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We report the first successful xenon flash ignition of freestanding porous Si films in air. The minimum flash ignition energy (Emin) first decreases and then increases with increasing the porous Si film thickness due to the competition between light absorption and heat loss. The Emin is lower for higher porosity film because high porosity reduces both the heat capacity and the thermal conductivity, facilitating the temperature rise. These results are important for initiating controlled porous Si combustion and preventing their unwanted combustion for safety reasons.

Aluminum (Al) is an attractive solid fuel for rocket propulsion and energy conversion systems due to its large volumetric energy density, earth abundance, and low cost. Nonintrusive optical flash ignition is attractive for many applications due to its simplicity and flexibility in controlling the area exposed to the flash. However, flash ignition of Al microparticles (MPs) is challenging due to their higher minimum flash ignition energy, which originates from weaker light absorption and higher ignition temperature compared to Al nanoparticles (NPs). Herein, the minimum flash ignition energy of Al MPs is reduced by the addition of WO3 NPs.