Energetic Additives for Hybrid Rocket Propulsion - Review

Hybrid propulsion offers safe, reliable and environment friendly alternative to conventional systems. There is a wide range of propellants and additives reported for hybrid propulsion. In this paper some energetic particles comprising metals, and light metal hydrides and their advantages in terms of regression behavior are discussed. Additive particles like aluminium, boron, boron carbide, tungsten, iron, carbon, magnesium, magnesium hydride, aluminium hydride, lithium aluminium hydride, ammonium perchlorate and ammonia borane are discussed. Regression rate enhancement of 20%-150% has been reported and found to be dependent on additive percentage. Metals have high density and heat of oxidation which helps in regression rate augmentation. Metal hydrides are good source of hydrogen varying from 7.6% for Magnesium hydride to 19.6% for Ammonia borane. These hydrides release nascent hydrogen during combustion and improve regression rate thereby boosting specific impulse and characteristic velocity of the rocket. Energetic particle laden hybrid rocket fuel has potential to make chemical propulsion safer, economical and sustainable.