Solid fuel for ramjets and rockets is generally some sort of plastic or rubber, oxidizer, and powdered aluminum. (The devil is in the details, don’t try this at home)
A new technology involving replace the aluminum particles aluminum-lithium alloy particles.
It prevents the formation of large aluminum droplets and corrosive combustion by-products: (paid subscription required)
A Purdue University spinoff will test an improved propellant for solid-fuel ramjet propulsion systems in hypersonic weapons under more than $1.1 million in contracts from the U.S. military.
Adranos is developing a solid rocket fuel, called Alitec, which uses aluminum-lithium (Al-Li) alloy powder instead of aluminum in the propellant mix, increasing fuel efficiency and reducing corrosive effects.
Aluminum powder is used in solid propellants as an additive to increase their density and combustion temperatures and stabilize the burn. But the metallic fuel forms large molten droplets that burn slowly. This results in a performance loss of up to 10%, which prevents a rocket from realizing its full range and payload capacity. The fuel also emits hydrochloric acid, which damages the environment and corrodes launch equipment.
Aluminum-lithium fuel has demonstrated increased performance through better combustion and higher efficiency. The large difference in boiling points between aluminum and lithium causes microexplosions of the metallic drops, reducing agglomerates. In addition, Al-Li virtually eliminates hydrochloric acid production while also improving theoretical specific impulse. Adranos calculates that Alitec could increase missile range by up to 68% and booster payload by 65%.
The latest contracts have been awarded by the Army’s Aviation and Missile Center and the Defense Department’s Rapid Reaction Technology Office. Under the contracts, tests at Purdue’s Zucrow Labs will use a heated air system capable of simulating a Mach 4 flight environment to determine Alitec’s functionality within a solid-fuel-ramjet hypersonic propulsion system.