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This is now the 16th publication of the series of special issues on plasma-assisted technologies. Once more, in this newest installment, the reader will encounter an expansive array of novel and innovative applications and developments in plasma-based systems. The varied range of topics is a tribute to the continued forward progression of the possibilities accessible through plasmas, and builds on the significant success of the previous special issues. [ABSTRACT FROM AUTHOR]

The authors report the results of design and experimental investigation of a high flow and high concentration NOx production system based on a radio frequency (RF) plasma torch for a variety of applications. Unique gas dynamics of the first stage avoids plasma disturbance by feeding quenching gas and enables NO oxidation into NO2 with a total NOx yield over 6% by mass. The developed system is tunable for NOx concentration, scalable for higher flow, applicable for various technological processes, flexible for using different plasma gases and quenching media, including gases, liquids, and solids. [ABSTRACT FROM AUTHOR]

This article reports results of the design and experimental investigation of a high-flow and high-concentration NOx production system based on a radio-frequency plasma torch for a variety of applications. The system includes a commercial APT-100 plasma torch with plume power from 25 to 35 kW, a double-stage quenching reactor with “fast” first stage and “slow” second stage, measuring unit, and auxiliary systems. The first stage allows quenching by any gas, such as air, air-based blends, and the products of recirculation. [ABSTRACT FROM AUTHOR]

This article reports results of modeling, design, and experimental investigation of a heat exchanger to be used downstream of a radio frequency plasma torch for a variety of applications. A heat exchanger is designed for a plasma generator with thermal power of 30 kW and a maximum air plasma temperature of about 6000 K. The design can also be scaled to accommodate higher power plasma generators. The proposed engineering approach is double stage quenching of intermediate and unstable products from plasma chemical reactions. The design can be used in various technological processes, particularly for fixing atmospheric nitrogen and obtaining nitrogen oxides. [ABSTRACT FROM AUTHOR]

This article presents the results of numerical CFD simulation of carbon black (CB) plasma synthesis from wood sawdust. The data on the content of sawdust pyrolysis products at different nitrogen plasma temperatures, different particle size distributions, and changes in the carbon-containing raw material consumption are presented. The obtained results could be used for the engineering of plasma systems for CB production from wood sawdust. [ABSTRACT FROM AUTHOR]

This article presents a new approach and preliminary modeling results of the temperature field nonuniformity reduction by using a multitorch radio frequency (RF) plasma system. This is also a way to achieve technical and economic feasibility for plasma systems with plume power over 200 kW, significantly reducing the development and production cycle. The mixing of plasma jets was numerically simulated by solving a system of equations, describing high-temperature turbulent plasma flows. The data obtained could be used for engineering of high-power plasma systems, including the ones for testing high-temperature thermal protection materials, waste to power, syntheses of new materials, and so on. [ABSTRACT FROM AUTHOR]

This paper presents the results of investigation of the possibilities to produce high volume and concentration of nitrogen oxides in inductively coupled plasma/radio frequency plasma for industrial applications. Calculations of the equilibrium composition of air and air–oxygen plasma at different temperatures and pressures have been conducted. The data obtained can be used to design and develop efficient systems for the nitrogen oxides synthesis. [ABSTRACT FROM AUTHOR]

This paper presents the results of preliminary modeling of the boron particles behavior in a mixing chamber downstream, the inductively coupled plasma or radio frequency (RF) torch, for boron nitride nanotubes (BNNTs) production. The 3-D computational fluid dynamics calculations of heating of boron particles by nitrogen plasma with plume power 15 and 30 kW in the mixing chamber with one and four feeding ports have been performed. The obtained results can be used for further design and optimization of the RF system for BNNTs production and new materials synthesis. [ABSTRACT FROM AUTHOR]

This paper presents the results of development and optimization of an industrial combined-cycle gas turbine system for plasma disposal of sewage sludge. The enhanced system flow diagram, critical elements selection, and heat and mass balance optimization provide a solid basis for prototyping a plant for the disposal of sewage sludge with up to 75% water content. [ABSTRACT FROM AUTHOR]

This paper presents the results of development and optimization of an industrial scale plant for the integrated plasma treatment of sewage sludge. The enhanced plant flow diagram, critical elements selection, and heat and mass balance optimization provide a solid basis for prototyping a plant for the treatment of digested sewage sludge with up to 75% water content. [ABSTRACT FROM AUTHOR]

This paper presents some preliminary estimates of the potential performance of a multipropellant RF plasma thruster and its format should be considered as a technical note. Interpolations of experimental results from similar devices found in the literature suggest that the first stage of such a thruster, based on well-established RF plasma torch technology, is essentially an electrothermal device. The specific impulse, in particular, is shown to be proportional to the square root of the specific power (power per unit mass flow rate). [ABSTRACT FROM AUTHOR]

This paper presents the results of theoretical investigations of a developed gas turbine integrated complex for production of a synthetic hydrocarbon liquid. This includes a natural gas plasma reforming system, a high-efficient heat recovery system, a power generation unit based on a gas turbine, and the Fischer–Tropsch reactor. Investigations of the complex efficiency are carried out, and critical parameters of the process are defined. [ABSTRACT FROM AUTHOR]

This paper presents the results of theoretical and experimental investigations of a developed synthesis gas afterburner based on an injector type plasma-assisted combustion system. The basic overall dimensions of the afterburner with the injecting device are determined. The design concept can provide higher performance, wider turndown ratios, more efficient synthesis gas combustion, and satisfaction of major ecological requirements. [ABSTRACT FROM AUTHOR]

Computer modeling has been used to provide more detailed information about the alternative catalyst-free methane-oxygen reformer for a small scale gas-to-liquid module. The basic input data include 3-MPa process pressure, oxygen as oxidizer, and oxidizer/fuel equivalence ratio about 3 to provide H2 to CO ratio $\ge 1.7$ needed for further direct liquefaction via Fisher-Tropsch processing. As a result, a reasonable temperature level of the reformer walls has been achieved that makes possible its engineering as the next step. [ABSTRACT FROM AUTHOR]

This paper presents the results of modeled investigations of a developed sewage sludge (biosolids) plasma treatment complex. This includes a multistage plasma sewage gasifier, high-efficient heat recovery system, and power generation unit based on a gas engine. Investigations of the treatment complex efficiency are carried out, critical parameters of the process, including specific power consumptions for the own needs, are defined for operation on sewage sludge with 24.6% humidity. Obtained results are planned to be used for the plasma gasifier geometry optimization and further system prototyping. [ABSTRACT FROM PUBLISHER]

Development and modeling have been performed for different schemes for a plasma-assisted, catalyst-free process for natural gas conversion into synthesis gas, at pressures up to 3 MPa. Two oxidizers, oxygen with different purity and oxygen-steam blends, have been used to obtain a H2-to-CO ratio over 1.8. This ratio qualifies the synthesis gas as an appropriate feedstock for further direct liquefaction via Fisher-Tropsch processing. The results obtained can be used for development of the catalyst-free natural gas reformers for small scale, gas-to-liquid technologies. [ABSTRACT FROM PUBLISHER]

This paper presents the results of modeled investigations of a developed flow diagram for a small scale (3–4 MW) combined cycle power plant with integrated plasma coal gasification. This includes a highly efficient heat recovery module, a multistaged plasma gasifier, and a gas turbine engine. Total efficiency of the coal conversion into electric power using direct-flow gasification and plasma process initiation could be in the range of 25%–36%, and is primarily dependent on gas turbine performance and the gasification method selected. [ABSTRACT FROM PUBLISHER]

This paper deals with the experiments on methane oxidation in a torch flame that is sustained in a combustion chamber by a low-current nonsteady-state plasmatron. The regimes of operation for such a system in a wide range of air–methane mixtures are analyzed. With the results of experiments, a torch flame generator with a heat power density per unit area at the exit of combustion chamber of about 1 kW/cm^2 is developed. The generator represents an independent unit that can be used in different applications. As an example of application, a usage of the generator in an installation for incineration of oil slimes is described. The flame with a total heat power at a level of 10 kW is directed to a furnace where it assists the burning process of an atomized water–slime composition. Typical content of water in the composition is from 40% to 50% and total expenditure of the composition in continuous mode of operation is from 400 to 600 L/h. The productivity of the installation with respect to slime incineration amounts to 0.25 m^3/h. [ABSTRACT FROM PUBLISHER]

This paper describes the plasma-assisted combustion system intended to generate a torch flame with a high power density per unit area. In the system, a kind of hybrid concept is proposed. A primary unit for combustion sustaining is a low-current nonsteady-state plasmatron with a low level of electric power. The plasmatron activates an air/hydrocarbon mixture and sustains the oxidation processes in the plasma torch. In turn, the heat power of the torch sustains the main burning process in the torch flame. The results of experiments on propane oxidation in the plasma torch of plasmatron in a wide range of equivalence ratio are presented. As applied to the combustion system design, the plasma torch can provide both the complete and the partial propane oxidation with syngas generation. [ABSTRACT FROM PUBLISHER]

The nine papers in this special issue focus on plasma assisted combustion. [ABSTRACT FROM AUTHOR]

Theoretical investigations of the working processes in a plasma coal pilot gasification system have been conducted. The obtained results and recommendations can be used for modeling the operational modes of plasma gasification system, as well as geometry optimization, and the engineering design of prospective power generation units. [ABSTRACT FROM AUTHOR]

This paper presents the results of development and experimental investigations of a plasma fuel nozzle (PFN) concept as the most prospective tool to realize plasma-assisted combustion in different heat engines. The results of plasma source selection and optimization, fuel atomizer options consideration and comparison, and influence on the combustion process parameters are reported. Experiments show that PFN is the most advanced solution for lean burn and low-Btu fuel combustors, STIG cycle turbines, flexi-fuel systems, and liquid and gaseous feedstock gasification units. [ABSTRACT FROM AUTHOR]

Theoretical and experimental investigations of the working processes in a plasma-assisted combustion and reformation system have been conducted. The selected concept can provide higher performance, wider turndown ratios, more efficient propellant utilization, demonstration of potential fuel flexibility, and satisfaction of major gravimetric and volumetric density requirements. Obtained results and recommendations can be used for hybrid-type plasma-assisted system operation modes, including modeling, geometry optimization, prospective propulsion, and power-generation unit designs and engineering. [ABSTRACT FROM AUTHOR]

Combustion dynamics are investigated for plasma-enhanced methane–air flames in premixed and nonpremixed configurations using a transient arc dc plasmatron. Planar laser-induced fluorescence images of hydroxyl (OH) and carbon monoxide (CO) radicals are obtained over a range of equivalence ratios ( \phi = 0.7 - 1.3), flow rates (6–18 LPM), and plasma powers (100–900 mA) to monitor radical propagation and in situ fuel reforming. The flow rates presented here are outside the range of normal flame stability. In the nonpremixed mode, the fuel is injected separately as a coflow around the plasma discharge, resulting in a unique two-cone flame front geometry, and the flame stability is mainly dependent on the flow dynamics. For premixed flames, partial oxidation occurs inside the chamber, resulting in higher energy conversion efficiencies, and stability is shown to be sensitive to the combustion chemistry. Both configurations are significantly influenced by in situ fuel reforming at higher plasma powers. [ABSTRACT FROM AUTHOR]

This paper presents quantitative planar laser- induced fluorescence (PLIF) imaging of nitric oxide (NO) in a transient-arc direct-current plasmatron igniter using premixed air/fuel mixtures. Quantitative measurements of NO are reported as a function of gas flow rate (20-50 standard cubic feet per hour), plasma power (100-900 mA, 150-750 W), and equivalence ratio (0.7-1.3). Images were corrected for temperature effects by using 2-D temperature field measurements obtained with infrared thermometry and calibrated by a more accurate multiline fitting technique. The signals were then quantified using an NO addition method and spectroscopic laser-induced fluorescence modeling of NO. NO PLIF images and single-point NO concentrations are presented for both plasma-discharge-only and methane/air plasma-enhanced combustion cases. NO formation occurs predominantly through N2(υ) + O → NO + N for the plasma-discharge-only case without combustion. The NO concentration for the plasma-enhanced combustion case (500-3500 ppm) was an order of magnitude less than the plasma-discharge-only case (8000-15 000 ppm) due to the reduction of plasma reactions by the methane. Experiments show the linear decay of NO from equivalence ratio 0.8-1.2 under the same flow condition and discharge current. [ABSTRACT FROM AUTHOR]

This paper describes the experiments with the plasma-assisted combustion system as applied to gaseous hydrocarbons. The system is based on a nonsteady-state gas-discharge plasmatron with a low average current. One of the subjects of the investigations is to elucidate a correlation between the discharge burning regimes in the plasmatron and the properties of the torch flame in the combustion chamber. Depending on the gas-discharge regimes and plasmatron design, the conditions of complete hydrocarbon combustion and partial oxidation have been demonstrated. Aside from that, the data on testing a special power supply intentionally developed for nonsteady discharge powering are presented. [ABSTRACT FROM AUTHOR]

In this paper, we report on the experimental investigations of two innovative technologies combined in one device, namely, the application of an initiated streamer microwave (MW) discharge for ignition and flame control in a reverse-vortex combustion chamber, also known as a Tornado combustor. The pulsed subcritical streamer MW discharge (SSD) in a quasi-optical wave beam was experimentally investigated in the atmospheric-pressure model of a Tornado combustor with transparent dielectric walls. The possibility of a surface MW streamer discharge formation at new conditions, particularly on the dielectric walls of the cylindrical combustion chamber, has been confirmed. The mechanism of SSD realization, at which the discharge development takes place in a volume of the combustion chamber, has been proposed. It was shown that SSD could be applied for ignition of fuel/air mixtures in an axial area of the reverse-vortex combustion-chamber bottom plate, which is normally used for a fuel feeding. [ABSTRACT FROM AUTHOR]

This paper presents thermodynamic and kinetic modeling of plasma-aided bituminous coal gasification. Distributions of concentrations, temperatures, and velocities of the gasification products along the gasifier are calculated. Carbon gasification degree, specific power consumptions, and heat engineering characteristics of synthesis gas at the outlet of the gasifier are determined at plasma air/steam and oxygen/steam gasification of Powder River Basin bituminous coal. Numerical simulation showed that the plasma oxygen/steam gasification of coal is a more preferable process in comparison with the plasma air/steam coal gasification. On the numerical experiments, a plasma vortex fuel reformer is designed. [ABSTRACT FROM AUTHOR]

This paper deals with the investigation of nonsteady- state discharge regimes in the plasmatron as applied to air-hydrocarbon mixtures. The electrode system is based on the design of a classical high-current arc plasmatron. Compared with a thermal plasmatron mode, the averaged discharge current in the described device has been decreased to about 0.2 A. Then, the discharge regime can be interpreted as a kind of glow discharge with the random transitions from glow to sparks. Two types of transitions have been observed: completed and noncompleted transitions. Completed transition is accompanied by the appearance of a high-conductivity spark channel, and for noncompleted transition, a low-conductivity diffuse channel arises. The discharge features have been investigated for plasmatrons with a long-length and with a short-length anode nozzle. The principal features of the nonsteady-state discharge behavior are the same for both designs. However, for the long nozzle, the discharge phenomena mainly proceed inside the anode cavity and for the short nozzle outside the cavity. Use of different designs of the plasmatron anode cavity offers to extend an area of plasmatron applications. [ABSTRACT FROM AUTHOR]

This is the tenth issue in a series of special issues on plasma-assisted technologies (PATs). Contributions from a growing field with many new multidisciplinary plasma applications have resulted in the largest issue to date. This follows on the success of the nine previous issues, dating back to the original IEEE-TPS Special Issue on Plasma-Assisted Combustion published in December 2006. [ABSTRACT FROM AUTHOR]

Oxidant selection is the highest priority for advanced coal gasification-process development. This paper presents comparative analysis of the Powder River Basin bituminous-coal gasification processes for entrained-flow plasma gasifier. Several oxidants, which might be employed for perspective commercial applications, have been chosen, including air, steam/carbon-dioxide blend, carbon dioxide, steam, steam/air, steam/oxygen, and oxygen. Synthesis gas composition, carbon gasification degree, specific power consumptions, and power efficiency for these processes were determined. The influence of the selected oxidant composition on the gasification-process main characteristics have been investigated. [ABSTRACT FROM AUTHOR]

The major advantages of a new plasma-assisted fuel reformation system are its cost effectiveness and technical efficiency. Applied Plasma Technologies has proposed its new highly efficient hybrid-type plasma-assisted system for organic fuel combustion and gasification. The system operates as a multimode multipurpose reactor in a wide range of plasma feedstock gases and turndown ratios. This system also has convenient and simultaneous feeding of several reagents in the reaction zone such as liquid fuels, coal, steam, and air. A special methodology has been developed for such a system in terms of heat balance evaluation and optimization. This methodology considers all existing and possible energy streams, which could influence the system's efficiency. The developed hybrid-type plasma system could be suitable for combustion applications, mobile and autonomous small- to mid-size liquid fuel and coal gasification modules, hydrogen-rich gas generators, waste-processing facilities, and plasma chemical reactors. [ABSTRACT FROM AUTHOR]

The mathematical model of a direct-current arc at atmospheric pressure and low currents has been proposed. This paper presents the results of 2-D simulations for an air arc within the plasmatron channel, as well as the anode, composite cathode, and external regions. The model does not employ any adjustable parameter and therefore enables direct comparison with the experiments. The model predictions were compared with the experimental data of a plasma igniter and indicated good agreement. [ABSTRACT FROM AUTHOR]

The major advantages of plasma treatment systems are cost effectiveness and technical efficiency. A new efficient electrodeless 1-MW hybrid plasma torch for waste disposal and coal gasification is proposed. This product merges several solutions such as the known inductive-type plasma torch, innovative reverse-vortex (RV) reactor and the recently developed nonequilibrium plasma pilot and plasma chemical reactor. With the use of the computational-fluid-dynamics-computational method, preliminary 3-D calculations of heat exchange in a 1-MW plasma generator operating with direct vortex and RV have been conducted at the air flow rate of 100 g/s. For the investigated mode and designed parameters, reduction of the total wall heat transfer for the reverse scheme is about 65 kW, which corresponds to an increase of the plasma generator efficiency by approximately 6.5%. This new hybrid plasma torch operates as a multimode, high power plasma system with a wide range of plasma feedstock gases and turn down ratio, and offers convenient and simultaneous feeding of several additional reagents into the discharge zone. [ABSTRACT FROM AUTHOR]

This paper deals with the investigation of a new regime in a plasma ignition and flame control system as applied to air-hydrocarbon mixtures. The system is based on the design of a classical high-current arc plasmatron. Compared .with a thermal plasmatron mode, the average discharge current in the described device has been decreased to about 0.1 A. Although average power dissipated in the discharge does not exceed 200 W and average gas temperature at the plasmatron exit for typical regimes of the discharge operation in air is less than 500 K, the device demonstrates reliable ignition and flame stabilization in a wide range of equivalence ratios. Physical mechanism of ignition is associated with the nonsteady-state properties of discharge. At a low current level, the discharge burns in a kind of glow mode, and because of the glow-to-spark transitions, the high-current nanosecond pulses are superimposed on the glow plasma background. Then, the spark discharge initiates the combustion process, which is efficiently sustained in the glow plasma. [ABSTRACT FROM AUTHOR]

This paper deals with investigations of gas discharge in a recently developed plasma pilot for ignition and flame control. The characteristic features of this discharge burning mode are extremely low current (about 0.1 A) and low average power (less than 100 W). However, ignition and flame stabilization in a wide range of equivalence ratios for air-hydrocarbon mixtures are demonstrated. The physical mechanism of ignition is associated with the nonsteady-state properties of discharge. At the low cur- rent level, discharge burns in a kind of glow mode, and because of the glow-to-spark transition, the high-current nanosecond pulses are superimposed on the glow plasma background. Then spark discharge initiates combustion process, which is efficiently sustained in the glow plasma. [ABSTRACT FROM AUTHOR]

This is the ninth issue in a series of special issues on plasma-assisted combustion (PAC), following the success of the first IEEE-TPS Special Issue on PAC (December 2006). [ABSTRACT FROM PUBLISHER]

An overview of the papers from the 8th International Conference on Plasma Assisted Technologies (ICPAT-8) that were published within the issue is presented, which include Integrated Plasma Gasification Combined Cycle Power Plant, materials-processing and plasma ignition systems for internal combustion engines.

The article the topics published within the issue including the application of plasmas to ignite processes, use of plasmas for fuel conversion or reformation and global climate change issues.

The article discusses various reports published within the issue, including one on the study of hydrocarbon decomposition through atmospheric-pressure plasma and another on the study of the hydrogasification of carbon using microwave plasma.

The article discusses contents of the current issue, with focus on plasma-assisted combustion (PAC). The aim of the issue is to offer an integrated forum on reporting research in the field. Of particular interest for this issue is the exposition of nonequilibrium plasma applications to combustion, particularly for improving combustion stability, efficiency, and reducing undesirable emissions.