High Temperature Gas Research Articles

An Interpretation Method of Gas–Water Two-Phase Production Profile in High-Temperature and High-Pressure Vertical Wells Based on Drift-Flux Model

With the increasing demand for oil and gas, the depth of some vertical gas wells can reach 6000 m. At this time, the downhole fluid is in a state of high temperature and pressure, and interpretation of the production logging output profile faces the problem of inaccurate production calculations and difficulty judging the water-producing layer. The drift-flux model is usually used to calculate the gas–water two-phase flow. The drift-flux model is widely used to describe the two-phase flow in pipelines and wells because of its accuracy and simplicity. The constitutive correlations used in drift-flux models, which specify the relative motion between phases, have been extensively studied. However, most of the correlations are only extended by laboratory data of small pipe diameters at standard temperature and pressure and do not apply to high-temperature and high-pressure large-diameter gas wells. Therefore, we improved the distribution coefficient and drift velocity of drift-flux correlations in this study for high-temperature and high-pressure gas wells with large pipe diameters. Therefore, this study improved the distribution coefficient and drift velocity of the drift-flux correlations for high-temperature and high-pressure gas wells with large pipe diameters. In practical application, the coincidence rates of gas production and water production calculated by the new drift-flux model were 12.68% and 19.39%, respectively. For high-temperature and high-pressure deep wells, the measurement errors of production logging instruments are significant, and surface laboratory pipelines are challenging to configure and equip with actual high-temperature and high-pressure conditions. Therefore, this study used the method of numerical simulation to study the flow characteristics of the two phases of high-temperature and high-pressure gas and water to provide a basis for identifying the water layer. Combined with the proposed drift-flux correlations and the new method of determining the water-producing layer, a new method of production profile interpretation of high-temperature and high-pressure gas wells is obtained.

Study on the Influence of Geological Parameters of CO2 Plume Geothermal Systems

At present, there are relatively few studies on the exploitation of geothermal resources in depleted high-temperature gas reservoirs with carbon dioxide (CO2) as the heat-carrying medium. Taking the high-temperature gas reservoir of the Huangliu Formation in the Yingqiong Basin as the research object, we construct an ideal thermal and storage coupling model of a CO2 plume geothermal system using COMSOL6.2 software to conduct a sensitivity analysis of geological parameters in the operation of a CO2 plume geothermal system. The simulation results show that, compared with medium- and low-temperature reservoirs, a high-temperature reservoir exhibits higher fluid temperature in the production well and a higher heat extraction rate owing to a higher initial reservoir temperature but has a shorter system operational lifetime; the influence of the thermal conductivity of a thermal reservoir on the CO2 plume geothermal system is relatively minor, being basically negligible; and the thinner the thermal reservoir is, the faster the fluid temperature in the production well decreases and the shorter the thermal breakthrough time. These findings form a basis for selecting heat extraction areas for CO2 plume geothermal systems and also provide a theoretical reference for future practical CO2 plume geothermal system projects.

Simulation and theoretical studies on the influence of removable panel deformation on the seal characteristics of ceramic wafer seal

Purpose The purpose of this study is to investigate the influence of geometric parameters of removable panels on the sealing characteristics of ceramic wafer seal structure subjected to high-temperature gas flow. Design/methodology/approach Based on the laminar flow Reynolds equation, the theoretical and numerical calculation models were constructed to investigate the influence of external convex deformation of removable panel on leakage rate. The theoretical formula for leakage rate after deformation of the removable panel was derived, and the flow field and leakage characteristics of ceramic wafer seal under different operating parameters were studied. Findings The leakage rate exhibits consistent trends between theoretical calculation, numerical simulation and experimental value, with a maximum discrepancy of 8.9%. This validates the accuracy of both the theoretical model and numerical simulation. As the deformation angle of the removable panel increases, the sealing gap gradually widens, resulting in a compromised sealing effect. Moreover, the leakage rate in the central region of the sealing area is lower compared to that at both ends. Originality/value The leakage of the ceramic wafer seal structure under the removable panel with different deformation angles can be monitored based on Reynolds equation. The pseudo-transient numerical calculation method can be used to determine the leakage value of the micro-state ceramic wafer seal structure. These research findings provide a theoretical foundation and numerical investigation approach for studying ceramic wafer seal structures.

Mass granulation of Al-promoted CaO-based sorbent via moulding-crushing methods for cyclic CO2 capture

Calcium looping (CaL) process, as an effective way to achieve CO2 mitigation from high-temperature flue gas streams, is one of the most promising alternatives to amine scrubbing (a well-established technology for industrial post-combustion CO2 capture). CaO sorbent is considered to be an ideal CO2 adsorption material. Moreover, the development of granulation/pelletization techniques along with the mass preparation of the CaO-based sorbent is imperative for realistic large-scale applications. This work proposes two practicable moulding-crushing techniques for the scale-up granulation of CaO-based sorbents, in which the kilogram-scale produced Al-promoted CaO-based sorbent powders were first moulded and subsequently crushed into the granules of target sizes. Three types of organic acids–acetic acid, citric acid and malonic acid were employed as peptizing agents to optimize the granulation process. As a result, the anti-attrition properties and compressive strength of the synthetic sorbents were elevated owing to the introduction of an appropriate amount of acetic or malonic acid, for it expedited the disintegration of the pseudo-boehmite (served as binder agent) particles into sol particles, which allowed for tighter bonding of sorbent particles. In addition, corncob powder acted as a pore-forming agent, enhancing the porous structure of the sorbent particles due to the gases released from the thermal decomposition of organic groups during calcination. Nevertheless, the results revealed that the porous and loose structure adversely affected the mechanical strength of the granules.

Deposition behavior of the gas-atomized 7075Al and TiB2/7075Al composite powders during cold spraying

To fabricate high-quality coatings or components of high-strength 7075Al alloy by cold spraying, it is essential to understand the impact behavior and bonding mechanisms of the feedstock powder particles. For providing a general comparison, 7075Al powder and TiB2/7075Al composite powder (7075Al alloy matrix reinforced with in-situ formed and uniformly dispersed nano-TiB2 particles) produced by gas-atomization were used as feedstocks in the present study. Single particle impact tests combined with finite element analysis (FEA) were performed on the pure Al and 7075Al-T6 substrates under different process parameter sets. To provide a more realistic description, the real powder strength and plastic parameters obtained by single-particle compression tests were used as input data in the FEA model. The results show that the presence of nano-TiB2 particles has significant strengthening effects on the composite powder, thus resulting in different plastic deformation behavior upon impact compared to 7075Al powder. When the composite particles impacted the soft material (pure Al), the substrate experienced a high degree of deformation, which led to high deposition efficiency due to the embedding effect. Comparatively, the hard substrate (7075Al-T6) was less deformed, whereas the composite particle was highly deformed. Compared to the composite particle, the 7075Al particle presented a slightly higher plastic deformation and pronounced metal jets, which led to a lower critical impact velocity for successful bonding. Interestingly, a fracture was observed at the grain boundaries of both 7075Al and TiB2/7075Al composite particles in the case of a high gas temperature regime, which probably revealed that the high shock energy associated with high-velocity impact led to such intergranular fracture.

Investigation on co-gasification performances of sewage sludge and polyolefins by thermogravimetric analyze and two-stage fixed bed reactor

Co-gasification of biomass with hydrogen-rich feedstock is a promising method to improve H2 yield. Thus, in this work, co-gasification performances and corresponding promotion/inhibition effects of sewage sludge (SS) and three types of polyolefins (PE, PP and PS) were investigated in the thermogravimetric analyze and two-stage fixed bed reactor. Thermogravimetric experiments results indicated that with the addition of polyolefins, the initial temperature of blends progressively elevated, while its terminal temperature declined, suggesting that adding polyolefins facilitated the decomposition of samples. The thermal degradation of blends was distinguished into two stages, and in the first stage, a negative interaction was found at 25 % polyolefins mass ratio, but a positive interaction was occurred at 50 % and 75 % polyolefins mass ratios. Meanwhile, in the second stage, a negative interaction was obtained for blending with PE, whereas an opposite result was observed for blending with PP or PS. Therefore, temperature, feedstock and mixing ratio interacted on synergy effects between SS and polyolefins. Besides, two-stage fixed bed experiments results suggested that a higher gasification temperature was beneficial for the production of syngas, particularly the H2 yield, and blending with polyolefins into SS enhanced the H2 content, with PE performing best. The synergy interactions between SS and polyolefins accelerated the concentrations of H2 and CH4, while declining the CnHm yield, demonstrating a stronger re-cleavage of macromolecules. Furthermore, the low heat value of syngas and carbon conversion efficiency for all the samples separately elevated and reduced with rising gasification temperature and polyolefins mass ratios. At 800 °C, the highest gasification efficiency of samples could be achieved with the addition of 50 % PP or PS. This study provides a basis for the application of SS and polyolefins co-gasification.

Experimental investigation of the characteristics of direct injection nozzle sprays in an afterburner environment

This study examined the atomization characteristics of direct injection nozzles under high-temperature, large-Mach inflow conditions using a high-speed camera. The effect of inflow conditions on fuel breakup length, fuel concentration field, and particle size spatial distribution was quantitatively analyzed by using image processing techniques. Experimental results indicate the following: 1) When the liquid-to-gas momentum ratio and inflow Mach number (Ma) are equal, the breakup length, fuel field boundary, and droplet distribution in the jet core region remain consistent for the same nozzle under room-temperature air and high-temperature gas conditions. 2) A breakup length model based on the breakup time of the liquid column is proposed. 3) The logarithmic fuel trajectory formula can effectively predict the physical phenomenon of the movement of fuel particles with the gaseous flow downstream of the injection point after their kinetic energy is depleted, with a prediction error of no >10 %. 4) The spatial distribution of particle sizes reveals that within the selected range of liquid-phase jet velocity, the distribution range of the Sauter mean diameter (SMD) of the jet core area in gas-flow environments with large Ma is similar. At the same axial position, a positive correlation exists between SMD and nozzle diameter. The results of this study have guiding importance for the design of integrated afterburner nozzles.

Technology for removing PM2.5 in clean coal processes

Most countries primarily utilize thermal power to meet their energy needs. However, thermal power generation generates a substantial amount of pollutants, such as particulate matter (PM), SOX, and NOX. These pollutants not only damage backend turbines and related equipment but also pollute the environment; thus, controlling their emissions is critical.This study developed a system operating under high temperature by integrating heating, pneumatic conveying, dust particulate supply, and filter material transport systems. This setup enables the simulation of the entry of syngas with PM at the output of a gasification unit. The developed composite filtration system was analyzed under various operational parameters, including different temperatures, inlet air velocities, and mass flow rates of filter material, to examine the changes in the dust particulate size distribution at its outlet and its PM2.5 collection efficiency. In a series of tests, the collection efficiency of this system reached at least 95% at operating temperatures between 20°C and 600°C. Each 100°C increase in the operating temperature resulted in a 0.63% decrease in the PM2.5 collection efficiency. The findings of this study lay the foundation for the future development of high-temperature gas purification systems.

JWST Observations of Young protoStars (JOYS). Overview of gaseous molecular emission and absorption in low-mass protostars

The Mid-InfraRed Instrument (MIRI) on board the James Webb Space Telescope (JWST) allows one to probe the molecular gas composition at mid-infrared (mid-IR) wavelengths with unprecedented resolution and sensitivity. It is important to study these features in low-mass embedded protostellar systems, since the formation of planets is thought to start in this phase. Previous studies were sensitive primarily to high-mass protostars. The aim of this paper is to derive the physical conditions of all gas-phase molecules detected toward a sample of 18 low-mass protostars as part of the JWST Observations of Young protoStars (JOYS) program and to determine the origin of the molecular emission and absorption features. This includes molecules such as CO$_2$, C$_2$H$_2$, and CH$_4$ that cannot be studied at millimeter wavelengths. We present JWST/MIRI data taken with the Medium Resolution Spectrometer (MRS) of 18 low-mass protostellar systems, focusing on gas-phase molecular lines in spectra extracted from the central protostellar positions. The column densities and excitation temperatures were derived for each molecule using local thermodynamic equilibrium (LTE) slab models. Ratios of the column densities (absorption) or total number of molecules (emission) were taken with respect to H$_2$O in order to compare these to ratios derived in interstellar ices. Continuum emission is detected across the full MIRI-MRS wavelength toward 16/18 sources; the other two sources (NGC 1333 IRAS 4B and Ser-S68N-S) are too embedded to be detected. The MIRI-MRS spectra show a remarkable richness in molecular features across the full wavelength range, in particular toward B1-c (absorption) and L1448-mm (emission). Besides H$_2$, which is not considered here, water is the most commonly detected molecule (12/16) toward the central continuum positions followed by CO$_2$ (11/16), CO (8/16), and OH (7/16). Other molecules such as 13CO$_2$, C$_2$H$_2$, 13CCH$_2$, HCN, C$_4$H$_2$, CH$_4$, and SO$_2$ are detected only toward at most three of the sources, particularly toward B1-c and L1448-mm. The JOYS data also yield the surprising detection of SiO gas toward two sources (BHR71-IRS1, L1448-mm) and for the first time CS and NH$_3$ at mid-IR wavelengths toward a low-mass protostar (B1-c). The temperatures derived for the majority of the molecules are 100--300 K, much lower than what is typically derived toward more evolved Class II sources ($ K). Toward three sources (e.g., TMC1-W), hot ($ K) H$_2$O is detected, indicative of the presence of hot molecular gas in the embedded disks, but such warm emission from other molecules is absent. The agreement in abundance ratios with respect to H$_2$O between ice and gas points toward ice sublimation in a hot core for a few sources (e.g., B1-c), whereas their disagreement and velocity offsets hint at high-temperature (shocked) conditions toward other sources (e.g., L1448-mm, BHR71-IRS1). Molecular emission and absorption features trace various warm components in young protostellar systems, from the hot core regions to shocks in the outflows and disk winds. The typical temperatures of the gas-phase molecules of $100-300$ K are consistent with both ice sublimation in hot cores as well as high-temperature gas phase chemistry. Molecular features originating from the inner embedded disks are not commonly detected, likely because they are too extincted even at mid-IR wavelengths by small, unsettled dust grains in upper layers of the disk.

Advanced oxide-stabilized zirconia ceramics for flue gas filtration in air purification systems

Air pollution, largely driven by industrial activities and fossil fuel combustion, poses a critical threat to both the environment and public health. Addressing emissions, particularly from factories operating at extremely high temperatures, demands advanced filtration technologies capable of withstanding such severe conditions. Ceramic filters have emerged as a promising solution due to their superior thermal stability, chemical resistance, and mechanical durability. Among these, oxide-stabilized zirconia (OSZ) ceramics have garnered significant attention for their potential in high-temperature flue gas filtration. OSZ ceramics enhance the intrinsic properties of zirconia, such as its high melting point and mechanical strength, while stabilizing its phases to prevent performance-degrading phase transformations. This review comprehensively examines the role of phase transformations in ZrO2 materials, alongside the fabrication methods, structural characteristics, and advantages of ZrO2 ceramics in air filtration applications. The review examines various stabilizing agents used to maintain phase stability and optimize material performance under extreme conditions, highlighting the benefits of OSZ in flue gas filtration. Additionally, it covers recent advancements in OSZ synthesis and application, addressing critical limitations such as production challenges and the environmental impacts of large-scale use. The discussion emphasizes the move toward sustainable development in air filtration technologies. Finally, the review provides a forward-looking perspective on future research needs, aiming to further optimize OSZ ceramics for more effective and widespread industrial air pollution control, with a focus on improving performance, scalability, and environmental sustainability.

Stabilization mechanism of emulsion gels of crude oil with low asphaltene, resin, and wax contents

The generation of semi-solid emulsion gels was observed in crude oil with low asphaltene, resin, and wax contents. The semi-solid emulsion gels were very stable and could not be effectively demulsified by conventional demulsifiers. To solve the problem of demulsification, crude oil component analysis, high-temperature gas chromatography, element analysis, Fourier transform infrared spectroscopy, oil–water interfacial tension measurement, and viscoelastic analysis of interface film were used to conduct a detailed study on the stability mechanism of the emulsion gels. The results show that crude oil has a low resin/asphaltene mass ratio and poor asphaltene solvation; thus, resin and asphaltene mainly exist as colloids at the oil–water interface. Meanwhile, the resin and asphaltene in the crude oil have high oxygen content and low acid number, indicating the existence of many phenolic hydroxyl groups. Therefore, strong hydrogen bonding between phenolic hydroxyl groups further enhances the structural strength of resin/asphaltene aggregates. In addition, the long carbon-chain wax in crude oil has poor solubility and is easy to precipitate when the temperature decreases. The long carbon chains easily form a three-dimensional network structure. Resin/asphaltene aggregates are adsorbed on the surface of water droplets, and their alkyl parts interact with the wax in crude oil to form a tight, three-dimensional network structure, which binds the water droplets. The water droplets aggregate without coalescing, resulting in crude oil emulsion gels and causing difficulties in demulsification.

Experimental investigation on flow and heat transfer characteristics of helium in rectangular narrow slit channel

Helium is utilized as coolant in high temperature gas cooled reactors. Rectangular narrow slit channels are commonly present in the core. The flow and heat transfer properties of helium significantly affect the core temperature and flow distribution. This paper experimentally investigates the flow and heat transfer properties of high temperature helium in rectangular narrow slit channel. The Reynolds numbers ranged from 468 to 9357, the temperature ratio of wall to bulk from 0.91 to 1.22, the helium outlet temperature up to 945 K, and the maximum heat flux density up to 0.101 MW/m2. In the experiment, the total and local convective heat transfer coefficients, along with the friction factors, are measured. Correlation equations for the Nusselt number and friction factor with respect to Reynolds number are derived. The primary findings are as below: the friction factors of helium in rectangular narrow slit channels are significantly larger than those calculated by current empirical correlations. In the turbulent zone, the measured local Nusselt numbers are in excellent accordance with the Gnielinski correlation; however, a significant discrepancy exists in the laminar zone. New flow heat transfer correlation equations are proposed on the bases of experimental data. Upon comparison, the total Nusselt numbers fall in the error of 10 %, and almost all local Nusselt numbers and the friction factors fall in the error of 20 %.

Impact of Gas Accumulation on the Stability of Parallel Upward Ventilation in High-Temperature Sloped Shafts of Deep Wells

To explore the causes and influencing factors of wind flow oscillations in high-temperature inclined aisles of deep wells under parallel upward ventilation, this study conducts a comprehensive investigation using theoretical analysis and numerical simulations. Based on the kinetic analysis of gas flow, a discriminant formula for wind flow reversal in the side branch is derived. Further analysis identifies initial wind speed and branch length as key factors influencing the reversal. Both gas pressure and thermal pressure contribute to wind flow reversal in the side branch, and the opposing directions of these pressures cause high-temperature gas to periodically flow between the two branches, resulting in wind flow oscillations. A higher initial wind speed can effectively reduce the oscillation amplitude due to increased initial kinetic energy and a larger pressure difference, but it does not extend the oscillation duration. Increasing the branch length can suppress wind flow oscillations by increasing airflow frictional resistance and damping.

Effect of Nozzle Type on Combustion Characteristics of Ammonium Dinitramide-Based Energetic Propellant

The present study explores the influence of diverse nozzle geometries on the combustion characteristics of ADN-based energetic propellants. The pressure contour maps reveal a rapid initial increase in the average pressure of ADN-based propellants across the three different nozzles. Subsequently, the pressure tapers off gradually as time elapses. Notably, during the crucial initial period of 0–5 μs, the straight nozzle exhibited the most significant pressure surge at 30.2%, substantially outperforming the divergent (6.67%) and combined nozzles (15.5%). The combustion product variation curves indicate that the contents of reactants ADN and CH3OH underwent a steep decline, whereas the product N2O displayed a biphasic behavior, initially rising and subsequently declining. In contrast, the CO2 concentration remained on a steady ascent throughout the entire combustion process, which concluded within 10 μs. Our findings suggest that the straight nozzle facilitated the more expeditious generation of high-temperature and high-pressure combustion gases for ADN-based propellants, expediting reaction kinetics and enhancing combustion efficiency. This is attributed to the reduced intermittent interactions between the nozzle wall and shock waves, which are encountered in the divergent and combined nozzles. In conclusion, the superior combustion characteristics of ADN-based propellants in the straight nozzle, compared to the divergent and combined nozzles, underscore its potential in informing the design of advanced propulsion systems and guiding the development of innovative energetic propellants.

Bamboo-derived aerogel with atomically dispersed Co as a high-performance bifunctional electrocatalyst for durable zinc-air batteries

The development of highly efficient and durable bifunctional electrocatalysts is crucial for rechargeable zinc-air batteries, which have garnered significant attention as a promising sustainable energy storage technology. Herein, a novel Co-N-C-1050 catalyst is synthesized using a high-temperature gas transport method, where high purity cobalt powder and bamboo biomass aerogel are treated with ammonia gas at 1050 °C. The resulting catalyst exhibits a 3D interconnected porous network composed of dense carbon fibers, which atomically dispersed Co, N, and C elements are uniformly distributed. The synergistic integration of highly active Co single atoms and N-doped 3D carbon fiber aerogel enables Co-N-C-1050 to demonstrate excellent bifunctional electrocatalytic performance for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), comparable to commercial Pt/C and RuO2 catalysts. This catalyst has a half-wave potential of 0.842 V for ORR and a potential of 1.472 V at 10 mA cm−2 for OER, outperforming N-C-1050 and benchmark catalysts. A zinc-air battery is driven by Co-N-C-1050 achieves a high power density of 135 mW/cm2 and exceptional stability over 138 h of charge/discharge cycling, surpassing the higher-cost Pt/C + RuO2 catalyst. This biomass aerogel based single-site Co-N-C catalyst offers a promising approach for developing high-efficiency and long-cycle-life zinc-air batteries.

Assessing the effect of minimally invasive lipid extraction on parchment integrity by artificial ageing and integrated analytical techniques

To assess the short and long-term effect of a newly developed minimally invasive lipid extraction method on parchment, sacrificial pieces of parchments were subjected to artificial ageing and investigated using various analytical methods. Lipids were extracted using our novel vacuum-aided extraction method and characterised by high-temperature gas chromatography (HTGC-FID). Lipids were identified as arising from degraded animal fats. The physical, molecular, and mechanical properties of the parchment samples before/after lipid extraction, and before/after ageing were assessed using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and pure shear single notch fracture testing. SEM imaging allowed for an assessment of potential structural changes of the collagen fibres while FTIR was used to investigate the possible molecular changes indicated by changes in amide I and II bands. Mechanical tests were used to record the changes in brittleness and stiffness occurring in the materials through lipid extraction and ageing. The multimodal investigation did not highlight measurable changes in the structural, molecular, and mechanical properties of the lipid-extracted parchment, thus indicating the suitability for the minimally invasive lipid extraction method to be applied to historical parchments.

Experimental study on surface temperature and emissivity of rotating turbine blades of a micro turbojet engine

The temperature of the rotating turbine blades of a turbojet engine must be known to assess the combustion state and improve turbine blade quality. Obtaining online temperature measurements of high-speed rotating turbine blades in high-temperature gas flow remains challenging. A multispectral radiation thermometry method without emissivity assumption is proposed to measure the temperature of high-speed rotating turbine blades of a micro turbojet engine. The relative radiative intensity is calculated by accounting for smooth changes in the wavelength using the moving narrowband method to determine the influence of emissivity on multispectral radiation thermometry results. The method’s performance in measuring the surface temperature of high-speed rotating objects is tested. The wavelength range of 970 nm to 1700 nm is selected because the radiation from gases is weaker in comparison to the radiation emitted by solid surfaces within this band. The spectral radiation of the turbine blade surface is measured at three rotational speeds: 38,000 r/min, 48,000 r/min, and 58,000 r/min. The results show that, unlike thermocouples that measure the temperature of the hot gas flow near the blade, multispectral radiation thermometry provides the average surface temperature with high consistency (with a deviation smaller than 50 K). Multispectral radiation thermometry can be applied to measure the surface temperature and emissivity of high-speed rotating objects, such as the blades of turbojet engines.

Study on heat release characteristics of the dual composite flame stabilizers for the dual-mode scramjet

The paper studies the heat release (HR) characteristics of a dual-mode scramjet equipped with the dual composite flame stabilizers under simulated free-stream conditions of Mach 6 and dynamic pressure of 30 kPa, through ground direct-connected tests and OpenFOAM numerical simulation. This study focuses on the three-dimensional distribution of subsonic/supersonic HR, local combustion modes, and the variations in HR during the ram-scram mode transition. The results indicate that the high-enthalpy jet transports the high-temperature and fuel-rich gas in the cavity to the mainstream through the ejection effect of the supersonic flow, causing the heat release zone to move to the mainstream. So that the mainstream subsonic-diffusion combustion zone is expanded and is evenly distributed, and then the HR trailing zone downstream of the thermal throat is shortened. The study highlights the different matching characteristics between subsonic flow and HR formed by the dual composite flame stabilizers under high and low equivalence ratio (ER). Optimized injection schemes need to be selected to obtain higher combustion efficiency at different equivalence ratios. In the region of the first-stage composite flame stabilizer, a distinct phenomenon of subsonic/supersonic mixed HR is observed. Subsonic HR predominates under the ramjet mode, while the subsonic HR tends to equal supersonic HR under the scramjet mode. Upstream of the thermal throat, subsonic HR exceeds 80%, and supersonic heat release has a tendency to gradually decrease. Furthermore, when the ER of two-stage dispersed injection is less than 0.5, the heating amount per kilogram of air is less than 1.06 MJ, and the thermal throat cannot be formed, causing the ram-scram mode transition to occur. Conversely, for single-stage concentrated injection, the boundary of ER and heating amount decreases. The study provides support for the design of injection schemes and the regulation of mode transition for dual-mode scramjet based on the HR performance.

Study on the aerodynamic characteristics of reentry capsule with obtuse head inverted cone under hypersonic chemical nonequilibrium flow

Abstract During spacecraft reentry, the aerodynamic characteristics of the reentry capsule with a sizeable obtuse head inverted cone (OBHIC) in a hypersonic state are the key factors in the design of controlled reentry trajectory, the design of trim angle of attack (AoA), and the accuracy of fall point of capsules. This paper establishes a numerical simulation algorithm of a hypersonic chemical nonequilibrium flow field by considering high-temperature real gas effects. The reentry capsule’s aerodynamic and flow field characteristics are predicted and analyzed. The component transport equations for chemical reactions are added to the Navier-Stokes equations, enabling precise modeling of gas molecule vibrational excitation and ionization processes. A half-model multi-block structured mesh is employed to construct the aerodynamic profile of the reentry capsule with OBHIC. The aerodynamic characteristics and pressure distribution of the reentry capsule were calculated and analyzed under the typical conditions of flight altitude of 40~80 km, flight velocity of 6~27 Ma, and AoA of 15°~24°. The results of the aerodynamic characteristics prediction show that the aerodynamic characteristics of the reentry capsule are little affected by the incoming flow velocity in a hypersonic state but significantly affected by the AoA. As the AoA increases, the lift coefficient CL increases linearly, the drag coefficient CD decreases linearly, the lift-to-drag ratio K rises linearly, and K increases from 0.19 to 0.29. In its hypersonic state, the reentry capsule exhibits a low lift-to-drag ratio, characterized by high drag and low lift coefficients. The results of this paper play an essential role in the reentry flight dynamics and reentry trajectory design of the reentry capsule. Moreover, it can further ensure the safety and reliability of the reentry flight of spacecraft.

Fabrication of high-performance SiC ceramic membranes modified using in situ grown mullite whiskers and high-temperature filtration

The gas permeance and particle removal efficiency of silicon carbide (SiC) membranes are the most important performance indicators for high-temperature gas filtration. The rational design of SiC membrane microstructure has a positive impact on the improvement of performance indicators. This work prepared SiC membranes modified by in situ grown mullite whiskers, optimized their preparation conditions and investigated their performance improvement. The membrane suspension composition and sintering temperature were optimized using Taguchi’s method and gas permeance as the target. The thickness of the membrane was regulated by adjusting the spraying cycles and solid content in membrane suspension. Results showed that best membrane performance was obtained when the content of sintering aids, MoO3, and AlF3·3H2O were 8, 12, and 12 wt%, respectively; the solid concentration in membrane suspension was 30 wt%; the number of spraying cycles was 2, and the temperature was 1350 °C. The resulting membrane obtained a pore size of 5.8 µm and the Darcy's permeability coefficient k was 8.58 × 10−12 m2. It also had good interfacial adhesion and thermal shock and corrosion resistances. The membrane achieved a PM2.5 removal rate of more than 99.9 % at room temperature and high temperatures (100 °C–400 °C) with a low pressure drop below 1.4 kPa. Overall, the SiC ceramic membranes are prospective candidates for dust-laden gas filtration at high temperatures.