Ignition and Flame Propagation Studies Over a Flat Fuel Surface.
Ignition and Flame Propagation Studies Over a Flat Fuel
Amos, B. T.
NIST GCR 92-604; 148 p. March 1992.
Sponsor:National Institute of Standards and Technology,
Available from: National Technical Information Service
(NTIS), Technology Administration, U.S. Department of
Commerce, Springfield, VA 22161.
1-800-553-6847 or 703-605-6000;
Fax: 703-605-6900; Rush
Service (Telephone Orders Only) 800-553-6847;
Order number: PB92-181056
fuels; ignition; flame propagation; combustion;
diffusion flames; predictive models; premixed flames;
radiation; surface temperature; radiation ignition
Numerical studies are performed which show the evolution
of the combustion process over a flat fuel surface
subjected to an external source of radiation. Ignition
is caused either by the high temperature of the fuel
surface or by radiation absorption by the fuel vapor.
The surface is assumed to be either in a zero gravity,
initially stagnant air environment or in a stagnation
point flow field. Regardless of the source of ignition
considered or the type of the flow field, the same
sequence of events is predicted. This sequence of
events begins with a pre-ignition, radiation dominated
phase in which fuel and air mix above the fuel surface.
After ignition occurs, there is a period of weak
chemical reaction, which is followed by a period of
stronger reaction in which a premixed flame front
develops. Before dying out the premixed flame front
separates the fuel from the oxygen and leaves behind a
diffusion flame. The combustion and radiation processes
are shown to have a large effect on the flow field in
the stagnation point flow cases. For the case in which
ignition is caused by gas phase absorption, the
radiation required to cause ignition is so high that an
opposed jet flow is created. In the case in which
ignition is caused by the hot fuel surface, the
radiation is lower and the boundary layer remains almost
intact. For both types of ignition the premixed flame
fronts produced heat fast enough that the expanding gas
is able to drive the incoming flow back from the fuel
surface. After the premixed flame front dies out
leaving the diffusion flame the incoming flow again
dominates and a boundary layer reappears.