Electrohydrodynamic jet stability of ionic liquid–hydroxylammonium nitrate (HAN) mixtures under thermochemical propulsion constraints

Hybrid propulsion systems combining electric and chemical propulsion have attracted considerable attention because they can provide both high specific impulse and high thrust within a single propulsion architecture. This study investigates the feasibility of ionic liquid–hydroxylammonium nitrate (HAN) mixtures as a single propellant for hybrid electro-chemical propulsion systems through electrospray experiments and thermodynamic performance analysis. Electrospray experiments were conducted under atmospheric conditions using a downward-oriented annular slit emitter to examine the effects of HAN concentration, applied voltage, and flow rate on jet morphology, droplet formation, and pulsation behavior. Increasing HAN concentration significantly altered electrospray characteristics by reducing viscosity and increasing electrical conductivity. Higher applied voltages promoted finer atomization and increased pulsating frequency, whereas higher flow rates generated larger droplets due to enhanced inertial effects. Among the tested compositions, mixtures containing 50%–75% HAN exhibited stable jet emission, favorable atomization characteristics, and enhanced pulsation response. To evaluate chemical propulsion performance, NASA chemical equilibrium with applications calculations were performed at a chamber pressure of 300 psia and a nozzle expansion ratio of 50. HAN-rich mixtures showed higher adiabatic flame temperatures, increased specific impulse, and lower molecular-weight combustion products. Overall, the results demonstrate that mixtures containing 50%–75% HAN provide the most favorable balance between electrospray stability and combustion performance. This study identifies an optimal propellant composition range (50%–75% HAN) that simultaneously satisfies the competing demands of electrohydrodynamic emission stability and chemical propulsion performance, providing a key design guideline for future single-propellant hybrid propulsion systems.