COOL FLAME PROPAGATION SPEEDS

Abstract

Cool flames are studied at reduced-gravity in a closed, unstirred, spherical reactor to minimize complexities associated with natural convection. Under such conditions, transport is controlled by diffusive fluxes and the flames are observed to propagate radially outward from the center of the reactor toward the wall. Intensified video records are obtained and analyzed to determine the flame radius as a function of time for different vessel temperatures (593–623 K) and initial pressures (55.2–81.4 kPa) using an equimolar (φ = 5) propane-oxygen premixture. Polynomial-fits are applied to the data and differentiated to determine the cool flame propagation speeds. In nearly all cases considered, the flame decelerates monotonically and in some cases, subsequently retreats towards the center of the reactor. The flame speed is also tabulated as a function of the flame stretch rate. Extrapolation of the cool flame speeds to zero stretch is then performed to determine the “unstretched” cool flame propagation speeds.

Keywords:

• Cool flames
• Flame speed
• Low-temperature combustion
• Reduced-gravity

Special thanks are offered to the NASA KC-135 crew, pilots and support staff. This work was funded by NASA grant NCC3-1008 and NSF GRFP.