IGNITION AND BEHAVIOR OF LAMINAR GAS-JET DIFFUSION FLAMES IN MICROGRAVITY

This paper presents the results of studies on the ignition and behavior of cylindrically symmetric, laminar diffusion flames of methane and propane in quiescent air under microgravity conditions. The experiments were conducted in the 2.2 s NASA-Lewis Research Center Drop Tower. The characteristics of gas-jet diffusion flames ignited in microgravity environments have not been reported in the past. In prior research, similar flames were ignited in normal gravity and then subjected to the microgravity condition once the flame was established. The different ignition methods result in different flame behavior and conclusions in relation to extinction, transient adjustment, and approach toward steady state in microgravity. Specifically, some of the flames of the previous studies, which were in a transient state or reportedly extinguished, reach a near-steady state when ignited in microgravity. In addition, low-flow-rate methane flames in the present study (filmed at 15 frames/s) were entirely blue, whereas blue was not discernible in the microgravity flames of the previous works (filmed at 400 frames/s). Based on these findings, it is concluded that some of the previously reported "extinguished" flames may have been blue (and not visible on the high-speed film). In this paper, comparisons between the two methods of ignition and observations of the flame behavior and distinct nature of flame color and luminosity are presented. Application of a steady-state, parabolic model has shown satisfactory agreement between the predicted and observed flame heights for those flames that reached a near-steady state in the 2.2 s period of microgravity. © 1990 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.