Combustion and Flame最新文献

{"title":"Quantifying uncertainties in the input–output identification of Flame Transfer Functions","authors":"Justus Florian Radack,&nbsp;Bayu Dharmaputra,&nbsp;Bruno Schuermans,&nbsp;Nicolas Noiray","doi":"10.1016/j.combustflame.2025.114398","DOIUrl":"10.1016/j.combustflame.2025.114398","url":null,"abstract":"<div><div>The Finite Impulse Response model of a flame subject to acoustic forcing can be identified from numerical simulations. It is often subsequently used to obtain the frequency domain Flame Transfer Function (FTF). Its estimation from a finite time series introduces uncertainty in the model coefficients, affecting the prediction of the system response when implemented in a thermoacoustic network model. Quantifying how this uncertainty affects the identified FTF is commonly achieved by repeatedly sampling from the distribution of the model coefficients to obtain numerous model realizations and computing their Fourier transform. In the present work, we instead provide the exact mathematical connection between the uncertainty in the time and frequency domain, and give the sampling distributions for the gain and phase of the transfer function. Confidence intervals can then be associated with each predicted FTF value from a single time series. Moreover, by setting a permissible range in the gain and phase of the FTF, the appropriate time series length of the simulation can be determined on the fly.</div><div><strong>Novelty and Significance Statement</strong></div><div>In this paper, a novel approach to quantify uncertainties in Flame Transfer Functions (FTFs), which are crucial for predicting thermoacoustic instabilities in combustion systems, is introduced. This research provides an exact mathematical connection between uncertainties in the time domain impulse response and their impact on FTF gain and phase in the frequency domain. We derive sampling distributions for the gain and phase of the FTF, which enables the assignment of confidence intervals to the Bode representation of the FTF. This advancement helps determine the necessary simulation duration to achieve a desired uncertainty level, improving the reliability and efficiency of thermoacoustic predictions.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"281 ","pages":"Article 114398"},"PeriodicalIF":6.2,"publicationDate":"2025-08-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144911603","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Publication / Copyright Information","authors":"","doi":"10.1016/S0010-2180(25)00460-2","DOIUrl":"10.1016/S0010-2180(25)00460-2","url":null,"abstract":"","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"280 ","pages":"Article 114423"},"PeriodicalIF":6.2,"publicationDate":"2025-08-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144917127","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Impact of gasoline composition on the effects of nitric oxide on autoignition and knock in a DISI engine","authors":"Namho Kim ,&nbsp;Magnus Sjöberg ,&nbsp;Dario Lopez-Pintor ,&nbsp;Naoyoshi Matsubara ,&nbsp;Koji Kitano ,&nbsp;Ryota Yamada ,&nbsp;Chiara Saggese","doi":"10.1016/j.combustflame.2025.114367","DOIUrl":"10.1016/j.combustflame.2025.114367","url":null,"abstract":"<div><div>Modern spark-ignition engines use exhaust gas recirculation (EGR) to dilute the charge and suppress knock, enabling the use of higher compression ratios and/or more optimum combustion phasing for higher efficiency. The effectiveness of EGR is affected by the composition of the fuel and its chemical-kinetic interactions with combustion products. Among those, nitric oxide (NO) has been shown to strongly affect autoignition reactivity. However, the impact of fuel composition of the effect of NO on reactivity is not well-understood.</div><div>In this study, engine experiments were conducted to assess the impact of NO seeded to the intake on knock-limited operation of two gasoline fuels (high cycloalkane content, or HCA, and high olefin content, or HO). Results showed that compositionally-different fuels responded differently to NO. HCA, which was less knock-limited than HO for NO &lt; 200 ppm, became more knock-limited for NO &gt; 200 ppm. Moreover, it was found that differences in knock between fuels were caused by differences in autoignition chemistry and not in the sequential autoignition process of the end gas that occurs due to thermal stratification. Chemical kinetic simulations were performed to better understand the experimental results. For HCA, intermediate-temperature heat release had a greater impact on autoignition reactivity than low-temperature heat release, while the opposite was observed for HO. For both fuels, NO enhances the magnitude of low-temperature heat release via NO + HO₂ → NO₂ + OH. The effect of NO on reactivity was stronger for HCA because OH produced from NO helped to overcome the OH quenching effect of cyclopentane, a main species in HCA. In contrast, HO had relatively strong inherent low-temperature chemistry arising from iso-octane, which reduced the impact of NO on reactivity. For the range of NO mole fractions tested in this study, in-cylinder NO increased fuel’s knock propensity, especially for fuels with mild low-temperature chemistry.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"281 ","pages":"Article 114367"},"PeriodicalIF":6.2,"publicationDate":"2025-08-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144911594","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"On electrode placement in plasma-assisted ignition of a scramjet flame-holder","authors":"Rajath Shetty ,&nbsp;Cesar Cardenas ,&nbsp;Luca Massa","doi":"10.1016/j.combustflame.2025.114408","DOIUrl":"10.1016/j.combustflame.2025.114408","url":null,"abstract":"<div><div>A multi-scale model for plasma-assisted combustion is developed to investigate how the location of the electrodes in the cavity affects the ignition of supersonic flows in nanosecond repetitive pulse discharges. A new approach to plasma-fluid coupling is investigated that relies on solving the detailed plasma and photon transport equations on a near-electrode block partition of the overall mesh during the pulse and synchronizing the thermochemical balances with the reactive-fluid mesh by interpolation. The approach reproduces experimental observations of assisted ignition: the formation of trailing-edge flames in high-enthalpy conditions, the formation of localized ignition kernels near the cathode for medium-enthalpy conditions, and the presence of a distributed region of elevated OH mass fraction for conditions leading to no ignition. The approach matches the experimental measurement of plasma-energy coupling. The analysis emphasizes the significance of fluid strain rate in plasma-fluid coupling. The location of the electrode is found to affect ignition by supporting a larger radical turnover by plasma when the electrodes are placed in regions of lower strain, leading to a thicker reaction region.</div><div><strong>Novelty, Significance, and Contributions</strong>: A novel computational approach to plasma-gas coupling is developed and validated. This approach was applied to investigate the influence of strain rate on the focusing of pre-ionization electrons in the low-shear region of cavity stabilizers. The authors identify a correlation between strain rate and radical turnover number. This study led to the determination of the contribution of electrode placement to the efficacy of plasma actuation in supersonic flame-holders. The importance of the cathode location to supersonic ignition is investigated for the first time in detail. This research presents a significant advancement of previously published works: it models photoionization from first principles and includes the gas-plasma interactions in a three-dimensional turbulent flow.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"281 ","pages":"Article 114408"},"PeriodicalIF":6.2,"publicationDate":"2025-08-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144908133","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Thermal decomposition kinetics of furfural and furfuryl alcohol","authors":"Xin Zhang ,&nbsp;Dapeng Liu ,&nbsp;Yingjia Zhang ,&nbsp;Zuohua Huang ,&nbsp;Aamir Farooq","doi":"10.1016/j.combustflame.2025.114435","DOIUrl":"10.1016/j.combustflame.2025.114435","url":null,"abstract":"<div><div>The thermal decomposition of furfural and furfuryl alcohol plays a crucial role in shaping their combustion characteristics and assessing their viability as biofuels. Despite their importance, significant discrepancies remain in the literature regarding their decomposition pathways and reaction kinetics. Understanding these processes is essential for accurately modeling their behavior in combustion systems and optimizing their use in sustainable energy applications. This study presents the first direct measurements of the decomposition of furfural and furfuryl alcohol in a shock tube at temperatures ranging from 1264 to 1694 K and pressures ranging from 0.88 to 1.24 bar. We monitored the reaction progress by tracking the time-resolved decay of furfural (<em>k</em>₁) and furfuryl alcohol (<em>k</em>₂) using deep UV absorption diagnostics at 213 nm and 222 nm, respectively. The determined rate coefficients exhibit Arrhenius behavior and may be described as (unit: s^–1, uncertainty: ±20 %):<span><span><span><math><mrow><msub><mi>k</mi><mn>1</mn></msub><mo>=</mo><mn>3.84</mn><mspace></mspace><mo>×</mo><mspace></mspace><msup><mn>10</mn><mn>13</mn></msup><mspace></mspace><msup><mrow><mi>e</mi></mrow><mrow><mo>(</mo><mfrac><mrow><mo>−</mo><mn>33677</mn></mrow><mi>T</mi></mfrac><mo>)</mo></mrow></msup><mspace></mspace><mrow><mo>(</mo><mn>1288</mn><mspace></mspace><mo>−</mo><mspace></mspace><mn>1694</mn><mspace></mspace><mtext>K</mtext><mo>)</mo></mrow></mrow></math></span></span></span><span><span><span><math><mrow><msub><mi>k</mi><mn>2</mn></msub><mo>=</mo><mn>2.22</mn><mspace></mspace><mo>×</mo><mspace></mspace><msup><mn>10</mn><mn>11</mn></msup><mspace></mspace><msup><mrow><mi>e</mi></mrow><mrow><mo>(</mo><mfrac><mrow><mo>−</mo><mn>25305</mn></mrow><mi>T</mi></mfrac><mo>)</mo></mrow></msup><mspace></mspace><mrow><mo>(</mo><mn>1264</mn><mspace></mspace><mo>−</mo><mspace></mspace><mn>1621</mn><mspace></mspace><mtext>K</mtext><mo>)</mo></mrow></mrow></math></span></span></span></div><div>At 1400 K, the thermal decomposition of furfuryl alcohol proceeds 2.3 times faster than that of furfural, with an activation energy lower by 16.6 kcal mol⁻¹. However, at higher temperatures, both reactions exhibit reduced structural dependence, converging to similar rates by 1600 K. Our measurements help resolve discrepancies in previously reported rate coefficients, which vary by two orders of magnitude. Furthermore, this study offers a comprehensive comparison of the thermal decomposition kinetics of five-membered cyclic compounds, underscoring the impact of ring architecture and side-chain substituents. The measured rate coefficients improve prediction accuracy and provide valuable validation targets for existing models, shedding light on deficiencies in the current literature.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"281 ","pages":"Article 114435"},"PeriodicalIF":6.2,"publicationDate":"2025-08-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144908253","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Effects of low pressure and low temperature on aluminum agglomeration, gas phase flow velocity, and condensed combustion products in solid propellants","authors":"Xiaohui Xue ,&nbsp;Tuanwei Xu ,&nbsp;Bozhi Hu ,&nbsp;Wenke Zhang ,&nbsp;Jianzhong Liu","doi":"10.1016/j.combustflame.2025.114440","DOIUrl":"10.1016/j.combustflame.2025.114440","url":null,"abstract":"<div><div>In this study, the agglomeration behavior, gaseous combustion products flow velocity and characteristics of condensed combustion products (CCPs) from a HTPB-based solid propellant were systematically investigated under low-pressure and low-temperature conditions. Furthermore, the underlying mechanisms of these environmental effects were discussed. High-speed microscopic imaging was employed to observe and quantify the agglomeration behavior near the burning surface. Meanwhile, the gaseous combustion product stream velocity in this region was analyzed using both kinetic modeling and theoretical calculations. Experimental results show that when pressure decreases from 1 atm to 0.5 atm, the agglomerate occurrence frequency drops by 90.2 %, the average particle size increases by 14.4 %, and the gaseous product velocity rises by 52.1 %. When reducing the ambient temperature from 20 °C to −40 °C leads to an 18.1 % decrease in agglomerate frequency and a 6.5 % reduction in average particle size, while its effect on gaseous velocity remains inconclusive. Characterization of CCPs reveals that both low pressure and low temperature significantly alter the particle size distribution and reduce the combustion efficiency of solid propellants. Within the experimental conditions of this study (0.3 atm to 1 atm, −40 °C to 20 °C), the impact of pressure changes is greater than that of temperature.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"281 ","pages":"Article 114440"},"PeriodicalIF":6.2,"publicationDate":"2025-08-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144908254","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"On the existence of propagating circular flames in narrow channels","authors":"Alba Domínguez-González ,&nbsp;Vadim N. Kurdyumov ,&nbsp;Antonio L. Sánchez ,&nbsp;Daniel Martínez-Ruiz","doi":"10.1016/j.combustflame.2025.114415","DOIUrl":"10.1016/j.combustflame.2025.114415","url":null,"abstract":"<div><div>Previous studies involving extremely fuel-lean hydrogen–air mixtures enclosed between two parallel plates have revealed that combustion can occur in the form of isolated nearly circular flames propagating steadily. The structure and propagation velocity of these reactive fronts is investigated here via asymptotic methods and numerical analysis, exploiting the disparity of scales present in the problem. The modeling approach, accounting for the non-unity value of the fuel Lewis number and the presence of stabilizing heat losses to the confining walls, considers a one-step irreversible reaction with an Arrhenius rate having a large activation energy. The drift velocity is assumed to be small compared to the planar flame speed, leading to a low-Péclet-number approximation consistent with the nearly circular flame shape. Under this approximation, the flow exhibits an asymptotic structure comprising a near-field region dominated by molecular transport, containing the thin flame front, and a far-field region where reactant convection becomes significant. Through matched asymptotic expansions, a continuous family of steady-state solutions is obtained, with the propagation speed depending non-monotonically on the flame radius. The solution includes a branch of superadiabatic flames with small radii, a branch of subadiabatic flames with large radii, and an intermediate connecting branch where the velocity increases with increasing flame size. Numerical integrations for flames propagating in channels yield solutions along the intermediate branch, suggesting that the other two branches may be artifacts of the asymptotic analysis. The numerical results confirm the existence of a continuum of flame solutions, with velocities and radii closely matching the theoretical predictions.</div><div><strong>Novelty and significance statement</strong></div><div>A new theoretical description of nearly circular premixed flames propagating between two parallel plates is derived through low-Péclet-number and large-activation-energy limits. The complete two-dimensional description – subject to conductive heat losses to the confining walls – provides analytical closure relations between the size, temperature, and propagation speed of the flame structure. Although a continuum of steady-state solutions, divided into three distinguished branches, is obtained from the theoretical analysis, numerical simulations confirm the validity of the intermediate branch only. This subset indicates that ring-like flames can exist in a range of sizes and propagating speeds for small enough Lewis numbers of the fuel. The significance of this finding is underscored by the ongoing interest in accurately understanding the physical phenomena governing fuel storage, handling, and the mitigation of hazardous scenarios in applications using highly diffusive fuels like hydrogen.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"281 ","pages":"Article 114415"},"PeriodicalIF":6.2,"publicationDate":"2025-08-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144903338","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Large eddy simulations of transcritical e-fuel sprays using real-fluid multiphase flamelet-based modeling","authors":"Mohamad Fathi,&nbsp;Stefan Hickel,&nbsp;Dirk Roekaerts","doi":"10.1016/j.combustflame.2025.114360","DOIUrl":"10.1016/j.combustflame.2025.114360","url":null,"abstract":"<div><div>This study introduces a new numerical framework for the accurate simulation of transcritical reacting sprays using a multiphase, real-fluid, flamelet-based model. The transcritical flamelet library is combined with large-eddy simulations (LES) and rapid vapor–liquid equilibrium calculations in the context of a modern multiphase thermodynamic approach to explore vaporization dynamics, ignition characteristics, and soot formation. Current applications focus on the combustion of polyoxymethylene dimethyl ethers (OMEs), which are carbon-neutral e-fuels, in transcritical high-pressure configurations. Validation against experimental data shows a strong match in ignition delay and penetration lengths. The analysis of three OME<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span>– n-dodecane fuel blends reveals differences in evaporation, ignition, and soot production. Adding OME<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span> to n-dodecane reduces soot production and shortens the liquid penetration length and ignition delay time. The findings highlight the importance of further investigation into the effects of transcritical states and fuel composition on combustion performance and emissions.</div><div><strong>Novelty and significance</strong></div><div>This work introduces a modeling technique for the use of transcritical counterflow flames in flamelet modeling, expanding the capabilities of large-eddy simulations with multiphase thermodynamics (LES-MT) to accurately modeling transcritical combustion. By incorporating real-fluid effects and two-phase interactions, the transcritical flamelet library provides a high-fidelity representation of the complex behaviors in high-pressure multiphase autoignition scenarios. This calibration-free approach can significantly improve our understanding of the transcritical combustion of emerging fuels such as OME<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span> or their combination with traditional fuels such as n-dodecane.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"281 ","pages":"Article 114360"},"PeriodicalIF":6.2,"publicationDate":"2025-08-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144903340","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Unsteady dynamics and mode transitions in hybrid hydrogen–aluminum detonations","authors":"Pikai Zhang ,&nbsp;Yong Xu ,&nbsp;Huangwei Zhang ,&nbsp;Zheng Chen","doi":"10.1016/j.combustflame.2025.114438","DOIUrl":"10.1016/j.combustflame.2025.114438","url":null,"abstract":"<div><div>The hybrid detonation of hydrogen–aluminum mixtures represents a promising fuel combination, leveraging the high energy density of aluminum (Al) and the low ignition energy of hydrogen. This study investigates one-dimensional detonation wave propagation in hydrogen<strong>–</strong>oxygen<strong>–</strong>argon mixtures containing suspended Al particles, using a Eulerian–Lagrangian approach. The effects of particle loading and size on detonation dynamics are systematically examined. As the particle loading increases, four distinct regimes of shock propagation behavior are identified, and the transitions among these regimes are interpreted. In particular, two steady propagation modes in Regime I and Regime II are associated with distinct detonation structures: single-front detonation (SFD) and quasi-double-front detonation (quasi-DFD), respectively. For the quasi-DFD structure, a compression region, arising from interphase momentum and heat transfer, forms within the particle induction zone. The destabilization of this compression region is identified as the direct cause of the pulsating phenomenon observed in Regime III. The underlying mechanism of the pulsating detonation wave is analyzed in details. Regime IV is characterized by detonation failure. Besides the gas dynamics, the characteristics of particle-phase combustion are investigated. The results indicate that particle surface reactions transition from being primarily governed by diffusion to being increasingly by surface reaction kinetics, which serves as the fundamental trigger for the onset of unstable detonation. These findings provide valuable insights into the underlying mechanisms of hybrid hydrogen<strong>–</strong>aluminum detonations.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"281 ","pages":"Article 114438"},"PeriodicalIF":6.2,"publicationDate":"2025-08-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144903339","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Spontaneous combustion of high-pressure hydrogen leakage in the different sudden-expand tubes","authors":"Xuhai Pan ,&nbsp;Hechen Du ,&nbsp;Anzhi Sun ,&nbsp;Xin Gu ,&nbsp;Yong Cao ,&nbsp;Min Hua","doi":"10.1016/j.combustflame.2025.114437","DOIUrl":"10.1016/j.combustflame.2025.114437","url":null,"abstract":"<div><div>The shock wave propagation characteristic and the hydrogen spontaneous combustion phenomenon in the sudden expansion tubes during the high-pressure hydrogen leakage are investigated. The influence of the burst pressure and the sudden expansion length on the leading shock wave, overpressure, and the spontaneous combustion mechanism is studied with four different lengths and types of sudden expansion tubes. The pressure histories captured by four positions are used to analyze the overpressure intensity, the shock wave intensity, and the overpressure decay rate. The photoelectric signals in four positions are used to determine the occurrence of hydrogen spontaneous combustion. Results show that the addition of a sudden expansion structure increases the likelihood of autoignition and advances the autoignition position as burst pressure rises, but the intensity of autoignited flames within the tube weakens with increasing length. As the total length of the sudden expansion section increases, shock wave velocity within the tube decreases more rapidly. At low pressures, when shock waves enter the first two types of sudden expansion tubes, their trend shows no obvious difference from that in ordinary straight tube. However, when entering the T3 tube with a longer sudden expansion section, a process of velocity decrease followed by stabilization is observed. Compared to straight tube, in the sudden expansion tube with a shorter sudden expansion section of the same total length, shock wave intensity inside the tube is notably reduced, and the overpressure decay rate increases. The T4 tube with a longer sudden expansion section exhibits particularly significant effects in reducing shock wave intensity, velocity, and overpressure decay rate, especially under high-pressure conditions.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"281 ","pages":"Article 114437"},"PeriodicalIF":6.2,"publicationDate":"2025-08-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144895263","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}