Electrothermal-chemical Research Articles

Study of Different Models of the Wall Ablation Process in Capillary Discharge

Wall ablation is a critical physical process in the capillary plasma generator for electrothermal-chemical (ETC) guns, and its characteristics directly determine the generator's performance. In this paper, three different ablation models for the capillary discharge are studied. First, based on a recently developed two-layer kinetic model that takes into account the structure of the sheath in the plasma-wall transition region, ablation characteristics of two typical materials used in the ETC gun plasma generator, polytetrafluoroethylene and polyethylene, are calculated. These data are required for magnetohydrodynamic (MHD) plasma modeling, and for analysis of the characteristics of different materials from the viewpoint of capillary material selection. Then, using discharge parameters of a typical ETC plasma generator working cycle, three widely used ablation models are compared and analyzed. These models are the two-layer kinetic model (model-K), a model based on the Langmuir law (model-L) and a simplified arc-wall interaction model (model-E). The time dependence of the ablation rate and total ablated mass are calculated with each method, and then the features of the different ablation models are discussed. It demonstrates that the model-K is the most reliable model in terms of predictions accuracy, while its computational efficiency is poorer when applied in MHD simulations compared with the model-E.

Experimental Studies of Propellant Loading Parameters and Plasma Flow-Field Interactions

Propellant-plasma interaction has been attracting great interests among most researchers for application to an electrothermal-chemical (ETC) gun. Previous works have shown that propellant-plasma interaction can enhance burning rates due to increased surface erosion of propellants as compared to that of conventional ignition. Plasma radiation and heat convection are the dominant mechanism of energy transfer based on both experimental data and numerical simulation. However, little literatures were reported about a detailed understanding of propellant loading parameters and the plasma flow-field distribution interactions, which is very important in deciding a successful propellant-charge design in ETC guns. The pressure-time curves during interrupted-burning process of different propellants such as triethyeneglycol dinitrate and single-base propellants ignited by plasma were recorded by pressure sensor in interrupted-burning setup. Influence of loading parameters, including loading density, distance between propellants and plasma jet, and propellant holding methods at the same selected location in plasma flow-field on plasma-ignition performance of propellants was discussed based on experimental results. As the loading density of propellants increases, the porosity of the propellant bed becomes small. Moreover, the penetrating depth of plasma into propellant bed shortens. Therefore, the plasma energy attenuates rapidly, and the ignition-delay time of propellants becomes longer. The ignition-delay time is longer when the distance between propellants and plasma jet increases. At the same selected location in plasma flow-field, different holding methods of propellant burning surface to plasma jet have less influence on the ignition, combustion process of propellants, and the ignition-delay time. The matching test results on propellant loading parameters and plasma flow-field distribution interaction play a major role in improving charge configurations at chosen plasma flow-field and understanding plasma-propellant interaction better.

Electrothermal-Chemical Ignition Research on 120-mm Gun in Korea

Electrothermal-chemical (ETC) propulsion with the control of a combustion process yet requires large electrical energies for an appreciable effect. Referring to the changed tendency of focusing ETC researches on the early ignition phase, the Agency for Defense Development (ADD), Korea, has been studying an electrothermal ignition for a 120-mm gun using a capillary plasma injector. Under the condition of a limited capillary geometry, design efforts with various liner materials have been done to achieve robust capillary discharges capable of transferring energies around 100 kJ. Electrical properties were estimated with the help of plasma theories and compared with experimental results. Experiments using a closed vessel and a gun-chamber simulator have been done to investigate the burning behaviors and the early phase of an electrothermal ignition, respectively. The closed vessel was designed for both a plasma and a conventional ignition. The burning rates could be obtained up to 70 MPa. The gun-chamber simulator was designed in the shape of the chamber of a 120-mm gun except for an acrylic chamber wall withstanding up to 30 MPa. Through prior tests using the closed vessel and the gun-chamber simulator, appropriate electrical energies and propellant have been selected. Firings of the full-scale 120-mm gun have been done using JA2 propellant. Electrical pulses of 1-2.5-ms duration in the energy from 20 to 120 kJ were applied. Aside from ignition capability, the results showed a possibility of a control on the peak pressure. Currently, ADD, Korea, continues the research to enhance the efficiency of the plasma injector, to compact the pulse forming network, and to investigate the electrothermal ignition properties of LOVA propellant.

Recent Activities in Electrothermal Chemical Launcher Technologies at BAE Systems

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> The three-year line of sight/beyond line of sight (LOS/BLOS) electrothermal chemical (ETC) launcher program, funded by the U.S. Army's Armament Research, Development and Engineering Center (ARDEC), Picatinny Arsenal, is a comprehensive effort to advance ETC launcher technologies. The program includes development of ETC plasma injectors for 120-mm M829A2s, build of a 100-kJ pulsed power supply small and robust enough to be realistically integrated into a combat vehicle, improvement of power connections to the gun to allow electromagnetic field containment and automated connection to the round, and tests of the completed ETC system with various chemical propellants and electrical energy levels. </para>

Development and Evaluation of a TSLGG— Application of an ETC Gun System to its First Stage

A new type of launcher, ETC-TSLGG, is a two-stage light gas gun (TSLGG) using the technology of electrothermal-chemical (ETC) gun for its first stage. ETC-TSLGG is an improved version of the ETC gun which we had researched previously. It is developed to speed up the projectile velocity and control of variation of delay time from the ignition signal to the projectile launch. It will be used as a projectile launcher in a counter impact. Therefore, launch timing of the projectile is very important. Adjusting charge voltage and inductance of coils in a 10-kJ condenser bank so that variation of delay time is as small as possible, we depressed jitter of launch timing within a microsecond order in ETC-TSLGG. In this study, we investigated the delay time generation process. In order to clarify the operational state, pressure sensors were mounted in the ignition chamber and the pump tube. We measured projectile velocity, delay time, discharge voltage profile, current profile, and pressure profiles at different charge voltage and inductance. It can be said from these profiles that the delay time jitter was stabilized at high charge voltage and low inductance. Moreover, we have demonstrated that the delay time jitter of ETC-TSLGG was 1/100 smaller than that of the conventional TSLGG

Electrothermal Chemical (ETC) Armament System Integration Into a Combat Vehicle

On August 18, 2004, BAE Systems achieved an industry first when we successfully fired a 120-mm electrothermal chemical (ETC) gun from a hybrid electric drive combat vehicle. This achievement, using a fully integrated 100-kJ pulsed power supply, was accomplished through a Cooperative Research and Development Agreement with the U.S. Army's Armament Research, Development and Engineering Center (ARDEC). ARDEC is the U.S. Army's center of excellence for armament systems development. The comprehensive series of tests demonstrated that pulsed power can be safely integrated into a combat vehicle. Both ETC and conventional rounds were fired in the same salvo via a round selection command issued through the vehicle's fire control system. An autoloader was employed to load the rounds and to eject the stub cases from the vehicle. The fully automatic breech power connection was designed so the electrical energy delivered from the pulsed power system reached only the propellant and no part of the cannon or vehicle

Integration and Test of a Second Generation Dual Purpose Pulse Forming Network Into the P&amp;E HWIL SIL

A second-generation dual purpose pulse forming network (DP-PFN) has been developed to power both the electro-thermal-chemical (ETC)/electro-thermal-ignition (ETI) lethality capability and the electro-magnetic armor (EMA) survivability capability improvements envisioned for future hybrid-electric vehicles. ETI decreases the ignition variability associated with the launching of conventional munitions by roughly a factor of ten which, in conjunction with the systems ballistic computer, greatly enhances hit probability of the round. ETC provides maximum performance in all conditions, including temperature compensation, resulting in increased lethality and range with higher average muzzle velocities. EMA uses stored electric energy to disrupt a shaped-charge jet and reduce it's depth of penetration. The second-generation DP-PFN for driving both ETI/ETC and EMA emulators is scheduled to be integrated into the power and energy (P&E) hardware-in-the-loop (HWIL) System Integration Laboratory (SIL) in Santa Clara, CA, in 2006. The DP-PFN is capable of providing either the short pulse lengths required by the EMA or the considerably longer pulse lengths required by the ETI/ETC gun as well as emulating various "degraded functionality" states such as loss of individual capacitors. Integration of this DP-PFN marks another great milestone for the SIL, ensuring that it continues to be capable of emulating all the major hybrid-electric mobility functions of a ground combat vehicle as well as the major lethality and survivability electrical loads. This paper describes the DP-PFN components, the overall DP-PFN design philosophy and the planned integration and testing of the DP-PFN in the P&E HWIL SIL

Modeling of the Plasma-Propellant Interaction

Plasma-propellant interaction for application to an electrothermal gun is studied theoretically. Electrothermal-chemical (ETC) guns are used for enhancement of the ignition and combustion of the energetic propellant. A detailed understanding of the dynamics of the plasma-propellant interaction is considered one of the key elements to the future success of practical ETC gun implementation. A model of the propellant ablation under plasma effect is developed based on the kinetic theory of ablation. The ablation model is coupled with a model of the plasma generation in the capillary discharge that allows calculation of the effective heat flux from the plasma. Calculations are performed for specific experimental conditions in which ablated mass of a double-base and a nitramine composite propellant are studied. An ablation model is used to predict the ablation rate of the propellant for different bulk plasma densities. An effective heat flux from the plasma is found which yields the experimentally determined ablated mass. One representative solution reproduces the experimentally determined ablated mass for the double-base propellant of 5.3 mg via an effective heat flux on the order of 4times108 J/m2s. The effective heat flux that corresponds to the experimentally measured ablated mass is determined for different propellants. Differences in the calculated effective heat flux between different propellants indicate that although heat convection from the plasma is the dominant source of energy, plasma radiation, and the optical properties of the propellants themselves cannot be ignored. The difference in plasma heat flux between propellants can readily be explained by partial absorption of plasma radiation consistent with the optical properties of the propellants

Overview of Some Recent EML Research in Russia

The overview summarizes the main electromagnetic activities in Russia since the 12th Electromagnetic Launch Technology Symposium in 2004. This research has been focused on the development and improvement of electro-discharge launchers, railguns, and electrothermal-chemical (ETC) launchers. Research efforts have been directed toward studying the physical phenomena and processes limiting the attainment of high velocities and operational resources of launchers. Considerable attention has been paid to solving problems related to material erosion, the manufacture of new materials and their testing in high-current arc discharges, and the search for new applications of launchers in science and engineering

Preliminary study of counter impact with two-stage light gas gun using electrothermal–chemical gun technology

Recently, hypervelocity impacts between space structures and space debris have been brought to attention with the advance of space development. The impact velocity at low earth orbit (LEO) is up to 15 km/s. Such impact velocity cannot be attained by the current two-stage light gas gun (TSLGG). Therefore we have a plan of counter impacts that used two sets of TSLGGs in order to raise impact velocity. There are three problems in order to realize the counter impacts. They are launch timing, recovery of target and alignment of gun axis. In this research, we considered launch timing of TSLGG among them. It is important to control variation of delay time from propellant ignition to projectile launch in the counter impacts. In a conventional TSLGG, combustion rate changes every time and impact position will vary widely. In order to stabilize combustion rate, we developed a new TSLGG that used the technology of electrothermal–chemical (ETC) gun for its 1st stage. In a conventional TSLGG, the variation of delay time is 20–30 ms. On the other hand, in a new TSLGG, we have succeeded in suppressing the delay time variation less than 200 μs. It is concluded that the TSLGG based on the technology of ETC gun is effective to control the delay time in this paper.

Strong synergistic effects in the combustion of propellants in H2 Plasmas

Electrothermal chemical (ETC) or plasma ignition of propellants has been investigated by observing the interactions of individual and combinations of the individual components of an ETC pulse with a thin film of propellant. Adjusting the applied dc bias of high-density hydrogen and argon plasmas, ions or electrons may be drawn to the film surface with defined energies and resulting in erosion of the film. Strong synergistic effects are observed between reactive hydrogen atoms and ion bombardment, and a physical model of the process is presented. These synergistic effects may be directly related to the short, highly reproducible ignition delay that characterizes the ETC ignition technology.

Ablation study in the capillary discharge of an electrothermal gun

In this paper, we study the ablation phenomena associated with the operation of a capillary discharge for an electrothermal gun. Electrothermal-chemical (ETC) guns are used for enhancement of ignition and combustion of an energetic propellant. One of the major components of the ETC system is a plasma source based on a capillary discharge. In this paper, a model of the capillary discharge is developed. In this model, primary attention is paid to the ablation phenomenon. Different characteristic subregions near the ablated surface, namely, a space-charge sheath, a Knudsen layer, and a hydrodynamic layer, are considered. In this formulation, the ablation rate is determined by the parameters at the edge of the Knudsen layer. The kinetic approach is used to determine the parameters at the interface between the kinetic Knudsen layer and the hydrodynamic layer. Coupling the solution of the nonequilibrium Knudsen layer with the hydrodynamic layer provides a self-consistent solution for the ablation rate. According to the model predictions, the peak electron temperature is about 1.4 eV, the polyethylene surface temperature is about 700 K, and the pressure is about 10 MPa. It is found that the ablation rate increases with the capillary length. The ablated mass and the predicted total pressure agree with previous experimental observations.

Evaluation of an electrothermal-chemical concept where propellant combustion is stimulated by conducting electric current through the flame

An evaluation of an electrothermal-chemical (ETC) concept where propellant combustion is stimulated by conducting electric current through the flame has been performed. For comparison, a brief presentation of the two most commonly used ETC solutions-plasma injection and current injection-is also made. Their basic function is outlined as well as their characteristic properties in various phases of the interior ballistic cycle. The ETC concept examined at FOI is described in a corresponding manner and qualitatively compared with the two previous ones. So far this concept is only experimentally examined in a closed vessel. The experimental results are analyzed with respect to the electric resistance in the combustion chamber and the electrothermal pressure increase. Using the latter, the influence of the added electric energy on the combustion is evaluated.

Reliable, highly reproducible plasma injectors for electrothermal and electrothermal-chemical launchers

The plasma injector is a major component within electrothermal (ET) or electrothermal-chemical (ETC) launcher. Soreq NRC has promoted for years the solid-propellant ETC (SPETC) gun concept, where the generated plasma serves to ignite the charge and to control its burning rate (for example, to eliminate the effect of the initial charge temperature on the propellant burning rate). From a system engineering point of view, there is an advantage in using small size plasma injectors. Such injectors have been designed, built, and tested in our laboratory in the past few years. We report about free jet (the plasma is injected to the atmosphere and not into propellant charge) experiments performed with certain models of such injectors. These injectors were designed for electrical energies in the range of hundreds of kilojoules and several hundred megawatts. The dependence of the mass losses from the ablative capillary and anode on the total electrical energy and power are presented. Although the limited scope of this presentation one can grasp from these data indications regarding the differences between the thermodynamic properties (temperature, density) of plasma jets produced by capillaries with different geometries, operated at various electrical energies and powers. A comparison between the energy carried by the plasma and metal droplets (resulting from anode melting) may give an indication about the relative contribution of these two factors to the propellant ignition.

Direct Measurement of Radiative Flux Incident upon Propellant during Plasma Propellant Interactions

AbstractThis paper sets out to describe some of the experimental work performed at QinetiQ, exploring the potential of electrothermal‐chemical (ETC) gun technology. Work performed primarily by the Fraunhofer‐Institut für Chemische Technologie (ICT) and supported by Technologiezentrum Nord (TZN), both in Germany, has been repeated and extended. Their work, which used aluminium plasma initiation wires, showed internal damage was being done to the structure of propellant grains with translucent (but not opaque) propellant formulations, both in exploding wire‐in‐air and in exploding wire closed vessel tests. This damage was shown to increase the gas generation rate in closed vessel tests. That work demonstrated the potential to use ETC plasma to alter the gas generation rate during combustion. If this could be achieved, then the piezometric efficiency of a gun system could be increased.

Spectral Acquisition and Calibration Techniques for the Measurement of Radiative Flux Incident upon Propellant

AbstractA technique for the absolute calibration of a time‐resolved spectrographic system has been developed at QinetiQ, specifically designed to be relevant to spectral acquisition from within the interior of translucent gun‐propellant samples. The technique has shown itself to be particularly useful in the realm of propellant ignition as it allows for the precise determination of the moment that propellant combustion processes begin, as well as measuring the incident radiative flux leading up to ignition. Scope exists to extend its use for high‐pressure measurements of the incident radiative flux during both conventional propellant burn and high‐powered electrothermal‐chemical (ETC) discharges. This paper sets out to describe both the technique and some of the pitfalls encountered during the development of the technique. The use of this technique in some of the experimental work performed at QinetiQ, including the results of measurements that compare the incident radiative flux with propellant ignition during both ETC discharges and conventional gunpowder burn, have been published separately; references for this experimental work are given in this paper.

National overview of the German ETC program

Today's investigations on electrothermal-chemical (ETC) guns concentrate on different methods of electrothermal plasma ignition technologies to be combined with ETC tailored propellants and their charge designs. It is the goal to obtain increased gun performance in terms of muzzle energy, muzzle velocity, and temperature compensation of the propellants. In the German ETC program, governmental agencies, research institutes, and industry are involved to investigate proper ETC technologies to be applied in large-caliber guns. Basic investigations as well as large-caliber firing demonstrations are included in the program. It is the goal of the current ETC phase to demonstrate muzzle energies up to 15 MJ out of a 120-mm smooth-bore gun barrel under operating conditions. This paper gives an overview of the program structure and briefly addresses the content of the subprograms performed in institutes as well as of the industrial investigations.

Overview of ETC research in Korea

In late 2000, an experimental 30-mm electrothermal-chemical (ETC) gun, a data acquisition system, and a 2.4-MJ pulse-forming network (PFN) consisting of eight 300-kJ modules were constructed, and serious research projects were started. During the past years, basic studies on the effect of the electric pulse in the process of ignition and propulsion of the gun have been done. Two types of ammunition, an exploding wire cartridge and a capillary plasma injector cartridge, were used in the experiments. The load resistance should be estimated well in order to deliver electric energies into the combustion chamber as a desired form in time. For that purpose, there has been an effort to model the load resistance of the ETC gun, which shows the dependence on the pressure of the combustion chamber. A study on a capillary plasma itself is also an important topic and is now in the beginning stage of research using spectroscopic diagnostics. The capillary plasma discharged in the open air provides useful information through the comparison with that discharged in the ETC gun. In the development and operation of the PFN, some problematic characteristics such as a high-voltage surge leading to a destruction of crowbar diodes occurred. A countermeasure was presented to solve the problem. High-current switches are also being studied. Vacuum rotary arc gap switch, pseudospark switch, triggered vacuum switch, and inverse-pinch switch are being studied for better and reliable operations. The ETC program in Korea is currently concentrating on the detailed investigation on the interaction of a plasma with propellants.

Capacitive pulsed power supply systems for ETC guns

Compact pulsed power supplies are required for electrothermal-chemical (ETC) guns to be installed in combat fighting vehicles. In order to meet the requirements for integration of pulsed power supply (PPS) systems in such vehicles, components with high degrees of energy and power density as well as complex system designs need to be realized. This paper gives the basic electric requirements of medium- and large-caliber ETC guns to be fulfilled by the appropriate PPS systems. From these requirements, design criteria for high-energy discharge modules and their auxiliary systems are derived. The design of a 120-kJ capacitor module to be applied for the large-caliber ETC gun currently under investigation at Rheinmetall, Unterleuss, Germany, is described. Finally, the paper gives some basic considerations on volume and weight requirements of capacitive PPS systems to be applied for rapid-fire and single-shot ETC guns due to the current status of the investigations at Rheinmetall.

Performance of 2.4-MJ pulsed power system for electrothermal-chemical gun application

In order to maximize electrothermal-chemical (ETC) gun performance, the power supply for the ETC gun driver needs to have a capability of producing a flexible current pulse. This current pulse forming can be realized by a combination of current pulses from multiple modularized capacitor banks. For this purpose, a 2.4-MJ pulse power system (PPS) has been developed. The 2.4-MJ PPS consists of eight modular 300-kJ capacitor banks (CBs). The 300-kJ CB modules are designed to operate independently and have a charging voltage of 22 kV and a current capability of 150 kA. Operation characteristics of 2.4-MJ PPS have been investigated. Various shapes of current pulse have been tried for a dummy resistive load and an ETC gun load. In this paper, we discuss some problems that take place during multiple modules operation and suggest solutions for these problems. We also show some experimental results when the 2.4-MJ PPS was applied to resistive dummy load and a 30-mm ETC gun load.