Investigation of the reaction kinetics of HTPB/AP/Al composites at high-heating rate

Due to its high energy density and process advantages, the HTPB/AP/Al composite system in solid propellants has become a mainstream formulation for engines. Analyzing the kinetics of aluminum oxidation and the mechanism of carbon and nitrogen polymerization is of key scientific significance to optimize the combustion efficiency of propellants and reduce the environmental impact. In this paper, the decomposition process at high heating rates due to the loading of trace samples with a high-energy pulsed laser (with a pulsed duration of 10ns, single-pulse energy of 100mJ, and a heating rate of ∼1013 K/s) is investigated by time-resolved laser-induced breakdown spectroscopy (TR-LIBS) and dual-wavelength temperature measurements. It is found that the CN and AlO molecular radiation exhibit temporal differences: the CN molecule peaks at 3μs (388.32nm) due to the C/N atomic composite reaction, whereas the AlO molecule (484.21nm), affected by the kinetic retardation of the aluminum oxidation, peaks at 15μs and lasts until 100μs. Calculations on the evolution of plasma temperature and electron density number confirm the predominance of ionization/dissociation of atoms in the high electron density phase. In contrast, neutral atom complexes dominate in molecular generation at low temperatures and low-density conditions. By establishing a three-parameter correlation model, including electron density, plasma temperature, and molecular radiation intensity, a multiscale spectroscopic experimentally derived kinetic framework is provided for better revealing the laws of energy release and the kinetics of high-temperature reactions. This work is of great significance for understanding energy release mechanisms, evaluating performance, and guiding formulation optimization of composite solid propellants.