Reactive Jet Research Articles

Frequency response analysis of a (non-)reactive jet in crossflow

Abstract

Damage Mechanism of PTFE/Al Reactive Charge Liner Structural Parameters on a Steel Target.

The incorporation of reactive material damage element technology in ammunition warheads is a research hotspot in the development of conventional ammunition. The research results are of great significance and military application value to promote the development of high-efficiency damage ammunition technology. In this paper, we aimed to understand the behavior of the reactive jet and its damage effect on a steel target by undertaking theoretical analysis, numerical simulation, and experimental research. We studied the influence of structural and material parameters on the shape of the reactive jet based on autodyn-2d finite element simulation software, and the formation behavior of the reactive jet was verified using a pulsed X-ray experiment. By studying the combined damage caused by the steel target penetrating and exploding the reactive jet, the influence of the structural and performance parameters, and the explosion height of the reactive jet liner on the damage effect to the steel target was studied. A static explosion experiment was carried out, and the optimal structural and performance parameters for the reactive material and explosion height of the reactive jet liner were obtained.

Recursive algorithm for modeling non-linear etching rates in reactive plasma jet based optical surface machining of borosilicate crown glass

Application-specific optical glass properties are achieved by utilizing complex material compositions. This can be problematic in reactive plasma-assisted deterministic surface processing since a non-volatile surface layer may form depending on the glass composition, which affects the etch rate and thereby the local etching depth. In this investigation, a model algorithm is proposed to tackle some restrictions in applying fluorine-based plasma jet as etching tool utilized for freeform surface machining of optics made of complex glass composition, like borosilicate crown glass (e.g., N-BK7®). In this regard, firstly an analytical model is proposed for estimating the depth-dependent etch rate function. Subsequently, a recursive simulation algorithm is introduced for convolving the derived depth-dependent etch rate function with the given dwell time matrix to simulate a deterministic freeform generation process. By the proposed simulation algorithm, the impeding influence of the residual layer on the reduction of etching depth is computed prior to a real experiment in order to scale the local dwell time to ensure the targeted local removal. Finally, the simulated freeform shape is compared with the corresponding result of an etching experiment to validate the feasibility of the proposed approach.

Combined reactive plasma jet-laser etching method for technical optical glass containing metal oxides

The machining of optical glass materials with beam technologies enables novel fabrication processes for innovative optical elements with freeform surfaces. However, the complex material composition of optical glass such as N-BK7® is challenging for non-abrasive, pure chemical machining. N-BK7 can be machined utilizing reactive atmospheric plasma jet (RAPJ) etching. However, the etching mechanism results in process-inherent surface composition changes that limit potential applications of RAPJ-machining. A residues layer is formed which causes a temporally changing etching behavior and an increased roughness. Therefore, a process sequence of utilizing RAPJ etching and laser cleaning is proposed and demonstrated that enables to overcome the stated limitations. In this cyclic sequence, N-BK7 optical glass is etched first with a fluorine-containing reactive atmospheric plasma jet resulting in an etched but also residues-modified surface. Thereafter, the residues are removed by pulsed UV laser irradiation without ablation of the glass. This combined laser-enhanced reactive plasma jet etching allows etching of optical glass with a higher average etching rate and smoother machined surfaces.

Droplet-Based Bioprinting Enables the Fabrication of Cell-Hydrogel-Microfibre Composite Tissue Precursors

Composites offer an opportunity to couple particular benefits of their constituents to achieve unique material properties that can be of extra value in many tissue engineering applications. Strategies combining hydrogels with fibre-based scaffolds can create more biologically and structurally functional tissue constructs. However, developing efficient and scalable approaches to manufacture such composites is challenging. Here, we use a droplet-based bioprinting system called Reactive Jet Impingement (ReJI) to integrate a cell-laden hydrogel with a microfibrous mesh. The ReJI system uses microvalves that are connected to different bio-ink reservoirs and directed to continuously jet bio-ink droplets at one another in mid-air where the droplets react and form a hydrogel that lands on a microfibrous mesh. We produce cell-hydrogel-fibre composites by embedding human dermal fibroblasts at two different concentrations (5 x 106 and 30 x 106 cells/ml respectively) in a collagen-alginate-fibrin hydrogel matrix and bioprint it onto a fibre-based substrate. Our results show that both types of cell-hydrogel-microfibre composites maintain high cell viability and promote cell-cell and cell-biomaterial interactions. The lower fibroblast density thereby triggers cell proliferation whereas the higher fibroblast density facilitates faster cellular organisation and infiltration into the microfibres. Additionally, the fibrous component of the composite is characterised by its high swelling properties and quick calcium ions release. The data indicate that the composite constructs we create offer an efficient way to create highly functional tissue precursors for laminar tissue engineering in particular wound healing and skin tissue engineering applications.

Stochastic Modeling of a Lifted Methane/Air Jet Flame with Detailed Chemistry

AbstractThis preliminary numerical study investigates a lifted methane/air jet flame in a vitiated coflow by means of the One‐Dimensional Turbulence (ODT) model. In the considered Cabra Burner configuration [Combust. Flame 143 491‐506 (2005)], a jet flame issues from a central nozzle into a vitiated coflow of hot combustion products from lean premixed hydrogen/air flames. ODT is a map‐based model for turbulent flow simulations which uses a stochastic formulation for the turbulent advection. The diffusion and reaction effects along the one‐dimensional domain are considered by temporally advancing deterministic evolution equations. ODT simulations are performed with a representation of the methane/air chemistry by a detailed 53‐species mechanism with 325 reactions. In this work, we present centerline profile of temperature and species concentrations obtained from ODT simulations using a cylindrical ODT‐formulation. Additionally, a two‐dimensional rendering of the temperature distribution is shown. Although the simulation of reactive jet configurations by means of ODT is not novel, the complex stabilization region depending on the flow conditions represents a challenge for the model. Considering the reduced order of the model, ODT is able to predict the flow characteristics and reasonably matches the existing experimental data.

A 2-D DNS study of the effects of nozzle geometry, ignition kernel placement and initial turbulence on prechamber ignition

A parametric direct numerical simulation study was conducted to investigate the effects of the initial flow field (quiescent or turbulent), nozzle inlet sharpness and width, main chamber composition (lean and stoichiometric), and ignition kernel placement in a two-dimensional prechamber (PC) ignition system. The strongly coupled operating and geometric parameters determine the time at which the flame exits the prechamber, the transient structure and penetration of the initially cold and subsequently hot reactive jet and their impingement on the lower main chamber (MC) wall, affecting the combustion mode and the fuel consumption rate. The temperature of the flame reaching and crossing the nozzle is affected by the flame exit time and is significantly lower than the adiabatic flame temperature of the planar flame, although no quenching is observed. Interaction with the flow field (strong small scale vortices for narrow and sharp entry nozzles, large vortices for wide nozzles) generated close to the exit increases the surface area of the flame and its interaction with the MC mixture. Jet penetration and impingement on the lower MC wall is determined by combustion in the PC and the flow field it generates in the main chamber. Impingement results in large scale vortical structures, which further contribute to the flame area increase and accelerate the consumption of the MC charge at later times. For the conditions studied, budget analysis shows that the main combustion mode is premixed deflagration with locally enhanced or reduced reactivity. Local flame–flame interactions which are more pronounced close to the nozzle exit and the lower MC wall can increase the propagation speed up to six times compared to the planar flame. The evolution of the probability density functions of different quantities is used to characterize the strongly transient process.

Influence of the Water Feed to the Body of a Rocket-Engine Exhaust Jet during its Flow into a Submerged Space

Elements of a homogeneous algorithm for numerical simulation of the thermogasdynamic parameters of a viscous two-phase nonequilibrium chemically reactive nonisobaric rocket-engine exhaust jet have been formulated within the framework of a two-velocity and two-temperature continuum model on the basis of “viscous-layer” and “narrow-channel” equations. By numerical calculation, the authors has established the basic regularities of the influence of the water feed, the mixing of the jet with air, and the afterburning of the high-temperature rocket-engine jet in the air oxygen on the flow structure and thermogasdynamic and thermophysical parameters of the jet.

Residual Layer Removal of Technical Glass Resulting from Reactive Atmospheric Plasma Jet Etching by Pulsed Laser Irradiation

Ultrahigh-precision machining of glass is indispensable for optical component fabrication and therefore for applications. In this regard, plasma jet assisted chemical etching technologies enable new fabrication processes for enhanced optical functionalities due to their deterministic localized machining capabilities. This technique has been successfully applied to fused silica and silicon. However, applications require specific glass properties are related to complex material compositions of the glass. Hence, reactive plasma etching of these optical glasses is a challenging task. For instance, etching of metal oxide containing glass like N-BK7 by a fluorine-based reactive atmospheric plasma jet (RAPJ) exhibits currently limitations due to the formation of non-volatile reaction products that remain on the glass surface as a layer. Therefore, a procedure consisting of RAPJ etching and laser ablation is proposed for the machining of N-BK7. The capability of laser-based removal of residual layers is compared to water-based solving of the residual layer. After RAPJ etching of N-BK7 using a CF4–O2 gas mixture with an average microwave power of 16 W, the samples are cleaned either by a water-based solvent or by the ablation with a nanosecond-pulsed ultraviolet laser. The laser irradiation with fluences of 2.8 J/cm2 results in a localized removal of the residual layer. It is demonstrated that the roughness of the laser-cleaned N-BK7 surface is similarly low as solvent-based cleaned samples but the pulsed laser enhanced cleaning allows a dry processing at atmospheric pressure as well as a localized processing with a high lateral resolution.

An investigation on effectiveness of temperature treatment for fluorine‐based reactive plasma jet machining of N‐BK7®

AbstractIn this study, a fluorine‐based reactive plasma jet is investigated as a promising tool for ultraprecise surface machining of N‐BK7®. Plasma‐generated particles react with an N‐BK7 surface to create volatile and nonvolatile compounds. The desorption of volatile compounds results in an etched surface, whereas nonvolatile compounds form a residual layer in the etched area, causing unpredictable effects on the etching rate. Surface temperature treatment is proposed to improve the machining procedure with respect to deterministic material removal, leading to predictable results. It is shown that, at an elevated surface temperature, the residual layer properties are modified in favor of improved etching performance. The etching behavior of N‐BK7 is compared with fused silica to verify the optimality of the obtained results.

Gelfand-type problem for turbulent jets

We consider the model of auto-ignition (thermal explosion) of a free round reactive turbulent jet introduced in [11]. This model falls into the general class of Gelfand-type problems and constitutes a boundary value problem for a certain semi-linear elliptic equation that depends on two parameters: α characterizing the flow rate and λ (Frank-Kamenetskii parameter) characterizing the strength of the reaction. Similarly to the classical Gelfand problem, this equation admits a solution when the Frank-Kamenetskii parameter λ does not exceed some critical value λ⁎(α) and admits no solutions for larger values of λ. We obtain the sharp asymptotic behavior of the critical Frank-Kamenetskii parameter in the strong flow limit (α≫1). We also provide a detailed description of the extremal solution (i.e., the solution corresponding to λ⁎) in this regime.

Chain damage effects of multi-spaced plates by reactive jet impact

Chain damage is a new phenomenon that occurs when a reactive jet impacts and penetrates multi-spaced plates. The reactive jet produces mechanical perforations on the spaced plates by its kinetic energy (KE), and then results in unusual chain rupturing effects and excessive structural damage on the spaced plates by its deflagration reaction. In the present study, the chain damage behavior is initially demonstrated by experiments. The reactive liners, composed of 26 wt%Al and 74 wt% PTFE, are fabricated through a pressing and sintering process. Three reactive liner thicknesses of 0.08 CD, 0.10 CD and 0.12 CD (charge diameter) are chosen to carry out the chain damage experiments. The results show a chain rupturing phenomenon caused by reactive jet. The constant reaction delay time and the different penetration velocities of reactive jets from liners with different thicknesses result in the variation of the deflagration position, which consequently determines the number of ruptured plates behind the armor. Then, the finite-element code AUTODYN-3D has been used to simulate the kinetic energy only-induced rupturing effects on plates, based on the mechanism of behind armor debris (BAD). The significant discrepancies between simulations and experiments indicate that one enhanced damage mechanism, the behind armor blast (BAB), has acted on the ruptured plates. Finally, a theoretical model is used to consider the BAB-induced enhancement, and the analysis shows that the rupturing area on aluminum plates depends strongly upon the KE only-induced pre-perforations, the mass of reactive materials, and the thickness of plates.

Prechamber ignition: An exploratory 2-D DNS study of the effects of initial temperature and main chamber composition

A numerical investigation was conducted to study ignition and the initial phases of methane combustion in a two-dimensional setup consisting of a pre- (PC) and main (MC) chamber. The effect of the wall thermal boundary condition (isothermal Tw=500 K or adiabatic), initial mixture temperature (Tu=300 and 800 K) and equivalence ratio in the main chamber (ϕMC=0.5 and 1.0) was studied. A stoichiometric mixture was used in the PC and the mixtures were initially quiescent in all cases. Flame propagation in the prechamber is affected mainly by the initial temperature, while the thermal state of the wall plays a minor role. The transient jet that is generated at the exit of the orifice connecting the two chambers creates an intense flow field with vortical structures that, depending on the initial temperature, persist for a long time or dissipate quickly affecting combustion in the main chamber. Depending on the local flow and mixing conditions close to the orifice exit, the hot jet can be broken into small kernels at low Tu or forms quickly a flame torch at hot conditions, strongly affecting ignition of the MC mixture and flame propagation in the main chamber. In the lean MC cases, the intense mixing with the stoichiometric PC mixture creates local compositions that are more favorable for ignition by the hot turbulent reactive jet that subsequently exits from the PC at a temperature that is significantly lower than the adiabatic flame temperature of the corresponding mixture. Despite the short residence time, the reactive state of the mixture is affected as it flows through the nozzle. The flame structures in the MC are described in terms of the progress variable and mixture fraction and compared to flamelet-type calculations. The local flame structure differs strongly from that of the 1-D unstrained premixed flame, particularly for the low Tu cases. The flamelet-type calculations show that ignition of the most reactive mixture is enhanced by the radicals in the hot reactive jet, while scalar dissipation rate accelerates the ignition of the whole mixture. The 2-D simulations show that ignition is significantly longer than what is predicted by the flamelet calculations.

LCA study of a new electrochemical and ultraviolet (EC-UV) combined system to decolourise and reuse textile saline effluents: Environmental evaluation and proposal to improve the production process

Abstract In this work, the environmental performance of the reactive Jet dyeing process and the subsequent wastewater treatment currently carried out in the textile companies is compared with a new system. The developed system combines the application of an electrochemical process with ultraviolet irradiation (EC-UV) to remove colour of effluents containing reactive dyes. EC-UV system is also able to prepare the discoloured effluents for its subsequent reuse in a new dyeing process. The developed system can operate in two modes: decolourisation and decolourisation plus reuse. This study compiles life cycle inventory data for both operation modes and compares their environmental impact with the conventional dyeing and wastewater treatment. The results show that the EC-UV system, running in “decolourisation mode” (ED scenario), has a better environmental performance than conventional decolourisation (CD scenario), since the tertiary treatment is eliminated. The environmental assessment for CD and ED scenarios shows that the dyeing process has the largest contribution to all the impact categories, mainly caused by the consumption of Na2CO3 and NaCl. When EC-UV system is running to treat and reuse water and salt (EDR scenario), the reconstitution step process, necessary to reuse effluents, has a great contribution in most of the impact categories. Based on the obtained results, a modification in the dyeing process has also been evaluated. The proposed modification substitutes the use of Na2CO3 by NaOH in the dyeing process, causing a great environmental improvement in all the impact categories for the EDR scenario, being this scenario the one with better environmental performance.

Reactive jet and cyclonic attrition analysis of ilmenite in chemical looping combustion systems

In chemical looping combustion (CLC), the chosen oxygen carrier’s (OC) reactivity maintenance and attrition propensity play key roles in determining its lifetime in such systems. Jet and cyclonic attrition are two main mechanisms of attrition in CLC systems, which typically use fluidized beds and cyclones. In contrast to standardized tests, that assess attrition characteristics under ambient and non-reacting conditions, a realistic evaluation must include the behavior under relevant high temperatures and cyclic oxidation-reduction. In this study, separate jet and cyclonic attrition test units were constructed to investigate the effects of temperature, fuel gas concentration and velocity on the performance of ilmenite, a natural ore-based OC in CLC. Testing showed that thermal and chemical effects were crucial to accurately determine the performance of ilmenite. For experiments conducted between 820°C and 970°C, the intermediate temperature of 895°C provided the best balance between high reactivity and material durability. Additionally, fuel gas concentration affected particle morphology evolution. Iron migration to the surface of the ilmenite particle was enhanced at higher fuel gas concentrations and resulted in reduced attrition rate, presumably due to sintering of the more highly reduced enriched iron phase on the particle surface. The laboratory jet and cyclonic attrition evaluation test units tested in this study can be used to investigate multiple parameters relevant for OC performance, including the degree of reduction, oxygen carrying capacity, attrition resistance, agglomeration, and optimum material operability conditions, as well as to extrapolate test data to determine OC replacement costs in a commercial CLC system.

Penetration Behavior of High-Density Reactive Material Liner Shaped Charge.

The traditional polytetrafluoroethylene (PTFE)/Al reactive material liner shaped charge generally produces insufficient penetration depth, although it enlarges the penetration hole diameter by chemical energy release inside the penetration crater. As such, a novel high-density reactive material liner based on the PTFE matrix was fabricated, and the corresponding penetration performance was investigated. Firstly, the PTFE/W/Cu/Pb high-density reactive material liner was fabricated via a cold pressing/sintering process. Then, jet formation and penetration behaviors at different standoffs were studied by pulse X-ray and static experiments, respectively. The X-ray results showed that the PTFE/W/Cu/Pb high-density reactive material liner forms an excellent reactive jet penetrator, and the static experimental results demonstrated that the penetration depth of this high-density reactive jet increased firstly and then decreased by increasing the standoff. When the standoff was 1.5 CD (charge diameter), the penetration depth of this reactive jet reached 2.82 CD, which was significantly higher than that of the traditional PTFE/Al reactive jet. Moreover, compared with the conventional metal copper jet penetrating steel plates, the entrance hole diameter caused by this high-density reactive jet improved 29.2% at the same standoff. Lastly, the chemical reaction characteristics of PTFE/W/Cu/Pb reactive materials were analyzed, and a semi-empirical penetration model of the high-density reactive jet was established based on the quasi-steady ideal incompressible fluid dynamics theory.

Behind‐Target Rupturing Effects of Sandwich‐like Plates by Reactive Liner Shaped Charge Jet

AbstractThis paper begins with experiments to investigate the behind‐target damage effects on sandwich‐like plates subjected to reactive liner shaped charge jet. Sandwich‐like plates, consisting of triple spaced aluminum plates filled with flame‐retardant foams, are placed under a steel target. The reactive liner shaped charge is initiated at a stand‐off of 1.0 CD, producing a reactive jet to perforate the steel target and then cause behind‐target damage effects on sandwich‐like plates. The experimental results show there is an unusual rupturing effect on sandwich‐like plates, which strongly depends upon the steel target thickness. Generally, the rupturing effects on sandwich‐like plates increase gradually with the steel target thickness decreasing from 60 mm to 40 mm. Then, the interaction mechanism between the reactive jet and target is discussed in three phases. The formation phase shows an expansion behavior of reactive jet, leading to the jet density less than the initial density. The penetration phase results in central holes on aluminum plates and provides a precondition for cracks. Then, the deflagration reaction phase causes a field of high temperature and high pressure inside the sandwich‐like plates, which enlarges the kinetic energy‐induced pre‐perforations and thereby causes the unusual rupturing effects. Finally, an analytical model for the rupturing damage to aluminum plate is developed and the relevant parameter is obtained approximately.

Application of PTFE/Al Reactive Materials for Double-Layered Liner Shaped Charge.

The penetration enhancement behaviors of a reactive material double-layered liner (RM-DLL) shaped charge against thick steel targets are investigated. The RM-DLL comprises an inner copper liner, coupled with an outer PTFE (polytetrafluoroethylene)/Al reactive material liner, fabricated via a cold pressing/sintering process. This RM-DLL shaped charge presents a novel defeat mechanism that incorporates the penetration capability of a precursor copper jet and the chemical energy release of a follow-thru reactive material penetrator. Experimental results showed that, compared with the single reactive liner shaped charge jet, a deeper penetration depth was produced by the reactive material-copper jet, whereas the penetration performance and reactive material mass entering the penetrated target strongly depended on the reactive liner thickness and standoff. To further illustrate the penetration enhancement mechanism, numerical simulations based on AUTODYN-2D code were conducted. Numerical results indicated that, with increasing reactive liner thickness, the initiation delay time of the reactive materials increased significantly, which caused the penetration depth and the follow-thru reactive material mass to increase for a given standoff. This new RM-DLL shaped charge configuration provides an extremely efficient method to enhance the penetration damage to various potential targets, such as armored fighting vehicles, naval vessels, and concrete targets.

Development of a model for ultra‐precise surface machining of N‐BK7® using microwave‐driven reactive plasma jet machining

AbstractIn this paper, extensive studies are conducted as key to overcoming several challenging limitations in applying fluorine‐based reactive plasma jet machining (PJM) to surface machining of N‐BK7®, particularly regarding the manufacture of freeform optical elements. The chemical composition and lateral distributions of the residual layer are evaluated by X‐ray photoelectron spectroscopy and scanning electron microscopy/energy‐dispersive X‐ray spectroscopy analysis aiming at clarifying the exact chemical kinetics between plasma generated active particles and the N‐BK7 surface atoms. Subsequently, a model is developed by performing static etchings to consider the time‐varying nonlinearity of the material removal rate and estimate the local etching rate function. Finally, the derived model is extended into the dynamic machining process, and the outcomes are compared with the experimental results.

Effect of wave shaper on reactive materials jet formation and its penetration performance

Abstract Wave shaper effect on formation behavior and penetration performance of reactive liner shaped charge (RLSC) are investigated by experiments and simulations. The reactive materials liner with a density of 2.3 g/cm3 is fabricated by cold pressing at a pressure of 300 MPa and sintering at a temperature of 380 °C. Experiments of the RLSC with and without wave shaper against steel plates are carried out at standoffs of 0.5, 1.0, and 1.5 CD (charge diameter), respectively. The experimental results show that the penetration depths and structural damage effects of steel plates decrease with increasing the standoff, while the penetration depths and the damage effects of RLSC without wave shaper are much greater than that with wave shaper at the same standoff. To understand the unusual experimental results, numerical simulations based on AUTODYN-2D code are conducted to discuss the wave shaper effect, including the propagation behavior of detonation wave, the velocity and temperature distribution of reactive jet, and penetration depth of reactive jet. The simulations indicate that, compared with RLSC without wave shaper, there is a higher temperature produced inside reactive jet with wave shaper. This unusual temperature rise effects are likely to be an important mechanism to cause the initiation delay time of reactive jet to decline, which results in significantly decreasing its penetration performance.