Solid composite propellants continue to play a key role in space and defense propulsion due to their high energy density, ease of handling, and manufacturing scalability. While several studies have investigated the effect of individual additives on propellant performance, most are limited to a fixed weight percentage or particle size, making it difficult to derive comprehensive design guidelines. This study presents a systematic comparative investigation into the influence of various additives (Al, Fe₂O₃, CuCr₂O₄, and thermite combinations) and their particle sizes/loadings on the performance of polyvinyl chloride (PVC)/ammonium perchlorate (AP)-based composite propellants. Over 30 distinct formulations were experimentally characterized for burn rate, density, adiabatic flame temperature (AFT), and mass flow rate to establish comprehensive performance trends and trade-offs. The results demonstrate that smaller metal particle sizes and higher additive loadings generally enhance burn rate and mass flow, indicative of catalytic effects. Thermochemical analysis supports the significant exothermic contribution of the Al–Fe₂O₃ thermite reaction (–851.5 kJ/mol) to increased combustion energy. Furthermore, calculated oxidizer-balance percentages correlate with AFT and burn rate, with near-stoichiometric formulations exhibiting peak performance. The highest theoretical thrust (∼73 N) was predicted for a Fe₂O₃-rich formulation aligning with high energy and burn rate. While the catalytic mechanisms of these additives are known, the key contribution of this work lies in the extensive, comparative dataset across a wide range of propellant compositions. This broad dataset serves as a valuable resource for optimizing propellant formulations, validating combustion models, and guiding future propellant design.

Hydrazinium nitroformate (HNF) is a chlorine-free, high-energy oxidizer with promising applications in green propulsion systems. This review examines the thermal decomposition, combustion kinetics, flame structure, and behavior of HNF, while critically evaluating the current body of literature. Thermal studies reveal that HNF undergoes two-stage decomposition, with exothermic peaks at 136°C and 138°C and an activation energy of 150 kJ/mol, determined using Kissinger and Ozawa methods. The decomposition products include nitroform, hydrazine, and nitrogen oxides, with a 72.5% weight loss in the first stage (105°C–142°C) and 24.5% in the second stage (142°C–210°C). Combustion studies identify a three-zone flame structure: fizz zone, dark zone, and luminous flame zone, with temperatures ranging from 1320 to 1540 K near the surface to 2720 K in the outer flame. HNF exhibits a high-pressure exponent (∼0.85), necessitating optimization through burn rate modifiers (BRMs) and advanced formulations. While HNF demonstrates superior specific impulse and reduced exhaust plume radiation compared to ammonium perchlorate (AP), its needle-like crystal morphology poses challenges for handling and propellant integration. This review emphasizes the need for advanced diagnostic techniques, computational modeling, and innovative BRMs, along with polymeric binders that are compatible with HNF and can improve the performance of HNF-based systems, offering valuable insights for green propellant development.

Modifications achieved in the ignition delay time of shellac-based pyrotechnic igniter using different additives of varying particle size are observed and compared. 40 different pyrotechnic compositions were prepared using five additives i.e. aluminium, magnesium, red iron oxide, naphthalene and activated carbon. Four particle sizes i.e. <75 μm, 75–150 μm, 150–300 μm, 300–600 μm and two weight percentages of the additives i.e. 3% and 5% were investigated. A base composition, without any additive, was also prepared to compare and investigate the effects of additives and their particle size on the ignition delay time of the composition. The incorporation of additives significantly reduced the ignition delay time of the base composition. Addition of 5% red iron oxide having a particle size of <75 µm, delivered the maximum decrement in ignition delay time i.e. by 49.7%. Naphthalene of particle size of <75 µm added as 3% in the composition weight, provided the minimum reduction in the ignition delay time i.e. by 13.7%. It was also observed that all of the additives exhibited a similar manner of decrement in ignition delay time as the particle size decreased, except for naphthalene which exhibited an opposite trend.