The combustion of metal suspensions occupies an important place in modern technology, such as propulsion or chemical safety. Metals have even been proposed as a possible carbon-free energy carrier as well as a propellant for in-situ production on the Moon or on Mars. It has been discovered that for a given field of parameters, the heterogeneous flames exhibit an unusual behavior. The flame cease to propagate as continuous fronts and become dominated by discrete effects, leading to low-velocity percolation-like propagation. This phenomenon has been reported in other areas of science such as in self-propagating high-temperature synthesis (SHS), chemical kinetics, or biology; the study of discrete flames in metal suspensions may therefore be crucial in understanding front propagation in many of these systems. Due to particle settling and buoyancy-driven disruptions of the flame, both caused by gravity, a clear parametric study of discrete flames can only be realized in microgravity environments. This lead to the PERWAVES experiment, performed in a microgravity environment aboard the European Space Agency sounding rocket Maxus 9, launched on April 7th, 2017. The tests involved the propagation of flames of iron suspensions dispersed in oxygen/xenon gas. The particle concentration was varied and two different oxygen/xenon proportions, 20%/80% and 40%/60% respectively, were used. It was found that flames propagate at low average speed (~1 cm/s), insensitive to combustion time of individual particles, in agreement with discrete regime predictions.
