In
combustion
Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combus ...
, flame stretch (
) is a quantity which measures the amount of stretch of the flame surface due to curvature and due to the outer velocity field strain. The early concept of flame stretch was introduced by Karlovitz in 1953, although the correct definition was introduced two decades later by
Forman A. Williams
Forman Arthur Williams (born January 12, 1934) is an American academic in the field of combustion and aerospace engineering who is Emeritus Professor of Mechanical and Aerospace Engineering at the University of California San Diego.
Education
Wil ...
in 1975.
George H. Markstein
George may refer to:
People
* George (given name)
* George (surname)
* George (singer), American-Canadian singer George Nozuka, known by the mononym George
* George Washington, First President of the United States
* George W. Bush, 43rd Presiden ...
studied flame stretch by treating the flame surface as a hydrodynamic discontinuity (known as
flame front
A premixed flame is a flame formed under certain conditions during the combustion of a premixed charge (also called pre-mixture) of fuel and oxidiser. Since the fuel and oxidiser—the key chemical reactants of combustion—are available througho ...
). The flame stretch is also discussed by
Bernard Lewis
Bernard Lewis, (31 May 1916 – 19 May 2018) was a British American historian specialized in Oriental studies. He was also known as a public intellectual and political commentator. Lewis was the Cleveland E. Dodge Professor Emeritus of Near ...
and Guenther von Elbe in their book. All these discussions treated flame stretch as an effect of flow velocity gradients. The stretch can be found even if there is no velocity gradient, but due to the flame curvature. So, the definition required a more general formulation and its precise definition was first introduced by
Forman A. Williams
Forman Arthur Williams (born January 12, 1934) is an American academic in the field of combustion and aerospace engineering who is Emeritus Professor of Mechanical and Aerospace Engineering at the University of California San Diego.
Education
Wil ...
in 1975
[Williams, F. A. (1975). " A Review of Some Theoretical Considerations of Turbulent Flame Structure." in analytical Numerical Methods for Investigation of Flow Fields with Chemical Reactions, Especially Related Fields to Combustion. In AGARD Conference Proceedings, 1975 (Vol. 164).] as the ratio of rate of change of flame surface area to the area itself
:
When
, the flame is stretched, otherwise compressed. Sometimes the flame stretch is defined as non-dimensional quantity
:
where
is the laminar flame thickness and
is the laminar propagation speed of unstretched
premixed flame
A premixed flame is a flame formed under certain conditions during the combustion of a premixed charge (also called pre-mixture) of fuel and oxidiser. Since the fuel and oxidiser—the key chemical reactants of combustion—are available througho ...
.
See also
*
Markstein number In combustion engineering and explosion studies, the Markstein number characterizes the effect of local heat release of a propagating flame on variations in the surface topology along the flame and the associated local flame front curvature. The di ...
References
{{Reflist, 30em
Fluid dynamics
Combustion