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Exploring the ignition, combustion, and agglomeration dynamics in aluminized NEPE propellants
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DOI：10.1016/j.combustflame.2026.115017.png)
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Abstract
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Nitrate ester plasticized polyether (NEPE) propellants are widely recognized for their high specific impulse, robust combustion stability, and substantial load-bearing capacity. The incorporation of aluminum particles further boosts their energy density and propulsion efficiency. However, a persistent challenge arises from the tendency of aluminum particles to agglomerate on the combustion surface, which often results in incomplete oxidation, nozzle clogging, and detrimental two-phase flow losses. To address these issues, this study presents a comprehensive experimental investigation into the ignition, combustion, and agglomeration behaviors of aluminum-containing NEPE propellants. A high-pressure, sealed combustion chamber was employed to conduct controlled ignition and burning tests. Ignition delay times and burning rates were recorded using a dual-photodiode setup, while high-resolution optical imaging captured the dynamics of aluminum agglomeration in real time. Post-combustion residues were collected and subjected to detailed analysis using scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDS) to characterize their microstructure, elemental composition, and particle size distribution. The findings reveal that elevated pressure and oxygen concentration notably reduce the ignition delay and enhance both combustion intensity and burning rate. Structurally, the aluminum agglomerates exhibit a molten aluminum core enveloped by a shell of mixed-phase alumina. The condensed combustion products (CCPs) were classified into five distinct morphologies: spherical agglomerates, fractured agglomerates, oxide-capped particles, interconnected agglomerates, and fine oxide smoke particles. The ultimate shape and size of these agglomerates appear to be governed by the dynamic interplay between molten aluminum coalescence and oxide shell rupture. Notably, as chamber pressure rises from 0.1 to 2.0 MPa, the mass-weighted average particle diameter (D43) of CCPs decreases by approximately 36% in nitrogen and 30% in air. The results indicate that both the ignition delay time and burning rate are strongly influenced by ambient pressure and oxygen concentration, while the D43 of aluminum agglomerates shows a negative correlation with the burning rate. This relationship arises because the burning rate governs the residence time of aluminum particles on the burning surface, thereby directly affecting the extent of agglomeration. Collectively, this study reveal a coupled interaction mechanism among ignition, combustion, and agglomeration processes within NEPE propellants.
Keywords:
Ignition dynamics
Combustion behavior
Aluminum agglomeration
NEPE propellants
Burning rate
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