Flame spread over solid materials under reduced buoyancy/gravity

Space exploration is a shared human aspiration that presents significant challenges, with fire being a major threat. The unique low-gravity, reduced-buoyancy environments of spacecraft and extraterrestrial habitats profoundly alter fluid dynamics, chemical reactions, and heat-mass transfer, leading to drastic changes in fire behavior. Understanding the solid material combustion under these conditions is vital for spacecraft fire safety and advances fundamental combustion science. This review synthesizes research on flame spread over solid materials under reduced buoyancy/gravity over the past half-century. It uniquely integrates the studies conducted in micro- and partial-gravities with ground-based experiments designed to mimic these environments. The review begins with the theoretical models defining the flame behavior and examines experimental findings from low gravities. These results reveal the important roles of “smothering” effects and radiative heat loss due to the suppressed natural convection, which drive a transition from two-dimensional to three-dimensional flame structures. Ground-based simulation methodologies, including reduced pressure environments and narrow channel apparatus, are critically examined for their ability to replicate low gravities. Stagnation point low-stretch diffusion flames are also included as a ground-based method to simulate the reduced-buoyancy effects on the spreading flame front from a more microscopic perspective. By comparing actual low-gravity data with simulated environments, the review introduces key similarity laws but also discusses the limitations of these methods in fully capturing low-gravity combustion dynamics. As the first integrated review of this topic, this work provides essential insights for ensuring the fire safety of human space exploration in the decades to come.