Effect of Chemical Kinetics on Concurrent-Flow Flame Spread over Solids: A Comparison Between Buoyant Flow and Forced Flow Cases

Abstract

The authors employed detailed numerical models with a one-step finite-rate chemical reaction to investigate the kinetic rate effect (through the variation of the pre-exponential factor) on concurrent flame spread rates over thin solids. It is found that flames in forced flow are less sensitive to the change of kinetics than flames in buoyant flow, and narrow samples are more sensitive to the change of kinetics compared with wide samples. The rate of chemical kinetics affects the flame spread rates primarily through two mechanisms: the amount of unburnt fuel vapors escaping from the reaction zone and the variation of induced flow velocity through flame temperature change in the case of the buoyant flames. Detailed analyses of the flame structure and flow pattern are presented for the forced- and buoyant-flow cases to explain their different degrees of sensitivity to the combustion reaction rate.

Keywords:

• Buoyant upward spread
• Chemical kinetics
• Concurrent forced-flow flame spread
• Flame structure
• Incomplete combustion

ACKNOWLEDGMENTS

This work is supported by NASA through grant NNC04AA58A, monitored by Drs. Gary Ruff and Kurt Sacksteder.

Notes

Note. B_g = B_g,ref = 3.95·10¹¹ cm³/g/s.