Toluene Flame Research Articles

Soot modeling of oxygen-depleted and highly sooty turbulent buoyant flames using the In Situ Adaptive Tabulation (ISAT) method

In this paper, a newly developed LSP-based soot (LSPTwoEq) modeling is systematically assessed in the Large Eddy Simulation (LES) of various turbulent buoyant flames against a previously developed LSP-based soot (LSPOneEq) model. Two turbulence-soot interaction (TSI) closure schemes are formulated based on the Eddy Dissipation Concept (EDC). Accordingly, two soot modeling frameworks consisting of the mentioned soot and their corresponding TSI models are applied in the simulations. An in situ Adaptive Tabulation (ISAT) implementation is also proposed to speed up the simulation of the TSI model formulated for the LSPTwoEq model. The results indicate that the proposed soot modeling framework is significantly more accurate for ethylene flames in reduced oxygen concentrations and a highly sooty toluene flame. The accuracy of both frameworks is comparable for the ethylene flame with an air co-flow. The speed-up gained by using the ISAT scheme is found to be a factor of four for the ethylene flame with an air co-flow and the toluene flame. It is larger than nine for the ethylene flames with reduced oxygen co-flow.

Kinetics of C5H4 isomer + H reactions and incorporation of C5H (x = 3 – 5) chemistry into a detailed chemical kinetic model

Abstract Although C5H4 isomers are detected in flames, they are not thoroughly incorporated into detailed chemical kinetics models (DCKMs). Here we use RRKM/ME modelling to simulate C5H4 + H reactions on a C5H5 potential energy surface. Kinetic studies indicate that C3H3 + C2H2 is the main fate but fall-off from the initial adduct isomer back to C5H4 + H cannot be ignored at relevant combustion temperatures of 900 to 2000 K. Calculated rate coefficient expressions were incorporated into a DCKM for a toluene flame, along with updates to other relevant reactions from the recent literature, particularly the open-chain 1-vinylpropargyl radical, l-C5H5. Obtained species mole fractions were found to be in good agreement with published experimental data for a low-pressure toluene flame, with a significant improvement in predicted concentration of the cyclopentadienyl radical. The presented DCKM will allow for further reactions of C5Hx species such as 1-vinylpropargyl to be included in combustion simulations.

Assessing the impact of multicomponent diffusion in direct numerical simulations of premixed, high-Karlovitz, turbulent flames

Implementing multicomponent diffusion models in numerical combustion studies is computationally expensive; to reduce cost, numerical simulations commonly use mixture-averaged diffusion treatments or simpler models. However, the accuracy and appropriateness of mixture-averaged diffusion has not been verified for three-dimensional, turbulent, premixed flames. In this study we evaluated the role of multicomponent mass diffusion in premixed, three-dimensional high Karlovitz-number hydrogen, n-heptane, and toluene flames, representing a range of fuel Lewis numbers. We also studied a premixed, unstable two-dimensional hydrogen flame due to the importance of diffusion effects in such cases. Our comparison of diffusion flux vectors revealed differences of 10–20% on average between the mixture-averaged and multicomponent diffusion models, and greater than 40% in regions of high flame curvature. Overall, however, the mixture-averaged model produces small differences in diffusion flux compared with global turbulent flame statistics. To evaluate the impact of these differences between the two models, we compared normalized turbulent flame speeds and conditional means of species mass fraction and source term. We found differences of 5–20% in the mean normalized turbulent flame speeds, which seem to correspond to differences of 5–10% in the peak fuel source terms. Our results motivate further study into whether the mixture-averaged diffusion model is always appropriate for DNS of premixed turbulent flames.

Effects of pressure on soot formation in laminar coflow methane/air diffusion flames doped with n-heptane and toluene between 2 and 8 atm

There is currently a lack of adequate understanding of soot formation in flames fueled with liquid hydrocarbons at elevated pressures. In this study, laminar coflow n-heptane and toluene doped CH4/air diffusion flames were numerically investigated under a constant carbon mass flow rate at pressures between 2 and 8 atm to understand how pressure affects the sooting propensity of these two main components of surrogate fuels mimicking gasoline. Numerical simulations were performed using a detailed reaction mechanism containing 175 species and 1175 reactions and a sectional soot model. Soot inception is modeled by collisions among pyrene, BAPYR and BGHIF. Soot surface growth and oxidation are modeled using the hydrogen abstraction acetylene addition (HACA) mechanism as well as PAH surface condensation. The predicted sensitivity of soot production to pressure is in better agreement with the measurements of Daca and Gülder (2017) when the soot aging effect is considered in HACA surface growth. The predicted soot concentrations are in overall good agreement with measurements. Propargyl recombination and propargyl reaction with propyne are important pathways for the formation of benzene. In methane+toluene flames, attack of toluene by H radical is an effective benzene formation pathway low in the flame, but the relative importance of benzene formation from toluene is reduced with increasing pressure. Although all the soot formation processes are enhanced with increasing pressure, PAH condensation is enhanced the most, followed by HACA and inception. At 6 and 8 atm, PAH condensation becomes comparable to HACA. The pressure dependence of the sooting propensity follows the order of methane+toluene < methane+n-heptane < methane, consistent with measurements. This result can be explained by the pressure dependence of benzene formation pathways, the kinetic effect of pressure, and the scrubbing effect of soot production on the gas-phase species involved in soot formation.

Soot size distribution in lightly sooting premixed flames of benzene and toluene

The evolution of particle size distribution function (PSDF) of soot in premixed flames of benzene and toluene was studied on a burner stabilized stagnation (BSS) flame platform. The cold gas velocities were changed to hold the maximum flame temperatures of different flames approximately constant. The PSDFs of all the test flames exhibited a bimodal distribution, i.e., a small-size nucleation mode and a large-size accumulation mode. It was observed that soot nucleation and particle growth in the benzene flame were stronger than those in the toluene flame at short residence times. At longer residence times, the PSDFs of the two flames were similar, and the toluene flame showed a larger particle size distribution range and a higher particle volume fraction than the benzene flame.

Estimating the internal and surface oxidation of soot agglomerates

Oxidation of soot takes place inside and on the surface of its constituent primary particles at a rate that depends on temperature, T, and O2 concentration. Even though accurate oxidation kinetics are essential in both industrial uses and environmental impact of soot, they are often derived neglecting internal particle oxidation and the structure of such soot agglomerates. Here, the detailed evolution of the fractal-like agglomerate soot mass, m, and mobility diameter, dm, during both internal and surface oxidation is determined by a moving sectional model. The model predictions are in excellent agreement with oxidation data of mature ethylene soot dm for T = 900–1200 K. The oxidation mode index, a, given by the ratio of the characteristic O2 reaction and diffusion times is used to quantify the contributions of internal and surface oxidation of soot. At low Τ (e.g., < 1100 K), O2 diffuses into the primary particles and reacts with bulk soot, hardly altering the dm and yielding a > 3. As T increases, surface oxidation becomes dominant, decreasing both dm and a. The common assumption that soot agglomerates are spheres underestimates their dm up to 50 % during oxidation. Coupling this detailed moving sectional model with soot mobility size distributions can yield realistic soot oxidation rates. Accounting for soot morphology and internal oxidation shows that the classic NSC rate increasingly underestimates (by 3–7 times) the oxidation rate of soot (from ethylene and toluene flames) with decreasing temperature (900–1800 K) and/or oxygen concentration (0.2–21 vol %).

Toluene pyrolysis in an electric ARC: Products analysis

Toluene pyrolysis in a submerged carbon arc produced at least 72 different molecular species as detected by gas-chromatography coupled with mass spectrometry (GC-MS). The most abundant products found were bibenzyl (1,2-diphenylethane), naphthalene and biphenylene. Furthermore, also diethynylbenzene isomers, fluorene, diphenymethane, indene and biphenyl were produced in appreciable amounts. The formation mechanisms of these and other minor products are discussed mainly in the light of the benzyl radical and its decay into other products. Among polyynes, only 1,3,5,7-octatetrayne was produced above 1% relative yield. The results are discussed in comparison to the products detected in toluene pyrolysis under other experimental conditions, such as shock tube pyrolysis and toluene flames. Furthermore, a comparison with the products obtained from the benzene pyrolysis is reported.

Experimental investigation of soot evolution in a turbulent non-premixed prevaporized toluene flame

The formation, growth, and oxidation of soot in turbulent prevaporized toluene diffusion flames stabilized on a jet-in-hot-coflow (JHC) burner are investigated in this study. Flame structure, local gas temperature as well as local soot volume fraction and primary soot particle diameter, are simultaneously detected by means of OH planar laser-induced fluorescence (PLIF), non-linear excitation regime two-line atomic fluorescence (nTLAF) of indium, and time-resolved (TiRe) laser-induced incandescence (LII), respectively. The collected data sets were used to generate joint statistics of soot properties and flame characteristics and provided new insights into the interaction of the OH layer and soot in turbulent flames. The interaction of OH and soot as a driving mechanism for soot oxidation is of particular interest as it has been proven to be challenging to model. Statistics of soot volume fraction and primary particle size in the OH layer are employed to gain deeper insights into the soot oxidation process. Mean soot volume fraction and primary soot particle size conditioned on temperature and OH signal intensity indicate that, due to differential diffusion of soot with respect to the chemical species, high soot volume fraction and primary soot particle diameter of up to 50 nm are present at low temperatures and low OH concentration. In the soot oxidation region, statistical analysis of the soot parameters disclose that clusters of high soot volume fraction mostly consist of large primary particles. Observations from instantaneous images and the presence of large primary particles inside the OH layer suggest that the oxidation is not sufficiently fast to burn the soot completely.

Effect of Toluene Addition on the PAH Formation in Laminar Coflow Diffusion Flames of n-Heptane and Isooctane

Characterization of soot formation is becoming more important for gasoline surrogate fuels, requiring a deeper understanding of the effect of toluene ratio on PAHs formation. In this work, the different size PAHs distribution in laminar diffusion flames was measured by PLIF technique, and the chemiluminescences of OH and CH radicals were recorded by ICCD coupled with band-pass filters. The effect of toluene addition to n-heptane and isooctane on the flame and PAHs formation was comparatively studied. Then, the chemical kinetic of PAHs was analyzed using the CHEMKIN Diffusion Flame model. The experimental results showed that the cool flame area ranks as n-heptane > isooctane > toluene may due to the NTC action. The OH intensity and flame lift-off height show a monotonous increasing trend with the toluene ratio. At the same toluene ratio, the peak OH intensity and flame lift-off height of n-heptane/toluene is lower than that of isooctane/toluene. The CH intensity in n-heptane, isooctane, and toluene flames shows completely different distribution characteristics. As the toluene ratio increases, the 320 nm-LIF in n-heptane and isooctane flames shows a weakening monotonous increasing trend with different inflection points. The 360/400/450 nm-LIF in n-heptane and isooctane flames show a nonmonotonic trend with different peak points. The peak point is 50% toluene ratio in n-heptane/toluene flames and 40% in isooctane/toluene flames, and it corresponds exactly to the smoke point of the flame. The kinetic analysis showed that the benzyl has a significant effect on the formation of A2–A4 through the generation of C10H9, C9H7, and C14H12. A1 trend is dominated by C6H5CH3 + H = A1 + CH3 and A1– + CH4 → A1 + CH3. The trends of A2, A3 and A4 are mainly dominated by the reactions between their own dehydrogenation groups with H2.

Experimental and kinetic modeling investigation of rich premixed toluene flames doped with n-butanol.

n-Butanol is a promising renewable biofuel and has a lot of advantages as a gasoline additive compared with ethanol. Though the combustion of pure n-butanol has been extensively investigated, the chemical structures of large hydrocarbons doped with n-butanol, especially for aromatic fuels, are still insufficiently understood. In this work, rich premixed toluene/n-butanol/oxygen/argon flames were investigated at 30 Torr with synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS). The blending ratio of n-butanol was varied from 0 to 50%, while the equivalence ratio was maintained at a quite rich value (1.75) for the purpose of studying the influence of n-butanol on the aromatic growth process. Flame species including radicals, reactive molecules, isomers and polycyclic aromatic hydrocarbons (PAHs) were identified and their mole fraction profiles were measured. A kinetic model of toluene/n-butanol combustion was developed from our recently reported toluene and n-butanol models. It is observed that the production of most toluene decomposition products and larger aromatics was suppressed as the blending ratio of n-butanol increases. Meanwhile, the addition of n-butanol generally enhanced the formation of most observed C2-C4 hydrocarbons and C1-C4 oxygenated species. The rate of production (ROP) analysis and experimental observations both indicate that the interaction between toluene and n-butanol in their decomposition processes mainly occurs at the formation of small intermediates, e.g. acetylene and methyl. In particular, the interaction between toluene and n-butanol in methyl formation influences the formation of large monocyclic aromatics such as ethylbenzene, styrene and phenylacetylene, making their maximum mole fractions decay slowly upon increasing the blending ratio of n-butanol compared with toluene and benzyl. The increase of the blending ratio of n-butanol reduces the formation of key PAH precursors such as benzyl, fulvenallenyl, benzene, phenyl and propargyl, which leads to a remarkable reduction in the formation of PAHs.

Physicochemical properties of soot generated from toluene diffusion flames: Effects of fuel flow rate

Aromatic hydrocarbons are commonly found in fossil-derived transportation fuels, and their combustion in engines produce most of the observed soot particles. Toluene is an important component of gasoline (about 6wt%), diesel (1–2wt%), and jet fuels (1–2wt%), and forms a part of their surrogates. This paper reports the nanostructures and chemical constituents of soot, formed in toluene diffusion flames at different fuel flow rates. High resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) are employed to study the physical properties of soot, while Fourier transform infrared spectroscopy (FTIR), electron energy loss spectroscopy (EELS), and elemental analysis are used to investigate its chemical properties. With increasing fuel flow rate, HRTEM and XRD analyses showed that the lateral size of aromatic layers in soot reduced, while the FTIR analysis revealed that the concentration of aliphatic and oxygenated groups decreased, and that of aromatic group increased. The elemental analysis showed that soot from lower fuel flow rates had more hydrogen and oxygen content than those from higher flow rates. The experimental observations indicate that both physical and chemical characteristics of soot derived from toluene flame are dependent on the fuel flow rate used for its production.

Laminar flame propagation and nonpremixed stagnation ignition of toluene and xylenes

Using the constant-pressure expanding spherical flame and nonpremixed stagnation pool experiments, the laminar flame speeds and nonpremixed ignition temperatures of toluene and the xylenes were experimentally determined at atmospheric and elevated pressures. The experimental situations were then computationally simulated using the kinetic models of Metcalfe et al. and of Narayanaswamy et al., and interrogated through sensitivity, reaction path and chemical explosive mode analyses. For the laminar flame speed study, both present and literature experimental results show that the toluene flame propagates faster than the xylene flames at all pressures, while the computation analyses show that this is primarily due to the fuel chemistry, with the attendant controlling reaction paths identified. For the nonpremixed stagnation ignition, experimental results show that toluene has lower ignition temperatures than the xylenes, and numerical analysis identifies that it is mainly due to the higher fuel diffusivity of toluene. Furthermore, the ignition temperatures of o-xylene are lower than those of m- and p-xylenes, and are suggested to be due to the formation of dimethylphenyl radicals with isolated H abstraction sites, which react with O2 for further chain branching. The computed ignition temperatures for all fuels are consistently higher than the experimental values, and chemical explosive mode analysis shows that the C1/H2 chemistry plays the dominant role in the ignition.

Structure of an n-heptane/toluene flame: Molecular beam mass spectrometry and computer simulation investigations

Molecular beam mass spectrometry was used to measure mole fraction profiles of the reactants, major reaction products and intermediates, including precursors of polycyclic aromatic hydrocarbons, in a premixed fuel-rich (equivalence ratio of 1.75) n-heptane/toluene/O2/Ar flame stabilized on a flat burner at atmospheric pressure. The ratio of the liquid volumes in the n-heptane/toluene mixture was 7: 3. The chemical structure of the flame was modeled using a detailed mechanism of chemical reactions tested against experimental data of other authors on n-heptane/toluene flames and comprising the reactions of formation of polycyclic aromatic hydrocarbons. The mechanism was extended with cross-reactions involving derivatives of n-heptane and toluene. Overall, the new experimental data are in satisfactory agreement with the numerical simulation results; however, there are differences between the measured and calculated mole fraction profiles of some species. Analysis shows that in the n-heptane/toluene flame, the main reactions leading to the formation of low-aromatic compounds (benzene and phenyl) are reactions typical of the pure toluene flame.

PAH structure analysis of soot in a non-premixed flame using high-resolution transmission electron microscopy and optical band gap analysis

Soot particles formed in a system of non-premixed liquid fuel flames supported on a wick-fed, smoke point test burner (ASTM D1322-08) were characterized by in-situ visible light extinction and thermophoretically-sampled high-resolution transmission electron microscopy measurements, HRTEM. The fuels studied were heptane, toluene and their iso-volumetric mixture (H50T50), given their relevance as surrogate fuels. Extinction measurements were used to calculate the soot volume fraction, Fv, and determine the optical band gap (OBG) as a function of flame position. The OBG was derived from the near-edge absorption feature using Tauc/Davis-Mott analysis. A direct band gap (r = 0.5) was selected for this analysis assuming that the electronic properties of soot are dominated by the molecular structure of the PAHs. For the HRTEM analysis, soot samples were collected at different locations in the flame using thermophoretic sampling and a fast-insertion technique. The images were then analyzed using a ‘lattice-fringe’ algorithm, to determine important parameters such as the fringe length. Polycyclic aromatic hydrocarbon (PAH) sizes were estimated from conjugation lengths obtained from OBG measurements and fringe lengths from HRTEM measurements. Across all studied flames, the peak Fv ranged from 3.4 ppm in the heptane flame to 17.6 ppm in the toluene flame. Despite this wide range, the average OBG across the different flames only varied from 2.05 eV in the H50T50 to 2.10 eV in the toluene flames, which is consistent with molecule lengths of between 0.96 nm and 0.99 nm. Lattice fringe analysis yielded slightly lower average fringe lengths between 0.91 and 0.99 nm throughout the different flames. Results of in-situ and ex-situ characterization of soot suggests that flames of different fuel nature and sooting stage undergo the transition from chemical to physical growth at a similar size, about the size of circumpyrene.

HRTEM evaluation of soot particles produced by the non-premixed combustion of liquid fuels

The morphology and nanostructure of soot particles as a function of fuel type in a laminar diffusion flame were studied. The fuels considered were heptane, toluene, the volumetric mixture 50% heptane – 50% toluene and a commercial gasoline. The structural features of soot sampled in the flame were inferred using HRTEM. An image analysis algorithm was developed to calculate the fringe length, tortuosity and inter-fringe spacing from HRTEM images. For the first time, the performance of the algorithm is tested against artificially generated TEM images with known geometries.Heptane flame produced the smaller primary particles followed by the heptane/toluene mixture and gasoline, toluene flame formed the largest particles. Toluene soot exhibits the longer and less curved fringes and more stacked layers. Heptane soot develops a similar degree of order as the aromatic flames but stronger oxidation at the tip reduces the fringe length and increases the tortuousity. There is no significant difference between the nanostructure of heptane/toluene mixture and the gasoline. The main differences in the nanostructure all the soot sampled was the degree of order of the PAHs within each particle. The fringe length was found to be similar for all the fuels, around the size of circumpyrene (C42 H16).

Fuel-Rich Premixed n-Heptane/Toluene Flame: a Molecular Beam Mass Spectrometry and Chemical Kinetic Study

&lt;p&gt;The mole fraction profiles of major flame species and intermediates including PAH precursors are measured in an atmospheric premixed burner-stabilized fuel-rich (&lt;em&gt;φ&lt;/em&gt; = 1.75) &lt;em&gt;n&lt;/em&gt;-heptane/toluene/O&lt;sub&gt;2&lt;/sub&gt;/Ar flame (&lt;em&gt;n&lt;/em&gt;-heptane/toluene ratio is 7:3 by liquid volume). These data are simulated with a detailed, extensively validated chemical kinetic reaction mechanism for combustion of &lt;em&gt;n&lt;/em&gt;-heptane/toluene mixture, involving the reactions of PAH formation. The mechanism is extended with cross reactions for &lt;em&gt;n&lt;/em&gt;-heptane and toluene derivatives. A satisfactory agreement between the new experimental data on the structure of &lt;em&gt;n&lt;/em&gt;-heptane/toluene flame and the numerical simulations is observed. The mechanism reported can be successfully used in the models of practical fuel surrogates for reproducing the formation of soot precursors. The analysis of the reaction pathways shows that in the flame of the &lt;em&gt;n&lt;/em&gt;-heptane/toluene blend (7:3 liquid volume ratio) the reactions dominant for the formation of the first aromatic ring (benzene and phenyl) are as those typical for pure toluene flames. The discrepancies between the measured and calculated species mole fractions are detected as well. The steps for the mechanism improvements are determined on the basis of the sensitivity analysis performed. To our knowledge, the measurements of mole fraction profiles of PAH and intermediates reported here, are the first of its kind and represent an unique data set extremely important for validation of chemical kinetic mechanisms for combustion of practical fuels.&lt;/p&gt;&lt;p&gt; &lt;/p&gt;

Influence of Combustion Conditions on Hydrophilic Properties and Microstructure of Flame Soot

Previous studies suggest that structure and reactivity of soot depend on combustion conditions like the fuel/oxygen ratio and nature of fuels. However, the essence of how combustion conditions affect physical and chemical properties of soot is still an open question. In this study, soot samples were prepared by combusting toluene, n-hexane, and decane under controlled conditions, and their hydrophilic properties, morphology, microstructure, content of volatile organic compounds, and functional groups were characterized. The hydrophilicity of n-hexane and decane flame soot increased with decreasing fuel/oxygen ratio, while it almost did not change for toluene flame soot. Fuel/oxygen ratio had little effect on the morphology of aggregates and the graphite crystallite size. The primary particle size and the content of volatile organic compounds on soot decreased with decreasing fuel/oxygen ratio. Less hydrophobic groups (C-H) and more hydrophilic groups (C═O) were observed on lean n-hexane and decane flame soot than that on the corresponding rich flame soot. Volatile organic compounds had little effect on the hydrophilicity of soot while the hydrophilicity correlated linearly with the ratio of C═O content to C-H content. The hydrophilic functional groups were found to be mainly located at graphene layer edges and on surface graphene layers in soot.

Soot predictions in premixed and non-premixed laminar flames using a sectional approach for PAHs and soot

A new soot model is presented, which has been developed for CFD applications, combining accuracy and efficiency. While the chemical reactions of small gas phase species are captured by a detailed chemical kinetic mechanism, polycyclic aromatic hydrocarbons (PAHs) and soot particles are represented by sectional approaches. The latter account for important mechanisms such as the formation of sections, their oxidation, the condensation of acetylene, and the collisions between sections. The model has been designed to predict soot for a variety of fuels with good accuracy at relatively low computational cost. Universal model parameters are applied, which require no tuning in dependence of test case or fuel. Soot predictions of ethylene, propylene, kerosene surrogate, and toluene flames are presented, which show good agreement with the experimental data. Furthermore, the importance of the correct choice for thermodynamic data of PAHs and soot is highlighted and the impact of heat radiation is discussed.

Investigation on chemical structures of premixed toluene flames at low pressure

Chemical structures of premixed toluene/O2/Ar flames with five equivalence ratios (0.75, 1.00, 1.25, 1.50, and 1.75) were studied at low pressure (4.0kPa). Synchrotron vacuum ultraviolet photoionization mass spectrometry was used for the isomeric detection of flame species and the measurements of their mole fractions. The global trends of the flame temperature and mole fractions of detected species with varying equivalence ratio were observed and discussed, drawing complete pictures for the chemical structures of premixed toluene flames. Based on the experimental results, a kinetic model was developed from previous models and updated with many recently studied reactions related to toluene decomposition and polycyclic aromatic hydrocarbons (PAHs) formation. The model was validated by simulating the measured mole fractions of flame species, showing good agreement in reproducing the maximum mole fractions of most observed species and their global trends with varying equivalence ratio. The rate of production analysis reveals the major formation and consumption channels of some key intermediates involved in toluene decomposition in the ϕ=0.75 and 1.75 flames, and the major formation channels of some large aromatics and typical PAHs in the ϕ=1.75 flame, indicating the importance of benzyl in toluene flames.

Experimental and Kinetic Modeling Evidences of a C7H6 Pathway in a Rich Toluene Flame

The structure of a laminar, premixed, and one-dimensional toluene-oxygen-argon (9.9 mol % C(7)H(8), 44.5 mol % O(2), and 45.6 mol % Ar) flame, with an equivalence ratio of 2 and burning at 36 Torr was analyzed by gas chromatography and molecular beam mass spectrometry (MBMS). Mole fraction profiles of 25 chemical species including permanent gases of combustion and first polycyclic aromatic hydrocarbons as naphthalene, methylnaphthalene isomers, biphenyl, and phenanthrene have been measured. A kinetic model based on recent literature data has been elaborated to compare with measurements. As suggested by recent theoretical studies, benzyl radical (C(7)H(7)) dissociation into fulvenallene (C(7)H(6)) + H and the reaction between C(7)H(6) and H giving cyclopentadienyl radical and acetylene have been included into the model. A comparison between experimental and predicted flame structures have allowed us to validate the kinetic model for rich toluene combustion. Moreover, MBMS measurements of mole fraction profiles corresponding to m/z ratios of C(7)H(7) and C(7)H(6) have permitted a specific validation of the theoretically postulated C(7)H(6) pathway in toluene flames.