Piloted CH4/Air Flames C, D, E, and F – Release 2.1
15-JUN-2007
Robert Barlow and Jonathan Frank
Sandia National Laboratories
Livermore, CA 94551-0969
barlow@v
www.v/TNF
INTRODUCTION
This file (SandiaPilotDoc21.pdf) provides documentation for the 1997 Sandia data set of multiscalar measurements in piloted methane-air jet flames [1] stabilized on a burner developed by Sydney University [2].  This information is made available as part of the International Workshop on Measurement and Computation of Turbulent Nonpremixed Flames [3] to facilitate collaborative comparisons of measur
ed and modeled results for selected turbulent flames.  The “preliminary” data release, which came before the TNF3 Workshop in 1998, included results for flame D only.  Scalar data from four piloted flames (C, D, E, and F) have been available by request since January 1999.  These flames have increasing velocity in the main jet and pilot and increasing probability of localized extinction.  The archive of scalar data (pmCDEF.zip or pmCDEF.tar.Z) included with this release is the same as that provided previously by request.  The purpose of Release 2.0 (January, 2003) was to expand the documentation to cover these four flames and update some aspects of the velocity boundary conditions.  The only change in this file, with Release 2.1, is the addition of Reference  [14], which presents previously unpublished results from the original experiments and describes long (6000-shot) records from flame D. Measured scalars include temperature, mixture fraction, N2, O2, H2O, H2, CH4, CO, CO2, OH, and NO.  CO is measured by Raman scattering and by LIF.  The CO-LIF measurements are more accurate and should be used in comparisons with models.  The data set includes axial and radial profiles of Reynolds- and Favre-average mass fractions and rms fluctuations, conditional statistics at each streamwise location, and complete single-shot data for all measured scalars.  Data included here and used for all TNF Workshop comparisons were obtained during the same experimental series as those reported by Barlow and Frank [1], but on different days, allowing for detailed mapping of each flame.  Experimental methods and measurement uncertainties are outline
d in [1] and further described in [4].  Data from flames A (laminar) and B (transitional) are not included in this archive.  Two component laser-Doppler anemometry (LDA) measurements in flames D, E, and F were performed at the Technical University of Darmstadt by Christoph Schneider et al. [5], and those data are available separately as noted below.
Flames D, E, and F have been modeled by several groups, and a partial list of modeling papers on these flames is provided in the reference list [6-10].  The Proceedings of the TNF3, TNF4, and TNF5 Workshops [3] include numerous graphical comparisons of measured and modeled results, as well as summaries of the modeling approaches used.
USE OF THE DATA
Please contact R. Barlow if you use or publish these data and are not already on the TNF email distribution list.  This will ensure that you will receive notification regarding TNF Workshop data sets and activities.
Averaged results and scatter plots of temperature and species mass fractions from these piloted flame experiments have already been widely published in modeling papers.  No special permission is needed to include these data in further publications.  However, we are preparing a paper (long overdu
e) on aspects of the data that have not yet been published, including such things as transport effects (turbulent stirring vs. differential molecular diffusion), radial variations in conditional statistics, and deviations from partial equilibrium [4].  Therefore, we request that researchers contact us before presenting or publishing any further statistical analysis of the scatter data for these flames.
NOTICE
This data release was prepared as an account of work sponsored by an agency of the United States Government.  Neither the United States Government, nor any agency thereof, nor any of their employees, nor any of the contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights.  Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government, any agency thereof or any of their contractors or subcontractors.  The views and opinions expressed herein do not necessarily state or reflect those of the United States Government, any agency thereof or any of their contractors or subcontractors.
GENERAL DESCRIPTION OF THE FLAMES
The burner geometry is the same as used in numerous previous investigations of piloted flames at Sydney University and Sandia [1,2].  The jet fluid is a mixture of three parts air and one part CH4 by volume.  This mixture significantly reduces the problem of fluorescence interference from soot precursors, allowing improved accuracy in the scalar measurements.  Partial premixing with air also reduces the flame length and produces a more robust flame than pure CH4 or nitrogen-diluted CH4.  Consequently, the flames may be operated at reasonably high Reynolds number with little or no local extinction, even with a modest pilot.  The mixing rates are high enough that these flames burn as diffusion flames, with a single reaction zone near the stoichiometric mixture fraction and no indication of significant premixed reaction in the fuel-rich CH4/air mixtures.
Flame D (Re=22400) has a small degree of local extinction [1].  It was selected as the initial target for TNF3 comparisons because high Reynolds number is desirable for model validation
and the small probability of local extinction allows for useful comparisons with models that do not include extinction.  Flames E and F have significant and increasing probability of local extinction above the pilot region, with flame F being close to global extinction of the downstream part of the flame.
The pilot is a lean (phi=0.77) mixture of C2H2, H2, air, CO2, and N2 with the same nominal enthalpy and equilibrium composition as methane/air at this equivalence ratio.  The flow rates to the main jet and the pilot are scaled in proportion for the C-F series, so that the energy release of the pilot is approximately 6% of the main jet for each flame. The burner exit was positioned approximately 15 cm above the exit of the vertical wind tunnel in the TDF laboratory. The flames were unconfined.
Fig. 1.  Flame D (left) with Nd:YAG laser beam and close-up of the pilot flame (right). BURNER DIMENSIONS
Main jet inner diameter, d  = 7.2 mm
Pilot annulus inner diameter = 7.7 mm  (wall thickness = 0.25 mm)
Pilot annulus outer diameter = 18.2 mm
Burner outer wall diameter  = 18.9 mm (wall thickness = 0.35 mm)
Wind tunnel exit            = 30 cm by 30 cm
BULK FLOW AND SCALAR BOUNDARY CONDITIONS
Coflow velocity  (Ucfl)      = 0.9 m/s (+/- 0.05 m/s) @ 291 K, 0.993 atm    Main jet composition        = 25% CH4, 75% dry air by volume
Main jet kinematic viscosity = 1.58e-05 m^2/s (from chemkin)
Main jet velocity @ 294K, 0.993 atm:
Ubulk_C  = 29.7 m/s (+/- 2 m/s)
Ubulk_D  = 49.6 m/s (+/- 2 m/s)
Ubulk_E  = 74.4 m/s (+/- 2 m/s)
Ubulk_F  = 99.2 m/s (+/- 2 m/s)
Elemental mass fractions in the jet and coflow that are used in calculating the mixture fraction are given below, under the definition of mixture fraction.
The flame stabilizer in the pilot is recessed below the burner exit, such that burnt gas is at the exit plane, as shown in Fig. 1.  The compositional boundary condition in the pilot for flame D was determined by matching the measurements at x/d=1 with calculations (by J-Y Chen) of laminar unstrained premixed CH4/air flames and then extrapolating to the conditions at burner exit plane, based on the estimated convective time up to x/d=1.  The pilot burnt gas velocity is determined from the cold mass flow rate, the density at the estimated exit condition, and the flow area of the pilot annulus.  The resulting pilot flame boundary conditions are tabulated below.  Separate calculations were performed to demonstrate that there are negligible differences in burnt gas composition for the pilot mixture vs. CH4/air at the same total enthalpy and equivalence ratio.
The pilot composition measured in the (nearly) flat portion of the radial profile at x/d=1 in flame D is:
phi      = 0.77
Fch      = 0.27
reaction diffusionYn2      = 0.734
Yo2      = 0.056
Yh2o      = 0.092
Yco2      = 0.110
Yoh      = 0.0022
The pilot composition at the burner exit for flame D is taken as that of an unstrained CH4/air premixed phi=0.77 flame at the point in the flame profile where T=1880 K, following the process outlined above.
phi      = 0.77
Fch      = 0.27
T        = 1880 K (+/- 50 K)    rho      = 0.180 kg/m^3          Yn2      = 0.7342
Yo2      = 0.0540
Yo        = 7.47e-4    Yh2      = 1.29e-4    Yh        = 2.48e-5    Yh2o      = 0.0942    Yco      = 4.07e-3    Yco2      = 0.1098    Yoh      = 0.0028    Yno      = 4.8e-06
We note that a similar composition (within experimental uncertainty) is obtained from a laminar diffusion flame calculation with the present fuel-air boundary conditions, equal species
diffusivities, and a relatively low strain rate (a ~ 20/s) at 0.27 mixture fraction.  We also note that this analysis to estimate the pilot composition at the exit plane has not been performed for the other flames.
Figure 2 shows that the measured pilot temperature in the flat region of the profile at x/d=1 is lower in flame F than in flames D and E.  Temperature measurements at the near-nozzle
locations (x/d=1,2,3) are somewhat less accurate than those further downstream because they are determined from Raman results (total number density) rather than Rayleigh scattering, and the differences are within the uncertainty in the temperature measurement.  The same can be said for the
small differences in measured pilot composition for these flames.  As far as we are aware, the scalar composition given here for the flame D pilot has been used for most model calculations of flames E and F.    This seems appropriate.  However, the sensitivity of model predictions to uncertainty the pilot boundary conditions is an important consideration, as noted by Tang et al.
[7], especially with regard to results for flame F, which is very close to global extinction.
The pilot bulk velocities corresponding to the above-specified conditions, the flow area of the pilot annulus, and the measured mass flow rates for the four flames are:
Uplt_C = 6.8 m/s (+/- 0.3 m/s)
Uplt_D = 11.4 m/s (+/- 0.5 m/s)
Uplt_E = 17.1 m/s (+/- 0.75 m/s)
Uplt_F = 22.8 m/s (+/- 1.0 m/s)
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100015002000-1.0-0.50.0
0.5  1.0  1.5  2.0
M i x t u r e  F r a c t i o n T e m p e r a t u r e  (K )r/d  Fig. 2.  Measured radial profiles of Favre-average mixture fraction and temperature at x/d=1 in
the four turbulent piloted flames.

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