Jet Torch Research Articles

Investigation of Subsonic to Supersonic Transition of a Low-Pressure Plasma Torch Jet

The plasma jet emanating out of a thermal plasma torch operating at low pressure ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 30$ </tex-math></inline-formula> mbar) has been investigated experimentally. Different anode exit diameters are chosen, and the torch is operated at various gas flows and discharge current and their thermodynamic outputs have been calculated. Current–voltage characteristics (CVC) of plasma torch with different anode geometries are explored highlighting their differences. Interesting correlations are found between the anode exit diameter and the threshold limit for subsonic to supersonic transition of the jet. The spectral analysis of the voltage fluctuations reveals the presence of different frequencies and also yields the threshold. The kinetic energy (KE) component of the plasma jet has a direct correlation with the oscillations in the arc voltage. In addition to restrike mode and Helmholtz mode, an acoustic mode of oscillations is also investigated. A new resonator model explaining the different oscillations occurring in the low-pressure operation is also presented. The Helmholtz mode oscillations are validated by comparing the experimental values with the theoretical calculations. The power associated with the Helmholtz mode and acoustic mode has direct correlation with the plasma velocity and acts as a signature of the transition from subsonic to supersonic regime.

The design and analysis of a novel low power atmospheric plasma jet torch for optical fabrication

Over the past few years, atmospheric Inductively Coupled Plasma (ICP) has aroused extensive attention in optical fabrication field since its chemical etching-based processing mode does not mechanically damage work-pieces. However, commercial Fassel-type torch are commonly employed in processing, and the high temperature plasma jet generated by commercial Fassel-type torch will cause thermal damage to optical elements. In this paper, an ICP jet torch is developed for optical fabrication, capable of maintaining plasma jet under a low power of 156 W. By reducing the minimum maintenance power of plasma jet, the processing temperature is down-regulated to 112 °C. To explain the low maintenance power principle in this research, the effect of radial confinement and axial pushing-off on the plasma are analyzed by simulation and experiment processes. Moreover, the effect of these two phenomena on the maintenance power is analyzed experimentally. Subsequently, the experiments are performed to verify the processing temperature, removal efficiency and removal stability of the torch. As revealed from the experimental results, the proposed torch exhibits the stability of footprint up to 97.5%.

The effect of the external acoustic waves on the plasma torch jet

Numerical experiments on the effect of the external acoustic waves on the plasma torch jet have been performed. The formation of a turbulent plasma torch jet upon application of an external acoustic waves is demonstrated.

ТЕОРИЯ РАСПЫЛИВАНИЯ ЖИДКОСТИ ФОРСУНКАМИ

The main characteristics are considered and calculations of the main indicators of nozzle devices are given. Laboratory tests of nozzles of various configurations were carried out to determine the working width of the spot at different distances to the irrigated surface and the angle of the spray pattern, and dependencies were established to determine their effective mode of operation. As a result of testing nozzles with different spray patterns when determining the impact force of the jet, it was found that as the spray angle increases, the value of the impact force of the jet F decreases. This is due to the fact, that with an increase in the initial jet velocity, the torch length reaches a maximum, not only does the kinetic energy increase, but the sizes (diameters) of the sprayed medium drops, which leads to a decrease in droplet mass and an increase in the aerodynamic resistance of the torch jet particles. A bench for determining the impact force of a jet of various nozzles was developed and test results were obtained. During operation, due to the erosive wear of the jet holes of the nozzles, its diameter increases, as a result, the working atomization pressure drops, and the number and size of large particles increase. Therefore, periodically it is necessary to check the diameter of the nozzle holes and not to use nozzles, that have a hole diameter greater than the initial one by 10 or more percent. In the study of nozzles, the dependences of nozzles’ characteristics on the initial parameters of the outflow of the liquid jet to the dispersity and shape of the torch were established. The values of irrigation spot width are established depending on the angle of the torch and the distance from the nozzle to the irrigated surface. The magnitude of the impact force of the jet, which occurs at the point of contact of the fluid jet with the irrigated surface, is determined.

Forced Combustion Characteristics Related to Different Injection Locations in Unheated Supersonic Flow

This work focuses on forced combustion with regards to the relationship between vent mixer models and several injection locations in unheated supersonic flow. A plasma jet torch was used to ignite the hydrogen-air mixture in a laboratory-scaled combustor duct. The flow field of the combustion was visualized with pressure and gas-sampling measurements. The vent mixers indicate good dispersion characteristics of the mixture for both parallel and normal 1 injections. However, forced combustion is dominantly governed by the injection rate toward the plasma jet (hot source) because the combustible region is restricted under the cold main flow. For this reason, the parallel injection, which provides the hydrogen-air mixture directly toward the plasma jet, shows good combustion performance. The normal 1 injection interacted with the vent mixers and shows slightly good combustion performance. Lastly, the normal 2 injection is little affected by the vent mixers and has poor combustion performance.

Investigation of flame establishment and stabilization mechanism in a kerosene fueled supersonic combustor equipped with a thin strut

The flame establishment and propagation processes in a supersonic combustor fueled by liquid kerosene at Mach 6 condition were observed by high speed photography. In this paper, a thin strut acted as the flame holder equipped in the center of the combustor. In the experiment condition, the Mach number in the inlet of the combustor is 2.8, with the stagnation state Tt=1680 K, Pt=1.87 MPa. The combustion establishment process and the flame characteristics in the supersonic combustor were well captured and reproduced by the high-speed camera, with the camera parameter of 5000 frames per second. Experimental results show that initial flame appears around the plasma jet torch in the recirculation zone at the tailing edge of the strut, and grows to form a steady flame in the center of main inflow. The attribute of the flame is partially premixed flame in the experimental conditions, and the flame could be divided into three main parts in accordance with the flame characteristics. By the analysis of the high speed images, different flame propagation patterns in the flame establishment processes are found in different equivalence ratios, the mechanism of which is explained in this paper.

Basic Characteristics of In-Liquid Plasma Jet and Electrode Damage

The most progress towards a practical method of fusing municipal waste incineration ash has been in the use of a plasma jet that employs arc discharge, a form of thermal plasma. However, a remaining problem is that stable plasma generation is prevented by melting of the nozzle of the plasma-jet torch by the high-temperature plasma flow. With the objective of developing high-speed fusion treatment for waste materials using an in-liquid plasma jet, basic research was conducted on plasma stability and the durability of plasma-jet torches, including electrodes and nozzles. Basic plasma jet characteristics such as the discharge voltage, current, and power value at the time of plasma jet generation were investigated experimentally. The relationship between the temperature distribution near the tip of a plasma jet torch and electrode damage was investigated by fluid-heat coupled analysis using the finite element method.

Equipment of the design of PJSC NKMZ for heat treatment of sheet

It is shown that improving the design of the roller-type machine towards providing the quenching and interrupted cooling modes (RQM) in the sheet rolling technology allows to expand the technological capabilities and manageability of the process. This provides decreased equipment weight and reduced time to reach the design performance. The feature of the process is that during the movement of the processed rolled stock, the RQM is divided into intensive and low-intensive cooling zones. The maximum cooling rate (over 120 deg/s) is achieved in the intensive cooling zone using the slit-type collector with the jet torch directed to the surface of the rolled stock at an angle of no more than 250 and the two-chamber collectors with flat-flame nozzles with the jet torch directed to the surface of the rolled stock at an angle of no more than 600. Using dual-chamber collectors significantly increased the manageability of the heat treatment process since the water consumption variation range has increased by at least 1.9 times. It is shown that the cooling system design in conjunction with the automated water supply control system allows to optimally distribute flows along the length and width of the sheet, and also establish favorable water supply ratios in the top and bottom of each cooling section. Due to the proposed technical solutions, the average cooling rate in intensive cooling zones extends throughout the section and amounts to at least 60°C/s in quenching of sheets with the thickness of up to 16 mm, and to a depth of 5-6 mm in quenching of 30 mm thick sheets. Flatness deviation of 8-50 mm thick sheets after quenching is fully compliant with the requirements of normal flatness in accordance with GOST 19903 and EN 10029.

Experimental study of free-convection flame propagation

The results of studying the burnout of diffusion jets flowing into stationary atmosphere in laminar, transitional and turbulent flows with the direction of the initial pulse in the range of angles from 0 to 360 relative to the vertical are presented in the paper. Experimental data on the values of relative curvilinear flame length, its projections on the axes Ox, Oy, the coordinates of the flame stabilization point in the range of Reynolds numbers from =500 to Re=15000 as functions of angle are obtained. The experimental data are presented in the form of characteristic curves and summarized as criteria equations that take into account the effect of free convection in the framework of the theory of jet torch burning on the position of the flame front, the geometry and volume of the combustion zone The results of photographing the process of jet combustion are presented. Recommendations on how to improve the combustion efficiency and the choice of optimal primary, geometrical and thermal parameters of the jet (Re number, Fr number, the relative length of the jet, the initial diameter of the jet, the position of the flame stabilization point, the angle relative to vertical) are given, and the thermophysical characteristics of diffusion reacting gas jet formation with account of free convection are shown.

하이퍼 혼합기를 사용한 저엔탈피 초음속 유동장 내연소 특성 연구

본 연구에서는 마하 2의 실험실 규모의 풍동장치에서 플라즈마 제트 토치를 점화기로 사용하여 강제점화에 대한 연소 특성을 연구하였다. 하이퍼 혼합기는 혼합기로 사용되었다. 수직분사의 경우, 하나는 하이퍼 혼합기의 웨지면에 충돌하도록 하였으며, 다른 하나는 차가운 주유동으로 바로 분사되도록 하였다. 하이퍼 혼합기와 충돌하는 경우 충돌된 연료는 분산되며 확산 혼합에 의해 혼합성능이 증대된다. 또한 혼합된 가스는 대부분 플라즈마 제트의 열원으로 유입되어 연소 성능을 증대시킨다. 하지만 주유동으로 직접 분사되는 경우는 초음속의 주유동 내에서 점화되지 못하고 많은 양의 연료가 소비된다. 따라서 강제점화방식의 연소의 경우에는 많은 양의 연료-공기 혼합물을 점화가 가능한 열원으로 공급하는 것이 중요하다. In this study, a forced ignition method with a plasma jet torch is studied in Mach 2 laboratory scaled wind-tunnel. The hyper-mixer is used as a mixer. For two normal injection cases, the one is collided against a wedge plate of the hyper-mixer and the other is directly injected into the cold main flow. For the first case, the hyper-mixer disperses the injected fuel, leading to the mixing enhancement. Furthermore, the fuel-air mixture is provided into the plasma hot gas, which enhances the combustion performance. However, the direct injection into the main flow method spends amount of fuel without ignition in the cold supersonic flow. In the end, for the forced combustion, it is important to supply the fuel-air mixture into the heat source.

Численное моделирование газодинамики факела ракетных двигателей

Численное моделирование газодинамики факела ракетных двигателей

Microbial Inactivation by Electric Discharge with Metallic Grid

The rapidly developing eld of plasma decontamination and medical applications was previously reviewed many times, e.g. in [1 5]; a paragraph devoted to action to bacteria is involved also in [6]; recently, a book devoted to this topic was also edited [7]. The non-thermal plasma for this purpose was mostly produced in air by dielectric barrier discharges, gliding arc, plasma torches and various corona discharges; we compared microbicidal properties of various corona discharges in [8]. In other papers [9, 10] we reported a new type of jet-like point-to-point DC electric discharge produced in atmospheric air and named cometary. We also described here the ability of cold plasma produced by this discharge to inhibit the growth of Escherichia coli and Staphylococcus epidermidis bacteria on agar plates and on human skin. The cometary discharge is similar to this one produced by devices called plasma jet torch, plasma pencil, or plasma needle, which generate the low-temperature plasma by RF in a stream of carrier gas [11, 12]. In the study [13], the mechanism of decontamination was studied using the grounded mesh electrode inserted between the positive electric discharge and the target sample, here a contaminated agar plate. This electrode (metallic grid) shielded the electric eld and trapped the charged particles, but allowed the neutral particles and UV light to reach the agar surface. The experimental arrangement used in this study is similar, except the use of cometary discharge and the inserting of electrically insulated metallic grid.

Examination of the Degreasing of Metal Surfaces by the Use of a Plasma Torch

AbstractMetal surfaces can be degreased via a combustion reaction upon the metal surface by the use of a plasma torch jet. The required energy and the reaction rate of the combustion reaction are examined here. It turns out that the reaction rate can limit the cleaning performance. In such case, the cleaning performance is not improved at higher powers. It is suggested to increase the temperature at which combustion takes place such that the cleaning performance can improve again at higher powers. (© 2013 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Plasma-assisted ignition for a kerosene fueled scramjet at Mach 1.8

By using a plasma jet (PJ) torch with 1.5 kW input power as an igniter, successful ignition for liquid-kerosene fueled combustion experiment was conducted in a direct-connected supersonic test facility. The incoming flow has total temperature of 950 K and local Mach number of 1.8, corresponding to Mach 4 flight condition. In this study, several optical techniques, including high speed photography, high speed schlieren photography, and planar laser scattering (PLS) technique, were combined to study the ignition process, flame propagation, and mixing features of liquid kerosene fuel with air around the cavity. The effect of fuel injection position, injection pressure, and feedstock gas on ignition performance has been analyzed. The results indicate that local mixing is a critical factor for ignition. It is also shown that the PJ torch with N2+H2 feedstock is superior to the PJ torch with N2 feedstock for the ignition of liquid-kerosene fuel. These results are valuable for the future optimization of kerosene-fueled scramjet engine when using a PJ torch as an igniter.

Combustion enhancement in a supersonic flow by simultaneous operation of DBD and plasma jet

A new strong ignition system combining a plasma jet (PJ) torch and a Dielectric Barrier Discharge (DBD) device in a supersonic flow was developed in this study. The DBD device, which generates nonequilibrium plasma and the PJ torch, which injects equilibrium plasma jet were installed straight on the bottom wall of the combustor. Nonequilibrium plasma was successfully generated in a supersonic flow by DBD. Discharge power of DBD was at most 10W, and it was considerably smaller than that for the PJ. Ignition test of hydrogen fuel perpendicularly injected into a supersonic airflow was conducted under simultaneous operation of the DBD device and the PJ torch. Although ignition never occurred by single operation of the DBD device in a non-heated supersonic flow, combustion enhancement effect by DBD on relatively weak and unstable flame was detected by simultaneous operation of it with the PJ torch. However, the combustion enhancement did not occur in a flow field where strong combustion occurred with only the PJ. The main mechanism of combustion enhancement by the DBD plasma was considered to be existence of O3. The O3 has a much longer lifetime than the other species and it accelerates ignition reaction of a H2/air mixture as almost the same as O radical.

着火促進を目的とした誘電体バリア放電の超音速流における動作特性

The authors developed a method to produce nonequilibrium plasma by dielectric barrier discharge (DBD) in supersonic flow and investigated the possibility for using it as an ignition enhancement technique in a high speed engine, such as a scramjet engine. The discharge characteristics were investigated by varying applied voltage and the flow Mach number. It was revealed from direct photographs that the discharges got stronger and the volume got larger as flow Mach number increased. Estimated discharge power indicated that nonequilibrium plasma could be generated by considerably small energy in comparison with thermal plasma such as a plasma jet torch, which is a typical thermal plasma. The emissions from several excited molecules and atoms were confirmed by spectroscopic measurement of the plasma. Ignition delay analysis revealed that the effect of ozone (O3) addition to shorten the ignition delay time of mixture is almost equal to those of O or H radicals.

Effect of fuel injection location on a plasma jet assisted combustion with a backward-facing step

Non-reacting and reacting experiments on the ignition by a plasma jet (PJ) torch were performed to understand the correlation between fuel injection location and combustion characteristics in unheated Mach 2 airflow. Fuel was injected through three sonic injectors in the recirculation region behind a backward-facing step: a parallel injector at 2 mm from the bottom wall and two normal injectors at 2 and 9 mm from the step wall. In order to mitigate the combustion pressure interaction with nozzle, an isolator was installed between the nozzle and combustor. The combustion performance of normal injection was little affected by the difference of fuel injection locations. Moreover, normally injected fuel was escaped not to be held in the recirculation region despite of low fuel injection rates. This led to lower combustion performance relative to the parallel injection which provided fuel not to leave the recirculation region. In this case, the role of the recirculation region was to fully hold fuel, and the PJ torch provided hot gases as a heat source and acted as a flame-holder to ignite fuel–air mixtures. In a low temperature inflow condition, combustible regions were constrained around the bottom wall where embedded with the PJ torch. When thermal choking occurred in the combustor, it induced shock train both in the combustor and isolator. Under this unstable condition, the combustion performance of the normal injection was lower than that of the parallel injection. This is because the normal injection led most fuel into low temperature incoming air-stream.

Effect of mixing ratio of N 2/O 2 feedstock on ignition by plasma jet torch

The ignition characteristics of N 2/O 2 plasma jet (PJ) in a high-speed flow were experimentally and analytically investigated. The effect of NO x , which was the major component in the N 2/O 2 PJ, on ignition was investigated by analyzing the ignition delay time. Results indicated that NO x had a strong catalytic effect on combustion reactions of H 2 and low-hydrocarbon fuels such as CH 4 and C 2H 4 at high pressure. Therefore, these results suggested that the N 2/O 2 PJ potentially had higher ignition ability than a pure O 2 or a pure N 2 PJ at high pressure. In the ignition test at atmospheric pressure, however, the PJ whose feedstock was composed of a larger mole fraction of O 2 more greatly enhanced ignition, and the O 2 PJ was most effective. A gas sampling showed that amount of the NO x in the N 2/O 2 PJ was much more than those in pure O 2 and N 2 PJs. These experimental results indicate atmospheric pressure was not high for appearance of the NO x catalytic effect. A local O 2 concentration around the ignition site was very important for successful ignition at low pressure, where the NO x catalytic effect was not strong.

Cr3C2-NiCr HVOF-Sprayed Coatings: Microstructure and Properties Versus Powder Characteristics and Process Parameters

Two 75%Cr3C2-25%NiCr feedstock powders with the same size distribution but different production process were characterized and found quite different in terms of morphology and phase composition. The powders were sprayed in a HVOF Diamond Jet (Sulzer Metco DJ-2600) torch with five different values of the oxygen-to-hydrogen ratio in order to assess the influence of this parameter on the microstructure and properties of the coatings. The results show that the closed and dense microstructure of one powder (Woka 7302) results in coatings with lower amount of decarburization, less oxide formation and higher toughness compared to coatings from the other powder (Praxair 1375). It was found that the O2/H2 ratio impacts mainly on the Young’s modulus, which almost doubled by changing the ratio from 0.40 to 0.50, and on toughness, but does not notably affect the Vickers hardness.

Stabilization of non-premixed flames in supersonic reactive flows

A Lagrangian framework is set out to describe turbulent non-premixed combustion in high speed coflowing jet flows. The final aim is to provide a robust computational methodology to simulate, in various conditions, the underexpanded GH2/GO2 torch jet that is used to initiate combustion in an expander cycle engine. The proposed approach relies on an early modelling proposal of Borghi and his coworkers. The model is well suited to describe finite rate chemistry effects and its recent extension to high speed flows allows one to take the influence of viscous dissipation phenomena into account. Indeed, since the chemical source terms are highly temperature sensitive, the influence of viscous phenomena on the thermal runaway is likely to be all the more pronounced since the Mach number values are high. The validation of the extended model has been recently performed through the numerical simulation of two distinct well-documented experimental databases. Only a brief summary of this preliminary validation step is provided here. The main purpose of the present work is to proceed with the numerical simulation of geometries that bring together the essential peculiarities of the underexpanded GH2/GO2 torch. The behavior of the corresponding supersonic coflowing jet flames for various conditions is discussed in the light of computational results. To cite this article: J.-F. Izard, A. Mura, C. R. Mecanique 337 (2009).