Facultad de Ciencias, UNED - Madrid
Laminar jet flames display an axisymmetric concave configuration
where the increase of local burning velocity by flame compression
(negative stretch) leads to robust flame tips which can withstand gas
blowing velocities several times larger than the planar flame burning
velocity.
The aim of this work was to carry out a study at the region around the
tip of strongly curved flames, where the classical linear relation
between local flame burning velocity and flame stretch [1] is no longer
applicable and is expected to be replaced by some nonlinear relation.
We have set up an experiment where the local values of the burning
velocity and of the curvature have been simultaneously measured along
the front of a jet flame [2, 3]. This has allowed us to experimentally
determine the planar flame propagation velocity and the Markstein
length, as well as to assess the validity of the linear relation at any
point of the flame front, from the quasi-conical skirt to the rounded
tip.
It turns out that the Markstein relation is not enough to give a full
satisfactory account of the experimental data because it does not
reproduce the departure from the linear behavior observed
experimentally, nor the multivaluedness of the burning velocity for the
same values of the stretch in flames with different heights
(corresponding to different blowing velocities of the feeding gas).
To account for the observed non-linear behavior, it seems natural to
extend the linear relation to include a term quadratic in the stretch
which should contain essentially the dependence on the gas blowing
velocity.
REFERENCES
[1] P. Garcia-Ybarra, C. Nicoli, P. Clavin, Combus. Sci. Technol. 42 (1984) 87–109.
[2] G. Garcia-Soriano, P.L. Garcia-Ybarra, F.J. Higuera, Flow Turbul. Combust. 89 (2012) 173–182.
[3] G. Garcia-Soriano, J.L. Castillo, F.J. Higuera, P.L. Garcia-Ybarra, C. R. Mecanique 340 (2012) 789–796.
