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Showing papers on "Diffusion flame published in 2019"


Journal ArticleDOI
TL;DR: A comprehensive review of the researches on various aspects of soot formation utilizing counterflow flames is provided in this paper, with focus on the most recent (post-2010) research progress.

276 citations


Journal ArticleDOI
08 Mar 2019-Energies
TL;DR: In this article, the evolution of in-flame soot species in a slow speed, buoyancy-driven diffusion flame is thoroughly studied with the implementation of the population balance approach in association with computational fluid dynamics (CFD) techniques.
Abstract: In this article, the evolution of in-flame soot species in a slow speed, buoyancy-driven diffusion flame is thoroughly studied with the implementation of the population balance approach in association with computational fluid dynamics (CFD) techniques. This model incorporates interactive fire phenomena, including combustion, radiation, turbulent mixing, and all key chemical and physical formation and destruction processes, such as particle inception, surface growth, oxidation, and aggregation. The in-house length-based Direct Quadrature Method of Moments (DQMOM) soot model is fully coupled with all essential fire sub-modelling components and it is specifically constructed for low-speed flames. Additionally, to better describe the combustion process of the parental fuel, ethylene, the strained laminar flamelet model, which considers detailed chemical reaction mechanisms, is adopted. Numerical simulation is validated against a self-conducted co-flow slot burner experimental measurement. A comprehensive assessment of the effect of adopting different nucleation laws, oxidation laws, and various fractal dimension and diffusivity values is performed. The results suggest the model employing Moss law of nucleation, modified NSC law of oxidation, and adopting a fractal dimension value of 2.0 and Schmidt number of 0.9 yields the simulation result that best agreed with experimental data.

150 citations


Journal ArticleDOI
01 Jan 2019-Carbon
TL;DR: In this article, the internal structure of a coflow diffusion flame was studied using high-resolution transmission electron microscopy, and the radial distribution of fringes within the particles was calculated from the fringe lengths, assuming planar peri-condensed PAHs.

89 citations


Journal ArticleDOI
01 Jan 2019-Energy
TL;DR: In this article, the characteristics of soot in the diffusion flames of methane and ethylene under different oxygen concentrations and the influence of mixing methane in ethylene on soot generation were investigated using thermophoretic sampling and subsequent transmission electron microscopy image analysis.

84 citations


Journal ArticleDOI
TL;DR: This work aims to combine the state-of-the-art experimental technique (that is, time-resolved volumetric tomography) with deep learning algorithms for rapid prediction of 3-D flame evolution, and believes this is the first time that online in situ prediction of3-D Flame evolution has become feasible.
Abstract: Online in situ prediction of 3-D flame evolution has been long desired and is considered to be the Holy Grail for the combustion community. Recent advances in computational power have facilitated the development of computational fluid dynamics (CFD), which can be used to predict flame behaviours. However, the most advanced CFD techniques are still incapable of realizing online in situ prediction of practical flames due to the enormous computational costs involved. In this work, we aim to combine the state-of-the-art experimental technique (that is, time-resolved volumetric tomography) with deep learning algorithms for rapid prediction of 3-D flame evolution. Proof-of-concept experiments conducted suggest that the evolution of both a laminar diffusion flame and a typical non-premixed turbulent swirl-stabilized flame can be predicted faithfully in a time scale on the order of milliseconds, which can be further reduced by simply using a few more GPUs. We believe this is the first time that online in situ prediction of 3-D flame evolution has become feasible, and we expect this method to be extremely useful, as for most application scenarios the online in situ prediction of even the large-scale flame features are already useful for an effective flame control.

66 citations


Journal ArticleDOI
TL;DR: Experimental evidence supporting the existence of PAH dimers in the proximity of the soot nucleation region of a methane laminar diffusion flame that gives strong evidence for the nucleation process to be kinetically rather than thermodynamically controlled is reported.
Abstract: The soot nucleation process, defined as the transition from molecular precursors to condensed matter, is the less understood step in the whole soot formation process. The possibility that polycyclic aromatic hydrocarbon (PAH) dimers, especially those containing moderate-sized PAHs, can play a major role in soot nucleation is a very controversial issue. Although PAH dimers have often been considered as potential soot precursors, their formation is not thermodynamically favored at a typical flame temperature, their binding energies being considered too weak to allow them to survive in this environment. Hereby, we report experimental evidence supporting the existence of PAH dimers in the proximity of the soot nucleation region of a methane laminar diffusion flame that gives strong evidence for the nucleation process to be kinetically rather than thermodynamically controlled.

63 citations


Journal ArticleDOI
01 Jan 2019
TL;DR: In this paper, the authors used a perforated plate to collect gases and aerosols ejected from the cell, reduce their flow speed and deliver them to a hot-wire igniter, which was used to initiate a diffusion flame.
Abstract: Lithium ion batteries (LIBs) are efficient, high-density electrical energy storage devices utilized in a perpetually increasing range of applications. One of the weaknesses of LIBs is that a small deviation from the normal operating conditions may cause an irreversible failure accompanied by a rapid self-heating and ejection of combustible gases and aerosols. The information on how much energy is released upon failure is critical for design of energy storage systems. In the current study, a novel technique, Copper Slug Battery Calorimetry (CSBC), was combined with oxygen consumption calorimetry to measure the rate of heat generated inside an LIB cell (PIHG) and the rate of heat generated as a result of combustion of ejected battery materials (PFlaming). A short duct equipped with a perforated plate was added to the original design of the CSBC apparatus to collect gases and aerosols ejected from the cell, reduce their flow speed and deliver them to a hot-wire igniter, which was used to initiate a diffusion flame. The exhaust from this flame was collected to measure the oxygen consumed in the combustion process and compute PFlaming. This approach to handling the ejected materials increased their combustion efficiency and eliminated thermal feedback from the flame to the cell, which enabled simultaneous measurement of PIHG and PFlaming. The new setup was employed to investigate thermally induced failure of an 1880 mA h prismatic LIB at various states of charge (SOC). It was determined that, at 100% SOC, this LIB released 33 ± 1.0 kJ of energy into the body of the cell and 113 ± 19 kJ was produced as a result of combustion of the ejected battery materials. The latter value is significantly greater than those previously reported for similarly sized cells, which can be explained by a more complete combustion achieved in this new apparatus.

61 citations


Journal ArticleDOI
01 Jan 2019
TL;DR: In this paper, the evolution of primary soot particles along the centreline of a co-flow laminar diffusion flame is studied experimentally and numerically along the centerline.
Abstract: The evolution of primary soot particles is studied experimentally and numerically along the centreline of a co-flow laminar diffusion flame Soot samples from a flame fueled with C2H4 are taken thermophoretically at different heights above the burner (HAB), their size and nano-structure are analysed through TEM The experimental results suggest that after inception, the nascent soot particles coagulate and coalesce to form larger primary particles ( ∼ 5 to 15 nm) As these primary particles travel along the centreline, they grow mainly due coagulation and condensation and a layer of amorphous hydrocarbons (revealed by HRTEM) forms on their surface This amorphous layer appears to promote the aggregation of primary particles to form fractal structures Fast carbonisation of the amorphous layer leads to a graphitic-like shell around the particles Further graphitization compacts the primary particles, resulting in a decrease of their size Towards the flame tip the primary particles decrease in size due to rapid oxidation A detailed population balance model is used to investigate the mechanisms that are important for prediction of primary particle size distributions Suggestions are made regarding future model development efforts Simulation results indicate that the primary particle size distributions are very sensitive to the parameterization of the coalescence and particle rounding processes In contrast, the average primary particle size is less sensitive to these parameters This demonstrates that achieving good predictions for the average primary particle size does not necessarily mean that the distribution has been accurately predicted

43 citations


Journal ArticleDOI
TL;DR: In this article, the characterization of a prototype miniCAST generator (5201 Type BC), which was designed to decouple the soot composition from the particle size and produce soot particles with high elemental carbon (EC) and BC content in a large size range, was reported.
Abstract: Flame-generated soot from miniCAST burners is increasingly being used in academia and industry as engine exhaust soot surrogate for atmospheric studies and instrument calibration. Previous studies have found that elemental carbon (EC) content of miniCAST soot is proportional to the mean particle size. Here, the characterization of a prototype miniCAST generator (5201 Type BC), which was designed to decouple the soot composition from the particle size and produce soot particles with high EC and BC content in a large size range, is reported. This prototype may operate either in a diffusion-flame or a partially premixed-flame mode, an option that was not available in former models. It was confirmed that soot properties, such as EC content and Angstrom absorption exponent (AAE), were linked to the overall flame composition. In particular, combustion under fuel-rich conditions provided particles with size coupled to the EC fraction and AAE, i.e. smaller particles exhibited a lower EC fraction and highe...

40 citations


Journal ArticleDOI
TL;DR: In this paper, a comprehensive analysis has been performed on a n-dodecane doped methane coflow diffusion flame, where PAHs have been analyzed with GC/MS while the particulates have been collected from the flame centreline for studying under a Transmission Electron Microscope (TEM).

34 citations


Journal ArticleDOI
TL;DR: The developed FLiPPID methodology can be applied to numerous other optical techniques for which smooth inverse Abel transforms are required, and is illustrated by calculating the soot temperature and volume fraction profiles inside a co-flow diffusion flame, both being significantly smoother than those produced by the alternative inversion methods.
Abstract: A new method is presented for performing the Abel inversion by fitting the line-of-sight projection of a predefined intensity distribution (FLiPPID) to the recorded 2D projections. The aim is to develop a methodology that is less prone to experimental noise when analyzing the projection of axisymmetric objects—in this case, co-flow diffusion flame images for color ratio pyrometry. A regression model is chosen for the light emission intensity distribution of the flame cross section as a function of radial distance from the flame center line. The forward Abel transform of this model function is fitted to the projected light intensity recorded by a color camera. For each of the three color channels, the model function requires three fitting parameters to match the radial intensity profile at each height above the burner. This results in a very smooth Abel inversion with no artifacts such as oscillations or negative values of the light source intensity, as is commonly observed for alternative Abel inversion techniques, such as the basis-set expansion or onion peeling. The advantages of the new FLiPPID method are illustrated by calculating the soot temperature and volume fraction profiles inside a co-flow diffusion flame, both being significantly smoother than those produced by the alternative inversion methods. The developed FLiPPID methodology can be applied to numerous other optical techniques for which smooth inverse Abel transforms are required.

Journal ArticleDOI
TL;DR: In this paper, the effect of oxygen concentrations on the formation and evolution of soot particles was investigated by analyzing soot morphology using SiC fiber deposition technique and thermophoretic sampling method in a co-flow diffusion ethylene flame.
Abstract: The effect of oxygen concentrations on the formation and evolution of soot particles was investigated by analyzing soot morphology using SiC fiber deposition technique and thermophoretic sampling method in a co-flow diffusion ethylene flame. Soot particles were examined via transmission electron microscopy at different heights along the flame centerline. Results show that the flame temperature exhibits a bimodal distribution. As the flame height increases, the flame distribution gradually changes from bimodal to unimodal, and the increase in oxygen concentration not only causes the flame height to decrease, but also causes the bimodal distribution of the flame more pronounced. The morphological evolution of soot deposits are strongly dependent on the oxygen concentration, radial and axial position, and flame temperature. Soot deposits along the flame centerline begin to be oxidized into dense flocculent and fibrous mesh structures with the flame temperature increases. In front of the flame, the oxidation is enhanced with temperature rise at the same height, resulting in more dense morphology of the soot deposits and the decrease in primary particle size. The results of thermophoretic sampling show that soot growth undergoes various stages of nucleation, growth, coagulation, agglomeration and oxidation, and the average particle size distributions of soot increase first and then decrease. The increase in oxygen concentration leads to advances in all stages of soot formation, including surface growth, agglomeration and oxidation. Additionally, the flame temperatures increase sharply as the increase of flame heights, leading to the soot aggregates to be oxidized to loose chain-like agglomerates.

Journal ArticleDOI
TL;DR: In this article, a combined extinction and radiation methodology has been developed with different wavelengths and applied on quasi-steady Diesel flame to obtain the soot amount and temperature distribution simultaneously by considering self-absorption issues.

Journal ArticleDOI
21 May 2019-Chaos
TL;DR: It is shown that a liquid-fueled diffusion-flame combustor can exhibit dynamics as complex as those of its gaseous- fueled premixed-flame counterparts and the need to be exceptionally careful when selecting a diagnostic signal from which to calculate nonlinear measures of self-excited thermoacoustic oscillations is highlighted.
Abstract: We experimentally investigate the nonlinear dynamics of a thermoacoustically self-excited aero-engine combustion system featuring a turbulent swirling liquid-fueled diffusion flame in a variable-length combustor. We focus on the steady-state dynamics via simultaneous measurements of the acoustic pressure in the combustor and the heat release rate (HRR) from the flame. When the combustor length is increased following the onset of thermoacoustic instability, we find that the pressure signal transitions from a period-1 limit cycle to chaos, whereas the HRR signal remains chaotic owing to the presence of an intrinsic hydrodynamic mode in the flame. When the hydrodynamic mode is filtered out of the data, we find that the pressure and HRR signals are in generalized synchronization. However, when the hydrodynamic mode is retained in the data, we find that the pressure and HRR signals are either weakly phase synchronized or desynchronized. This study has two main contributions: (i) it shows that a liquid-fueled diffusion-flame combustor can exhibit dynamics as complex as those of its gaseous-fueled premixed-flame counterparts and (ii) it highlights the need to be exceptionally careful when selecting a diagnostic signal from which to calculate nonlinear measures of self-excited thermoacoustic oscillations, because our experiments show that the pressure and HRR signals can be desynchronized by the presence of a hydrodynamic mode in the flame at a frequency different from that of the dominant thermoacoustic mode.

Journal ArticleDOI
01 Jan 2019
TL;DR: In this paper, a simple kinematic balance is shown to predict the shape of the front and the propagation velocity reasonably well in the limit of low stretch and low curvature, when the stoichiometric mixture fraction departs appreciably from 1/2, one of the premixed wings is dominant to such an extent that the diffusion flame and the other premixed flame are very weak by comparison.
Abstract: Most studies of triple flames in counterflowing streams of fuel and oxidizer have been focused on the symmetric problem in which the stoichiometric mixture fraction is 1/2. There then exist lean and rich premixed flames of roughly equal strengths, with a diffusion flame trailing behind from the stoichiometric point at which they meet. In the majority of realistic situations, however, the stoichiometric mixture fraction departs appreciably from unity, typically being quite small. With the objective of clarifying the influences of stoichiometry, attention is focused on one of the simplest possible models, addressed here mainly by numerical integration. When the stoichiometric mixture fraction departs appreciably from 1/2, one of the premixed wings is found to be dominant to such an extent that the diffusion flame and the other premixed flame are very weak by comparison. These curved, partially premixed flames are expected to be relevant in realistic configurations. In addition, a simple kinematic balance is shown to predict the shape of the front and the propagation velocity reasonably well in the limit of low stretch and low curvature.

Journal ArticleDOI
TL;DR: In this article, a study of ignition dynamics in a turbulent DME/methane-air mixture under reactivity controlled compression ignition (RCCI) conditions was conducted using direct numerical simulation.

Journal ArticleDOI
01 Jan 2019
TL;DR: In this paper, the role of initial momentum and buoyancy on flame length is quantitatively described by a modified Froude number Frm, and an approximate predictive correlation of flame length was derived based on the governing equations.
Abstract: This work presents a modeling and experimental analysis on the flame length of buoyant turbulent slot diffusion flame. An approximate predictive correlation of flame length is derived based on the governing equations. The role of initial momentum and buoyancy on flame length is quantitatively described by a modified Froude number Frm. The physical model indicates that the flame length of a turbulent slot flame is proportional to (Frm)1/3 and (Frm)0 respectively when the flame is buoyancy-dominated and momentum-dominated. The results, for the first time, give a physical verification on the previous scaling laws on buoyant turbulent slot flame in literature. Slot flame tests are conducted using two burners (for which the width W and length L are respectively 0.9 mm × 20.5 mm and 5.5 mm × 86 mm) and four kinds of high-purity hydrocarbon gas fuels (methane, acetylene, ethane and propane). Experimental data show that the radial temperature profiles of buoyant turbulent slot flames can be well described by a Gaussian function normalized by the temperature radius, which is independent of axial position and flame scale. Moreover, experimental data verify that the physical model applies for different fuel supply rates, types of fuels and flame scales. Additionally, the results indicate that the turbulent slot flame is buoyancy-dominated when Frm 107. Finally, it is indicated that the scale effect of turbulent slot flame is closely associated with the flame temperature under different flame scales.

Journal ArticleDOI
22 Feb 2019-Fuel
TL;DR: It is proposed that due to the spheroidal shape of the large primary particles, the secondary surface growth is primarily a result of polyaromatic hydrocarbon (PAH) condensation during re-entrainment of mature soot into the fuel-rich region followed by subsequent liquid layer carbonization in the high-temperature environment of the flame front.

Journal ArticleDOI
TL;DR: In this article, the influence of hydrogen addition on appearance of swirling and non-swirling inverse diffusion flame (IDF) along with emissions characteristics are investigated experimentally, and the combustion characteristics including flame length, axial and radial temperature variation, and noise level are analyzed for hydrogen addition in methane by mass basis for constant energy input and by volume basis for a constant volumetric fuel flow rate.

Journal ArticleDOI
TL;DR: In this paper, the chemical structure effects of alkylbenzenes (1,2,4-trimethylbenzene (124TMB) and n-propylbenzenes (PBZ)) on soot formation in a laminar diffusion flame were experimentally and numerically investigated.

Journal ArticleDOI
01 Aug 2019-Carbon
TL;DR: In this article, the temporal and spatial dependence of soot precursors growth mechanisms in an ethylene/oxygen/argon counterflow diffusion flame is investigated. But the results in this paper highlight the importance of modeling counterflow flames in two or three dimensions.

Journal ArticleDOI
TL;DR: In this paper, the authors employed a linear global stability analysis to investigate buoyancy-induced flickering of axisymmetric laminar jet diffusion flames as a hydrodynamic global mode.
Abstract: The present study employs a linear global stability analysis to investigate buoyancy-induced flickering of axisymmetric laminar jet diffusion flames as a hydrodynamic global mode. The instability-driving interactions of the buoyancy force with the density differences induced by the chemical heat release are described in the infinitely fast reaction limit for unity Lewis numbers of the reactants. The analysis determines the critical conditions at the onset of the linear global instability as well as the Strouhal number of the associated oscillations in terms of the governing parameters of the problem. Marginal instability boundaries are delineated in the Froude-number/Reynolds-number plane for different fuel-jet dilutions. The results of the global stability analysis are compared with direct numerical simulations of time-dependent axisymmetric jet flames and also with results of a local spatio-temporal stability analysis.

Journal ArticleDOI
TL;DR: In this paper, the effects of blending dimethyl ether (DME) and hydrogen (H2) with methane (CH4) have been numerically studied in the context of counterflow diffusion flames, and a reaction mechanism consisting of 974 reaction steps among 146 species with updated thermodynamic and transport properties has been developed.

Journal ArticleDOI
01 Jan 2019
TL;DR: In this paper, the authors used the computational fluid dynamics-discrete element method (CFD-DEM) model of compressible flow to numerically investigate the flame structure during shock-wave-induced coal-dust combustion, which poses a significant risk in coal mines.
Abstract: We used the computational fluid dynamics–discrete element method (CFD–DEM) model of compressible flow to numerically investigate the flame structure during shock-wave-induced layered coal-dust combustion, which poses a significant risk in coal mines. This represents the first attempt to apply a CFD–DEM model to compressible reactive gas–particle flow. The Eulerian–Lagrangian model for compressible gas–particle flow was extended to simulate shock–particle interactions in a reactive flow field. The particle interactions were predicted by the DEM, and source terms for homogeneous and heterogeneous reactions were included in the governing equations. The calculations were validated for inert particle dispersion from shock–particle interactions and flame propagation velocity in layered coal-dust combustion. The results were consistent with those from previous experiments. Furthermore, the flame structure in layered coal-dust combustion was revealed using the CFD–DEM approach. The simulation of the layered coal-dust combustion indicated that the shock wave was initially generated by gas detonation in a narrow channel with coal-dust particles at the bottom. The predicted propagation mechanism during layered coal-dust combustion was consistent with that reported in a previous numerical study based on the Eulerian–Eulerian approach (Hoium et al., 2015). Moreover, the flame comprised a leading shock wave and diffusion flame; the coal-dust particles were dispersed and heated by the shock wave and combustion products, respectively. The diffusion flame structure propagated at 350–500 m/s, resulting in devolatilization behind the reaction front. However, the CFD–DEM results indicated that the particle dispersion heights were higher than those predicted by the Eulerian–Eulerian approach (despite similarities in the inert particle dispersion results of these methods), attenuating the compression wave from the reaction front and slowing the leading shock wave.

Journal ArticleDOI
15 Apr 2019-Fuel
TL;DR: In this article, the effect of preheated oxyfuel combustion with fuel and/or oxygen preheating was evaluated at laboratory-scale (25kW) using a tri-coaxial burner generating a non-premixed turbulent BFG-O2 flame.

Journal ArticleDOI
01 Jan 2019
TL;DR: In this paper, a combined use of Modulated Absorption/Emission (MAE) and Laser Induced Incandescence (LII) techniques is presented in order to identify and quantify sources of experimental errors and to extend the existing database for the Yale laminar diffusion burner flame.
Abstract: Control of soot emission raises fundamental issues and has important practical implications requiring a full understanding of soot production and oxidation processes. The research reported in the present paper intends to contribute to the studies carried out within the frame of the International Sooting Flame workshop (ISF) on laminar sooting flames. The objective is to identify and quantify sources of experimental errors and to extend the existing database for the Yale laminar diffusion burner flame. This will especially enable more comprehensive comparisons among different experimental techniques and numerical simulations. To this end, a combined use of Modulated Absorption/Emission (MAE) and Laser Induced Incandescence (LII) techniques is presented in this work. Results are compared with already existing experimental data in terms of soot volume fraction, soot temperature and primary particle size distribution, highlighting the high variability of the experimental data depending on the measurement techniques as well as the underlying assumptions and post-processing methods. These complementary original data may serve to guide the validation of numerical modeling in this configuration.

Journal ArticleDOI
TL;DR: In this paper, the thermodynamic properties of flame-street were investigated using a reaction flow solver based on the OpenFOAM framework, and it was found that the flame street can be established only at a moderate level of heat loss to the wall, which would result in either a single short edge flame or a long continuous edge flame.

Journal ArticleDOI
01 Jan 2019
TL;DR: In this article, an analysis of the mechanisms of autoignition-controlled flame initiation and flame stabilization in a non-premixed jet in crossflows, using simultaneous high-speed tomographic particle image velocimetry, OH-PLIF and line-of-sight flame emissions, is presented.
Abstract: This paper describes an analysis of the mechanisms of autoignition-controlled flame initiation and flame stabilization in a nonpremixed jet in crossflows, using simultaneous high-speed (10 kHz) tomographic particle image velocimetry, OH-PLIF and line-of-sight flame emissions. Measurements are conducted on a turbulent, transverse, reacting propane jet issued into a crossflow generated by combustion of natural gas at an equivalence ratio of 0.4 with the crossflow velocity of 10 m/s, the crossflow temperature of 1350 K and the jet momentum flux ratio of 41. While several prior studies have analyzed the lifted character of the flame in similar configurations, we show that several dynamic processes precede the leading edge of the lifted diffusion flame, including formation and evolution of “autoignition kernels”, “flame kernels” and “flame fragments”. “Autoignition kernels”, i.e., discrete compact reaction zones with the peak hydroxyl (OH) fluorescence intensity below that of the diffusion flame, initiate preferably at bulges along the jet periphery where the strain rates and the scalar dissipation rates are lower. The autoignition kernel grows in both size and the OH-fluorescence intensity as it convects downstream. An autoignition kernel transitions into a propagating flame kernel, which quickly gets distorted and elongated in the direction of the principal expansion strain rate to form a flame fragment. Neighboring flame fragments merge with each other and with the downstream diffusion flame via edge-flame propagation. Merging of upstream flame fragments with the downstream diffusion flame results in an upstream advancement of the diffusion-flame front. The diffusion flame front is intrinsically unsteady because of the rather random formation and evolution of autoignition kernels, flame kernels and flame fragments, presumably due to the stochastic velocity, the strain rate and mixture-fraction oscillations.

Journal ArticleDOI
TL;DR: In this article, the authors demonstrate feasibility of enhancing the flame control authority, by combining a high peak ionization fraction generated by a ns pulse discharge with the electrohydrodynamic (EHD) force applied on a long time scale, using a single plasma generator.

Journal ArticleDOI
01 Jan 2019
TL;DR: The near-limit diffusion flame regimes and extinction limits of dimethyl ether at elevated pressures and temperatures are examined numerically in the counterflow geometry with and without radiation at different oxygen concentrations.
Abstract: The near-limit diffusion flame regimes and extinction limits of dimethyl ether at elevated pressures and temperatures are examined numerically in the counterflow geometry with and without radiation at different oxygen concentrations. It is found that there are three different flame regimes—hot flame, warm flame, and cool flame—which exist, respectively, at high, intermediate, and low temperatures. Furthermore, they are governed by three distinct chain-branching reaction pathways. The results demonstrate that the warm flame has a double reaction zone structure and plays a critical role in the transition between cool and hot flames. It is also shown that the cool flame can be formed in several different ways: by either radiative extinction or stretch extinction of a hot flame or by stretch extinction of a warm flame. A warm flame can also be formed by radiative extinction of a hot flame or ignition of a cool flame. A general €-shaped flammability diagram showing the burning limits of all three flame regimes at different oxygen mole fractions is obtained. The results show that thermal radiation, reactant concentration, temperature, and pressure all have significant impacts on the flammable regions of the three flame regimes. Increases in oxidizer temperature, oxygen concentration, and pressure shift the cool flame regime to higher stretch rates and cause the warm flame to have two extinction limits. At elevated temperatures, it is found that there is a direct transition between the hot flame and warm flame at low stretch rates. The results also show that, unlike the hot flame, the cool flame structure cannot be scaled by using pressure-weighted stretch rates due to the its significant reactant leakage and strong dependence of reactivity on pressure. The present results advance the understanding of near-limit flame dynamics and provide guidance for experimental observation of different flame regimes.