Perturbed boundary layer diffusion flames. Ph. D. thesis

Technical Report · Sun Mar 01 04:00:00 EST 1987

OSTI ID:6628576

Ang, J A

Thermal cracking is shown to have a significant effect on the temperature profiles in a boundary layer diffusion flame. Measurements of temperature profiles in a sooting free flow flame are compared with classic flame sheet model results. This comparison reveals a large overprediction of temperatures in the region between the fuel surface and the flame. The principle cause of this overprediction is the neglect of thermal cracking in the flame sheet model. The endothermicity of the cracking phenomena is analytically treated in a forced flow flame through the introduction of new Shvab-Zeldovich variables and a simple cracking sheet model, analogous to the flame sheet model. Two new parameters D sub cr and Q' are found which control the temperature at which cracking occurs and the amount of energy absorbed in the process. A second possible cause for the temperature overprediction is the sink effect of radiative heat transfer from soot in the boundary layer. This effect and the effects of wall emission and normal buoyancy on a horizontal boundary layer diffusion flame are studied by perturbing the cracking sheet solution. The principle effect of soot radiation is an increased blowing rate at the wall. This blowing is offset by the radiative wall emission. The postulated sink effect of soot emission is negligible. The major buoyancy effect is primarily the inducement of a velocity overshoot.

• Research Organization: California Univ., Berkeley (USA)
• OSTI ID: 6628576
• Report Number(s): N-87-18628; NBS-GCR-87-526
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400800* -- Combustion
Pyrolysis
& High-Temperature Chemistry
BOUNDARY LAYERS
DATA
EMISSION SPECTRA
ENERGY TRANSFER
EXPERIMENTAL DATA
FLAMES
HEAT TRANSFER
INFORMATION
LAYERS
MATHEMATICAL MODELS
NUMERICAL DATA
RADIANT HEAT TRANSFER
SOOT
SPECTRA
TEMPERATURE DISTRIBUTION