Axial Injection Research Articles

Contribution of optical emission spectroscopy measurements to the understanding of TiO2 growth by chemical vapor deposition using an atmospheric-pressure plasma torch

The plasma jet of an atmospheric-pressure chemical vapor deposition system, namely, the axial injection torch, was diagnosed by optical emission spectroscopy (OES) in the conditions corresponding to titanium oxide deposition. Titanium tetraisopropoxide (TTIP) was used as the Ti organometallic precursor. The determination of the spatially-resolved excitation temperatures in the discharge allowed the determination of relative concentrations of atomic emitting species. The entrainment of air was estimated by measuring the relative quantity of N and O atoms in the discharge. The decomposition of TTIP was estimated by measuring the relative concentration of atomic Ti. It was shown that the air is rapidly introduced and distributed in the discharge while TTIP is progressively decomposed. Space-resolved OES measurements allowed to highlight titanium-depletion regions in the discharge. In light of previous results, it was suggested that these Ti-depletion regions reflect TiO2 gas phase nucleation processes. They are thus expected to affect the deposition growth mechanisms: Ti-rich regions would contribute to surface deposition (heterogeneous phase reactions) whereas Ti-depletion regions would contribute to the TiO2 particles deposition (homogeneous phase reactions).

Scaling Parameters of Swirling Oxidizer Injection in Hybrid Rocket Motors

Hybrid rockets present some disadvantages, mainly low regression rate and combustion inefficiencies. A promising technology to solve both is swirling oxidizer injection, which enhances the wall heat flux and the mixing of the combustion reactants and thus increases the regression rate and the combustion efficiency. A numerical investigation is carried out with a commercial computational fluid dynamics code. This type of analysis can really help with the comprehension of the physical phenomena hidden behind the experimental measurement, and so it can be a powerful aid in the preliminary development and testing of hybrid motors. The first step of this numerical investigation is to study the initial motor geometry, increasing the complexity of the system with the addition of each component one by one to better understand which parameters influence the swirling flowfield inside the combustion chamber. Afterward, a comparison between the axial and swirl injection is done, analyzing the qualitative differences in the flowfields and the quantitative ones in the performance. The central and most important part of this numerical study is focused on the inspection of the motor performance related to several scaling parameters.

Recent developments in plasma spray processes for applications in energy technology

This work focuses on recent developments of plasma spray processes with respect to specific demands in energy technology. High Velocity Atmospheric Plasma Spraying (HV-APS) is a novel variant of plasma spraying devoted to materials which are prone to oxidation or decomposition. It is shown how this process can be used for metallic bondcoats in thermal barrier coating systems. Furthermore, Suspension Plasma Spraying (SPS) is a new method to process submicron-sized feedstock powders which are not sufficiently flowable to feed them in dry state. SPS is presently promoted by the development of novel torch concepts with axial feedstock injection. An example for a columnar structured double layer thermal barrier coating is given. Finally, Plasma Spray-Physical Vapor Deposition (PS-PVD) is a novel technology operating in controlled atmosphere at low pressure and high plasma power. At such condition, vaporization even of high-melting oxide ceramics is possible enabling the formation of columnar structured, strain tolerant coatings with low thermal conductivity. Applying different conditions, the deposition is still dominated by liquid splats. Such process is termed Low Pressure Plasma Spraying-Thin Film (LPPS-TF). Two examples of applications are gas-tight and highly ionic and electronic conductive electrolyte and membrane layers which were deposited on porous metallic substrates.

Axial suspension plasma spraying of Al2O3 coatings for superior tribological properties

Suspension plasma spray is a relatively new thermal spray technique which enables feeding of fine powder to produce advanced coatings for varied applications. This work investigates the difference in structure and performance of Al2O3 coatings manufactured using conventional micron-sized powder feedstock and a suspension of sub-micron to few micron sized powder. Axial injection was implemented for deposition in both cases. The effect of feedstock size and processing on the tribological performance of the two coatings was of specific interest. The coatings were characterized by Optical and Scanning Electron Microscopy, micro-hardness and scratch resistance testing, and their dry sliding wear performance evaluated. The suspension sprayed coatings yielded significantly higher scratch resistance, lower friction coefficient and reduced wear rate compared to conventional coatings. The improved tribological behaviour of the former is attributable to finer porosity, smaller splat sizes, and improved interlamellar bonding.

Experimental Study of the Swirling Oxidizer Flow in HTPB/N2O Hybrid Rocket Motor

Effects of swirling oxidizer flow on the performance of a HTPB/N2O Hybrid rocket motor were studied. A hybrid propulsion laboratory has been developed, to characterize internal ballistics characteristics of swirl flow hybrid motors and to define the operating parameters, like fuel regression rate, specific impulse, and characteristics velocity and combustion efficiency. Primitive variables, like pressure, thrust, temperature, and the oxidizer mass flow rate, were logged. A modular motor with 70 mm outer diameter and variable chamber length is designed for experimental analysis. The injector module has four tangential injectors and one axial injector. Liquid nitrous oxide (N2O) as an oxidizer is injected at the head of combustion chamber into the motor. The feed system uses pressurized air as the pressurant. Two sets of tests have been performed. Some tests with axial and tangential oxidizer injection and a test with axial oxidizer injection were done. The test results show that the fuel grain regression rate has been improved by applying tangential oxidizer injection at the head of the motor. Besides, it was seen that combustion efficiency of motors with the swirl flow was about 10 percent more than motors with axial flow.

Numerical Simulation of Suspension Plasma Spraying with Axial Injection

Numerical Simulation of Suspension Plasma Spraying with Axial Injection

3D simulation of the ion-beam transport in bending magnets and electrostatic deflectors

The equations and algorithms for calculating the charged-particle-beam dynamics in bending magnets and electrostatic deflectors, which are used in the ion-beam transport lines and spectrometers, are presented. Calculations of the electromagnetic field 3D maps are illustrated. The value of the electromagnetic-field nonlinearities and their effect on the particle dynamics are analyzed. The simulation of the ion dynamics in the axial injection beam line of the DC-280 cyclotron and GALS spectrometer created at the JINR Laboratory of Nuclear Reactions (FLNR) is described.

Emissions of a Wet Premixed Flame of Natural Gas and a Mixture With Hydrogen at High Pressure

It is generally accepted that combustion of hydrogen and natural gas mixtures will become more prevalent in the near future, to allow for a further penetration of renewables in the European power generation system. The current work aims at the demonstration of the advantages of steam dilution, when highly reactive combustible mixtures are used in a swirl-stabilized combustor. To this end, high-pressure experiments have been conducted with a generic swirl-stabilized combustor featuring axial air injection to increase flashback safety. The experiments have been conducted with two fuel mixtures, at various pressure levels up to 9 bar and at four levels of steam dilution up to 25% steam-to-air mass flow ratio. Natural gas has been used as a reference fuel, whereas a mixture of natural gas and hydrogen (10% hydrogen by mass) represented an upper limit of hydrogen concentration in a natural gas network with hydrogen enrichment. The results of the emissions measurements are presented along with a reactor network model. The latter is applied as a means to qualitatively understand the chemical processes responsible for the observed emissions and their trends with increasing pressure and steam injection.

Characterization of multi-hole nozzle sprays and internal flow for different nozzle hole lengths in direct-injection diesel engines

Multi-hole nozzles have a wide range of application in the fuel supply system of modern diesel engines, although single-hole nozzles dominate basic internal flow and spray research. The parameters of the nozzle geometry are crucial factors that can alter the internal flow dynamics of the nozzle and the consequent spray behaviours. The novelty of this study lies in implementing the application of practical prototype mini-sac multi-hole diesel nozzles to experimental and numerical studies. The internal flow and spray characteristics generated by practical multi-hole (10-hole) nozzles with different sac wall thicknesses (0.4 mm, 0.6 mm and 0.8 mm) were investigated in conjunction with a series of experimental and computational methods using a constant injection quantity (2 mm3/hole). Globally, the analysis mainly concentrated on different nozzle flow dynamics, different injection processes and different spray morphologies. Specifically, the high-speed video observation method was applied to visualize the injection processes and the spray evolution of different nozzles inside a high-pressure vessel. Furthermore, numerical simulations were conducted to reveal the three-dimensional nature of the internal flow inside different configurations; this was instructive in helping us to understand better the mechanism behind the spray behaviours. The results indicate that intense cavitating, turbulent and spiral rotating flow patterns occur inside practical multi-hole nozzles, and the consequent sprays emerging from the nozzles are perturbed, asymmetrical and unstable in both the near field and the far field. Moreover, a decrease in the nozzle hole length can increase the effects of cavitation, turbulence, the void fraction and the axial and radial injection velocity components on the nozzle hole exit; this is accompanied by an intriguing longer injection duration, wider near-field and far-field spray widths, a lower injection rate, and overlapping or even shorter spray propagation. However, these changes are not linear, and different parameters have different sensitivities to the variation in the nozzle hole length.

Low power consumption suspension plasma spray system for ceramic coating deposition

Suspension plasma spraying (SPS) is a modification of conventional plasma spray techniques that has been developed to overcome the challenge of using nano-sized particles in plasma spray processes. The novel feature of using nano-sized particles in the form of a suspension makes the SPS process promising for several applications and for improving the performance of plasma spray coatings. The focus of this study is to develop a new SPS system that consumed low power and gas to deposit ceramic coatings.Several ceramic coatings, such as titanium dioxide (TiO2), aluminum oxide (Al2O3), yttrium oxide (Y2O3), and yttria-stabilized zirconia (8YSZ), were successfully fabricated using only Ar as the plasma gas at a low power of 27kW with the new SPS system. The new system is characterized by lower power and gas consumption (only Ar as plasma gas) and axial injection. It is a unique SPS system based on a twin-cathode-type plasma spray gun. The gun has three plasma torches, the main one is called a P-torch (anode) and the two sub-torches are called N-torches (cathodes). The main plasma torch has a reversed polarity (with a cathode nozzle and an anode electrode). The two sub-torches have normal polarity (with an anode nozzle and a cathode electrode). During operation, electric power is supplied between the anode of the P-torch and the two cathodes of the N-torches, so that the so called hairpin-shape of the plasma jet can be maintained. The system requires only argon as the plasma gas (without using any other gases). The voltage (enthalpy of the plasma jet) with Ar is high enough (150V) for melting ceramic powders, which results in a gas consumption SPS system compared to the other available SPS systems. Furthermore, the electrode of the main torch (P-torch) is a hollowed anode, so that axial feeding of spraying materials could be carried out in this system, which is the best method for spraying. In this configuration, the particles are injected into the center of the plasma jet along the axis of its flow. Therefore, the feedstock suspension would be fully entrapped and melted within the plasma before deposition on the substrate surface.

Plasma torch for supersonic plasma spray at atmospheric pressure

This work presents a plasma torch able to operate at supersonic regime with axial injection of feedstock. In contrast to commonly used linear scheme, the principal axis of the plasma torch is perpendicular to feedstock injection direction, which is aligned with coming out plasma jet. The plasma torch has slightly ascending current voltage characteristics and fixed arc length. Electrical, thermal and kinetic characteristics outlined from comparison with conventional linear plasma spray torches are intermediate between APS, HVOF and VPS. The plasma torch developed in this work has an elevated arc voltage (370V) and low arc current (100A), which contribute to increase the electrode life and decrease the arc voltage relative fluctuation (10%). According to in-flight particle monitoring the CoNiCrAlY particles were sprayed at 500m/s and temperature of 2400°C, whereas the 7%YSZ at 491–683m/s and 2535–2636°C.

Finite Element Modeling and Analysis of Powder Stream in Low Pressure Cold Spray Process

Low pressure cold gas dynamic spray (LPCGDS) is a coating process that utilize low pressure gas (5–10 bars instead of 25–30 bars) and the radial injection of powder instead of axial injection with the particle range (1–50 μm). In the LPCGDS process, pressurized compressed gas is accelerated to the critical velocity, which depends on length of the divergent section of nozzle, the propellant gas and particle characteristics, and the diameters ratio of the inlet and outer diameters. This paper presents finite element modeling (FEM) of powder stream in supersonic nozzle wherein adiabatic gas flow and expansion of gas occurs in uniform manner and the same is used to evaluate the resultant temperature and velocity contours during coating process. FEM analyses were performed using commercial finite volume package, ANSYS CFD FLUENT. The results are helpful to predict the characteristics of powder stream at the exit of the supersonic nozzle.

Hot electrons injection in carbon nanotubes under the influence of quasi-static ac-field

The theory of hot electrons injection in carbon nanotubes (CNTs) where both dc electric field (Ez), and a quasi-static ac field exist simultaneously (i.e. when the frequency ω of ac field is much less than the scattering frequency v (ω⪡v or ωτ⪡1, v=τ−1) where τ is relaxation time) is studied. The investigation is done theoretically by solving semi-classical Boltzmann transport equation with and without the presence of the hot electrons source to derive the current densities. Plots of the normalized current density versus dc field (Ez) applied along the axis of the CNTs in the presence and absence of hot electrons reveal ohmic conductivity initially and finally negative differential conductivity (NDC) provided ωτ⪡1 (i.e. quasi- static case). With strong enough axial injection of the hot electrons, there is a switch from NDC to positive differential conductivity (PDC) about Ez≥75kV/cm and Ez≥140kV/cm for a zigzag CNT and an armchair CNT respectively. Thus, the most important tough problem for NDC region which is the space charge instabilities can be suppressed due to the switch from the NDC behaviour to the PDC behaviour predicting a potential generation of terahertz radiations whose applications are relevance in current-day technology, industry, and research.

Properties and parameters of the electron beam injected into the mirror magnetic trap of a plasma accelerator

The parameters of the injector of an axial plasma beam injected into a plasma accelerator operating on the basis of gyroresonance acceleration of electrons in the reverse magnetic field are determined. The trapping of the beam electrons into the regime of gyroresonance acceleration is numerically simulated by the particle- in-cell method. The optimal time of axial injection of the beam into a magnetic mirror trap is determined. The beam parameters satisfying the condition of efficient particle trapping into the gyromagnetic autoresonance regime are found.

Electron injection for enhanced energy gain by a radially polarized laser pulse in vacuum in the presence of magnetic wiggler

We present a scheme of electron injection for enhanced electron energy gain by using a radially polarized (RP) laser pulse in vacuum under the influence of magnetic wiggler. The inherent symmetry of an RP laser pulse enforces the trapping and acceleration of electrons in the direction of propagation of laser pulse during laser electron interaction. A magnetic wiggler encircles the trajectory of accelerated electron and improves the strength of v→×B→ force which supports the retaining of betatron resonance for longer duration and leads to enhance electron acceleration. Four times higher electron energy is observed with a RP laser pulse of peak intensity 8.5×1020 W/cm2 in the presence of magnetic wiggler of 10.69 kG than that in the absence of magnetic wiggler. We have also analyzed the electron injection for enhanced energy gain and observe that the electron energy gain is relatively higher with a sideway injection than that of axial injection of electron. Injection angle δ is optimized and found that at δ=10° to the direction of propagation of laser pulse, maximum energy is obtained.

Influence of Microstructure on Thermal Properties of Axial Suspension Plasma-Sprayed YSZ Thermal Barrier Coatings

Suspension plasma spraying is a relatively new thermal spaying technique to produce advanced thermal barrier coatings (TBCs) and enables production of coatings with a variety of structures—highly dense, highly porous, segmented, or columnar. This work investigates suspension plasma-sprayed TBCs produced using axial injection with different process parameters. The influence of coating microstructure on thermal properties was of specific interest. Tests carried out included microstructural analysis, phase analysis, determination of porosity, and pore size distribution, as well as thermal diffusivity/conductivity measurements. Results showed that axial suspension plasma spraying process makes it possible to produce various columnar-type coatings under different processing conditions. Significant influence of microstructural features on thermal properties of the coatings was noted. In particular, the process parameter-dependent microstructural attributes, such as porosity, column density, and crystallite size, were shown to govern the thermal diffusivity and thermal conductivity of the coating.

Swirl Injection Effects on Hybrid Rocket Motors

In the last decades, hybrid rocket engines have been increasingly studied and used in space vehicles. However, the low regression rates and specific impulses still represent major drawbacks to this technology. The objective of this study was to quantify the relative improvement of regression rate values with the use of a swirling flow injector in comparison to an axial injector. Seven tests were conducted with axial injection and seven with swirl injection. Regression rate results were compared, and it was found that swirl injection improved regression rates in 50% for mass fluxes higher than 45 kg∙s -1 ∙m -2 . It was possible to see radiation, kinetic and diffusion theory on the logarithmic plot of regression rate per oxidizer flux yielded by both injectors. A strong agreement with experimental findings of regression rates in the literature parameters is reported.

An ion-beam injection line for the ELASR storage ring at KACST

A versatile ion injector beam-line has been developed for the specific use in the multi-purpose low-energy, storage ring facility at the King Abdulaziz City for Sciences and Technology (KACST) in Riyadh, Saudi Arabia. It incorporates a purpose-developed, high-resolution mass analyzing magnet and it is thereby dedicated to provide the ELASR storage ring with beams of ions of specific mass. It is also intended to operate independently as a single-pass experiment. This versatile ion-injection line was constructed in a staged approach, in which an axial injection version was built first, commissioned and is currently operating. The injection line in its final design is now being assembled and commissioned at KACST.

Air injection methods: The key to a better performance of airlift pumps

This paper presents a comprehensive experimental investigation on the effect of air injection methods on the performance of airlift pumps. The effect of air–water two-phase flow patterns and the phase interaction is presented. The present airlift pump utilizes various air injectors specially designed to enable air injection radially, axially, dual (radial and axial), or with a swirl effect at the air inlet ports. In addition, two air injection modes including steadily and pulsating, at different injection frequencies, are investigated at different two-phase flow patterns. The results have shown that the performance of airlift pumps does not only depend on the design of air injector, but also on the dynamics of air injection method. The pulsating mode of air injection is found to control the intermittent flow pattern in the pump riser and consequently able to keep the pump operating within the best efficiency range. The maximum efficiency of the pulsating axial injection operating at a frequency of 1Hz has improved by 60% over that of typical steady axial injection and by 24% over that of steady dual injection. Furthermore, the performance of airlift pumps with dual injector is improved by synchronizing the injected air at both axial and radial injection ports. The improvement in this arrangement is attributed to the better utilization of available compressed air, reduction of axial air penetration and minimization of water reverse flow in the riser pipe.

Design and Characteristics of a Laminar Plasma Torch for Materials Processing

Thermal plasma jets have been widely used in various materials processing techniques. However, the conventional thermal plasma torches usually generate turbulent plasma jets with the disadvantages of high axial temperature gradient, a short jet length and difficulties in the process control relatively, limiting its applications to materials processing. Therefore, this paper proposes a new laminar plasma torch (LPT) working with pure nitrogen to generate laminar plasma jet (LPJ). Its design and structural characteristics, e.g. segmented anode, axial gas injection, parallel water cooling structure, etc., are detailed to ensure the stability, the favorable temperature and velocity distribution of the generated LPJ. Experiments on the characteristics of the LPT showed that the generated LPJ possessed high specific enthalpy (ranging between 10 and 90 kJ/g), long jet length (maximum length: 480 mm) and low axial temperature gradient, and its output power a current and the gas flow rate. In addition, the thermal efficiency of the LPT was experimentally determined to be ranging between 25 and 45 %. Furthermore, experiment and simulation on the application of the LPJ for surface quenching verified the even radial temperature distribution of the plasma jet and high heat flux density brought to the surface.