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

The growing demands for environmentally sustainable and cost-effective space propulsion have reinvigorated research into Hybrid Rocket Engines (HREs), particularly those utilizing nitrous oxide (N2O) as an oxidizer. This paper provides a comprehensive review of recent N2O applications in rocket propulsion systems, with a primary focus on hybrid applications. The paper presents a technical overview of N2O’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 N2O 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 N2O’s viability.