Jump to content

Markstein number

From Wikipedia, the free encyclopedia

This is an old revision of this page, as edited by Sunlitsky (talk | contribs) at 14:35, 9 July 2024. The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

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 dimensionless Markstein number is defined as:

where is the Markstein length, and is the characteristic laminar flame thickness. The larger the Markstein length, the greater the effect of curvature on localised burning velocity. It is named after George H. Markstein (1911—2011), who showed that thermal diffusion stabilized the curved flame front and proposed a relation between the critical wavelength for stability of the flame front, called the Markstein length, and the thermal thickness of the flame.[1] Phenomenological Markstein numbers with respect to the combustion products are obtained by means of the comparison between the measurements of the flame radii as a function of time and the results of the analytical integration of the linear relation between the flame speed and either flame stretch rate or flame curvature.[2][3][4] The burning velocity is obtained at zero stretch, and the effect of the flame stretch acting upon it is expressed by a Markstein length. Because both flame curvature and aerodynamic strain contribute to the flame stretch rate, there is a Markstein number associated with each of these components.[5]

Clavin–Williams formula

The Markstein number with respect to the unburnt gas mixture for a one step reaction in the limit of large activation energy asymptotics was derived by Paul Clavin and Forman A. Williams in 1982.[6] The Markstein number then is

where

  • is the gas expansion ratio defined with density ratio,
  • is the Zel'dovich number,
  • is the effective Lewis number of the deficient reactant (either fuel or oxidizer or a combination of both)
  • is the dilogarithm function.

and the Markstein number with respect to the burnt gas mixture is derived by Clavin (1985)[7]

When temperature dependence of transport coefficients are taken into account, the Clavin–Williams formula becomes[8]

where

Here

is the ratio of density-thermal conductivity product to its value in the unburnt gas;
is the ratio of temperature to its unburnt value, defined such that .

The function , in most cases, is simply given by , where , in which case, we have

where is some cut-off at the lower limit since the integral is diverges logarathmically when .

Second Markstein number

In general, Markstein number for the curvature effects and strain effects are not same in real flames.[9][8] In that case, one defines a second Markstein number as

See also

References

  1. ^ Oran E. S. (2015). "A tribute to Dr. George H. Markstein (1911–2011)". Combustion and Flame. 162 (1): 1–2. doi:10.1016/j.combustflame.2014.07.005.
  2. ^ Karpov V. P.; Lipanikov A. N.; Wolanski P. (1997). "Finding the markstein number using the measurements of expanding spherical laminar flames". Combustion and Flame. 109 (3): 436. doi:10.1016/S0010-2180(96)00166-6.
  3. ^ Chrystie R.S.M.; Burns I.S.; Hult J.; Kaminski C.F. (2008). "On the improvement of two-dimensional curvature computation and its application to turbulent premixed flame correlations". Measurement Science and Technology. 19 (12): 125503. Bibcode:2008MeScT..19l5503C. doi:10.1088/0957-0233/19/12/125503. S2CID 21642877.
  4. ^ Chakraborty N, Cant RS (2005). "Influence of Lewis number on curvature effects in turbulent premixed flame propagation in the thin reaction zones regime". Physics of Fluids. 17 (10): 105105–105105–20. Bibcode:2005PhFl...17j5105C. doi:10.1063/1.2084231.
  5. ^ Haq MZ, Sheppard CG, Woolley R, Greenhalgh DA, Lockett RD (2002). "Wrinkling and curvature of laminar and turbulent premixed flames". Combustion and Flame. 131 (1–2): 1–15. doi:10.1016/S0010-2180(02)00383-8.
  6. ^ Clavin, Paul, and F. A. Williams. "Effects of molecular diffusion and of thermal expansion on the structure and dynamics of premixed flames in turbulent flows of large scale and low intensity." Journal of fluid mechanics 116 (1982): 251–282.
  7. ^ Clavin, Paul. "Dynamic behavior of premixed flame fronts in laminar and turbulent flows." Progress in Energy and Combustion Science 11.1 (1985): 1–59.
  8. ^ a b Clavin, Paul, and Geoff Searby. Combustion Waves and Fronts in Flows: Flames, Shocks, Detonations, Ablation Fronts and Explosion of Stars. Cambridge University Press, 2016.
  9. ^ Clavin, P., & Graña-Otero, J. C. (2011). Curved and stretched flames: the two Markstein numbers. Journal of fluid mechanics, 686, 187-217.