A study of solid ramjet fuel containing boron–magnesium mixtures

Metalized solid fuels offer significant performance advantages for solid fuel ramjets (SFRJs), but their utility depends critically on particle ignition behavior, combustion timescales, and transport through the highly non-uniform flame stabilized downstream of a flameholding feature. This study examines the dispersion, evolution, and flow-flame interaction of boron carbide (B4C) particles in a rectangular, optically accessible SFRJ combustor using 5-kHz Mie scattering and filtered chemiluminescence diagnostics under flight representative post-inlet conditions with unvitiated heated air (2.5 lb/s, 720 F) and an 87 psia chamber environment. Lorenz-Mie predictions show that surface-oxidized B4C exhibits scattering intensities orders of magnitude higher than soot under parallel polarized illumination at a 90 degree collection angle, enabling selective visualization of additive particles even within the strongly sooting near-wall region. High speed Mie scattering imaging resolves distinct particle transport pathways governed by backward facing step recirculation, hydrodynamic vortex shedding, and downstream redistribution driven by shear layer dynamics. Filtered chemiluminescence measurements indicate that metalized operation modifies the reacting shear layer, increases fluctuation intensity in hydrodynamically unstable regions, and shifts the peak heat release signature downstream relative to pure HTPB operation. Coefficient of variance analysis further reveals that the addition of B4C heightens temporal unsteadiness in the reacting shear layer and redeveloping boundary layer while main- taining similar flame stabilization behavior near the fuel surface. The combined Mie scattering and chemiluminescence diagnostics provide spatially and temporally resolved characterization of B4C particle clouds and their coupling to core SFRJ flow structures, offering new insight into particle entrainment, residence time modulation by recirculation and vortex transport, and the mechanisms that determine whether metalized additives actively contribute to combustion in practical SFRJ configurations. These results visualize the challenges of achieving effective parti- cle ignition and sustained energy release in high speed, shear dominated ramjet environments and highlight the importance of understanding metal particle transport physics when designing next generation SFRJ systems employing high energy density additives.

High-speed air-breathing propulsion systems, such as solid fuel ramjets (SFRJ), are important for space exploration and national security. The development of SFRJ requires high-performance solid fuels with excellent mechanical and combustion properties. One of the current solid fuel candidates is composed of high-energy particles (e.g., boron (B)) and polymeric binder (e.g., hydroxyl-terminated polybutadiene (HTPB)). However, the opposite polarities of the boron surface and HTPB lead to poor B particle dispersion and distribution within HTPB. Herein, we demonstrate that the surface functionalization of B particles with nonpolar oleoyl chloride greatly improves the dispersion and distribution of B particles within HTPB. The improved particle dispersion is quantitatively visualized through X-ray computed tomography imaging, and the particle/matrix interaction is evaluated by dynamic mechanical analysis. The surface-functionalized B particles can be uniformly dispersed up to 40 wt % in HTPB, the highest mass loading reported to date. The surface-functionalized B (40 wt %)/HTPB composite exhibits a 63.3% higher Young's modulus, 87.5% higher tensile strength, 16.2% higher toughness, and 16.8% higher heat of combustion than pristine B (40 wt %)/HTPB. The surface functionalization of B particles provides an effective strategy for improving the efficacy and safety of B/HTPB solid fuels for future high-speed air-breathing vehicles.

The significant increase of available electric power for the propulsion unit onboard satellites makes high and ultra-high specific impulse thrusters attractive for different applications and missions. Especially thrusters of the radio frequency type show a great potentiality for high Isp applications. Two different rf-thrusters are described: The RIT15LP engine optimized for a moderate input power consumption and the RIT15S designed for a high specific impulse. The main, but only difference between these engines is the extraction grid system. During the development of RIT15LP, principle improvements of rfthrusters were invented. The given description of RIT15LP is focused on these performance improvements whereas the advantages of the rf-principle for (ultra-) high specific impulse applications were pointed out on basis of the RIT15S thruster. The function principle of gridded ion thrusters can be described as a two step process. In the first step the propellant is ionized and after that, in the second step it is accelerated in the electrostatic fields of an ion extraction and acceleration grid system. Both tasks a nearly independent from each other. The acceleration has no effect on the ionisation process and therefore the beam velocity can simply be controlled by the selection of the voltages applied to the grid system. Amoung different types of electric thrusters this is a unique feature of all gridded ion engines. In contrast, the use of other electric propulsion concepts requires often deep changes in the thruster design for an increased beam velocity. For example, it was necessary to invent a two stage concept for SPTs to reach a beam velocity comparable with that of gridded thrusters. Such efforts are not required in case of the later ones. Presently, the beam velocity of gridded ion thrusthers is merely limited by their electric input power consumption and not in a conceptional way. It is important to be aware that the specific input power consumption (the total consumption of electric power Ptot over the thrust F, usually given in>luWatt per Millinewton') of any kind of thruster is a simple function of the beam velocity Vbeam and the electric efficiency of the thrusters rjel:

The Space Exploration Initiative requires the development of nuclear thermal and nuclear electric technologies for space propulsion for future Luna and Mars missions. Sandia National Laboratories has proposed a new nuclear thermal propulsion concept that uses fission fragments to directly heat the propellant up to 1000 K or higher above the material temperatures. The concept offers significant advantages over traditional solid‐core nuclear rocket concepts because of higher propellent exit temperatures, while at the same time providing for more reliable operation due to lower structure temperatures and lower power densities. The reactor can be operated in either a steady‐state or pulsed mode. The steady‐state mode provides a high thrust and relatively high specific impulse, as compared to other nuclear thermal concepts. The pulsed mode requires an auxillary radiator for cooling, but has the possibility of achieving very high specific impulses and thrust scaleable to the radiator size. The propellant temperatures are limited only by thermal radiation and transient heat conduction back to the substrate walls.

High specific impulse ion propulsion is of concern as primary propulsion system for various interplanetary explorers. A high specific impulse microwave discharge ion engine has been developed in Japan Aerospace Exploration Agency (JAXA) since 2003. The aim of this development is achieving a specific impulse of 10,000sec with an ion acceleration voltage of 15kV. New electro-static grid made of carbon-carbon composite material and various high voltage insulating components such as a DC block and a propellant isolator were developed. The authors fabricated a prototype model of the ion engine, and successfully operated it. The paper describes the outline and the experimental result of demonstration test of the high specific impulse microwave discharge ion engine

Application-oriented modeling and optimization of tailored Li-ion batteries using the concept of Diffusion Limited C-rate

One of the biggest challenges for the application of materials extrusion (ME) technology in the pharmaceutical sector is the lack of ready-to-use polymeric materials (filaments) of pharmaceutical quality. To overcome this challenge materials extrusion can be combined with the Hot Melt Extrusion (HME) process enabling the production of filaments using pharmaceutically approved polymers with incorporated drugs. This manuscript presents a step by step approach for the formulation of additively manufactured tablets containing a high melting point API (hydrochlorothiazide, HCT, T m = 266-268 °C) with two pharmaceutically approved polymers (polyvinyl alcohol, PVA and hydroxypropyl methylcellulose acetate succinate, HPMCAS) of different technological and pharmaceutical properties via combined HME and ME processing. The thermal properties of a model drug were adapted to the processing window of both HME and ME by obtaining a hydrochlorothiazide: nicotinamide cocrystal (HCT:NIC) with a lower melting point (T m = 173.3 °C) than the starting material. Two plasticizers were used - triethyl citrate (TEC) for HPMCAS and sorbitol (SOR) for PVA. Blends containing 10-50 wt. % of plasticizer were prepared using the fusion method and thoroughly analysed using PXRD, DSC, and FTIR enabling the selection of formulations for further HME processing. Placebo filaments with 10-30 wt. % of plasticizer were obtained and their mechanical properties and ME processability were assessed to select a polymer blend with desirable process parameters. Finally, the filaments containing 20 wt. % of plasticizer with HCT or the HCT:NIC cocrystal were produced and processed using ME to form tablets. The phase of the drug (crystalline or amorphous), mechanical properties of filaments and tablets as well as the drug content in the obtained materials were assessed using PXRD, DSC, and FTIR followed by materials imaging with polarising microscopy and SEM. The cocrystal formation not only enabled to modify the melting point of the drug to match the temperature of both processes but also improved the mechanical properties of the filaments which is important for ME processing. In the case of PVA based formulations the cocrystal turned amorphous upon HME processing forming flexible and printable filaments. In contrast, the drug embedded in HPMCAS based filaments formed crystals that affected the mechanical properties of the extrudates. The mechanical properties of the obtained tablets and the release profile of the drug from the AM tablets were enhanced as compared to the materials obtained using conventional methods, i.e. tableting and encapsulation. • High melting drugs can be incorporated into pharmaceutically approved polymers in the form of cocrystals via combined HME and ME processing, • Modification of physicochemical properties of the API via cocrystal formation enables successful processing of high melting point APIs into elastic filaments, • Low miscibility of the drug with polymers and the presence of crystalline drug in the filaments may result in brittle materials difficult to process via ME, • Openwork 3D tablet structure and cocrystal formation substantially improve drug dissolution.

Improvement of UV resistance and mechanism in polypropylene wax on wood surface through maleic anhydride and β-nucleating agent modification

Our research group works to gain a fundamental understanding of how to program and process nanoscale building blocks into functional structures, and the structure-property relationships of the resulting nanostructured materials. We seek to develop new nano-materials and methods for batteries, supercapacitors, fuel cells, and printable electronics. For building blocks we mainly utilize monodisperse nanoparticles made through colloidal chemistry. One issue that has yet to be adequately addressed for colloidal nanoparticles is their adherence to each other and to the electrically conductive support. In this talk I will discuss our recent results overcoming critical challenges to create functional assemblies from nanoparticles using electrophoretic deposition (EPD). For batteries, we have found that EPD can be used to form additive-free battery electrodes from colloidal nanoparticles. Typically, polymeric binders are necessary to adhere the particles to each other and the substrate, and carbon additives are necessary to increase conduction. These additives, however, generate a weight increase of 10−40%. We have found that EPD creates a strong electrical and mechanical bond for nanoparticles adhesion, enabling the batteries to perform at maximum capacity. This innovation increases the power density by reducing the overall volume. We have demonstrated high-performing anodes of cobalt oxide, Ge, and metal sulfides. The Co3O4films show high gravimetric (>830 mAh/g) and volumetric capacities (>2100 mAh/cm3) even after 50 cycles. The additive-free Ge nanoparticle films show stable capacities past 50 cycles at 750 mAh/g. Using EPD methods we have made additive-free nanoparticle electrodes for supercapacitors. We synthesized a series of Co-Mn-O stoichiometries to understand how cationic substitution affects performance. We find that the highest-performing Co−Mn mixture has a 1:1 ratio of Co to Mn and shows an energy density of 26.6 Wh/kg with a specific capacitance of 173.6 F/g. This nanoparticle electrode delivers the highest power density of 3.8 kW/Kg at a 5 A/g constant current discharge. The energy density and power density delivered by the optimal mixture is ~6× and ~3× higher, respectively, than that of pure Co3O4 electrodes. The specific capacitance for the Co-Mn mixture is also ~4× better than the pure Co3O4supercapacitor. For electrocatalysis, we compare EPD-deposited nanoparticle films to the conventional dropcast method. We study cobalt oxide thin films for the oxygen reduction/oxygen evolution reactions (ORR and OER). In examining the film’s catalytic properties we find that the electrophoretically deposited nanoparticles outperform the dropcast films by as much as 2.5 for the oxygen reduction reaction and 2.6 and the oxygen evolution reaction when accounting for both surface area and mass. This process results in this significant catalytic improvement in oxygen reduction/evolution performance which cannot be duplicated by dropcast films with the same loading. We have applied these techniques to make printable electronics: Using our surface treatment methods to link the nanoparticles, and the EPD method for deposition, we make copper sulfide films with high conductivity and high mobilities. We show that our nanoparticle films have conductivities that are on par with many bulk copper sulfide films (~75 S·cm-1), without the need for heat-treatments. D.-H. Ha*, T. Ly*, J.M. Caron, H. Zhang and R.D. Robinson, “A General Method for High-Performance, Additive-Free Li-ion Battery Electrodes from Colloidal Nanoparticles: The Case of MnS, Cu2-xS, and Ge,” ACS Appl. Mater. Inter. 7, 25053-25060 (2015) DOI: 10.1021/acsami.5b03398 D.H. Ha, M.A. Islam, and R.D. Robinson, “Binder-free and Carbon-free Nanoparticle Batteries: A Method for Nanoparticle Electrodes without Polymeric Binders or Carbon Black,” Nano Letters 12, 5122-5130 (2012). http://dx.doi.org/10.1021/nl3019559 S.D. Perera, X. Ding, A. Bhargava, R. Hovden, A. Nelson, L.F. Kourkoutis, R.D. Robinson, “Enhanced supercapacitor performance for equal Co-Mn stoichiometry in colloidal Co3-xMnxO4 nanoparticles, in additive-free electrodes,” accepted Chem. Mater. (2015) 10.1021/acs.chemmater.5b02106 M. Fayette, A. Nelson, and R.D. Robinson, “Electrophoretic Deposition Improves Catalytic Performance of Co3O4 Nanoparticles for Oxygen Reduction/Oxygen Evolution Reactions,” Journal of Materials Chemistry A 3, 4274–4283 (2015). DOI: 10.1039/C4TA04189EO.O. Otelaja, D.-H. Ha, T. Ly, H. Zhang, and R.D. Robinson, “Highly Conductive Cu2-xS Nanoparticle Films through Room Temperature Processing, and an Order of Magnitude Enhancement of Conductivity via Electrophoretic Deposition,” ACS Applied Materials and Interfaces 6, 18911–18920 (2014). http://dx.doi.org/10.1021/am504785f

Molecular dynamics(MD) simulations were performed on the energeticmolecular perovskite (C6H14N2)[NH4(ClO4)3], with excellent detonationproperties, thermal stability, and high specific impulse, which isa potential replacement for AP as the next generation propellants.The cohesive energy density, binding energy, pair correlation function,maximum bond length (Lmax) of the N–Htrigger bond, and mechanical properties of the (C6H14N2)[NH4(ClO4)3] were reported. The calculated cohesive energy density and bindingenergy decrease with increasing temperature, indicating a gradualdecrease in the thermal stability with temperature. In addition, H···Ohydrogen bonding interactions have been found based on the resultsof pairwise correlation functions. The maximum length (Lmax) of the N–H trigger bond was calculated andused as a criterion to theoretically judge the impact sensitivity.The maximum bond length of the N–H trigger bond grows graduallywith temperature; however, it does very slightly yet gradually above373 K. This suggests that an increase in temperature leads to a higherimpact sensitivity and lower thermal stability. However, this effectbecomes less pronounced when the temperature surpasses 373 K. Moreover,the calculated mechanical data indicate that as the temperature rises,the material’s stiffness, hardness, yield strength, and fracturestrength all decrease. The material’s ductility shows an upwardtrend with increasing temperature, reaching its peak at 373 K andsubsequently declining as the temperature continues to rise.

Mechanical behavior and constitutive model of NEPE solid propellant in finite deformation

Performance measurement and evaluation of an ionic liquid electrospray thruster

Applicability of Iodine as a propellant for hall Effect thrusters: Performance parameters prediction

Small-scale ramjets are promising air-breathing engines for high-speed propulsion in military, due to their high specific impulse, low aerodynamic drag and good compatibility with operating systems. The challenges of designing a miniature ramjet combustor mainly stem from insufficient space and short flow residence time for good mixing and burning, and difficulties in flame stabilization. Impossible utilization of relatively large air-blast fuel injectors in a small combustor provides more difficulties for the design. The trapped vortex combustor (TVC) concept, locking a pilot flame inside a cavity instead of exposing it to the main stream, provides a simple but effective solution for flame stabilization. In this thesis, a TVC designed for a small ramjet operating at Mach 4.0 is numerically investigated by using ANSYS FLUENT v14.5 and a large eddy simulation (LES) code from Stanford. The results show that the optimal cavity size that traps a vortex inside can be determined by calculating the drag coefficient. Because the designed small combustor does not have bypass air directed into the cavity, injecting all the fuel directly in the optimal cavity always leads to an overly fuel-rich condition. However, when the fuel is injected in the upstream with a proper fuel/air momentum flux ratio, part of fuel goes into the cavity and the rest directly flows over it.

Thermodynamic performance analysis of ramjet engine at wide working conditions