Aerospace Engineering, Fuel Technology, Energy Engineering and Power Technology, Multidisciplinary
12
Scopus Publications
Scopus Publications
Unraveling the Transition from Standard to Reactive Atomization of Hypergolic Propellants Fábio A. S. Mota, Gabriel S. Dias, Lihan Fei, Chenglong Tang Journal of Propulsion and Power, 2026 The rocket propulsion community is actively seeking nontoxic, stable propellants to replace hazardous hydrazine-based options. This study provides a comprehensive analysis of the hypergolic ignition and spray characteristics of a newly developed eco-friendly self-igniting fuel (named PAHyp 3) with rocket-grade hydrogen peroxide (RGHP), using an impinging jet apparatus. Using synchronized high-speed visible shadowgraph and infrared imaging, the transition from standard atomization to reactive bubbly atomization was revealed by modulating propellant reactivity. Infrared imaging aids in tracking spray breakup, mixing, and the liquid-to-gas transition of droplets, providing valuable insights. To better understand the mixing and reactive bubbly dynamics before ignition, a simplified oxidation mechanism is proposed based on infrared imaging of hypergolic and non-hypergolic samples. This work reveals key multiphase reaction behaviors, including bubble nucleation and growth, bubbly droplet burst (microexplosion), and gas-phase combustion dynamics, along with insights into the reaction kinetics. Unlike non-hypergolic propellants, hypergolic combinations exhibit unique droplet dynamics characterized by bubble nucleation, expansion, and rapid consumption via internal and external evaporation. These mechanisms result in accelerated droplet disintegration and a shorter lifespan. The findings provide insights applicable to other hydrogen-peroxide-based bipropellants as well as to conventional hydrazine-based systems.
Characterizing Hypergolic Propellants Using Impinging Jets and Droplets in Acoustic Levitation Fábio A. S. Mota, Gabriel S. Dias, Lihan Fei, Yajie Zhang, Yanju Wei, et al. Journal of Propulsion and Power, 2025 This study presents an experimental investigation into the hypergolic ignition process of nontoxic propellants. Multispectral high-speed imaging was employed to capture the dynamic combustion process and temperature history across three distinct ignition setups. Six fuel samples containing different proportions of [Formula: see text]-tetramethylethylenediamine (TMEDA) and [Formula: see text]-methyldiethanolamine (MDEA), catalyzed with 1–2 wt% copper nitrate trihydrate (referred to as PAHyp 1), paired with rocket-grade hydrogen peroxide (RGHP) as the oxidizer, were selected. Formulations with higher concentrations of TMEDA containing 2 wt% catalyst paired with 95 wt% RGHP yielded ultrafast ignition delays as short as 7.6 ms in drop tests. Additionally, as binary droplet collision is a common occurrence in spray combustion, an acoustic levitator was proposed to study the ignition behaviors of droplet–droplet collision. The collision of binary droplets in the levitator, conducted at lower impact velocities, resulted in a minimum ignition delay time of about 17 ms. It was observed that depending on the size of the droplets and collision angle, ignition may not occur. This new approach to studying the dynamics of hypergolic ignition without “wall effects” has shown promise due to its ease of implementation. Finally, two fuel samples were selected to conduct ignition tests under flow conditions with an impinging jet apparatus. Remarkably, it was demonstrated that the addition of only 1 wt% is sufficient to achieve fast ignition with 90% hydrogen peroxide. Results from this new recipe indicate that samples containing at least 50% MDEA remain chemically stable for over 1 year and demonstrate competitive ignition and thermodynamic performance compared to conventional hydrazine-based fuels.
Simultaneous analysis of swirl spray dynamics using a telecentric shadowgraphy system Danilo A Machado, Fernando S Costa, Gabriel S Dias, Fábio A S Mota Measurement Science and Technology, 2025 Pressure swirl injectors generate conical hollow sprays with a liquid film adjacent to the exit nozzle. This paper describes macroscopic and microscopic parameters of sprays and disturbances of the liquid films formed by dual pressure swirl injectors, utilizing a telecentric shadowgraphy optical system. High-speed images with kHz frequencies were used for the simultaneous measurement of spray cone angles, breakup lengths, mean droplet velocities and wave amplitude ratios. Two injectors were tested with inner nozzles having Abramovich geometric constants K int = 2 and 2.125 and external nozzles with geometric constants K ext = 2.9 and 1.9792, respectively. Water was used as test fluid and the injection pressures were varied from 0.05 to 0.5 MPa. Simultaneous data from the same set of images allowed the calculation of the maximum surface wave growth rate. The results indicated that the maximum surface wave growth rate varies approximately linearly with the injection pressure. Measured maximum amplitude ratios of the conical liquid film disturbances varied in the range 2.32 < ln ( η bu / η 0 ) < 4.61, relatively close to recent experimental data on conical liquid films, but significantly lower than the calculated values for planar liquid films. The maximum amplitude ratio is a crucial parameter to determine breakup lengths. A new semi-empirical equation is proposed to describe the disturbance ratios of conical liquid films of pressure swirl injectors.
Schlieren Image Velocimetry of Swirl Sprays Danilo Almeida Machado, Fernando de Souza Costa, José Carlos de Andrade, Gabriel Silva Dias, Gustavo Alexandre Achilles Fischer Flow Turbulence and Combustion, 2023
