Propellant Particles Research Articles

Models for actin polymerization motors

Actin polymerization drives cell membrane protrusions and the propulsion of intracellular pathogens. The molecular mechanisms driving actin polymerization are not yet fully understood. Various mathematical models have been proposed to explain how cells convert chemical energy released upon actin polymerization into a pushing force on a surface. These models have attempted to explain puzzling properties of actin-based motility, including persistent attachment of the network to the membrane during propulsion and the interesting trajectories of propelled particles. These models fall generally into two classes: those requiring filament (+)-ends to fluctuate freely from the membrane to add subunits, and those where filaments elongate with their (+)-ends persistently associated with surface through filament end-tracking proteins ("actoclampin" models). This review compares and contrasts the key predictions of these two classes of models with regard to force-velocity profiles, and evaluates them with respect to experiments with biomimetic particles, and the experimental evidence on the role of end-tracking proteins such as formins and nucleation-promoting factors in actin-based motility.

Modeling and Simulation of Solid Propellant Particle Path in the Combustion Chamber of a Solid Rocket Motor

Modeling and Simulation of Solid Propellant Particle Path in the Combustion Chamber of a Solid Rocket Motor

Projectile dynamics at low barrel pressures

A mathematical model for a projectile shot at low pressures in the space behind the projectile space is developed. The pressure rise is limited because of the nonsimultaneity of propellant ignition and combustion and the discharge of the propellant combustion products through the gap between the projectile and the walls of the gun barrel. The kinetic characteristics of flame propagation over the propellant particles are determined. A comparison of calculation and experimental data is performed. The calculation results are used in designing 2A85 self-propelled launchers and upgrading 2A30 self-propelled launchers.

Decomposition of Aluminum Hydride Under Solid Rocket Motor Conditions

The decomposition rate of aluminum hydride powder was measured at slightly elevated temperatures (400-500 K) using the pressure rise due to the released hydrogen. This information is important for understanding the combustion behavior of aluminum hydride when used in propellants and explosives. The thermolysis measurements fit well to an Arrhenius-type exponential fit, with a preexponential of 3.29e9 1/s and an activation energy of 97.6 kJ/mol. Two-dimensional simulations of aluminum particles in a propellant mixture were also performed to determine the temperature and velocity history of the particles in a burning propellant. Using this information and extrapolating the measured dehydrogenation rates, It was determined that alane will decompose before being ejected off of the propellant surface. This prediction suggests that the hydrogen will be available to react in the primary flame zone of the rocket motor, and will thus impact the stoichiometry in this region. The decomposition process could also affect the surface characteristics of the burning propellant.

New Kinetics for a Model of Heterogeneous Propellant Combustion

In earlier work we describe an unsteady, three-dimensional, phase-coupled combustion code which, with the use of a random packing algorithm to construct model propellants, and the use of a homogenization strategy to account for unresolvably small propellant particles, can be used for the simulation of heterogeneous propellant combustion. This work uses a simple two-step kinetic model for ammonium perchlorate (AP)/hydroxyl-terminated polybutadiene (HTPB) combustion which fails to accurately predict variations in the burning rate with AP concentration for a homogenized AP/HTPB blend supporting a one-dimensional flame. Here we describe a three-step model, one which captures the three flames of the Beckstead-Derr-Price (BDP) combustion model, and show that kinetic parameters can be adopted so that one-dimensional AP burning rates and one-dimensional AP/HTBP blend burning rates can be correctly predicted. We discuss the stability of the underlying flame structures and highlight a difficulty that arises in these instability-prone systems when simple kinetic models are used to describe them. The combustion model, with the new kinetics, is used to reexamine the burning of random packs, and improved agreement with the experimental burning rates of Miller packs is demonstrated. We also reexamine the problem of sandwich-propellant combustion and investigate the trend in surface shape and burning-rate variations with pressure and binder width. These trends are compared with experimental results of Price. The sandwich configuration is used to measure the importance of the primary diffusion flame of the BDP model.

Surface Energy and Interparticle Force Correlation in Model pMDI Formulations

To compare experimental measurements of particle cohesion and adhesion forces in a model propellant with theoretical measurements of the interfacial free energy of particulate interactions; with the aim of characterizing suspension stability of pressurized metered dose inhalers (pMDIs). Interparticulate forces of salbutamol sulfate, budesonide, and formoterol fumarate dihydrate were investigated by in situ atomic force microscopy (AFM) in a model propellant 2H,3H perfluoropentane. The surface thermodynamic properties were determined by contact angle (CA) and inverse gas chromatography (IGC). Experimental data were compared with theoretical work of adhesion/cohesion using a surface component approach (SCA), taking into account both dispersive and polar contributions of the surface free energy. Results indicated that the measured forces of interaction between particles in model propellant could not be accounted for by theoretical treatment of the dispersive surface free energies via CA and IGC. A correlation between theoretical work of adhesion/cohesion and AFM measurements was observed upon the introduction of the polar interfacial interactions within the SCA model. It is suggested that the polar contributions of the surface free energy measurements of particles may play a crucial role in particle interaction within propellant-based systems. Together with the application of a SCA model, this approach may be capable of predicting suspension stability of pMDI formulations.

Tetrafluoroethane (HFC 134A) propellant-driven aerosols of proteins.

Develop metered-dose propellant-driven aerosols of proteins using tetrafluoroethane (HFC 134A) as propellant. Proteins were lyophilized with the propellant-soluble surfactants Triton X-100, Triton X-405, Laureth-9, Brij-30, Nonidet-40, and diethylene glycol monoethylether and then charged with propellants. Small particle aerosols of the experimental protein bovine gamma globulin were produced. The fraction of aerosolized respirable-sized protein particles (< 4-5 microns) increased after dispersion of particles in propellant with agitation by shaking. Scanning electron microscopy of respirable-sized protein aerosols demonstrated bead-like particles in grape-like clusters. Vigorous shaking of propellant-suspended particles for 2 minutes or more reduced the size of clusters and reduced the diameters of the protein-containing subparticles that constituted the clusters. A 50:50 ratio of HFC 134A and dimethylether (DME) propellants improved the respirability of protein aerosols compared to HFC 134A as the sole propellant. Protein/surfactant particles first dispersed in DME and then diluted in HFC 134A propellant most efficiently produced respirable-sized, propellant-driven, protein aerosols.

Limits of detonation propagation in a suspension of propellant particles in vacuum in a tube

The problem of stationary detonation in vacuum with monopropellant particles propagating in a tube is formulated and analyzed numerically. It is shown that friction and heat removal onto the tube walls affect the structure of a disperse wave. The dependences of the detonation velocity on the tube diameter, the size of the propellant particles, and on their mass concentration have been determined, and the limits of detonation propagation have been found.

Numerical modeling of composite propellant response to drop weight impact

Abstract Finite element analysis is used to study the dynamic response of propellant subjected to drop weight impact. The model of the propellant incorporates varying amounts of ammonium perchlorate (AP) particles to account for stress concentrations due to sample inhomogeneity. The intent of this study is to examine locations which may lead to critical initiation shear stresses such as AP sliding on AP or AP sliding on steel. The initial full AP model used a 60% (by weight) solids loading corresponding to a research propellant formulated for a companion experimental program. Due to the unusually high number of slidelines which are needed to model the friction between the AP particles and surrounding media, the code was not capable of compiling the full model. Other models have been run to examine the effects of a few AP particles on the resulting stress state in the propellant. These models show significant increases in the maximum shear stress at locations immediately surrounding the AP particles. Quantitative comparisons are also made between homogeneous propellant and AP–in–propellant models. Two–dimensional geometric constraints of the code are also discussed. In particular, it is shown the default axisymmetric and the alternative plane strain geometries have limitations which do not allow for proper modeling of the particles. Finally, the limitations of using hydrocodes for simulating the effects of particles in propellant are discussed along with recommendation for further work.

Characterization of Smokeless Powder Flakes from Fired Cartridge Cases and from Discharge Patterns on Clothing

Abstract Shooting experiments over short distances (30 to 50 cm) deposited apparently non-burnt and partially burned flakes of smokeless powder propellants on clothing around the bullet holes. An approach was made to compare the propellant particles recovered from the clothing with those from a particular cartridge. Evidence of this kind may help the police to identify a shooter in cases when weapon or bullet or both are not found. Gas chromatography and high-pressure liquid chromatography were the analytical techniques used. A series of shooting tests with various types of ammunition produced by different manufacturers was performed. The analyses were expected to reveal which of the shootings used the same kind of ammunition. Predictions were correct in all these experiments. The analyses of propellant particles collected from clothing or from fired cartridges could also distinguish between a number of different production lots from the same manufacturer.

The identification of individual propellant particles

An identification procedure for single propellant particles is described. It involves the techniques of infrared microspectrophotometry and gas chromatography-mass spectrometry and is capable of detecting all the main propellant constituents including nitrocellulose.

Identification of tandem bullets.

The possibility of identifying tandem bullets, causing separate entry holes on one or two victims, or found separately at the scene of a crime, is investigated. The phenomenon of tandem bullets has been studied to evaluate the physical evidence. The presence of deep indentations of propellant particles on the exposed lead base cavity, along with patches of striations on the inner periphery of the cavity, have been found to be useful physical evidence to conclude that the bullet had moved in tandem and was a lodged bullet. An outward protrusion of the base acts as corroborative physical evidence that the bullet was the striking bullet.

Quasi‐Static compaction studies for DDT investigations. Ball Propellants

AbstractA Quasi‐Static compaction study has been performed on a number of ball propellants to complement studies of dynamic compaction behaviour, shock sensitivity, and deflagration‐to‐detonation transition (DDT) behaviour that are currently being conducted for high porosity granular beds of such materials. These ball propellants are of interest because they are simple, unfilled propellant systems. Many of them have particles which are spherically shaped, a geometry that facilitates numerical modeling of the DDT process. Four Olin ball propellants, designated as WC 140, TS 3660, Type A Fluid, and Winchester #231, have been investigated in detail by simultaneously measuring applied force, transmitted force, and porous bed displacement. An average axial compressive force per unit radial cross‐sectional area of the solids in the porous bed, called the „intragranular stress”︁, is then calculated as a function of percent theoretical maximum density for values ranging initially from 44%–58%, to final values greater than 85%, depending on the ball propellant. A microscopic examination was performed on a number of recovered samples that had been compacted to various stress levels to identify the nature and extent of plastic deformation and fracture in the propellant particles and to provide insight into compaction mechanisms and associated pore structures in the compacted porous bed. A brief discussion relating these considerations to hot spot formation and DDT behaviour is also presented.

Experimental Study of the Combustion Processes in Granular Propellant Beds

Catastrophic failure of propulsion and gun systems has been attributed to abnormal combustion within granular propellant charges. The effects of igniter strength, propellant type, deterrent concentration, and projectile motion on the overall transient combustion processes in granular propellant beds were studied experimentally. The results show that igniter strength significantly affects the duration of the induction period and the accelerative behavior of the pressure front traveling through the bed; a weaker igniter causes a more pronounced pressure front acceleration. A large igniter volume was found to reduce the rate of flame-spreading and pressurization processes. Combustion of slightly deterred propellants produced very rapid flame spreading, higher peak pressures, and higher pressurization rates than regularly deterred propellants. Propellant particle geometry was found to greatly affect the rate of total mass consumption within a propellant bed and thereby influence the peak pressures and pressure wave phenomena within the bed.

New Kinetics for a Model of Heterogeneous Propellant Combustion

In earlier work we describe an unsteady, three-dimensional, phase-coupled combustion code which, with the use of a random packing algorithm to construct model propellants, and the use of a homogenization strategy to account for unresolvably small propellant particles, can be used for the simulation of heterogeneous propellant combustion. This work uses a simple two-step kinetic model for ammonium perchlorate (AP)/hydroxyl-terminated polybutadiene (HTPB) combustion which fails to accurately predict variations in the burning rate with AP concentration for a homogenized AP/HTPB blend supporting a one-dimensional flame. Here we describe a three-step model, one which captures the three flames of the Beckstead-Derr-Price (BDP) combustion model, and show that kinetic parameters can be adopted so that one-dimensional AP burning rates and one-dimensional AP/HTBP blend burning rates can be correctly predicted. We discuss the stability of the underlying flame structures and highlight a difficulty that arises in these instability-prone systems when simple kinetic models are used to describe them. The combustion model, with the new kinetics, is used to reexamine the burning of random packs, and improved agreement with the experimental burning rates of Miller packs is demonstrated. We also reexamine the problem of sandwich-propellant combustion and investigate the trend in surface shape and burning-rate variations with pressure and binder width. These trends are compared with experimental results of Price. The sandwich configuration is used to measure the importance of the primary diffusion flame of the BDP model.

Flame-Spreading and Combustion in Packed Beds of Propellant Grains

This paper is concerned with the prediction of the pressure history during the process of flame-spreading and combustion of solid-propellant grains as would occur, for example in a gun cartridge. Solution of the governing conservation equations for the two-phase media requires the use of empirical relations to account for the physical processes of momentum and energy interaction between the solid grains and hot propellant gas. The results indicate the extreme importance of these interaction relations on the predictions of the pressure and velocity field. and at the other is a projectile which will begin to move at a given prescribed pressure. This 'piston then moves through a long length of channel of the same cross section as the cham- ber, in order that the flow processes following piston motion can be followed. A predescribed igniter mass flow provides gaseous products which, in turn, ignite the bed. Since solid propellants have high burning rates, the rate of gas generation within the chamber is high. Therefore, the pressure is rising rapidly during this flame-spreading process. The pressure rises enhances the pressure-dependent burning rate of the propellant, the result of which is a rapidly accelerating combustion process, with generally steep gradients along the length of the chamber. This gradient results in a high-velocity flow of the gases toward the piston end and into the unburned portion of the propellant. Hence, the flame-spreading and pressurization is rapid, and the entire burn is completed in a matter of milliseconds, if the ignition source is strong enough. Looking at flow process taking place, one may determine the effect on the particle bed. The hot igniter gases initially are driven into a quiescent bed of propellant particles. These ignite the particles nearest the igniter source. The mass generation and subsequent pressurization occur, and a flowfield develops within the chamber. The propellant par- ticles exert a drag force on the flowing gases and are ac- celerated. As shot-start pressure is approached, the entire bed usually has been set into motion.J Throughout the burn, the particles continue to decrease in size as they burn. Kuo and Summerfield2 have pioneered the analysis of packed-bed solid-propellant combustion.