Electrothermal-chemical Research Articles

Research on Potential Equilibrium of Dynamic Combustion Performance in Electrothermal-Chemical Launching

The interior ballistic potential equilibrium theory is used to analyse the parameters at the potential equilibrium points of pressure curves of 30mm conventional launching experiment and electrothermal-chemical (ETC) launching experiments. Analysis shows that: compared to the conventional launching experiment, (1) the time for ETC launching experiment to arrive the potential equilibrium point is apparently shortened; (2) the relative burnt percentages of the propellants at the potential equilibrium points are smaller in ETC launching tests. And the curves of gas generation brisance in the three ETC launching experiments are consistent. Then based on the measured pressure curves, the actual gas generation functions in chamber for conventional launching experiment and ETC launching experiments are fitted respectively. Using the average actual gas generation functions to replace the shape functions which are derived from the hypothesis of Geometric Combustion Law, the interior similarity equations of ETC Gun are established with the potential equilibrium point as the reference state. The calculated pressure curve obtained by solving the interior ballistic similarity equations of electrothermal chemical gun is in good agreement with the experimental pressure curve. Therefore, it is expected that the interior similarity equations of ETC Gun could predict the experimental pressure curve.

Electrical and Optical Test of a Semi-Combustible Plasma Generator via a Plasma Ignition Simulator

Electrothermal-chemical (ETC) launch technology can considerably increase the ballistic performance and optimize the fire range and range overlap of a 155-mm unimodular charge howitzer. To discuss the plasma ignition process of a semi-combustible plasma generator (SCPG) with a special tubular semi-combustible medium, a plasma ignition simulator (PIS) for the 155-mm unimodular charge howitzer is designed and manufactured to provide a realistic chamber environment. The optical and electrical measurements of a hybrid arc controlled ablation (ACA) plasma are operated via several sensors, a high-speed digital camera, and a compact spectrometer. Test results show that the PIS can satisfy the design requirements of the research of the plasma ignition process. When the discharge voltage is 6.5 kV, hybrid plasma propagation in the simulator chamber is observed and detected. The electronic excitation temperature of the hybrid plasma is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\approx 15$ </tex-math></inline-formula> 860 K, and the hybrid plasma propagation velocity is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\approx 1000$ </tex-math></inline-formula> m/s. These transient propagating hybrid plasmas are enough to ignite all unimodular charges in the chamber within 1.0 ms. The results provide an important reference for future ETC launch tests.

Pulsed Discharge Characteristics of a Semicombustible Plasma Generator for ETC Launchers

A semicombustible plasma generator (SCPG), including a special tubular semicombustible medium, is introduced to improve the discharge property of the plasma generator and enhance the electrothermal–chemical (ETC) launch efficiency. The new structure of SCPG is mixed with both capillary plasma generator (CPG) and discharge rod plasma generator (DRPG). After the design and simulation, the electrical characteristics of this SCPG are discussed with both static test and dynamic tests. Results show that the SCPG is a resistive load with low inductance, which has stable and consistent electrical parameters. With the increase of discharge voltage, the peak current of SCPG is increased and the equivalent resistance of SCPG is decreased. The peak voltage is nearly 1.3 kV and the pulse current bottom width is more than 3.5 ms. Compared with the DRPG, the load characteristics of SCPG are in a stable and consistent trend during the pulsed discharge process as the same as DRPG. Also, the SCPG has longer stable working times and better stable working parameters and performance. This SCPG will promote the interaction between the plasma and propellants in the chamber.

Development of a 200-kJ Capacitive Pulsed Power System for Vehicular Electrothermal-Chemical Launcher

This article has designed a 200-kJ pulsed power system (PPS) for electrothermal-chemical (ETC) guns to be installed in combat vehicle. The PPS consists of a pulse-forming network, a primary power, a high-voltage (HV) charger, and a remote control system. Two independent 100-kJ pulsed power units (PPUs) are integrated in a compact frame to build the pulse-forming network. A charging system consisting of a primary power and a 30-kW charger charges two PPUs simultaneously, and it is also integrated into the PPS. In each PPU, a pulse capacitor, a semiconductor switch stack, an inductor, a dump device, and a data acquisition system are integrated. The PPU is designed to achieve a peak output current up to 30 kA at a maximum charging voltage of 10 kV. After all the subsystems are integrated, the equivalent experiments are carried out with resistive load. The experimental results show that the PPS can flexibly adjust the output current waveform to meet the application requirements. The design ideas and results in this article have engineering application value in improving the performance of a PPS-based ETC launch system.

Firing range optimization of a 155mm uni-modular charge howitzer by ETC technology

Electrothermal-chemical (ETC) launch technology can accurately control and enhance the ignition and combustion of solid propellants to improve the consistency and accuracy of ballistics. In this paper, a calculation model including the transient burning rate formula and six-degree-of-freedom rigid body trajectory equation is established to simulate both interior and exterior ballistics processes for a 155mm uni-modular charge howitzer. The simulation results show that the muzzle velocities are optimized via the ETC technology. The 155mm uni-modular charge ETC howitzer can effectively obtain the minimum range, increase the range overlap and maximum range, and improve the ballistic stability and consistency.

Numerical Simulation of Plasma‐Propellant Interaction Under the Non‐Fourier Model

AbstractDue to the signicant characteristics of shorter and more reproducible ignition delay, plasma ignition becomes one of the key technologies of electrothermal‐chemical (ETC) propulsion. Plasma ignition is a complex heat transfer process, characterized by high temperature, high pressure, micro‐scale and extremely short duration. Under such extreme conditions, the assumption that the propagation speed of thermal disturbance is infinite in Fourier's law is no longer applicable. As such, for accurate prediction the non‐Fourier model with dual‐phase‐lag (DPL) is adopted to describe the interaction process between the plasma and the propellant. The temperature history of propellant is obtained by Dufort‐frankel numerical difference method. The numerical results obtained by DPL model are compared with the results by the Fourier model and Cattaneo‐Vernotte (C−V) model, it shows that the DPL model occupies preferable prediction performance. Additionally, the effects of plasma temperature, particle radius and absorber thickness on ignition delay are discussed. It finds that the ignition delay decreases with the increase of plasma temperature, increases with the increase of particle radius, and increases with the increase of absorber thickness. The numerical results based on DPL model are verified by the experimental results as well.

Design and manufacture of a 100 kA coaxial pulsed power cable for plasma generator and PPS in ETC guns

Based on our previous pulsed current and internal overvoltage test data and the experience of common commercial high power cables, a 100 kA coaxial pulsed power cable is designed and manufactured to adapt the coaxial electric energy breech transmission between the plasma generator and the pulsed power supply (PPS) in electrothermal-chemical (ETC) guns. The index parameters are analyzed and determined. Semi-conductor layers and a shield stiffener are introduced to prevent the deformation and burst of the pulsed power cable structurally. The semi-conductor layer can eliminate the air gap and balance the electric field in the cable. The shield stiffener can multiply the mechanical strength to restrain the strong electrodynamic force produced by the core dislocation of the outer conductor. The multi-coupling of electromagnetic field, stress field and thermal field analysis are established to assist in aided design of electrical strength, mechanical strength and temperature rise characteristics. Both a DC voltage withstand test and pulsed discharge tests are introduced to verify and inspect the performance and dynamic response of the pulsed power cable. The 25 kV/5min DC voltage withstand test result shows that the sample leakage current is nearly 3 μA and no abnormal phenomena of the pulsed power cable sample occurred. The pulsed discharge tests show that the sample can sustain the 100 kA peak current. Furthermore, this 100 kA coaxial pulsed power cable can satisfy the ETC test requirements.

Numerical simulation on the pressure wave in a 30 mm electrothermal-chemical gun with the discharge rod plasma generator

Abstract An axisymmetric two-dimensional (2D) internal ballistic model including the transient burning rate law is used to simulate the 30 mm electrothermal-chemical (ETC) launch with the discharge rod plasma generator (DRPG). The relationship between the pressure wave and the initial parameters, such as input electric power, discharging timing sequence, loading density and propellant web thickness, is researched through the change of initial parameters in the model. In the condition of synchronous discharging, the maximum of the pressure wave can be controlled while the ratio of the input electric energy to the propellant chemical energy (electric energy ratio) is less than 0.11. If the electric energy ratio is larger than 0.11, the maximum of the pressure wave increases rapidly with the electric energy ratio. With the increasing of the electric energy ratio, the change of the first negative amplitude value can be ignored. In the condition of timing sequence discharging, the allowed input electric energy ratio to control the pressure wave is proportional to the current pulse duration. At the high electric energy ratio, the maximum of the pressure wave is inverse proportional to the current pulse duration. The pressure wave increases with the increasing of the loading density. But the allowed electric energy ratio to control the pressure wave and the variation trend of the first negative amplitude wave value doesn't change. During the discharging of the DRPG, the influence of changing propellant web thickness in ETC launch can be ignored.

Simulation of two-dimensional interior ballistics model of solid propellant electrothermal-chemical launch with discharge rod plasma generator

Abstract Instead of the capillary plasma generator (CPG), a discharge rod plasma generator (DRPG) is used in the 30 mm electrothermal-chemical (ETC) gun to improve the ignition uniformity of the solid propellant. An axisymmetric two-dimensional interior ballistics model of the solid propellant ETC gun (2D-IB-SPETCG) is presented to describe the process of the ETC launch. Both calculated pressure and projectile muzzle velocity accord well with the experimental results. The feasibility of the 2D-IB-SPETCG model is proved. Depending on the experimental data and initial parameters, detailed distribution of the ballistics parameters can be simulated. With the distribution of pressure and temperature of the gas phase and the propellant, the influence of plasma during the ignition process can be analyzed. Because of the radial flowing plasma, the propellant in the area of the DRPG is ignited within 0.01 ms, while all propellant in the chamber is ignited within 0.09 ms. The radial ignition delay time is much less than the axial delay time. During the ignition process, the radial pressure difference is less than 5 MPa at the place 0.025 m away from the breech. The radial ignition uniformity is proved. The temperature of the gas increases from several thousand K (conventional ignition) to several ten thousand K (plasma ignition). Compare the distribution of the density and temperature of the gas, we know that low density and high temperature gas appears near the exits of the DRPG, while high density and low temperature gas appears at the wall near the breech. The simulation of the 2D-IB-SPETCG model is an effective way to investigate the interior ballistics process of the ETC launch. The 2D-IB-SPETC model can be used for prediction and improvement of experiments.

Study of the expansion characteristics of a pulsed plasma jet in air

In the background of electrothermal-chemical (ETC) emission, an investigation has been conducted on the characteristics of a freely expanding pulsed plasma jet in air. The evolutionary process of the plasma jet is experimentally investigated using a piezoelectric pressure sensor and a digital high-speed video system. The variation relation in the extended volume, axial displacement and radial displacement of the pulsed plasma jet in atmosphere with time under different discharge voltages and jet breaking pressures is obtained. Based on experiments, a two-dimensional axisymmetric unsteady model is established to analyze the characteristics of the two-phase interface and the variation of flow-field parameters resulting from a pulsed plasma jet into air at a pressure of 1.5–3.5 MPa under three nozzle diameters (3 mm, 4 mm and 5 mm, respectively). The images of the plasma jet reveal a changing shape process, from a quasi-ellipsoid to a conical head and an elongated cylindrical tail. The axial displacement of the jet is always larger than that along the radial direction. The extended volume reveals a single peak distribution with time. Compared to the experiment, the numerical simulation agrees well with the experimental data. The parameters of the jet field mutate at the nozzle exit with a decrease in the parameter pulse near the nozzle, and become more and more gradual and close to environmental parameters. Increasing the injection pressure and nozzle diameter can increase the parameters of the flow field such as the expansion volume of the pulsed plasma jet, the size of the Mach disk and the pressure. In addition, the turbulent mixing in the expansion process is also enhanced.

Mechanism of plasma ignition in electrothermal-chemical launcher

Abstract Plasma generator is a core component in an electrothermal-chemical (ETC) launcher. Its work state directly influences the launch efficiency of a system. The interaction between plasma and propellants is a very important mechanism in ETC technology. Based on the transient radiation model and open air plasma jet experiment, the mechanism of plasma ignition process is analyzed. Results show that the surface temperature of local solid propellant grain can quickly achieve the ignition temperature under the action of early transient plasma radiation. But it needs enough time to maintain the high energy flow to make self-sustained combustion of solid propellant grains. Because of the limited space characteristics of transient radiation, the near-field propellant grains can gain enough energy by the strong transient radiation to be ignited and achieve self-sustained combustion. The far-field propellant grains mainly gain the energy by the activated particles in plasma jet to be ignited and self-sustained combustion. Experiments show that plasma jet always has a high flow velocity in the area of the cartridge. Compared with conventional ignition, the solid propellant grains can obtain more quick and uniform ignition and self-sustained combustion by this kind of ablation controlled arc (ACA) plasma via energy skin effect of propellant grains, pre-heat temperature mechanism and high efficient jet diffusion.

Study of the pitting effects during the pre-ignition plasma–propellant interaction process

The propellant ignition mechanism has become a central issue in the electrothermal chemical (ETC) launch technology, and the pre-ignition plasma–propellant interactions are critical in determining the ignition characteristics. In this work, both an open-air ablation test and an interrupted burning test are conducted for three different propellants. A fused silica window, which is transparent in all relevant wavelengths, is utilized to investigate the role of the plasma radiation. Surface pitting of the propellants after interaction with the plasma is analyzed using a scanning electron microscope (SEM). The effect of pits on the plasma ignition is then studied and a possible formation mechanism of pits is proposed. The input heat flux and the surface temperature of the propellants are obtained by solving a pre-ignition plasma–propellant interaction model. The results shed light on the pre-ignition plasma ignition mechanisms and will assist in the development of propellants for an ETC launcher.

Application of transient burning rate model of solid propellant in electrothermal-chemical launch simulation

A 30mm electrothermal-chemical (ETC) gun experimental system is employed to research the burning rate characteristics of 4/7 high-nitrogen solid propellant. A modified 0D internal ballistic model is established to simulate the ETC launch. According to the measured pressure and electrical parameters, a transient burning rate law including the influence of enhanced gas generation rates (EGGR) coefficient by electric power and pressure gradient (dp/dt) is added into the model. The EGGR coefficient of 4/7 high-nitrogen solid propellant is equal to 0.005MW-1. Both simulated breech pressure and projectile muzzle velocity accord with the experimental results well. Compared with Woodley’s modified burning rate law, the breech pressure curves acquired by the transient burning rate law are more consistent with test results. Based on the parameters calculated in the model, the relationship among propellant burning rate, pressure gradient (dp/dt) and electric power are analyzed. Depending on the transient burning rate law and experimental data, the burning of solid propellant under the condition of plasma is described more accurately.

Study of High-Enthalpy Electrothermal Energetic Plasma Source Concept

The electrothermal (ET) energetic plasma source (ETEPS) is a different concept in which the ablation mechanism is forced inside of the open-ended capillary that has energetic liner, a propellant. The generation of the ET plasma results from Joule heating and radiant heat transport to the liner. The discharge initiates erosive burn of the propellant, and the mixed plasma-propellant gasification produces high-enthalpy energetic flow. In the ablation-dominated source, the eroded materials from the solid propellant liner are mixed inside the source before they flow out as a result of the large pressure gradient. The energetic ET source also has another concept in which no ablation occurs and the plasma is generated from the injection of energetic gasses or liquids into the confined open-ended capillary. The ablation-free source generates the plasma from the dissociation of the gaseous/liquid components, which in turn releases the chemical energy of these propellants and mixes the energy with the electrical energy of the plasma. This concept is different from ET chemical (ETC) sources; it generates the propellant or energetic flow without requiring a combustion chamber. It also provides mixing at the ionic level not available in current configurations of ETC launchers, igniters, or thrusters. The ET plasma code ETFLOW-EN was developed to computationally simulate the plasma generation and flow in energetic ET capillary discharges to predict the behavior of the energetic source with the use of lined solid propellants. Operation with liquid/gaseous energetic forms in a nonablative capillary is also a character of this concept and is part of the ETFLOW code. The results of using different forms of energetic materials in solid, liquid, and gaseous mixtures have shown the applicability of ETEPS to produce high-enthalpy energetic plasma flows with sufficient parameters suitable for ETC launch applications. Plasma and flow parameters at the capillary exit were investigated at different mixing ratios.

Hyper Jet Focused-Injection Tapered Capillary Plasma Source Concept

The concept of tapered capillary is introduced as a method of injecting focused plasma jet into the breach of bulk-loaded electrothermal-chemical (ETC) launcher. Tapered capillaries will operate in the confined controlled arc regime, and they can provide the advantage of producing focused hyper plasma jets useful for ignition of ETC systems at controlled plasma temperatures and pressures. The concept is also useful for focused implantation of plasma ions on substrates with desired patterns. Such tapered capillaries can inject plasmas at peak kinetic temperatures in the range of 14000-21000 K (~1.2-1.8 eV) and considerable jet pressures of 10-70 MPa for an input discharge current of 20-30 kA over a short pulselength of 100-150 μs. A tapered geometry made of Lexan polycarbonate with 16.8-mm inlet and 8.8-mm outlet radii produces a plasma jet with a plasma temperature of 14253 K (1.23 eV) at a peak bulk velocity of 4.027 km/s with a 10.38-MPa exit pressure, and a total ablated mass of 10.56 mg. Reducing the tapering to 12.6-mm inlet and 6.6-mm outlet radii produces a plasma jet with a plasma temperature of 16382-K (1.411 eV) at a bulk velocity of 4.34 km/s and a total of 23.27-mg ablated mass. Further reduction in the tapering to 8.4-mm inlet and 4.4-mm outlet radii produces a plasma jet with a plasma temperature of 20954 K (1.8 eV) at a bulk velocity of 4.89 km/s with a 70.78-MPa exit pressure, and a total ablated mass of 15.09 mg. The preliminary study shows that the narrow tapering angle produces higher pressure, temperature, velocity, and more ablated mass. Radiant heat flux at the taper exit varies from 2.2 GW/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> for the wider tapers to 6.24 GW/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> for the narrower ones.

Calculation of Plasma Radiation in Electrothermal-Chemical Launcher

A numerical model of radiation has been adopted for electrothermal-chemical (ETC) launcher, in which Monte Carlo method and statistical physics are employed to simulate the process of a capillary plasma source in an ETC launcher. The effect on propellant grains with different average absorption coefficients is discussed. The plasma-propellant interaction is also discussed when combined with a thermal model. Results show that the strong instantaneous radiation is responsible for the transmission of energy to the propellant grains leading to ignition. The efficiency of energy absorption in the propellant bed always maintains a high level. Radiant energy caused by plasma is concentrated around the plasma injector. And the “hot zone” efficiency is mainly affected by the properties of propellant grains within a small field around the plasma injector.

Energy Skin Effect of Propellant Particles in Electrothermal–Chemical Launcher

A numerical model of radiation has been employed by using a Monte Carlo method and statistical physics to simulate the process of a capillary plasma source for an electrothermal-chemical launcher. The effect of plasma on propellants with different physical parameters is discussed. The plasma-propellant interaction when the radiation model is combined with a thermal model is also discussed. Results show that radiant energy only causes a small field around the plasma injector in the propellant bed. The responses of energy flux and propellant particles to radiation are both on the order of picoseconds. The strong instantaneous radiation is not only the dominant effect of energy transport in hot plasma but is also responsible for the transmission of energy to the propellant particles leading to ignition. This energy skin effect on the propellant-particle surface appears to be the main cause of plasma ignition.

Study on the Characteristics of Different Plasma Ignition Schemes

Plasma ignition mechanisms have always been the central issue in the electrothermal-chemical (ETC) launch technology. Generally, there are two types of ignition schemes, namely, the axial discharge scheme and the radial discharge scheme, and the two schemes are supposed to have different ignition characteristics. This work is devoted to study the features of different plasma ignition schemes in the ETC launch devices. A capillary discharge setup and a gap discharge setup are utilized in the experiments to represent the axial and radial discharge ignition schemes, respectively, and three types of propellants are used in the study. Using the measured data in the experiments, plasma heat fluxes are solved by a plasma-propellant interaction model. In addition, the propellant surface conditions are investigated by a scanning electron microscope after the plasma ignition experiments. The surface conditions of propellants in different ignition schemes display distinct features, which are analyzed to shed light on the characteristics of different ignition schemes and the responses of different propellants. Results are supposed to help in interpreting the plasma-propellant interaction mechanisms in different ignition schemes and provide references for the optimization design of plasma ignition installations in the ETC launch devices.

150 kJ Compact Capacitive Pulsed Power System for an Electrothermal Chemical Gun

A 150 kJ compact capacitive pulsed power system (CCPPS) capable of delivering electrical energy into an electrothermal chemical (ETC) gun on a vehicle has been studied. The CCPPS provides pulsed electrical energy into a capillary plasma injector which generates plasma of tens of thousands <TEX>$^{\circ}K$</TEX> in temperature and has a nonlinear resistance depending on the current. The design requirements of the CCPPS are as follows: the maximum power of 250 MW, the pulse width of about 0.6 ms, the volume of no more than 0.5 cubic meter, the efficiency of energy transfer over 80 % and the repetition rate of 4~5 times per minute. The constructed CCPPS is composed of four 37.5 kJ capacitor bank modules in parallel to make a trapezoid pulse shape and to satisfy the design requirements. Each module is designed to achieve high reliability, safety, efficiency and energy density to endure severe operating conditions. The results of the performance test on the CCPPS using a 120 mm ETC gun are described.

Three-stage superconducting XRAM generator

XRAM generators can be used for powering pulse loads demanding peak power ratings up to the gigawatt range, such as magneto-forming devices, ETC (electrothermal-chemical) guns, high-power microwaves, and railguns. They are a valid alternative to power capacitors being currently at the limits of their technology. In order to improve the XRAM generator in terms of efficiency, the German-French Research Institute of St. Louis (ISL) investigated in cooperation with the G2Elab the use of high-temperature superconducting coils for an XRAM generator. Moreover, as the XRAM switching principle can be integrated into a superconducting magnetic energy storage (SMES) system, a superconducting XRAM generator has the ability to hold its energy available on demand for a longer time than currently employed high-density power capacitors. Our three-stage superconducting XRAM test case reached a maximum charging current of 200 A, discharging a magnetic energy of 84 kJ at 600 A peak current into a 27 mΩ load during a 34 s long discharge. This is the first report in the literature on successful experiments with a superconducting XRAM generator.