Understanding and predicting the temporal response of laser-induced incandescence from carbonaceous particles

Emission Spectroscopy-Based Sensor System to Correlate the In-Cylinder Combustion Temperature of a Diesel Engine to NOx Emissions

Due to a rising importance of the reduction of pollutant, produced by conventional energy technologies, the knowledge of pollutant forming processes during a combustion is of great interest. In this study the in-cylinder temperature, of a near series diesel engine, is examined with a minimal invasive emission spectroscopy sensor. The soot, nearly a black body radiator, emits light, which is spectrally detected and evaluated with a modified function of Planck's law. The results show a good correlation between the determined temperatures and the NOx concentration, measured in the exhaust gas of the engine, during a variety of engine operating points. A standard deviation between 25 K and 49 K was obtained for the in-cylinder temperature measurements.

Simultaneous Inversion of Particle Size Distribution, Thermal Accommodation Coefficient, and Temperature of In-Flame Soot Aggregates Using Laser-Induced Incandescence

Measuring the size distribution and temperature of high-temperature dispersed particles, particularly in-flame soot, holds paramount importance across various industries. Laser-induced incandescence (LII) stands out as a potent non-contact diagnostic technology for in-flame soot, although its effectiveness is hindered by uncertainties associated with pre-determined thermal properties. To tackle this challenge, our study proposes a multi-parameter inversion strategy-simultaneous inversion of particle size distribution, thermal accommodation coefficient, and initial temperature of in-flame soot aggregates using time-resolved LII signals. Analyzing the responses of different heat transfer sub-models to temperature rise demonstrates the necessity of incorporating sublimation and thermionic emission for accurately reproducing LII signals of high-temperature dispersed particles. Consequently, we selected a particular LII model for the multi-parameter inversion strategy. Our research reveals that LII-based particle sizing is sensitive to biases in the initial temperature of particles (equivalent to the flame temperature), underscoring the need for the proposed multi-parameter inversion strategy. Numerical results obtained at two typical flame temperatures, 1100 K and 1700 K, illustrate that selecting an appropriate laser fluence enables the simultaneous inversion of particle size distribution, thermal accommodation coefficient, and initial particle temperatures of soot aggregates with high accuracy and confidence using the LII technique.

Laser-induced incandescence for non-soot nanoparticles: recent trends and current challenges

Laser-induced incandescence (LII) is a widely used combustion diagnostic for in situ measurements of soot primary particle sizes and volume fractions in flames, exhaust gases, and the atmosphere. Increasingly, however, it is applied to characterize engineered nanomaterials, driven by the increasing industrial relevance of these materials and the fundamental scientific insights that may be obtained from these measurements. This review describes the state of the art as well as open research challenges and new opportunities that arise from LII measurements on non-soot nanoparticles. An overview of the basic LII model, along with statistical techniques for inferring quantities-of-interest and associated uncertainties is provided, with a review of the application of LII to various classes of materials, including elemental particles, oxide and nitride materials, and non-soot carbonaceous materials, and core-shell particles. The paper concludes with a discussion of combined and complementary diagnostics, and an outlook of future research.

Laser-induced incandescence for non-soot nanoparticles: recent trends and current challenges

Laser-induced incandescence (LII) is a widely used combustion diagnostic for in situ measurements of soot primary particle sizes and volume fractions in flames, exhaust gases, and the atmosphere. Increasingly, however, it is applied to characterize engineered nanomaterials, driven by the increasing industrial relevance of these materials and the fundamental scientific insights that may be obtained from these measurements. This review describes the state of the art as well as open research challenges and new opportunities that arise from LII measurements on non-soot nanoparticles. An overview of the basic LII model, along with statistical techniques for inferring quantities-of-interest and associated uncertainties is provided, with a review of the application of LII to various classes of materials, including elemental particles, oxide and nitride materials, and non-soot carbonaceous materials, and core-shell particles. The paper concludes with a discussion of combined and complementary diagnostics, and an outlook of future research.

Laser-induced incandescence for non-soot nanoparticles: recent trends and current challenges

Laser-induced incandescence (LII) is a widely used combustion diagnostic for in situ measurements of soot primary particle sizes and volume fractions in flames, exhaust gases, and the atmosphere. Increasingly, however, it is applied to characterize engineered nanomaterials, driven by the increasing industrial relevance of these materials and the fundamental scientific insights that may be obtained from these measurements. This review describes the state of the art as well as open research challenges and new opportunities that arise from LII measurements on non-soot nanoparticles. An overview of the basic LII model, along with statistical techniques for inferring quantities-of-interest and associated uncertainties is provided, with a review of the application of LII to various classes of materials, including elemental particles, oxide and nitride materials, and non-soot carbonaceous materials, and core-shell particles. The paper concludes with a discussion of combined and complementary diagnostics, and an outlook of future research.

Time-Resolved Laser-Induced Incandescence Measurements on Aerosolized Nickel Nanoparticles

This work presents the first quantitative analysis of time-resolved laser-induced incandescence (TiRe-LII) measurements on aerosolized nickel nanoparticles in several gases and over a range of laser fluences. A measurement model composed of spectroscopic and heat transfer submodels is used to recover the particle size distribution parameters and the thermal accommodation coefficient (TAC). A qualitative analysis of the results reveals evidence of nonincandescent laser-induced emission temporally aligned with the laser pulse, and more laser energy is absorbed than can be accounted for from the modeled spectral absorption cross section of the nanoparticles. The TiRe-LII inferred particle size parameters were generally consistent with values found from ex situ transmission electron microscopy (TEM) analysis. The TACs for nickel nanoparticles in polyatomic gases were larger than those in monoatomic gases, which may indicate chemisorption.

Suppression of unpolarized background interferences for Raman spectroscopy under continuous operation

A time-resolving filtering technique developed to improve background suppression in Raman spectroscopy is presented and characterized. The technique enables separation of signal contributions via their polarization dependency by the addition of a waveplate to a normal measurement system and data post-processing. As a result, background interferences of broadband laser-induced fluorescence and incandescence, as well as flame luminosity and blackbody radiation, were effectively suppressed from Raman spectra. Experimental setting parameters of the method were investigated under well-controlled conditions to assess their impact on the background-filtering ability, and the overall trend was understood. The fluorescence background was effectively suppressed for all investigated settings of modulation period, number of accumulations, and recording duration, with the spectrum quality preserved after the filtering. For practical application, the method was tested for measurements in a sooting flame accompanied by a strong luminosity and interfering laser-induced background signals. The technique resulted in a 200-fold decrease of the background and allowed for quantitative analyses of concentrations and temperatures from the filtered data. Thus, the method shows strong potential to extend the applicability of Raman spectroscopy, in particular for in situ diagnostics under challenging experimental conditions.

Thermal properties of lipid bilayers derived from the transient heating regime of upconverting nanoparticles

Heat transfer and thermal properties at the nanoscale can be challenging to obtain experimentally. These are potentially relevant for understanding thermoregulation in cells. Experimental data from the transient heating regime in conjunction with a model based on the energy conservation enable the determination of the specific heat capacities for all components of a nanoconstruct, namely an upconverting nanoparticle and its conformal lipid bilayer coating. This approach benefits from a very simple, cost-effective and non-invasive optical setup to measure the thermal parameters at the nanoscale. The time-dependent model developed herein lays the foundation to describe the dynamics of heat transfer at the nanoscale and were used to understand the heat dissipation by lipid bilayers.

Simultaneous determination of primary particle size distribution and thermal accommodation coefficient of soot aggregates using low-fluence LII

For the ill-posed inverse problem of LII-based nanoparticle size measurement, recovered primary particle size distribution (PPSD) is sensitive to the uncertainty of LII model parameters. In the absence of reliable prior knowledge, the thermal accommodation coefficient (TAC) and fractal-dependent shielding factor are often required to be inferred simultaneously with the PPSD. In the simplified LII model for low fluence regime, TAC and fractal-dependent shielding factor are combined to define a new fractal-dependent TAC. The present study theoretically verified the feasibility of inferring PPSD and fractal-dependent TAC from the normalized LII signals. Moreover, the inversion is independent of prior knowledge of most full LII model parameters, which is attributed to low laser fluence, normalized signal, and fractal-dependent TAC.

A Review of Terminology Used to Describe Soot Formation and Evolution under Combustion and Pyrolytic Conditions

This review presents a glossary and review of terminology used to describe the chemical and physical processes involved in soot formation and evolution and is intended to aid in communication within the field and across disciplines. There are large gaps in our understanding of soot formation and evolution and inconsistencies in the language used to describe the associated mechanisms. These inconsistencies lead to confusion within the field and hinder progress in addressing the gaps in our understanding. This review provides a list of definitions of terms and presents a description of their historical usage. It also addresses the inconsistencies in the use of terminology in order to dispel confusion and facilitate the advancement of our understanding of soot chemistry and particle characteristics. The intended audience includes senior and junior members of the soot, black carbon, brown carbon, and carbon black scientific communities, researchers new to the field, and scientists and engineers in associated fields with an interest in carbonaceous material production via high-temperature hydrocarbon chemistry.

Sublimation Kinetics for Individual Graphite and Graphene Nanoparticles (NPs): NP-to-NP Variations and Evolving Structure-Kinetics and Structure-Emissivity Relationships

A single nanoparticle (NP) mass spectrometry method was used to measure sublimation rates as a function of nanoparticle temperature (T_NP) for sets of individual graphite and graphene NPs. Initially, the NP sublimation rates were ∼400 times faster than those for bulk graphite, and there were large NP-to-NP variations. Over time, the rates slowed substantially, though they remained well above the bulk rate. The initial activation energies (E_a values) were correspondingly low and doubled, as a few monolayers worth of material was sublimed from the surfaces. The high initial rates and low E_a values are attributed to large numbers of edge, defect, and other low coordination sites on the NP surfaces, and the changes are attributed to atomic-scale "smoothing" of the surface by preferential sublimation of the less stable sites. The emissivity of the NPs also changed after heating, more frequently increasing. The emissivity and sublimation rates were anticorrelated, leading to the conclusion that high densities of low-coordination sites on the NP surfaces enhance sublimation but suppress emissivity.

On determining soot maturity: A review of the role of microscopy- and spectroscopy-based techniques

Incomplete combustion is the main source of airborne soot, which has negative impacts on public health and the environment. Understanding the morphological and chemical evolution of soot is important for assessing and mitigating the impact of soot emissions. Morphological and chemical structures of soot are commonly studied using microscopy or spectroscopy, and the best technique depends on the parameter of interest and the stage of soot formation considered (i.e., maturity). For the earliest stages of soot formation, particles exhibit simple morphology yet complex and reactive chemical composition, which is best studied by spectroscopic techniques sensitive to the large number of soot precursor species. The only microscope that can offer some morphological information at this stage is the scanning probe microscopy, which can image single polycyclic aromatic hydrocarbons, the precursors of soot. A broader range of types of spectrometers and microscopes can be used by increasing the soot maturity. Mature soot is primarily carbon, and exhibits complex fractal-like morphology best studied with electron microscopy and techniques sensitive to thin oxide or organic coatings. Each characterization technique can target different morphological and chemical properties of soot, from the early to the late stage of its formation. Thus, a guideline for the selection of the appropriate technique can facilitates studies on environmental samples involving the presence of soot.

Candle flame soot sizing by planar time-resolved laser-induced incandescence

Soot emissions from flaming combustion are relevant as a significant source of atmospheric pollution and as a source of nanomaterials. Candles are interesting targets for soot characterization studies since they burn complex fuels with a large number of carbon atoms, and yield stable and repeatable flames. We characterized the soot particle size distributions in a candle flame using the planar two-color time-resolved laser induced incandescence (2D-2C TiRe-LII) technique, which has been successfully applied to different combustion applications, but never before on a candle flame. Soot particles are heated with a planar laser sheet to temperatures above the normal flame temperatures. The incandescent soot particles emit thermal radiation, which decays over time when the particles cool down to the flame temperature. By analyzing the temporal decay of the incandescence signal, soot particle size distributions within the flame are obtained. Our results are consistent with previous works, and show that the outer edges of the flame are characterized by larger particles ([Formula: see text]), whereas smaller particles ([Formula: see text]) are found in the central regions. We also show that our effective temperature estimates have a maximum error of 100 K at early times, which decreases as the particles cool.

Analysis of the Influence of the Conduction Sub-Model Formulation on the Modeling of Laser-Induced Incandescence of Diesel Soot Aggregates

Laser-induced incandescence (LII) is a powerful diagnostic technique allowing quantifying soot emissions in flames and at the exhaust of combustion systems. It can be advantageously coupled with modeling approaches to infer information on the physical properties of combustion-generated particles (including their size), which implies formulating and solving balance equations accounting for laser-excited soot heating and cooling processes. Properly estimating soot diameter by time-resolved LII (TiRe-LII), nevertheless, requires correctly evaluating the thermal accommodation coefficient αT driving the energy transferred by heat conduction between soot aggregates and their surroundings. To analyze such an aspect, an extensive set of LII signals has been acquired in a Diesel spray flame before being simulated using a refined model built upon expressions accounting for soot heating by absorption, annealing, and oxidation as well as cooling by radiation, sublimation, conduction, and thermionic emission. Within this framework, different conduction sub-models have been tested while a corrective factor allowing the particle aggregate properties to be taken into account has also been considered to simulate the so-called shielding effect. Using a fitting procedure coupling design of experiments and a genetic algorithm-based solver, the implemented model has been parameterized so as to obtain simulated data merging on a single curve with experimentally monitored ones. Eventually, values of the thermal accommodation coefficient have been estimated with each tested conduction sub-model while the influence of the aggregate size on the so-inferred αT has been analyzed.

Defining regimes and analytical expressions for fluence curves in pulsed laser heating of aerosolized nanoparticles

Fluence curves are a powerful tool for understanding the mechanisms underlying nanosecond pulse laser heating of aerosolized nanoparticles, which is relevant to laser-induced incandescence (LII). This paper presents analytical expressions encompassing the entirety of the fluence domain considered in LII and uses them to formally define fluence regimes. The derived expressions and non-dimensional parameters facilitate one of the first comparisons of published experimental fluence curves. This procedure provides physical insight into the laser-nanoparticle interaction and highlights inconsistencies in the application of LII models to analyze the data.

Novel electric thermophoretic sampling device with highly repeatable characteristics

A novel thermophoretic sampling device for probing nanoparticle aggregates in all types of flames as well as in particle-laden gases and aerosols is presented. For the motion of the sampling probe, a tubular electric linear motor is utilized, and its design and operation are described in detail. The spatial and temporal performance is determined from oscilloscope measurements and high-speed recordings of one motion profile featuring three different resident times. Motion sequences offering a minimum residence time of 3 ms and a maximum velocity of 4.1 m s^-1 simultaneously providing smooth probe movement and minimal vibrations are feasible. For a stroke length of 100 mm, maximum deviations between sampling and setpoint positions of 0.14 mm in axial, 0.02 mm in horizontal, and 0.36 mm in vertical direction are determined, respectively. The evaluation of standard deviations among individual motion sequences for every time step shows high precision in all directions of movement. The influence of probe invasion on a laminar premixed flame produced using a McKenna burner is characterized employing high-speed recordings. Soot radiance intensities are temporally evaluated in four regions of interest near the sampling probe where maximum changes in the order of 20% are observed. Thermophoretic sampling was performed on the flame at 17 mm height above burner using ethene and ethyne as fuels with an equal equivalence ratio of 2.7. Morphological soot aggregate properties are derived from comprehensive transmission electron microscopy analysis and show satisfying results.

Biocompatible Label-Free Detection of Carbon Black Particles by Femtosecond Pulsed Laser Microscopy

Although adverse health effects of carbon black (CB) exposure are generally accepted, a direct, label-free approach for detecting CB particles in fluids and at the cellular level is still lacking. Here, we report nonincandescence related white-light (WL) generation by dry and suspended carbon black particles under illumination with femtosecond (fs) pulsed near-infrared light as a powerful tool for the detection of these carbonaceous materials. This observation is done for four different CB species with diameters ranging from 13 to 500 nm, suggesting this WL emission under fs near-infrared illumination is a general property of CB particles. As the emitted radiation spreads over the whole visible spectrum, detection is straightforward and flexible. The unique property of the described WL emission allows optical detection and unequivocal localization of CB particles in fluids and in cellular environments while simultaneously colocalizing different cellular components using various specific fluorophores as shown here using human lung fibroblasts. The experiments are performed on a typical multiphoton laser-scanning microscopy platform, widely available in research laboratories.

Black carbon emissions in gasoline vehicle exhaust: a measurement and instrument comparison

A pilot study was conducted to evaluate the performance and agreement of several commercially available black carbon (BC) measurement instruments, when applied to the quantification of BC in light-duty vehicle (LDV) exhaust. Samples from six vehicles, three fuels, and three driving cycles were used. The pilot study included determinations of the method detection limit (MDL) and repeatability. With respect to the MDL, the real-time instruments outperformed the time-integrated instruments, with MDL = 0.12 mg/mi for the AE51 Aethalometer, and 0.15 mg/mi for the Micro Soot Sensor (MSS), versus 0.38 mg/mi for the IMPROVE_A thermal/ optical method, and 0.35 mg/mi for the OT21_T Optical Transmissometer. The real-time instruments had repeatability values ranging from 30% to 35%, which are somewhat better than those of the time-integrated instruments (40-41%). These results suggest that, despite being less resource intensive, real-time methods can be equivalent or superior to time-integrated methods in terms of sensitivity and repeatability. BC mass data, from the photoacoustic and light attenuation instruments, were compared against same-test EC data, determined using the IMPROVE_A method. The MSS BC data was well correlated with EC, with R2 = 0.85 for the composite results and R2 = 0.86 for the phase-by-phase (PBP) results. The correlation of BC, by the AE51, AE22, and OT21_T with EC was moderate to weak. The weaker correlation was driven by the inclusion of US06 test data in the linear regression analysis. We hypothesize that test-cycle-dependent BC:EC ratios are due to the different physicochemical properties of particulate matter (PM) in US06 and Federal Test Procedure (FTP) tests. Correlation amongst the real-time MSS, PASS-1, AE51, and AE22 instruments was excellent (R2 = 0.83-0.95), below 1 mg/mi levels. In the process of investigating these BC instruments, we learned that BC emissions at sub-1 mg/mi levels can be measured and are achievable by current-generation gasoline engines.

IMPLICATIONS

Most comparison studies of black carbon (BC) measurement methods were carried out in the ambient air. This study assesses the agreement among various BC measurement instrument in emissions from light-duty gasoline vehicles (LDGVs) on standard test cycles, and evaluates applicability of these methods under various fuel types, driving cycles, and engine combustion technologies. This research helps to fill in the knowledge gap of BC method standardization as stated in the U.S. Environmental Protection Agency (EPA) 2011 Report to Congress on Black Carbon, and these results demonstrate the feasibility of quantification of BC at the 1 mg/mi PM standard in California Low Emission Vehicle III regulations.

Absolute cooling rates of freely decaying fullerenes

The cooling rates of C60- have been measured in an electrostatic storage ring between several hundred mus and several tens of ms with one-photon laser excitation. The absolute energy scale is established by the photon energy, and the cooling time interval is derived from the nonexponential decay of the ensemble of hot molecules. The energy decreases due to the combined action of depletion and thermal emission of IR photons with a total energy loss rate that varies inversely proportional to time, 0.9 eV/t. The radiative component decreases from a few hundred eV/s at submillisecond time scales to several tens of eV/s at 20 ms and confirms that the crossover from depletion to predominantly radiative cooling occurs around 5 ms. The method is applicable to any large molecule or cluster which decays spontaneously, irrespective of the specific decay channel.

Application of laser-induced incandescence to suspended carbon black particles

For the first time, to the best of our knowledge, laser-induced incandescence (LII) has successfully been applied to carbon black suspensions. A linear correlation between the experimentally derived signal decay time and the mean primary particle size, determined by transmission electron microscopy, for different carbon black particles was found. Moreover, a nonlinear relation similar to that known from measurements of aerosols was observed for the peak LII signal and the laser fluence. Despite different heat transfer properties, the signal decay time was not influenced by the solvents used.

Particle formation from pulsed laser irradiation of soot aggregates studied with a scanning mobility particle sizer, a transmission electron microscope, and a scanning transmission x-ray microscope

We investigated the physical and chemical changes induced in soot aggregates exposed to laser radiation using a scanning mobility particle sizer, a transmission electron microscope, and a scanning transmission x-ray microscope to perform near-edge x-ray absorption fine structure spectroscopy. Laser-induced nanoparticle production was observed at fluences above 0.12 J/cm(2) at 532 nm and 0.22 J/cm(2) at 1064 nm. Our results indicate that new particle formation proceeds via (1) vaporization of small carbon clusters by thermal or photolytic mechanisms, followed by homogeneous nucleation, (2) heterogeneous nucleation of vaporized carbon clusters onto material ablated from primary particles, or (3) both processes.

Absorption correction of two-color laser-induced incandescence signals for soot volume fraction measurements

A numerical iterative procedure is presented for the evaluation of the effect of signal absorption in two-color laser-induced incandescence measurements. The correction process is applied to our experimental data in an axisymmetric flame [Appl. Opt. 44, 7414 (2005)]. The influence of signal trapping on peak soot temperature and on soot volume fraction has been found to be minimal. Some numerical tests were performed to investigate the effects of soot concentration, flame size, and soot refractive index on the magnitude of the signal absorption correction.

Two-color laser-induced incandescence (2C-LII) technique for absolute soot volume fraction measurements in flames

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.

Measurement of polystyrene nanospheres using excimer laser fragmentation fluorescence spectroscopy

Monodisperse polystyrene nanospheres with a mean diameter of 102 nm are photofragmented with 193 nm light in N2 at laser fluences from 1 to 20 J/cm2. Carbon atom fluorescence at 248 nm from the disintegration of the particles is used as a signature of the polystyrene. The normalized fluorescence signals are self-similar with an exponential decay lifetime of approximately 10 ns. At fluences above 17 J/cm2, optical breakdown occurs and a strong continuum emission is generated that lasts significantly longer. A non-dimensional parameter, the photon-to-atom ratio (PAR), is used to interpret the laser-particle interaction energetics. Carbon fluorescence from polystyrene particles is compared with that from soot, and a similarity between the two particles is observed when normalized with PAR. Carbon emission from bulk polystyrene was also measured. Similar emission signals were observed, but the breakdown threshold of the surface is significantly lower at 0.2 J/cm2.

Assessment of soot particle vaporization effects during laser-induced incandescence with time-resolved light scattering

Although laser-induced incandescence (LII) has been successfully used for soot volume fraction and particle size measurements, uncertainties remain regarding issues of soot vaporization leading to mass loss and morphological changes occurring in soot due to intense heating. Prompt LII detection schemes are often based on the assumption that the associated time scale is shorter than the time scale of soot vaporization or sublimation. The validity of such assumptions is the focus of the current study. Time-resolved light-scattering measurements were made in combination with LII measurements to quantify soot particle vaporization effects resulting from the LII laser pulse. The light-scattering measurements revealed a sharp decrease in total soot particle mass during the time course of the 25 ns full-width LII laser pulse for fluences in the range of 0.5 J/cm2. Light-scattering theory was used to invert the scattering data, revealing approximately 80%-90% reductions in the soot particle volume for LII fluences of 0.47 and 0.61 J/cm2. In addition, the time-resolved scattering measurements show that the time scale of soot vaporization is completely confined to the LII laser pulse itself. Light scattering revealed no soot vaporization only for fluences of approximately 0.1 J/cm2, which is consistent with recent work on low-fluence LII. Possible mechanisms for soot vaporization are discussed, notably for near-threshold fluences.

Simultaneous planar laser-induced incandescence, OH planar laser-induced fluorescence, and droplet Mie scattering in swirl-stabilized spray flames

Simultaneous planar laser-induced incandescence, hydroxyl radical planar laser-induced fluorescence, and droplet Mie scattering are used to study the instantaneous flame structure and soot formation process in an atmospheric pressure, swirl-stabilized, liquid-fueled, model gas-turbine combustor. Optimal excitation and detection schemes to maximize single-shot signals and avoid interferences from soot-laden flame emission are discussed. The data indicate that rich pockets of premixed fuel and air along the interface between the spray flame and the recirculation zone serve as primary sites for soot inception. Intermittent large-scale structures and local equivalence ratio are also found to play an important role in soot formation.

Time-resolved laser-induced incandescence of soot: the influence of experimental factors and microphysical mechanisms

We present a data set for testing models of time-resolved laser-induced incandescence of soot. Measurements were made in a laminar ethene diffusion flame over a wide range of laser fluences at 532 nm. The laser was seeded to provide a smooth temporal profile, and the beam was spatially filtered and imaged into the flame to provide a homogeneous spatial profile. The particle incandescence was imaged onto a fast photodiode. The measurements are compared with the standard Melton model [Appl. Opt. 23,2201 (1984)] and with a new model that incorporates physical mechanisms not included in the Melton model.