ABSTRACT
One of the problems in combustors that utilize premixed ames is the attainment
of stable performance over an extended range of operation (turndown ratio). The
condition, at which the combustion wave is driven back causing the ame to be
extinguished when the ow velocity exceeds the burning velocity everywhere in
the ow eld, is of particular interest to this study. The physical mechanisms
responsible for the blow-out limits and ame stabilization of jet ames is still
a topic of extensive research [1, 2]. The ame stabilization technique discussed
approach to this complex phenomenon, which can be summarized as follows.
The burning velocity depends upon a number of variables such as the mixture
strength, the ame temperature, and thermal and molecular diusivities of the
mixture [3]. In practical systems, the nozzle exit velocity prole has spatial vari-
ation that greatly in uences the ame stability. Typically, the ame is stabilized
within the shear layer region where the velocities are lower. When the ow rate
is very high, the velocity in the ame exceeds the burning velocity everywhere
and the ame blows out. It is generally accepted that the limiting speed that
can be achieved while keeping the ame anchored to the nozzle exit is deter-
mined by the maximum sustainable strain rate measured at the nozzle exit. By
the introduction of a small countercurrent ow, the strain eld in the nozzle
exit region is eectively altered to achieve conditions for ame anchoring and
stabilization.
