30 August 2025, Volume 46 Issue 9

    

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  Experimental and Numerical Investigation of Water Droplet Bag Breakup

  SONG He, CHANG Shinan

  Journal of Engineering Thermophysics. 2025, 46(9): 2791-2798.

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  Bag breakup is a typical breakup mode of the Supercooled Large Droplet (SLD) in the field of aircraft icing. The deformation and breakage processes of a water droplet in continuous airflow is studied by combining experimental and numerical simulation methods. A regime map is drawn to give the physical boundary of the bag breakup mode. The deformation ratio, velocity of the initial droplet and size distribution of the secondary droplets are analyzed, and the causes of droplet morphology evolution in each stage of the bag breakup mode are explained. The results show that the range of gaseous Reynolds number and Weber number corresponding to the bag breakage mode are 3100∼4250 and 12∼18, respectively. At the disk moment, the horizontal deformation ratio of the droplet is about 0.4, and it varies slightly with the increase of gaseous Weber number. While, the vertical deformation ratio of the droplet increases gently with the increasing gaseous Weber number. When the gaseous Weber number is 13.4, the droplet breaks in the bag breakup mode. The dimensionless size distribution of the secondary droplets ranges from 0 to 0.28, showing a unimodal distribution, and the peak value appears when the dimensionless size of the secondary droplet is 0.024. This study plays a crucial role in improving the physical model of SLD bag breakup and advancing the simulation accuracy of SLD icing.
  
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  Robust Optimization of Distributed Energy Systems Considering Uncertainty and Nonlinearity

  XU Ronghong, MA Huan, ZHAO Tian, XIN Yonglin, WU Dongyi, CHEN Qun

  Journal of Engineering Thermophysics. 2025, 46(9): 2799-2808.

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  With the increasing integration of renewable energy, the inherent uncertainty of energy sources and loads, coupled with the nonlinear coupling characteristics of multi-energy systems, poses significant challenges to the operation and management of distributed energy systems. This paper accounts for the nonlinear characteristics of electricity-heat transmission and conversion processes by incorporating a heat current model and a column-and-constraint generation algorithm, proposing a two-stage robust optimization model and a bilevel iterative optimization algorithm. Compared to a simplified robust optimization model that neglects nonlinear characteristics, the proposed approach reduces operating costs by 3.2%. Furthermore, the results demonstrate that in actual system operation, the proposed algorithm effectively mitigates the infeasibility risk of robust scheduling strategies caused by model simplifications, thereby verifying its economic efficiency and robustness. 
  
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  Experimental Study of Liquid Phase Density and Surface Tension of Basic Lubricating Oil

  ZHOU Yulong, YU Guoliang, YANG Jian, WU Jiangtao

  Journal of Engineering Thermophysics. 2025, 46(9): 2809-2814.

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  Synthetic lubricating oil is widely used in various types of refrigeration and heat pump equipment, and its thermophysical properties are the basic data for analyzing thermodynamic energy efficiency, heat transfer performance and pressure drop along the way, which is of great significance for evaluating and optimizing the system structure. In this paper, a set of low-temperature and high-pressure pendant drop surface tension experimental measurement system was developed, and the liquid phase density and surface tension of basic lubricating oils (POE, PVE and PAG) were studied by using vibrating tube density meter and pendant drop surface tension experimental system, and the measured temperature range was 243.15∼363.15 K, and the extended uncertainty of liquid phase density and surface tension measurement was within 0.2% and 0.1 mN·m⁻¹, respectively. The experimental results show that the liquid phase density and surface tension of the base lubricating oil decrease with the increase of temperature, and the absolute average deviation between the calculated value and the experimental value of the correlation equation is less than 0.04% and 0.5%, respectively.
  
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  Performance Analysis of Bifacial Photovoltaic Modules Based on Optical-Thermal-Electrical-Environmental Coupling

  XU Shijie, XIAO Lan, DU Jie, WU Shuangying, CHEN Zhili

  Journal of Engineering Thermophysics. 2025, 46(9): 2815-2822.

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  To investigate the operating characteristics of bifacial photovoltaic (BPV) module in a specific region, an optical model integrating direct solar radiation and sky-scattered radiation was proposed, a thermal model of coupled environment was constructed, and an electrical model based on discrete method was introduced. The effects of ground reflectivity (R) and solar incidence angle (θ) on the performance of BPV module operating in Shapingba District, Chongqing (29◦33′9.08′′N, 106◦27′36.60′′E) were investigated by using the coupled optical-thermal-electricalenvironmental method and compared with the results based on average temperature electrical model. The results indicate that instantaneous electrical efficiency (η_el) decreases with the increase of R, while instantaneous electrical power (P) of BPV module is the opposite. When tilt angle of module exceeds local latitude, η_el increases and P decreases with the increase of θ. Conversely, when the tilt angle is less than local latitude, η_el decreases and P increases with increasing θ. The temperature uniformity of module improves as R and θ increase. The maximum relative deviations of P and η_el calculated by discrete method and average temperature method are 1.64% and 1.66%, respectively.
  
  
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  Performance Study of CO₂/Low-GWP Mixed Refrigerant in Vapor Injection Heat Pump Systems

  HOU Beiran, LI Minxia, ZHANG Ce, WANG Zhipeng, ZHANG Jiaxing, DONG Liwei, TIAN Hua

  Journal of Engineering Thermophysics. 2025, 46(9): 2823-2830.

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  As a natural refrigerant, CO₂ exhibits excellent environmental performance and low production costs, making it an ideal replacement for high-GWP refrigerants. To enhance system efficiency, vapor injection technology, characterized by its simple structure and reliable operation, has been widely employed in CO₂ heat pump systems. However, these systems still face significant challenges in practical applications due to inherent issues such as high operating pressures and substantial throttling losses. To address these challenges, this study incorporates three low-pressure refrigerants into the CO₂ heat pump system to improve operational efficiency and reduce system pressure. The research findings demonstrate that the CO₂/R161 system surpasses traditional CO₂ heat pump systems in terms of energy efficiency. The CO₂/R161 system achieves up to a 17.6% increase in efficiency under various thermal demand conditions and a maximum pressure reduction of 33.7% at an outlet water temperature of 85°C, compared to conventional CO₂ heat pump systems.
  
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  Optimization of Heliostat Field Layout Based on Adaptive Leader Coot Optimization Algorithm

  GAO Bo, LIU Sheng, YANG Xiangyu

  Journal of Engineering Thermophysics. 2025, 46(9): 2831-2838.

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  Aiming at the optimization problem of heliostat layout in solar tower power plants, a heliostat layout optimization scheme based on the adaptive leader coot optimization algorithm is proposed. Based on the Spiral layout, three objective functions of heliostat field optical efficiency, daily potential highest collected energy, and energy collected per unit cost are introduced as evaluation criteria for heliostat field optimization layout. By introducing chaotic parameters generated by Tent mapping into the coot optimization algorithm, adding dynamic disturbance factors and adaptive weights, the algorithm’s optimization ability in high-dimensional complex engineering optimization problems is improved. Finally, taking the Lhasa heliostat field as an example, the optical efficiency of the heliostat field has been improved to 62.35% after optimization by the adaptive leader coot optimization algorithm. The typical daily highest potential daily energy collection has increased by about 4.2×10⁸ kJ, 2.9×10⁸ kJ, 3.5×10⁸ kJ, and 6.2×10⁸ kJ, respectively, providing an efficient heliostat field layout scheme for tower solar power plants.
  
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  Study on the Influence of Cold Storage Energy on the Start-up Characteristics of the Liquid Air Energy Storage System With Dual-stage Liquid-phase Cold Energy Storage

  ZHOU Yufei, DING Xingqi, YANG Ming, LI Da, DUAN Liqiang, ZHANG Hanfei

  Journal of Engineering Thermophysics. 2025, 46(9): 2839-2849.

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  The cold cycle is crucial for the performance of the liquid air energy storage (LAES) system, but there is currently a lack of detailed research on the establishment process of the cold cycle. This article proposes a simplified dynamic modeling method for multi-stream heat exchangers, and based on this, builds a full-process dynamic model of an LAES system using dual-stage liquidphase fluids for cold energy storage. A study is conducted on the impact of cold storage energy on the start-up characteristics of the dual-stage liquid-phase cold storage LAES system, revealing the steps and dynamic performance of cold cycle establishment. The research results indicate that under design conditions with sufficient cold storage energy, liquid air is generated around 30.3 seconds after the start-up, and the air liquefaction rate reaches 95% of the final stable value after approximately 640 seconds. In the absence of cold storage energy to start, liquid air is generated at the 844th second and requires continuous operation for 10.35 days to fully store the liquid air tank. To achieve the design performance, 7 consecutive discharging and charging cycles are required. The research results can provide useful references for the initial start-up of actual LAES power plants or the loss of cold storage energy caused by unexpected situations.
  
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  Simulation and Experimental Study of Combustor-coupled Thermoacoustic Stirling Generator

  JIN Qingyue, MA Zhuang, XUE Jianhua, CHENG Yangbin, MA Ying, YU Guoyao, LUO Ercang

  Journal of Engineering Thermophysics. 2025, 46(9): 2850-2857.

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  The combustor-coupled free-piston Stirling engine has attracted considerable attention in areas such as distributed heat and power generation due to its wide fuel adaptability. This paper presents an experimental study on a novel gas combustor coupled with a free-piston Stirling engine, and compares the experimental results with simulation results. Firstly, the output characteristics, energy flow, and losses of the system are analyzed. Secondly, the effects of fuel flow rate and load on the system’s output performance are investigated. The results indicate that under the rated conditions of fuel flow rate at 0.54 m³/h and external resistance of 20 Ω, the power generation system can achieve 1.53 kW output electric power. The combustor’s heat absorption efficiency is 30.1%, with fuel-to-electricity efficiency and thermoelectric efficiency reaching 9.8% and 32.4% respectively. Furthermore, the output electric power increases as the external resistance decreases, while the fuel-to-electricity efficiency shows a trend of initially increasing and then decreasing with increasing fuel flow rate.
  
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  Design of Blade Type Swirl Distortion Generator and Analysis About Effect of Distortion Characteristics on Compressor Performance

  LIAN Haojun, ZHANG Min, DU Juan, BA Dun, NIE Chaoqun

  Journal of Engineering Thermophysics. 2025, 46(9): 2858-2868.

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  This paper studies the swirl distortion flow field characteristics and its impact on compressor performance through numerical simulation methods. A blade-type swirl distortion generator with adjustable stagger angle was designed. Comparing the flow fields under different geometric parameters, it is found that the blade stagger angle and the support ring position of the distortion generator change the intensity and spatial position of the vortex respectively, which in turn affects the intensity of the swirl distortion. The stagger angle of blades at different positions mainly affects the vortex intensity of local flow field, and has a certain impact on the flow field in other areas through altering the coupling between vortices. The change in the position of the support ring causes the position of the vortex core. The impact of this swirl distortion on the aerodynamic performance of a 1.5-stage transonic axial compressor is then analyzed. Results show that the swirl distortion reduces the stability margin by 11.91%, but the maximum efficiency is relatively increased by 0.32%. Further flow field analysis shows that the swirl distortion mainly changes the inlet flow angle of rotor blade, thereby deteriorating the stability margin. However, the inlet distortion leads to reduction in the total pressure loss of the stator and hence increases the efficiency.
  
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  Study on Improving the Stability of Blocked and Overloaded Type Stall Rotor by the Self-Circulating Casing Treatment

  YAN Song, CHU Wuli, LUO Dahui

  Journal of Engineering Thermophysics. 2025, 46(9): 2869-2880.

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  This work used numerical methods to study on improving the stability of a rotor with both blocked and overloaded type stall by the self-circulating casing treatment (SCT). The study found that for the rotor whose tip flow field was aggravated by the low velocity flow zone induced by tip leakage flow and the suction surface flow separation, the SCT can only achieve significant enhancing stability effect by simultaneously considering its suction effect and jet effect, that is, suppressing both the low velocity flow zone induced by tip leakage flow and suction surface flow separation. When the suction position covers the most blockage zone in the blade passage, the enhancing stability effect of the SCT is the best, and the stall margin improvement of the rotor is as high as 12.86%. The study on the mechanism of enhancing stability found that, the jet effect of the SCT can improve the inlet condition of blade tip and restrain the tip leakage flow, the suction effect can suction the low velocity flow zone. Under the combined action of jet effect and suction effect, the breakdown of tip leakage vortex and flow separation of suction surface are inhibited, and the blade tip flow condition is improved, thus the aerodynamic stability of rotor is improved.
  
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  Numerical Simulation of Multiple Ducted Fans With a Boundary-Layer Ingestion S-shaped Duct

  JIA Wei, ZHANG Congcong, KONG Qingguo

  Journal of Engineering Thermophysics. 2025, 46(9): 2881-2890.

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  To address the interaction between an S-shaped duct and distributed ducted fans under boundary layer ingestion conditions, a numerical simulation was performed using a method based on the body force model. The effects of the incoming flow boundary layer thickness and the rotational speed of the ducted fans on their aerodynamic performance were studied. The results show that a single vortex with opposite rotation directions are formed at the inlets of the two edge fans, whereas a pair of vortices is formed at the intermediate fans due to the boundary layer ingestion. As the boundary layer thickness increases, the aerodynamic performance of the two edge fans decreases the most, and the change in aerodynamic performance is primarily related to the direction of the swirl angle. When a single ducted fan operates at an off-design rotational speed, its influence on the adjacent fans is limited. When two ducted fans operate at an off-design rotational speed, their influence on the aerodynamic performance of the adjacent fans is relatively large. 
  
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  Study on Flow Field Characteristics of Tandem Heated Cylinders

  CHEN Shikang, GANG Dundian, FENG Yuan, MI Qi

  Journal of Engineering Thermophysics. 2025, 46(9): 2891-2897.

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  The heater constitutes a critical component in conventional hypersonic wind tunnels. Within direct-heat electric heaters, the internal flow configuration generally comprises an array of heated columns, where convective heat transfer between the airflow and high-temperature columns facilitates thermal elevation. This internal flow regime can be conceptually simplified as a heatedcolumn-wrapped flow configuration. In this investigation, the flow field characteristics of a seriesconnected dual-heated cylindrical system were experimentally analyzed through schlieren imaging and particle image velocimetry (PIV). Experimental results revealed that under low wall temperature conditions, the separation vortex between the two columns exhibited periodic shedding behavior. As wall temperature increased, the separation vortex downstream of the first column shifted rearward, approaching the second column, while the vortex structure behind the second column progressively adopted a flow pattern analogous to single-column wrapping upon establishment of a stable intercolumn recirculation zone. Furthermore, at low wall flow rates, the first column’s separation vortex demonstrated regular shedding cycles. However, when flow velocity exceeded a critical threshold, the primary separation vortex abruptly dissipated, accompanied by the formation of a stable recirculation zone between the columns. Notably, under these high-flow conditions, the secondary column’s separation vortex regenerated completely, ultimately transitioning toward a single-cylinder flow mode.
  
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  Optimization of Turbine Blade Incidence Angle Adaptability Based on Graph Neural Networks

  CHEN Tianyou, CAI Le, WANG Songtao

  Journal of Engineering Thermophysics. 2025, 46(9): 2898-2905.

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  To achieve fast and accurate prediction of the aerodynamic characteristics of turbine blade profiles over a wide range of incidence angles, this study utilizes the GAT-5 model to predict the total pressure loss of two-dimensional turbine blades under wide incidence angles based on smallscale experimental data. The model was also used to validate the predictions, and the results demonstrate that the GAT-5 model exhibits high prediction accuracy. Notably, the predictions at a 30° incidence angle closely match the experimental data, a level of precision unattainable with the CFD calculations used in this study. Furthermore, by integrating the GAT-5 model with optimization tools, the optimized blade profile, while slightly increasing the profile loss at negative incidence angles, significantly reduces aerodynamic losses at positive incidence angles. This indicates that the GAT-5 model has substantial potential for optimizing the adaptability of turbine blade profiles over a wide range of incidence angles.
  
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  Contour-Based PSP Image Reconstruction Method Under Limited Optical Path Conditions

  ZHANG Jun, OUYANG Bo, LI Ruiyu, GAO Limin, LIN Shiyan

  Journal of Engineering Thermophysics. 2025, 46(9): 2906-2914.

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  In the field of internal flow field with limited optical path, such as compressor cascade experiment, three-dimensional reconstruction of image is crucial for pressure measurement of Pressure Sensitive Paint (PSP). The key to the three-dimensional reconstruction process is to accurately obtain the projection matrix between the measured model and the camera, while the existing methods are limited by the number and distribution of feature points. In this paper, a Contour Matchingbased Direct Linear Transformation (CM-DLT) is proposed. This method draws on the idea of iterative closest point algorithm, optimizes the projection matrix by matching the image contour and the re-projection contour of the 3D model, and improves the reconstruction accuracy of the 3D pressure. In the benchmark experiment, the effects of 3D contour point cloud dispersion, initial feature point noise, number and distribution on the CM-DLT algorithm are studied. Subsequently, the CM-DLT method was successfully applied to the compressor cascade PSP experiment, and the three-dimensional pressure distribution on the blade surface was obtained. The results demonstrate that reducing the dispersion of 3D contour point cloud is beneficial to improve the accuracy of CM-DLT algorithm. In addition, the CM-DLT method has strong anti-interference ability and can effectively realize the accurate reconstruction of three-dimensional pressure.
  
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  Research on Load Characteristics of 2 MW Wind-to-Heat Combined Power Generation Unit

  MENG Jianlong, SUN Xiangyu, REN Qianru, CAI Chang, LIU Qian, ZHONG Xiaohui, LI Qingan

  Journal of Engineering Thermophysics. 2025, 46(9): 2915-2922.

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  The Wind-to-Heat Combined Power Generation Unit is one of the innovative and efficient utilization forms of wind energy. The coupling of the compressor and generator results in differences in the load characteristics of the unit compared to both wind turbine and wind-to-heat units. To investigate the load characteristics of the combined power generation unit, this study establishes a model of the Wind-to-Heat Combined Power Generation Unit based on the OpenFAST and MATLAB/Simulink simulation platforms for joint simulation. The relevant load data of the unit is obtained and compared with the load data of wind turbine units and wind-to-heat units of the same power rating. The analysis shows that the loads in the y and z directions of the blade, as well as in the x direction of the hub, are all greater than the corresponding load data of the wind turbine unit, and are slightly smaller compared to the wind-heat unit. When the compressor is connected, the load significantly increases, and the variation trend is similar to that of the
  wind-to-heat unit. 
  
  
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  Noise Prediction Method and Application of Backward Centrifugal Fan

  LIU Meiyi, SUN Tao

  Journal of Engineering Thermophysics. 2025, 46(9): 2923-2932.

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  As a key indicator of fan performance, the noise of the fan has received more attention. This paper develops an empirical method for centrifugal fans noise evaluation. It is based on typical specific noise level of backward centrifugal fans, correlates the total pressure and flow rate, and performs efficiency correction. The prediction results of a given centrifugal fan with experimental data show that the noise results of empirical methods have a small deviation from the results of acoustic analogy method. Then based on the empirical method, a low noise design of the given fan was carried out. The results obtained by coupling the unsteady numerical simulation and acoustic analogy method show that, the noise of the redesigned fan was significantly reduced compared to the original fan, and the A-sound level decreased by 6.2 dB at the highest efficiency work point, which verifies the validity of this method for the low noise design of the backward centrifugal fan. 
  
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  Impact Mechanism of Load Variation on Full Coverage Film Cooling of Stator Cascade

  WU Yiyang, LI Xueying, REN Jing, GAO Dawei, TANG Hongfen, LIU Shuaiwei

  Journal of Engineering Thermophysics. 2025, 46(9): 2933-2941.

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  Gas turbines have excellent peak-shaving capabilities and often operate under part-load conditions deviating from the design point, which leads to a decline in overall efficiency and turbine cooling performance. To investigate the impact of load variation on film cooling performance, this study employs numerical simulations to analyze the aerodynamic performance and cooling effectiveness of the first-stage stator vane of a GE-E3 turbine under varying expansion ratios (π) and coolant pressure ratios (β) The results show that increasing π improves the overall efficiency of the vane, though excessively high values may cause local flow losses; β has a relatively minor effect on the overall efficiency At various π levels, the film cooling effectiveness on the suction side is higher than that on the pressure side. The film cooling effectiveness increases with β initially and then decreases, reaching its peak at β =1.05. During load regulation, careful matching between π and β is essential.
  
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  CO₂-ECBM and Its Main Control Parameters Based on the Improved Thermal-fluid-force Coupling Model

  WANG Xin, YANG Xinquan, LIANG Bing, SUN Weiji, XU Jun, WANG Fang, YANG Xinle, LI Weizhong, SONG Yongchen

  Journal of Engineering Thermophysics. 2025, 46(9): 2942-2957.

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  CO₂-ECBM engineering has the dual benefits of energy development and carbon emission reduction, and the coupled numerical simulation of heat-fluid-force multiphysics is an effective way to explore the replacement of CH₄ by CO₂. In this paper, by improving the apparent permeability model, the thermal-fluid-force fully coupled model is improved, and the dynamic apparent permeability, gas-water two-phase seepage, non-isothermal competitive adsorption, and coal seam strain are proposed and verified, and the main control parameters are further studied. The results show that the apparent permeability is affected by the size of capillary pores and microfractures, viscous flow, Kundsen diffusion, and surface diffusion of adsorbed gas. The change of pore fracture size is determined by the seepage process and volume strain in the reservoir. The flow process in the reservoir is affected by the coupling of gas pressure and volumetric strain, and the higher the pressure, the greater the influence of viscous flow on the apparent permeability. The effects on volumetric strain from low to high are reservoir temperature, gas mixture pressure, reservoir geological conditions, and gas adsorption/desorption. Higher CO₂ injection pressure has a positive effect on H₄ production and CO₂ sequestration. The higher initial temperature of the coal seam increases the difficulty of CO₂ gas adsorption, the displacement effect decreases, and the CO₂ storage decreases.
  
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  Measurement of Gas-liquid Two-phase Flow Rates Using a Dynamic-Driven Swirler

  WANG Haocun, XU Qiang, ZHANG Xuemei, MA Xiaojun, LI Lulu, GUO Liejin

  Journal of Engineering Thermophysics. 2025, 46(9): 2958-2965.

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  Accurate measurement of gas-liquid flow rates has become a challenge in the field of multiphase flow measurement. In this paper, a new dynamic-driven swirler device is designed to take tap water and air as the working fluid, and the variation characteristics and patterns of throttling differential pressure and radial differential pressure at different swirler speeds and gas-liquid flow rates are investigated. The results show that with the increase of two-phase flow rates, the throttling differential pressure monotonically increases, while the radial differential pressure shows three different trends under different flow patterns, and at low gas-liquid flow rates, increasing the swirler speed broadens the stabilization interval of the radial differential pressure, thus obtaining a wider measurement range. In addition, this paper introduces slip ratio and differential pressure correction coefficients to modify the separated flow model, and establishes a new model for gas-liquid flow measurement. In the experimental case, the measurement errors of the liquid and gas flow rates are ±3.2% and ±22%, respectively, when the swirler is static (swirler speed is 0), while the measurement errors are ±2.5% and ±9.6%, respectively, when the swirler speed is 600 r·min⁻¹.
  
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  Numerical Investigation on Self-transport Behaviors of Droplets on Conical Surfaces

  DING Yi, JIA Li, YIN Liaofei, DANG Chao, CHANG Fangzheng

  Journal of Engineering Thermophysics. 2025, 46(9): 2966-2973.

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  The regulation of droplet self-transport behavior driven by curvature gradients on substrate surfaces has significant potential for applications in advanced technologies such as fog harvesting and oil-water separation. This study investigated the anti-gravity self-transport behavior of droplets on the vertical conical surfaces. A numerical method was proposed, which discretized the continuous self-transport process of droplets into multiple isolated wetting states along the path. By constructing a free energy minimization equation, the morphological characteristics of the gas-liquid interface, the variation of the surface free energy, and the driving force along the path were obtained for locally steady-state droplets. Furthermore, an empirical balance relationship among the driving force, gravity, and adhesion resistance was established to elucidate the self-transport dynamics of droplets. The results indicated that both the surface free energy and the self-transport driving force decreased with increasing self-transport height. Droplets with smaller surface tension and larger volume exhibited a greater self-transport driving force. The variation of the droplet self-transport velocity along the path, calculated using the empirical dynamic model, showed good agreement with the experimental results.
  
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  Study on Enhancing Chip Cooling Characteristics Based on Manifold Microchannels

  WANG Jin, ZHANG Borui, HE Yurong

  Journal of Engineering Thermophysics. 2025, 46(9): 2974-2980.

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  Manifold microchannels are widely used in high-power chip cooling and other applications due to their efficient heat dissipation performance. Under higher heat fluxes, bubble accumulation tends to occur at the bottom of the manifold microchannels, significantly reducing the heat dissipation performance. To address this issue, this study investigates the bubble growth characteristics and flow heat transfer behavior within the manifold-type microchannel using computational fluid dynamics methods. The study also employs an equal heat transfer area design approach to optimize the bottom structure of the microchannel to improve bubble dynamics. The results indicate that the optimized microchannel structure significantly shortens the bubble growth and stretching times, accelerates bubble detachment, and effectively suppresses bubble accumulation at the bottom. The effective control over the bubble growth process improves the heat transfer performance of the channel wall, reduces the average temperature at the bottom of the device, and strengthens the heat dissipation performance of the device. This study provides a theoretical basis for the optimization design of manifold microchannel radiators.
  
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  Inverse Heat Transfer Methods and Application Researches: Progress, Challenges and Directions

  WAN Shibin, YU Yan, WANG Kun

  Journal of Engineering Thermophysics. 2025, 46(9): 2981-3005.

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  Inverse heat transfer problems involve the estimation of the internal characteristics or thermal boundary conditions by using the internal or surface temperature measurements in the heat transfer system. Inverse heat transfer problems widely exist in scientific and technological fields such as energy and power engineering, metallurgical engineering, intelligent mechanical manufacturing, biomedical engineering, and aerospace. In the past half century, research on the calculation methods and applications of inverse heat transfer problems have been very active. In this article, the research progress on the application of inverse heat transfer problems is surveyed and the research progress of calculation methods for inverse heat transfer problems is systematically elaborated; the current challenges and future development directions of the calculation methods and application research of inverse heat transfer problems have been laid out to promote the development of numerical calculation technology and applications for inverse heat transfer problems, empower production practice with research of heat transfer inverse problems, contribute to the construction of industrial digital twins, and contribute to the implementation of China’s digital transformation national strategy. 
  
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  Study on Features of Energy-Mass Transfer and Conversion Inside a Rocking-type Photothermal Reactor

  TENG Liang, XUAN Yimin

  Journal of Engineering Thermophysics. 2025, 46(9): 3006-3012.

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  Solar driven CO2 capture and thermochemical fuel synthesis are becoming one of the most promising renewable energy technologies to cope with the global energy crisis and environmental problems, and to realize “peak carbon emission and carbon neutral”. However, the concentrated solar-driven thermochemical reaction faces the problems of radiant energy concentration, localized overheating, and serious mismatch of energy and mass flow, which leads to the insufficient utilization of reactive gas conversion and solar energy. In this paper, the original rocking-type reaction system was developed, the internal multi-physical field coupling correlation and synergistic evolution characteristics
  were simulated and analyzed, the energy-mass transfer mechanism was elucidated, and the controlling factors of the carbon capture rate and energy conversion efficiency were clarified, which is expected to provide a reference for the design of the photothermal reactor as well as the theoretical system of the solar energy carbon capture and conversion, and provide technological support for the realization of China’s “dual-carbon” strategic goal. It is expected to provide a reference basis for the design of photovoltaic reactor and the theoretical system of solar carbon capture and conversion, and provide technical support for the realization of China’s “dual-carbon” strategy.
  
  
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  Preparation and Thermophysical Properties of Hydrated Salt Phase Change Nanocapsules

  ZHU Xiaoyun, CHEN Ying, SHENG Xinxin, LI Jun, CHEN Kai, ZHANG Jialuan

  Journal of Engineering Thermophysics. 2025, 46(9): 3013-3017.

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  Due to their high energy storage density, high latent heat, non-flammability, low price, hydrated salt phase change materials process a broad prospect in the field of thermal energy storage. However, the shortcomings, such as its corrosion, phase separation and poor cycle stability, greatly limit its practical application. In this study, Na₂HPO₄·12H₂O was encapsulated in a polyurea shell layer of about 50 nm by interfacial polymerization to prepare the Na₂HPO₄·12H₂O@polyurea nanocapsule (NanoPCM). The results show that the phase change enthalpy of the NanoPCM is 153.39 J/g, and the enthalpy of the NanoPCM is basically unchanged after 1000 heating and cooling cycles. What’s more, the NanoPCM possesses excellent cycle stability and no phase separation phenomenon occurred. In addition, the problem of metal corrosion caused by hydrated salt is largely solved via the nanocapsule method.
  
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  Research on the Cooling Design Performance of Lithium-Ion Battery Based on PCM

  SHI Tianlu, AN Zhoujian, DU Xiaoze

  Journal of Engineering Thermophysics. 2025, 46(9): 3018-3026.

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  Due to the spatial limitations of electric vehicles, a more concise and lightweight battery thermal management system is needed to ensure the safety of lithium-ion batteries. In this study, a cylindrical lithium-ion battery internal and external cooling model based on phase change materials (PCM) was designed, and the effectiveness of the cooling design and the accuracy of the numerical model were verified. The effects of different cooling methods, PCM melting temperature, PCM latent heat, and PCM thermal conductivity on battery cooling performance were systematically evaluated from the perspectives of maximum temperature, maximum temperature difference, and temperature distribution. The results showed that using an internal cooling method based on PCM can achieve bidirectional heat transfer, reduce heat transfer resistance, lower temperature gradients, and make the temperature distribution more uniform. PCM with higher latent heat can effectively reduce the maximum temperature of the battery and improve the uniformity of the battery temperature distribution. The thermal conductivity of PCM has almost no effect on the maximum temperature and maximum temperature difference of the battery and has a relatively small effect on improving battery cooling performance.
  
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  Experimental Study on Flow Regime Transition in Grille-particle Composite Packed Bed

  JIA Haonan, TIAN Yuhang, YANG Jian, WANG Qiuwang

  Journal of Engineering Thermophysics. 2025, 46(9): 3027-3032.

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  The Grille-particle composite packed bed has garnered significant attention due to their ability to facilitate rapid and orderly particle packing. This study focuses on Grille-particle composite packed channels with a channel-to-particle diameter ratio of 1, investigating flow regime transition characteristics through local porosity analysis and visualization experiments. The results reveal that variations in local porosity at different positions within the packed channel lead to differences in the hydraulic Reynolds number (Re_H) at which flow regime transitions occur. However, the influence of dimpled structures on local porosity is relatively minor. Based on the flow characteristics in Region A, the Re_H marking the end of the laminar flow regime is approximately 278.43 for smooth particle packed channels and 268.04 for dimpled particle packed channels. Similarly, the Re_H indicating the onset of a turbulent-like flow regime is approximately 358.89 for smooth particle packed channels and 321.65 for dimpled particle packed channels.
  
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  Study on Characteristics of Heat and Water Recovery From Flue Gas by Hydrophilic Hollow Fiber Membrane

  XIAO Liehui, YANG Minlin, CHEN Jiechao, GE Ya, HUANG Simin

  Journal of Engineering Thermophysics. 2025, 46(9): 3033-3037.

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  Efficient and economical recovery of water and heat from flue gas of coal-fired power plants is an important way to achieve energy saving and emission reduction. Due to the low cost and high packing density of polymeric membrane, this paper uses hydrophilic hollow fiber membrane instead of traditional ceramic membrane. Based on the principle of heat and mass transfer of water vapor condensation and penetration, the heat and vapor of flue gas can be transported across membrane. The recovery characteristics and economy of a new type of hydrophilic polymeric membrane condenser (HPMC) were analyzed by establishing a physical and mathematical model. The results show that the recovery performance of HPMC and hydrophilic ceramic membrane condenser (HCMC) is similar under the same membrane area. With the increase of membrane area, the water/heat recovery flux per unit membrane area of HPMC decreases, but the water/heat recovery per unit volume increases. The recovered water cost of HPMC is at least 93.5% lower than that of HCMC, which has significant economic value.
  
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  Study on Heat Extraction Characteristics of Hot Dry Rock by Injecting Supercritical CO₂ into U-type Well

  CHEN Zhichao, HE Miao, CHEN Xin, YUAN Qingrui, SUN Pengcheng

  Journal of Engineering Thermophysics. 2025, 46(9): 3038-3047.

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  In order to study the heat extraction characteristics of supercritical carbon dioxide (SCO₂) in closed-loop geothermal system and its influencing factors, a temperature field model of hot dry rock extraction by circulating SCO₂ in U-shaped wells was constructed, and the model was solved by finite volume method. On this basis, the heat transfer law of SCO₂ and water in the wellbore is studied, and the sensitivity analysis of the parameters affecting the outlet temperature and heat recovery power is carried out. The results show that when the temperature difference between the production well and the injection well reaches 160°C, the density difference will reach 500 kg/m³, and such a significant density difference will produce an obvious density-driven thermosiphon. Under the same injection and production pressure difference, the outlet temperature and thermal production power of SCO₂ are increased by 19.8% and 28.8% respectively compared with that of water. Sensitivity parameter analysis shows that a larger injection flow will increase the heat recovery power, but will reduce the outlet temperature, and there is an optimal injection pressure (16 MPa), under which the outlet temperature and heat recovery power reach the maximum. This study can provide reference and theoretical reference for closed-loop geothermal exploitation. 
  
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  Study on the Annual Thermal Characteristics of Buried Pipe Group in Refrigeration-heat Storage-heating Integrated Thermal Energy System

  ZHANG Jie, NIU Chen, ZHU Xiaohua

  Journal of Engineering Thermophysics. 2025, 46(9): 3048-3056.

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  The integrated refrigeration-heat storage-heat supply system is one of the important models to realize the commercialization of geothermal energy. In order to investigate the heat transfer characteristics of the system, a numerical model of the heat transfer of the buried pipe group is established in this paper, the influence of design factors such as pipe type, pipe diameter, well spacing and layout form on the annual performance of integrated thermal energy system is studied. The results show that the heat capacity of W-type buried pipe is increased by 3% and 4% respectively compared with that of single U-type pipe The heat-supply capacity of the soil can be significantly enhanced by the formation heat storage in the cooling and heating stages. The heat storage capacity of 50°C is 25% and 12% higher than that of 40°C, respectively. The research results can provide theoretical and technical support for the design, optimization and operation of integrated energy system with middle-shallow geothermal energy as the main heat source.
  
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  Synergistic Transport of Trace Air for Lithium-Carbon Dioxide Battery

  ZHANG Zhuojun, XIAO Xu, YAN Aijing, TAN Peng

  Journal of Engineering Thermophysics. 2025, 46(9): 3057-3060.

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  To address the dynamics and transport issues that limit the performance of lithiumcarbon dioxide batteries, this work investigates the effect of trace air-carbon dioxide co-transport on battery performance and battery design for enhanced transport. Based on a precisely controlled test platform, it is revealed that trace air co-transport can improve the discharge platform of the battery by about 140% and the reduced reaction kinetics. The gas transport area is dramatically enhanced by the integrated electrode and bi-directional cell structure design. By adjusting the carbon electrode loading and optimizing the operating current density, a high-energy-density lithium carbon dioxide battery of 800 Wh/kg was achieved.
  
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  Ammonia Combustion Stability and Pollutant Generation Mechanisms for Combustion Engines

  ZHANG Meng, RUAN Yangfan, XIAO Tong, CHEN Jian, SI Gengfan, WEI Xutao, WANG Jinhua, HUANG Zuohua

  Journal of Engineering Thermophysics. 2025, 46(9): 3061-3075.

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  Global warming is one of the major challenges for the mankind. In order to reduce CO₂ emissions, it is necessary to build a new low-carbon/carbon-free and sustainable energy system. Ammonia, with its excellent fuel properties and carbon-free characteristics, as well as its ease of liquefaction and storage, shows great potential for development in the energy transition. However, there are challenges in the ammonia combustion process, including flame instability and high NO_x emissions. This paper reviews options to improve the flame stability and reduce NO_x emissions of ammonia through the addition of reactive small molecules, hydrogen-ammonia co-combustion, oxygen-enriched combustion technology, plasma-assisted combustion, and mild combustion. When hydrogen-ammonia fuel is used in combustion engine oriented, the ammonia combustion flame is more stable at high pressure, and the rich and lean combustion blowout equivalence ratio can be slightly prolonged by increasing the pressure due to the enhanced combustion intensity and denser flame at high pressure. Liquid ammonia has energy consumption and cost issues for combustion engine applications, but the stability of its spray flame can be improved by preheating the air and co-firing small molecule fuels.
  
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  Dynamic Study on Oxidation Coking Characteristics of RP-3 Aviation Kerosene

  DAI Weikang, JIN Kairu, KUANG Jiujie, WU Lingnan, TIAN Zhenyu

  Journal of Engineering Thermophysics. 2025, 46(9): 3076-3083.

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  The structural evolution of coke produced by oxidizing RP-3 aviation kerosene in a quartz tube was investigated using Raman spectroscopy. The influence of temperatures at 550°C, 575°C, 600°C, and 625°C on the coke evolution under normal pressure was examined. The gas reaction pathways of RP-3 were revealed through chemical reaction kinetics analysis of the model fuel. The coking process of RP-3 aviation kerosene can be categorized into five stages: gas reaction stage, physical settling stage, surface reaction stage, internal reaction stage, and layer accumulation stage. Both the surface and interior reaction times decrease with increasing temperature. Based on naphthalene conversion to A4, the coke conversion rates for aviation kerosene in this study were 0.43% (575°C), 0.66% (600°C), and 0.81% (625°C).
  
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  Comprehensive Weighted Sum of Gray Gases Model for Gas and Soot Radiative Characteristics of Hydrogen-blended Natural Gas Combustion Based on a High-resolution Database

  JIN Guopei, SHAN Shiquan, WANG Xinran, YU Jinhong, ZHOU Zhijun, WANG Zhihua, CEN Kefa

  Journal of Engineering Thermophysics. 2025, 46(9): 3084-3091.

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  This paper proposes a comprehensive weighted sum of gray gases (WSGG) model suitable for accurately capturing the gas and soot radiative characteristics of hydrogen-blended natural gas combustion. The model is based on the line-by-line (LBL) method using the HITEMP2010 spectral database. Compared to traditional WSGG models developed for conventional air-fuel combustion, this model can provide more accurate medium radiation property calculations. Through validation against emissivity data  and several one-dimensional test cases, the proposed model is shown to achieve results closely matching the benchmark model. Therefore, it can be reliably used for medium radiation calculations in actual engineering applications involving hydrogen-blended natural gas combustion, providing a robust foundation for burner design optimization and CFD calculations.
  
  
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  Research on the Smoke Spread Distance in a Double-Deck Tunnel Under Single-Sided Key Smoke Extraction

  WANG Zhan, HU Jiahao, FANG Zheng, TANG Zhi

  Journal of Engineering Thermophysics. 2025, 46(9): 3092-3100.

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  This study uses a scaled-down model of a double-deck shield tunnel with a branch pipe smoke extraction system as the prototype, focusing on a single-sided smoke extraction mode where only the fan on the side near the fire source is activated. A CFD numerical simulation model is established to compare and validate the experimental phenomena. Based on this, fire simulation conditions under different fire source conditions and smoke extraction fan volumes are carried out. The study explores the variation patterns of tunnel make-up airflow under fire and non-fire conditions in the single-sided smoke extraction mode, elucidating the mechanism by which fire smoke spreads further downstream. Additionally, it quantitatively demonstrates that the ratio of longitudinal smoke spread distances along both sides of the tunnel is approximately inversely proportional to the ratio of make-up air volumes on both sides of the tunnel.
  
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  Effect of Methane Addition on the Combustion and Explosion Characteristics of Hydrogen

  GAO Kai, JIN Kaiqiang, XIAO Huahua

  Journal of Engineering Thermophysics. 2025, 46(9): 3101-3108.

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  This paper discusses the effects of methane as a suppressive gas addition on hydrogen-air explosions from both experimental and theoretical perspectives. The results show that the addition of 2% methane increases the net rate of production of H free radicals in lean hydrogen-air mixtures, and more H free radicals participate in the reaction zone, which increases the flame instability, and eventually leads to the increase of explosion overpressure and laminar burning velocity. For stoichiometric and rich hydrogen-air mixtures, with the increase of methane volume fraction, the explosion parameters of hydrogen-air mixtures decrease monotonically. The reason is that methane can react with active free radicals to reduce the concentration of active free radicals in the reaction zone. Furthermore, the dehydrogenation of methane to produce methyl radicals can further decrease the concentration of active free radicals, leading to a transformation from active free radicals to inactive ones and thus slowing down the chain reaction rate.
  
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  Research Progress on Adaptability of High Alkali Coal Burning by Liquid Slag Removal

  FAN Cunjiang, GUO Xinwei, WU Xiaojiang, JIANG Yanchi, XU Zhitao, WANG Wei, ZHUO Lanting, TANG Yaoyi

  Journal of Engineering Thermophysics. 2025, 46(9): 3109-3118.

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  The high content of Na/Ca/Fe in high alkali coal in Xinjiang is the root cause of strong slagging and contamination in the combustion process. Although the main anti-slagging and pollution measures adopted at present are helpful to reduce the slagging and pollution degree of high alkali coal in Xinjiang and improve the proportion of mixed burning of high alkali coal in Xinjiang, it is still difficult to realize long cycle and high load total burning of high alkali coal. Especially for some high alkali coal with high iron content in Xinjiang, its furnace slagging is very serious, which further increases the difficulty of burning this kind of coal completely. For this reason, it is possible to burn this kind of coal by liquid slagging combustion. Based on the characteristics of high alkali coal quality in Xinjiang, this paper analyzes and summarizes the characteristics of melting slagging, viscosity-temperature and alkali metal release of typical high alkali coal liquid slagging combustion, and the latest research progress of burning high alkali coal by liquid slagging combustion at home and abroad. Under the combustion mode of liquid slag discharge, most of the low-melt substances in the high-alkali coal ash can be preferentially melted through the hightemperature combustion in the cyclone burner or the furnace, so as to realize the modification of the flue gas fly ash at the furnace outlet, and reduce the viscosity of the flue gas fly ash at the furnace outlet and the concentration of the flue gas key fly ash; In addition, by improving the ratio of slag to cement and increasing the mixing strength of high temperature flue gas and liquid slag film, the contamination degree of convection heating surface at the tail of liquid slag removal boiler can be further reduced.
  
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  Characteristics of Ammonia Oxygen-enriched Combustion Under O₂/H₂O and O₂/N₂ Atmosphere

  GAO Jilu, ZHANG Yu, ZHAO Yijun, ZENG Guang, SUN Shaozeng

  Journal of Engineering Thermophysics. 2025, 46(9): 3119-3133.

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  Oxy-fuel combustion is the crucial technology for achieving future zero-carbon, highefficiency ammonia power generation. Its development is limited by high flame temperature and nitrogen oxide emissions. Diluent technology, which includes nitrogen and steam dilution strategies, is essential for controlling flame temperature and NO_x emissions. This study numerically investigates the effects and mechanisms of steam and nitrogen dilution on flame speed, NO emissions, temperature, and extinction stretch rate in oxy-ammonia combustion. The results indicate that steam dilution’s inhibition efficiency of flame speed exhibits 1.22∼1.38 times compared to nitrogen dilution, and steam dilution reduces flame temperature and NO emissions more significantly. Under fuel-rich conditions, the inhibition of steam on flame temperature and NO emissions are further enhanced, while steam dilution increases NO emissions under fuel-lean conditions. Ammonia-rich flames with steam dilution are more prone to extinction than those with nitrogen dilution, and the extinction stretch limit narrows significantly under fuel-rich conditions.
  
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  Study on the Mixing and Pilot Diesel Ignition Characteristics of High-pressure Liquid Ammonia Spray

  XIONG Qian, HAN Kai, SHI Xinru, DENG Nannan, LIANG Dezhi, LIU Long

  Journal of Engineering Thermophysics. 2025, 46(9): 3134-3141.

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  A 520 mm diameter constant volume bomb model was constructed using the CONVERGE software to investigate the effects of the ammonia/diesel injector angle, ammonia/diesel injector injection angle and ammonia injection timing on mixing and pilot diesel ignition characteristics of high pressure liquid ammonia spray. The results show that optimal contact positions and diesel flame development area can elevate the peak of heat release rate. Smaller angle between ammonia/diesel injector is beneficial for the intersection of ammonia spray with the flame, enhancing the ignition effect. Larger injector injection angle will accelerate the ignition timing of ammonia spray. The impact location of ammonia spray on the flame is influenced by the ammonia injection timing, and collision position has an impact on ammonia ignition and emissions. Proper control of the injection timing helps optimize the contact between ammonia spray and the diesel flame.