The spatial scalar structure of premixed turbulent stagnation point flames

Conference · Sun Apr 01 04:00:00 EDT 1990

OSTI ID:7020788

Shepherd, I G; Cheng, R K; Goix, P J

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.

• Research Organization: Lawrence Berkeley Lab., CA (USA)
• Sponsoring Organization: DOD; DOE/ER
• DOE Contract Number: AC03-76SF00098
• OSTI ID: 7020788
• Report Number(s): LBL-28884; CONF-900704--11; ON: DE90014189; CNN: F-44620-76-C-0083
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400800* -- Combustion
Pyrolysis
& High-Temperature Chemistry
AIR
ALKANES
CHEMICAL REACTION KINETICS
COMBUSTION KINETICS
DATA ANALYSIS
FLAMES
FLOW MODELS
FLUIDS
GASES
HYDROCARBONS
KINETICS
LASERS
MATHEMATICAL MODELS
METHANE
ORGANIC COMPOUNDS
REACTION KINETICS
REYNOLDS NUMBER
SCALAR FIELDS
TURBULENCE