Flame Speed Measurements Research Articles

Laminar flame speed measurements of ethylene at high preheat temperatures and for diluted oxidizers

Laminar flame speeds of ethylene are measured and the results are compared to predictions based on detailed chemical kinetic mechanisms. As important aspects of jet fuel chemistry involve ethylene, the flame speeds are determined at conditions relevant to jet engine combustors that have not been previously investigated, specifically high preheat temperatures (up to 650 K) and reduced O2 levels (down to 15% mole fraction in the oxidizer). The latter is relevant to staged-combustion and vitiation, where there is partial pre-burning of the oxidizing flow; so flame speeds are also measured with both CO2 and N2 dilution. Flame speed measurements of ethylene-air mixtures at room temperature conditions agree well (within 10%) of measurements with previous results from the literature and the chemical kinetic mechanism predictions. As the preheat temperature is increased to 650 K and with N2 dilution, the chemical mechanism predictions agree reasonably well with the measurements (generally within 10%). With CO2 dilution of the oxidizer, however, larger prediction discrepancies are found. The mechanisms over predict the measured flame speeds, and the prediction error increases with the amount of CO2 in the oxidizer. Analysis of different possible sources of discrepancy point to the third-body efficiency of CO2 as a likely reason; specifically, it may be underestimated for three-body association reactions such as H + O2 (+M) ⇔ HO2 (+M).

Tailored mixture properties for accurate laminar flame speed measurement from spherically expanding flames: Application to H[formula omitted]/O[formula omitted]/N[formula omitted]/He mixtures

The uncertainty on the laminar flame speed extracted from spherically expanding flames can be minimized by using large flame radius data for the extrapolation to zero stretch-rate. However, at large radii, the hydrodynamic and thermo-diffusive instabilities would induce the wrinkling of the flame surface and limit the range of usable data. In the present study, we have employed the flame stability theory of Matalon to tailor the properties of the initial mixture so that onset of cellular flame would occur at a pre-determined, large radius. This approach was employed to measure the laminar flame speeds of H2/O2/N2/He mixtures with equivalence ratios from 0.6 to 2.0, at pressures of 50/80/100 kPa and initial temperature of 300 K. For most experiments we performed, the uncertainty related to the extrapolation to zero stretch-rate (performed with the linear curvature model) was below 2% as shown by the position of the data points in the (Lb/Rf,U, Lb/Rf,L) plan, where Lb is the burned Markstein length; and Rf,L and Rf,U are the flame radii at the lower and upper bounds of the extrapolation range. Unsteady 1-D simulations using four chemical mechanisms were performed to show that unstretched laminar flame speed can be well-characterized with relative error below 10% for most conditions. The flame dynamical response to stretch rate could be captured by the mechanisms only under some conditions. Further analyses on critical flame radius were carried out: (i) the dominant parameters were identified based on a local sensitivity analysis; and (ii) the uncertainty on the predicted critical radius was determined through an uncertainty propagation approach. Uncertainty in critical flame radius calculation comes mostly from the uncertainty on fundamental transport and kinetic data. The present work indicates that although the stability theory of Matalon provides a well defined framework to tailor the mixture properties for improved flame speed measurement, the inaccuracy of some of the required parameters can result in significantly over-estimated critical radius for cellular flame onset which compromises the accuracy of the tailoring procedure.

Measurements of the laminar flame speed of premixed, hydrogen-air-argon stagnation flames

As the foundation for detailed hierarchical combustion chemistry models, the accuracy of the hydrogen oxidation mechanism is paramount to achieve truly predictive models. The recent introduction of new chemically termolecular reactions to this system suggests that our understanding of this fundamental chemistry could have initially been plagued with structural inaccuracies that have been carried along in the development of larger thermochemical mechanisms. Consequently, there is a need for additional independent experimental data in various experimental setups to assess the accuracy of model predictions. An atmospheric jet-wall stagnation-flame configuration is used in this work to measure the reactivity of premixed, lean-to-rich hydrogen-air flames diluted with argon. Mixtures with estimated adiabatic flame temperatures of ∼1800K are obtained by argon dilution to maintain the oxygen-nitrogen ratio while allowing for stable, laminar flames over the desired conditions. The accuracy of various thermochemical mechanisms available in the literature is assessed with direct comparisons of the velocity profiles in the stagnation configuration obtained through Particle Tracking Velocimetry to the solution of the quasi–1D flame simulation. Unstretched laminar flame speeds (SLo) are subsequently inferred using a direct comparison technique between the experiments and the simulations at multiple stretch values, similarly to a non-linear extrapolation to unstretched conditions. Significant discrepancies are observed between model predictions and experimental measurements, which supports the current efforts in model development. The inaccuracies in kinetic rates of the hydrogen oxidation model must first be resolved to avoid optimization and validation errors in the hierarchical development of increasingly complex hydrocarbon mechanisms.

Laminar Flame Speed Measurements of Kerosene-Based Fuels Accounting for Uncertainties in Mixture Average Molecular Weight

Abstract New laminar flame speed experiments have been collected for some kerosene-based liquid fuels: Jet-A, RP-1, and diesel fuel #2. Accurately understanding the combustion characteristics of these, and all kerosene-based fuels in general, is an important step in developing new chemical kinetics mechanisms that can be applied to these fuels. It is well known that the precise composition of these fuels changes from one production batch to the next, leading to significant uncertainty in the mixture average properties. For example, uncertainty in a fuel blend's molecular weight can have a noticeable effect on defining an equivalence ratio for a typical fuel–air mixture, of the order of 15%. Because of these uncertainties, fuel mole fraction, XFUEL, is shown to be a more appropriate parameter for comparison between different batches of fuel. Additionally, a strong linear correlation was detected between the burned-gas Markstein length and the equivalence ratio. This correlation is shown to be useful in determining the acceptability and accuracy of individual data points. Spherically expanding flames were measured over a range of fuel mole fractions corresponding to equivalence ratios of φ = 0.7 to φ = 1.5, at initial conditions of 1 atm and 403 K in the high-temperature, high-pressure (HTHP) constant volume vessel at Texas A&M University. These new results are compared with the limited set of laminar flame speed data currently available in the literature for this fuel.

Measurements and Data Analysis Review of Laminar Burning Velocity and Flame Speed for Biofuel/Air Mixtures

Precise measurement and prediction of flame speed and laminar burning velocity are essential for premixed combustion properties characterization, turbulent combustion models validation, progress, and validation of chemical kinetic models. Besides, the problem of lack of fossil fuel, planet pollution, and production of several fuel alternatives led researchers to reexamine the process of combustion and optimize fuel consumption. So, it would be necessary to know the change of laminar burning velocity and flame speed with thermodynamic conditions to understand the impression of practical applications in all combustion systems as working pressures and temperatures are extensively higher than the atmospheric conditions. Several investigations work regarding flame speed and laminar burning velocity had been achieved. However, a detailed literature review of methods and techniques used to measure these two parameters and the effect of operating factors for different fuels focusing on biofuels is presented in this paper for ease of reviewing.

Understanding the antagonistic effect of methanol as a component in surrogate fuel models: A case study of methanol/n-heptane mixtures

Methanol is a widely used engine fuel, blend component, and additive. However, no systematic auto-ignition data or laminar flame speed measurements are available for kinetic studies of the effect of methanol as a blending or additive component. In this work, both ignition delay times and laminar flame speeds of pure methanol, n-heptane and their blends at various blending ratios were measured at engine-relevant conditions. Results show that increasing methanol in a blend promotes reactivity at high temperatures and inhibits it at low temperatures, with the crossover temperature occurring at approximately 970–980 K with it being almost independent of pressure. The experimental data measured in this work, together with those in the literature are used to validate NUIGMech1.1, which predicts well the experimental ignition delay times and laminar flame speeds of the pure fuels and their blends over a wide range of conditions. Furthermore, kinetic analyses were conducted to reveal the effects of methanol addition on the oxidation pathways of n-heptane and the dominant reactions determining the fuel reactivities. It is found that competition for ȮH radicals between methanol and n-heptane plays an important role in the auto-ignition of the fuel blends at low temperatures. At high temperatures, methanol produces higher concentrations of HȮ2 radicals which produce two ȮH radicals either through the production of H2O2 and its subsequent decomposition or through direct reaction with Ḣ atoms. This promotes the high temperature reactivity of methanol/n-heptane mixtures for ignition delay times and laminar flame speeds, respectively.

저시간 분해능으로 인한 화염 속도 분석의 불확실성

This paper analyzes the effect of low temporal resolution on the accuracy of determining the local flame speed for experimental measurements and simulations. Flame speed measurement of moving flames requires the evaluation of a temporal derivative of flame front motion. Measurements have limited temporal resolution, which can lead to a bias error in the calculation of flame speed. The error associated with the temporal resolution was derived in the leading order effect on sampling time. In order to demonstrate the error term, we employed numerical examples. Artificial flame solutions are generated by solving the G-equation with prescribed flow fields and fine spatial/temporal resolutions. By varying the sampling time step, we demonstrated the error can lead to negative values of the measured flame speed. Furthermore, when coarse sampling time steps are used, the calculated flame speed also exhibits a spurious curvature dependency. Lastly, the associated error can be estimated by spatial gradients of the flame front for convection dominated flows.

The critical lower radius limit approach for laminar flame speed measurement from spherically expanding stretched flames

Spherically expanding flames are severely affected by flame stretch in the early stage of combustion and therefore stretch models are of great importance in determining the uncertainty of experimental laminar flame speeds (SL) and burned gas Markstein lengths (Lb). In order to prevent the existing large scatter in experimental data of these two fundamental flame parameters, the effect of the lower radius limit for the flame speed calculation on extrapolation results of the stretch models was investigated through spherically expanding flames under constant pressure. Methane, hydrogen, propane, and iso-octane fuels were tested to account for both hydrocarbon and non-hydrocarbon fuels with different evolutions in the burned gas Markstein length when equivalence ratio is increased. Results show that there is a critical lower radius limit (RL,critical), where all laminar flame speed and burned gas Markstein length values obtained by the extrapolation of the stretch models converge to the same laminar flame speed and burned gas Markstein length. The value of the critical lower radius limit strongly depends on the burned gas Markstein number (Mab) and this dependency can be shown with |Mab|=0.8424*RL,critical for fuel/oxidizer mixtures with −0.48 mm ≤ Lb ≤ 1.23 mm (or, −0.62 ≤ Mab ≤ 2.60). Finally, laminar flame speeds and burned gas Markstein lengths of methane, hydrogen, propane, and iso-octane flames that were corrected according to the critical lower radius limit approach proposed in the present study were compared to previously published experimental results.

Thermal-pyrolysis induced over-driven flame and its potential role in the negative-temperature dependence of iso-octane flame speed at elevated temperatures

Recently, high-temperature flame speed measurement up to 900 K has been successfully realized at Stanford University using a conventional shock tube, assisted by laser ignition and chemiluminescence image systems. For a near stoichiometric iso-octane/O2/N2/He mixture at atmospheric pressure, their results show that while flame speed increases with increasing unburnt temperature in the low and high-temperature range, it decreases with increasing unburnt temperature in the intermediate temperature regime (750–800 K). The measurement time for the flame initiation and propagation is orders of magnitude shorter than the first-stage ignition delay time, implying that the unburnt mixture upstream of the flame is largely chemically frozen. Therefore, such non-monotonic behavior in the flame speed is unlikely to be induced by autoignition chemistry. To understand this interesting phenomenon, 1-D transient simulation of spherical flame initiation and propagation with different ignition energy has been performed and compared with the experiment data. It is shown that for the relatively low ignition energy 7.5 mJ, an over-driven flame regime characterized by flame speeds and stretch rates well above the steady-state values occurs in the intermediate temperature range. The chemical structure of an over-driven flame involves substantial fuel thermal decomposition in the preheat zone, followed by C1-C4 oxidation in the reaction zone. It is found that the non-monotonicity in the observed flame speed is strongly correlated with the occurrence of over-driven flames in simulations. These results demonstrate a new flame structure which can potentially explain the observed non-monotonic flame speed for iso-octane at high temperatures. Higher ignition energy or smaller ignition kernel is suggested in future experiments to mitigate such over-driven effects.

Electrostatic sensors – Their principles and applications

Over the past three decades electrostatic sensors have been proposed, developed and utilised for the continuous monitoring and measurement of a range of industrial processes, mechanical systems and clinical environments. Electrostatic sensors enjoy simplicity in structure, cost-effectiveness and suitability for a wide range of installation conditions. They either provide unique solutions to some measurement challenges or offer more cost-effective options to the more established sensors such as those based on acoustic, capacitive, optical and electromagnetic principles. The established or potential applications of electrostatic sensors appear wide ranging, but the underlining sensing principle and resultant system characteristics are very similar. This paper presents a comprehensive review of the electrostatic sensors and sensing systems that have been developed for the measurement and monitoring of a range of process variables and conditions. These include the flow measurement of pneumatically conveyed solids, measurement of particulate emissions, monitoring of fluidised beds, on-line particle sizing, burner flame monitoring, speed and radial vibration measurement of mechanical systems, and condition monitoring of power transmission belts, mechanical wear, and human activities. The fundamental sensing principles together with the advantages and limitations of electrostatic sensors for a given area of applications are also introduced. The technology readiness level for each area of applications is identified and commented. Trends and future development of electrostatic sensors, their signal conditioning electronics, signal processing methods as well as possible new applications are also discussed.

Combined isochoric and isobaric acquisition methodology for accurate flame speed measurements from ambient to high pressures and temperatures

The present paper addresses measurement techniques of the most important fundamental property of a combustible mixture, the laminar flame speed. The accurate determination of this parameter has been investigated carefully using two different approaches: the constant pressure method based on the flame front trajectory obtained by means of a Schlieren optical technique, and the constant volume method based only on the pressure-time history recorded during the combustion process. Methane/air flames are selected, because they are relevant for many technical applications and believed to be well understood. Measurements were performed using two high-pressure, high-temperature constant volume vessels at RWTH and ICARE. First, uncertainties stemming from experiments are quantified, and the different sources of errors are identified. Second, the assumption that the unburned gas is compressed isentropically due to the burned gas expansion is verified experimentally for the first time to the authors’ knowledge. More importantly, it was found that combining the two approaches can provide high-fidelity data w.r.t. stretch, radiative heat loss, and instabilities. The data will be very helpful for mechanism development and combustion modeling. Ideally, both approaches are applied simultaneously in the same vessel to obtain a high confidence level in the measured data. Finally, a methodology is proposed to provide flame speeds over a wide range of pressures and temperatures up to 14 bars and 620 K, close to engine-relevant conditions.

A comprehensive experimental and improved kinetic modeling study on the pyrolysis and oxidation of propyne

To improve our understanding of the combustion characteristics of propyne, new experimental data for ignition delay times (IDTs), pyrolysis speciation profiles and flame speed measurements are presented in this study. IDTs for propyne ignition were obtained at equivalence ratios of 0.5, 1.0, and 2.0 in ‘air’ at pressures of 10 and 30 bar, over a wide range of temperatures (690–1460 K) using a rapid compression machine and a high-pressure shock tube. Moreover, experiments were performed in a single-pulse shock tube to study propyne pyrolysis at 2 bar pressure and in the temperature range 1000–1600 K. In addition, laminar flame speeds of propyne were studied at an unburned gas temperature of 373 K and at 1 and 2 bar for a range of equivalence ratios. A detailed chemical kinetic model is provided to describe the pyrolytic and combustion characteristics of propyne across this wide-ranging set of experimental data. This new mechanism shows significant improvements in the predictions for the IDTs, fuel pyrolysis and flame speeds for propyne compared to AramcoMech3.0. The improvement in fuel reactivity predictions in the new mechanism is due to the inclusion of the propyne + HȮ2 reaction system along with ȮH radical addition to the triple bonds of propyne and subsequent reactions.

Proper interpretation and overall accuracy of laminar flame speed measurements of single- and multi-component liquid fuels

Low-vapor pressure liquid fuels, particularly kerosene-based fuels, are notoriously difficult to use in precision laboratory-scale flame experiments. This difficulty could result in several sources of uncertainty when preparing fuel-air mixtures for laminar flame speed experiments in constant-volume vessels. To accurately measure the experimental uncertainties in a spherical, laminar flame, n-decane, a component of several popular kerosene-based surrogate fuels was utilized in a methodical study to elucidate and minimize the primary sources of error and to determine a realistic, overall measurement uncertainty. This careful study allowed for isolated analysis of the overall behavior of the fuel (such as whether or not the fuel is condensing) and the accuracy of the instrumentation used. The results show that for the single-component liquid fuel, equivalence ratio could be accurately measured to within φ=±0.03 and flame speed to within 2.79 cm/s. One of the primary sources of discrepancy and confusion when presenting and comparing laminar flame speed data of complex, liquid fuel mixtures is the identification of the average fuel molecule. This seemingly trivial detail is actually a very important property of the fuel because it leads to the determination of φ, which is commonly used as the independent variable of laminar flame speed plots. However, when reported at all, the uncertainty in the average molecular weight of these fuels is on the order of 15%. Because of this large uncertainty, φ is shown to not be the most useful parameter for comparing different data sets. Rather, fuel mole fraction, XFUEL, is much more useful as it describes the overall amount of fuel in the mixture, and plotting laminar flame speeds as a function of XFUEL results in better agreement amongst different data sets from the literature for Jet-A.

Laminar flame speed and shock-tube multi-species laser absorption measurements of Dimethyl Carbonate oxidation and pyrolysis near 1 atm

Dimethyl Carbonate (DMC) is a carbonate ester that can be produced in an environment-friendly way from methanol and CO2. DMC is one of the main components of the flammable electrolyte used in Li-ion batteries, and it can also be used as a diesel fuel additive. Studying the combustion chemistry of DMC can therefore improve the use of biofuels and help developing safer Li-ion batteries. The combustion chemistry of DMC has been investigated in a limited number of studies. The aim of this study was to complement the scarce data available for DMC combustion in the literature. Laminar flame speeds at 318 K, 363 K, and 463 K were measured for various equivalence ratios (ranging from 0.7 to 1.5) in a spherical vessel, greatly extending the range of conditions investigated. Shock tubes were used to measure time histories of CO and H2O using tunable laser absorption for the first time for DMC. Characteristic reaction times were also measured through OH* emission. Shock-tube spectroscopic measurements were performed under dilute conditions, at three equivalence ratios (fuel-lean, stoichiometric, and fuel-rich) between 1260 and 1660 K near 1.3 ± 0.2 atm, and under pyrolysis conditions (98%+dilution) ranging from 1230 to 2500 K near 1.3 ± 0.2 atm. Laminar flame speed experiments were performed around atmospheric pressure. Detailed kinetics models from the literature were compared to the data, and it was found that none are capable of predicting the data over the entire range of conditions investigated. A numerical analysis was performed with the most accurate model, underlining the need to revisit at least 3 key reactions involving DMC.

Measurement of the adiabatic flame speed and overall activation energy of a methane enriched H2/CO/CO2/N2 low heating value mixture

The objective of this work is to investigate the effect of the methane blending in the adiabatic laminar flame speed and overall activation energy of a CO/CO2 rich, low calorific value, syngas fuel premixed combustion with air. The measurements were performed in a McKenna flat flame burner at constant equivalence ratio, unburned temperature and pressure. A flame asymptotic model curve-fitted to the measurements provided the overall activation energy and adiabatic laminar flame speed. The mixtures tested presented lower heating values from 4.5 MJ/kg to 50 MJ/kg as the CH4 fraction was changed from 0% to 100%. While the measured laminar flame speed remained approximately constant for all fuels tested, the overall activation energy evidenced the higher reactivity of the mixture blended with 20% CH4. Predictions using GRI-Mech 3.0 and San Diego mechanisms closely followed the measurements of the laminar flame speed for higher methane content, but deviations were found for the fuels with higher hydrogen content. Conversely, the mechanisms underpredicted the values of overall activation energy for all mixtures tested. A sensitivity analysis revealed the competition between the CO wet oxidation and the chain branching formation of OH and the increase in reactivity as the fraction of CH4 increased from 0 was related to a switch from a higher sensitivity of the former by the later.

Back to basics – NO concentration measurements in atmospheric lean-to-rich, low-temperature, premixed hydrogen–air flames diluted with argon

Ideally, nitric oxide (NO) production pathways would be measured individually to understand the formation mechanisms at a fundamental level. Unfortunately, the four production routes in hydrocarbon combustion cannot be fully decoupled. Hydrogen combustion at low flame temperatures eliminates prompt-NO and mitigates thermal production, such that only the N2O and NNH pathways remain as significant production routes. The H2/O2 system, whose base chemistry has been studied in great detail, offers an excellent platform to validate nitrogen chemistry by limiting the possibility of error propagation during model calibration. The current work presents measurements of velocity, temperature, and NO concentration in premixed, jet-wall stagnation, hydrogen–air flames at atmospheric pressure, diluted with argon to maintain adiabatic flame temperatures below 1800 K. Measurements of reference flame speeds, Su,ref, obtained with particle tracking velocimetry, highlight the modeling differences in H2/O2 chemistry from a selection of thermochemical mechanisms, especially in lean flames affected by preferential diffusion. Laser induced fluorescence measurements in lean-to-rich flames (ϕ=0.7–1.5) yield concentrations of NO from 2 to 0.5 ppm, respectively. Simulated NO profiles cover one order of magnitude in predicted signal intensity. Fortunately, recent mechanisms with accurate descriptions of the N2O and NNH pathways predict NO concentrations within experimental uncertainties for multiple operating conditions.

Studies of the dynamics of autoignition assisted outwardly propagating spherical cool and double flames under shock-tube conditions

The initiation, propagation, and transition of the autoignition assisted spherical cool flame and double flame are studied numerically and experimentally using n-heptane/air/He mixtures under shock-tube experimental conditions over a wide range of temperatures. The primary goal of the current study is to understand the effects of the ignition Damkohler number, ignition energy, flame curvature, and autoignition-induced flow compression on the propagation of spherical flames to ensure the proper interpretation of shock-tube flame speed measurements at engine-relevant conditions. The results show that at high ignition Damkohler number, there are three different flame regimes, cool flame, double flame, and hot flame. The cool flame speed accelerates dramatically with the increase of ignition Damkohler number. In addition, it is found that the change of flame regime, low-temperature autoignition, flame stretch, and autoignition-induced flow compression result in a complicated non-linear dependence of flame speed on stretch. The results also reveal that the spherical cool flame has much lower Markstein length compared to the hot flame at T > 600 K. Moreover, it is found that both the autoignition assisted cool flame and the trailing hot flame front in the double flame can propagate much faster that the hot flame alone at the same mixture conditions, leading to a nonlinear dependence of flame speed on the mixture initial temperature. The simulated flame trajectories and the flame speed dependence on temperature agree qualitatively well with the shock-tube experiments. A quantitative criterion to ensure the accurate speed measurement of the cool and hot flame is proposed. The present study provides important physical insight and guidance for the flame speed measurement using a shock-tube at engine relevant conditions.

A comprehensive kinetic model for dimethyl ether and dimethoxymethane oxidation and NOx interaction utilizing experimental laminar flame speed measurements at elevated pressure and temperature

Laminar flame speeds of dimethyl ether and dimethoxymethane at pressures from 1 to 5 bar and initial temperatures from 298 to 373 K were determined experimentally using a constant volume spherical vessel and a heat flux burner setup. This study is the first to report dimethoxymethane laminar flame speeds at a pressure higher than 1 bar. Using these experimental data along with data available in the literature, a new kinetic model for the prediction of the oxidation behavior of dimethyl ether and dimethoxymethane in freely propagating and burner stabilized premixed flames, in shock tubes, rapid compression machines, flow reactors, and a jet-stirred reactor has been developed. The experimental results from the present work and literature are interpreted with the help of the derived kinetic model. This newly developed reaction mechanism considers the redox chemistry of NOx to accommodate the influence of the oxygen level on the onset of fuel conversion and interconversion of NO and NO2. The current model suggests that an increased O2 level promotes the HO2 production, which in turn leads to the formation of OH radicals, which promotes the combustion of the fuel/air mixture under lean conditions. The increase of OH radical concentrations is mainly via the NO/NO2 interconversion reaction channel, NO+HO2=NO2+OH, NO2+H=NO+OH, CH3OCH3+NO2=CH3OCH2+HONO, followed by the thermal decomposition of HONO. This work extends the kinetic database and helps to improve the understanding of dimethyl ether and dimethoxymethane combustion behavior. The kinetic model presented in this work can serve as a base model for hydrocarbons and oxygenated fuels higher than C2.

Measurements of the laminar burning velocities of rich ethylene/air mixtures

Laminar burning velocities of premixed ethylene/air flames were investigated under fuel lean and rich conditions. The laminar burning velocities were measured with the heat flux method at atmospheric pressure and unburnt gas temperatures of 298 K. The measurements have been performed for the equivalence ratio range of Φ = 0.7–2.5 using stabilized and flat flames on a perforated burner plate under adiabatic conditions. This is the first time that experimental measurements with the heat flux method of the ethylene/air flames under super fuel rich conditions are performed. The experimental data were compared against predictions using three different kinetic models and published flame speed. The measured flame speeds agree with other published data within the error margin. The experimental and predicted laminar flames do agree at fuel lean conditions, but there are some notable discrepancies under fuel rich conditions.

Laminar Burning Velocity Measurement Using the Filtered Broadband Natural Emissions of Species

Laminar flame speed plays a fundamental role in understanding hydrocarbon chemistry and is the basis of turbulent flame modeling. The main objective of this research is to visualize a flame and measure its speed using a new optical diagnostic technique, which is based on the natural radiative emissions of various species, mainly hydrocarbons, water and carbon dioxide. This new technique has two main advantages over the Schlieren method. First only one optical access is needed, and second, the preheat zone and the flame front can be observed, and their radiative emission can be quantified. In addition, the condition of the unburned gas in front of the flame can be studied using the new technique to evaluate some of the hypotheses behind unstretched flame speed measurement, such as the trivial change of the unburned gas state. To evaluate and validate the new optical diagnostic technique, the flame propagation of methane, oxygen and nitrogen mixtures was studied using species infrared radiative emissions at...