Laser-induced Incandescence Research Articles

Detection of tar brown carbon with a single particle soot photometer (SP2)

Abstract. We investigate the possibility that the refractory, infrared-light-absorbing carbon particulate material known as “tarballs” or tar brown carbon (tar brC) generates a unique signal in the scattering and incandescent detectors of a single particle soot photometer (SP2). As recent studies have defined tar brC in different ways, we begin by reviewing the literature and proposing a material-based definition of tar. We then show that tar brC results in unique SP2 signals due to a combination of complete or partial evaporation, with no or very little incandescence. Only a subset of tar brC particles exhibited detectable incandescence (70 % by number); for these particles the ratio of incandescence to light scattering was much lower than that of soot black carbon (BC). At the time of incandescence the ratio of light scattering to incandescence from these particles was up to 2-fold greater than from soot (BC). In our sample, where the mass of tar was 3-fold greater than the mass of soot, this led to a bias of <5 % in SP2-measured soot mass, which is negligible relative to calibration uncertainties. The enhanced light scattering of tar is interpreted as being caused by tar being more amorphous and less graphitic than soot BC. The fraction of the tar particle which does incandesce was likely formed by thermal annealing during laser heating. These results indicate that laser-induced incandescence, as implemented in the SP2, is the only BC measurement technique which can quantify soot BC concentrations separately from tar while also potentially providing real-time evidence for the presence of tar. In contrast, BC measurement techniques based on thermal–optical (EC: elemental carbon) and absorption (eBC: equivalent BC) measurements cannot provide such distinctions. The optical properties of our tar particles indicate a material similarity to the tar particles previously reported in the literature. However, more- and less-graphitized tar samples have also been reported, which may show stronger and weaker SP2 responses, respectively.

Particulate emissions measurements by laser-based techniques in a boiler fueled by wood pellets

This paper describes mainly laser-based techniques applied to a boiler fueled by wood pellets which is a real complicated combustion system. To our knowledge, laser-induced incandescence (LII) and extinction are used to characterize particulate emission at the exhaust for the first time because laser diagnostics are generally applied to laboratory flames, automotive engines and aeroengines. The 30-kW boiler was first characterized by temperature mapping in the combustion chamber and particle diameter analysis by scanning mobility particle sizer at the exhaust and inside the first combustion chamber for a better understanding of the running of this complex combustion system. Non-intrusive laser-based diagnostics including broadband LII, two-color LII and laser extinction excited at 1064 nm have been employed to study the particulate emissions at the exhaust of the boiler during the start-up and the steady-state phases of the boiler. The cross analysis of the experimental results obtained with the different diagnostics shows that particle size distributions, particles volume fractions and the temperature distribution are strongly dependent on the boiler cycle linked to the pellets loading. Laser extinction and LII-based methods provided complementary information about the particulate emissions. The LII technique probes incandescent soot particles formed during the combustion of pellets, while laser extinction detects both soot and non-incandescent particles (such as dust, fly ashes).

Chemical effects of hydrogen addition on soot formation in counterflow diffusion flames: Dependence on fuel type and oxidizer composition

We experimentally studied and kinetically modeled the effects of hydrogen addition on soot formation in methane and ethylene counterflow diffusion flames (CDFs). To isolate the chemical effects of hydrogen in such flames, we also ran a set of experiments on flames of the same base fuels but with the addition of helium. Specifically, we measured the soot volume fractions of the flames using the planar laser-induced incandescence technique. We simulated detailed sooting structures by coupling the gas-phase chemistry with the polycyclic aromatic hydrocarbon (PAH)-based soot model, using a sectional method to resolve the soot particle dynamics. Our experimental and numerical results show that hydrogen chemically inhibits soot formation in ethylene CDFs. While in methane flames, it is interesting to observe that the difference in soot production between the hydrogen- and helium-doped cases became much smaller when the oxygen concentration in the oxidizer stream (XO) was reduced. This suggests that for methane CDFs the chemical soot-inhibiting effects of hydrogen was highly dependent on oxidizer composition (i.e., XO). Explanations are provided through detailed kinetic analysis concerning the effects of hydrogen addition on the growth of PAH, soot inception, and soot surface growth processes. Our results suggest that hydrogen's chemical role in soot formation not only depends on fuel type (ethylene or methane), it also may be sensitive to oxidizer composition.

Particle Size Measurement of Reaction Product Aerosol of Sodium-Oxygen

A multi-level scenario simulation system as a safety infrastructure technology is required for design optimization, safety margin adjustment, and innovative technology developments of sodium-cooled fast reactor (SFR). In order to properly implement the Verification and Validation (V & V) of the simulation system, it is indispensable to ensure experimental database of sodium chemistry as specific SFR safety issue. In this study, measurement results of aerosols generated by sodium-oxygen reaction for sodium fire event were reported with the aim of clarifying the radiation heat transport phenomena in the reaction field. The sodium-oxygen counter-flow diffusion flame was formed one-dimensionally above the sodium pool by the reaction between sodium vapour and oxygen. Argon (Ar) including 2% oxygen were introduced to a liquid sodium pool (temperature: 820K) under the reduced pressure condition (0.05MPa). Ar guard flows were employed to stabilize the reaction. The reaction continued more than 600 seconds without any changes in terms of flame shape and position. Aerosol size was measured as a function of Z (the distance from the sodium pool surface) and r (the distance from the center of the sodium pool). Laser Induced Incandescence (LII) and the Mie scattering method using the different wavelength laser beams (405nm, 450nm, 520nm, 532nm, 638nm and 650nm) were employed to ensure the measurement accuracy. Aerosol sizes from several hundred nm to 1 μm were measured in this reaction field and the aerosol size increased toward the sodium pool. This stemmed largely from aerosol growth and polymerization because the flow rate decreased near the sodium pool. It was also confirmed that the size of aerosol measured by LII was in good agreement with the measurement using the Mie scattering method under the same conditions. The refractive index of the aerosol was also evaluated to be 1.42-0.5i.

Laser-induced emission of TiO2 nanoparticles in flame spray synthesis

Oxide nanoparticles are widely studied because of their unique properties, including their crystalline phase, surface area, and porosity, which make them attractive for several applications. These properties are related to the increase in the surface/volume ratio when moving from the bulk to the nanoscale. For this reason, a diagnostic tool capable of monitoring the nanoparticle size and concentration during synthesis is particularly valuable. The laser-induced incandescence technique is widely used to provide such information. This study explored the applicability of this technique to TiO2 nanoparticles in flame spray synthesis. The fluorescence, flame emission, and incandescence signals were investigated. Time-resolved spectral measurements were first carried out on TiO2 nanoparticles deposited on a filter. At low laser fluences, the fluorescence signal of anatase TiO2 nanoparticles was detected. At higher fluences, the incandescence signal appeared. A fluence threshold limit that depended on the matrix effect was observed, above which breakdown phenomena occur. Then, laser-induced incandescence spectral measurements were performed on the flame spray at different heights above the burner and different acquisition delay times. The analysis showed the applicability and challenges in using this diagnostic tool in flame spray synthesis.

Laser-induced incandescence on metal nanoparticles: validity of the Rayleigh approximation

Time-resolved laser-induced incandescence (TiRe-LII) is increasingly being used to characterize non-carbonaceous nanoparticles. However, there exist several measured phenomena, particularly on metal nanoparticles, that cannot be explained using traditional models. This paper shows that some of these phenomena may be due to errors caused by the Rayleigh approximation of Mie theory, which is a standard approach for modeling the spectral absorption of carbonaceous nanoparticles but is generally invalid for metal nanoparticles. Other measurement phenomena can be explained by combining Mie theory with a polydisperse particle size distribution or by considering the change in the refractive index as the nanoparticles melt. Also, the effect of the nanoparticle charge on optical properties is investigated and is found to have a negligible effect on the TiRe-LII model.

Effects of Detection Wavelengths on Soot Volume Fraction Measurements Using the Auto-Compensating LII Technique

ABSTRACT Soot particles in the detection volume in general have different temperatures due to non-uniform laser fluence and particle size distribution. The thermal radiation intensity displays different temperature dependence at different wavelengths. The effective soot temperature inferred from the ratio of laser-induced incandescence (LII) signals in the auto-compensating LII (AC-LII) technique is dependent on the detection wavelengths and affects the measured soot volume fraction. This paper numerically investigates the effects of detection wavelengths on the inferred soot effective temperature and volume fraction under conditions relevant to laminar diffusion flames at atmospheric pressure and for three representative laser fluence distributions. Numerical calculations were conducted using an LII model for a laser pulse of 5.8 ns FWHM and 1064 nm and assuming a lognormal primary particle size distribution and neglecting the aggregation effect. LII signals were modeled at four wavelength bands centered at 420, 560, 680, and 790 nm and the effective soot temperature was derived over three pairs of LII signals, namely [420, 560 nm], [560, 680 nm], and [680, 790 nm]. The two shortest and two longest detection wavelengths respectively result in the highest and lowest effective soot temperature when the laser fluence is non-uniform. The inferred soot volume fraction displays the opposite trend as the effective soot temperature. The effective soot temperature is biased toward the highest values and AC-LII always underestimates the soot volume fraction. The detection wavelengths should be carefully selected to minimize the impact of non-uniform laser fluence and at the same time to maximize the accuracy of effective soot temperature.

Effects of Flame Temperature on PAHs and Soot Evolution in Partially Premixed and Diffusion Flames of a Diesel Surrogate

In this paper, polycyclic aromatic hydrocarbons (PAHs) and soot formation in rich partially premixed flames and nonpremixed flames were studied using a blend of n-heptane and toluene. The flames were diluted with Ar, N2, and CO2 to control the flame temperature. Laser-induced fluorescence, laser-induced incandescence, and two-color pyrometry were used to study the effects of flame temperature on the PAHs and soot evolution. Results show that temperature distributions are similar for different gas dilutions at low flow rates. However, the higherature area increases dramatically in size at high flow rates and it depends on diluents in the order Ar > N2 > CO2 with regard to flame temperature. With an increase in the flow rate of Ar, the higher growth rate of flame temperature and bigger region of higherature region can lead to a higher growth rate from small to large PAHs and higher soot volume fraction. However, for CO2 dilution, the increased flow rate results in the increase of formation of large PAHs, but soot formation is reduced due to the fact that lower flame temperature suppresses the soot formation. Therefore, it can be concluded that the evolution of PAHs and soot strongly depends on flame temperature. (Less)

On the influence of wall distance and geometry for high-pressure n-dodecane spray flames in a constant-volume chamber

To isolate the effect of flame–wall interaction from representative operating conditions of an internal combustion engine, experiments were performed in a constant-volume pre-burn vessel. Three different wall geometries were studied at distances of 32.8, 38.2, and 46.2 mm from a single-hole 0.09-mm orifice diameter fuel injector. A flat wall provides a simplified case of flame–wall interaction. To mimic the division of a jet into two regions by the piston bowl rim in an engine, a two-dimensional confined wall is used. A third, axisymmetric confined wall geometry allows a second simplified comparison to numerical simulations in a Reynolds-averaged Navier–Stokes framework. As a limiting situation for a free jet, the distance from the injector orifice to the end wall of the chamber is 95 mm. Thermocouples installed in the end wall provided insights into local heat losses for reference cases without a wall insert. The test conditions were according to the Engine Combustion Network Spray A guidelines with an ambient temperature of 900 K and an ambient density of 22.8 kg/m3 with 15% O2. Flame structures were studied using high-speed OH* chemiluminescence with integrated single-shot OH PLIF and combined with pressure-based apparent heat release data to infer combustion progress and spray behavior. Soot was studied in a qualitative manner using high-speed natural luminosity imaging with integrated high-speed laser-induced incandescence. Overall, increased mixing upon interaction with the surfaces is observed to increase early heat release rate and to significantly reduce soot, with the nearest wall distance showing most effect. The flat wall gives rise to the most significant effects in all cases.

Experimental and numerical study of soot formation in counterflow diffusion flames of gasoline surrogate components

Soot formation is experimentally and numerically investigated in laminar counterflow diffusion flames burning ethylene and three typical gasoline surrogate components; n-heptane, iso-octane, and toluene. Laser-induced incandescence and a light extinction technique are employed to determine the soot volume fraction within the well-controlled region of the burner. The experiments are performed across a wide range of strain rates and stoichiometric mixture fractions. From the experimental data, sensitivities of soot formation on strain rate and stoichiometric mixture fraction are derived for each fuel. The fuels show significantly different sensitivities. For iso-octane and n-heptane, a higher sensitivity of soot production on the strain rate is observed as compared to ethylene and toluene. Moreover, the sensitivities of soot formation on the strain rate increase with increasing stoichiometric mixture fraction. One-dimensional simulations of the flames investigated experimentally were performed using two different detailed chemical kinetic mechanisms, detailed chemical soot models, and the hybrid method of moments as well as a discrete sectional method to describe soot dynamics. The models are capable of predicting the soot volume fraction of the ethylene flames with remarkable accuracy, whereas for the gasoline surrogate components, the overall soot volume fractions are overpredicted for all tested models. In iso-octane flames, soot nucleation and PAH condensation rates are particularly enhanced. A reaction pathway analysis shows that in ethylene flames, the formation of benzene mostly originates from acetylene, while for iso-octane, large amounts of iso-butenyl form propyne, propargyl, and then benzene.

Simultaneous imaging of soot volume fraction, PAH, and OH in a turbulent n-heptane spray flame

Soot formation and oxidation in a turbulent n-heptane jet spray flame are investigated through simultaneous imaging of quantitative soot volume fraction (fv), flame-front (OH), and soot-precursor marked by smaller (2–4 ring) polycyclic aromatic hydrocarbons (PAH). Laser-induced incandescence (LII) and laser-induced fluorescence (LIF) techniques are used. The spray flame is composed of a dual branch axisymmetric structure. The inner composite branch (B1) consists of fuel-lean and non-premixed reaction zones, whereas combustion in the outer branch (B2) occurs in a non-premixed mode. Frequent local flame extinctions occur along B1, while no extinctions are observed in B2. Consequently, the soot inception occurs near B2. In the onset of soot detection (fv ≥ 0.03 ppm) region, soot layers are thinner than those from downstream regions where soot occupies nearly the same area as of PAH. Soot generally oxidizes across the flame-front as evidenced from the absence of soot-OH overlap. The soot structures are intermittent with peak soot probability of 60%. The most probable peak fv measures 1 ppm, while the conditional mean is 0.42 ppm which is 2.5 times that of time-averaged fv. Conditional mean fv shows monotonically increasing trend with height. The flame lift-off height and local extinctions do not instantaneously influence the soot concentration, possibly due to larger convective and soot formation timescales. Soot-PAH correlations are explored. However, no strong instantaneous correlations are noted, most likely due to different chemical timescales of soot and the imaged smaller-PAH. Nevertheless, a few distinct trends are noted in soot-PAH correlations. fv weakly increases with the PAH-LIF intensity. The PAH intensity from soot onset to peak region decreases, while both soot and PAH are nearly consumed at a local flame-tip (oxidation) region. The soot-PAH overlap decreases consistently from soot onset to oxidation region. The reported database and deduced insights can aid in the development and validation of soot models in two-phase reacting flows.

Soot formation and flame structure in swirl-stabilized turbulent non-premixed methane combustion

The relationships between flow field, flame structure, and soot distribution were investigated experimentally in turbulent 4 kW non-premixed swirl flames of methane and air at three different air supply rates. Auto-compensating laser-induced incandescence, particle image velocimetry, OH planar laser induced fluorescence, and OH* chemiluminescence techniques were used to measure soot volume fractions and primary soot particle size, velocity fields, OH, and OH* fields, respectively. While the instantaneous values of soot volume fractions were similar among the flames, the time-averaged soot volume fraction decreased by nearly a factor of three for a 7% increase in the air flow rate due to increased soot intermittency. Peak soot volume fractions occurred between two shear layers caused by the central fuel jet injection, recirculation zone, and swirling air jet interfaces. The decrease in soot towards the air side corresponded to locations with elevated OH, demonstrating its role in soot oxidation. The velocity measurements showed that engulfing the jet through a stronger recirculation rate induced by the higher air velocity enhanced the turbulent mixing between the recirculating fluid and fuel jet, and led to a shorter fuel jet penetration length. The reduction in soot volume fraction with air flow rate therefore is associated with greater turbulent mixing and higher oxidation rate in the recirculation zone. In contrast, the primary soot particle size, whose range was between 30 and 60 nm, did not show a dependence on the air flow rate. These results highlight the sensitivity of soot processes to fluid mechanics under turbulent conditions.

PAHs and soot formation in laminar partially premixed co-flow flames fuelled by PRFs at elevated pressures

This study investigated polycyclic aromatic hydrocarbons (PAHs) and soot formation characteristics in laminar jet flames fuelled by primary reference fuels (PRFs) at elevated pressures. Qualitative PAHs and quantitative soot profiles were acquired by using laser-induced fluorescence and laser-induced incandescence, respectively. The backpressure of flames ranged from 1 bar to 5 bar. Proper flames with the volume fraction of iso-octane in PRFs varying between 0% and 100% and flame equivalent ratio varying between 3.0 and 11.4 were stabilised in a pressurised chamber. The effects of backpressure, equivalent ratio and iso-octane ratio on PAHs and soot formation were evaluated. PAHs and soot formation can be promoted by increasing iso-octane ratio, equivalent ratio and backpressure. The data suggest that PAHs with large molecular size are more sensitive to the increase of backpressure compared with those with small molecular size. Backpressure played a positive role in the growth of PAHs size. The averaged soot volume fraction showed an approximate power-law relation with pressure. The measured averaged soot volume fraction was proportional to pn. Pressure exponent n was 1.34–2.17, 1.41–2.12 and 1.56–2.20 at equivalent ratios of 6.2, 8.5 and 11.4, respectively.

Classification of iron oxide aerosols by a single particle soot photometer using supervised machine learning

Abstract. Single particle soot photometers (SP2) use laser-induced incandescence to detect aerosols on a single particle basis. SP2s that have been modified to provide greater spectral contrast between their narrow and broad-band incandescent detectors have previously been used to characterize both refractory black carbon (rBC) and light-absorbing metallic aerosols, including iron oxides (FeOx). However, single particles cannot be unambiguously identified from their incandescent peak height (a function of particle mass) and color ratio (a measure of blackbody temperature) alone. Machine learning offers a promising approach for improving the classification of these aerosols. Here we explore the advantages and limitations of classifying single particle signals obtained with a modified SP2 using a supervised machine learning algorithm. Laboratory samples of different aerosols that incandesce in the SP2 (fullerene soot, mineral dust, volcanic ash, coal fly ash, Fe2O3, and Fe3O4) were used to train a random forest algorithm. The trained algorithm was then applied to test data sets of laboratory samples and atmospheric aerosols. This method provides a systematic approach for classifying incandescent aerosols by providing a score, or conditional probability, that a particle is likely to belong to a particular aerosol class (rBC, FeOx, etc.) given its observed single particle features. We consider two alternative approaches for identifying aerosols in mixed populations based on their single particle SP2 response: one with specific class labels for each species sampled, and one with three broader classes (rBC, anthropogenic FeOx, and dust-like) for particles with similar SP2 responses. Predictions of the most likely particle class (the one with the highest mean probability) based on applying the trained random forest algorithm to the single particle features for test data sets comprising examples of each class are compared with the true class for those particles to estimate generalization performance. While the specific class approach performed well for rBC and Fe3O4 (≥99 % of these aerosols are correctly identified), its classification of other aerosol types is significantly worse (only 47 %–66 % of other particles are correctly identified). Using the broader class approach, we find a classification accuracy of 99 % for FeOx samples measured in the laboratory. The method allows for classification of FeOx as anthropogenic or dust-like for aerosols with effective spherical diameters from 170 to >1200 nm. The misidentification of both dust-like aerosols and rBC as anthropogenic FeOx is small, with <3 % of the dust-like aerosols and <0.1 % of rBC misidentified as FeOx for the broader class case. When applying this method to atmospheric observations taken in Boulder, CO, a clear mode consistent with FeOx was observed, distinct from dust-like aerosols.

Investigating temporal variation in the apparent volume fraction measured by time-resolved laser-induced incandescence

In many time-resolved laser-induced incandescence (TiRe-LII) experiments, it is common practice to relate the intensity emitted by laser-heated nanoparticles to the detected LII signal through a factor (here called the intensity scaling factor, ISF) that includes the particle volume fraction and other parameters that may not be the focus of the analysis. While, in the absence of evaporation or sublimation, the ISF should theoretically remain constant with respect to time, recent multi-wavelength measurements show that, in reality, it may vary with both time and fluence. We consider four candidate effects that contribute to this behavior: particle annealing; polydispersity in the nanoparticle-size distribution; background luminosity due to emission from nanoparticles in the line-of-sight before and behind the probe volume; and the temporal resolution of the detector. We demonstrate these effects by simulating TiRe-LII data for in-flame soot at atmospheric pressure, using new simplified heat transfer and annealing models. Analysis of experimental signals collected from flame-generated soot at atmospheric pressure reveals trends in the ISF similar to those predicted by simulations. These temporal variations provide important insights that can help to diagnose problems in TiRe-LII experiments and improve TiRe-LII models.

Laser-induced incandescence versus photo-acoustics: implications for qualitative soot size diagnostics

Laser-induced incandescence at high-repetition rates can in principle be used to resolve the temporal evolution of soot processes. The intrusive character of this technique, however, requires due care of historical effects associated with multiple exposures of individual soot particles to laser light. On the other hand, repetitive heating and cooling opens up an independent, acoustic detection channel. We illustrate a photo-acoustic soot volume fraction measurement, and show that the comparison to simultaneously recorded laser-induced incandescence provides qualitative information on soot growth. Experiments are performed on a propane-fueled, co-flow stabilized diffusion flame, and signals are collected at varying heights above the burner deck. Results show a clear correlation between the laser-induced incandescence and photo-acoustic signals; small deviations are interpreted as a qualitative indicator for the particle size.

Detector calibration and measurement issues in multi-color time-resolved laser-induced incandescence

Time-resolved laser-induced incandescence is used to infer the size distribution of gas-borne nanoparticles from time-resolved pyrometric measurements of the particle temperature after pulsed laser heating. The method is highly sensitive to aspects of the measurement strategy that are often not considered by practitioners, which often lead to discrepancies between measurements carried out under nominally identical conditions. This paper therefore presents a well-documented calibration procedure for LII systems and quantifies the uncertainty in pyrometric temperatures introduced by this procedure. Calibration steps include corrections for: (1) signal baseline, (2) variable transmission through optical components, and (3) detector characteristics (i.e., gain and spectral sensitivity). Candidate light sources are assessed for their suitability as a calibration reference and the uncertainty in calculated calibration factors is determined. The error analysis is demonstrated using LII measurements made on a sooting laminar diffusion flame. We present results for temperature traces of laser-heated particles determined using two- and multi-color detection techniques and discuss the temperature differences for various combinations of spectral detection channels. We also summarize measurement artifacts that could bias the LII signal processing and present strategies for error identification and prevention.

Can soot primary particle size distributions be determined using laser-induced incandescence?

Soot from combustion processes often takes the form of fractal-like aggregates, assembled of primary particles, both of which obey polydisperse size distributions. In this work, the possibility of determining the primary particle size distribution through time-resolved laser-induced incandescence (TiRe-LII) under the influence of thermal shielding of polydispersely distributed aggregates is critically investigated for two typical measurement situations: in-flame measurements at high temperature and a soot-laden aerosol at room temperature. The uncertainty attached to the quantities is evaluated through Bayesian inference. We show how different kinds of prior knowledge concerning the aggregation state of the aerosol affect the uncertainties of the recovered size distribution parameters of the primary particles. To obtain reliable estimates for the primary particle size distribution parameters, specific information about the aggregate size distribution is required. This is especially the case for cold bath gases, where thermal shielding has a large effect. Furthermore, it is crucial to use the full duration of the usable LII signal trace to recover the width of the size distribution with small uncertainties. The uncertainty attached to TiRe-LII inferred primary particle size parameters becomes considerably larger when additional model parameters are considered.

Investigation of Soot Formation in a Novel Diesel Fuel Burner

In the present work, a novel burner capable of complete pre-vaporization and stationary combustion of diesel fuel in a laminar diffusion flame has been developed to investigate the effect of the chemical composition of diesel fuel on soot formation. For the characterization of soot formation during diesel combustion we performed a comprehensive morphological characterization of the soot and determined its concentration by coupling elastic light scattering (ELS) and laser-induced incandescence (LII) measurements. With ELS, radii of gyration of aggregates were measured within a point-wise measurement volume, LII was employed in an imaging approach for a 2D-analysis of the soot volume fraction. We carried out LII and ELS measurements at different positions in the flame for two different fuel types, revealing the effects of small modifications of the fuel composition on soot emission during diesel combustion.

Laser-induced incandescence for soot measurements in an aero-engine combustor at pressures up to 20 bar

Soot is one of the most discussed pollutants in ground and air traffic. Moreover, its effect as source of intense radiation is significant as soon as locally rich mixtures occur, especially at in-creased pressure. This motivates the need to better understand soot formation and oxidation in turbulent, pressurised environment in order to prevent its emission as much as possible. A detailed understanding of the underlying processes can be gained when correlating sophisticated CFD modelling with well-defined validation experiments at technical conditions. LII has proven to be a valuable diagnostic to quantitatively monitor soot distributions inside combustion processes. However, application to pressurized gas turbine combustors has rarely been published for several reasons. Here, we present trends for soot distributions inside at technical combustor operated between 4 and 20 bar at realistic geometries and flow rates. Considerations on tackling typical challenges at technical conditions are presented. The resulting time-averaged soot distributions serve to determine positions of soot formation and oxidation as well as quantification of soot concentrations under the highly challenging technical conditions of the study. In general, soot concentrations were found to be relatively low. In combination with data derived independently from the present work, involving the application of other diagnostics (OH and kerosene distributions as well as temperatures), a good validation data set is available to support soot modellers.