The
ionic liquid dual-mode propellant, mainly composed of hydroxylammonium
nitrate (HAN), 1-ethyl-3-methylimidazolium ethyl sulfate ([Emim][EtSO4]), and H2O, has shown good capabilities for both
chemical and electrospray space propulsion. This work focuses on the
chemical performance of the propellant by investigating its decomposition
and burning processes. First, the thermogravimetric–Fourier
transform infrared spectroscopy measurement is employed to identify
different stages of the propellant decomposition, including water
vaporization and decompositions of HAN and [Emim][EtSO4]. The effects of the Ir/Al2O3 catalyst, H2O mass fraction, and heating rates on the decomposition process
are analyzed, and the gaseous products are measured. It is found that
the decomposition of HAN and [Emim][EtSO4] is coupled with
the oxidation of small intermediates. The kinetic parameters of overall
catalytic decomposition/oxidation reactions at different stages are
determined by fitting the thermogravimetric (TG) curves. Then, the
burning of the propellant is organized in a well-designed optical-accessible
catalytic bed with a controllable preheating device and a fixed flow
rate of 2 mL/min. The ignition delay and burning evolution are determined
from the time-resolved temperature sampling at four different axial
positions. When the spatially averaged preheating temperature is 130–180
K, the ignition delay varies from 0 to 60 s, mainly controlled by
the prior HAN decomposition rate. Finally, a one-dimensional model
incorporating kinetic parameters from TG fitting is established to
characterize the ignition process of the propellant, which quantitatively
elucidates the effect of preheating on the ignition delay.