Associate Professor of Aeronautics and Astronautics
Benhidjeb-Carayon, Alicia ; Drolet, Michael ; Gabl, Jason ; Pourpoint, Timothée
Journal of Propulsion and Power, Mar/Apr 2019, Vol.35(2), pp.466-474
This paper reports on the reactivity and hypergolicity of different solid fuels with both nitrogen tetroxide (NTO) and mixed oxides of nitrogen (MON) oxidizers using drop tests. The main objectives of the study were to identify hypergolic additives for use with a paraffin-based hybrid fuel, and to quantify the influence of pressure on the reactivity of these different potential additives. As expected, it was found that ignition delays decrease as pressure increases. With 75 wt.% NTO and 25 wt.% nitric oxide (MON-25) and borane-trimethylamine, a decrease in minimum ignition delays of 95% was observed when pressure was increased by 50 psi, whereas pararosaniline base went from nonhypergolic to hypergolic over the same pressure range. Also, all the compounds tested showed longer ignition delays with increasing concentration of nitric oxide. Finally, common features observed in silyl amides, amides, and organic compounds were investigated. Further work will be needed to verify whether these preliminary trends can be generally applied to the selection of additional solid hypergolic propellants.
Mathews, Joshua ; Gabl, Jason ; Pourpoint, Timothée
Journal of Propulsion and Power, Sep/Oct 2019, Vol.35(5), pp.964-972
Biphasic dispersion fuels (BDFs) are multiphase mixtures in which liquid droplets are trapped in a solid binder to form stable hybrid propellant grains. As the flame transfers heat to the fuel grain surface, the internal pressure of the liquid droplets rises, leading to microexplosions that force small droplets and fuel vapors into the flame zone. The combined effects of the liquid fuel being dispersed in the combustion chamber and the craters formed by surface-level microexplosions should lead to high combustion efficiencies and high regression rates. As an initial step in developing BDF, nonionic surfactants and a high shear homogenizing unit were used to emulsify water and ethanol in paraffin wax. The mixtures were cooled and casted into cylindrical fuel grains, and their performance was evaluated with gaseous oxygen in an optically accessible hybrid rocket motor. Results indicate that both BDF formulations exhibited increased regression rates, relative to neat paraffin wax, at all oxidizer mass fluxes tested. The water-based fuels demonstrated up to a 32% increase in regression rate and a 1% increase in average combustion efficiency, relative to neat paraffin fuels. The ethanol-based fuels demonstrated up to a 95% increase in regression rate and a 4% decrease in average combustion efficiency, relative to neat paraffin fuels.
Early Liquid and Gas Phase Hypergolic Reactions between Monomethylhydrazine and Nitrogen Tetroxide or Red Fuming Nitric Acid
Black, Ariel T ; Drolet, Michael P ; Pourpoint, Timothée L
Combustion Science and Technology, 02 November 2019, Vol.191(11), pp.1990-2005
Monomethylhydrazine (MMH) fuel and nitrogen tetroxide (NTO)-based oxidizers embody the state of the art for hypergolic propellants. Despite their wide use, a detailed understanding of the full reaction chemistry between MMH and NTO, from early liquid phase reactions to ignition in the gas phase, is lacking. The gas phase reactions are relatively well understood with several spectroscopic techniques well suited to probe gaseous reaction zones and numerous computational chemistry studies supporting the experimental data. The present paper focuses on the early liquid phase reactions with a method devoted to the determination of Arrhenius preexponential factors and activation energies for global, single-step liquid phase chemical reaction models for MMH-NTO and MMH-red fuming nitric acid (RFNA) systems. Using a temperature and atmosphere controlled droplet contact chamber, the liquid phase induction delay times of MMH-RFNA and MMH-NTO were examined by capturing drop on drop tests at frame rates from 100,000 to 500,000 fps. Results indicate induction delays on the order of 30–100 microseconds and 10–40 microseconds for MMH-RFNA and MMH-NTO, respectively, and distinct reaction rate parameters for both pairs of propellants.