Combustion Behaviour of ADN-Based Green Solid Propellant with Metal Additives: A Comprehensive Review and Discussion

Solid propellants play a crucial role in various civil, scientific, and defence-related aerospace propulsion applications due to their efficient energy release, high energy density, low fabrication cost, and ease of operation. Ammonium dinitramide (ADN) has gained considerable attention as a potential oxidizer for green solid propellants due to its high oxygen content, significant energy density, non-toxicity, and non-polluting combustion products, leading to lower environmental impact. As ADN is a new desirable oxidizer in the field of solid propellants, understanding the practicality and viability of the use of ADN in composite solid propellants necessitates a thorough understanding of its chemical and thermal decomposition pathways in addition to its combustion characteristics in the presence of other ingredients. ADN is being explored as an alternative to the traditionally used ammonium perchlorate (AP), a toxic oxidizer containing chlorine (Cl). Additionally, AP monopropellants often suffer from moderate burning rates and poor mechanical strength. To address these limitations, researchers have explored the incorporation of metal additives, such as aluminium (Al), magnesium (Mg), and metalloid boron (B), to enhance the combustion performance and burn rate of AP. These metals not only act as energy-rich additives but also influence the combustion process through various mechanisms. The incorporation of metal additives into ADN has shown promising enhancements in the overall energetic performance of green solid propellants. This review aims to provide an in-depth analysis of the thermal decomposition of ADN and its combustion behaviour, along with the combustion of ADN-based solid propellants with metal additives. Finally, based on an extensive review of the existing literature, various research pathways for focused future collaborative efforts are identified to further advance ADN-based "green" solid propellants.