Flame Speed Measurements Research Articles

Effects of water vapor addition on the laminar burning velocity of oxygen-enriched methane flames

The effects of steam addition on the laminar burning velocity of premixed oxygen-enriched methane flames are investigated at atmospheric pressure. Experiments are carried out with an axisymmetric burner on which laminar conical flames are stabilized. A newly devised steam production system is used to dilute the reactants with water vapor. The oxygen-enrichment ratio in the oxidizer, defined as O 2/(O 2 + N 2) (mol.), is varied from 0.21 (air) to 1.0 (pure oxygen). The equivalence ratio ranges from 0.5 to 1.5 and the steam molar fraction in the reactive mixture is varied from 0 to 0.50. For all compositions examined, the reactive mixture is preheated to a temperature T u = 373 K. Laminar flame speeds are determined with the flame area method using a Schlieren apparatus. The deviations induced by stretch effects due to aerodynamic strain and flame curvature are assessed using Particle Imaging Velocimetry measurements and flame images, and these data are used to estimate the uncertainty of the flame speed measurements. The experiments are completed by numerical simulations conducted with the PREMIX code using different detailed kinetic mechanisms. It is shown that the laminar flame speed of CH 4/O 2/N 2/H 2O ( v) mixtures features a quasi-linear decrease with increasing steam molar fraction, even at high steam dilution rates. Numerical predictions are in good agreement with experimental data for all compositions explored, except for low dilution rates X H 2 O < 0.10 in methane–oxygen mixtures, where the flame speed is slightly underestimated by the calculations. It is also shown that steam addition has a non-negligible chemical impact on the flame speed for methane–air flames, mainly due to water vapor high chaperon efficiency in third-body reactions. This effect is however strongly attenuated when the oxygen concentration is increased in the reactive mixture. For highly oxygen-enriched flames, steam can be considered as an inert diluent.

Effects of diluents on the ignition of premixed H 2/air mixtures

A computational study is performed to investigate the effects of diluents on the ignition of premixed H 2/air mixtures. The ignition processes for fuel lean, stoichiometric, and fuel rich H 2/air mixed with different diluents (He, Ar, N 2, and CO 2) are simulated with detailed chemistry and variable thermodynamic and transport properties. The minimum ignition energies (MIE) for different diluents at different dilution ratios are obtained. It is found that the change of the MIE with the dilution ratio consists of two regimes: in the first regime with a small value of dilution ratio, diluent addition has little effect on the MIE and in the second regime with dilution ratio above a certain value, the MIE increases exponentially with the dilution ratio. The kinetic and radiation effects of dilution are assessed by conducting sensitivity analysis and using the optically thin model, respectively. The thermal and flame-dynamic effects of dilution, characterized by the adiabatic flame temperature and Markstein length, respectively, are also discussed. Moreover, the dilution limits for H 2/air mixtures at different equivalence ratios are obtained. The dilution limits predicted by present ignition calculation are found to agree well with those based on laminar flame speed measurements at micro-gravity conditions. The ranking in terms of the effectiveness on ignition inhibition for stoichiometric H 2/air is shown to be in the order of Ar, N 2, He, and CO 2. The dilution limit is of practical interest since it is a measure of the efficiency of the diluent in fire prevention and suppression.

Measurement of laminar flame speeds and flame stability analysis of tert-butanol–air mixtures at elevated pressures

Laminar flame speeds and Markstein lengths of tert-butanol–air premixed mixtures were measured over a wide range of equivalence ratios at different initial temperatures and pressures by using the spherically propagating flame in a constant volume combustion chamber. Effects of Markstein number, flame thickness and density ratio at two sides of flame front on flame instability were analyzed combined with the schlieren photos. Results show that the unstretched flame propagation speeds and laminar flame speeds of the tert-butanol–air mixtures increase with the increase of initial temperature and decrease with the increase of initial pressure. Peak values of laminar flame speeds present at equivalence ratio of 1.1 regardless of initial pressure and temperature. Markstein length decreases with the increase of initial pressure. Flame front instability increases as equivalence ratio and initial pressure increase. Cellular structure appears at elevated pressure. The combined effect of diffusional–thermal instability and hydrodynamic instability leads to the increase of flame instability as initial pressure increases.

Laminar Flame Speed Measurements and Modeling of Pure Alkanes and Alkane Blends at Elevated Pressures

Alkanes such as methane, ethane, and propane make up a large portion of most natural gas fuels. Natural gas is the primary fuel used in industrial gas turbines for power generation. Because of this, a fundamental understanding of the physical characteristics such as the laminar flame speed is necessary. Most importantly, this information is needed at elevated pressures to have the most relevance to the gas turbine industry for engine design. This study includes experiments performed at elevated pressures, up to 10 atm initial pressure, and investigates the fuels in a pure form as well as in binary blends. Flame speed modeling was done using an improved version of the kinetics model that the authors have been developing over the past few years. Modeling was performed for a wide range of conditions, including elevated pressures. Experimental conditions include pure methane, pure ethane, 80/20 mixtures of methane/ethane, and 60/40 mixtures of methane/ethane at initial pressures of 1 atm, 5 atm, and 10 atm. Also included in this study are pure propane and 80/20 methane/propane mixtures at 1 atm and 5 atm. The laminar flame speed and Markstein length measurements were obtained from a high-pressure flame speed facility using a constant-volume vessel. The facility includes optical access, a high-speed camera, a schlieren optical setup, a mixing manifold, and an isolated control room. The experiments were performed at room temperature, and the resulting images were analyzed using linear regression. The experimental and modeling results are presented and compared with previously published data. The data herein agree well with the published data. In addition, a hybrid correlation was created to perform a rigorous uncertainty analysis. This correlation gives the total uncertainty of the experiment with respect to the true value rather than reporting the standard deviation of a repeated experiment. Included in the data set are high-pressure results at conditions where in many cases for the single-component fuels few data existed and for the binary blends no data existed prior to this study. Overall, the agreement between the model and data is excellent.

Erratum to: Geometrical Properties and Turbulent Flame Speed Measurements in Stationary Premixed V-flames Using Direct Numerical Simulation

Three dimensional, fully compressible direct numerical simulations (DNS) of premixed turbulent flames are carried out in a V-flame configuration. The governing equations and the numerical implementation are described in detail, including modifications made to the Navier–Stokes Characteristic Boundary Conditions (NSCBC) to accommodate the steep transverse velocity and composition gradients generated when the flame crosses the boundary. Three cases, at turbulence intensities, u′/sL, of 1, 2, and 6 are considered. The influence of the flame holder on downstream flame properties is assessed through the distributions of the surface-conditioned displacement speed, curvature and tangential strain rates, and compared to data from similarly processed planar flames. The distributions are found to be indistinguishable from planar flames for distances greater than about 17δth downstream of the flame holder, where δth is the laminar flame thermal thickness. Favre mean fields are constructed, and the growth of the mean flame brush is found to be well described by simple Taylor type diffusion. The turbulent flame speed, sT is evaluated from an expression describing the propagation speed of an isosurface of the mean reaction progress variable \(\tilde{c}\) in terms of the imbalance between the mean reactive, diffusive, and turbulent fluxes within the flame brush. The results are compared to the consumption speed, sC, calculated from the integral of the mean reaction rate, and to the predictions of a recently developed flame speed model (Kolla et al., Combust Sci Technol 181(3):518–535, 2009). The model predictions are improved in all cases by including the effects of mean molecular diffusion, and the overall agreement is good for the higher turbulence intensity cases once the tangential convective flux of \(\tilde{c}\) is taken into account.

Modes of particle combustion in iron dust flames

The so-called argon/helium test is proposed to identify the combustion mode of particles in iron dust flames. Iron powders of different particle sizes varying from 3 to 34 μm were dispersed in simulated air compositions where nitrogen was replaced by argon and helium. Due to the independence of the particle burning rate on the oxygen diffusivity in the kinetic mode, the ratio between the flame speeds in helium and argon mixtures is expected to be smaller if the particle burning rate is controlled by reaction kinetics rather than oxygen diffusion. Experiments were performed in a reduced-gravity environment on a parabolic flight aircraft to prevent particle settling and buoyancy-driven disruption of the flame. Uniform suspensions of the iron powders were produced inside glass tubes and a flame was initiated at the open end of the tube. Quenching plate assemblies of various channel widths were installed inside the tube and pass or quench events were used to measure the quenching distance. Flame propagation was recorded by a high-speed digital camera and spectral measurements were used to determine the temperature of the condensed emitters in the flame. The measured flame speeds and quenching distances were in good agreement with previously developed one-dimensional, dust flame model where the particles are assumed to burn in a diffusive mode and heat losses are described on a volumetric basis. However, a significant drop of the ratio of flame speeds in helium and argon mixtures was observed for finer 3 μm particles and was attributed to a transition from the combustion controlled by diffusion for larger particles to kinetically controlled burning of micron-size particles. In helium mixtures, the lower flame temperatures measured in suspensions of fine particles in comparison to larger particles reinforces this assumption.

Laminar dust flames in a reduced-gravity environment

The propagation of laminar dust flames in suspensions of iron in gaseous oxidizers was studied in a low-gravity environment onboard a parabolic flight aircraft. The reduction of buoyancy-induced convective flows and particle settling permitted the measurement of fundamental combustion parameters, such as the burning velocity and the flame quenching distance over a wide range of particle sizes and in different gaseous mixtures. Experimentally measured flame speeds and quenching distances were found in good agreement with theoretical predictions of a simplified analytical model that assumes particles burning in a diffusive mode. However, the comparison of flame speeds in oxygen–argon and oxygen–helium iron suspensions indicates the possibility that fine micron-sized particles burn in the kinetic mode. Furthermore, when the particle spacing is large compared to the scale of the reaction zone, a theoretical analysis suggests the existence of a new so-called discrete flame propagation regime. Discrete flames are strongly dependent on particle density fluctuations and demonstrate directed percolation behavior near flame propagation limits. The experimental observation of discrete flames in particle suspensions will require low levels of gravity over extended periods available only on orbital platforms.

Measurements of laminar flame speeds of liquid fuels: Jet-A1, diesel, palm methyl esters and blends using particle imaging velocimetry (PIV)

Laminar flame speeds of practical fuels including Jet-A1, diesel, palm methyl esters (PME) and blends of PME with diesel and Jet-A1 fuels are determined using the jet-wall stagnation flame configuration and particle imaging velocimetry (PIV) technique. The PME/Jet-A1 and PME/diesel blends are prepared by mixing 10%, 20% and 50% of PME with Jet-A1 and diesel fuels by volume respectively. The experiments are performed over a range of stoichiometries at elevated temperature of 470K and atmospheric pressure under premixed conditions. The reference flame speed and imposed strain rates are determined from the two dimensional velocity profiles. Subsequently, laminar flame speeds are derived by extrapolating the reference flame speed back to zero strain rates. Experimental results are compared to experimental and simulation data from the literature for large n-alkanes and practical fuels. The results show that laminar flame speeds of Jet-A1 fuel are similar to those of n-decane and n-dodecane, indicating their potential use as surrogate fuels. Peak laminar flame speeds for diesel/air and PME/air mixtures at 470K are similar, around 86.7 and 86.5cm/s at equivalence ratios around 1.10 and 1.14 respectively, and that both mixtures exhibit lower flame speeds compared to n-decane and n-dodecane at fuel-leaner and stoichiometric conditions. Blending PME with Jet-A1 and diesel leads to reduced laminar flame speeds on the lean side but increased on the rich side.

Experimental studies of the fundamental flame speeds of syngas (H2/CO)/air mixtures

Syngas laminar flame speed measurements have been carried out at atmospheric pressure and ambient temperature using spherically expanding flames. Mixture compositions ranging from 5/95% to 50/50% H2/CO and equivalence ratios from 0.4 to 5.0 have been investigated. Both state-of-the-art linear and non-linear extrapolation methodologies have been tested and extracted laminar flame speeds have been compared to datasets available in the literature as well as computations using two leading kinetic mechanisms for syngas combustion. Syngas flame sensitivities to stretch have been characterized by extracting the corresponding Markstein lengths. In order to explain important disparities found for rich syngas flames among datasets of the literature, computations have been performed to quantify the possible extent of velocity reduction corresponding to small contents of iron pentacarbonyl.

Experimental and numerical study of the accuracy of flame-speed measurements for methane/air combustion in a slot burner

Measuring the velocities of premixed laminar flames with precision remains a controversial issue in the combustion community. This paper studies the accuracy of such measurements in two-dimensional slot burners and shows that while methane/air flame speeds can be measured with reasonable accuracy, the method may lack precision for other mixtures such as hydrogen/air. Curvature at the flame tip, strain on the flame sides and local quenching at the flame base can modify local flame speeds and require corrections which are studied using two-dimensional DNS. Numerical simulations also provide stretch, displacement and consumption flame speeds along the flame front. For methane/air flames, DNS show that the local stretch remains small so that the local consumption speed is very close to the unstretched premixed flame speed. The only correction needed to correctly predict flame speeds in this case is due to the finite aspect ratio of the slot used to inject the premixed gases which induces a flow acceleration in the measurement region (this correction can be evaluated from velocity measurement in the slot section or from an analytical solution). The method is applied to methane/air flames with and without water addition and results are compared to experimental data found in the literature. The paper then discusses the limitations of the slot-burner method to measure flame speeds for other mixtures and shows that it is not well adapted to mixtures with a Lewis number far from unity, such as hydrogen/air flames.

On interaction of centrally-ignited, outwardly-propagating premixed flames with fully-developed isotropic turbulence at elevated pressure

A new apparatus for the study of turbulent premixed flames at atmospheric and elevated pressures is proposed. The apparatus includes a high-pressure fan-stirred cruciform burner, the inner chamber, which is resided in a relatively large pressure-absorbing safety chamber (the outer chamber). Both chambers are optically accessible, allowing direct visualization and measurement of flame and turbulence interactions. The inner burner applies the same turbulence generating mechanism as that previously reported by Shy et al. [10], capable of generating intense near-isotropic turbulence. The additional modification lies in its vertical vessel which has four sensitive pressure-releasing valves installed symmetrically, so that the pressure difference between the inner and outer chambers during explosion can be eliminated. Flame speed measurements for centrally-ignited, outwardly-propagating lean CH4–air flames at the equivalence ratio ϕ=0.8 under both quiescent and turbulent conditions are conducted over an initial pressure range of p=0.1–1MPa. It is found that, contrary to the popular scenario for laminar flames, the coupling influence of elevated pressure and turbulence significantly enhances turbulent flame speeds. Our experimental data show that the unstretched laminar burning velocities (SL) decrease with p−0.52, while turbulent burning velocities (ST) increase with p0.14 when a constant turbulent fluctuating velocity u′≈1.4m/s is applied. In terms of the power law relation proposed by Kobayashi and his co-workers, we found that ST/SL≈1.07[(u′/SL)(p/p0)]0.44 where p0 is the atmospheric pressure, showing a similar increasing trend but with much lower values of ST/SL to what they found in a Bunsen-type burner. It is suggested that ST∼p0.14 is attributed to further flame surface area increment induced by the enhancement of hydrodynamic instability due to the decrease of kinematic viscosity at elevated pressure.

Laminar flame speed measurements of dimethyl ether in air at pressures up to 10 atm

Laminar flame speed measurements of dimethyl ether/air mixtures were made at 1, 5, and 10 atm with equivalence ratios ranging from 0.7 to 1.6. All experiments were performed in a large cylindrical constant-volume bomb with optical access. A new method for converting flame images into flame radii was used. Results reported in other studies were investigated, and some explanations on the disparities found are presented. A full uncertainty analysis was performed combining precision errors from data scatter with predicted systematic errors. Uncertainties ranging between 4.2% and 8.6% were found depending on the equivalence ratio and initial pressure. Experimental results agreed well with some other spherical flame experiments and counterflow flame measurements, but were found to be much lower than PIV-based stagnation flame results. Also, two spherical flame studies deviated significantly both in magnitude and trend. Critical radii and Peclet numbers, defined by the onset of rapid flame acceleration, were recorded for all high-pressure experiments. Markstein lengths were measured and showed a decreasing trend with increasing equivalence ratio. Three different methods were used to define the laminar flame thickness, and large disparities were found between them. In this study, the modeled temperature gradient method for the definition of flame thickness is preferred over other methods. Modeling was performed with the latest version of a C3 chemical kinetics mechanism. Good agreement is seen between the experimental results and the model at all pressures. Emphasis is placed in this paper on reporting experimental uncertainties, calculated density ratios, flame temperatures, and flame radii ranges used for data analysis, and the results resolve some discrepancies seen in the literature for dimethyl ether flame speeds.

Nonlinear effects of stretch on the flame front propagation

In all experimental configurations, the flames are affected by stretch (curvature and/or strain rate). To obtain the unstretched flame speed, independent of the experimental configuration, the measured flame speed needs to be corrected. Usually, a linear relationship linking the flame speed to stretch is used. However, this linear relation is the result of several assumptions, which may be incorrected. The present study aims at evaluating the error in the laminar burning speed evaluation induced by using the traditional linear methodology. Experiments were performed in a closed vessel at atmospheric pressure for two different mixtures: methane/air and iso-octane/air. The initial temperatures were respectively 300 K and 400 K for methane and iso-octane. Both methodologies (linear and nonlinear) are applied and results in terms of laminar speed and burned gas Markstein length are compared. Methane and iso-octane were chosen because they present opposite evolutions in their Markstein length when the equivalence ratio is increased. The error induced by the linear methodology is evaluated, taking the nonlinear methodology as the reference. It is observed that the use of the linear methodology starts to induce substantial errors after an equivalence ratio of 1.1 for methane/air mixtures and before an equivalence ratio of 1 for iso-octane/air mixtures. One solution to increase the accuracy of the linear methodology for these critical cases consists in reducing the number of points used in the linear methodology by increasing the initial flame radius used.

The effect of pre-heating on flame propagation in nanocomposite thermites

Flame propagation in a confined tube configuration was evaluated for aluminum (Al) and molybdenum trioxide (MoO 3) thermites starting at room temperature and pre-heated up to 170 °C. Flame propagation was analyzed via high speed imaging diagnostics and temperatures were monitored with thermocouples. Experiments were performed in a semi-confined flame tube apparatus housed in a reaction chamber initially at standard atmospheric pressure. The flame propagation behavior for the nano-particle thermite was compared to micron particle thermite of the same composition. Results indicate that increasing the initial temperature of the reactants results in dramatically increased flame speeds for nanocomposite thermite (i.e., from 627 to 1002 m/s for ambient and 105 °C pre-heat temperature, respectively) and for micron composite thermite (i.e., from 205 to 347 m/s for ambient and 170 °C pre-heat temperature, respectively) samples. Experimental studies were extended giving a cooling time for the heated thermites prior to ignition and flame propagation. It is shown that when 105 °C and 170 °C pre-heated thermites are cooled at a rate of 0.06 K/s, almost the same flame speeds are obtained as thermites at ambient temperature. However, when the cooling rate is increased to 0.13 K/s, the measured flame speeds approach the flame speeds of pre-heated samples.

Measurement of turbulent flame speed of natural gas/air mixtures at elevated pressure

Abstract Turbulent flame speeds were measured over a range of pressures to 0·8 MPa using a jet flow apparatus fired with a synthetic mixture representing a mid-European natural gas. The equivalence ratio O was 0·9. The gas contained significant proportions of ballast gases and higher hydrocarbons. The method adopted was the ‘flame angle’ technique, using schlieren imaging to obtain the flame vertex angle from the peak density gradient. Image analysis techniques were developed to reduce interpretation errors and give an unbiased result. The data show higher flame speeds than those obtained with pure methane at elevated pressures, using similar methodology, and has an application in numerical modelling of combustors.

Derivation of burning velocities of premixed hydrogen/air flames at engine-relevant conditions using a single-cylinder compression machine with optical access

With respect to hydrogen internal combustion engines beside turbulence also flame front instabilities of high-pressure combustion provoke an acceleration of the flame. To account for this effect within engine simulations, it is suggested to include the impact of flame front instabilities directly into a “quasi-laminar” burning velocity that is an input for turbulent combustion models. Premixed hydrogen/air flames are investigated in a single-cylinder compression machine using OH-chemiluminescence and in-cylinder pressure analysis. Values of burning velocities are calculated from flame front velocities considering thermal expansion effects. A flame speed correlation is derived which covers temperatures and pressures of the unburned mixture, relevant for internal combustion engines, ranging from 350 K to 700 K and 5 bar to 45 bar. Values of air/fuel equivalence ratio cover lean and rich regimes between 0.4 ≤ λ ≤ 2.8. For an evaluation of stretch and instability effects a comparison to fundamental laminar burning velocities of a one-dimensional flame computed with a detailed chemical kinetic-mechanism is given. At high-pressure conditions flame speed measurements demonstrate that flame front instabilities have an accelerating effect on the value of laminar burning velocities, which cannot be reproduced by computations with a chemical model. A linear stability analysis is applied in order to estimate the magnitude of instabilities. The proposed “quasi-laminar” burning velocity does not account for interaction between turbulence and instability effects. Consequently, at increasing turbulence levels partially counter-balancing of instabilities by turbulence is not followed which may allegorize a possible limitation of the suggested approach.

Spherical expanding flames in H 2–N 2O–Ar mixtures: flame speed measurements and kinetic modeling

Although ignition of hydrogen–nitrous oxide mixtures is a serious issue for nuclear waste storage and semi-conductor manufacturing, available flame speed data have not been recently updated and thermodiffusive stability is not known. In order to palliate this, the flame speed of a hydrogen–nitrous oxide mixture diluted in Ar (60% mol) was measured in a spherical bomb as a function of equivalence ratio. The initial pressure and temperature were held constant around ambient conditions. It is shown that the unstretched flame speed of the hydrogen–nitrous oxide mixture is relatively low for a hydrogen-based mixture, with a maximum of 56 cm/s for the stoichiometric condition. Further, hydrogen–nitrous oxide–argon flames appear unstable with respect to thermodiffusive effects at an equivalence ratio of 1. The downward flammability limit of hydrogen–nitrous oxide–argon was observed for hydrogen content of 8 mol%. The modeling of these experimental data has been performed with three recently developed models. All kinetic schemes give satisfactory predictions of the experimentally observed data. Sensitivity and reaction pathway analysis have demonstrated that the dynamic of the system is dominated by the reaction N 2O + H = N 2 + OH which governs the rate of energy release.

Explosions in closed pipes containing baffles and 90 degree bends

There is a general lack of information on the effects of full-bore obstacles on combustion in the literature, these obstacles are prevalent in many applications and knowledge of their effects on phenomena including burning rate, flame acceleration and DDT is important for the correct placing of explosion safety devices such as flame arresters and venting devices. In this work methane, propane, ethylene and hydrogen–air explosions were investigated in an 18 m long DN150 closed pipe with a 90 degree bend and various baffle obstacles placed at a short distance from the ignition source. After carrying out multiple experiments with the same configuration it was found that a relatively large variance existed in the measured flame speeds and overpressures, this was attributed to a stochastic element in how flames evolved and also how they caused and interacted with turbulence to produce flame acceleration. This led to several experiments being carried out for one configuration in order to obtain a meaningful average. It was shown that a 90 degree bend in a long tube had the ability to enhance flame speeds and overpressures, and shorten the run-up distance to DDT to a varying degree for a number of gases. In terms of the qualitative effects on these parameters they were comparable to baffle type obstacles with a blockage ratios of between 10 and 20%.

The Generation of a Compact n-Heptane / Toluene Reaction Mechanism Using the Chemistry Guided Reduction (CGR) Technique

Abstract The present study describes the compilation and validation of a compact reaction mechanism for the oxidation of n-heptane, toluene and its mixtures using the Chemistry Guided Reduction (CGR) approach. By the module-wise composition of validated reaction schemes and the successive application of chemical lumping and redundant species removal for the n-heptane oxidation model, a compact mechanism is generated for reference fuel blends of n-heptane and toluene. The new mechanism is validated for recently published OH-concentrations histories and ignition times from shock tube studies, HCCI engine experiments and flame speed measurements. The good agreement between experiment and prediction demonstrates the general applicability of the CGR method.

Effects of compression and stretch on the determination of laminar flame speeds using propagating spherical flames

The effects of flow compression and flame stretch on the accurate determination of laminar flame speeds at normal and elevated pressures using propagating spherical flames at constant pressure or constant volume are studied theoretically and numerically. The results show that both the compression-induced flow motion and flame stretch have significant impacts on the accuracy of flame speed determination. For the constant pressure method, a new method to obtain a compression-corrected flame speed (CCFS) for nearly constant pressure spherical bomb experiments is presented. Likewise, for the constant volume method, a technique to obtain a stretch-corrected flame speed (SCFS) at elevated pressures and temperatures is developed. The validity of theoretical results for both constant pressure and constant volume methods is demonstrated by numerical simulations using detailed chemistry for hydrogen/air, methane/air, and propane/air mixtures. It is shown that the present CCFS and SCFS methods not only improve the accuracy of the flame speed measurements significantly but also extend the parameter range of experimental conditions. The results can be used directly in experimental measurements of laminar flame speeds.