Jet Torch Research Articles

Suitability of C2-, C3-Hydrocarbon Fuels for Plasma Ignition in High-Speed Flow

The suitability of hydrocarbon fuels for plasma ignition in high-speed flow was numerically and experimentally investigated. Numerical analysis of ignition delay time showed that the effects of additions of radicals and NO x on ignition delay times of C 3 H 8 and dimethyl ether were very slight in comparison with those for C 2 H 4 . Ignition tests of C 3 H 8 and dimethyl ether fuels by a plasma jet torch in a supersonic flow confirmed such a low sensitivity to additions of radicals and NO x . The amounts of combustion of C 3 H 8 ignited by the plasma jet were smaller than that of C 2 H 4 , though ignition delay times of those fuels without radical addition were almost the same as that of C 2 H 4 . In the case of fuel injection upstream of the plasma jet, the amounts of combustion of C 3 H 8 and dimethyl ether fuels increased with the mole fraction of O 2 in the feedstock gas to the plasma jet torch, the same as with CH 4 and C 2 H 4 . This result indicates that the local O 2 concentration around the igniter is very important for success in attainment of strong combustion and flameholding in a high-speed flow.

Characteristics and Mechanisms of Dynamic Oxidation for ZrB<sub>2</sub>-SiC Based UHTC

The present study focuses on the dynamic oxidation resistance of five representative ZrB2-SiC based ultra-high temperature ceramics (UHTCs): ZrB2-SiC, ZrB2-SiC-Si3N4, ZrB2-SiC-TiB2, ZrB2-SiCHfB2 and ZrB2-SiC-ZrC using oxyacetylene torch and arc jet testing. The effects of second phase incorporation (Si3N4, TiB2, HfB2, ZrC) on oxidation resistance were compared and analyzed. The mechanism of oxidation based on experimental results and thermodynamic calculations were explored. Some approaches to improvement of oxidation resistance and future directions of UHTC are also presented.

A novel design of a plasma jet torch igniter in a scramjet combustor

A plasma jet (PJ) torch igniter with a novel configuration in a scramjet combustor was developed, and ignition tests of the new torch were conducted in supersonic flow. Two PJ torches with different feedstocks were arranged in a straight line in the direction of flow. A H 2/N 2 PJ (H 2 mole fraction was 0.30) was selected for the upstream PJ, and an O 2 PJ was selected for the downstream PJ. This combination (H 2/N 2–O 2 PJs) had many advantages to other combinations and it compared with N 2–N 2 PJs. The experiment was conducted using an intermittent suction-type wind tunnel and a two-dimensional contoured nozzle. The Mach number of the main flow was 2.3. The total temperature and total pressure of the main flow were those of the room condition. Three kinds of fuels (H 2, C 2H 4, and CH 4) at room temperature were tested. The fuel was injected normal to the main stream at the sonic speed from the orifice located upstream of the twin PJs. In experimental results, the twin PJs developed in this paper showed that ignition in supersonic flow was successful for both fuels of H 2 and hydrocarbon, even at the lowest electric power input to the PJs (about 2.5 kW in total for two torches). Moreover, the superiority of the H 2/N 2–O 2 PJs to the N 2–N 2 PJs was shown for all fuels, though basic flow structure formed by injection of twin PJs was same.

The non-explosive removal market in the Gulf of Mexico

Decommissioning offshore oil and gas structures represents the end of the production life cycle when wells are plugged and abandoned, infrastructure is removed, and the site is remediated and cleared of debris. The purpose of this paper is to examine the non-explosive severance techniques commonly employed in decommissioning, and to describe the business, engineering, and market environment of cutting services in the Gulf of Mexico (GOM). The management of decommissioning activities, the bid process, and the severance subcontractor network that operates in the GOM is presented, along with the basic cutting activities performed in decommissioning. The science and technology of mechanical, abrasive water jet, diamond wire, and diver torch methods is reviewed, and the factors that play a role in the decision to use explosive or non-explosive severance methods is described. The general structure of non-explosive service contracts is outlined, and the size of the severance market is estimated.

Three-dimensional flow and heat transfer in thermal plasma systems

Three-dimensional (3-D) modeling of thermal plasma systems is still a challenging problem. Modeling results recently obtained in our group are briefly presented in this paper concerning the 3-D flow and heat transfer characteristics of the thermal plasma reactor, plasma jet and non-transferred arc plasma torch. A well-validated non-commercial computer code is employed in the study. It is shown that when particulate-matter and its carrier-gas are injected into a plasma reactor through a single port at the side-wall of reactor, appreciable 3-D flow and heat transfer effects will appear and cannot be well modeled by any two-dimensional models. The 3-D effects influence the particle motion and heating within the reactor. For a plasma jet with lateral injection of carrier-gas and particles, the 3-D effects are also shown to be non-negligible. Marked 3-D special features of the flow and heat transfer within DC non-transferred arc plasma torches have been demonstrated even for the torch with completely axi-symmetrical geometrical configuration, working gas admission and electrical current connection. The predicted results are well consistent with experimental observation. Further research requirement is also discussed in this paper.

Measurements of C2 and CH concentrations and temperatures in a dc arc jet using cavity ring-down spectroscopy

Cavity ring-down spectroscopy has been used to measure the absorbances, concentrations and temperatures of C2(a3Πu v=0) and CH(X2Π v=0) radicals in a ⩽10 kW dc arc jet used for chemical vapor deposition (CVD) of polycrystalline diamond films and operated with CH4/H2/Ar gas mixtures. Gas temperatures derived from the intensities and widths of rotationally resolved C2 d3Πg−a3Πu spectral lines are 3300±200 K in the free plume, rising to ∼4800 K close to the substrate on which the diamond film is grown. For an input power of ∼6 kW, a 3.3% CH4/H2 ratio with excess Ar and a pressure of 50 Torr, the conditions typically employed for diamond film CVD, concentrations of C2(a) are between 6.0±0.2×1012 and 1.5±0.2×1013 cm−3 in the free plume at distances >5 mm from the substrate. These values are derived assuming a 1 cm column length as implied by spatially resolved studies of C2(d−a) optical emission; the spread reflects the decline in performance of the arc jet torch heads over time. The concentration of CH(X) in the free plume is 7.0±1.3×1012 cm−3 under similar operating conditions. Within 5 mm of the substrate, the measured absorption by both radicals rises steeply. The concentrations of C2(a) and CH(X) increase with added CH4 at fixed powers of 5.5 and 5.8 kW, but for mixing ratios in excess of 5% CH4/H2, the concentrations of both radicals become invariant. Measured C2(a) absorbance also increases with power input to the arc jet, but the CH absorbance is independent of this operating parameter.

Analysis of a high-velocity oxygen-fuel (HVOF) thermal spray torch part 1: Numerical formulation

The fluid and particle dynamics of a high-velocity oxygen-fuel torch are analyzed using computational fluid dynamic techniques. The thermal spray device analyzed is similar to a Metco Diamond Jet torch with powder feed. The injection nozzle is axisymmetric with powder and a carrier gas injected on the centerline, premixed fuel and oxygen fed from an annulus, and air cooling injected from an annulus along the interior surface of the aircap. The aircap is a conically converging nozzle that achieves choked flow conditions at the exit; a supersonic, underexpanded jet develops externally. A two-dimensional, axisymmetric geometry is assumed; the equations for mass, momentum, and energy conservation are solved for both the gas and the particle phases. The combustion process is modeled using approximate equilibrium chemistry with dissociation of the gas with a total of nine species. Turbulent flow is modeled by a two-equation model for turbulent kinetic energy and dissipation rate that includes compressibility effects on turbulent dissipation. Particles are modeled as a lumped-heat-capacity system and are considered to melt upon attaining the required latent heat of fusion. An iterative, implicit, finite-volume numerical method is used to solve the coupled gas and particle equations inside and outside the torch. A companion paper presents the results of the numerical simulation and discusses in detail the gas and particle dynamics.

Analysis of a high-velocity oxygen-fuel (HVOF) thermal spray torch part 2: Computational results

The fluid and particle dynamics of a high-velocity oxygen-fuel (HVOF) torch are analyzed using computational fluid dynamic (CFD) techniques. The thermal spray device analyzed is similar to a Metco Diamond Jet torch with powder injection. The details of the CFD simulation are given in a companion paper. This paper describes the general gas dynamic features of HVOF spraying and then discusses in detail the computational predictions of the present analysis. The gas velocity, temperature, pressure, and Mach number distributions are presented for various locations inside and outside the torch. The two-dimensional numerical simulations show large variations in gas velocity and temperature both inside and outside the torch due to flow features such as mixing layers, shock waves, and expansion waves. Characteristics of the metal spray particle velocity, temperature, trajectory, and phase state (solid or liquid) are also presented and discussed. Particle velocities and temperatures are shown to be lower for this type of torch than previously believed.

画像処理法を用いた火花点火機関における火炎伝播の解析

To obtain a better understanding of the combustion process in a spark ignition engine with or without an unscavenged horizontal prechamber, the flame propagations in both the pre-and main chambers are simultaneously visualized with a high speed camera. By using a CCD video camera and a A/D converter, the flame photographs are converted into digital data and are image-processed with a personal computer to make more clear the flame front and to clarify its brightness level in the burnt gas region.Consequently, the images of flame front for each crank angle enhanced by thresholding and edge-detecting techniques are used to make flame propagation maps, which are able to examine in detail the effect of torch jet on the combustion process. In addition, the brightness distributions of burnt gas obtained from the flame image data in the main combustion chamber show a resonable agreement with the gas temperature diagrams measured by an infrared pyrometer.

Flow characteristics of a motored spark ignition engine with a prechamber.

To understand the effect of a torch jet on the flow characteristics in a prechamber spark ignition engine, a laser Doppler anemometer (LDA) is used to measure the velocity in a main chamber under the motored condition. The engine is operated at a constant speed of 1000 rpm with a wide open throttle (WOT). The mean velocity, turbulence intensity and turbulence scales are calculated by a cycle-resolved analysis with a cut-off frequency of 650 Hz. The reasonable selection of the cut-off frequency is based on the ensemble-averaged power spectra. During the expansion stroke, the mean velocity, turbulence intensity and integral length scale are found to be strongly affected by the torch jet flow, which is dominated by the torch nozzle area size.

Numerical simulation of a two-dimensional flow field in a motored engine with a prechamber using a k-.EPSILON. turbulence model.

To understand flow behavior during the compression and expansion strokes in a reciprocating engine with a horizontal prechamber, spatial and temporal distributions of flow velocity, turbulence intensity, turbulence kinetic energy and its dissipation rate in both the pre- and main chambers are calculated numerically using a two-dimensional flow model and k-e turbulence model. As a consequence, the velocity vectors, the contour maps of turbulence kinetic energy and its dissipation rate are found to be influenced considerably by the torch jet flow or torch nozzle size. Further, the spatial and temporal distributions of velocity and turbulence in the main chamber are in reasonable agreement with the ones measured using a LDA, only within small crank angle range near the top dead center (TDC) able to be maintained two-dimensionality in the flow field.

Basic Characteristics of Gas Tunnel Type Plasma Jet Torch

The basic characteristics of a gas-tunnel type plasma-jet torch has been experimentally investigated. The pressure along the central axis of the gas tunnel could be reduced to a very low value. The plasma jet produced in this low-pressure gas tunnel was longer than a conventionally produced jet, and had a positive volt-ampere characteristic. The potential gradient reached more than 40 V/cm and the energy density was estimated to be more than 106 W/cm2.

Ignition and burning process in a divided chamber bomb

Ignition and burning mechanisms of the main chamber mixture by a torch jet were experimentally investigated using a divided chamber bomb. The effects of the nozzle diameter and volume ratio on the structure of the torch jet, ignition process, and subsequent burning process in the main chamber were minutely examined, in both uniform and stratified charges, by measurements of ion current, light emission, OH-emission (306.4 nm), initial torch jet velocity, and main chamber pressure histories and by schlieren photography. The structure of the torch jet was greatly influenced by the nozzle diameter and volume ratio independently of the main chamber mixture ratio. According to the physical and chemical characteristics obtained for it, the structure of the torch jet could be classified into four types, and the ignition and burning processes in the main chamber could also be classified into four patterns depending on the torch jet structure: pattern I, chemical chain ignition and well-dispersed burning; pattern II, composite ignition and well-dispersed burning followed by wrinkled laminar burning; pattern III, flame kernel torch ignition and wrinkled laminar burning; and pattern IV, flame front torch ignition and wrinkled laminar burning. Combustion characteristics such as main chamber pressure and net burning time in the main chamber also showed their own peculiar features. Examination of the lean flammability limit gave a possibility of lean burning outside of the normal flammability limit by using divided chamber systems. From these results combustion pattern II was found to be most favorable for lean burning.

副室付エンジンにおけるトーチ噴流の可視化

To understand the striking difference in heat release rate between the vertical and horizontal torch nozzle in a prechamber spark ignition engine, the torch flow patterns remained on the piston and both the valves heads are visualized by the oil-film technique, changing the number, sectional area and direction of torch nozzle, respectively.As a result, the jet velocity of torch nozzle is confirmed to decrease proportionally as the nozzle increases in diameter or number. Furthermore, it is revealed that combustion in the main chamber with vertical torch nozzle is accelerated by strong turbulence due to the torch jet impingement, and then it shows not only a sharp peak in heat release rate, but also earlier completion in combustion than that of horizontal torch nozzle.

Design and economic constraints of thermal rock weakening techniques

Analytical predictions of the rock weakening by thermal sources are used to compare the relative cost of enhancing rock excavation by lasers, electron beams, microwaves, radiant heaters and torches. These estimates indicate that the expense of microwaves is prohibitive while radiant heaters are the least expensive at $0·14/ft 3. Jet torches are also desirable at an energy cost of $0·18/ft 3. Design limitations for the various methods are noted and equipment costs range from $50,000 for electron beams to $300 for flame torches. When energy costs, equipment costs and design limitations are all considered the jet torch seems the most promising using commercially available equipment. Considerable design effort when applied to radiant heaters could produce an even more efficient system for weakening hard rock.

低圧気中におけるプラズマジェットの磁場中の諸特性(第1報)

In the welding technology, it may be interesting to examine the magnetic control of a plasma jet flame. In this report is described the experimental result on the fundamental properties of plasma jet flame in a magnetic field.The distribution of field strength in the cusp type or mirror type magnetic field, each of them were made by two coils Ml and M2, was measured as a preliminary research. The plasma jet was injected to the low pressure vessel along the axis of magnetic field, as shown in Fig. 1.Photographic observations show that the plasma jet flame flows in the direction of magnetic line of force. Radial distribution of total pressure of the plasma jet flame was measured with use of a pitot tube on the mid-plane between coil Mt and coil M2. In general, the total pressure of plasma jet in the mirror type magnetic field was higher than that in cusp type field. Higher values were observed at relatively constricted region near the central axis of plasma jet.Total pressure rises as the are current incrases, but is almost invariant with the arc voltage in this experiment.The thermal efficiency of the plasma jet torch was also investigated. The amount of energy contained in plasma flame is expressed as ηVI, η being thermal efficiency of torch.It has been found that the total pressure varies with the amount of plasma energy ηVI.

100,000-kw. Turbine generator, largest of its type in the world

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.