Two polymorphic hydrogen peroxide solvates of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20; wurtzitane is an alternative name to iceane) were obtained using hydrated α-CL-20 as a guide. These novel H2O2 solvates have high crystallographic densities (1.96 and 2.03 g cm−3, respectively), high predicted detonation velocities/pressures (with one solvate performing better than ϵ-CL-20), and a sensitivity similar to that of ϵ-CL-20. The use of hydrated materials as a guide will be important in the development of other energetic materials with hydrogen peroxide. These solvates represent an area of energetic materials that has yet to be explored.

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Hydrogen Peroxide Solvates of 2,4,6,8,10,12‐Hexanitro‐2,4,6,8,10,12‐hexaazaisowurtzitane

Ablative materials are commonly used to protect the nozzle metallic housing and to provide the internal contour to expand the exhaust gases in both solid and hybrid rockets. Because of interaction with hot gas, these materials are chemically eroded during rocket firing, with a resulting nominal performance reduction. The objective of the present work is to study the erosion behavior of graphite nozzles in hybrid engines at different operating conditions and compare results with those obtained for solid motors. A main distinctive feature of hybrid engine operating conditions is, in fact, a greater concentration of oxygen-containing combustion products than solid motors. The adopted approach relies on a validated full Navier–Stokes flow solver coupled with a thermochemical ablation model that takes into account heterogeneous chemical reactions at the nozzle surface, rate of diffusion of the species through the boundary layer, ablation species injection in the boundary layer, heat conduction inside the nozzl...

Numerical Analysis of Nozzle Material Thermochemical Erosion in Hybrid Rocket Engines

This paper deals with an experimental investigation into the stability behavior of a hybrid rocket where gaseous oxygen is fed with either an axial conical subsonic nozzle or a radial injector. The influence of the oxidizer-injection configurations on the motor stability is thoroughly examined. These distinct oxidizer-injection techniques allowed unveiling key and so far unreported features of the hybrid rocket combustion stability, especially emphasizing the role of vortex shedding which occurs in both the pre- and postcombustion chamber. Axial and radial injectors caused completely stable and unstable combustor operations, respectively, and this fact has been attributed to the fluid dynamics and unsteady heat release at the entrance of the fuel grain port. In particular, the unstable combustion in the radial-flow injector motor was dominated by low-frequency pressure oscillations, around 10-20 Hz. These low-frequency pressure oscillations were always accompanied by longitudinal acoustic modes. In some cases, the pressure oscillations abruptly increased, reaching peak-to-peak amplitude close to 70% of the mean chamber pressure, which is somewhat unusual for hybrid engines. Vortex shedding in the aft-mixing chamber is considered as the main driving mechanism of this latter behavior.

Acoustics, Vortex Shedding, and Low-Frequency Dynamics Interaction in an Unstable Hybrid Rocket

Clean and highly efficient production of solar fuels as well as the effective methods to store the solar fuels have long been sought to solve global energy and environmental issues. Among solar fuels such as gaseous hydrogen and carbon monoxide, aqueous hydrogen peroxide (H2O2) is an ideal chemical for energy storage, because the endothermic H2O2 decomposition produces only water and oxygen. In addition, H2O2 can be transported in plastic containers with a high energy density. H2O2 can be converted to electricity using H2O2 fuel cells without membrane, composed of an anode and a cathode, which selectively catalyze H2O2 oxidation or reduction. The one-compartment structure without membrane is more promising to develop low-cost fuel cells as compared with a two-compartment structure with expensive membranes. This article provides a focused review of recent developments and future perspectives of H2O2 fuel cells without membranes, combined with H2O2 production from seawater and dioxygen in the air utilizing solar energy.

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Hydrogen Peroxide used as a Solar Fuel in One‐Compartment Fuel Cells

Nomenclature A = Arrhenius preexponential constant, mm/s B = blowing parameter, ρf r/(Gcf /2) Bmod = modified blowing parameter, B exp(q′′ r /q′′ c ) cs = fuel specific heat, J/kg · K cf = skin-friction coefficient cp = gas isobaric specific heat, J/kg · K C∗ = characteristic exhaust velocity, m/s D = diameter, cm D = mass diffusivity, m2/s Da = Damkohler number Dh = hydraulic diameter, cm Ea = activation energy, kcal/mole G = local, bulk mass flux, kg/m2 · s h = enthalpy, J/kg; port height, mm Isp = specific impulse, s k = absorption coefficient, kinetic rate constant K = concentration L = length of fuel slab, cm Le = Lewis number Np = particle number density Nu = Nusselt number O/F = oxidizer to fuel mass mixture ratio Pr = Prandtl number p = pressure, atm or MPa q′′ = heat flux, W/m2

Review of Solid-Fuel Regression Rate Behavior in Classical and Nonclassical Hybrid Rocket Motors

This paper was aimed at analyzing the static engine firings results obtained by means of a hybrid rocket where gaseous oxygen was supplied into axial-symmetric polyethylene cylindrical grains through two different injector configurations: an axial conical subsonic nozzle and a radial injector. The axial injector is considered interesting because of its easy design and the remarkable feature that it produces no significant pressure oscillations for the stabilizing effect due to the hot gas recirculation zone established within the combustion port. To take advantage of its qualities, the assessment of the regression rate variations under the flow field generated by this configuration is required. For the investigated set of operating conditions, the instantaneous regression rates exhibit a time-and-space dependence caused by the impinging jet zone dynamics, while the average regression rates are higher and less mass flux dependent than those achieved with the radial injection motor and expected from the turbulent flow through pipes. A comparison to the data from the radial injector was further drawn in terms of combustion efficiency, fuel consumption profiles, and combustion stability. The radial injector, at the same mass flux and pressure, produces lower regression rates, high pressure oscillations and worse combustion efficiency at the same L*, but more uniform fuel consumption.

Influence of a Conical Axial Injector on Hybrid Rocket Performance

Trade-off between paraffin-based and aluminium-loaded HTPB fuels to improve performance of hybrid rocket fed with N2O

An experimental performance evaluation, conducted with static firings of a laboratory-scaled hybrid rocket burning gaseous oxygen and several fuel combinations, aimed at raising the fuel regression rate is addressed in this paper. Pure hydroxyl-terminated polybutadiene has been tested as a baseline fuel and compared to hydroxyl-terminated polybutadiene loaded with nano- or micrometer-sized aluminum, nanosized Viton®-coated aluminum, magnesium hydride, magnesium, nanosized iron, and iron with magnesium. After a first exploratory test series in which both radial- and axial-injection arrangements have been analyzed, an axial nozzle has been selected to feed oxygen into single-port fuel grains; in that configuration, the port diameter effect upon the regression rate has been further investigated, revealing faster regression with larger port diameters at a given mass flux. The outcomes in terms of regression rate, combustion efficiency, and motor stability are examined. A thorough comparison with the available...

Experimental Investigation into the Effect of Solid-Fuel Additives on Hybrid Rocket Performance

Performance comparison between two different injector configurations in a hybrid rocket

This paper describes the development of a novel catalytic system capable of decomposing hydrogen peroxide. The system is based on ceramic honeycombs in yttria-stabilized zirconia, with manganese oxides as the active phase. The effectiveness of different catalyst preparation procedures, entirely developed in house, has been evaluated using a plug-flow reactor operating with diluted hydrogen peroxide vapors. A monopropellant test bench has been then assembled to verify the performance of a selected number of catalytic samples in a test environment closer to the actual operating conditions of a space propulsion system: the catalysts have demonstrated decomposition efficiencies exceeding 90%. The concept has been finally scaled up to a hybrid configuration based on the utilization of hydrogen peroxide as the oxidizer and high-density polyethylene as the fuel: the possibility to ignite and reignite the fuel grain has been demonstrated and propulsive efficiencies close to 90% have been measured.

A. Russo Sorge

Papers

Influence of a Conical Axial Injector on Hybrid Rocket Performance

Trade-off between paraffin-based and aluminium-loaded HTPB fuels to improve performance of hybrid rocket fed with N2O

Experimental Investigation into the Effect of Solid-Fuel Additives on Hybrid Rocket Performance

Performance comparison between two different injector configurations in a hybrid rocket

Novel Structured Catalysts for Hydrogen Peroxide Decomposition in Monopropellant and Hybrid Rockets