaller, due to the effective separation of the volumetric heating process and the surface dependent heat conduction cooling. In high-fluence regime, the peak soot temperature increases more significantly with decreasing the laser pulse duration. There seem no advantages using a shorter laser pulse than the commonly employed 6 ns FWHM one in the high-fluence regime.
In summary, a shorter laser pulse offers advantages over the typical 5 to 10 ns duration one in some low-fluence LII applications where it is desirable to suppress the effect of heat conduction, such as particle size determination in high pressures and evaluation of E(m). However, it does not seem to offer advantages in highfluence regime. Relationship between LII Signal and Soot Volume Fraction – Effect of Primary Particle Diameter Polydispersity
Fengshan Liu, Gregory J. Smallwood
LII has been increasingly applied to measure the concentration and size of nano-particles, such as combustion generated soot in flames, in-cylinder, and engine exhaust, black carbon in the atmosphere, and other synthesized nano-particles. The basis of LII concentration measurement is the assumption that the LII signal is proportional to the particle volume fraction, while the principle of LII particle sizing is the particle size dependence of heat conduction cooling after the laser pulse. In this work, the discussion is focused on measurement of volume fraction of combustion generated soot using LII.
Two approaches have been developed to conduct quantitative LII measurements of the soot concentration. The conventional method detects the LII signal at one wavelength in the visible and seeks a calibration constant using a known source of particle concentration, i.e., SLII = C×fv. The second one is the more recently developed two-color LII or auto-compensating LII. In this method, absolute LII intensities are detected at two wavelengths in the visible spectrum to infer the soot temperature based on the pyrometry principle. This method does not require a known particle source to arrive at a calibration constant. However, it requires the knowledge of both relative and absolute values of E(m) at the two detection wavelengths, which represents the main uncertainty of the two-color LII method. The calibration constant C in the conventional LII method in general is not constant under conditions other than those of the calibration. Since soot temperature is determined in the two-color LII method, the two-color LII method can be viewed as a special version of the conventional LII method in which the calibration constant is obtain in situ.
It is shown numerically that for a polydisperse primary soot particles the soot temperature derived in two-color LII is biased towards the temperature of those larger and hotter particles. As smaller particles cool faster than larger ones, smaller particles gradually ‘disappear’, leading to a decrease soot volume fraction determined by the two-color LII. Based on numerically results, the relationship between LII signal and soot volume fraction can be summarized as: (1) It is linear in the two-color LII during and shortly after the laser pulse in the low-fluence regime (2) It is linear in the two-color LII only briefly around the peak of the laser
pulse in the high-fluence regime (3) It is in general non-linear in the conventional LII method Novel soot volume fraction measurement through ratiopyrometry and absolute light calibration
Bin Ma and Marshall B. Long Yale University, 15 Prospect St, New Haven, CT, USA
bin.ma@yale.edu
Novel ratio pyrometry and absolute light calibration methods have been developed to obtain soot temperature and volume fraction in axisymmetric flames. A consumer digital single lens reflex camera has been fully characterized and utilized as a pyrometer. The incandescence from soot was imaged at the three wavelengths of the camera’s color filter array (CFA). Temperatures were calculated by two-color ratio pyrometry using a lookup table approach. While temperatures can be extracted from color ratios, soot volume fraction requires an absolute light calibration of the detector. The absolute light intensity calibration was provided by a flame-heated Stype thermocouple. The spectral emissivity of S-type thermocouple wires (Pt and Pt10% Rh) was measured in the visible range. The measured spectral emissivity, temperature, and diameter of the heated thermocouple wires allow them to serve as a light source with spectral radiance that can be calculated by Planck’s law. Soot volume fraction measurements were carried out on four different flames with varying levels of soot loading. The results have been compared with previous LII results and excellent agreement has been achieved.
Modeling laser-induced incandescence of soot integrating spatial and temporal dependences of parameters involved in energy and mass balances
Mohammed Mobtil1,2, Romain Lemaire1,2 1Université Lille Nord de France, F-59000 Lille, France 2EMDouai, EI, F-59500 Douai, France
romain.lemaire@mines-douai.fr 1 H.A. Michelsen, F. Liu, B.F. Kock, H. Bladh, A. Boiarciuc, M. Charwath, T. Dreier, R. Hadef, M. Hofmann, J. Reimann, S. Will, P.-E. Bengtsson, H. Bockhorn, F. Foucher, K.-P. Geigle, C. Mounaïm-Rousselle, C. Schulz, R. Stirn, B. Tribalet, R. Suntz - Modeling laser-induced incandescence of soot: a summary and comparison of LII models - Applied Physics B, 87, 503-521 (2007) 2 H. Bladh, J. Johnsson, P.-E. Bengtsson - On the dependence of the laser-induced incandescence (LII) signal on soot volume fraction for variations in particle size - Applied Physics B, 90, 109-125 (2008) EVOLUTION OF THE LASER INDUCED INCANDESCENCE SIGNALS OF SOOT PARTICULES MEASURED IN LOWPRESSURE METHANE FLAMES
T. Mouton*, P. Desgroux, X. Mercier Physicochimie des Processus de Combustion et de l’Atmosphère (PC2A), UMR CNRS 8522, Université Lille 1 Sciences et Technologies. 59655 Villeneuve d’Ascq Cedex, France thomas1.mouton@ed.univ-lille1.fr
The understanding of soot formation mechanisms in flames, and more specifically the nucleation process, is still under debate. To deal with this crucial step, low pressure laminar flames are particularly well suited because of the large reaction zone, offering the possibility of examining the early soot formation zone. The number of soot particles is however much lower than at atmospheric pressure, requiring the use of sensitive techniques such as Laser Induced Incandescence (LII).
In this work, we have used the LII technique to probe soot particles formed in various low-pressure premixed methane/oxygen/nitrogen flames stabilised for different equivalent ratio ( = 2.32, 2.05, 1.95) and pressure (P = 18.66 kPa (140 torr) and 26.66 kPa (200 torr)). Heating of the particles has been achieved by using the 1064 nm excitation wavelength of a YAG laser, the energy profile of which has been shaped as top hat. Temporal LII signals were measured by a photomultiplier whereas we complementary used an intensified CCD camera coupled to spectrometer in order to record the associated emission spectra. Measurements have been done for different heights above the burner (HAB), included the very beginning (nucleation step) of the soot formation processes in the flames.
By this way, we observed significant and surprising differences, mainly concerning the evolution of the temporal signal according the flame height, between the lowest equivalent ratio ( =1.95 and 2.05) and the reference flame ( =2.32). While this last flame is characterised by the increase of the LII decay with HAB, corresponding to the increase of the particles size as expected, no such evolution is observed for the two other ones. In these conditions, the temporal LII decays remain constant for all the heights above the burner, therefore questioning about the nature of the formed species. As a consequence, examination has been focused on those flames including fluence curves, measurement of relative volume fraction profiles and spectral analysis. Influence of LII on Soot Optical Properties
in Reference Flames K. Thomson1, K-.P. Geigle2, D. Snelling1, F.Liu1, M. Köhler2, G. Smallwood1 1National Research Council, Ottawa, Canada, kevin.thomson@nrc-cnrc.gc.ca
2German Aerospace Centre (DLR), Stuttgart, Germany
When analyzing LII emission signals, it is typically assumed that the optical
properties of soot are not affected by this rapid heating. However, from the literature
it is known that the laser irradiances typical of ‘plateau LII’ can lead to significant
modification of soot particles and even the formation of new particles [
To study the optical properties of laser heated soot, we have monitored the extinction coefficient of soot aerosols within the standard Gülder and McKenna burners as a function of time while simultaneously heating the aerosol with laser pulses typical of LII. Extinction coefficient measurements were made at wavelengths of 405, 488, 632, and 804 nm and for a range of 1064 nm pulsed laser fluences.
We present a rich database of normalized extinction measurements which give clues into the complex consequences of rapid laser heating of soot aerosols. Normalized extinction coefficients show an enhancement of the propensity of soot to absorb light over the time interval of the laser heating. A partial relaxation of this enhancement is evident on the soot cooling time frame suggesting that the enhancement is in part due to a temperature based phenomena such as particle expansion or temperature dependent optical properties. A sustained residual enhancement is observed in the McKenna soot data, indicative of a permanent change to the soot optical properties, possibly due to graphitization. The variation of the normalized extinction coefficient in the McKenna burner diminishes with decreasing probe wavelength. This relates to the presence of non-soot material which absorbs light in the UV wavelengths, but is not heated by the 1064 nm laser. For the higher soot concentrations of the Gulder burner, heat transfer to the gas phase leads to a gas temperature change and expansion which decreases the attenuation propensity of the medium. The soot is more efficiently heated than the McKenna soot, with sublimation initiated at lower fluences and greater sublimation at a given fluence. This suggests a higher refractive index absorption function, E(m ) for the Gulder soot. Normalized extinction coefficient measurements at 405 nm in the Gulder flame at very high fluences demonstrate that the materials vaporized from soot reform into species which are capable of absorbing 405 nm radiation, thus masking the sublimation effect on normalized extinction coefficient.
Both reversible and non-reversible changes to soot’s ability to attenuate light have been demonstrated in McKenna and Gulder flame soot. These variations should be further quantified and incorporated into LII emission interpretation theory. Evaluation of particle sizes of iron-oxide nano-particles in a low-pressure flame-synthesis reactor by simultaneous application of TiRe-LII and PMS
B. Tribalet, A. Faccinetto, T. Dreier, C. Schulz
Institute for Combustion and Gasdynamics (IVG), and Center for Nanointegration (CENIDE),
University of Duisburg-Essen, 47048 Duisburg, Germany, thomas.dreier@uni-due.de
Laser-induced incandescence (LII) has become a common method for in-situ
analysis of particle size and visualization of particle volume fractions predominantly
for soot diagnostics in a wide range of applications. Besides lower signal strength
due to less strongly absorbing material and lower heat-up temperatures, one of the
main challenges when applying LII to non-carbon nanoparticles is the poor data base
of relevant particle thermophysical properties, e.g., heat conduction, accommodation
coefficients, vaporization enthalpy and high-temperature chemistry for describing
particle cooling due to convection, vaporization, and other effects. In the present
work the measured laser-induced emission signals from flame-synthesized iron oxide
(Fe2O3) nanoparticles were evaluated in terms of particle sizing by using a modified
version of the TiRe-LII model developed by Kock et al. [
Iron oxide nanoparticles were synthesized in a rich, premixed H2/O2/Ar lowpressure (30 mbar) flat flame in a low-pressure flame reactor that was doped with ppm-levels of Fe(CO)5 as precursor material. By moving the burner relative to the fixed measurement location (determined by either the laser beam or a sampling nozzle for the particle mass spectrometer (PMS), respectively) the particle residence time in the reactor can be varied. The particles were heated by a frequency-doubled Nd:YAG laser and time-resolved LII-signal traces were recorded perpendicular to the beam axis by a two-color detection unit equipped with narrow band-pass filters with center-wavelengths at 500 and 700 nm, respectively, in front of two high-speed photomultipliers with integrated amplifiers. Additional to the time-resolved measurements, LII signals were detected spectrally-resolved using a spectrometer with an intensified CCD camera. The PMS with a molecular-beam sampling system was attached to the burner chamber for simultaneous particle sizing.
To determine a phenomenological evaporation heat flux term in the energy balance, temperature decay curves obtained by two-color pyrometry were fitted through variation of a parameterized form of the particle evaporation term. With these evaporation parameters, LII-signal traces were evaluated in terms of particle size. The obtained size parameters were verified by corresponding PMS measurements for the same flame conditions. In addition, it was possible to calculate the energy accommodation coefficient αT of the present particle material at several experimental conditions. Emission spectra taken right after laser heating did not vary significantly in shape as a function of laser fluence.
The combination of TiRe-LII and online molecular beam particle sampling with subsequent particle mass spectrometry in low-pressure flames is a promising approach for fundamental research on the characteristics of LII of various nanoparticle materials.
Preference: Poster Presentation 1. B. F. Kock, B. Tribalet, C. Schulz, and P. Roth, "Two-color time-resolved LII applied to soot particle sizing in the cylinder of a Diesel engine," Combust. & Flame 147, 79–92 (2006).