Transient Nano-Dense Molecular States as a Persistence–Stabilization Closure for Combustion Nanoparticle Inception

Nanoparticle inception remains one of the least constrained steps in predictive combustion particle modeling. In soot models, detailed gas-phase chemistry can describe fuel decomposition, aromatic growth, PAH chemistry, radical pathways, oxidation, surface growth, and coagulation, yet the conversion of molecular precursors into the first persistent particles is often represented by empirical nucleation rates, selected dimerization reactions, or source terms into a first particle bin. Similar uncertainty occurs in inorganic flame-aerosol models, where the earliest molecular-to-particle transition is frequently reduced to classical or semi-empirical nucleation expressions. This paper formulates the transient nano-dense molecular state (NDMS) hypothesis as a practical persistence–stabilization closure for this inception gap. NDMS is defined as a transient, non-equilibrium, locally dense ensemble of associated molecular or sub-molecular precursor units that remains reversible on the dissociation timescale and contributes to particle inception only when chemical or structural stabilization competes successfully with dissociation and other losses. The framework separates precursor association, cluster dissociation, competing non-stabilizing loss, and stabilization into distinct model components. It introduces an operational density-enhancement criterion, association- and stabilization-weighted precursor descriptors, bounded stabilization probabilities, and a minimal zero-dimensional demonstration. Implementation routes are outlined for detailed chemistry, sectional population balances, moment methods, and reduced CFD closures. For soot, the framework provides a structured way to couple PAH clustering with radical-driven stabilization and chemical aging. For inorganic systems, illustrated using TiO₂ formation, NDMS is treated cautiously as a system-specific modeling architecture for reactive oxide-cluster formation rather than as evidence of a universal microscopic pathway. The hypothesis is presented as falsifiable: it should be retained only where constrained NDMS closures improve inception-specific observables such as onset location, pressure dependence, early particle number density, precursor sensitivity, and cluster-sensitive diagnostics.