Major Species Concentrations Research Articles

Application of a Decoupling Methodology for Development of Skeletal Oxidation Mechanisms for Heavy n-Alkanes from n-Octane to n-Hexadecane

A series of skeletal mechanisms was developed based on a decoupling methodology to describe the oxidation of n-alkanes from n-octane to n-hexadecane. In the decoupling methodology, a fuel oxidation mechanism is divided into two parts: one is an extremely simplified model for species with a carbon atom number larger than two to simulate the ignition characteristics of n-alkane; the other is a detailed mechanism for H2/CO/C1 to predict the concentrations of small molecules, laminar flame speed, and extinction strain rate. The new skeletal mechanism includes only 36 species and 128 reactions for each n-alkane from n-octane to n-hexadecane. The mechanism was extensively validated against the experimental data in a shock tube, jet-stirred reactor, flow reactor, counterflow flame, and premixed laminar flame. Good agreements on ignition delay, the concentrations of major species, laminar flame speed, and extinction strain rate between the predictions and measurements were obtained over wide ranges of temperature, pressure, and equivalence ratio, which demonstrates the capability of the decoupling methodology to build skeletal oxidation mechanisms for n-alkanes. Due to the compact size of the new skeletal mechanism, it can be easily integrated into the computational fluid dynamics (CFD) simulation.

Predicted Water Chemistry in the Primary Coolant Circuit of a Supercritical Water Reactor

Among the six types of Generation IV reactors, the supercritical water reactor (SCWR) is the only one that adopts light water as the reactor coolant. Different from the boiling, two-phase coolant in the core of a traditional boiling water reactor (BWR), the coolant in an SCWR would remain in one phase throughout the entire primary coolant circuit (PCC) due to its much higher operating temperature (>374°C) and pressure (>22.1 MPa). For a conventional BWR, the coolant is relatively oxidizing due to the presence of hydrogen peroxide and oxygen, directly or indirectly produced via water radiolysis. This outcome eventually leads to degradation of structural materials, primarily stress corrosion cracking. In an SCWR, the solubility of oxygen in the reactor coolant is extremely high. In the absence of the gas stripping effect in a single-phase coolant, worse degradation phenomena are expected to appear in the structural and core components. To ensure proper designs of the structural components and suitable selection of the materials to meet the requirements of operation safety, it would be of great assistance to the design engineers of an SCWR to be aware of the intrinsic state of water chemistry in the entire PCC. Since SCWRs are still at the stage of conceptual design and no practical data are available, a computer model was developed for determining the water chemistry variation and the corrosion behavior of metallic materials in the PCC of a conceptual SCWR. Radiolysis parameters used for calculating the concentrations of major redox species (i.e., [O2], [H2], and [H2O2]) in the reactor coolant were collected from literature reports. However, the lack of sufficient data necessitated that some were derived by extrapolation. Calculations indicated that the concentrations of the two major oxidizing species (H2O2 and O2) could become extremely high at locations inside or near the core, considerably higher than those in typical BWRs. It was therefore speculated that the structural materials in an SCWR may be exposed to an environment not only at a much higher temperature but also one that is more oxidizing than that in a conventional BWR.

Experimental study of industrial gas turbine flames including quantification of pressure influence on flow field, fuel/air premixing and flame shape

A commercial swirl burner for industrial gas turbine combustors was equipped with an optically accessible combustion chamber and installed in a high-pressure test-rig. Several premixed natural gas/air flames at pressures between 3 and 6bar and thermal powers of up to 1MW were studied by using a variety of measurement techniques. These include particle image velocimetry (PIV) for the investigation of the flow field, one-dimensional laser Raman scattering for the determination of the joint probability density functions of major species concentrations, mixture fraction and temperature, planar laser induced fluorescence (PLIF) of OH for the visualization of the flame front, chemiluminescence measurements of OH* for determining the lift-off height and size of the flame and acoustic recordings. The results give insights into important flame properties like the flow field structure, the premixing quality and the turbulence–flame interaction as well as their dependency on operating parameters like pressure, inflow velocity and equivalence ratio. The 1D Raman measurements yielded information about the gradients and variation of the mixture fraction and the quality of the fuel/air mixing, as well as the reaction progress. The OH PLIF images showed that the flame was located between the inflow of fresh gas and the recirculated combustion products. The flame front structures varied significantly with Reynolds number from wrinkled flame fronts to fragmented and strongly corrugated flame fronts. All results are combined in one database that can be used for the validation of numerical simulations.

Organic and inorganic markers and stable C-, N-isotopic compositions of tropical coastal aerosols from megacity Mumbai: sources of organic aerosols and atmospheric processing

Abstract. To better understand the sources of PM10 samples in Mumbai, India, aerosol chemical composition, i.e., total carbon (TC), organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC), and inorganic ions were studied together with specific markers such as methanesulfonate (MSA), oxalic acid (C2), azelaic acid (C9), and levoglucosan. The results revealed that biofuel/biomass burning and fossil fuel combustion are the major sources of the Mumbai aerosols. Nitrogen-isotopic (δ15N) composition of aerosol total nitrogen, which ranged from 18.1 to 25.4‰, also suggests that biofuel/biomass burning is a predominate source in both the summer and winter seasons. Aerosol mass concentrations of major species increased 3–4 times in winter compared to summer, indicating enhanced emission from these sources in the winter season. Photochemical production tracers, C2 diacid and nssSO42−, do not show diurnal changes. Concentrations of C2 diacid and WSOC show a strong correlation (r2 = 0.95). In addition, WSOC to OC (or TC) ratios remain almost constant for daytime (0.37 ± 0.06 (0.28 ± 0.04)) and nighttime (0.38 ± 0.07 (0.28 ± 0.06)), suggesting that mixing of fresh secondary organic aerosols is not significant and the Mumbai aerosols are photochemically well processed. Concentrations of MSA and C9 diacid present a positive correlation (r2 = 0.75), indicating a marine influence on Mumbai aerosols in addition to local/regional influence. Backward air mass trajectory analyses further suggested that the Mumbai aerosols are largely influenced by long-range continental and regional transport. Stable C-isotopic ratios (δ13C) of TC ranged from −27.0 to −25.4‰, with slightly lower average (−26.5 ± 0.3‰) in summer than in winter (−25.9 ± 0.3‰). Positive correlation between WSOC/TC ratios and δ13C values suggested that the relative increment in 13C of wintertime TC may be caused by prolonged photochemical processing of organic aerosols in this season. This study suggests that in winter, the tropical aerosols are more aged due to longer residence time in the atmosphere than in summer aerosols. However, these conclusions are based on the analysis of a limited number of samples (n=25) and more information on this topic may be needed from other similar coastal sites in future.

Development of a Phenomenological Soot Model Coupled with a Skeletal PAH Mechanism for Practical Engine Simulation

A new chemical mechanism with 12 species and 26 reactions for formation of polycyclic aromatic hydrocarbons (PAHs) was developed and integrated into a skeletal mechanism for oxidation of primary reference fuel (PRF). Coupled with the new skeletal PRF-PAH mechanism, an improved phenomenological soot model was further constructed based on our previous work. By validating against the experimental data on the related PAHs in four premixed laminar flames of n-heptane/iso-octane and three counterflow diffusion flames of n-heptane, it is indicated that the major species concentrations were well reproduced by the model. Moreover, validations of the new soot model show that the soot yield, particle diameter, and number density were predicted with reasonable agreement with the experimental data in a rich n-heptane shock tube over wide temperature and pressure ranges. Compared with the soot model with acetylene as precursor species, the new model agrees better with the measurement, which proves the necessity of incl...

Determination of temperature and concentrations of main components in flames by fitting measured Raman spectra

The procedure of deriving flame temperature and major species concentrations by fitting measured Raman spectra in hydrocarbon flames is described. The approach simplifies the calibration procedure to determine temperature and major species concentrations from the measured Raman spectra. The calculations of the Raman spectra are performed using data online positions and cross sections from the current literature. Utilizing all spectral information for deriving temperature and major species concentrations substantially increases accuracy, while interferences can easily be detected and filtered out of the measured spectrum. Temperatures from the separate Raman spectra of N2, H2O, O2, CO2 and CO are systematically compared with each other over the span of more than 1,700 K. The agreement between them is generally better than 100 K. The developed procedure also allows us to determine the mole fractions of the major species with absolute accuracy of ±10 %.

CFD Simulation of the Fused Silica Synthesis Furnace

The synthesis process of the fused silica glass uses chemical vapor deposition (CVD) method in a furnace. The synthesis process involves complicated physical-chemical phenomena such as turbulence, combustion, radiation, two-phase flow, and so on. A CFD simulation has been carried out for an industrial furnace and process. The simulation result including temperature and major species concentration then is input to CHEMKIN to calculate the radical equilibrium concentration on the fused silica surface. The trend of the simulated fused silica surface temperature is consistent with the measured refraction index showing that the surface temperature is one of the most important parameters influencing the refractive index uniformity of the fused silica product.

Formation of Fine Particulate Matter in a Domestic Pellet-Fired Boiler

This study concentrates on the formation of fine particulate matter (PM) in a domestic pellet-fired boiler and includes a detailed characterization of the combustion process inside the combustion chamber of the boiler. Measurements of local mean gas temperatures, major gas species concentrations, and PM concentrations and size distributions are reported for a representative boiler operating condition. In addition, a number of selected PM samples were also morphologically and chemically characterized. The results revealed that (i) most particles present aerodynamic diameters below 1 μm, regardless of the measurement location, and the mass size distributions peak in the size range of 50–130 nm; (ii) early in the flame, the PM size distributions present a bimodal size distribution, but this attribute vanishes as the final stages of the combustion process are approached; (iii) soot particles are rapidly formed early in the combustion process, but these carbon-rich particles also oxidize rapidly in the near burner region; (iv) the aerodynamic diameter corresponding to the maximum amount of particles increases slightly from the fuel bed until ≈4/5 of the combustion chamber height; (v) for a given measurement location and particle sizes below 1 μm, the PM chemical composition varies marginally among size ranges, indicating that the existing chemical compounds tend to form different size aggregates of similar composition; (vi) the element mass concentration varies according to the measurement location; early in the combustion process, the PM is dominated by carbon, with smaller amounts of O and Si, while in the final stages of the combustion process, the PM composition is dominated by inorganic material; and (vii) large fractions of the alkali metals are present as chlorides in the fine PM, and small fractions of the alkalis are present as sulfates.

Improved Phenomenological Soot Model for Multicomponent Fuel Based on Variations in PAH Characteristics with Fuel Type

Integration of a skeletal polycyclic aromatic hydrocarbon (PAH) model with a toluene reference fuel (TRF) oxidation model was used to develop a skeletal TRF-PAH model. A phenomenological soot model, coupled with the new TRF- PAH model, was modified based on the experimental observation that fuels with different molecular structures produce PAHs and soot in different ways. The new TRF-PAH model was validated against experimental data for the relevant PAHs for the oxidation/pyrolysis of toluene in a jet-stirred reactor, flow reactor, and shock tube. The results show that the PAH model can reproduce the experimental data for the major species concentrations. The predicted benzene concentration in the oxidation of alkanes and aromatic hydrocarbons indicates that the molecular structure of the fuel significantly affects the PAH formation pathway. The improved soot model was validated against measured soot yields from the pyrolysis of toluene, toluene/n-heptane mixtures, and toluene/isooctane mixtures in a shock tube, as well as toluene oxidation. The results show that the predicted soot yields obtained using the new soot model are in reasonable agreement with the experimental data over a wide operating range. Finally, the soot model was used to predict the soot emissions from a diesel engine fueled with TRF20. The results indicate that the TRF-PAH combustion model and the new soot model can reproduce the combustion and emission characteristics well.

An integrated pathway system modeling of Saccharomyces cerevisiae HOG pathway: a Petri net based approach

Biochemical networks comprise many diverse components and interactions between them. It has intracellular signaling, metabolic and gene regulatory pathways which are highly integrated and whose responses are elicited by extracellular actions. Previous modeling techniques mostly consider each pathway independently without focusing on the interrelation of these which actually functions as a single system. In this paper, we propose an approach of modeling an integrated pathway using an event-driven modeling tool, i.e., Petri nets (PNs). PNs have the ability to simulate the dynamics of the system with high levels of accuracy. The integrated set of signaling, regulatory and metabolic reactions involved in Saccharomyces cerevisiae's HOG pathway has been collected from the literature. The kinetic parameter values have been used for transition firings. The dynamics of the system has been simulated and the concentrations of major biological species over time have been observed. The phenotypic characteristics of the integrated system have been investigated under two conditions, viz., under the absence and presence of osmotic pressure. The results have been validated favorably with the existing experimental results. We have also compared our study with the study of idFBA (Lee et al., PLoS Comput Biol 4:e1000-e1086, 2008) and pointed out the differences between both studies. We have simulated and monitored concentrations of multiple biological entities over time and also incorporated feedback inhibition by Ptp2 which has not been included in the idFBA study. We have concluded that our study is the first to the best of our knowledge to model signaling, metabolic and regulatory events in an integrated form through PN model framework. This study is useful in computational simulation of system dynamics for integrated pathways as there are growing evidences that the malfunctioning of the interplay among these pathways is associated with disease.

Experimental study on the influence of the thermal input on the reaction zone under flameless oxidation conditions

The reaction zone of a small-scale laboratory combustor operating under flameless oxidation conditions is examined with the aid of hydroxyl radical chemiluminescence (OH*) imaging and measurements of local mean gas temperatures and local mean major gas species (O2, CO2, CO, unburnt hydrocarbons and NOx) concentrations along the combustor axis, as a function of the fuel (methane) thermal input, which was varied between 7 and 13kW. As the fuel thermal input increases, the reaction zone, as typified by the OH* distribution, enlarges and, simultaneously, moves progressively closer to the combustor exit (exhaust) due to the increase in the central jet momentum, while maintaining constant the excess air level. The excess air values used in the present study were low enough to preserve the flameless combustion regime regardless of the fuel thermal input, with the combustor yielding very low NOx (<6ppm@15% O2) and CO emissions (<14ppm@15% O2) regardless of the fuel thermal input. The low NOx emissions, almost independent of the fuel thermal input, are attributed to the suppression of the thermal mechanism promoted by the flameless oxidation regime. Despite being always low, the CO emissions increase with the fuel thermal input presumably because of the lower residence times associated with the higher burner thermal loads.

Experimental evaluation of the performance of a flameless combustor

The aim of this study was to investigate experimentally the flameless oxidation phenomena. Experiments have been performed in a small-scale combustor fired with methane, and include detailed measurements of local mean temperatures and concentrations of major gas species for four representative combustor operating conditions, and flue-gas measurements for 27 operating conditions to quantify the combustor performance as a function of the excess air coefficient, inlet air velocity, fuel thermal input and preheat temperature of the combustion air. It was demonstrated that for the present combustor it is possible to establish flameless conditions over a wide range of operating conditions. The detailed in-combustor data show that the temperature and the O2 mole fraction fields are relatively uniform, and that the maximum mean temperatures reached throughout the combustion chamber are relatively moderate, below 1500 °C, even under conditions in which the level of preheating of the combustion air is relatively high. The flue-gas data reveal that NOx emissions are always very low regardless of the combustor operating conditions. However, the CO and HC emissions, and thus the combustion efficiency, are strongly affected by the levels of excess air and preheating of the combustion air. It was found that the combustion efficiency correlates reasonably well with the parameter (Tair/Tfuel)×(m˙fuel/m˙air), varying linearly with it if its value is below ≈0.1 and remaining equal to approximately 100% otherwise.

Hetero-/homogeneous combustion of ethane/air mixtures over platinum at pressures up to 14 bar

The hetero-/homogeneous combustion of fuel-lean ethane/air mixtures over platinum was investigated experimentally and numerically at pressures of 1–14bar, equivalence ratios of 0.1–0.5, and surface temperatures ranging from 700 to 1300K. Experiments were carried out in an optically accessible channel-flow reactor and included in situ 1-D Raman measurements of major gas phase species concentrations across the channel boundary layer for determining the catalytic reactivity, and planar laser induced fluorescence (LIF) of the OH radical for assessing homogeneous ignition. Numerical simulations were performed with a 2-D CFD code with detailed hetero-/homogeneous C2 kinetic mechanisms and transport. An appropriately amended heterogeneous reaction scheme has been proposed, which captured the increase of ethane catalytic reactivity with rising pressure. This scheme, when coupled to a gas-phase reaction mechanism, reproduced the combustion processes over the reactor extent whereby both heterogeneous and homogeneous reactions were significant and moreover, provided good agreement to the measured homogeneous ignition locations. The validated hetero-/homogeneous kinetic schemes were suitable for modeling the catalytic combustion of ethane at elevated pressures and temperatures relevant to either microreactors or large-scale gas turbine reactors in power generation systems. It was further shown that the pressure dependence of the ethane catalytic reactivity was substantially stronger compared to that of methane, at temperatures up to 1000K. Implications for high-pressure catalytic combustion of natural gas were finally drawn.

An experimental and numerical investigation of the hetero-/homogeneous combustion of fuel-rich hydrogen/air mixtures over platinum

The hetero-/homogeneous combustion of hydrogen/air mixtures over platinum was investigated experimentally and numerically in a channel-flow configuration at fuel-rich equivalence ratios ranging from 2 to 7, pressures up to 5bar and wall temperatures 760–1200K. Experiments involved in situ one-dimensional Raman measurements of major gas-phase species concentrations over the catalyst boundary layer and planar laser induced fluorescence (LIF) of the OH radical, while simulations included an elliptic 2-D model with detailed heterogeneous and homogeneous reaction mechanisms. The employed reaction schemes reproduced the measured catalytic reactant consumption, the onset of homogeneous ignition, and the post-ignition flame shapes at all examined conditions. Although below a critical pressure, which depended on temperature, the intrinsic gas-phase kinetics of hydrogen dictated lower reactivity for the fuel-rich stoichiometries when compared to fuel-lean ones, homogeneous ignition was still more favorable for the rich stoichiometries due to the lower molecular transport of the deficient oxygen reactant that resulted in modest catalytic reactant consumption over the gaseous induction zone. Above the critical pressure, the intrinsic gaseous hydrogen kinetics yielded higher reactivity for the rich stoichiometries, which resulted in vigorous gaseous combustion at pressures up to 5bar, in contrast to lean stoichiometry studies whereby homogeneous combustion was altogether suppressed above 3bar. Computations at fuel-rich stoichiometries in practical channel geometries indicated that homogeneous combustion was not of concern for reactor thermal management, since the larger than unity Lewis number of the deficient oxygen reactant confined the flames to the core of the channel, away from the solid walls.

고압에서 예혼합 CH4-Air 화염의 축소 반응 메카니즘

에러 최소 연결 방법(SEM-CM) 및 반복적 화학종 제거 민감도를 적용한 반응 메카니즘 감소 방법을 갖고, 고압에서 메탄-공기 예혼합 화염에 대한 축소 반응 메카니즘을 개발하였다. 최대 5% 이내의 에러 조건에서 얻어진 축소 반응 매카니즘은 43개 화학종과 554개 기초반응식으로 구성되어 있다. 고압조건에서 다양한 초기온도, 당량비를 갖는 메탄-공기 화염에 대하여 상세 화학반응 메카니즘과 축소 반응 메카니즘으로부터 얻어진 화염구조는 비교되었고, 결과는 잘 일치하였다. 따라서 개발된 축소 반응 메카니즘은 고압에서 화염속도, 화염온도, 주 화학종 및 부 화학종의 농도 등을 재생할 수 있다.

Comparison of Different Global Combustion Mechanisms Under Hot and Diluted Oxidation Conditions

Moderate and intensive low-oxygen dilution (MILD) combustion is a new combustion technology. It features as combustion under a hot and diluted oxidation condition. The objective of this article is to optimize global mechanisms for predicting the major species concentration of CH4 combustion under MILD condition. For this purpose, six different global combustion mechanisms, including the four-step mechanism of Jones and Lindstedt (1988), the two-step mechanism of Westbrook and Dryer (1981), and several modified versions of them, were investigated. Reference calculations were also conducted with detailed chemical kinetic mechanism GRI-Mech 3.0. The interaction between turbulence and chemistry was modeled by eddy dissipation concept (EDC). All of these global mechanisms are validated first by a fictitious plug flow reactor and then by a non-premixed turbulent jet flame of a H2/CH4 fuel mixture (Dally et al., 2002). The results show that modified the Westbrook and Dryer mechanism (WD4), which includes both CO oxidation rate and H2 oxidation rate modification, shows the best agreement with experiment.

Determination of the biogenic secondary organic aerosol fraction in the boreal forest by NMR spectroscopy

Abstract. The study investigates the sources of fine organic aerosol (OA) in the boreal forest, based on measurements including both filter sampling (PM1) and online methods and carried out during a one-month campaign held in Hyytiälä, Finland, in spring 2007. Two aerosol mass spectrometers (Q-AMS, ToF-AMS) were employed to measure on-line concentrations of major non-refractory aerosol species, while the water extracts of the filter samples were analyzed by nuclear magnetic resonance (NMR) spectroscopy for organic functional group characterization of the polar organic fraction of the aerosol. AMS and NMR spectra were processed separately by non-negative factorization algorithms, in order to apportion the main components underlying the submicrometer organic aerosol composition and depict them in terms of both mass fragmentation patterns and functional group compositions. The NMR results supported the AMS speciation of oxidized organic aerosol (OOA) into two main fractions, which could be generally labelled as more and less oxidized organics. The more oxidized component was characterized by a mass spectrum dominated by the m/z 44 peak, and in parallel by a NMR spectrum showing aromatic and aliphatic backbones highly substituted with oxygenated functional groups (carbonyls/carboxyls and hydroxyls). Such component, contributing on average 50% of the OA mass throughout the observing period, was associated with pollution outbreaks from the Central Europe. The less oxidized component was enhanced in concomitance with air masses originating from the North-to-West sector, in agreement with previous investigations conducted at this site. NMR factor analysis was able to separate two distinct components under the less oxidized fraction of OA. One of these NMR-factors was associated with the formation of terrestrial biogenic secondary organic aerosol (BSOA), based on the comparison with spectral profiles obtained from laboratory experiments of terpenes photo-oxidation. The second NMR factor associated with western air masses was linked to biogenic marine sources, and was enriched in low-molecular weight aliphatic amines. Such findings provide evidence of at least two independent sources originating biogenic organic aerosols in Hyytiälä by oxidation and condensation mechanisms: reactive terpenes emitted by the boreal forest and compounds of marine origin, with the latter relatively more important when predominantly polar air masses reach the site. This study is an example of how spectroscopic techniques, such as proton NMR, can add functional group specificity for certain chemical features (like aromatics) of OA with respect to AMS. They can therefore be profitably exploited to complement aerosol mass spectrometric measurements in organic source apportionment studies.

Synthesis of mesoporous nanocrystalline TiO2 films in a premixed H2/O2/Ar flame

The synthesis of mesoporous nanocrystalline TiO2 films in a premixed (in vol %) 12.9/14.4/72.7 H2/O2/Ar flame doped with 0.1% titanium tetraisopropoxide [Ti(OC3H7)4] was studied. Stabilization of the flame and deposition of TiO2 nanoparticles were carried on the plane of a rotating disk. Spatial distributions of temperature and concentrations of major species in the flame were investigated. The applicability of the employed kinetic reaction scheme and the calculation method to the description of the structure of the investigated flame was tested. It was established that this method can be used to synthesize spherical crystalline nanoparticles of the anatase polymorphic form of TiO2 with an average diameter of 12 nm and a narrow size distribution (σ = 1.45), which can be used in the production of solar cells and gas analyzer sensors.

CFD modelling of oxy-coal combustion in an entrained flow reactor

Oxy-fuel combustion is seen as one of the major options for CO 2 capture for both new and existing coal fired power stations. Coal is burned with a mixture of oxygen and recycled flue gas to obtain a rich CO 2 stream ready for sequestration. Computational fluid dynamics (CFD) tests for coal combustion under different O 2/CO 2 (21–35% vol O 2) atmospheres in an entrained flow reactor (EFR) were carried out using three coals of different volatile matter content. The temperature profiles, burning rates, burnout and concentration of major species, such as O 2, CO 2, CO, were predicted and compared with an air reference case. A decrease in gas temperature and burning rate was observed for 21% O 2/79% CO 2 environment in comparison to the air reference case due to the difference in gas properties between N 2 and CO 2. Experimental coal burnouts obtained in the EFR, were used to test the accuracy of the CFD model. The numerical results showed a decrease in coal burnout when N 2 was replaced by CO 2 for the same oxygen concentration (21%), but an improvement in the O 2/CO 2 atmosphere for an oxygen concentration higher than 30%. The numerical results for oxy-coal combustion were in good agreement with the experimental results.

The structure of premixed and stratified low turbulence flames

Practical combustion systems typically operate in stratified regimes to leverage the advantages of a spatially varying mixture fraction field. Although these benefits are well known in industry, the fundamental physics underpinning these effects are currently an area of active research. In this paper simultaneous Rayleigh–Raman–LIF measurements of temperature and major species concentrations along a line are used to investigate the structure of a weakly turbulent stratified flame. Concurrent cross-planar OH-PLIF enables the extraction of flame orientation relative to the measurement line, as well as flame front curvature. The behavior of major species concentrations with respect to temperature is found to agree well with laminar flames at the local mixture fraction, even in stratified flows. However, measurements of the surface density function, ∣∇ c∣, and scalar dissipation, χ c , suggest that both premixed and stratified flames are spatially thicker at the microscale than corresponding laminar flames.