Multiscalar measurements of turbulence-chemistry interactions in nonpremixed flames Page: 3 of 10
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Streamwise Evolution of Flame Structure and Radical Concentrations
OH PLIF images in hydrogen jet flames  have revealed a streamwise evolution of the spatial structure of the regions
of high OH concentrations from thin layers near the nozzle to broad zones near the flame tip. Multiscalar measurements by
Barlow et al. [12,20] and Cheng et al.  have shown that there is a corresponding evolution in chemical structure that has
some important implications, particularly with regard to thermal NO formation and the modeling of that process. Figure 2
shows scatter plots of temperature, and the mole fractions of 02, H2, H20, and OH at two streamwise stations relative to the
visible flame length, L, in a jet flame of H2 into air . Also plotted on each graph are the adiabatic equilibrium curves and
calculated results for steady strained laminar flames with strain parameters of a = 100/s and 1000/s, which are far from
0 0.02 0.04 0.06 0.08
0 0.02 0.04 0.06 0.08
0.015 - -
* *. a=100/s
. . . 4- / a =1000/s
0.010 :'I ;V
0.005 - - Equilibrium
0.00 0.02 0.04 0.06 0.08
0.02 0.04 0.06 0.08
Fig. 2. Scatter plots of temperature, the mole fractions of 02, H2, H20, and OH at two axial locations in a hydrogen jet
flame . The lower graphs are for x=18 and the upper graphs are for x=3U4, where L is the visible flame length. Also
shown in each graph are the adiabatic equilibrium curves and results from two laminar flame calculations.
Near the base of the flame (x=U8), where reaction zones are thin, the measurements show features that are similar to the
strained laminar flames. The measured OH mole fractions are significantly above equilibrium and are comparable to those in
the laminar flames. The scatter plot of temperature has a broad peak that falls below the peak in the equilibrium curve. For
fuel-lean conditions the measured temperatures tend to lie above the equilibrium curve and follow a bowed trajectory similar to
the laminar flame curves. These trends can be attributed to the combined effects of turbulent strain and differential diffusion in
the thin reaction layers near the flame base.
NZ '+a 10 s '
. . . , .. x= 3 4
: T Equilibrum
NZ a =10/s -
- H20 JH
- - 1 - -
* *i'~-.'* . 4
* " " _ : k : a=100/s
I. ~ *a =1000/s
' '.--. . '- Equilibrium -
m, - ... -. -
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Barlow, R.S. Multiscalar measurements of turbulence-chemistry interactions in nonpremixed flames, article, December 1, 1995; Livermore, California. (digital.library.unt.edu/ark:/67531/metadc621016/m1/3/: accessed October 17, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.