Green rocket propulsion: overview of nitrous oxide applications with emphasis on hybrid systems

• N 2 O’s role in HREs is reviewed with emphasis on kinetics and fuel choice. • Safety challenges of N 2 O decomposition are critically discussed. • N 2 O is compared to H 2 O 2 in green propulsion performance metrics. • Showerhead, vortex, and swirl injectors are assessed for regression rate boost. The growing demands for environmentally sustainable and cost-effective space propulsion have reinvigorated research into Hybrid Rocket Engines (HREs), particularly those utilizing nitrous oxide (N 2 O) as an oxidizer. This paper provides a comprehensive review of recent N 2 O applications in rocket propulsion systems, with a primary focus on hybrid applications. The paper presents a technical overview of N 2 O’s physical and chemical properties, including its decomposition kinetics and safety considerations, comparing it with other green oxidizers such as hydrogen peroxide. The role of N 2 O in monopropellant, bipropellant, and hybrid propulsion architectures is also discussed. Special attention is paid to the challenges associated with hybrid propulsion, including low fuel regression rates and combustion efficiency, and the injector technologies developed to mitigate them. Injector designs such as showerhead, vortex, pressure-swirl, and impinging configurations are reviewed in the context of their influence on atomization and fuel-oxidizer mixing. Experimental findings, historical applications and recent technological advances are surveyed to provide a well-rounded assessment of N 2 O’s viability.