In order to understand the processes involved in the laser-induced incandescence (LII) technique, the value of soot temperature at the peak of the incandescence signal has been studied. To this purpose, an absolute two-color LII technique has been applied on ethylene and methane diffusion flames, based on the comparison with a calibrated tungsten ribbon lamp. The dependence of peak temperature on the fluence has been investigated by using a sharply edged probe beam. Above a certain fluence threshold a value close to 4000 K was obtained for both flames at all locations, that means in largely different soot conditions. At a suitably selected laser fluence, radial and axial profiles of peak soot temperature and volume fraction were performed. Soot volume fraction data have been validated with results from laser extinction technique measurements. The quite low values observed for methane prove the sensitivity of the LII technique. Moreover, a discussion about soot refractive index is presented. In the visible region a test of its influence on both soot volume fraction and soot peak temperature was carried out, while in the infrared the heating process was analyzed.

An original approach of laser-induced incandescence consisting in the simultaneous recording of the two-color-time-resolved and 2D LII signal is described in this paper. The application of this approach in an atmospheric pressure diffusion flame fueled with isooctane as well as inside the combustion chamber of a diesel engine is presented. Soot volume fraction and primary particle diameters are calculated, and the results are discussed. The mean diameter estimated by fitting the LII modeled curve on the experimental one is compared with the results obtained through soot sampling and microscope analyzing. The influence of the thermal accommodation coefficient and soot refractive index function is also discussed.

Time-resolved laser-induced incandescence (TR-LII) was applied for the determination of particle sizes during carbon-particle formation from supersaturated atomic carbon vapor that was generated by laser photolysis of carbon suboxide (C3O2) at room temperature. Thus, the solid carbon particles were formed under hydrogen-free conditions. The TR-LII technique was used for in situ size measurement of growing carbon particles and samples of final particles were analyzed by transmission electron microscopy (TEM). It was found that the particles grow to a final size of 4–12 nm within 0.02–1 ms. The properties of the obtained particles depend on the initial conditions in the reaction volume, i.e. concentration of carbon suboxide, pressure and type of gas diluter, photolysis wavelength, and laser pulse energy. The comparison of TR-LII and TEM particle sizing results yields information about the effective thermal energy accommodation coefficients for He, Ar, CO, and C3O2 molecules on carbon particles.

The paper by De Iuliis et al. [Appl. Opt. 44, 7414 (2005)] contains a mistake in the printing of the parentheses in Eq. (9). The correction of the equation is given here.

Laser-induced incandescence (LII) has proved to be a useful diagnostic tool for spatially and temporally resolved measurement of particulate (soot) volume fraction and primary particle size in a wide range of applications, such as steady flames, flickering flames, and Diesel engine exhausts. We present a novel LII technique for the determination of soot volume fraction by measuring the absolute incandescence intensity, avoiding the need for ex situ calibration that typically uses a source of particles with known soot volume fraction. The technique developed in this study further extends the capabilities of existing LII for making practical quantitative measurements of soot. The spectral sensitivity of the detection system is determined by calibrating with an extended source of known radiance, and this sensitivity is then used to interpret the measured LII signals. Although it requires knowledge of the soot temperature, either from a numerical model of soot particle heating or experimentally determined by detecting LII signals at two different wavelengths, this technique offers a calibration-independent procedure for measuring soot volume fraction. Application of this technique to soot concentration measurements is demonstrated in a laminar diffusion flame.

The two-color version of time-resolved laser-induced incandescence (TR-LII) as well as rapid particle probing and transmission electron microscopy (TEM) were applied to the size measurement of chain-like iron particles, synthesized by thermal decomposition of ironpentacarbonyl (Fe(CO)5, IPC) in a hot-wall flow reactor. Both argon and nitrogen were used as carrier gases in different experiments. TR-LII theory considers particle heat transfer and particle evaporation for the interpretation of the measured signals in terms of particle size. The heat transfer from the particle to the surrounding was assumed to proceed under free molecular conditions, which requires the knowledge of the translational energy accommodation coefficient aT during particle cooling. By fitting calculated TR-LII cooling curves to the measured signals, it was possible to determine both aT and the mean primary particle diameter of an assumed lognormal size distribution. Close to the TR-LII measurement section, particles were rapidly sampled and analyzed by TEM. For the obtained chain-like agglomerated particle structures, the TR-LII measured size is in excellent agreement with the TEM determined primary particle size. The method was further validated by variation of the heat-up laser energy density in a wide range of conditions, and the resulting TR-LII diameter was found to be independent of it.

Double-pulse laser-induced desorption with elastic laser scattering (LIDELS) is a diagnostic technique capable of making time-resolved, in situ measurements of the volatile fraction of diesel particulate matter (PM). The technique uses two laser pulses of comparable energy, separated in time by an interval sufficiently short to freeze the flow field, to measure the change in PM volume caused by laser-induced desorption of the volatile fraction. The first laser pulse of a pulse-pair produces elastic laser scattering (ELS) that gives the total PM volume, and also deposits the energy to desorb the volatiles. ELS from the second pulse gives the volume of the remaining solid portion of the PM, and the ratio of these two measurements is the quantitative solid volume fraction. In an earlier study, we used a single laser to make real-time LIDELS measurements during steady-state operation of a diesel engine. In this paper, we discuss the advantages and disadvantages of the two LIDELS techniques and present measurements made in real diesel exhaust and simulated diesel exhaust created by coating diffusion-flame soot with single-component hydrocarbons. Comparison with analysis of PM collected on quartz filters reveals that LIDELS considerably underpredicts the volatile fraction. We discuss reasons for this discrepancy and recommend future directions for LIDELS research.

Temperature histories of nanosecond-pulsed laser-heated soot particles of different primary particle diameters and different aggregate sizes were calculated using an aggregate-based heat transfer model. Relatively low laser fluences were considered to ensure maximum particle temperatures were below about 3800 K to avoid soot particle sublimation. After the laser pulse, the temperature of soot particles in larger aggregates decreases more slowly than that of particles in smaller aggregates due to the increased shielding effect. For a given aggregate size, the temperature of particles of smaller diameter decays faster as a result of a larger surface area-to-volume ratio. The effective temperature of soot particles in the laser probe volume was calculated based on the ratio of thermal radiation intensities of soot particles at 400 and 780 nm to simulate the experimentally measured soot particle temperature using two-color optical pyrometry. The effect of aggregate size distribution of soot particles on the effective particle temperature was investigated under different initial temperatures.

Quasi-simultaneous measurements of temperature and soot volume fraction in pressurized and atmospheric flames are presented. A dual-flame burner concept yielded stable laminar flames for a variety of equivalence ratios, pressures, and fuels, and permitted the investigation of flames without the influence of soot oxidation. A CARS-based technique (shifted vibrational CARS) for temperature measurements, which offers high accuracy over the entire relevant temperature and soot concentration range, is described. Comparison of temperature measurements in the nonsooting part of a laminar diffusion flame at atmospheric pressure by SV-CARS and conventional N2 Q-branch CARS yielded excellent agreement. This new technique was applied to quasi-1D laminar flames with soot concentrations up to 10 ppm and pressures up to 5 bar. The temperature profiles measured in these flames were combined with soot concentration measurements using LII; calibration and correction for signal trapping yielded quantitative soot volume fraction data. The temperature and soot concentration data were combined to generate a comprehensive dataset for the validation of an improved kinetic soot model for the prediction of soot formation in premixed combustion at elevated pressure.

An experimental investigation into soot formation in laminar premixed flames at atmospheric and elevated pressures (1–5 bar) has been conducted. The flames were produced in a dual-flame burner enclosed in a pressure housing. Quantitative soot volume fraction measurements were obtained using laser-induced incandescence coupled with a quasi-simultaneous absorption measurement for calibration; the data were corrected for signal trapping using an â€\~{}â€\~{}onion peeling’’ algorithm. Temperature measurements were obtained using shifted vibrational coherent anti-Stokes Raman scattering, which yields well-resolved, accurate temperature measurements in sooting and nonsooting environments. Results are presented for stable homogeneous flames using air as oxidizer and ethylene, propylene, and toluene as fuels. The variation of soot volume fraction and temperature with height above burner and as a function of fuel,equivalence ratio, and pressure are presented and discussed. The present soot data are well represented by a first-order growth rate law. The data identify trends and features useful for the validation of numerical models of soot formation.

Papers

1. Heat conduction issues in laser-induced incandescenceS.-A. Kuhlmann, J. Reimann, S. Will
2. A detailed experimental and theoretical comparison of spatially-resolved laser-induced incandescence signalsH. Bladh, J. Delhay, Y. Bouvier, E. Therssen, P-E. Bengtsson, P. Desgroux
3. Investigations of the mechanisms involved in LII particle detectionH. A. Michelsen, M. Y. Gershenzon, P.O. Witze
4. Influence of polydisperse distributions of both primary particle and aggregate sizes on soot temperature in low-fluence laser-induced incandescenceF. Liu, M. Yang, F. A. Hill, G. J. Smallwood, D. R. Snelling
5. 2-Color LII measurements of carbon black: Interpretation for quantitative measurement of finenessB.J. Stagg
6. Wavelength-dependence of refractive index function of soot particle by two-color laser induced incandescenceY. Bouvier, E. Therssen, P. Desgroux
7. An LII technique independent of ex-situ calibration by detecting absolute light intensityD. R. Snelling, G. J. Smallwood, F. Liu, Ö. L. Gülder, W. D. Bachalo
8. Laser-induced processes in carbon generated in an argon arcJ.D. Black, M.P. Johnson
9. An investigation of soot nanoparticulate in a vacuumV. Beyer, D.A. Greenhalgh
10. Laser-induced incandescence measurements in a laminar co-annular non-premixed methane/air flame at pressures of 0.5 to 4.0 MPaK. A. Thomson, D. R. Snelling, G. J. Smallwood, F. Liu
11. Laser-induced incandescence and shifted vibrational CARS in laminar premixed flames at atmospheric and elevated pressuresK.P. Geigle, M.S. Tsurikov, W. Meier, V. Krüger, R. Hadef
12. Laser-induced incandescence and multi-line NO thermometry for soot diagnostics at high pressuresM. Hofmann, H. Kronemayer, B. F. Kock, C. Schulz
13. Soot particulate size measurements in a heavy duty Diesel engineB. Bougie, L.C. Ganippa, A.P. van Vliet, N.J. Dam, W.L. Meerts, J.J. ter Meulen
14. Modeling of time-resolved laser-induced incandescence (TIRE-LII) transients for particle sizing in high-pressure spray combustion environmentsT. Dreier, B. Bougie, L. Ganippa, N. Dam, T. Gerber, J.J. ter Meulen
15. Application of TR-LII for the study of carbon vapor condensation at room temperatureA. Eremin, E. Gurentsov, M. Hofmann, C. Schulz
16. Planar laser-induced incandescence of iron particles in welding fumesO. Lucas, Z. Alwahabi, V. Linton
17. Time-resolved laser-induced-incandescence (TR-LII) for iron-particle sizingB. Kock, J. Knipping, H.R. Orthner, C. Kayan, C. Schulz, P. Roth
18. Laser-induced incandescence of free and surface-adsorbed particlesT. Schittkowski, D. Böker, D. Brüggemann
19. In-situ determination of gas-to-particle reaction generated nanoscaled particlesM. Charwath, T. Lehre, R. Suntz, H. Bockhorn
20. Two-dimensional imaging of soot volume fraction and OH in turbulent jet diffusion flames spanning low to high mixing ratesN. H. Qamar, Z.T. Alwahabi, G. J. Nathan, K. D. King

Posters

1. Peak soot temperature in laser-induced incandescence measurementsS. De Iuliis, F. Cignoli, G. Zizak
2. Soot volume fractions and primary particle size estimations by means of simultaneous time-resolved and 2D laser-induced incandescenceA. Boiarciuc, F. Foucher, C. Mounaïm-Rousselle
3. Time-resolved laser-induced incandescence applied to in-cylinder Diesel particle sizingB. F. Kock, C. Schulz, P. Roth
4. Gas-phase temperature imaging in sooting flames by multi-line NO-LIF thermometryH. Kronemayer, M. Hofmann, K. Omerbegovic, C. Schulz
5. A critical evaluation of the thermal accommodation coefficient of soot determined by the laser-induced incandescence techniqueF. Liu, D. R. Snelling, G. J. Smallwood

We report on spatially and temporally resolved optical diagnostic measurements of propagation and combustion of diesel sprays introduced through a single-hole fuel injector into a constant volume, high-temperature, high-pressure cell. From shadowgraphy images in non-reacting environments of pure nitrogen, penetration lengths and dispersion angles were determined for non-vaporizing and vaporizing conditions, and found to be in reasonable agreement with standard models for liquid jet propagation and break-up. Quasi-simultaneous two-dimensional images were obtained of laser elastic light scattering, shadowgraphs and spectrally integrated flame emission in a reacting environment (cell temperature 850 K). In addition laser-induced incandescence was employed for the identification of soot-loaded regions. The simultaneously recorded spray images exhibit remarkable structural similarity and provide complementary information about the spray propagation and combustion process. The measurements also reveal the fuel vapor cloud extending well beyond the liquid core and close to the nozzle tip. Ignition takes place close to the tip of the spray within the mixing layer of fuel vapor and surrounding air. Soot is formed in the vapor core region at the tip of the liquid fuel jet. Our results support recently developed phenomenological model on diesel spray combustion.

Laminar nonpremixed methane–air flames were studied over the pressure range of 0.5 to 4 MPa using a new high-pressure combustion chamber. Flame characterization showed very good flame stability over the range of pressures, with a flame tip rms flicker of less than 1% in flame height. At all pressures, soot was completely oxidized within the visible flame. Spectral soot emission (SSE) and line-of-sight attenuation (LOSA) measurements provided radially resolved measurements of soot volume fraction and soot temperature at pressures from 0.5 to 4.0 MPa. Such measurements provide an improved understanding of the influence of pressure on soot formation and have not been reported previously in laminar nonpremixed flames for pressures above 0.4 MPa. SSE and LOSA soot concentration values typically agree to within 30% and both methods exhibit similar trends in the spatial distribution of soot concentration. Maximum soot concentration depended on pressure according to a power law, where the exponent on pressure is about 2 for the range of pressures between 0.5 and 2.0 MPa, and about 1.2 for 2.0 to 4.0 MPa. Peak carbon conversion to soot also followed a power-law dependence on pressure, where the pressure exponent is unity for pressures between 0.5 and 2.0 MPa and 0.1 for 2.0 to 4.0 MPa. The pressure dependence of sooting propensity diminished at pressures above 2.0 MPa. Soot concentrations measured in this work, when transformed to line-integrated values, are consistent with the measurements of Flower and Bowman for pressures up to 1.0 MPa [Proc. Combust Inst. 21 (1986) 1115–1124] and Lee and Na for pressures up to 0.4 MPa [JSME Int. J. Ser. B 43 (2000) 550–555]. Soot temperature measurements indicate that the overall temperatures decrease with increasing pressure; however, the differences diminish with increasing height in the flame. Low down in the flame, temperatures are about 150 K lower at pressures of 4.0 MPa than those at 0.5 MPa. In the upper half of the flame the differences reduce to 50 K.

A two-color version of the laser-induced incandescence (2C-LII) technique was implemented for measuring absolute soot volume fraction in flames. By using a calibrated tungsten ribbon lamp, soot peak temperatures were measured as a function of fluence at several locations in an ethylene diffusion flame by using a steeply edged laser beam profile. Above a certain fluence threshold, peak temperatures were tightly distributed just above 4000 K independent of the particle size and number density. Radial profiles of soot volume fraction were obtained and compared (not calibrated) with results from the laser extinction technique. Good agreement showed the validity of the 2C-LII technique at a controlled fluence.

Effective temperatures of pulsed-laser-heated soot particles were derived from their thermal emission intensities using optical pyrometry in a laminar ethylene coflow diffusion flame. The present study concerns conditions of relatively low laser fluences under which soot particles are heated to temperatures below 3500 K to avoid complications of soot particle vaporization in both the experiment and the numerical calculations. The current nanoscale heat transfer model for laser-induced incandescence (LII) of soot was improved to account for the effect of the fractal structure of soot aggregates on the rate of heat loss to the surrounding gas. Mean primary soot particle diameter and mean aggregate size at the location of measurement were determined using the technique of thermophoretic sampling/transmission electron microscopy analysis. Numerical calculations based on the improved LII model were conducted to predict the soot particle temperature with known gas temperature, the heat conduction coefficient, the primary particle diameter, and the mean aggregate size, as well as values of assumed soot absorption function E(m) and the thermal accommodation coefficient of soot. The experimentally observed soot temperature history, characterized by the peak value and the temporal decay rate, cannot be reproduced numerically using the values of E(m) and a found in the literature. By utilizing the experimental peak temperature and temporal decay rate new values of E(m) at 1064 nm and the thermal accommodation coefficient were determined. Uncertainties in the derived values of E(m) and the thermal accommodation coefficient caused by the uncertainty in the primary soot particle diameter and the mean aggregate size were analyzed. A novel method to determine the values of the soot absorption function E(m) and the thermal accommodation coefficient was developed in the present study.

Experimental data on the probability distribution of N, from which Ng and σ2g are derived, for soot aggregates sampled within a laminar diffusion flame environment have not been published. The objective of the present investigation is to report such experimental data and to gain a better understanding of the distribution of N of soot aggregates thermophoretically sampled from a laminar ethylene/air diffusion flame by analyzing thousands of aggregates in TEM (transmission electron microscopy) images.