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Title: The spatial scalar structure of premixed turbulent stagnation point flames

Abstract

A high speed tomographic technique is used to quantify the spatial scalar structure of stagnation flow stabilized premixed flames. Studies are performed on CH{sub 4}/Air and C{sub 2}H{sub 4}/Air turbulent flames with equivalence ratios ranging from 0.75 to 1.0. The gas velocity at the nozzle exit is 5 m/s, the turbulence intensity is 7%, the integral length scale 3 mm and hence the turbulence Reynolds number is 70. The light source is a copper vapor laser which produces 20 ns, 5 mJ pulses at a 4 KHz repetition rate. Cylindrical lenses transform the 38 mm circular laser beam to a sheet 50 mm high and 0.6 mm thick. A high speed Fastax camera is used to record the tomographic images formed by the scattering of light from oil droplets seeded in the reactant flow which disappear at the flame front. The films are digitized and the wrinkled flame front extracted from the images by a thresholding technique. The integral scalar length scales proposed in the model of Bray-Champion-Libby are deduced from the tomographic movies by numerically constructing flame crossing sequences from the burned and unburned probability density functions of flame crossing length and performing a spectral analysis of these sequences.more » The integral scalar length scales are found to be similar to the integral length scales of the incident turbulence. A fractal analysis was performed on the flame boundaries to characterize the flame geometry and provide from an estimate of the flame surface area a measure of the turbulent burning rate. The flame area increase is found to underestimate the turbulent burning velocity when compared with direct measurements of the flow velocity at the cold boundary. 12 refs., 2 tabs.« less

Authors:
; ;
Publication Date:
Research Org.:
Lawrence Berkeley Lab., CA (USA)
Sponsoring Org.:
USDOD; DOE/ER
OSTI Identifier:
7020788
Report Number(s):
LBL-28884; CONF-900704-11
ON: DE90014189; CNN: F-44620-76-C-0083
DOE Contract Number:  
AC03-76SF00098
Resource Type:
Conference
Resource Relation:
Conference: 23. Combustion Institute symposium on combustion, Orleans (France), 22-27 Jul 1990
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; FLAMES; FLOW MODELS; SCALAR FIELDS; METHANE; COMBUSTION KINETICS; AIR; DATA ANALYSIS; LASERS; REYNOLDS NUMBER; TURBULENCE; ALKANES; CHEMICAL REACTION KINETICS; FLUIDS; GASES; HYDROCARBONS; KINETICS; MATHEMATICAL MODELS; ORGANIC COMPOUNDS; REACTION KINETICS; 400800* - Combustion, Pyrolysis, & High-Temperature Chemistry

Citation Formats

Shepherd, I G, Cheng, R K, and Goix, P J. The spatial scalar structure of premixed turbulent stagnation point flames. United States: N. p., 1990. Web.
Shepherd, I G, Cheng, R K, & Goix, P J. The spatial scalar structure of premixed turbulent stagnation point flames. United States.
Shepherd, I G, Cheng, R K, and Goix, P J. Sun . "The spatial scalar structure of premixed turbulent stagnation point flames". United States.
@article{osti_7020788,
title = {The spatial scalar structure of premixed turbulent stagnation point flames},
author = {Shepherd, I G and Cheng, R K and Goix, P J},
abstractNote = {A high speed tomographic technique is used to quantify the spatial scalar structure of stagnation flow stabilized premixed flames. Studies are performed on CH{sub 4}/Air and C{sub 2}H{sub 4}/Air turbulent flames with equivalence ratios ranging from 0.75 to 1.0. The gas velocity at the nozzle exit is 5 m/s, the turbulence intensity is 7%, the integral length scale 3 mm and hence the turbulence Reynolds number is 70. The light source is a copper vapor laser which produces 20 ns, 5 mJ pulses at a 4 KHz repetition rate. Cylindrical lenses transform the 38 mm circular laser beam to a sheet 50 mm high and 0.6 mm thick. A high speed Fastax camera is used to record the tomographic images formed by the scattering of light from oil droplets seeded in the reactant flow which disappear at the flame front. The films are digitized and the wrinkled flame front extracted from the images by a thresholding technique. The integral scalar length scales proposed in the model of Bray-Champion-Libby are deduced from the tomographic movies by numerically constructing flame crossing sequences from the burned and unburned probability density functions of flame crossing length and performing a spectral analysis of these sequences. The integral scalar length scales are found to be similar to the integral length scales of the incident turbulence. A fractal analysis was performed on the flame boundaries to characterize the flame geometry and provide from an estimate of the flame surface area a measure of the turbulent burning rate. The flame area increase is found to underestimate the turbulent burning velocity when compared with direct measurements of the flow velocity at the cold boundary. 12 refs., 2 tabs.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {1990},
month = {4}
}

Conference:
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