NASA Logo

NTRS

NTRS - NASA Technical Reports Server

Back to Results
Strain-Rate-Free Diffusion Flames: Initiation, Properties, and QuenchingFor about a half century, the stabilization of a steady planar deflagration on a heat-sink-type flat-flame burner has been of extraordinary service for the theoretical modeling and diagnostic probing of combusting gaseous mixtures. However, most engineering devices and most unwanted fire involve the burning of initially unmixed reactants. The most vigorous burning of initially separated gaseous fuel and oxidizer is the diffusion flame. In this useful idealization (limiting case), the reactants are converted to product at a mathematically thin interface, so no interpenetration of fuel and oxidizer occurs. This limit is of practical importance because it often characterizes the condition of optimal performance (and sometimes environmentally objectionable operation) of a combustor. A steady planar diffusion flame is most closely approached in the laboratory in the counterflow apparatus. The utility of this simple-strain-rate flow for the modeling and probing of diffusion flames was noted by Pandya and Weinberg 35 years ago, though only in the last decade or so has its use become internationally common place. However, typically, as the strain rate a is reduced below about 20 cm(exp -1), and the diffusion-flame limit (reaction rate much faster than the flow rate) is approached, the burning is observed to become unstable in earth gravity. The advantageous steady planar flow is not available in the diffusion-flame limit in earth gravity. This is unfortunate because the typical spatial scale in a counterflow is (k/a)(sup 1/2), where k denotes a characteristic diffusion coefficient; thus, the length scale becomes large, and the reacting flow is particularly amenable to diagnostic probing, as the diffusion-flame limit is approached. The disruption of planar symmetry is owing the fact that, as the strain rate a decreases, the residence time (l/a) of the throughput in the counterflow burner increases. Observationally, when the residence time exceeds about 50 msec, the inevitably present convective (Rayleigh-Benard) instabilities, associated with hot-under-cold (flame-under-fresh-reactant) stratification of fluid in a gravitational field, have time to grow to finite amplitude during transit of the burner.
Document ID
19970020562
Acquisition Source
Legacy CDMS
Document Type
Conference Paper
Authors
Fendell, Francis
(TRW Space and Electronics Group Redondo Beach, CA United States)
Rungaldier, Harald
(TRW Space and Electronics Group Redondo Beach, CA United States)
Gokoglu, Suleyman
(NASA Lewis Research Center Cleveland, OH United States)
Schultz, Donald
(NASA Lewis Research Center Cleveland, OH United States)
Date Acquired
August 17, 2013
Publication Date
May 1, 1997
Publication Information
Publication: Fourth International Microgravity Combustion Workshop
Subject Category
Inorganic And Physical Chemistry
Accession Number
97N21835
Funding Number(s)
CONTRACT_GRANT: NAS3-27264
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.
Document Inquiry

Available Downloads

There are no available downloads for this record.
No Preview Available