Calcium fluoride promoting the combustion of aluminum powder

Aluminum (Al) powder as an additive can enhance the specific impulse of propellants. However, it is hard to completely burn due to its aggregates in the combustion of propellants. To improve the combustion of Al powder, calcium fluoride (CaF 2 ) was added to micron-sized Al powder to form the Al/CaF 2 mixture, whose thermal behaviors, ignition and combustion performance, and combustion products were investigated. Micron-sized Al powder with CaF 2 addition can decrease its ignition delay time and increase its self-sustaining combustion time. The corresponding values can be decreased by more than 65% and increased by more than 16%, respectively. Compared with micron-sized Al powder, an obvious gas-phase combustion occurs in the Al/CaF 2 mixture. The agglomeration mechanism of Al combustion in the Al/CaF 2 mixture were analyzed. On the one hand, the uneven distribution of oxidant leads to a pressure difference during combustion to accelerate Al agglomeration; on the other hand, the melting-agglomeration-combustion process occurs because the melting temperature and the ignition temperature of Al have a big difference. In addition, an improved Al combustion mechanism was established. • CaF 2 can decrease the ignition delay time and increase the self-sustaining combustion time of Al powder. • The addition of CaF 2 can cause an obvious gas-phase combustion of Al powder. • The presence of pressure difference causes Al agglomeration during combustion. • The process of Al agglomeration and gas-phase combustion was captured in detail. • The optimized gas phase combustion mechanism of Al powder was established.