Multiscalar measurements of turbulence-chemistry interactions in nonpremixed flames Page: 1 of 10
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Invited paper for the 1995 Fall Technical Meeting of the Eastern States Section: The Combustion Institute of
October 16-18, 1995, Worcester Polytechnic Institute, Worcester, MA
Multiscalar Measurements of Turbulence-Chemisf CE C I V FD
Interactions in Nonpremixed Flames 2
N 0V 2 2 9995
R. S. BARLOW
Sandia National Laboratories, Livermore, California 94551-0969
Selected results from experiments conducted over the past several years involving simultaneous multiscalar point
measurements in turbulent nonpremixed flames are reviewed in this paper. In these experiments, spontaneous Raman
scattering and Rayleigh scattering measurements of the major species and temperature were combined with laser-induced
fluorescence measurements of minor species. The most important feature of these experiments is that they provide detailed
data on the instantaneous relationships among species concentrations, temperature, and derived scalar quantities that reflect the
state of mixing or the progress of reaction. These data allow quantitative comparisons of the thermochemical states in
turbulent flames with those in idealized representations, such as steady strained laminar flames, perfectly stirred reactors, or
adiabatic equilibrium. The data may also be compared with results (measured or calculated) from unsteady laminar flames and
from direct numerical simulations (DNS) of turbulent reacting flows. Such comparisons provide insights into the
fundamental nature of turbulence-chemistry interactions, and they allow one to examine the validity of some of the basic
assumptions that turbulent combustion models are built upon. Furthermore, these data allow quantitative evaluations of the
predictive accuracy, strengths, and limitations of a wide variety of combustion models.
Raman/Rayleigh measurements using flashlamp-pumped dye lasers in turbulent jet flames of H2, CO/H2, and CH4 were
pioneered by Drake and coworkers [1-4] and Dibble and coworkers [5-8], and have also been reported by Correa and Gulati
[9,10]. The first simultaneous Raman/Rayleigh/LIF experiments in turbulent flames involved measurements of OH radical
using a second laser system, as described by Barlow et al. [1.1,12]. In this two laser approach, the temperature and major
species data were used to correct linear fluorescence signals for shot-to-shot variations in Boltzmann fraction and collisional
quenching rate. Pitz and coworkers [13,14] have demonstrated that a single tunable excimer laser (248 nm) can be used to
measure OH as well as the major species and temperature, and there are now several research groups applying this approach.
These OH data have provided information on the effects of turbulence on the radical pool in H2  and CH4  jet flames.
Hydroxyl has also proven to be a sensitive indicator of localized extinction in highly strained turbulent flames [16-18]. For
the purposes of understanding turbulence-chemistry interactions and evaluating combustion models, 0-atoms and H-atom
measurements would probably be of even greater use than OH. However, quantitative LIF techniques for these radicals are
more difficult than for OH.
Nitric oxide was the second LIF species to be added to the multiscalar system at Sandia , based upon the maturity of
NO fluorescence as a quantitative diagnostic in laminar flames and the need to learn more about the role of turbulence-
chemistry interactions in the formation of this important pollutant. An extensive investigation of thermal NO formation in
H2 jet flames has been completed , and experimental results have been compared with predictions of Monte Carlo pdf and
Conditional Moment Closure (CMC) models . Experiments on NO formation in bluff-body-stabilized flames have also
been conducted .
Recently, a third LIF system was added for measurements of CO . The motivations are two-fold. First, the Raman
scattering measurements of CO in hydrocarbon flames suffer from fluorescence interferences from soot precursors [10,23], and
better accuracy in the CO measurements is needed to evaluate models for hydrocarbon combustion in nonpremixed flames.
Interferences have been found to be minimal for the two-photon LIF measurements of CO in these flames. Second, the
detection limit for the LIP method is lower than for Raman scattering from CO. Simultaneous measurements of NO and CO
at low concentrations, combined with measurements of major species, temperature, and OH, open the door for investigations
of the role of turbulence-chemistry interactions in NO formation and CO burnout in premixed and partially premixed
In the limited space available, we will briefly outline the diagnostic system, then use results from experiments at Sandia
to touch on four topics: 1) the streamwise development of reaction zone structure and radical concentrations in hydrogen jet
flames; 2) some aspects of turbulence-chemistry interactions in methane flames; 3) differential species diffusion; and 4) the
conditional statistics of species concentrations and temperature, as related to thermal NO formation. These results will be
discussed in terms of their implications for combustion modeling.
EXPERIMENTAL APPROACH AND DIAGNOSTICS
The primary objectives of the experiments reviewed here have been to investigate fundamental aspects of turbulence-
chemistry interactions in nonpremixed flames and to provide data that will be useful for the evaluation and further
development of turbulent combustion models. Geometries have included axisymmetric jet flames [12,20] and piloted jet
flames [13-15] that can be modeled using parabolic marching methods, as well as bluff-body-stabilized flames [14,25], which
include recirculation zones. Fuels and fuel combinations have included H2, H2/CO, H2/CH4, CH4, CH30H, C2H50H, and
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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/m1/1/?rotate=90: accessed October 20, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.