Showing papers on "Premixed flame published in 2016"
TL;DR: In this article, the transition from CH4/H2 mixtures to periodic oscillations was investigated under acoustically coupled and uncoupled conditions in a 50kW swirl stabilized combustor.
141 citations
TL;DR: In this paper, the authors investigate spray flames at three different ambient oxygen levels in engine relevant conditions using the Large Eddy Simulation (LES) and the flamelet generated manifold (FGM) methods.
118 citations
TL;DR: In this article, a CFD study on fundamental flame characteristics of premixed H2-air combustion in a planar porous micro-combustor is carried out, where the effects of flow conditions and properties of the porous medium on the wall temperature, species concentration, flame temperature, flame location, and flame speed are examined individually.
112 citations
TL;DR: In this article, a multiscale model was developed in conjunction with Schlieren photography to measure laminar burning speeds and to investigate flame structures of H2/CO/air mixtures.
92 citations
TL;DR: In this paper, the effect of the plate length on the blowout limit of CH4/air flames was numerically investigated, and it was shown that the flame blowout threshold increases firstly and then decreases with an increasing plate length.
91 citations
TL;DR: In this paper, a series of direct numerical simulations (DNS) of premixed n-heptane/air flames, modeled with a 35-species finite-rate chemical mechanism, whose conditions span a wide range of unburnt Karlovitz numbers and flame density ratios.
Abstract: To better understand the two-way coupling between turbulence and chemistry, the changes in turbulence characteristics through a premixed flame are investigated. Specifically, this study focuses on vorticity, ω, which is characteristic of the smallest length and time scales of turbulence, analyzing its behavior within and across high Karlovitz number (Ka) premixed flames. This is accomplished through a series of direct numerical simulations (DNS) of premixed n-heptane/air flames, modeled with a 35-species finite-rate chemical mechanism, whose conditions span a wide range of unburnt Karlovitz numbers and flame density ratios. The behavior of the terms in the enstrophy, ω^2 = ω ⋅ ω, transport equation is analyzed, and a scaling is proposed for each term. The resulting normalized enstrophy transport equation involves only a small set of parameters. Specifically, the theoretical analysis and DNS results support that, at high Karlovitz number, enstrophy transport obtains a balance of the viscous dissipation and production/vortex stretching terms. It is shown that, as a result, vorticity scales in the same manner as in homogeneous, isotropic turbulence within and across the flame, namely, scaling with the inverse of the Kolmogorov time scale, τ_η. As τ_η is a function only of the viscosity and dissipation rate, this work supports the validity of Kolmogorov’s first similarity hypothesis in premixed turbulentflames for sufficiently high Ka numbers. Results are unaffected by the transport model, chemical model, turbulent Reynolds number, and finally the physical configuration.
90 citations
TL;DR: In this paper, the authors investigated the mechanism underlying the flame transition to the ORZ/OSL and proposed a criterion for its occurrence, in an acoustically uncoupled combustion system.
88 citations
TL;DR: In this paper, a 1D planar premixed cool flame induced by a hot pocket is simulated for DME/O2/N2 mixtures with detailed chemistry and transport, demonstrating the existence of a residence time window for quasi-steady propagation.
84 citations
TL;DR: In this paper, the authors used the transported probability density function (TPDF) method to model the combustion of an n-dodecane spray in a high pressure, high temperature chamber, known as Spray A, using data resulting from modelling using the TPDF.
81 citations
TL;DR: In this paper, self-sustaining premixed cool flames are successfully stabilized in a dimethyl ether/oxygen counterflow burner through ozone addition, creating a new platform for the quantitative measurement of cool flame extinction limits, ignition limits, and structure as well as validation of low-temperature chemical kinetic models.
80 citations
TL;DR: In this article, the effects of inlet velocity, equivalence ratio, and channel width on amplitude and frequency of the repetitive extinction-ignition phenomenon were investigated numerically for hydrogen-air mixtures in a heated micro channel.
TL;DR: In this paper, an experimental study on the self-acceleration characteristics and laminar flame speed of CO/H2/air mixtures was conducted at elevated pressures up to 0.6 MPa with spherical outwardly expanding flames.
TL;DR: In this article, a review of the constant-volume propagating spherical flame method for laminar flame speed measurement is presented, where the authors discuss the sources of discrepancies in the results obtained by different groups for the same mixture.
Abstract: Laminar flame speed is one of the most important intrinsic properties of a combustible mixture. Due to its importance, different methods have been developed to measure the laminar flame speed. This paper reviews the constant-volume propagating spherical flame method for laminar flame speed measurement. This method can be used to measure laminar flame speed at high pressures and temperatures which are close to engine-relevant conditions. First, the propagating spherical flame method is introduced and the constant-volume method (CVM) and constant-pressure method (CPM) are compared. Then, main groups using the constant-volume propagating spherical flame method are introduced and large discrepancies in laminar flame speeds measured by different groups for the same mixture are identified. The sources of discrepancies in laminar flame speed measured by CVM are discussed and special attention is devoted to the error encountered in data processing. Different correlations among burned mass fraction, pressure, temperature and flame speed, which are used by different researchers to obtain laminar flame speed, are summarized. The performance of these correlations are examined, based on which recommendations are given. Finally, recommendations for future studies on the constant-volume propagating spherical flame method for laminar flame speed measurement are presented.
TL;DR: In this article, the exact solution for the problem of condensed material surface burning in a flow of oxidant in the case of steady flame over fuel layer is presented within the frame of assumption of fuel gasification and gas phase chemical reacting in a diffusion flame.
TL;DR: In this paper, multivariate linear regression methods have been applied to investigate the sensitivities of pre-vaporized global combustion behaviors to individual combustion property targets of the fuels, including Derived Cetane Number (DCN), H/C ratio, mean molecular weight, and smoke point.
TL;DR: It is shown that advective processes in premixed reacting flows contribute to energy backscatter near the scale of the flame, unlike the net down-scale transfer of energy found in the unburnt reactants.
Abstract: Spectral kinetic energy transfer by advective processes in turbulent premixed reacting flows is examined using data from a direct numerical simulation of a statistically planar turbulent premixed flame. Two-dimensional turbulence kinetic-energy spectra conditioned on the planar-averaged reactant mass fraction are computed through the flame brush and variations in the spectra are connected to terms in the spectral kinetic energy transport equation. Conditional kinetic energy spectra show that turbulent small-scale motions are suppressed in the burnt combustion products, while the energy content of the mean flow increases. An analysis of spectral kinetic energy transfer further indicates that, contrary to the net down-scale transfer of energy found in the unburnt reactants, advective processes transfer energy from small to large scales in the flame brush close to the products. Triadic interactions calculated through the flame brush show that this net up-scale transfer of energy occurs primarily at spatial scales near the laminar flame thermal width. The present results thus indicate that advective processes in premixed reacting flows contribute to energy backscatter near the scale of the flame.
TL;DR: In this paper, the lift-off mechanism of swirl stabilized premixed flames was investigated using high repetition rate OH planar laser induced fluorescence (PLIF), particle image velocimetry (PIV), and OH * chemiluminescence.
TL;DR: In this paper, the effects of hydrogen and carbon monoxide addition on premixed methane/air flame dynamics in a heated narrow channel are numerically investigated using a time accurate, compressible flow solver along with the DRM-19 reaction mechanism.
TL;DR: In this article, a simulation of turbulent premixed flames at high Karlovitz numbers is performed using detailed chemistry and their effects on turbulent flame speed, geometry of the reaction zone, and fuel burning rate are analyzed.
TL;DR: In this article, the authors show that the model of a flame at rest can misrepresent the generation of entropy waves, and how it leads to paradoxical results concerning the conservation of mass and volume flow rates across the flame.
TL;DR: In this article, a system of non-premixed liquid fuel flames supported on a wick-fed, smoke point test burner (ASTM D1322-08) was characterized by in-situ visible light extinction and thermophoretically-sampled high-resolution transmission electron microscopy measurements, HRTEM.
TL;DR: In this article, an analytical expression for the local displacement flame speed (S d ) of a temperature isosurface is considered, and the contributions of transport, chemistry, and kinematics on the displacement flame speeds at different turbulence-flame interaction conditions are identified.
TL;DR: In this paper, a micro tubular channel with an external heating provided by three hydrogen/oxygen flames positioned at the downstream side of the tube was used for micro-combustion.
TL;DR: In this paper, the laminar flame speeds of gaseous CH4/air mixtures were investigated at elevated temperature and high pressure conditions in regards to the importance of this intermediate oxygenated molecule in hydrocarbon oxidation.
TL;DR: In this article, a mesoscale bluff-body combustor was developed, and the flame blow-off limits of CH 4 /air mixtures were experimentally obtained, which showed that the bluff body can effectively expand the flame stabilization limit.
TL;DR: In this article, a large eddy simulation (LES) was employed to study the flame stabilization process in a hydrogen fueled scramjet combustor with a rearwall-expansion cavity.
TL;DR: In this paper, the effects of premixing ratio (L/D) on lower and upper flammability limits over a range of oxidizer Reynolds number were investigated, and a set of experiments were performed considering air and oxy-combustion premixed flames stabilized over a perforated-plate burner.
TL;DR: In this article, the effect of synthetic exhaust gas recirculation (SEGR) as the diluent on flame structure and laminar burning speed was investigated in two constant volume spherical and cylindrical chambers.
TL;DR: In this paper, a volumetric velocity field in the vicinity of the flame front was reconstructed using high-speed chemiluminescence imaging, stereoscopic and tomographic particle image velocimetry, and a three-dimensional flame front reconstruction technique.
TL;DR: In this paper, a hybrid large-eddy / Reynolds-averaged Navier-Stokes simulations of turbulence/chemistry interactions occurring within a ramp-injected, hydrogen-fueled scramjet combustor are presented.