Air Flames Research Articles

Effects of CO2 and N2 Dilution on the Combustion Characteristics of H2/CO Mixture in a Turbulent, Partially Premixed Burner.

Herein, the influences of CO2 dilution, N2 dilution, and CO2/N2 (in which half of the N2 is replaced by CO2) dilution on the combustion characteristics of a turbulent, partially premixed CO/H2–air flame were experimentally investigated in terms of the flame structure, flame temperature, and CO and CO2 concentrations in flames. TDLAS (tunable diode laser absorption spectroscopy) technique and an infrared gas analyzer were used for such purposes. CO2 dilution not only increases more momentum but also reduces the reaction rate. This results in a much longer flame length than that under N2 dilution. Compared with N2 dilution, the LH (axial length of the high-temperature reaction zone) values for the same levels of CO2 dilution and CO2/N2 dilution are much longer. The highest CO concentration in the CO2 diluted flame is higher than that in the CO/H2 flame and that in the CO2/N2 diluted flame is higher than in that the N2 diluted flame. The sizes of the main chemical reaction zone in CO2 and CO2/N2 diluted flames are larger than that in the N2 diluted flame. The inflection points in the rates of variation of the flame temperature and the CO and CO2 concentrations verify that CO2 dilution creates lower intensities and lower rates of chemical reactions, compared with N2 dilution.

Solar photocatalytic degradation of organic pollutants from indoor air using novel direct flame combustion based hollow nanocomposite of Pd/Anatase–Rutile TiO2 mixed phase and evaluation of the biocompatibility

The conventional methods (calcinations) are used to prepare diverse types of nanoparticles, however, to introduce specific properties for their applications, new strategy is required. Therefore, direct air flame combustion is a new technique utilized to synthesize novel nanoparticles instead of calcinations in the oven. In this work, the air flame combustion was used to prepare a new junction of anatase– rutile (A/R) mixed phase TiO2 deposited with palladium nanoparticles (Pd NPs). Herein, an A/R phase junction was obtained by flame combustion of carbon sphere templates. The novel nanocatalyst was characterized using XRD, SEM, TEM, UV–Vis light spectroscopy and SBET method for surface properties. It shows a higher performance during the photocatalytic degradation of formaldehyde gas pollutant under solar irradiation. The enhancement of catalytic activity was found to be 18-fold higher than the commercial TiO2-P25. The results of CO2 generated via the formaldehyde degradation by the novel nanophotocatalyst showed a high photocatalytic efficiency of 60%. Moreover, in the field application, it showed 75% formaldehyde removal when applied in the kitchen indoor air; it reveals also a wide array of antimicrobial activity. Therefore, this system will be more promising in various industrial applications.

Laser-Induced Breakdown Spectroscopy (LIBS) For The Characterization Of Methane-Air Laminar Diffusion Flame

Laser-induced breakdown spectroscopy (LIBS) was applied for the characterization of the methane-air laminar diffusion flame, revealing the spatial distribution of its composition. From the measurement, it was found that distribution of the atomic and ionic N emissions produced by the flame had obvious differences, which were mainly distributed in the air area and flame area, respectively. A comparison of the LIBS spectra of air, methane gas, and methane-air laminar diffusion flame showed that the atomic N emissions were mainly produced by the excitation of N2, and the ionic N emissions were more related to the N-containing combustion products. In addition, the correlation between typical emissions and the flame temperature measured by thermocouple was estimated to show that the tendency of the changes in temperature can be characterized by C2 emission intensities. This work provides a new method for real-time online flame temperature measurement, and also provides a reference for revealing the formation process and conversion pathway of each component in the flame.

Data-driven subfilter modelling of thermo-diffusively unstable hydrogen–air premixed flames

This article is dedicated to Moshe Matalon on the occasion of his 70th birthday, for his numerous contributions to the field of combustion and, in particular, to the rich and varied topic of premixed flame stability. Here, we follow in his footsteps and propose a subfilter modelling framework for thermo-diffusively unstable premixed flames, such as lean hydrogen–air flames. Performing an optimal estimator analysis for the unfiltered and filtered heat release rate of the lean premixed hydrogen–air flames, the latter is found to require at least two scalars for an appropriate representation while for large filter sizes, the heat release appears to require only one scalar for parametrisation. As a result, we develop a modelling strategy based on the construction of thermochemical tables for each unclosed term as a function of two variables as well as the filter size. The framework is based on the filtered tabulated chemistry approach, where, in lieu of a one-dimensional unstretched flame, we adopt a data-driven paradigm and filter fully resolved two-dimensional simulations of variable size. Models originating from small- and medium-sized simulations are tested a-priori on a large-size simulation, thus highlighting the role of the lateral domain in the dataset used for tabulation. The concept of a minimum domain size is thus discussed, leading to a dataset exhibiting the minimal properties for sufficiently accurate thermochemical tables. The strategy is shown to be more accurate than a classical one-dimensional filtered tabulated chemistry approach and shows promise in future LES modelling of laboratory and industrial scale hydrogen flames.

Lagrangian analysis of enstrophy dynamics in a highly turbulent premixed flame

A Lagrangian analysis approach is used to examine the effects of heat release on the dynamics of the enstrophy during highly turbulent premixed combustion. The analysis is performed using data from a direct numerical simulation of a statistically planar premixed methane–air flame at a Karlovitz number of 100. Through cumulative, conditional, and correlation analyses, we show, consistent with prior studies, that vortex stretching and baroclinic torque both increase enstrophy at these highly turbulent conditions, while viscous transport and dilatation both lead to enstrophy destruction. However, although vortex stretching and viscous transport are individually an order of magnitude greater than all other terms in the enstrophy budget, the cumulative and combined effect of these two terms along Lagrangian trajectories is roughly only twice as large as the combined cumulative effect of dilatation and baroclinic torque. Moreover, trajectories that exhibit an increase in enstrophy through the flame are found to frequently have cumulative contributions from budget terms outside a single standard deviation of the mean contribution, indicating that enstrophy production at such highly turbulent conditions is associated with relatively infrequent but large values of dynamical terms. Lagged correlations further reveal a small but measurable contribution of baroclinic torque in enstrophy production, but these increases are overwhelmed, on average, by concurrent decreases in enstrophy due to viscous transport and dilatation. Taken together, these results provide further understanding of enstrophy dynamics in highly turbulent premixed flames.

Inverted conical methane/air flame shape transformation under acoustic excitation

An inverted conical plane-symmetrical premixed methane–air flame under acoustic excitation was investigated experimentally. The flame was a conical one stabilized by a thin transverse rod. The Reynolds numbers were varied within 400–3000, and the fuel equivalence ratios were 0.8–1.4. Such a flame can take the shape of two fundamentally different types: M—when the flame front attaches both to the nozzle edge and stabilization rod; V—only to the stabilization rod. The transition conditions from one front configuration to another (M–V and V–M) were studied under various excitation parameters. Acoustic disturbances with a frequency of up to 420 Hz and an amplitude of longitudinal velocity pulsations up to 10% of the mean flow velocity excited the flame. New experimental data were obtained on the conditions corresponding to the M–V and V–M transitions. Qualitative and quantitative parameters of the hysteresis effect at which M–V and V–M transitions are realized, similar to the case of swirling flames, were revealed. The frequencies at which the acoustics most strongly affects the M–V and V–M transitions conditions were found. The hysteresis deterioration for M–V and V–M transitions was shown for the first time. It was noted that the conditions for the hysteresis deterioration are close to the theoretical frequency of the descent of vortices from the nozzle edge. The local maxima of the characteristic Strouhal numbers corresponding to the features of the minimum divergence of the flow velocities at the M–V and V–M transitions were determined.

Laminar burning velocity measurements of ethanol+air and methanol+air flames at atmospheric and elevated pressures using a new Heat Flux setup

A new setup for burning velocity measurements of liquid fuels at elevated pressures using the Heat Flux method has been constructed. The burner design has been improved comparing to previous studies in this and other laboratories. Laminar burning velocities were determined experimentally for ethanol+air and methanol+air mixtures over a range of conditions including equivalence ratio (0.8 to 1.3), inlet gas temperature (318–338 K), and pressure (1–5 bar). Experimental uncertainties have been determined and analyzed. The overall accuracy of the burning velocity, SL, was evaluated to be better than ±1 cm/s for atmospheric pressure and ±1.5 cm/s at elevated pressure conditions. Experimental results at 1 atm are in good agreement with recent literature data. To compare the present measurements with the literature data often obtained at other initial temperatures and pressures, an empirical expression SL = SL0 (T/T0)α (p/p0)β, which correlates the burning velocity at a specific temperature, T, and pressure, p, with that at standard conditions indicated by superscripts 0, was implemented. At a fixed temperature, pressure dependence at each equivalence ratio can be analyzed. It was found that power exponents β derived in the present work and from the literature data possess large scattering. The best agreement was found between the present results and experimental literature data from spherical flames using non-linear stretch correction models. Burning velocities at atmospheric as well as elevated pressures and power exponents β have been also compared with kinetic modeling results using several detailed kinetic mechanisms, showing a fair to a good agreement. As the new results are accurate and free from stretch effects, they form a new source of reliable data for validation of the reaction mechanisms.

Temporal dynamics of femtosecond-TALIF of atomic hydrogen and oxygen in a nanosecond repetitively pulsed discharge-assisted methane–air flame

The temporal dynamics of the spatial distribution of atomic hydrogen and oxygen in a lean methane–air flame, forced by a nanosecond repetitively pulsed discharge-induced plasma, are investigated via femtosecond two-photon absorption laser-induced fluorescence technique. Plasma luminescence that interferes with the fluorescence from H and O atoms was observed to decay completely within 15 ns, which is the minimum delay required for imaging measurements with respect to the discharge occurrence. During discharge, H atoms in the excited state rather than the ground state, produced by electron-impact dissociation processes, are detected at the flame front. It was found that the temporal evolution of H and O fluorescence intensity during a cycle of 100 µs between two discharge pulses remains constant. Finally, the decay time of O-atoms produced by the discharge in the fresh methane–air mixture was about 2 µs, which suggests a faster reaction between O-atoms and methane than in air.

Laminar burning velocities of propionic acid + air flames: Experimental, modeling and data consistency study

Laminar burning velocities of propionic acid + air flames have been determined using the heat flux method at atmospheric pressure and initial gas mixture temperature of 348 K over the range of equivalence ratios 0.7–1.3. The detailed kinetic model of the authors was extended by the reactions of propionic acid and its intermediates. Attention has been paid to the proper description of the formation and consumption of 1,1-propenediol, methyl ketene, and acrylic acid. New experimental results have been compared with the modelling using this kinetic mechanism and the mechanism of Zhang et al. (2021). The comparison of the new and available from the literature measurements obtained at different initial temperatures with predictions of the two models allowed for analysis of the data consistency for the burning velocities of propionic acid, as well as for acetic and formic acids. Inconsistencies of some datasets for these short-chain carboxylic acids were identified and discussed.

Flame versus air atmospheric gliding arc plasma treatment of polypropylene‐based automotive bumpers: Physicochemical characterization and investigation of coating properties

AbstractIn this research, the polypropylene (PP) sheets used for automotive bumper surface were treated using two methods: air atmospheric gliding arc plasma and flame modifications. Atomic force microscopy was applied to study the morphology of surfaces before and after treatment processes. While calculating the surface free energy (SFE), contact angle of the surfaces was measured, and the chemical composition of the PP surface was analyzed using X‐ray photoelectron spectroscopy. Surface modifications by gliding arc plasma increased the ratio of the oxygen and nitrogen atoms on the surface by 100%, indicating that polar chemical functionalities form on the surface. The surface morphology was highly affected by gliding arc plasma treatments, which triggered an impact on roughness and etching. It was also found that the SFE was drastically increased by certain modifications. Noticeable improvement was also observed in wettability by the gliding arc plasma technique. In the next stage, polyurethane paints were coated on the treated and untreated PP surfaces. Then, we examined the flame and gliding arc plasma treatments' effect on coating properties of PP bumper, adhesion analysis, water immersion resistance, and sulfuric acid resistance. Finally, high‐pressure carwash test and gloss analysis were conducted on the treated and untreated coated sheets, respectively.

Investigation of Swirl Stabilized CH4 Air Flame with Varied Hydrogen Content by using Computational Fluid Dynamics (CFD) to Study the Temperature Field and Flame Shape

In the current paper, numerical simulations of the combustion of turbulent CH4-H2 are presented employing the standard k-epsilon and the RNG k-epsilon for turbulence closure. The Fr-ED concept is carried out to account for chemistry/ turbulence interaction. The hydrogen content is varied in the fuel stream from 0% to 100%. The numerical solutions are validated by comparison with corresponding experimental data from the Combustion Laboratory of the University of Milan. The flow is directed radially outward. This method of fuel injection has been already been explored experimentally. The results show that the structure of the flame is described reasonably and both standard k-ɛ and RNG k- ɛ models can predict the flame shape. The general aspect of the temperature profiles is well predicted. The temperature profiles are indicating a different trend between CH4 and CH4/H2 fuel mixtures.

Experimental investigation of combustion dynamics and NOx/CO emissions from densely distributed lean-premixed multinozzle CH4/C3H8/H2/air flames

Lean-premixed fuel-flexible combustion technology capable of operating on a wide range of fuels, including high or pure hydrogen, is expected to play a crucial role in reducing nitrogen oxides and carbon dioxide emissions from heavy-duty gas turbine engines, ultimately in achieving energy system decarbonization. However, fuel-flexible operations, particularly with high hydrogen content fuels, require a fundamental, drastic change from conventional nozzle architecture. The use of a number of small-scale multitube injectors – also referred to as micromix nozzles – is indispensable to reduce the likelihood of flashback events in ultra-fast premixed hydrogen flames. At present, the vast majority of what is known about the fundamental mechanisms of combustion dynamics and emissions stem from intensive research in large-scale swirl-stabilized flames. The behavior of small-scale multinozzle flames governed by isolated or collective movements of constituent flames remains, however, largely unexplored. To address these questions, we use densely distributed sixty-injector mesoscale flames as a platform to explore the influence of a full range of CH4/C3H8/H2 fuel blends – including all possible combinations of a blend of two different fuels (CH4 + C3H8, CH4 + H2, C3H8 + H2) and three different fuels (CH4 + C3H8 + H2), as well as single-component fuels (CH4, C3H8, H2) – on combustion dynamics and exhaust emissions under a constant adiabatic flame temperature condition. Here, we show that while the nitrogen oxide emissions are almost unaffected by the fuel compositions considered here, the variation of fuel composition has a significant impact on self-excited instabilities, which tend toward higher frequency oscillations with increasing hydrogen concentration. From phase-resolved OH PLIF measurements for a 50/50 mixture of CH4 and H2, we identify the creation, evolution, and annihilation of an array of coherent vortical structures as the mechanism responsible for sound generation and flame surface modulations without strong interactions between adjacent flames. In contrast, the behavior of the 50% C3H8 + 50% H2 case is dictated primarily by periodic merging and separation of neighboring reactant jets, leading to large-scale asymmetric oscillations in the transverse direction. Given the substantial change in transport properties, effective Lewis number-related interpretation provides a reasonable explanation for the different behaviors of a cluster of small-scale flames.

Experimental and Kinetic Investigation of Stoichiometric to Rich NH3/H2/Air Flames in a Swirl and Bluff-Body Stabilized Burner

Ammonia (NH3) is an inorganic substance considered as a promising fuel for power sector decarbonization. As a result of the absence of carbon in its structure, ammonia is capable of producing energy with zero CO2 emissions when burned. However, the combustion of NH3 presents several challenges as a result of its low reactivity and low flame speed as well as the formation of large quantities of nitrogen oxides (NOx) and frequent ammonia slip. A suggested solution for gas turbines is the use of rich-to-lean approaches, with a fuel-rich first-stage combustion, which mitigates NOx formation, followed by a lean phase for the oxidation of the remaining reactants, improving combustion efficiency. To help assess this concept, the present work investigates experimentally and computationally the combustion of ammonia/air mixtures, enriched by hydrogen (H2) for enhanced burning characteristics, in a swirl and bluff-body stabilized burner, at stoichiometric to fuel-rich conditions. Stability tests were performed for a fixed thermal input (2.8 kW), and flames of fuel/air equivalence ratios of 1.0, 1.1, and 1.2, with molar fractions of ammonia in fuel of 0.7 and 0.8, were studied. Temperature profiles along the combustor axis were measured, and flue gas measurements for NOx emissions and unburned NH3 and H2 concentrations were performed for the six studied flames. Computational simulations were performed using a chemical reactor network coupled with recent kinetic mechanisms to compare species trends and further understand the NOx formation and NH3 conversion into hydrogen, through rate of production analyses. It was found that the present laboratory combustor performed well in terms of flame stability, also generating low levels of NOx emissions in all fuel-rich conditions. H2 was detected in high concentrations in the flue gas, partially originated from ammonia dissociation, and is followed by high unburned ammonia emissions. Both H2 and NH3 emissions increase with the equivalence ratio. A secondary, spontaneous diffusion flame was observed above the combustor, proving that the flue gas may subsequently be burned. Higher fractions of hydrogen in the fuel generate more unburned ammonia but also higher H2 concentrations in the flue gas. The predictions based on a reactor network model coupled with the evaluated kinetic mechanisms presented good agreement with the experimentally observed species trends and fair agreement with species values.

Fabrication and Testing of Carbon Foams by Kraft Lignin

Carbon foams have been prepared using Kraft lignin as the solely resource. No catalysts, foaming/blowing agents, surfactants, and/or crosslinking agents are used for the foam preparation. The process includes pressing carbon foam precursors into molds followed by formation of lignin foam through heating and carbonization/graphitization of the lignin derived foams. The resultant lignin carbon foam (LCF) has an open-cell structure with densities ranging from about 0.18 g/cm3 to 0.68 g/cm3. The compressive strengths of LCFs increase with increasing of bulk density, from 7.03 ± 1.25 MPa of LCF1 to 30.16 ± 2.41 MPa of LCF7, and thermal conductivity is strongly influenced by the bulk density with increase from 0.21±0.02 W/(m·K) to 0.75±0.01 W/(m·K). The bulk electrical conductivities of LCF samples increase with increasing of bulk densities from 701 S/m to 2031 S/m. The LCF samples were evaluated for resistance to fire and native subterranean termites. LCF samples exhibit excellent fire resistance, no damage occurred when the LCF sample was exposed to an oxyacetylenic flame in air over 1050 °C for more than 3 minutes. Termite testing showed no degradation to the LCF samples after the evaluation.

Impact of Syngas Addition to Methane on Laminar Burning Velocity

Abstract Exhaust gas recirculation (EGR) in spark-ignited (SI) engines is a key technique to reduce in-cylinder NOx production by decreasing the combustion temperature. The major species of the exhaust gas in rich combustion of natural gas are hydrogen and carbon monoxide, which can subsequently be recirculated to the cylinders using EGR. In this study, the effect of hydrogen and carbon monoxide addition to methane on laminar burning velocity and flame morphology is investigated. Due to the broad flammability limit and high burning velocity of hydrogen compared to methane, this addition to the gaseous mixture leads to an increase in burning velocity, less emissions production, and a boost to the thermal efficiency of internal combustion engines. Premixed CH4–H2–CO–air flames are experimentally investigated using an optically accessible constant volume combustion chamber (CVCC) accompanied with a high-speed Z-type Schlieren imaging system. Furthermore, a numerical code is applied to quantify the laminar burning velocity based on the pressure rise during flame propagation within the CVCC. According to the empirical and numerical results, the addition of hydrogen and carbon monoxide enhances laminar burning velocity while influencing the flame structure and development.

Emissions Performance of Staged Premixed and Diffusion Combustor Concepts for an NH3/Air Flame With and Without Reactant Humidification

Abstract Renewably generated ammonia offers a form of carbon-free chemical energy storage to meet the differences between uncertain supply and fluctuating demand and has the potential to support future energy requirements. The storage/transportation characteristics of NH3 are favorable compared with H2; however, there are combustion research challenges to enhance fuel reactivity while reducing harmful emissions production. The purpose of this work was to evaluate different fuel delivery concepts for a representative gas turbine combustor. An experimental and numerical comparison was made between swirl-stabilized premixed and diffusion NH3–air flames at elevated inlet temperature (473 K). The exhaust NOx and NH3 emissions generated from each concept were quantified to optimize combustor performance. High-speed OH* and NH2* chemiluminescence was employed to characterize the change in flame topology with variation in fuel–air equivalence ratio, and the resultant influence on measured emission concentrations. Chemiluminescence intensities were shown to elucidate changes in sampled exhaust emissions, enabling detailed analysis of intermediate chemistry. A comparison was made between experimental data and kinetic simulations, demonstrating the sensitivity of NOx emissions to premixed fuel–air equivalence ratio. A comparison was also made between exclusive primary airflow, and the staged introduction of secondary air, to quantify the change in NOx production between each configuration and improve fuel burnout. Secondary air loadings were incrementally increased through the combustor. Finally, reactant humidification was employed as a secondary process for NOx reduction, having shown favorable performance with NH3–H2 mixtures, with the efficacy compared for both premixed and diffusion configurations.

Lattice-Boltzmann modeling of a turbulent bluff-body stabilized flame

This Letter reports the first large eddy simulation of a turbulent flame using a lattice-Boltzmann model. To that end, simulation of a bluff-body stabilized propane–air flame is carried out, showing an agreement similar to those available in the literature. Computational costs are also reported, indicating that lattice-Boltzmann modeling of reactive flows is competitive, with around 1000cpuh required to simulate one residence time in the 1.5 m burner.

In-situ fabrication of lightweight SiC(Al, rGO) bulk ceramics derived from silicon oxycarbide for aerospace components

Abstract An ingenious strategy to prepare in-situ formed SiC(Al, rGO) bulk polymer-derived ceramics (PDCs) from re-pyrolyzing SiC(Al, rGO)p/polyaluminocarbosilane-vinyltriethoxysilane-graphene oxide (PACS-VTES-GO, PAVG) blends is highlighted. Flexible PAVG modified by Al with highly cross-linked structure effectively improves molecular weight and formability of precursors. Rigid SiC(Al, rGO)p fillers provide high mechanical properties owing to their unique microstructure which is consistent with SiC(Al, rGO) bulk PDCs. β-SiC nanocrystals are well dispersed in amorphous SiOxCy/Cfree, and rGO exhibits good compatibility with SiOxCy/Cfree. Besides, possible Al2O3 is beneficial to relaxing thermal stress at β-SiC nanocrystalline boundaries. Interestingly, introduction of Al could avoid coarsening of β-SiC grains to enhance elevated temperature resistance. Furthermore, effect of re-pyrolysis temperature on the formation and microstructure of SiC(Al, rGO) bulk PDCs was also investigated. Particularly, lightweight samples re-pyrolyzed at 1300 °C display optimal fracture toughness (3.32 MPa m1/2), compressive strength (177.16 MPa) and flexural strength (51.25 MPa), high ceramic yield (94.46%) and low linear shrinkage (4.38%), by far superior to those of most PDCs. As treated via precursor infiltration and pyrolysis (PIP) route and heated by butane gun flame in air, such products possess stable structures under elevated temperatures and have potential emerging uses in aerospace components.

Modelling laminar diffusion flames using a fast convergence three-dimensional CVFEM code

Laminar diffusion flames have been employed extensively to investigate the effects of physical and chemical-related parameters on combustion phenomena. Attention has been given to improve combustion models while keeping the two-dimensional (2D) axisymmetric approach and simplified boundary conditions. The flow structure due to the discrete jet nature of the reactants claims a more realistic inlet boundary condition for the burner plate which can only be accomplished if the solution domain is 3D. In this work, we present a novel 3D simulation code for the analysis of non-premixed laminar flames of methane and air, considering detailed inlet boundary conditions. The code is based on the control volume finite element method, written in MATLAB environment. To accomplish that a novel flow-oriented upwind scheme was implemented for the advection terms of the conservation equations. Combustion modelling can be carried out by either an enhanced flame sheet model in which an enthalpy equation is integrated in combination with the mixture fraction equation or detailed reaction schemes. Radiative heat losses were accounted for in the added energy equation. Three-dimensional numerical predictions, based on the flame sheet model, were able to simulate the near-wall gas temperature and inflow velocity field of a set of perforated plate burner with different porosities. It was found that the discrete nature of the injection of fuel and oxidiser, inflow boundary condition, plays a significant role on flame shape and length. Much better agreement between published experimental data and numerical predictions was obtained, particularly regarding flame structure, species mass fractions and temperature distribution of non-premixed laminar flames regardless of the adopted simplified combustion model. It was observed that flame length decreased as the burner porosity increased, up to a certain limit. The modified flow-oriented scheme greatly improved solution stability and computational time of the reacting system predictions.

Numerical Study on the Route of Flame-Induced Thermoacoustic Instability in a Rijke Burner

The self-excited thermoacoustic instability in a two-dimensional Rijke-type burner with a center-stabilized premixed methane–air flame is numerically studied. The simulation considers the reacting flow, flame dynamics, and radiation model to investigate the important physical processes. A finite volume-based approach is used to simulate reacting flows under both laminar and turbulent flow conditions. Chemical reaction modeling is conducted via the finite-rate/eddy dissipation model with one-step reaction mechanisms, and the radiation heat flux and turbulent flow characteristics are determined by using the P-1 model and the standard k-ε model, respectively. The steady-state reacting flow is first simulated for model verification. Then, the dynamic pressure, velocity, and reaction heat evolutions are determined to show the onset and growth rate of self-excited instability in the burner. Using the fast Fourier transform (FFT) method, the frequency of the limit cycle oscillation is obtained, which agrees well with the theoretical prediction. The dynamic pressure and velocity along the tube axis provide the acoustic oscillation mode and amplitude, also agreeing well with the prediction. Finally, the unsteady flow field at different times in a limit cycle shows that flame-induced vortices occur inside the combustor, and the temperature distribution indicates that the back-and-forth velocity changes in the tube vary the distance between the flame and honeycomb in turn, forming a forward feedback loop in the tube. The results reveal the route of flame-induced thermoacoustic instability in the Rijke-type burner and indicate periodical vortex formation and breakdown in the Rijke burner, which should be considered turbulent flow under thermoacoustic instability.