- Author
-
Jhalani, A.
- Title
- Numerical Study of Stretch in Partially Premixed Flames.
- Coporate
- University of Illinois at Chicago
- Keywords
-
premixed flames
|
flame stretch
|
equations
|
combustion
|
flame surface
|
validation
|
flame spread
|
chemical reactions
|
diffusion
- Identifiers
- numerical model; debugging and validation; hydrodynamic model; identification of flame surface; derivation of stretch; details of the post-processor; choice of scalars; flame curvature; stretch distribution; effect of equivalence ratio
- Abstract
- This work investigates stretch effects in partially premixed flames. The numerical code FDS, that is in development stage at NIST was used for the present study. The code was validated and found to behave well for the simulated conditions. A post processor was written and validated for stretch analysis. Flames are stretched due to the interactions between nonuniform flow along the flame, flame front curvature, and flame motion. Variations in the stretch rate induce local variations In the flame temperature and the mass burning rate. It is generally accepted that the flame propagation speed varies linearly with the retch rate for weak stretching. The objective of this study was to obtain a better understanding of stretch effects on rich premixed flames through a numerical simulation of flames established on a slot burner, particularly at larger values of stretch rate and flame curvature. The flame surface is identified by postprocessing the field variables obtained from a numerical simulation which employs single-step reaction model for the chemistry. This study considers atmospheric steady rich two-dimensional rich premixed methane-air flames established on a slot burner. The flames are established by maintaining a flow of a rich air-fuel mixture through the inner slot and of air through the two outer slots. The method provides reasonably grid-independent results. There is good agreement between the numerical predictions and experimental observations made in our laboratory. The contribution of the hydrodynamic stretch is very high in the curved region due to the higher flow divergence at the tip. In regions of high curvature (at the flame tip) the magnitude of stretch due to curvature is one order higher than that of stretch due to hydrodynamic straining.