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A multichannel gliding arc (MCGA) plasma is used to control the jet-wake stabilized combustion in a Mach 2.92 cavity-based and ethylene-fueled scramjet combustor. Optical diagnostic methods (including high-speed photography, schlieren, and planar laser-induced fluorescence with acetone tracer) combined with plasma kinetic simulations and Reynolds-averaged Navier–Stokes/large-eddy simulations were employed to investigate the combustion behaviors. The results show that the flame is mainly located near the cavity leading edge and operated at the jet-wake stabilized mode. When the MCGA plasma is added at the upstream wall of the cavity leading edge, the vigorous region of the flame spreads upstream 6.5 times longer than the original one without the plasma. Once the plasma is turned off, the flame returns back to the cavity leading edge. The species [Formula: see text] (Nitrogen in the excited state) and hydrogen atoms produced by the plasma are favorable for igniting the flame near the plasma, and the average penetration depth of the fuel above the plasma is increased by about 10%. Intense combustion near the plasma occurs with higher pressure, establishing the recirculation zone with the boundary-layer separation. The combined effects of the reactive species produced, the elevated temperature, and the modified flowfield induced by the plasma contribute to the MCGA-controlled behaviors of jet-wake stabilized combustion.

With the development of aviation industry, it is urgently to investigate the soot formation properties of aviation kerosene to better control the soot emissions. The dilutive, chemical and radiative effects of CO2 on the soot inception, condensation and hydrogen abstraction acetylene addtion (HACA) growth processes in laminar co-flow Jet-A1 kerosene diffusion flames were numerically investigated by employing detailed chemical mechanisms and soot sectional models. The results showed that the addition of CO2 dramatically decreased the maximum temperature (by 92 K) and soot volume fraction (by 41.0%). The dilutive effect of CO2 contributed the most to the decrease of temperature and soot volume fraction. It also was the main factor in the decrease of soot inception, condensation and HACA growth processes. The chemical effect of CO2 had little impact on the decomposition of fuels into light hydrocarbons, but obviously limited the growth of light hydrocarbons to A1. The radiative effect of CO2 decreased the maximum temperature and soot volume fraction by 13 K and 5.2% (from 1.92-1.82 ppm). It had little impact on the soot inception, condensation and HACA growth rates.

This study experimentally investigated the combustion process in a cavity-based supersonic combustor at the inflow condition of Mach 2.92 with stagnation pressure 2.6 MPa and stagnation temperature 1530 K. Time-averaged flame distribution and oscillation characteristics were revealed by post-processing CH* chemiluminescence images. Wall pressures along the combustor bottom wall were also measured to provide quantitative information. Representative cascaded injection set-ups upstreaming the cavity were selected to compare ethylene flame characteristics. It is found that the combustion process is approaching thermal chocking when increasing the equivalence ratio to 0.8 according to the one-dimensional analysis of the Mach number distribution. At the same equivalence ratio, increasing the number of the cascaded injectors by lowering the injection pressure is not beneficial for the combustion enhancement, indicating that the injection pressure is also a key factor affecting the combustion heat release. However, increasing the injection pressure can cause obvious flame oscillations above the cavity as well as increasing the axis distance of the injectors. As a result, the injection scheme with two cascaded injectors which have the injection distance of 0.1 and 0.4 time the length of the cavity floor, respectively, upstreaming the cavity is suggested as a favorable scheme for scramjet applications.

Photofragmentation laser-induced fluorescence (PF-LIF) of methyl radical ( CH 3 ) and planar laser-induced fluorescence (PLIF) of formaldehyde ( CH 2 O ) were simultaneously carried out in premixed methane-air turbulent flames to visualize flame structure and extract quantitative features of CH 3 and CH 2 O layers. A CH 3 layer is located along the edge of a CH 2 O layer, and they partially overlap with each other. CH 3 is closer to the reaction zone of a premixed flame compared with CH 2 O that is regarded as a typical marker of the preheating zone. The results show that the CH 3 can be served as a flame marker for the transitional zone between the preheating zone and the reaction zone. The thicknesses of CH 3 and CH 2 O layers and their distances were then quantitatively estimated to reduce the influence of layer merging and strong curvature. It was found that the broadening of CH 2 O layers against turbulence is more sensitive than that of CH 3 layers. In stoichiometric and rich flames, layer broadening was clearly observed even with a slightly increased Karlovitz number.

The dynamic mixedness characteristics of a bluff-body stabilized turbulent jet under transverse acoustic excitations are investigated using high-repetition-rate acetone planar laser-induced fluorescence (PLIF) at 7 kHz and multipoint scanning hot-wire measurements. Acetone mixedness imaging is made for the turbulent jet to assess the interaction between the turbulent jet and the imposed transverse acoustic excitations at a driving frequency of 50 Hz. The high-repetition-rate acetone PLIF images show that the acetone mixedness distribution swings left and right frequently under the transverse acoustic excitation, and the deflection angle can reach about 6°. The mixedness area of a turbulent jet flow can also be increased by 13.3% when excited by a transverse acoustic wave. Meanwhile, the sequence of acetone instantaneous PLIF images illustrates how the wrinkled edges are generated when acoustic excitations are imposed. The curvature of the acetone PLIF interface shows that the portion of large curvatures increases to 1.6 times after applying an acoustic wave of 123 dB. Multipoint hot-wire measurements further stress that the turbulence intensity at the transverse acoustic excitation of 123 dB increases to be about 1.3 times the natural turbulence. The proper orthogonal decomposition results show that the large and small scales of the jet wrinkles both increase with the sound pressure level. RANS transient simulation also implies that a stronger turbulent kinetic energy distribution and distorted velocity streamlines can be achieved inside the turbulent jet due to the transverse acoustic excitation. They can further lead to increased mixing between the turbulent jet and the surrounding air.

The combustion modes in two different scramjet combustors with the mass flow rates of 1.8 kg/s and 3.6 kg/s are experimentally investigated to explore the scaling effects on supersonic combustion with a Mach number 2.0 inflow. It is found that the scramjet combustor with a larger scale can broaden the flame rich blowout limit. As the Equivalence Ratio (ER) increases, the combustion in the small-scale combustor maintains in the cavity-stabilized mode, and the flamebase moves downstream along the cavity shear layer; however, the combustion in the large-scale combustor gradually transfers from the cavity-stabilized mode to the jet-wake-stabilized mode. The differences in the cavity residence time, the ignition delay time and the Damkohler number caused by different scales of the scramjet combustor are likely to account for the scaling effects on the combustion modes.

A gliding arc discharge with an averaged power of 200 W at atmospheric pressure was used to support the supersonic combustion of ethylene fuel with an inflow speed of Mach number 2.92. The instantaneous wall pressure of the combustion chamber and the high-speed CH* chemiluminescence imaging were simultaneously measured to show the characteristics of the gliding arc plasma assistance combustion. The results show that the gliding arc increases the average wall pressure. Specifically, as for the fuel injector near the front step of the cavity, the wall pressure downstream of the aft ramp wall increased at different global equivalence ratios, even increasing the wall pressure upstream of the fore wall of the cavity at an equivalence ratio of 0.1. For the injector away from the fore wall of the cavity, the presence of the gliding arc promotes the wall pressure downstream of the aft ramp wall. In the presence of the gliding arc, the emission intensity and the area of the flame in the cavity are weakened at a low global equivalence ratio (0.10–0.12), whereas the effect is not significant at a range of the total equivalence from 0.15 to 0.2. In the high equivalence ratios from 0.22 to 0.29, the gliding arc plasma plays a significant role in combustion enhancement owing to an increase in the emission intensity and the area of the cavity flame.

Flame stabilization with cavity-strut injection of ethylene in a single-side expansion scramjet combustor is experimentally investigated in a Mach 2.1 supersonic flow. Two cavity geometries with different length-to-depth ratios of 3.2 and 4.5 and two injection schemes with different injection distances upstream the cavity are used to compare their combustion characteristics in this study. Flame dynamics with different cavity geometries and injection schemes are visualized comprehensively using high-speed imaging and static pressure measurements. Two different combustion stabilization modes are recognized, including the jet wake mode and the cavity shear layer mode. The transition process between the two modes is also observed in the experiments. Flame oscillations are often accompanied by the transition of the combustion modes. It is indicated that although increasing the cavity length-to-depth ratio can strengthen the exchange of momentum and heat to promote combustion, it also leads to intensified flame oscillations. When the injection distance upstream of the cavity increases, the flame oscillations become more intense, and the total heat release from the combustor decreases accordingly. In order to obtain a robust combustion process, it is suggested that the flame should be stabilized in the cavity shear layer mode and the mode transition should be suppressed to some extent.

A gliding arc discharge with an averaged power of 630 W at atmospheric pressure was used to ignite an ethylene-fueled scramjet combustor with an inflow speed of Mach number 2.92. The instantaneous power of the plasma and the high-speed CH* chemiluminescence imaging of the ignition process was simultaneously measured to show dynamic characteristics of the gliding arc plasma-assisted ignition. The results show that the power spikes of the spark-type discharges are the key factor to generate the flame kernel in the scramjet combustor and the instantaneous power can reach 3168 W during the power spikes. The flame kernel ignited by the gliding arc discharge can be developed to form an initial flame, which can become larger with increasing contained discharge energy of the gliding arc. Moreover, a comparison between the successful initial flame and the failed initial flame is performed to demonstrate that the larger area of the successful initial flame can propagate for achieving the mainstream flame, whereas the failed initial flame generated multiple times until the successful initial flame was observed. It is concluded that the successful initial flame contains more discharge energy during the initial flame formation, leading to form the resident flame in the recirculation zone.

Metal coatings can protect the fragile optical fiber sensors and extend their life in harsh environments. However, simultaneous high-temperature strain sensing in a metal-coated optical fiber remains relatively unexplored. In this study, a nickel-coated fiber Bragg grating (FBG) cascaded with an air bubble cavity Fabry-Perot interferometer (FPI) fiber optic sensor was developed for simultaneous high temperature and strain sensing. The sensor was successfully tested at 545 °C for 0-1000 µɛ, and the characteristic matrix was used to decouple temperature and strain. The metal layer allows easy attachment to metal surfaces that operate at high temperatures, enabling sensor-object integration. As a result, the metal-coated cascaded optical fiber sensor has the potential to be used in real-world structural health monitoring.

Medical image segmentation is a fundamental step in medical analysis and diagnosis. In recent years, deep learning networks have been used for precise segmentation. Numerous improved encoder–decoder structures have been proposed for various segmentation tasks. However, high-level features have gained more research attention than the abundant low-level features in the early stages of segmentation. Consequently, the learning of edge feature maps has been limited, which can lead to ambiguous boundaries of the predicted results. Inspired by the encoder–decoder network and attention mechanism, this study investigates a novel multilayer edge attention network (MEA-Net) to fully utilize the edge information in the encoding stages. MEA-Net comprises three major components: a feature encoder module, a feature decoder module, and an edge module. An edge feature extraction module in the edge module is designed to produce edge feature maps by a sequence of convolution operations so as to integrate the inconsistent edge information from different encoding stages. A multilayer attention guidance module is designed to use each attention feature map to filter edge information and select important and useful features. Through experiments, MEA-Net is evaluated on four medical image datasets, including tongue images, retinal vessel images, lung images, and clinical images. The evaluation values of the Accuracy of four medical image datasets are 0.9957, 0.9736, 0.9942, and 0.9993, respectively. The values of the Dice coefficient are 0.9902, 0.8377, 0.9885, and 0.9704, respectively. Experimental results demonstrate that the network being studied outperforms current state-of-the-art methods in terms of the five commonly used evaluation metrics. The proposed MEA-Net can be used for the early diagnosis of relevant diseases. In addition, clinicians can obtain more accurate clinical information from segmented medical images.

Interferometric Rayleigh scattering technique is commonly employed to measure single-point velocity fluctuation and its standard deviation in a high-speed flow due to many benefits, such as high accuracy, easy data interpretation, and high sampling rate. However, this technique suffers from a severe problem often referred to as the weak Rayleigh scattering signal, especially in the supersonic and hypersonic flow with an extremely low gas molecule density. An asymmetry cavity structure that could cost-effectively improve the Rayleigh scattering (RS) signal of interest is designed and used in the interferemetric Rayleigh scattering technique. The ZEMAX simulations suggest that the parallel beam can be repeatedly reflected in the resonant cavity and can be focused in a measurement region with the order of 0.67 mm×1.31 mm. The number of propagating rays inside the cavity can reach about 50. The fidelity of this proposed cavity is then verified by the Rayleigh scattering imaging experiments. Results show that this cavity allows the laser beam to reflect several times in the resonant cavity, and the RS signal intensity in the major axis can be 10.4 times larger than that of the incident laser. The cavity is finally employed under realistic supersonic flow velocity measurements, where the results conclusively illustrate that the Rayleigh scattering signal of interest in a single direction can be improved by a factor of 4∼5. In addition, the bi-directional (both the axial and radial directions) velocity parameters can also be obtained simultaneously. The axial velocity and its standard deviation are similar to conventional single-line ones.

Methyl linolenate (C18-3) is a type of unsaturated fatty acid methyl ester with high biological activity. Membrane separation of C18-3 from tallow seed oil methyl ester by supported ionic liquids membranes (SILM) containing carrier Ag+ was successfully achieved in this study. The interaction between Ag+ and C18-3 was explored by density functional theory (DFT). High selectivity to C18-3 was mainly due to the π/inverse π complexation interactions between Ag+ and C=C bonds. The effects of ionic liquid structure, carrier Ag+ concentration, adjacent phase flow rates and membrane pore size on permeability and selectivity to C18-3 were examined. The existence of 1-hexene in the stripping phase and carrier Ag+ can facilitate C18-3 transport. Good separation performance was achieved by the 0.45 μm nylon membrane impregnated with ionic liquid [BMIm]BF4 containing AgBF4. C18-3 was enriched from 16.7% in the feed phase to higher than 75% in the product. Moreover, adding a hydrophobic PVDF protective membrane to form a composite membrane was an effective method to increase the SILM stability and membrane lifetime by about twice compared with a single nylon membrane.

Methyl linolenate was separated from its analogues by a new extraction system constructed by solvent, imidazolium based ionic liquids and cuprous salt. Firstly, the effect of ionic liquid on the dissolution of CuCl in acetonitrile, N,N-dimethylformamide (DMF), methanol and water was evaluated by visual observation. [C4Mim][Cl] can improve the dissolution of CuCl in acetonitrile. Then, for the new system as acetonitrile-ILs-CuCl, extraction equilibrium, distribution ratio and selectivity of methyl linolenate and its analogues were determined by gas chromatography analysis and the mass balance. The extraction time, IL structures and CuCl concentrations were investigated. Distribution ratio decreased slightly, but selectivity increased significantly with the addition of CuCl, [C4Mim][Cl] or [C4Vim][NTF2] into acetonitrile. [C4Vim][NTF2] had higher selectivity than [C4Mim][Cl]. But the selectivity of the system combining CuCl with [C4Vim][NTF2] was much lower than with [C4Mim][Cl]. For the CuCl-[C4Mim][Cl]-acetonitrile, the extraction efficiency was better than CuCl-acetonitrile, increasing Cu+ concentration effectively improved the separation selectivity when ratio of CuCl/[C4Mim][Cl] was less than 1. Compared with previous aqueous AgNO3 extractions, the method of using CuCl is a much cheaper and practical way to enrich unsaturated fatty acid.

The ultra-wide band (UWB) radar sensor is widely used in Radar-based Life Detecting System for search and rescue due to its short detection time, high penetrating power and low energy consumption. However, performance of non-contact detection is limited in complex post-disaster environments due to the noise and clutter. In this paper, a hybrid feature extraction method based on Hilbert-Huang Transform (HHT), Fast Fourier Transform (FFT) and correlation analysis is proposed to obtain the echo signal features. Then a classification model based on support vector machine (SVM) is established to identify the respiratory information embedded in the echo signal. The experimental results show that the proposed method can accurately identify the location of human body through different obstacles.

Planar laser-induced fluorescence (PLIF) techniques have been widely used for flame structure visualization in recent years. Nevertheless, most of the studies were concerned with qualitative analysis of the obtained images and the quantitative analysis were much fewer. This work presents a quantitative feature extraction method to process the ribbon structures that are captured in images and represent the radical layers in flames. The extracted features include ridge lines, curvatures, and thicknesses. This method was demonstrated by processing the images of methyl (CH3) photofragmentation laser-induced fluorescence (PF-LIF) and formaldehyde (CH2O) PLIF measurements in stoichiometric, premixed methane/air flames. The flames were generated by a McKenna burner under the Reynolds numbers of 1930, 3870, and 5800. The ridge lines followed well with the wrinkled layers of CH3 and CH2O. The CH2O layers were thickened, but the CH3 layers had minor change with increased Reynold numbers.

The effect of combustion on a gliding arc (GA) discharge is investigated using simultaneous measurements of current and voltage waveforms, as well as imaging and spectroscopic analysis of plasma and flame luminescence. Attributed to the existence of flame, the breakdown voltage and current peak are reduced and the bright sparks during breakdown are dampened. The intrinsic reason is largely owing to the thermal effect of flame. Electrical breakdown is mainly determined by the reduced electric field strength (E/N), which is inversely proportional to temperature. Assuming a constant E/N for breakdown, the combustion-induced temperature increment gives rise to a reduction of the breakdown voltage. The gas composition seems to have less impact on the breakdown voltage. However, the addition of CH 4 can induce more radicals (e.g., H atoms) that enhance the intensity of relevant spectral emissions, especially from OH*. Due to the transport of relatively long-lived radicals, the width of the plasma column of the GA discharge is broadened to form a local reaction zone, serving as a flame holder. Interestingly, the plasma channel moves more smoothly as the flame is present. It implies that the flow field is less turbulent owing to combustion.

Whereas discharge characteristics of a gliding arc have previously been investigated in a low-speed subsonic flow without considering the effect of shock waves and extremely high turbulence, we here studied an important physical feature of the gliding arc in a supersonic flow that generates complex shock waves and extremely high turbulence. The gliding arc in a 1.2 Mach supersonic jet air flow is investigated by high-speed imaging, schlieren imaging, electrical measurements, and the large eddy simulation. The experimental results show that high-repetition transitions between the spark-type discharges and the glow-type discharge with a frequency of 1.4–2.1 MHz can be observed in the supersonic flow after the gliding arc is generated between the narrowest gap of knife-shaped electrodes, whereas the similar phenomena are invisible in a low-speed subsonic flow. It can be recognized that the high-repetition transitions occur in the region with complex structures of shock waves and expansion waves. The large velocity/density gradient generated by the complex wave structures and the small-scale vortices produced by the strong turbulence is located near the position where the high-repetition transitions occur. The high-repetition transitions between the spark-type discharges and the glow-type discharges are found to be mainly caused by the combined effects of the strong turbulent eddy transportation in the supersonic flow and the drastic change in the flow properties across the shock wave, shedding light on the mechanism of the high-repetition discharge transitions of the gliding arc in a supersonic flow.

Reliable and fast ignition of scramjet engine is quite important in consideration of high velocity and low pressure of inlet air. Successful ignition requires that sufficient ignition energy be injected into the flame kernel so that the flame propagates outwardly beyond the critical initial radius of the critical flame. Larger critical flame initiation radius is required during the preliminary stage of scramjet engine so advanced ignition technology for scramjet engines is urgently needed. In this study, multichannel plasma igniter (MCPI) is proposed to induce a relatively larger ignition kernel for the purpose of achieving successful ignition in scramjet engines. Ignition experiments in a model scramjet combustor fueled by ethylene were conducted with inflow conditions of Ma = 2.52, stagnation pressure P 0 = 1.6 MPa and stagnation temperature T 0 = 1600 K. Ignition processes of SI and MCPI at different fuel injection schemes were captured by CH∗ chemiluminescence imaging and flame luminosity imaging technology. Results reveal that MCPI with five channels generates 5 times more ignition energy than SI and MCPI can generate much larger plasma volume and activated area which can induce a relatively larger initial flame kernel. The CH intensity of MCPI was about 2.2 times larger than that of conventional SI. Besides, it was shown that the lean ignition limit of scramjet combustor through MCPI was extended by 20–26% than that through SI and the ignition time was reduced by approximately 50%. MCPI with an injection 10 mm upstream the cavity demonstrates the best performance in this study.

Experimental investigations of laser-induced plasma (LIP) ignition processes were conducted in an ethylene-fueled scramjet combustor with a rear-wall-expansion cavity. The results were obtained und...

The ignition processes in an ethylene-fueled supersonic combustor excited by laser-induced plasma (LIP) were investigated experimentally under the condition of inflow Ma number of 2.92. The LIP excitation was implemented near the center floor of a flameholding cavity. Optical measurements, including simultaneous CH∗/OH∗ chemiluminescence imaging and Schlieren photography, were used to investigate the ignition processes. It is found that the CH∗ and OH∗ initiated by the LIP are mainly in the region between the cavity front wall and the LIP excitation site. The CH∗ and OH∗ are quenched rapidly, in particular at a low fueling rate. After a short delay, the distribution of CH∗ and OH∗ appears in the region between the rear wall of the cavity and the LIP excitation site, showing the onset of ignition therein. A stable flame was established in the shear layer between the downstream part of the cavity and the outer supersonic flow. It is concluded that the ignition processes excited by the LIP can be divided into a LIP initiation regime and a transient ignition reaction regime. Both the fueling rate and the LIP energy significantly affect the cavity ignition processes. Increasing the fueling rate or the laser energy can shorten the ignition processes in the cavity. A weak ignition mode and an intense ignition mode are postulated to explain the combustion behavior of the ignition processes in the cavity-based supersonic combustor.

Ignition and flame stability in supersonic flow have always been the key problems of research in scramjet. In addition, ignition is difficult and the cavity flameholder is susceptible to support the flame stability under extreme conditions such as low equivalent ratio. In recent years, gliding arc plasma is recognized to expand ignition and extinction limit with lower energy consumption in the field of plasma assisted ignition due to its heating and chemical effects. In this paper, a gliding arc igniter has been designed and compared with the traditional spark plug in order to quantify the ignition ability. The igniter has the same size with the spark plug, using low-power AC gliding arc to carry out ethylene ignition test in Ma = 2.52 Ma supersonic flow. The average power of gliding arc discharge is 1199 W. A high-speed camera and CH⁎ chemiluminescence were used to make combustion diagnosis. Founded in the same discharge period, the lean ignition limit of the gliding arc is lower than the ignition limit of the spark. The average expansion of ethylene ignition limit is 17%. The ignition process is that gliding arc continues to generate the initial flame kernels during the discharge period, but it is extinguished continuously due to the strong convection. Until generating an initial flame kernel which can successfully propagate the flame. The ignition process can be divided into four stages. It continues to generate new flame kernels in flame propagation process. Gliding arc reignites the fuel and generates the new flame kernels after forming a stable flame, appearing intermittent ignition in the cavity. The high equivalent ratio can make ignition delay time shorter, generating initial flame kernels more frequently. The heating effect of the gliding arc and reignition character make the thermal product and ethylene occur intermittent combustion more often in the cavity, increasing the area of the combustion reaction. Gliding arc plasma can achieve combustion enhancement during the flame stabilization process. The shear layer of flame thickness increased by the average of 2 mm on S-B-1 and G-B-1 conditions. Compared with the traditional spark ignition, gliding arc broaden the lean blow-off limit in different stages may be the significant reason for broadening lean ignition limit. It concludes that gliding arc makes the flame's ignition limit closer to the flame's blow-off limit.

Laser-induced plasma (LIP) ignition processes in a cavity-based scramjet combustor were investigated experimentally in this study. CH⁎ spontaneous emission recorded at a flame rate of 50 kHz was used to characterize the ignition and flame stabilization processes. Numerical calculation was also performed to characterize the non-reacting flow-field structures. Effect of cavity fueling schemes on the LIP ignition process in the rear-wall-expansion cavity was then examined. It is found that the cavity fueling scheme acts as a dominant factor in a LIP ignition process. After a LIP ignition in the cavity rearward, the initial flame kernel is likely to anchor and grow directly in the rearward of the cavity under cavity upstream fueling schemes. However, the flame kernel will propagate towards the cavity leading edge and grow there under cavity direct fueling schemes. It is concluded that both chemical and turbulent issues of the flow-field affect the LIP ignition process. Local fuel-rich environment inside the cavity is favorable for a LIP ignition process, and the fueling scheme with parallel fuel injectors upstream the cavity is most favorable for a LIP ignition which presents a stable combustion process.

Spark ignition processes in an ethylene-fueled scramjet combustor with a rear-wall-expansion geometry were investigated experimentally at the inflow condition of Ma = 2.92 with a stagnation pressure 2.6 MPa and a stagnation temperature 1530 K. Optical measurements including OH ∗ , CH ∗ spontaneous emission and high-speed photography of flame luminosity, were carried out to characterize the ignition and stabilization processes of the flame. Static pressure measurements were also conducted to provide quantitative information of wall-pressure distributions of the combustor. Effects of ignition locations and fuel injection schemes on the ignition possibility, initial flame propagation and flame stabilization processes were studied. It was found that the injection scheme with two parallel injectors (10 mm upstream the cavity) is more favorable for ignition than that with two cascaded injectors (30 mm and 10 mm upstream the cavity). The ignition location near the cavity rear-wall always shows a better ignition performance for both these schemes. It was demonstrated that spark plasma can enhance the combustion during the flame stabilization process. The injection scheme with two cascaded injectors (30 mm and 10 mm upstream the cavity) is more sensitive to the spark plasma than that with two parallel injectors (10 mm upstream the cavity). The injection scheme with two cascaded injectors (30 mm and 10 mm upstream the cavity) is also favorable for the flame stabilization process.

A multi-channel gliding arc (MCGA) plasma was utilized to suppress combustion mode transition in a hydrogen-fueled cavity-based scramjet combustor with an inflow speed of Ma2.92. Several optical and electrical techniques, including OH* chemiluminescence, optical emission spectrum, discharge waveform acquisition, and pressure measurements, were employed to show the characteristics of the MCGA discharge and the processes of the combustion mode transitions. When the MCGA is off, the flame frequently oscillates between a cavity shear-layer mode and a cavity-stabilized mode at a low global equivalence ratio, whereas the flame is more likely to be kept in the cavity-stabilized mode when the MCGA is on. The ratio of the cavity-stabilized mode increases from 28.2% to 93% when the plasma is on. The combustion frequently oscillates between a cavity-stabilized mode and a jet-wake stabilized mode at a high global equivalence ratio, but the mode transitions can be suppressed significantly in the presence of the MCGA. The ratio of the jet-wake stabilized increases from 21.9% to 48.8% when the MCGA is on. The Proper Orthogonal Decomposition (POD) method is employed to analyze the oscillation, and it is found that the mean energy content of the large-scale oscillation across the different modes can be significantly suppressed by the MCGA. A plausible explanation can be mainly related to the reactions of N 2 * species with O generated by the MCGA, which increases the temperature in the vicinity of the plasma. The temperature rises spread to the entire cavity with higher backpressure, and results in better mixing and more intense combustion, leading to the suppression of the combustion mode transitions.

Precise control of the discharge in space and time is of great significance for better applications of discharge plasma. Here, we used a femtosecond laser filament to trigger and guide a high-voltage DC pulse discharge to achieve spatiotemporal control of the discharge plasma. In space, the discharge plasma is distributed strictly along the channel generated by the femtosecond laser filament. The breakdown voltage threshold is reduced, and the discharge length is extended. In time, the electrical parameters such as the electrode voltage and the electrode gap affect discharge delay time and jitter. By optimizing the parameters, we can achieve sub-nanosecond jitter of the discharge. Based on the spatiotemporal control of the discharge, we applied filament-triggered discharge for one-dimensional composition measurements of the gas flow field. Besides, the technique shows great potential in studying the spatiotemporal evolution of discharge plasma.