Abstract
An analytical study is presented for describing a flame in a shear layer flow formed between a gaseous fuel stream and an oxidizer stream, moving at different velocities. The diffusion flamesheet approximation is addressed. It is shown how the shear layer flow-field driven by various ratios of free- flows velocities influences flame properties. The role of the “equivalence ratio for diffusion flames”, that is, the product of stoichiometric ratio and the concentration ratio of fuel/oxidizer at the outer flows, is analyzed, in terms of flame shape and location. Flame shapes regimes are described in terms of equivalence ratio and velocity ratio. A “turning point” is revealed in the shift of the flame location from one stream towards the other with increasing Schmidt number. The value of the corresponding “turning point” equivalence ratio, in which the flame shift changes direction, is found to be governed by the velocity profile and specifically by the free stream velocity ratio. Moreover, this ratio is shown to control also the sensitivity of the flame location to changes in the value of the Schmidt number. Downstream velocity deceleration is also addressed, with respect to flame location and flame shape, showing a shift of the flame towards the fuel stream and a change in flame curvature. This study of the location and shape of such a flame configuration elucidates the ways these flame characteristics may be manipulated. It also points out the general region of the main production of air-pollutants in related combustion cases which exist in industry and in the outdoor-atmosphere where fire is occurring between two flows of different chemical species moving at different velocities.
Highlights
When a shear layer is formed between two streams, one, a gaseous fuel stream and the other an oxidizer, a diffusion flame may occur under the appropriate conditions
A similar statement was made by Burke and Schumann in their 1928 work that analyzes a diffusion flame in the case of two concentric streams flowing at the same constant velocity
When analyzing the parameters influencing the flame properties in this configuration, the effect of the velocity ratio U II / U I on the flame shape is found to be of high importance, and could be addressed by making use of Eqs. (27) and (37), which leads to f'
Summary
When a shear layer is formed between two streams, one, a gaseous fuel stream and the other an oxidizer, a diffusion flame may occur under the appropriate conditions. In terms of research this configuration is attractive due to the fact that, in spite of being physically two dimensional, it can be reduced to a one dimensional problem, by an appropriate similarity transformation, whilst at the same time preserving the essential features of the combustion Analysis of this system can lead to conclusions that are applicable in more complex systems, in a manner analogous to the way that the study of flames in a laminar stagnation flow is the basis for the turbulent situation (Peters, 1984). A two dimensional steady laminar shear flow is considered It is formed by two gaseous streams moving at different velocities, where one is basically the combustible species and the other, an oxidizer, in addition to an inert gas.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
