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Title: Internal structure of a premixed turbulent flame

Abstract

A pulsed laser and a multielement detector have been used to make instantaneous Rayleigh profiles along a line through a turbulent flame front thus eliminating the effects of flame front motion. The flame front in a premixed turbulent flame moves randomly about a mean position, giving rise to the visually observed flame brush or time-averaged flame thickness which is larger than the instantaneous thickness of the reaction zone. The physical characteristics and statistical properties of such turbulent flames reported previously were deduced from the time histories of Rayleigh scattered laser light at one or two points within the reaction zone. The study was conducted on a premixed propane-air flame stabilized on a rod at the exit plane of a square burner. Turbulence-producing screens below the burner exit controlled turbulent length scales while intensity was controlled with inlet mixture velocity. Turbulence properties of the cold reactants were determined by hot-wire anemometry. Mean and fluctuating velocity in the unburnt and burnt gases were measured using laser Doppler velocimetry. At the low level of turbulence studied, the instantaneous flame front thickness was found to be only slightly greater than the laminar flame thickness, and the magnitude of the density fluctuations only slightly greatermore » than the cold flow turbulence intensity. Mean and rms values of density and velocity; density and velocity probability density functions; spatial density correlations; and comparison of data with the Bray-Moss-Libby model are presented.« less

Authors:
; ;
Publication Date:
Research Org.:
Southern Illinois Univ., Carbondale (USA); Sandia National Labs., Albuquerque, NM (USA)
OSTI Identifier:
6710933
Alternate Identifier(s):
OSTI ID: 6710933; Legacy ID: DE83001948
Report Number(s):
SAND-82-8865; CONF-821035-7
ON: DE83001948
DOE Contract Number:
AC04-76DP00789
Resource Type:
Conference
Resource Relation:
Conference: Combustion Insitute symposium on western states section, Livermore, CA, USA, 11 Oct 1982
Country of Publication:
United States
Language:
English
Subject:
42 ENGINEERING; FLAMES; DENSITY; FLAME PROPAGATION; TURBULENCE; PROPANE; COMBUSTION; ANEMOMETERS; COMBUSTION KINETICS; EXPERIMENTAL DATA; LASERS; THEORETICAL DATA; VELOCIMETERS; ALKANES; CHEMICAL REACTION KINETICS; CHEMICAL REACTIONS; DATA; HYDROCARBONS; INFORMATION; KINETICS; MEASURING INSTRUMENTS; NUMERICAL DATA; ORGANIC COMPOUNDS; OXIDATION; PHYSICAL PROPERTIES; REACTION KINETICS; THERMOCHEMICAL PROCESSES 420400* -- Engineering-- Heat Transfer & Fluid Flow

Citation Formats

Rajan, S., Smith, J.R., and Rambach, G.D. Internal structure of a premixed turbulent flame. United States: N. p., 1982. Web.
Rajan, S., Smith, J.R., & Rambach, G.D. Internal structure of a premixed turbulent flame. United States.
Rajan, S., Smith, J.R., and Rambach, G.D. Fri . "Internal structure of a premixed turbulent flame". United States. doi:.
@article{osti_6710933,
title = {Internal structure of a premixed turbulent flame},
author = {Rajan, S. and Smith, J.R. and Rambach, G.D.},
abstractNote = {A pulsed laser and a multielement detector have been used to make instantaneous Rayleigh profiles along a line through a turbulent flame front thus eliminating the effects of flame front motion. The flame front in a premixed turbulent flame moves randomly about a mean position, giving rise to the visually observed flame brush or time-averaged flame thickness which is larger than the instantaneous thickness of the reaction zone. The physical characteristics and statistical properties of such turbulent flames reported previously were deduced from the time histories of Rayleigh scattered laser light at one or two points within the reaction zone. The study was conducted on a premixed propane-air flame stabilized on a rod at the exit plane of a square burner. Turbulence-producing screens below the burner exit controlled turbulent length scales while intensity was controlled with inlet mixture velocity. Turbulence properties of the cold reactants were determined by hot-wire anemometry. Mean and fluctuating velocity in the unburnt and burnt gases were measured using laser Doppler velocimetry. At the low level of turbulence studied, the instantaneous flame front thickness was found to be only slightly greater than the laminar flame thickness, and the magnitude of the density fluctuations only slightly greater than the cold flow turbulence intensity. Mean and rms values of density and velocity; density and velocity probability density functions; spatial density correlations; and comparison of data with the Bray-Moss-Libby model are presented.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Fri Oct 01 00:00:00 EDT 1982},
month = {Fri Oct 01 00:00:00 EDT 1982}
}

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  • A turbulent premixed flame stabilized at a rod flame holder has been examined to verify the blow-off mechanism related with the turbulence characteristics. The turbulence characteristics inside and around the flame were measured by LDV to estimate the effective turbulence structure for evaluation of blow-off mechanism. The turbulence characteristics change at the combustion condition from those of approach mixture and the turbulence intensity increases at the shear layer region and the Euler integral scale reduces its size. The small scale turbulence represented by Taylor scale or Kolmogorov scale increases its size according to the temperature rise caused by chemical reactionmore » at the burned region or reaction region. The corrugated wake flame formed at the downstream of the stable flame is composed of a lot of flame sections projected to burned gas and unburned gas, which lowers or increases local equivalence ratio caused by preferential diffusion effect. The blow-off limit data were obtained for various turbulence characteristics of approach flow. The blow-off data were successfully divided into two groups regardless of approach flow turbulence by relating the local blow-off equivalence ratio with the local turbulence Karlovitz number both of which were estimated on the bases of the concave or convex flame outlines measured on the images of laser tomography.« less
  • Propagation of turbulent flames in spark-ignition engines is considered from the viewpoint of the different possible regimes of premixed turbulent combustion. Nondimensional parameters defining known combustion regimes are reviewed, and numerical values of these parameters are estimated for both research and production engines. The reaction-sheet regime is inferred to apply at least for some operating conditions, and therefore literature on turbulent flame propagation in the reaction-sheet regime is reviewed. Implications of these results on interpretations of existing experimental observations of combustion in engine cylinders and on modeling of turbulent flame propagation in engines are discussed. 112 refs.
  • The influence of the Lewis number on turbulent flame front geometry is investigated in a premixed turbulent stagnation point flame. A laser tomography technique is used to obtain the flame shape, a fractal analysis of the multiscale flame edges is performed and the distribution of local flame front curvature is determined. Lean H[sub 2]/Air and C[sub 3]H[sub 8]/Air mixtures with similar burning rates were investigated with Lewis numbers of 0.33 and 1.85 respectively. At the conditions studied the laminar H[sub 2]/Air mixture is unstable and a cellular structure is observed. Turbulence in the reactant is generated by a perforated platemore » and the turbulent length scale (3mm) and intensity (7%) at the nozzle exit are fixed. The equivalence ratio is set so that the burning velocity is the same for all the cases. Results show clearly that the turbulent flame surface area is dependent on the Lewis number. For a Lewis number less than unity surface area production is observed. The shape of the flame front curvature distribution is not found to be very sensitive to the Lewis number. For the H[sub 2]/Air mixture the distribution is skewed toward the positive values indicating the presence of cusps while for the C[sub 3]H[sub 8]/Air mixture the distribution is more symmetrical. In both cases the average curvature is found to be zero, and if the local burning speed varies linearly with curvature, the local positive and negative burning velocity variations due to curvature will balance.« less
  • The influence of the Lewis number on turbulent flame front geometry is investigated in a premixed turbulent stagnation point flame. A laser tomography technique is used to obtain the flame shape, a fractal analysis of the multiscale flame edges is performed and the distribution of local flame front curvature is determined. Lean H{sub 2}/Air and C{sub 3}H{sub 8}/Air mixtures with similar burning rates were investigated with Lewis numbers of 0.33 and 1.85 respectively. At the conditions studied the laminar H{sub 2}/Air mixture is unstable and a cellular structure is observed. Turbulence in the reactant is generated by a perforated platemore » and the turbulent length scale (3mm) and intensity (7%) at the nozzle exit are fixed. The equivalence ratio is set so that the burning velocity is the same for all the cases. Results show clearly that the turbulent flame surface area is dependent on the Lewis number. For a Lewis number less than unity surface area production is observed. The shape of the flame front curvature distribution is not found to be very sensitive to the Lewis number. For the H{sub 2}/Air mixture the distribution is skewed toward the positive values indicating the presence of cusps while for the C{sub 3}H{sub 8}/Air mixture the distribution is more symmetrical. In both cases the average curvature is found to be zero, and if the local burning speed varies linearly with curvature, the local positive and negative burning velocity variations due to curvature will balance.« less