摘要:

We have investigated the effect of burner surface temperature and mass flow on OH and CH radical mole fraction profiles in 10 Torr premixed methane/oxygen flames. Experimental flames were monitored using both flame emission and laser induced fluorescence. Modeling predictions using Sandia flame codes are compared to experimental results. An inverse relationship between mass flow and flame front distance from the burner is observed and modeled. Lean methane/oxygen flames stabilize closer to the burner than rich flames when mass flow is held constant. For methane/oxygen flames at 10 Torr, the effect on the location of the flame front as judged by the OH and CH profiles of a ± 10% measurement uncertainty in the experimental gas flow or a ± 10% uncertainty in the burner surface temperature, cannot be measured within experimental precision.

ISSN:0010-2202    

DOI:10.1080/00102209408935392

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

We consider premixed gaseous flames propagating between parallel plates (Hele-Shaw cell) and qualitatively analyze how the resulting losses of momentum and heat affect the flame stability for wavelengths of wrinkling that noticeably exceed the plate spacing. Modelling the flame as an effective interface and using Euler-Darcy equations for the gas on both sides, we firstly show that friction to adiabatic walls modify the Landau-Darrieus instability in two ways: a damping coefficient is brought in, along with a Saffman-Taylor type of instability. Being due to friction-induced pressure gradients, the latter may even dominate the stabilizing influence of gravity for downwardly propagating fronts in narrow channels.

ISSN:0010-2202    

DOI:10.1080/00102209408935393

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Ordered states of cellular flames on circular porous plug burners consist of concentric rings of cells. At certain values of the flow rate and equivalence ratio a transition is made to a state in which entire rings of ceils rotate. The direction of rotation depends only on the initial conditions. Our observations of rotating cellular flames include a single rotating ring, an outer ring rotating about a single inner cell, a rotating inner ring surrounded by a fixed outer ring, and two corotating or counterrotaling concentric rings. A rotating ring of cells can also make a transition to a modulated rotating state in which the shapes of the cells and the speed of rotation periodically change. In another rotating mode, a single central cell takes the shape of a spiral which rotates inside a fixed outer ring of cells. The physical characteristics of these modes are described and comparisons with relevant theoretical studies are made.

ISSN:0010-2202    

DOI:10.1080/00102209408935394

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Ordered states of cellular flames, consisting of concentric rings of approximately equally sized cells, are observed over a wide range of parameters in our experiments using heavy hydrocarbon-air mixtures on a circular porous plug burner at low pressure. These ordered states have been found with cell numbers ranging from five to thirty. At a critical value of the flow rate, which depends on the equivalence ratio, a transition to a disordered state is observed, in which the ring structure disappears; the cells change their shape, size and number; and they move about in an irregular manner.

ISSN:0010-2202    

DOI:10.1080/00102209408935395

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Our previous experiments on the dynamics of premixed flames on circular porous plug burners have demonstrated a variety of periodic pulsating flames with different spatial and temporal characteristics. In the radial mode the circular flame front expands and contracts, periodically changing its radial extent. As the system parameters are adjusted near the extinction boundary, a sequence of transitions is observed. First, the radial mode loses its circular symmetry but remains periodic. Next, it undergoes a transition to a chaotic state. Finally, it makes a transition to extinction. All periodic pulsating modes are separated from the extinction boundary by a region of chaotic dynamics. The characteristics of chaotic flame dynamics beyond the extinction limit are discussed. The spatial and temporal characteristics of this chaotic mode are discussed and compared with the relevant theoretical studies.

ISSN:0010-2202    

DOI:10.1080/00102209408935396

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The paper presents numerical simulations of three-dimensional Bunsen burner polyhedral premixed flames within the framework of a weakly nonlinear semi-phenomenological model for flame interface dynamics. In addition, for slot-burners, experimental observations were made and measurements were obtained of the limit velocity for transition from polyhedral to smooth flame.

ISSN:0010-2202    

DOI:10.1080/00102209408935397

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Our previous experiments have shown that cellular flames form ordered states consisting of concentric rings of cells. The numbers of cells in the inner and outer rings change independently in integer steps as the flow rate is increased. In this paper we report the observation of states characterized by a hopping motion in which cells abruptly change their angular position in the ring. This hopping proceeds sequentially to the other cells in the ring. The hopping states are typically observed in isobutane-air cellular flames at parameter values between those corresponding to two consecutive ordered states. The physical characteristics of these states are similar to those of modulated traveling waves found by Bayliss, Matkowsky and Riecke in numerical simulations of the full equations that describe the thermodiffusive instability. The similarities and differences between our experimental results and their theoretical predictions are discussed.

ISSN:0010-2202    

DOI:10.1080/00102209408935398

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Markstein, in his seminal study of cellular flames, divided the dynamics of one-dimensional cellular flames into two classes: steady and unsteady. In this paper we report four distinct types of chaotic motion of cellular flames on circular porous plug burners: ordered states in which cells arranged in concentric rings execute small amplitude chaotic oscillations; disordered states in which the ring structure is broken and cells of unequal size and shape move around in an irregular manner; intermittently ordered states in which, for most of the time, there is a highly irregular cellular structure which abruptly evolves into ordered states of concentric rings lasting for varying lengths of time; and pulsating-cellular states in which an ordered state of cellular flames interacts with the radial mode of pulsating flames. These four types of chaotic cellular flames fill the explored parameter space. The spatial and temporal characteristics of each of these modes are described, and these results are compared with other experiments on cellular flames and relevant theoretical studies.

ISSN:0010-2202    

DOI:10.1080/00102209408935399

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The detailed kinetic scheme includes 47 chemical species involved in 202 reaclions. Analyses of results indicate that indeed the novel reaction channel is important for ethane combustion description. Analyses of OH formation and consumption rates permit to explain the negative temperature coefficient, which is simulated according to the peculiar ethane property.

ISSN:0010-2202    

DOI:10.1080/00102209408935400

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A flat flame simulation was performed to model experimental data from a dich-loromethane/methane/air flame. A detailed elementary reaction mechanism was used to carry out the simulation and to obtain insights about key chemical processes occurring in various regions of the flame. The flame was at stoichiometric conditions with a CI/H ratio of 0.34. The PREMIX flat flame program was used to obtain the calculated results. Comparisons between calculation and experiment were good for the three reactants and five of the seven stable intermediates for which experimental data were available. Calculated CO2and CO profiles were also good, but were found to be offset from experiment by 0.02 cm, with the calculated profiles occurring too late in the flame. A reaction rate analysis found that the flame developed in three stages, an initiation stage, a chlorine inhibited oxidation stage, and finally CO burnout by the reaction CO + OH. The initiation stage was dominated by chlorine abstraction of H atoms from the fuel species and recombination of dichloromethyl, chloromethyl and methyl radicals to C2's. This initiation stage was found to occur in the flame at temperatures of 1070 K to 1500K. The oxidation stage was characterized by temperatures between 1500 K and 1660 K. CO2formation from CO + OH was found to be inhibited in the initiation stage and oxidation stage. Once the temperature reached 1660 K OH radicals became available through the endothermic reactions O + H2O and O + HCI, and CO + OH became the dominant pathway for CO2formation.

ISSN:0010-2202    

DOI:10.1080/00102209408935401

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor