Achieving efficient combustion with low electric energy of copper-catalyzed hydroxylamine nitrate gel materials via thermal transfer optimization

Abstract

Hydroxylamine nitrate-based gel propellant (HAN-GP) materials have received attention due to their special electro-ignition properties, repeatable ignition characteristics, and green, pollution-free advantages. However, as a gel material, HAN-GP has higher conductivity than solid materials, which leads to reduced heat accumulation and may act as a conductor, thereby extending the ignition delay time and greatly limiting its application as a fuel for microthrusters. In this study, a copper-catalyzed HAN-GP was reported, which advances the decomposition temperature of the propellant and increases the heat transfer rate during the propellant's electrolytic process, thereby shortening ignition delay and achieving efficient combustion. By adding 0.2% copper powder, the decomposition temperature of the modified propellant is 77 °C lower than that of the baseline. At room temperature (30 °C), HAN-GP containing 0.2% copper powder (sample 3) increased the thermal diffusivity from 0.12 to 0.55 mm² s⁻¹ and the thermal conductivity from 0.08 to 0.16 W m⁻¹ K⁻¹, significantly enhancing its thermal conduction performance and heat transfer efficiency. Due to early thermal decomposition and rapid heat conduction effects, the ignition delay of sample 3 (300 ms) was reduced by 64% compared to the baseline (839 ms) at 225 V and 8 mL min⁻¹. The total energy consumption of sample 3 decreased from 2500 J to 1800 J at 225 V and 4 mL min⁻¹, which is a reduction of 28%. Additionally, it was found that its ignition energy could be further reduced to 30 J after multiple ignitions.