Ignition and combustion characteristics of single Al-Li alloy fuel microparticles in CO2 atmosphere

Introducing tiny elemental lithium (Li) into aluminum (Al) to form Al-Li alloy has been proved to be a promising potential in substituting for Al in air. However, the ignition and combustion performance of Al-Li in CO₂ atmosphere (as one of main gas products of propellant pyrolysis) has not been investigated. In this work, a comparative study was conducted on the laser-induced ignition and combustion characteristics of individual micron-sized Al-Li alloy (2.5 wt % Li) particles and pure Al fuel particles in CO₂ atmosphere. It was found that the addition of Li prolonged the ignition delay of Al by 116.1 %, which is significantly different with the behavior in air or oxygen atmosphere. The intermediate products during ignition were acquired by accurate quenching technology via controlling the laser operation time to the millisecond level, and its characterization results revealed the presence of Li₂CO₃, indicating that Li in the Al-Li alloy could firstly react with CO₂ to form Li₂CO₃ during ignition, which restricted the expansion of particles and thus prolonged the ignition delay. In comparison to pure Al, the combustion flame propagation of Al-Li in CO₂ atmosphere was constrained, and the micro-explosion performance was mitigated, while there was no significant difference in the combustion temperature on the influence of overall exothermic performance. Finally, the ignition and combustion mechanism of Al-Li alloy in CO₂ was proposed and revealed, through combining with the characteristic analysis of the combustion residues and intermediate products.