Width Of Reaction Zone Research Articles

Effect of processing temperature on interface microstructure of diffusion welded joint of super-duplex stainless steel and zirconium alloy with nickel alloy interlayer

In the present study, super-duplex stainless steel (SDSS) and zirconium alloy (ZrA) was vacuum welded using nickel alloy (NiA) interlayer by the diffusion welding process. The welded joints were processed from 800 to 950 °C in steps of 50 °C using 4-MPa compressive load for 75 min. The joints were characterised using optical microscopy, scanning electron microscopy, electron probe micro-analyser, and x-ray diffractometer. The SDSS│NiA interface is planar in nature for all welding temperatures; however, layer-wise Ni5Zr, Ni10Zr7, NiZr, and NiZr2 reaction products were observed at the NiA│ZrA interfaces. The reaction products and width of these products increase with welding temperature. At both the interfaces, hardness values gradually increase with an increase in welding temperature. NiA│ZrA interface exhibited higher hardness as compared to the SDSS│NiA interface due to the presence of layer wise intermetallics. Joints reached a maximum tensile strength of ∼370 MPa (with an elongation of ∼7.9 %) when the joints were processed at 900 °C due to optimal reaction zone width and the least embrittling effect of the respective intermetallics. At lower temperatures, fracture surfaces of welded assemblies showed featureless morphology and voids present due to the poor coalescence of mating surfaces. At higher welding temperatures, the fracture surface of the transition joint preferred brittle fracture mode due to the cleavage planes with different alignments with insignificant volume fraction of voids on the fractography.

Study on explosion reaction mechanism and energy release characteristics of HMX-based explosives containing B-Al

To explore the application of the micro-sized B-Al (boron-aluminum) compound powder in enhanced blast explosive(EBX) and thermobaric explosive(TBX), three HMX-based explosives containing B-Al (PF-1, PF-2 and PF-3)were designed and prepared. The ignition and combustion characteristics of various samples (micro- and nano-sized B, B-Al compound powders without and with HMX) under different pressures and atmospheres were studied by a laser ignition and combustion experimental system, and the flame evolution images and emission spectral characteristic parameters of the ignition and combustion process were obtained. The structures of detonation reaction zone of ideal and non-ideal explosives were studied by PDV (photonic doppler velocimeter), and the characteristic parameters and explosion reaction mechanism of wave profile were obtained. The energy output characteristics of explosives containing B-Al were evaluated by air blast and underwater explosion test. The results show that nano-sized B has better ignition and combustion characteristics than micro-sized B; the ignition and combustion property of B-Al compound powder with HMX is obviously superior to that of B-Al compound powder. PBX-1 is an ideal explosive, and the reaction zone width is 44ns, whilePF-1 and PF-3 are typical non-ideal explosives, the reaction zone widths are 112ns and 102ns, respectively. In the air blast and underwater explosion test, under the detonation of HMX, the combustion of micro-Al can promote the afterburning effect of micro-B, which releases a great amount of combustion heat, then generates expansible products with higher temperature and pressure, and finally increases the duration of fireball and total energy in underwater explosion.

Observations on Detonation Growth of Lead Azide at Microscale.

Lead azide (LA) is a commonly used primary explosive, the detonation growth of which is difficult to study because it is so sensitive and usually has a small charge size in applications. We used photon Doppler velocimetry (PDV) and calibrated polyvinylidene fluoride (PVDF) gauges to reveal the detonation growth in LA, which was pressed in the confinements with controlled heights. The particle-velocity profiles, output pressure, unsteady detonation velocity, reaction time, and reaction-zone width were obtained and analyzed. Three phases of detonation propagation of LA microcharges are discussed. The volume reactions occur at the beginning of detonation in LA microcharges without forming complete shock profiles. Then the shock front is fast with a slow chemistry reaction zone, which is compressed continuously between the height of 0.8 mm and 2.5 mm. Finally, the steady detonation is built at a height of 2.5 mm. The stable detonation velocity and CJ pressure are 4726 ± 8 m/s and 17.12 ± 0.22 GPa. Additionally, the stable reaction zone time and width are 44 ± 7 ns and 148 ± 11 μm. The detailed detonation process has not previously been quantified in such a small geometry.

Numerical study on the characteristics of a nano-aluminum dust-air jet flame

Nano-sized aluminum dust is quite attractive in the application scenarios with limited residence time. This study simulated an aluminum nanoparticle-air jet flame in a burner that was proposed to characterize the mixing and burning properties of dust and air in a classical ramjet configuration. The model considers the flow of gas phase by employing three-dimensional multicomponent Navier-Stokes equations, and the aluminum particles via the Lagrange approach. A combustion sub-model was developed to characterize the heat convection, radiation and combustion processes of nano-sized aluminum particles. Thereafter, the model was validated by comparing with experimental results of dust jet flow and aluminum particle combustion. With the present model, the characteristics of flow field, and variations of particle temperature, heat release and statuses etc. were examined in detail, by which the mixing zone and flame structure were defined. The results showed that the nano-aluminum particles in the inner mixing layer were firstly ignited by the hot co-flow air and burned, and these particles in the core jet region were ignited downstream. Once the aluminum particles were ignited, they burned out promptly in this burner. The effects of particle size were evaluated, and the results show that the lengths of mixing layer and reaction zone, as well as the width of reaction zone reduce with decreasing particle size, whereas the width of mixing layer stays the same.

Build Up and Characterization of Ultraslow Nuclear Burn-Up Wave in Epithermal Neutron Multiplying Medium

Abstract A study is carried out on the build-up and characterization of ultraslow nuclear burn-up wave in epithermal neutron multiplying medium for slab geometry. Uranium-plutonium fissile medium is considered for the calculation. Transient part of the wave is characterized by transient time (TT), transient length (TL), and TT and TL are defined as the time and distance required to develop asymptotic neutron flux propagating through the media. Steady-state part of the wave is characterized with wave velocity and reaction zone width (full width half maximum (FWHM) and full width 10% of maximum (FW10M)). Parametric studies are carried out for different enrichment of 235U and different values of external source of neutron. It is observed that TT, TL, FWHM, and FW10M decrease with the increase in enrichment. The velocity of the wave increases with the enrichment of 235U. This study is beneficial for understanding the characteristics of nuclear burn-up wave in epithermal region as it will help in further researches in this area.

Determination of chemical reaction zone width for emulsion explosive Poremit 1A based on uncertainty principle of quantum mechanics

Determination of chemical reaction zone width for emulsion explosive Poremit 1A based on uncertainty principle of quantum mechanics

Numerical Modelling of Detonation Reaction Zone of Nitromethane by EXPLO5 Code and Wood and Kirkwood Theory

The detonation reaction zone of nitromethane (NM) has been extensively studied both experimentally and theoretically. The measured particle velocity profile of NM shows the existence of a sharp spike followed by a rapid drop over the first 5-10 ns (fast reaction). The sharp spike is followed by a gradual decrease (slow reactions) which terminate after approximately 50-60 ns when the CJ condition is attained. Based on experimental data, the total reaction zone length is estimated to be around 300 μm. Some experimental observations, such as the reaction zone width and the diameter effect, can be satisfactorily reproduced by numerical modelling, provided an appropriate reaction rate model is known. Here we describe the model for numerical modelling of the steady state detonation of NM. The model is based on the coupling thermochemical code EXPLO5 with the Wood-Kirkwood detonation theory, supplemented with different reaction rate models. The constants in the rate models are calibrated based on experimentally measured particle velocity profiles and the detonation reaction zone width. It was found that the model can describe the experimentally measured total reaction time (width of reaction zone) and the particle velocitytime profile of NM. It was found also that the reaction rate model plays a key role on the shape of the shock wave front. In addition, the model can predict the detonation parameters (D, pCJ, TCJ, VCJ, etc.) and the effect of charge diameter on the detonation parameters.

Влияние скорости распространения и ширины зоны турбулентного пламени на концентрацию несгоревших углеводородов и полноту сгорания топлива в двигателе с искровым зажиганием

The investigation considers how combustion efficiency and exhaust gas (unburnt hydrocarbon) toxicity are linked to the fundamental flame propagation characteristics (flame propagation velocity and reaction zone width). We present combustion efficiency and unburnt hydrocarbon concentration as functions of fundamental flame propagation characteristics, maximum flame temperature, flame failure temperature and thickness of the unburnt fuel layer adjacent to the combustion chamber walls. Comparing combustion efficiency computed according to the equation proposed to combustion efficiency derived by using an experimentally obtained indicator diagram showed that the data are in good agreement. We studied the connection between unburnt hydrocarbon emission and combustion efficiency. We detected that increasing combustion efficiency leads to lower unburnt hydrocarbon emission, which is explained by reduction of the unburnt fuel ratio in the layer adjacent to the wall. We propose a new technique for calculating unburnt hydrocarbon amount in engine exhaust gases. We show that our technique makes it possible to determine the chemical composition of the air-fuel mixture and the values of flame propagation characteristics that ensure a decrease in unburnt hydrocarbon emission. The results of our study may be used to develop or refine methods of increasing combustion efficiency of composite fuels and reducing exhaust gas toxicity in combustion chambers of internal combustion engines and other power plants.

Effects of hydrogen on the interfacial reaction between Ti[sbnd]6Al[sbnd]4V alloy melt and Al2O3 ceramic shell

Effects of hydrogen on the interfacial reaction between Ti6Al4V (Ti64) alloy melt and Al2O3 ceramic shell were studied by arc-melting in H2/Ar gaseous mixture. The thickness of interfacial reaction layer between Ti64 alloy melt and Al2O3 ceramic shell without hydrogenation is 80 μm. But the thickness of reaction layer can be reduced to 10 μm at a hydrogen partial pressure of 20 kPa, which is better than the thickness of interface layer between Ti64 alloy and widely used Y2O3 shells. At Ti64 casting surface, the content of β-soft ductile phase is increased and the width of both reaction zone and transition zone are reduced with the increase of hydrogen partial pressure, thus reduces the hardness and the element diffusion distance. Therefore, Hydrogen can effectively control the interfacial reaction in the process of titanium alloy investment casting, and Al2O3 ceramic will be a kind of very promising shell material.

Experimental investigation of detonation waves instabilities in liquid high explosives

Experimental investigation of unstable detonation front structure in mixtures of liquid high explosives (nitromethane and FEFO—bis-(2-fluor-2.2-dinitroethyl)-formal) with inert diluents (acetone, methanol, DETA—diethylene triamine) has been carried out. Inhomogeneities have been registered by electro-optical camera NANOGATE 4BP allowing to make 4 frames with the exposure time 10 ns. According to experimental results the detonation front in nitromethane–acetone mixture is unstable. It is evident that pulsations on detonation front do not form spatial periodic structure and their dimensions differ several times. But mean longitudinal size of pulsation is about 500 μm at 20 wt% of acetone concentration. This means that the typical size of cell equals to reaction zone width. The same structure of cellular front have been registered in 70/30 FEFO–methanol mixture. Second kind of instability, failure waves, was observed in neat nitromethane at the free surface. In this case the stability loss result in turbulent flow which is clearly detected in the shots obtained. Adding small amount of DETA (0.5 wt%) results in disappearance of the failure waves and flow stabilization. The effect is caused by the fact that DETA sharply accelerates initial rate of chemical reaction because it is sensitizer for nitromethane.

Gas detonation cell width prediction model based on support vector regression

Abstract Detonation cell width is an important parameter in hydrogen explosion assessments. The experimental data on gas detonation are statistically analyzed to establish a universal method to numerically predict detonation cell widths. It is commonly understood that detonation cell width, λ , is highly correlated with the characteristic reaction zone width, δ . Classical parametric regression methods were widely applied in earlier research to build an explicit semiempirical correlation for the ratio of λ / δ . The obtained correlations formulate the dependency of the ratio λ / δ on a dimensionless effective chemical activation energy and a dimensionless temperature of the gas mixture. In this paper, support vector regression (SVR), which is based on nonparametric machine learning, is applied to achieve functions with better fitness to experimental data and more accurate predictions. Furthermore, a third parameter, dimensionless pressure, is considered as an additional independent variable. It is found that three-parameter SVR can significantly improve the performance of the fitting function. Meanwhile, SVR also provides better adaptability and the model functions can be easily renewed when experimental database is updated or new regression parameters are considered.

A parameterization of the Richtmyer–Meshkov instability on a premixed flame interface induced by the successive passages of shock waves

The interactions of a sinusoidal premixed flame interface with successive shock waves are studied by numerically solving the two-dimensional, reactive Navier–Stokes equations with high resolution schemes. The focus is the development of the perturbations on the flame interface due to the Richtmyer–Meshkov (RM) instability. A single irreversible chemical reaction for a C2H4+3O2+4N2 mixture is used to represent the combustion process during the interactions. Three cases of interactions, with different initial incident shock wave strengths (Ma=1.2, 1.7 and 2.2), are studied. The multiple interactions between the flame interface and the shock and its reflection waves lead to interesting new observations that have not been presented before. To parameterize the interactions, we introduce a time scale decoupling assumption, and propose to use two decoupled time scales, i.e., the decoupled chemical reaction time scale τC and the decoupled RM instability time scale τRM. Based on this assumption, τC is considered to be decoupled from τRM, so that both time scales can be defined and determined independently. Specifically, τRM is defined as the reciprocal of vorticity magnitudes that can be obtained by performing the computations of two-dimensional RM instability in a chemically frozen flow that removes the effect of chemical reactions. On the other hand, τC is defined as the ratio of reaction zone width of an un-stretched, laminar, premixed flame to propagating speed of the flame, during the one-dimensional laminar flame propagation without considering two-dimensional RM instability. Using these definitions, our calculations show that both τC and τRM decrease with the successive interactions of the shock waves with the flame interface in all three cases, and that τC is larger than τRM at early stages of interactions and then rapidly decreases to a level comparable with τRM at later stages of interactions. We compare the two-dimensional visualizations of the perturbation development on the interface in reactive flows with those in chemically frozen flows. The comparison shows that RM instability plays an important role in early evolution, but chemical reactions dominate later, and that the evolution is correlated with the variations of τC and τRM for all cases studied here. The quantitative correlations between the ratio of τC to τRM and chemical heat release rate in all three cases are calculated. The good correlations indicate the advantage of the approaches to determine τC and τRM proposed in present study. The observation that the ratio of τC to τRM is independent of the initial strength of incident shock wave suggests that the ratio reflects the nature of reactive RM instability, hence provides a new dimensionless parameter for understanding such flows.

Evaluation of detonation characteristics of aluminum/JP-10/air mixtures at stoichiometric concentrations

In order to investigate the heterogeneous detonation characteristics of aluminum particles/JP-10/air mixtures, the gas–solid two phase flow and detonation models were established using the discrete phase model (DPM) and turbulent combustion model, and detonation properties of the aluminum particles/JP-10/air mixtures were simulated. At stoichiometric concentrations of the solid particle–gas mixtures, and four different mass ratios (100% aluminum particles/air, 60% aluminum particles/40% gaseous JP-10/air, 40% aluminum particles/60% gaseous JP-10/air, 100% gaseous JP-10/air), results reveal that obvious reaction relaxation phenomenon exists in aluminum particles detonation process, however, addition of gaseous JP-10 to aluminum particles obviously contributes to higher steady detonation propagation velocity and extended reaction zone width. Furthermore, 60% aluminum particles/40% JP-10/air mixture achieves the highest detonation velocity up to 2128m/s, detonation pressure of 3.7MPa, efficiently enhanced reaction zone width of 0.369m, and the reaction times of JP-10/air and aluminum particles/air of 2.07μs and 5.65μs, respectively.

Investigation of subgrid-scale mixing of reactive scalar perturbations from flamelets in turbulent partially premixed flames

Recent studies of subgrid-scale (SGS) mixing and turbulence-chemistry interaction have shown that turbulent flames contain different structures. In flamelet structures diffusion of reactive scalars and chemical reaction are tightly coupled. Most mixing models used in probability density and filtered density methods, however, are based on non-reactive scalars. To investigate the effects of the coupling on the diffusion we decompose a reactive scalar into a steady flamelet part and perturbations from it. The diffusion of the former can be obtained from a suitably chosen flamelet solution while the latter is unclosed. The conditionally filtered diffusion and dissipation of the reactive scalar perturbations are analyzed using high-resolution line images obtained in turbulent partially premixed (Sandia) flames. For SGS scalar containing flamelets, the perturbation diffusion has characteristics similar to that of a non-reactive scalar, in contrast with the flamelet part. The functional form of the conditionally filtered diffusion is well described by the Interaction by Exchange with the Mean (IEM) model. Our perturbation analysis of the flamelet equation shows that for perturbations having length scales smaller than the reaction zone width, the reactive scalar diffusion is largely controlled by the mixture fraction field, thus having the characteristics of non-reactive scalar mixing. For perturbations with length scales larger than the reaction width, the conditionally filtered diffusion has the same form as non-reactive scalar mixing, with the mixing time scale determined by the flamelet. The IEM model predictions based on this mixing time scale are in good agreement with the experimental results for a range of SGS conditions, suggesting that the perturbations are consistent with unsteady flamelets for the conditions studied. Thus, mixing models based on non-reactive scalars can potentially model the SGS mixing accurately. The results in the present study can be useful for developing a unified mixing model that can predict all combustion regimes accurately.

Effect of H2 addition on combustion characteristics of dimethyl ether jet diffusion flame

In this paper, experiments and numerical calculations were conducted to investigate the effect of H2 addition on dimethyl ether (DME) jet diffusion flame behaviors, in terms of thermal and chemical structures, reaction zone size, flame entrainment, and NOx and CO emission indices. A wide range of H2 additions from pure DME to pure H2 were involved herein, while maintaining the volumetric flow rate of fuel mixture constant. The results indicate that when H2 mole fraction in the fuel mixture exceeded 60%, the blended fuel was converted to H2-dominated. Besides, the flames behaved rather distinctly at the DME- and H2-dominated regimes. With the increment in H2 addition, flame temperature, H2, H, O, and OH concentrations increased gradually, but concentrations of the intermediate hydrocarbons (such as CO, CH2O, CH2, and CH3) decreased on the contrary. Additionally, after the flame became H2-dominated, the species concentrations varied increasingly quickly with H2 addition. The reaction zone length and width decreased nearly linearly with H2 addition at the DME- and H2-dominated regimes. But the decreasing speed of reaction zone length became faster after the flame was converted to H2-dominated. At the DME-dominated regime, the dependence of flame entrainment coefficient (Ce) on H2 addition was rather small. While at the H2-dominated regime, Ce increased increasingly quickly with H2 addition. Moreover, with the increment in H2 addition, NOx emission index increased and CO emission index decreased gradually. In addition, at the DME-dominated regime, NOx emission index increased fairly slowly with H2 addition; while at the H2-dominated regime, it increased significantly. The optimal H2 addition to DME was 60vol.% in the practical engineering.

Characterization of atomization and combustion in moderately dense turbulent spray flames

This paper presents a study of spray jets and flames where the liquid fuel loading in the carrier air is such that there are substantial liquid–liquid interactions close to the exit plane. The burner consists of an air-blast atomizer located within a wide hot co-flow used to stabilize turbulent auto-igniting spray flames. Laser/phase Doppler anemometry, microscopic backlit imaging coupled with advanced image processing, broadband chemiluminescence and OH-PLIF imaging are utilized. A key focus here is on a novel characterization of the spray boundary condition in terms of non-spherical shapes of fluid fragments. Three different classes of shapes, namely: ligaments, droplets, and large, generally irregular objects are examined. Statistics for each of these fragments are computed in a range of sprays and it is found that their size and probability of occurence depends on the initial Weber number and fuel/air mass ratio (F/A). The change in chemiluminescence emission that is measured as a function of the F/A ratio trends in the same manner as the change in the size of the largest non-spherical objects in the spray. In addition, it is found that changes in the growth of reaction zone width occur as estimated from OH images of laser induced fluorescence, and this is also controlled by the F/A ratio. Therefore, the spray structure at the exit plane may partly dictate the downstream flame characteristics; and this could be largely due to the presence of non-spherical fragments and hence the different rates of atomization and vapourization amongst the different sprays. The burner, as well as the classification of the spray introduced here, while complex, can form a platform for the improvement of models for moderately dense reacting sprays.

Modeling of the Heat and Kinetic Phenomena Accompanying the Different Material Joining Using Solid-Phase Synthesis

Two-dimensional model of different material joining using solid-phase synthesis has been formulated. The model represents two-dimensional coupled thermal conductivity problem with allowance for the heat release due to chemical reaction course in an adhesive composition. The problem has been solved numerically with the help of a non-explicit difference scheme, coordinate splitting and linear double-sweep method. The influence of thermophysical parameters difference on the temperature and conversion degree fields, reaction zone width and conversion zone propagation velocity have been determined.

Effect of the density of an emulsion explosive on the reaction zone width

This paper presents experimental dependences of the width of the reaction zone and detonation critical diameter on the initial density with a variation in the density of an emulsion high explosive from 0.5 to 1.33 g/cm3. Glass microballoons were used as a sensitizer. The emulsion explosive is characterized by an U-shaped dependence of the critical diameter on the density, and the reaction time and the width the reaction zone increase monotonically with the density of the explosive. The detonation pressure of the studied compositions varies in the range of 0.6–12 GPa.

Effect of Heat Treatment on the Microstructure and Microchemistry of Explosive Welded Joints of Ti-5Ta-1.8Nb and 304L SS

Explosive welding process was used for joining Ti-5Ta-1.8Nb alloy to 304L austenitic stainless steel to avoid the formation of intermetallic phases at the interface which otherwise form in fusion welding processes. Both X-ray diffraction and electron microprobe based analysis showed the absence of intermetallic phases at the weld interface within their detection limits. Strain induced phase transformation due to the deformation induced by explosive welding was observed in both the base materials. The 'as received' explosive joints were further heat treated at 873 and 1073 K for durations in the range of 1 to 20 h to select appropriate temperature for further processing subsequent to welding. Detailed analysis using electron microprobe showed considerable microstructural and micro chemical modification at the weld interface due to inter-diffusion of Fe, Ti, Cr and Ni. The width and number of reaction zones varied as a function of heat treatment temperature and time. From the experiments, it was inferred that even the lowest temperature-time combination, i.e. 873 K-1h, is not suitable for heat treatment of explosive joints of Ti-5Ta-1.8Nb/SS 304L, and further lowering of the process temperature is required.

Effect of Heat Treatment on the Microstructure and Microchemistry of Explosive Welded Joints of Ti-5Ta-1.8Nb and 304L SS

Explosive welding process was used for joining Ti-5Ta-1.8Nb alloy to 304L austenitic stainless steel to avoid the formation of intermetallic phases at the interface which otherwise form in fusion welding processes. Both X-ray diffraction and electron microprobe based analysis showed the absence of intermetallic phases at the weld interface within their detection limits. Strain induced phase transformation due to the deformation induced by explosive welding was observed in both the base materials. The 'as received' explosive joints were further heat treated at 873 and 1073 K for durations in the range of 1 to 20 h to select appropriate temperature for further processing subsequent to welding. Detailed analysis using electron microprobe showed considerable microstructural and micro chemical modification at the weld interface due to inter-diffusion of Fe, Ti, Cr and Ni. The width and number of reaction zones varied as a function of heat treatment temperature and time. From the experiments, it was inferred that even the lowest temperature-time combination, i.e. 873 K-1h, is not suitable for heat treatment of explosive joints of Ti-5Ta-1.8Nb/SS 304L, and further lowering of the process temperature is required.