Diffusion flame

About: Diffusion flame is a research topic. Over the lifetime, 9266 publications have been published within this topic receiving 233522 citations.

Numerical and experimental studies of ethanol flames

Abstract: Ethanol combustion is investigated on the basis of a new chemical-kinetic mechanism consisting of 192 elementary steps among 36 species, augmented by 53 additional steps and 14 additional species to address the formation of oxides of nitrogen and 43 steps and 7 species to address formation of compounds involving three carbon atoms. The mechanism is tested against shock-tube autoignition-delay data, laminar burning velocities, counterflow diffusion-flame extinction and measurements of structures of counterflow partially premixed and diffusion flames, the last of these newly completed and reported here for the first time. These measurements, on ethanol–air flames at a strain rate of 100 s −1 , employing prevaporized ethanol with a mole fraction of 0.3 in a nitrogen carrier stream, were made for the pure diffusion flame and for a partially premixed flame with a fuel-side equivalence ratio of 2.3 and involved thermocouple measurements of temperature profiles and determination of concentration profiles of C 2 H 5 OH, CO, CO 2 , H 2 , H 2 O, O 2 , N 2 , CH 4 , C 2 H 6 and C 2 H 2 + C 2 H 4 by gas chromatographic analysis of samples withdrawn through fine quartz probes. Computational investigations also were made of profiles of oxides of nitrogen and other potential pollutants in similar partially premixed flames of ethanol and other fuels for comparison purposes. The computational results are in reasonable agreement with experiment and perform as well as or better than predictions of other, generally much larger, mechanisms available in the literature. Further research is, however, warranted for providing additional and more stringent tests of the mechanism and its predictions.

Theoretical analysis of the evolution from ignition kernel to flame ball and planar flame

Abstract: Dynamics of flame kernel evolution with and without external energy addition has been investigated analytically and numerically. Emphasis is placed on the effects of radiation heat loss, ignition power and Lewis number on the correlation and transition between the initial flame kernel, the self-extinguishing flame, the flame ball, the outwardly propagating spherical flame and the propagating planar flame. The present study extends previous results by bridging the theories of the non-adiabatic stationary flame balls and travelling flames and allowing rigorous consideration of radiation heat losses. The results show that the effects of radiation heat loss play an important role in flame regimes and flame transition and result in a new isolated self-extinguishing flame. Furthermore, it is found that radiation heat losses significantly increase the critical ignition radius and result in three different dependences of the minimum ignition power on the Lewis number. Comparisons between the results from the tran...

Extinction of Strained Premixed Laminar Flames With Complex Chemistry

Abstract: Conclusions derived from the solution of premixed laminar flames in a stagnation point flow are important in the determination of chemically controlled extinction limits and in the ability to characterize the combustion processes occurring in turbulent reacting flows. In the neighborhood of the stagnation point produced in these flames, a chemically reacting boundary layer is established. For a given equivalence ratio, the input flow velocity can be varied and solutions can be determined for increasing values of the strain rate. As the strain rate increases, the flame nears extinction. Recent experimental, computational and theoretical work has shown that extinction of these flames can be achieved by either flame stretch or by a combination of flame stretch and incomplete chemical reaction. Extinction by flame stretch is possible when the Lewis number of the deficient reactant is greater than a critical value and extinction resulting from both flame stretch and incomplete chemical reaction is pos...

Evidence for the transition from the diffusion-limit in aluminum particle combustion

Abstract: This work presents experimental evidence that the transition from gas-phase diffusion-limited combustion for aluminum particles begins to occur at a particle size of 10 μm at a pressure of 8.5 atm. Measurements of the particle temperature by AlO spectroscopy and three-color pyrometry indicate that the peak temperature surrounding a burning particle approaches the aluminum boiling temperature as particle size is decreased to 10 μm when oxygen is the oxidizer. This reduction indicates that reactions are occurring at or near the particle surface rather than in a detached diffusion flame. When CO 2 is the oxidizer, the combustion temperatures remain near the aluminum boiling temperature for particles as large as 40 μm, indicating that the flame is consistently near the surface throughout this size range. Burn time measurements of 10 and 2.8 μm powders indicate that burn time is roughly proportional to particle diameter to the first power. The burn rates of micron- and nano-particles also show strong pressure dependence. These measurements all indicate that the combustion has deviated from the vapor-phase diffusion limit, and that surface or near-surface processes are beginning to affect the rate of burning. Such processes would have to be included in combustion models in order to accurately predict burning characteristics for aluminum with diameter less than 10 μm.