Showing papers on "Diffusion 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 morphology and nanostructure of soot particles as a function of fuel type in a laminar diffusion flame were studied, and an image analysis algorithm was developed to calculate the fringe length, tortuosity and inter-fringe spacing from HRTEM images.
135 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, the effects of adding hydrogen and carbon dioxide simultaneously to fuel on soot formation in an axisymmetric laminar coflow ethylene/air diffusion flame at atmospheric pressure were investigated.
114 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 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, a detailed kinetic model for DMC pyrolysis and high-temperature combustion consisting of 257 species and 1563 reactions was developed, and the performance of the kinetic model was then analyzed using detailed chemical composition information.
77 citations
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 article, the evolution of the nascent soot particle size distribution function (PSDF) was determined by mobility sizing for two series of atmospheric pressure premixed ethylene flames in the burner stabilized stagnation flame configuration.
TL;DR: In this paper, the authors evaluated the refractive index of soot generated by a miniCAST, an ethylene diffusion flame, and a PALAS GFG by interpreting specific extinction measurements in the near-UV spectrum with the help of an improved RDG-FA theory.
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: In this paper, a new model for condensation of polycyclic aromatic hydrocarbons (PAHs) on the surface of soot particles is developed based on the reversibility of the process.
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 paper, the validity and limitations of the constant non-unity Lewis number approach in the description of molecular mixing in laminar and turbulent flames are explored, and three test cases have been selected, including a lean, highly unstable, premixed hydrogen/air flame, a lean turbulent premixed n-heptane/air mixture flame, and a Laminar ethylene/air coflow diffusion flame.
Abstract: Accurate computation of molecular diffusion coefficients in chemically reacting flows can be an expensive procedure, and the use of constant non-unity Lewis numbers has been adopted often as a cheaper alternative. The goal of the current work is to explore the validity and the limitations of the constant non-unity Lewis number approach in the description of molecular mixing in laminar and turbulent flames. To carry out this analysis, three test cases have been selected, including a lean, highly unstable, premixed hydrogen/air flame, a lean turbulent premixed n-heptane/air flame, and a laminar ethylene/air coflow diffusion flame. For the hydrogen flame, both a laminar and a turbulent configuration have been considered. The three flames are characterised by Lewis numbers which are less than unity, greater than unity, and close to unity, respectively. For each flame, mixture-averaged transport simulations are carried out and used as reference data. The current analysis suggests that, for numerous combustion configurations, the constant non-unity Lewis number approximation leads to small errors when the set of Lewis numbers is chosen properly. For the selected test cases and our numerical framework, the reduction of computational cost is found to be minimal.
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, 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 soot characteristics of binary mixtures of n-heptane and toluene and a commercial gasoline were studied using a differential mobility spectrometer (DMS).
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 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, a generalized method to estimate a 2D distribution of temperature and wavelength-dependent emissivity in a sooty flame with spectroscopic radiation intensities is proposed.
Abstract: A generalized method to estimate a two-dimensional (2D) distribution of temperature and wavelength-dependent emissivity in a sooty flame with spectroscopic radiation intensities is proposed in this paper. The method adopts a Newton-type iterative method to solve the unknown coefficients in the polynomial relationship between the emissivity and the wavelength, as well as the unknown temperature. Polynomial functions with increasing order are examined, and final results are determined as the result converges. Numerical simulation on a fictitious flame with wavelength-dependent absorption coefficients shows a good performance with relative errors less than 0.5% in the average temperature. What's more, a hyper-spectral imaging device is introduced to measure an ethylene/air laminar diffusion flame with the proposed method. The proper order for the polynomial function is selected to be 2, because every one order increase in the polynomial function will only bring in a temperature variation smaller than 20 K. For the ethylene laminar diffusion flame with 194 ml min−1 C2H4 and 284 L min−1 air studied in this paper, the 2D distribution of average temperature estimated along the line of sight is similar to, but smoother than that of the local temperature given in references, and the 2D distribution of emissivity shows a cumulative effect of the absorption coefficient along the line of sight. It also shows that emissivity of the flame decreases as the wavelength increases. The emissivity under wavelength 400 nm is about 2.5 times as much as that under wavelength 1000 nm for a typical line-of-sight in the flame, with the same trend for the absorption coefficient of soot varied with the wavelength.
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.
TL;DR: In this article, a three-dimensional direct numerical simulation (DNS) of a turbulent lifted DME slot jet flame was performed at elevated pressure to study interactions between chemical reactions with low-temperature heat release (LTHR), negative temperature coefficient (NTC) reactions and shear generated turbulence in a jet in a heated coflow.