Non-reactive Gas Research Articles

Understanding flame behaviors under gradient magnetic fields: The dynamics of non-reacting gas jets

Gradient magnetic fields impact fluid dynamics through Kelvin forces, altering flame behavior. Key complexities such as the interaction of magnetic fields with thermal gradients and chemical reactions within flames remain largely unexplored. By isolating variables such as heat release and thermal convection, this study aims to delve into fundamental mechanisms by which gradient magnetic fields affect the fluid dynamics of flames. This research adopts nitrogen, helium, argon and oxygen as jet gases, focusing exclusively on the fluid dynamics of non-reacting flow. Experimental techniques and Computational Fluid Dynamics (CFD) simulations are employed to explore the effects of varying gas species and magnetic field strengths. Results demonstrate that gas density significantly impacts jet behavior, with paramagnetic oxygen concentrating in areas of stronger magnetic fields, and other gases like helium, nitrogen, and argon showing distinct behaviors based on their molar mass. The study also establishes an optimized energy conservation equation that accurately predict jet height, considering factors such as buoyant and Kelvin forces. By studying the flow behavior of non-reacting gases under magnetic fields, the results are ultimately extended to estimate flame heights and elucidate the mechanisms of air-to-fuel diffusion.

In silico monitoring of non-reactive gas blistering on crystalline substrates

Blistering from gas aggregation occurs very rarely on solid substrates; however, it is commonly observed under high-pressure gas or plasma environments. This is due to the repeated aggregation process of gas molecules penetrating beneath the surface, but it has been difficult to find cases that demonstrate the dynamic mechanism on the atomic level. In this study, the dynamics of physical bombardment of argon atoms on the flat monocrystalline silicon substrate are simulated to propose an initiation principle for gas-aggregate formation. Simulations of extremely large numbers of argon atoms bombarding a limited area of single crystal silicon revealed inhomogeneous aggregation properties consistent with the experimental observations. Particularly, the results suggest that momentum transfer formed by collisions between argon trapped in the surface grooves and the argon used for bombardment is the governing factor for the aggregation behavior. The aggregated argon clusters grow in the in-plane direction while generating stress propagation in the thickness direction, ultimately causing an expansion pressure that lifts the adjacent silicon surface upwards. Our work provides a deterministic understanding of the initiation process of blister formation, which rarely occurs in physical sputtering on defect-free substrates.

Methodology for the quantification of the absorption potential of greenhouse - and pollutant gases by climbing plants used in façade greening; a case study on ivy (Hedera helix)

How much do specific climbing plants contribute to the cleansing or absorption of harmful greenhouse and pollutant gases; often regarded as the main environmental threat in cities due to their adverse effects on human health? One of the main hurdles in the quantification of such ecosystem services is associated with the difficulty to obtain and design systems that provide detailed information on the interaction between various gases and the plant in question. To tackle these questions, two highly precise and accurate instruments, namely a mid-infrared laser absorption spectrometer (TDL) and a cavity-ring-down spectrometer (CRDS) were used to monitor the fate of gases when exposed to façade climbing plants like ivy. In a laboratory setting, a relaxation type of experiment was used consisting of a reaction chamber equipped with plant species and continuously flushed by synthetic air. This setup was used to determine the timescales of decay after short injections of the above-mentioned gases. After these injections, all gases followed simple exponential decay curves. N2O, a non-reactive (inert) tropospheric gas, was used as a reference to which all other gases were compared and thereby quantified. This paper focuses on the detailed description of methods and processes to analyse the gas-absorptive behaviour of plants when exposed to gaseous pollutants. For demonstration purposes, quantified absorption features of nitrogen oxide (NO2) are presented for ivy of the variety Hedera helix “Plattensee”. Results of this method of quantification showed that - as compared to N2O (control), - NO2 had a reduced residence time (time scale) of 100 s, while N2O resulted in a 600 s residence time (indicating no interference with the plant). This is equivalent to a 0.3 cm/s deposition velocity/ absorption rate of NO2 under light conditions.

Sulfonated Chitosan Gel Membrane with Confined Amine Carriers for Stable and Efficient Carbon Dioxide Capture.

Capturing carbon dioxide (CO2) from flue gases is a crucial step towards reducing CO2 emissions. Among the various carbon capture methods, facilitated transport membranes (FTMs) have emerged as a promising technology for CO2 capture owing to their high efficiency and low energy consumption in separating CO2. However, FTMs still face the challenge of losing mobile carriers due to weak interaction between the carriers and membrane matrix. Herein, we report a sulfonated chitosan (SCS) gel membrane with confined amine carriers for effective CO2 capture. In this structure, diethylenetriamine (DETA) as a CO2-mobile carrier is confined within the SCS gel membrane via electrostatic forces, which can react reversibly with CO2 and thus greatly facilitate its transport. The SCS ion gel membrane allows for the fast diffusion of amine carriers within it while blocking the diffusion of nonreactive gases, like N2. Thus, the prepared membrane exhibits exceptional CO2 separation capabilities when tested under simulated flue gas conditions with CO2 permeance of 1155 GPU and an ultra-high CO2/N2 selectivity of above 550. Moreover, the membrane retains a stable separation performance during the 170 h continuous test. The excellent CO2 separation performance demonstrates the high potential of gel membranes for CO2 capture from flue gas.

Using Surface-Enhanced Raman Spectroscopy to Probe Surface-Localized Nonthermal Plasma Activation.

Low-temperature, nonthermal plasmas generate a complex environment even when operated in nonreactive gases. Plasma-produced species impinge on exposed surfaces, and their thermalization is highly localized at the surface. Here we present a Raman thermometry approach to quantifying the resulting degree of surface heating. A nanostructured silver substrate is used to enhance the Raman signal and make it easily distinguishable from the background radiation from the plasma. Phenyl phosphonic acid is used as a molecular probe. Even under moderate plasma power and density, we measure a significant degree of vibrational excitation for the phenyl group, corresponding to an increase in surface temperature of ∼80 °C at a plasma density of 2 × 1010 cm-3. This work confirms that surface-localized thermal effects can be quantified in low-temperature plasma processes. Their characterization is needed to improve our understanding of the plasma-induced activation of surface reactions, which is highly relevant for a broad range of plasma-driven processes.

Atomic Layer Etching of GaN and AlGaN Using CH4/H2, H2 and HCl Chemistry

Modern microelectronic components for high-power and high-frequency applications require reliability and reproducibility of the production processes. Atomic layer etching (ALE) represents a key technology for achieving these requirements.An ALE sequence is characterized by a chemical modification step that affects only the top atomic layer of the surface (adhesion) and an ion assisted non-reactive inert gas etching step that removes only this chemically modified area due to creation of volatile byproducts. These two steps are separated by inert gas purge. This grants the etching of single atomic layers. The etching step can be triggered by thermal energy or kinetic energy by impinging particles (e.g. ion bombardment by a plasma). The low energy required for ALE guarantees low-damage etching.In literature ALE processes using Cl2 are often reported. In this work, the results of plasma-enhanced ALE of GaN and AlGaN using different chemistries of CH4/H2, H2 and HCl as etch gases are presented. The experiments were performed with a highly customized etch facility equipped with a capacitively coupled plasma source (CCP, 60 MHz) and a substrate bias generator (RF, 2 MHz). The investigations were carried out on epitaxially deposited GaN on sapphire with masks of protective resist and SiO2 as well as GaN-AlGaN heterostructures with patterned SiO2 maskings. For process analysis optical emission spectroscopy (OES) was carried out. The etching rate and roughness were determined by ellipsometry and atomic force microscopy (AFM) as well as scanning electron microscopy (SEM).Observations by OES indicate a successful excitation and dissociation of the etching molecules. With rising plasma powers physical sputtering effects were revealed. At the beginning of the process development continuous etching processes were examined. With CH4/H2 chemistry using GaN samples it was found that the etching behavior is strongly influenced by the type of masking material. Protective resist resulted in a low etch rate of 7.5 nm/min and significant damage of the masking material. The cause of this behavior is assumed to be redeposition of material by interaction of methane, resist, and plasma. With the change to a hard mask of SiO2 etch rates of 45 to 72 nm/min were achieved, increasing with RF-power and CH4/H2 ratio. Adding methane led to detrimental side effects such as dendrite growth and wall formation on the transient region of unmasked to former masked sample areas. In the further development of the ALE process an etch chemistry using only hydrogen as the chemical etchant was used resulting in an etch per cycle (EPC) of about 3 Å for GaN samples. Further investigations of ALE with hydrogen etch chemistry on GaN-AlGaN samples revealed that AlGaN, in contrast to pure GaN, could not be etched successfully with this chemistry.Substituting CH4/H2 or H2 to HCl enables the etch of AlGaN. The investigations carried out indicate that this etching process is also a self-limiting ALE. AFM measurements revealed an EPC of 1.2 Å for lower RF-powers (50 W). Increasing the RF power to 150 W only slightly enhance the EPC to 2.0 Å. The surface roughness tends to decrease with rising RF-power from 50 to 300 W.

An age- and sex-specific biokinetic model for radon * *This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the US Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published

Publication 137 of the International Commission on Radiological Protection (ICRP) describes a biokinetic model for radon used to derive dose coefficients for occupational intake of radon isotopes. The model depicts transfer of inhaled or ingested radon to blood, exchange of radon between blood and tissues, and gradual loss of radon from the body based on physical laws governing transfer of a non-reactive and soluble gas between materials. This paper describes an age- and sex-specific variation of that model developed for use in an upcoming ICRP series of reports on environmental intake of radionuclides by members of the public titled ‘Dose Coefficients for Intakes of Radionuclides by Members of the Public’. The proposed model modifies the model structure and transfer coefficients presented in Publication 137 to allow more realistic dosimetric treatment of bone marrow and breast and expands the model to address pre-adult ages, based on the physical principles used in the development of the model of Publication 137 together with anatomical and physiological changes occurring during human development.

Role of Ar dilution of SiH4/PH3 gas mixture on PECVD based film growth process, hydrogen bonding configuration, and optical properties of n-type a-Si:H thin films

Amorphous silicon is considered as one of the most promising materials for solar cell applications due to its enhanced optical absorption, high temperature coefficient of resistance, controllable forbidden-band gap, and to reduce the costs of solar panels. In this study, we took notice of the film growth, hydrogen bonding configuration, and optical properties of the phosphorus doped a-Si:H films by varying the dilution of silane using argon gas. Argon gas is a chemically non-reactive gas, but it affects the percentage of silicon atoms during processing. A change in growth process and microstructure factor with varying Ar gas flow is observed, which causes changes in the optical properties of P-doped a-Si:H films. The proportion of SiH bonding rises with increasing argon flow rate, as seen by the infrared-absorption spectra. According to optical tests of the films, the refractive index of the films rises with the Ar flow rate, whereas the band gap Eg decreases. Dilution of SiH4 results in a good-quality film with increased optical conductivity. We established experimental proof of a correlation between band gap and refractive index and compared it with previously reported theoretical models. An investigation into the band gap's dependency on Urbach energy revealed its linearity.

Molecular Dynamics Study of Gas–Surface Interactions on -Cristobalite Surface

In the present work, nonreactive gas–surface interactions between nitrogen molecules and a -cristobalite surface are analyzed using the molecular dynamics framework. A sampling method is employed to perform trajectory calculations, and the tangential momentum accommodation coefficient is computed. The credibility of the reactive force field potential to model cristobalite is investigated, and the effect of the surface and gas temperatures on the tangential momentum accommodation coefficient is studied in detail. The obtained value of the tangential momentum accommodation coefficient (from molecular dynamics analysis) is used as an input parameter in the Maxwell gas–surface interaction model using the direct simulation Monte Carlo method to investigate the surface heat flux on the nose region of a model reentry vehicle. The computed heat-flux results obtained using a molecular-dynamics-derived accommodation coefficient are found to be in excellent agreement with the experimental data.

Characteristics of flame acceleration and deflagration-to-detonation transition enhanced by SF6 jet-in-cross-flow/flame interaction

Jet-in-crossflow (JICF), as a turbulence generator, is proposed to promote the flame acceleration and deflagration-to-detonation transition (DDT) process. Previous work has suggested that JICF using CO2 or Ar was in favor of flame acceleration under optimal conditions. The competition mechanism between the positive combustion-enhancement effect caused by jet-induced turbulence and the negative combustion-inhibition caused by non-reactive gas has been demonstrated. It is worth noting that the difference in molar weight between the medium of JICF and the combustible mixture may significantly impact deflagration propagation prior to DDT. Thus, in this work, to investigate the flame propagation perturbed by the enhancement on the difference in molar weight between the JICF medium and combustible mixture, an experimental study of the flame propagation perturbed by SF6 JICF is carried out. By adjusting the injection pressure (Pj) of the SF6 JICF, the characteristics of flame propagation and DDT are analyzed. The results showed that the flame can accelerate to the onset of detonation within a short run-up distance in the cases with SF6 JICF. Schlieren images of flame evolution show that the flame disturbed by SF6 JICF rapidly transitions to a wrinkled flame. It is suggested that the SF6 JICF-enhanced turbulence promotes flame acceleration and DDT. The effect of SF6 JICF on the flame characteristics can be concluded in two aspects: one is that the inhomogeneously distributed vortices that are induced by JICF cause a nonuniform diffusion of SF6 in the tube, resulting in a nonuniform dilution of the combustible mixture near the jet; another one is that the vortices induced by JICF stretch the flame surface to increase the flame area. Increasing the injection pressure could promote the formation of complex wrinkles in the flame, however, it shows few further improvements in promoting DDT. Different jet mediums are also tested, and the results show that SF6 JICF can shorten the run-up distance significantly compared with helium and nitrogen JICF. The small and densely distributed wrinkles significantly increase the flame area to enhance heat release. The flame disturbed by SF6 JICF could accelerate to the local sound speed of the unburnt mixture, which results in the facilitation of the precursor shock wave formation. After the flame passes through the SF6 JICF, it remains a larger acceleration rate and then transitions to quasi-detonation rapidly. The conclusion of this work could help to qualitatively understand the positive effect of JICF-induced turbulence on flame acceleration and DDT. It also provides a relatively efficient and safe technology to promote detonation initiation in the design of detonation engines.

Numerical simulations of solid cerium ejecta transporting in vacuum and in non-reactive and reactive gases

When a shock wave impacts a roughened metal/gas interface, metal ejecta particles emit and transport in the gas. The exchanges of momentum and energy between ejecta particles and the gas occur. If active metal particles transport in the reactive gas, the heat released by a chemical reaction could change these exchanges. In this paper, we use numerical simulations to study solid cerium ejecta transporting in a vacuum, and in non-reactive and reactive gases. In vacuum, the emitted ejecta could self-similarly expand neglecting the particle interaction. In the non-reactive gas (He), ejecta particles slow down by the gas resistance and have the exchanges of momentum and energy with the gas. In the reactive gas (D2), the ejecta particles also slow down. The exothermic reaction could induce the temperature rise of the ejecta and the gas, which could induce changes in physical property values of the gas after the shock wave and the velocity of the shock wave. The numerical result shows that the maximum temperature of the ejecta may appear in the middle of the mixture zone, which may result from the ejecta temperature being controlled by two competitive effects. Furthermore, the maximum ejecta temperature increases rapidly in the beginning and then becomes steady. Finally, the ejecta with a different initial size distribution is investigated. The ejecta with a smaller maximum size has a larger maximum particle temperature, a larger gas temperature after the shock wave, and a larger chemical reaction function of the ejecta at the same moment.

Numerical analysis on the effect of diluted hydrogen fuel by a fixed amount of supplied hydrogen using a quasi-three-dimensional solid oxide fuel cell model

Solid oxide fuel cell (SOFC) has excellent fuel flexibility for various fuels. Despite some drawbacks like storage and transportation, hydrogen stands up as the best fuel for SOFC. Hydrogen fuel is diluted non-reactive gas species before it is supplied to the SOFC. In this study, a quasi-three-dimensional SOFC model with real microstructure is used to analyse the effect of the diluted fuel mixture. The hydrogen fuel is diluted with nitrogen and a small amount of steam. The mole amount of hydrogen within fuel mixtures is kept constant. On the other hand, the air that is supplied to the air channel of the SOFC remains unchanged. It is found that the cell that is supplied with the highest concentration of hydrogen has the highest performance due to its high partial pressure of hydrogen within the fuel mixture. Such a high partial pressure promotes a low anode concentration loss. Also, the cell that is supplied with a low hydrogen concentration is unable to benefit from its high average cell temperature as its performance is drained by the low partial pressure of hydrogen within the fuel mixture.

Neutral transport during etching of high aspect ratio features

This paper studies the transport of neutral etch species in cylindrical holes, which are of interest for advanced memory devices. The etching of these devices utilizes ions and neutral reactive species, which must travel to the etch front deep inside the feature. For gas pressures in the millitorr and feature sizes in the nanometer range, neutrals reach the bottom of an etching feature via the Knudsen transport1,2. For an aspect ratio of depth to diameter of 100:1, the flux at the bottom of the feature is only 1.3% of the incoming flux. This is a challenge for etching of advanced memory devices with ever increasing aspect ratios. We present computational results for the neutral transport in high aspect ratio features as a function of aspect ratio, profile shape, and surface processes such as adsorption, desorption, and diffusion of neutral species. Pertinent parameters are varied over a wide range to identify salient trends. When available, we include values for the case of fluorine radicals on silicon and silicon oxide in the parameter scans. The results predict that steady state transmission probability increases meaningfully in the presence of surface diffusion. Spontaneous and collision induced desorption of adsorbed neutrals on their own does not change steady state transmission probability, but they affect the time to reach it. In the presence of surface diffusion, however, spontaneous desorption increases the transmission probability, while desorption due to collisions with co-flowing nonreactive gas reduces it. These results indicate an enhancement of neutral transport at low surface temperatures that facilitate physisorption and surface diffusion.

The effect of background argon gas pressure on parameters of plasma produced by Dc- glow discharge

Non-thermal plasmas have become popular as plasma technology has advanced in various fields, including waste management, aerospace technology, and medicinal applications. They can be used to replace combustion fuels in stationary hall motors and need little effort to keep running for longer periods of time. To improve overall system performance, non-reactive gases such as )Xe, Ar, and Kr) are utilized in pure or mixed form to generate plasma. Since DC glow discharge is a fundamental topic of importance, these gases have been researched. The paper concentrates on 2-D modeling and simulation. DC glow-discharge tubes are utilized with argon gas to create plasma and learn about its properties. The magnitude of the electron density, increases with rising pressure, whilst the rest of the parameters gradually decrease with increasing pressure

Surface topologies and self interactions in reactive and nonreactive Richtmyer–Meshkov instability

The reactive Richtmyer–Meshkov instability (RMI) exhibits strong wrinkling of a reactive flame front after an interaction with a shock wave. High levels of deformation and wrinkling can cause the flame surface to intersect with itself, leading to the events of flame self interactions (FSI). As FSI can have a significant influence on the development and topology of the flame surface, it should be considered an important factor affecting the burning characteristics of the flame. The topological structure and statistics of FSI are analyzed using data from high-fidelity simulations of a planar shock wave interacting with a statistically planar hydrogen/air flame for stoichiometric, lean and nonreactive gas mixtures. FSI events are detected by searching for critical points in the field of the reaction progress variable c and divided into the following topological categories: burned gas mixture pocket (BP), unburned gas mixture pocket (UP), tunnel formation (TF) and tunnel closure (TC). It is found that reactivity and flame thickness are decisive factors, influencing the frequency and topological distribution of the detected FSI events. While in early RMI-stages the FSI is found to be mainly dependent on the flame thickness, later stages are heavily influenced by the reactivity, as high reactivity quickly burns out emerging wrinkled structures (in the stoichiometric case) leading to massively reduced levels of FSI. The findings are further supported by the results from the nonreactive case, which at later stages of the RMI closely resembles the less reactive lean case. Analysis of the topology distribution over time and conditioned over c, reveals further differences between the lean and stoichiometric case, as the strong wrinkling and mixing encountered with the lean case facilitates the build up of many pocket-type and tunnel-type interactions throughout the wrinkled flame front. For the stoichiometric case, mainly tunnel-type and unburned pocket topologies are found in the narrow flame funnels extending into the burned gas.

The Role of Convective Up- and Downdrafts in the Transport of Trace Gases in the Amazon.

Deep convective clouds can redistribute gaseous species and particulate matter among different layers of the troposphere with important implications for atmospheric chemistry and climate. The large number of atmospheric trace gases of different volatility makes it challenging to predict their partitioning between hydrometeors and gas phase inside highly dynamic deep convective clouds. In this study, we use an ensemble of 51,200 trajectories simulated with a cloud-resolving model to characterize up- and downdrafts within Amazonian deep convective clouds. We also estimate the transport of a set of hypothetical non-reactive gases of different volatility, within the up- and downdrafts. We find that convective air parcels originating from the boundary layer (i.e., originating at 0.5km altitude), can transport up to 25% of an intermediate volatility gas species (e.g., methyl hydrogen peroxide) and up to 60% of high volatility gas species (e.g., n-butane) to the cloud outflow above 10km through the mean convective updraft. At the same time, the same type of gases can be transported to the boundary layer from the middle troposphere (i.e., originating at 5km) within the mean convective downdraft with an efficiency close to 100%. Low volatility gases (e.g., nitric acid) are not efficiently transported, neither by the updrafts nor downdrafts, if the gas is assumed to be fully retained in a droplet upon freezing. The derived properties of the mean up- and downdraft can be used in future studies for investigating convective transport of a larger set of reactive trace gases.

Interaction of Shock Waves with Water Saturated by Nonreacting or Reacting Gas Bubbles.

A compressible medium represented by pure water saturated by small nonreactive or reactive gas bubbles can be used for generating a propulsive force in large-, medium-, and small-scale thrusters referred to as a pulsed detonation hydroramjet (PDH), which is a novel device for underwater propulsion. The PDH thrust is produced due to the acceleration of bubbly water (BW) in a water guide by periodic shock waves (SWs) and product gas jets generated by pulsed detonations of a fuel–oxidizer mixture. Theoretically, the PDH thrust is proportional to the operation frequency, which depends on both the SW velocity in BW and pulsed detonation frequency. The studies reported in this manuscript were aimed at exploring two possible directions of the improvement of thruster performances, namely, (1) the replacement of chemically nonreacting gas bubbles by chemically reactive ones, and (2) the increase in the pulsed detonation frequency from tens of hertz to some kilohertz. To better understand the SW-to-BW momentum transfer, the interaction of a single SW and a high-frequency (≈7 kHz) sequence of three SWs with chemically inert or active BW containing bubbles of air or stoichiometric acetylene–oxygen mixture was studied experimentally. Single SWs and SW packages were generated by burning or detonating a gaseous stoichiometric acetylene–oxygen or propane–oxygen mixture and transmitting the arising SWs to BW. The initial volume fraction of gas in BW was varied from 2% to 16% with gas bubbles 1.5–4 mm in diameter. The propagation velocity of SWs in BW ranged from 40 to 580 m/s. In experiments with single SWs in chemically active BW, a detonation-like mode of reaction front propagation (“bubbly quasidetonation”) was realized. This mode consisted of a SW followed by the front of bubble explosions and was characterized by a considerably higher propagation velocity as compared to the chemically inert BW. The latter could allow increasing the PDH operation frequency and thrust. Experiments with high-frequency SW packages showed that on the one hand, the individual SWs quickly merged, feeding each other and increasing the BW velocity, but on the other hand, the initial gas content for each successive SW decreased and, accordingly, the SW-to-BW momentum transfer worsened. Estimates showed that for a small-scale water guide 0.5 m long, the optimal pulsed detonation frequency was about 50–60 Hz.

The temperatures of ejecta transporting in vacuum and gases

In this work, we measure continuous thermal radiance from evolving clouds of liquid metal fragments ejected into vacuum, nonreactive, and reactive gas. We implement a model for the thermalization of the ejecta and gas and use this to constrain the absolute temperature of the ejecta cloud. This model enables further analyses of ejecta thermal behavior under a variety of conditions.

Effects of jet/flame interaction on deflagration-to-detonation transition by non-reactive gas jet in a methane-oxygen mixture

Jet-in-crossflow (JICF) is a potential and reliable technique that can promote flame acceleration and deflagration-to-detonation transition (DDT). Most of the previous researches utilized combustible mixture or oxygen as the medium of JICF, therefore the detonation enhancement effect may be partly attributed to the chemical properties of the jet, and the purely turbulent effect induced by JICF on DDT has not been fully understood. In our previous work, the non-reactive gas jet affected flame propagation indirectly by separating the injection and ignition in the control sequence. A competing mechanism between the positive combustion-enhancement effect caused by jet-induced turbulence and the negative non-reactive gas-inhibition effect on combustion has not been found, the non-reactive gas jet with high pressure and short duration time was also verified to be beneficial for precursor shock wave formation and flame acceleration. However, no detonation was observed in the work. In this paper, the non-reactive jet interacts with the flame propagation directly by overlapping the working time of the jet and ignitor partly, and the effect of jet parameters including injection pressure and time delay on DDT is investigated systematically. The results show that the flame affected by the non-reactive gas jet with a high-pressure ratio and a short time delay can transit to detonation in a short run-up distance successfully. The schlieren images of the flame evolution process illustrate that the flame interacted by the jet experiences four states: layered flame, wrinkled flame, cellular flamelets, and turbulent flame. Kelvin–Helmholtz (K-H) instability and Rayleigh-Taylor (R-T) instability dominate in the flame distortion. The characteristic timescales of the flow and reaction are computed in the four flame states, turning out that as the flame evolving, the turbulent intensity of the flame is enhanced. Damköhler number (Da) on the flame front eventually converges to [1,2] demonstrates the characteristic timescales of the turbulence and reaction are on the same order, and the turbulence dominates the flame evolution.

Investigation of the effect of turbulence induced by double non-reactive gas jet on the deflagration-to-detonation transition

Jet-in-crossflow (JICF) is proved to be advantageous to accelerate flame propagation and stimulate the deflagration-to-detonation transition (DDT) process in the recent decade. Studies focused on the performance of the jet of combustible mixture or reactive gas on facilitating the DDT process are carried out, and the results show that the combustible JICF can promote the flame transition to detonation efficiently. Although most investigations attribute the ability of the JICF on promoting DDT to the turbulent effect induced by the jet, the combustion-enhancement effect of the jet medium is seldom considered. In our previous work, it is proposed that the non-reactive gas jet in an optimal condition can accelerate flame propagation and promote the precursor shock wave formation. Hence, the performance of the multi-jet of non-reactive gas on facilitating the DDT process is worth investigating. In this paper, three different double jet placement methods are designed: parallel, staggered, and opposite positioned, and their performances on accelerating flame propagation and promoting the DDT process are investigated systematically. The results indicate that the staggered jet can accelerate the flame to detonation within a short run-up distance whereas the parallel jet and the opposite jet can only make the flame accelerate slightly. The schlieren images of flame evolution affected by double jet indicate that the complicated reactivity gradients generate on the flame surface while the flame is disturbed by the double jet. The interaction between the staggered jet and the flame induces local explosions, which results in a prominent increase of the flame area and a large volumetric burning rate. For the opposite jet, its negative effect of combustion-inhibition of the aggregated CO2 overwhelms the positive effect of turbulence-enhancement on the flame acceleration.