Opportunities and challenges of combustion in microgravity

This review considers the opportunities for enhanced fundamental combustion understanding from experiments where effects of buoyancy are eliminated, and the new challenges of fire safety considerations in nonbuoyant (spacecraft) environments. The following specific microgravity combustion phenomena are considered: stretched flames, flamefront instabilities, flammability limits and near-limit phenomena of gaseous premixed flames; structure, stability and soot processes in gaseous nonpremixed flames; flame propagation, smoldering and materials synthesis in heterogeneous premixed flames; flame spread, gasification and combustion in heterogeneous nonpremixed flames; flame-inhibiting atmospheres, fire detection and extinguishment in spacecraft environments; and ground-based (drop tower and aircraft), sounding rocket and space-based (shuttle, space station) microgravity combustion research facilities that are either available or anticipated. The findings of the review highlight how buoyancy has impeded the rational development of combustion science, precluding observations of fundamental one-dimensional configurations, low Reynolds number flows and other limiting conditions that have been invaluable for developing understanding in other areas of science. Thus, experiments at microgravity provide an opportunity to finally merge theories and experiments for classical problems in order to advance the fundamental understanding of combustion phenomena. Additionally, combustion processes have been shown to be very different at normal gravity and microgravity so that improved understanding of combustion at microgravity is needed in order to address fire and explosion safety considerations for spacecraft.