Modeling vaporization and combustion processes in staged and externally-ignited HTP/RP-1 green bipropellant systems

In the pursuit of replacing toxic hydrazine-based propellants, high-test peroxide (HTP) combined with RP-1 represents a promising option for green medium-thrust-class storable bipropellants targeting in-space propulsion applications. Yet, numerical investigations of vaporization and combustion characteristics of HTP/RP-1 thrusters are relatively scarce in the literature. Thus, in the present study, we first formulate a pseudo-molecule surrogate and a Bayesian-inference-based four-component surrogate to mimic RP-1 physicochemical properties, equipping them with 119- and 122-species chemical reaction mechanisms, respectively, developed following the hybrid-chemistry (HyChem) approach. Consequently, we characterize staged and externally-ignited HTP/RP-1 bipropellant systems by investigating the influence of the RP-1 surrogate formulation strategy and of the hydrogen peroxide concentration in the HTP oxidizer on (i) thermochemical equilibrium and rocket propulsive performances, (ii) zero-dimensional vaporization of isolated HTP and RP-1 droplets, while accounting for real-fluid thermophysical modeling and high-pressure vapor–liquid equilibrium interfacial thermodynamics, and (iii) ignition characteristics of HTP/RP-1 mixtures, while accounting for real-fluid thermodynamics and the distillation characteristics of the four-component RP-1 surrogate mixture. While hydrogen peroxide concentration constantly impacts the propulsive and vaporization figures of merit more than the RP-1 surrogate variability, leveraging a multi-component RP-1 surrogate delivers an increase of up to 2 s in the specific impulse prediction compared with the pseudo-molecule formulation. Nonetheless, the RP-1 surrogate complexity affects ignition delay time predictions to an extent comparable with hydrogen peroxide concentration as the multi-component RP-1 surrogate features preferential vaporization, with relative discrepancies between RP-1 surrogates even exceeding 200%. In summary, we provide a collection of methodologies and instruments that pave the way toward extensively using computational fluid dynamics (CFD) to assess vaporization, mixing, combustion, and propulsive performances in HTP-based staged or externally-ignited bipropellant systems.