基于火焰加速和燃爆转变准则的氢气点火安全性研究

采用点火器对可燃混合气体进行预先点火是严重事故下的1种可供选择的氢气缓解措施。基于σ准则和λ准则可以评估氢气燃烧时发生火焰加速(FA)和爆燃向爆炸的转变(DDT)的可能性。本文分析密闭房间中氢气早期和晚期点火的过程。分析结果表明，点火器在空间的合理布置和初次点火时间的控制，可有效移除事故前期的氢气。本方法能用于确定核电站干式安全壳内氢气点火器的数量、位置和点火时间。     

Effect of actuating voltage and discharge gap on plasma assisted detonation initiation process

The influence of actuating voltage and discharge gap on plasma assisted detonation initiation by alternating current dielectric barrier discharge was studied in detail.A loose coupling method was used to simulate the detonation initiation process of a hydrogen–oxygen mixture in a detonation tube under different actuating voltage amplitudes and discharge gap sizes.Both the discharge products and the detonation forming process assisted by the plasma were analyzed.It was found that the patterns of the temporal and spatial distributions of discharge products in one cycle keep unchanged as changing the two discharge operating parameters.However,the adoption of a higher actuating voltage leads to a higher active species concentration within the discharge zone,and atom H is the most sensitive to the variations of the actuating voltage amplitude among the given species.Adopting a larger discharge gap results in a lower concentration of the active species,and all species have the same sensitivity to the variations of the gap.With respect to the reaction flow of the detonation tube,the corresponding deflagration to detonation transition(DDT) time and distance become slightly longer when a higher actuating voltage is chosen.The acceleration effect of plasma is more prominent with a smaller discharge gap,and the benefit builds gradually throughout the DDT process.Generally,these two control parameters have little effect on the amplitude of the flow field parameters,and they do not alter the combustion degree within the reaction zone.     

The Advantages of Non-Thermal Plasma for Detonation Initiation Compared with Spark Plug

In this paper, the characteristics of detonation combustion ignited by AC-driven non-thermal plasma and spark plug in air/acetylene mixture have been compared in a double-tube experiment system. The two tubes had the same structure, and their closed ends were installed with a plasma generator and a spark plug, respectively. The propagation characteristics of the flame were measured by pressure sensors and ion probes. The experiment results show that, compared with a spark plug, the non-thermal plasma obviously broadened the range of equivalence ratio when the detonation wave could develop successfully, it also heightened the pressure value of detonation wave. Meanwhile, the detonation wave development time and the entire flame propagation time were reduced by half. All of these advantages benefited from the larger ignition volume when a non-thermal plasma was applied.     

A Steam-Plasma Igniter for Aluminum Powder Combustion

High-temperature ignition is essential for the ignition and combustion of energetic metal fuels,including aluminum and magnesium particles which are protected by their highmelting-temperature oxides.A plasma torch characterized by an ultrahigh-temperature plasma plume fulfills such high-temperature ignition conditions.A new steam plasma igniter is designed and successfully validated by aluminum power ignition and combustion tests.The steam plasma rapidly stabilizes in both plasma and steam jet modes.Parametric investigation of the steam plasma jet is conducted in terms of arc strength.A high-speed camera and an oscilloscope method visualize the discharge characteristics,and optical emission spectroscopy measures the thermochemical properties of the plasma jet.The diatomic molecule OH fitting method,the Boltzmann plot method,and short exposure capturing with an intensified charge coupled device record the axial distributions of the rotational gas temperature,excitation temperature,and OH radical distribution,respectively.The excitation temperature at the nozzle tip is near 5500 K,and the gas temperature is 5400 K.     

AP1000核电厂氢气点火器功能分析

采用集总参数分析程序对AP1000核电厂安全壳内氢气点火系统功能进行了分析和验证。在定义的包络事故工况下,氢气最大瞬时释放速率达300kg/min。计算表明：在无点火措施情况下,AP1000安全壳局部隔间的氢气浓度较高,隔间内的气体处于可燃状态,且接近爆燃向爆炸转变（DDT）状态;在实施点火措施情况下,氢气浓度得到有效控制,氢气点火系统能消除严重事故下氢气所引起的风险。     

Discharge and jet characteristics of gliding arc plasma igniter driven by pressure difference

Stable combustion in an afterburner can help increase the thrust of the engine in a short time, thereby improving the maneuverability of a fighter. To improve the ignition performance of an afterburner, a twin-duct ignition platform was designed to study the performance of a gliding arc plasma igniter in close-to-real afterburner conditions. The research was carried out by a combination of experiments and simulations. The working environment of the igniter was explored through a numerical simulation. The results showed that the airflow ejected from the radiating holes formed a swirling sheath, which increased the anti-interference ability of the airflow jet. The influence of the pressure difference between the inlet and outlet of the igniter (Δp), the flow rate outside the igniter outlet (W₂), and the installation angle (α) on the single-cycle discharge energy (E) as well as the maximum arc length (L) were studied through experiments. Three stages were identified: the airflow breakdown stage, the arc evolution stage, and the arc fracture stage. E and L increased by 107.3% and 366.2%, respectively, with Δp increasing from 10 to 70 Torr. The relationship between L and Δp obtained by data fitting is L = 3 − 2.47/(1 + (Δp/25)⁴). The relationship of L at different α is L_α=0° > (L_α=45° and L_α=135°) > L_α=180° > L_α=90°. E and L decrease by 18.2% and 37.3%, respectively, when Δp = 45 Torr and W₂ is increased from 0 to 250 l min⁻¹.     

Application study on plasma ignition in aeroengine strut-cavity-injector integrated afterburner

To increase the thrust-weight ratio in next-generation military aeroengines,a new integrated afterburner was designed in this study.The integrated structure of a combined strut-cavity-injector was applied to the afterburner.To improve ignition characteristics in the afterbumer,a new method using a plasma jet igniter was developed and optimized for application in the integrated afterburner.The effects of traditional spark igniters and plasma jet igniters on ignition processes and ignition characteristics of afterburners were studied and compared with the proposed design.The experimental results show that the strut-cavity-injector combination can achieve stable combustion,and plasma ignition can improve ignition characteristics.Compared with conventional spark ignition,plasma ignition reduced the ignition delay time by 67 ms.Additionally,the ignition delay time was reduced by increasing the inlet velocity and reducing the excess air coefficient.This investigation provides an effective and feasible method to apply plasma ignition in aeroengine afterburners and has potential engineering applications.     

Study on the influence of the discharge voltage on the ignition process of Hall thrusters

A high-speed charge-coupled device camera was used to capture images of the plume and acceleration channel of a Hall effect thruster during ignition at different discharge voltages. To better understand the influence of changes in the discharge voltage on the plasma parameters during thruster ignition, a particle-in-cell numerical model was used to calculate the distribution characteristics of the ion density and electric potential at different ignition moments under different discharge voltages. The results show that when the discharge voltage is high, the ion densities in the plume and acceleration channel are significantly higher at the initial phase of thruster ignition; with the gradual strengthening of the ignition process, the propellant avalanche ionization during thruster ignition occurs earlier and the pulse current peak increases. The main reason for these phenomena is that the change in the discharge voltage results in different energy acquisitions of the emitted electrons entering the thruster channel.     

Plasma-Assisted Chemistry in High-Speed Flow

Fundamental problems related to the high-speed combustion are analyzed. The result of plasma-chemical modeling is presented as a motivation of experimental activity. Numerical simulations of the effect of uniform non-equilibrium discharge on the premixed hydrogen and ethylene-air mixture in supersonic flow demonstrate an advantage of such a technique over a heating. Experimental results on multi-electrode non-uniform discharge maintenance behind wallstep and in cavity of supersonic flow are presented. The model test on hydrogen and ethylene ignition is demonstrated at direct fuel injection to low-temperature high-speed airflow.     

Numerical and experimental investigation of plasma plume deflection with MHD flow control

This paper presents a composite magneto hydrodynamics(MHD) method to control the lowtemperature micro-ionized plasma flow generated by injecting alkali salt into the combustion gas to realize the thrust vector of an aeroengine.The principle of plasma flow with MHD control is analyzed.The feasibility of plasma jet deflection is investigated using numerical simulation with MHD control by loading the User-Defined Function model.A test rig with plasma flow controlled by MHD is established.An alkali salt compound with a low ionization energy is injected into combustion gas to obtain the low-temperature plasma flow.Finally,plasma plume deflection is obtained in different working conditions.The results demonstrate that plasma plume deflection with MHD control can be realized via numerical simulation.A low-temperature plasma flow can be obtained by injecting an alkali metal salt compound with low ionization energy into a combustion gas at 1800–2500 K.The vector angle of plasma plume deflection increases with the increase of gas temperature and the magnetic field intensity.It is feasible to realize the aim of the thrust vector of aeroengine by using MHD to control plasma flow deflection.     

Development of DETAC and its application to the hydrogen detonation analysis

In this study, a numerical analysis code (DETAC, Detonation Analysis Code) for hydrogen detonation during the reactor severe accident was developed using Fortran 90 language, and the simulation was performed for the hydrogen detonation. A global-chemistry model was adopted to simulate the chemical reaction. The Euler equations were solved using third-order Runge-Kutta method with fifth-order weighted essentially non-oscillatory scheme handling the convection flux. Afterward, the hydrodynamics solver was verified by comparison of predicted results and exact solutions of four cases of shock tube problems. A hydrogen detonation in a pipe was simulated to verify this code by comparing the results with the classical C-J theory. Furthermore, this code was applied to the hydrogen detonation analysis in the compartment of BWR building. Two cases with different ignition locations were analyzed in this paper and the maximum pressure of these cases were 7.5 MPa and 8.0 MPa, respectively. The pressure and the temperature during detonation were affected by the ignition location. The results indicated that the possibility of reactor building destruction exists if the hydrogen detonation occurs.     

Electrical and aerodynamic characteristics of sliding discharge based on a microsecond pulsed plasma supply

Plasma flow control technology has broad prospects for application. Compared with conventional dielectric barrier discharge plasma actuators (DBD-PA), the sliding discharge plasma actuator (SD-PA) has the advantages of a large discharge area and a deflectable induced jet. To achieve the basic performance requirements of light weight, low cost, and high reliability required for UAV (Unmanned Aerial Vehicle) plasma flight experiments, this work designed a microsecond pulse plasma supply that can be used for sliding discharge plasma actuators. In this study, the topology of the primary circuit of the microsecond pulse supply is determined, the waveform of the output terminal of the microsecond pulse plasma supply is detected using the Simulink simulation platform, and the design of the actuation voltage, the pulse frequency modulation function and the construction of the hardware circuit are achieved. Using electrical diagnosis and flow field analysis, the actuation characteristics and flow characteristics of sliding discharge plasma under microsecond pulse actuation are studied, the optimal electrical actuation parameters and flow field characteristics are described.     

Experimental investigation on DBD plasma reforming hydrocarbon blends

To improve the'detonation-supporting'performance of fuel-rich catalytic combustion products,DBD plasma,stimulated by adjustable nanosecond pulse power supply,was used to further regulate the components and concentrations of the hydrocarbon blends.In this paper,the parameters including load voltage,frequency,rising(falling)edge,pulse width and feeding flow rate were changed respectively,and the corresponding concentration and proportion change of the components in blend gas were investigated.According to the experiment result,it was found that when the discharge frequency is low,the plasma mainly promotes the transformation of light gaseous substances,while it mainly promotes the conversion to heavy hydrocarbons when the frequency is larger.Increasing load voltage will strengthen this trend.The controlling and reforming effect of plasma on the blend gas will decrease with the increase of voltage rising(falling)edge and the feeding flow rate.The regulation effect will be strengthened with the increase of pulse width under 200 ns.With the increase of discharge intensity,the'carbon'settles on the walls of the reactor,which will change the dielectric constant,leading to the loss of control of the discharge.     

Discharge characteristics and reactive species production of unipolar and bipolar nanosecond pulsed gas-liquid discharge generated in atmospheric

In this paper,unipolar pulse (including positive pulse and negative pulse) and bipolar pulse voltage are employed to generate diffuse gas-liquid discharge in atmospheric N2 with a trumpet-shaped quartz tube.The current-voltage waveforms,optical emission spectra of excited state active species,FTIR spectra of exhaust gas components,plasma gas temperature,and aqueous H2O2,NO2-,and NO3-production are compared in three pulse modes,meanwhile,the effects of pulse peak voltage and gas flow rate on the production of reactive species are studied.The results show that two obvious discharges occur in each voltage pulse in unipolar pulse driven discharge,differently,in bipolar pulse driven discharge,only one main discharge appears in a single voltage pulse time.The intensities of active species (OH(A),and O(3p)) in all three pulsed discharge increase with the rise of pulse peak voltage and have the highest value at 200 ml min-1 of gas flow rate.The absorbance intensities of NO2 and N2O increase with the increase of pulse peak voltage and decrease with the increase of gas flow rate.Under the same discharge conditions,the bipolar pulse driven discharge shows lower breakdown voltage,and higher intensities of excited species (N2(C),OH(A),and O(3p)),nitrogen oxides (NO2,NO,and N2O),and higher production of aqueous H2O2,NO2-,and NO3-compared with both unipolar positive and negative discharges.     

Enhanced removal of ultrafine particles from kerosene combustion using a dielectric barrier discharge reactor packed with porous alumina balls

Ultrafine particles(UFPs) are harmful to human beings, and their effective removal from the environment is an urgent necessity. In this study, a dielectric barrier discharge(DBD) reactor packed with porous alumina(PA) balls driven by a pulse power supply was developed to remove the UFPs(ranging from 20 to 100 nm) from the exhaust gases of kerosene combustion. Five types of DBD reactors were established to evaluate the effect of plasma catalysis on the removal efficiency of UFPs. The influences of gas flow rate, peak voltage and pulse frequency of different reactors on UFPs removal were investigated. It was found that a high total UFP removal of91.4% can be achieved in the DBD reactor entirely packed with PA balls. The results can be attributed to the enhanced charge effect of the UFPs with PA balls in the discharge space. The UFP removals by diffusion deposition and electrostatic attraction were further calculated,indicating that particle charging is vital to achieve high removal efficiency for UFPs.     

Discharge characteristics and reactive species production of unipolar and bipolar nanosecond pulsed gas–liquid discharge generated in atmospheric N_2

In this paper,unipolar pulse (including positive pulse and negative pulse) and bipolar pulse voltage are employed to generate diffuse gas–liquid discharge in atmospheric N_2with a rumpetshaped quartz tube.The current–voltage waveforms,optical emission spectra of excited state active species,FTIR spectra of exhaust gas components,plasma gas temperature,and aqueous H_2O_2,NO_2~-,andNO_3~-production are compared in three pulse modes,meanwhile,the effects of pulse peak voltage and gas flow rate on the production of reactive species are studied.The results show that two obvious discharges occur in each voltage pulse in unipolar pulse driven discharge,differently,in bipolar pulse driven discharge,only one main discharge appears in a single voltage pulse time.The intensities of active species (OH(A),and O(3p)) in all three pulsed discharge increase with the rise of pulse peak voltage and have the highest value at 200 ml min~(-1)of gas flow rate.The absorbance intensities of NO_2and N_2O increase with the increase of pulse peak voltage and decrease with the increase of gas flow rate.Under the same discharge conditions,the bipolar pulse driven discharge shows lower breakdown voltage,and higher intensities of excited species (N_2(C),OH(A),and O(3p)),nitrogen oxides (NO_2,NO,and N_2O),and higher production of aqueous H_2O_2,NO_2~-,andNO_3~-compared with both unipolar positive and negative discharges.     

Impulse-coupling coefficients from a pulsed-laser ablation of semiconductor GaAs

1 Introduction When a pulsed-laser beam with sufficiently high power density is focused onto a solid surface, the area irradiated by the laser beam rapidly vaporizes, ionizes, and generates plasma [1]. The vaporized materials mi- grate from the surface and initiate a shock wave, then a laser-supported detonation (LSD) wave is ignited by either the breakdown of the vaporized material or the actual breakdown of the air above the surface [2, 3]. When the plasma apart from the surface and LSD wa…     

Effect of shock wave formation on propellant ignition in capillary discharge

In order to study the effect of shock wave formation on propellant ignition in capillary discharge, the shock wave formation process was analyzed using experimental and theoretical methods; the plasma jet temperature was measured, and closed bomb and 30 mm gun experiments were carried out. The results show that the first shock wave has a smaller value and larger range of influence, while the second shock wave has a larger value and smaller range of influence. A plasma jet can generate a shock wave at the nozzle according to the calculated plasma pressure and velocity, which is well confirmed by experiments and calculations. The plasma jet temperature is high during the formation of a shock wave and then decreases sharply. Plasma ignition can increase the burning rate of a propellant by about 30% by increasing the burning surface area of the propellant. Compared to conventional ignition, the average maximum chamber pressure and average muzzle velocity of plasma ignition are increased by 9.1 MPa and 29.3 m·s−1(∼3%), respectively, in a 30 mm gun. Plasma ignition has strong ignition ability and short ignition delay time due to the generation of a shock wave. By increasing the burning rate of the propellant, the muzzle velocity can be greatly improved when the maximum chamber pressure increases a little. The characteristics of the shock wave can be applied in the application of the capillary discharge plasma. For example, it can be applied in fusion, launching and combustion.     

Comparison of discharge characteristics and methylene blue degradation through a direct-current excited plasma jet with air and oxygen used as working gases

Through using a direct-current driven plasma jet operated underwater, degradation of methylene blue(MB) is investigated with air and oxygen used as working gases. With a low power voltage,a plasma plume extends from the needle electrode, which is purple in air. It turns pink after it bridges the two electrodes. During the process, oxygen plasma remains white. Discharge operates in a pulsed mode or a continuous one, which depends on the magnitude of power voltage. For the pulsed mode, oxygen discharge has a shorter plume and a higher pulse frequency than air discharge under the same power voltage. For the same current of the continuous mode, both power and gap voltages of oxygen discharge are higher than those of air discharge. Moreover, MB degradation efficiency increases with increasing power voltage or initial concentration of MB solution. Compared with air discharge, oxygen discharge has a higher degradation efficiency with the same power voltage and treatment time. The pulsed oxygen discharge with power voltage of about 6.5 k V has the highest efficiency in degrading MB dye, reaching approximately 85.8% after 10 min treatment. As a comparison, after 10 min treatment in air discharge, the highest degradation efficiency is 63.7%, which appears in the continuous mode at a power voltage of 10.6 kV. Besides, optical spectra from the discharges are also compared for the two types of working gases.     

Application of High Energy Protons in Inertial Confinement Fusion by Using the Fast Ignitor Concept for DT Fusion

A short-laser-pulse driven ion flux is examined as a fast ignitor candidate for inertial confinement fusion. The main mechanism for ion acceleration is charge separation in a plasma due to high-energy electrons driven by the laser inside the target. Another very new branch of fast ignition research is the investigation of the use of laser generated proton beams. In the present paper aims to provide insights into the feasibility of the fast ignition concept with high energy beams of protons generated in laser–plasma interactions. The optimum parameters of an ion beam and laser pulse that are suitable for an ignition spark in a hot precompressed DT fuel are estimated as a rough guide. Also, in this paper we estimate the radius of Deuterium–Tritium (DT) fuel pellet that is equal to the protons range in DT plasma.