Fuel–oxidizer integrated ionic liquid for electrically controlled solid propellants based on hydroxylammonium nitrate

Hydroxylammonium nitrate-based electrically controlled solid propellants (HAN-ECSP) combine safety and thrust controllability but suffer from low energy output and incomplete combustion due to HAN's limited thermal stability and a lack of compatible fuels. This study introduces a fuel–oxidizer integrated ionic liquid (IL) 1-ethyl-3-methylimidazolium perchlorate ([Emim][ClO₄]) into HAN-ECSP formulations to enhance electrically controlled combustion performance. The [Emim]⁺ cation scavenges electrophilic radicals, suppressing premature HAN decomposition during early thermal stages. In the process of electrically controlled combustion, the degradation of [Emim]⁺ occurred due to the ·OH radicals that were generated at the anode during electrification, subsequently promoting combustion. Simultaneously, it rapidly amalgamated with the free radicals produced during the combustion process to terminate chain reactions upon power interruption. This mechanism significantly reduced both ignition and extinguishment delays to less than 100 ms—a duration notably shorter than that observed in conventional HAN-ECSPs. Additionally, this method eliminated the traditional reliance on water for flame extinguishment. The oxidizer ClO₄⁻ shifts the decomposition temperature range of Polyvinyl alcohol to lower temperatures and enhances its degree of decomposition. Through their synergistic action, the IL-ECSP achieve a more thorough thermal decomposition and a more concentrated heat release profile. The volumetric combustion heat of 20%IL-ECSP reached 16,687.06 J/cm³, which was 70% higher than that of ECSP without IL (9835.45 J/cm³). Moreover, increasing the [Emim][ClO₄] content broadens the voltage-regulated range of the propellant's average burning rate and yields higher average burning rates and combustion temperatures during burning. This work therefore presents a novel formulation strategy for HAN-ECSPs that enhances energy output while preserving excellent electrical controllability.