Pub Date : 2025-12-31DOI: 10.1016/j.combustflame.2025.114740
Yeonse Kang, Fabian Hampp
<div><div>High-momentum jet-stabilised combustors promise fuel flexibility with low non-CO<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> emissions, yet compact integration with liquid fuels remains challenging. This study quantifies how low-swirl (<span><math><mrow><msub><mrow><mi>S</mi></mrow><mrow><mi>N</mi></mrow></msub><mo>≤</mo></mrow></math></span> 0.3) air perturbations stabilise a pressure-swirl spray and the ensuing turbulent jet flame using seven additively manufactured swirlers. Spray atomization is characterised by shadowgraphy and phase-Doppler interferometry; combustion is analysed via time-resolved OH<span><math><msup><mrow></mrow><mrow><mo>∗</mo></mrow></msup></math></span> chemiluminescence and NO<span><math><msub><mrow></mrow><mrow><mi>X</mi></mrow></msub></math></span> emissions. Introducing low swirl seeds small-scale turbulence and suppresses coherent structures near the central injector, yielding thinner liquid brushes, <span><math><mrow><msub><mrow><mi>d</mi></mrow><mrow><mn>32</mn></mrow></msub><mo><</mo></mrow></math></span> 10<!--> <span><math><mi>μ</mi></math></span>m, and <span><math><mo>∼</mo></math></span>50% more stable radial fuel placement relative to the no-swirl baseline. The resulting fuel distribution becomes more homogeneous in space and time, producing shorter, more symmetric flames (length reduced by up to <span><math><mo>∼</mo></math></span>65%) with diminished heat-release fluctuations. Proper orthogonal decomposition and spectra indicate a progression from jet-stabilised to mixed-mode and swirl-influenced regimes with no dominant resonant peak. A local fuel-loading metric links stabilisation to fuel placement at the nozzle edge, connecting spray organisation to flame symmetry and intermittency, relevant to the formation of non-CO<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> emissions. While the axially compact flame incurs moderately elevated NO<span><math><msub><mrow></mrow><mrow><mi>X</mi></mrow></msub></math></span> (10–30<!--> <!-->ppm at comparable load) in the present geometry, these increases are operationally manageable and can, for example in prefilming configurations, be translated into net emission benefits via symmetry-driven mixing improvements, outlining a clear optimisation pathway. Thus, embedding flow modulators such as low-swirlers can advance compact, liquid-fuel combustors for micro gas turbines and future hybrid aero-engine concepts.</div><div><strong>Novelty and Significance</strong></div><div>The current work investigates the implementation of additively manufactured low-swirl nozzles in a liquid-fuelled, high-momentum jet-stabilised combustor. Seven swirler configurations with vane angles <span><math><mrow><mrow><mo>|</mo><msub><mrow><mi>α</mi></mrow><mrow><mi>v</mi></mrow></msub><mo>|</mo></mrow><mo>=</mo><mn>0</mn><mo>,</mo><mo>±</mo><mn>15</mn><mo>,</mo><mo>±</mo><mn>30</mn><mo>,</mo><mo>±</mo><mn>45</mn></mrow></mat
{"title":"Low-swirl effects on spray flames for compact jet-stabilised combustion systems","authors":"Yeonse Kang, Fabian Hampp","doi":"10.1016/j.combustflame.2025.114740","DOIUrl":"10.1016/j.combustflame.2025.114740","url":null,"abstract":"<div><div>High-momentum jet-stabilised combustors promise fuel flexibility with low non-CO<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> emissions, yet compact integration with liquid fuels remains challenging. This study quantifies how low-swirl (<span><math><mrow><msub><mrow><mi>S</mi></mrow><mrow><mi>N</mi></mrow></msub><mo>≤</mo></mrow></math></span> 0.3) air perturbations stabilise a pressure-swirl spray and the ensuing turbulent jet flame using seven additively manufactured swirlers. Spray atomization is characterised by shadowgraphy and phase-Doppler interferometry; combustion is analysed via time-resolved OH<span><math><msup><mrow></mrow><mrow><mo>∗</mo></mrow></msup></math></span> chemiluminescence and NO<span><math><msub><mrow></mrow><mrow><mi>X</mi></mrow></msub></math></span> emissions. Introducing low swirl seeds small-scale turbulence and suppresses coherent structures near the central injector, yielding thinner liquid brushes, <span><math><mrow><msub><mrow><mi>d</mi></mrow><mrow><mn>32</mn></mrow></msub><mo><</mo></mrow></math></span> 10<!--> <span><math><mi>μ</mi></math></span>m, and <span><math><mo>∼</mo></math></span>50% more stable radial fuel placement relative to the no-swirl baseline. The resulting fuel distribution becomes more homogeneous in space and time, producing shorter, more symmetric flames (length reduced by up to <span><math><mo>∼</mo></math></span>65%) with diminished heat-release fluctuations. Proper orthogonal decomposition and spectra indicate a progression from jet-stabilised to mixed-mode and swirl-influenced regimes with no dominant resonant peak. A local fuel-loading metric links stabilisation to fuel placement at the nozzle edge, connecting spray organisation to flame symmetry and intermittency, relevant to the formation of non-CO<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> emissions. While the axially compact flame incurs moderately elevated NO<span><math><msub><mrow></mrow><mrow><mi>X</mi></mrow></msub></math></span> (10–30<!--> <!-->ppm at comparable load) in the present geometry, these increases are operationally manageable and can, for example in prefilming configurations, be translated into net emission benefits via symmetry-driven mixing improvements, outlining a clear optimisation pathway. Thus, embedding flow modulators such as low-swirlers can advance compact, liquid-fuel combustors for micro gas turbines and future hybrid aero-engine concepts.</div><div><strong>Novelty and Significance</strong></div><div>The current work investigates the implementation of additively manufactured low-swirl nozzles in a liquid-fuelled, high-momentum jet-stabilised combustor. Seven swirler configurations with vane angles <span><math><mrow><mrow><mo>|</mo><msub><mrow><mi>α</mi></mrow><mrow><mi>v</mi></mrow></msub><mo>|</mo></mrow><mo>=</mo><mn>0</mn><mo>,</mo><mo>±</mo><mn>15</mn><mo>,</mo><mo>±</mo><mn>30</mn><mo>,</mo><mo>±</mo><mn>45</mn></mrow></mat","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"285 ","pages":"Article 114740"},"PeriodicalIF":6.2,"publicationDate":"2025-12-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145881336","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}
Pub Date : 2025-12-30DOI: 10.1016/j.combustflame.2025.114739
Jinguo Sun , Kailun Zhang , Yupan Bao , Christian Brackmann , Mattias Richter , Alexander A. Konnov , Andreas Ehn
Direct, time-resolved measurements of the amino radical (NH2) are critical for understanding plasma-assisted ammonia (NH3) combustion, in terms of both plasma-accelerated NH3 decomposition and reduced NOx emission, yet such data remain scarce. The current study focuses on the spatiotemporal characteristics of NH2 using laser-induced fluorescence (LIF) in a quasi-one-dimensional NH3/air flame subjected to a pin-to-pin nanosecond pulsed discharge (NPD), and comparatively analyzes the plasma effects in both the unburnt and burnt zones. In the unburnt zone for both lean and rich flames, a considerable amount of NH2 is observed with signal intensities of 3–4 times that in the flame front without plasma, demonstrating the capability of NPD in enhancing NH3 decomposition. The spatial and temporal dynamics of plasma-produced NH2 are explored over timescales ranging from hundreds of nanoseconds to milliseconds following a single NPD pulse. The results indicate that NH2 reaches its peak before 700 ns after the discharge initiation, highlighting the role of plasma kinetics in dissociating NH3 through electrons, excited nitrogen molecules, and O(1D). The generated NH2 subsequently undergoes an exponential decay with a characteristic lifetime of 3–4 μs. This consumption is mainly driven by combustion kinetics, where several diverging pathways are identified as possible reaction routes. Moreover, a “butterfly-like” distribution of plasma-produced NH2, is characterized by lower signals and faster decay in the center, both of which are attributed to the higher temperature within the center of discharge channel. In the burnt zone, NH2 is only detected in the rich flame, and decays much faster (∼1.3 μs) compared to the unburnt zone. The unique experimental data of plasma-produced NH2 provide valuable insights into plasma-assisted NH3 combustion and deliver critical experimental data for the development and refinement of kinetic models.
{"title":"Spatiotemporal imaging of NH2 in plasma-assisted NH3 combustion via nanosecond pulsed discharge","authors":"Jinguo Sun , Kailun Zhang , Yupan Bao , Christian Brackmann , Mattias Richter , Alexander A. Konnov , Andreas Ehn","doi":"10.1016/j.combustflame.2025.114739","DOIUrl":"10.1016/j.combustflame.2025.114739","url":null,"abstract":"<div><div>Direct, time-resolved measurements of the amino radical (NH<sub>2</sub>) are critical for understanding plasma-assisted ammonia (NH<sub>3</sub>) combustion, in terms of both plasma-accelerated NH<sub>3</sub> decomposition and reduced NO<sub>x</sub> emission, yet such data remain scarce. The current study focuses on the spatiotemporal characteristics of NH<sub>2</sub> using laser-induced fluorescence (LIF) in a quasi-one-dimensional NH<sub>3</sub>/air flame subjected to a pin-to-pin nanosecond pulsed discharge (NPD), and comparatively analyzes the plasma effects in both the unburnt and burnt zones. In the unburnt zone for both lean and rich flames, a considerable amount of NH<sub>2</sub> is observed with signal intensities of 3–4 times that in the flame front without plasma, demonstrating the capability of NPD in enhancing NH<sub>3</sub> decomposition. The spatial and temporal dynamics of plasma-produced NH<sub>2</sub> are explored over timescales ranging from hundreds of nanoseconds to milliseconds following a single NPD pulse. The results indicate that NH<sub>2</sub> reaches its peak before 700 ns after the discharge initiation, highlighting the role of plasma kinetics in dissociating NH<sub>3</sub> through electrons, excited nitrogen molecules, and O(<sup>1</sup>D). The generated NH<sub>2</sub> subsequently undergoes an exponential decay with a characteristic lifetime of 3–4 μs. This consumption is mainly driven by combustion kinetics, where several diverging pathways are identified as possible reaction routes. Moreover, a “butterfly-like” distribution of plasma-produced NH<sub>2</sub>, is characterized by lower signals and faster decay in the center, both of which are attributed to the higher temperature within the center of discharge channel. In the burnt zone, NH<sub>2</sub> is only detected in the rich flame, and decays much faster (∼1.3 μs) compared to the unburnt zone. The unique experimental data of plasma-produced NH<sub>2</sub> provide valuable insights into plasma-assisted NH<sub>3</sub> combustion and deliver critical experimental data for the development and refinement of kinetic models.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"285 ","pages":"Article 114739"},"PeriodicalIF":6.2,"publicationDate":"2025-12-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145881337","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}
Pub Date : 2025-12-29DOI: 10.1016/j.combustflame.2025.114744
Jose I. Guerrero, Mirko Gamba
This work presents a framework to obtain reference-free combustion efficiency measurements in rotating detonation engines using a chemical balance model and a time-averaged H2O mole fraction. Because a time-resolved pressure measurement was not available, a new post-processing method was developed to estimate a time-averaged H2O mole fraction directly from time-resolved partial pressure measurements. The approach is demonstrated in an RDE with a 50% converging exit nozzle. Temperature and H2O were measured in-situ at 1 MHz using a single-ended scanned-wavelength-modulation spectroscopy sensor. Results across a range of equivalence ratios (–1.5) and mass flowrates (150–350 g/s) showed combustion efficiencies of 50%–65%, with uncertainties between 14%–16% for most cases. Clear trends were identified between combustion efficiency, equivalence ratio, and wave speed ratios ( CJ). This framework enables accurate characterization of energy conversion losses in RDEs and supports future performance optimization.
Novelty and Significance Statement
This work involves the development and application of a novel method for measuring the combustion efficiency of H2-air rotating detonation engines (RDEs) using a chemical balance model and measurable state quantities. The approach is innovative for three reasons: (1) it defines combustion efficiency based on a conserved quantity (mass), allowing the pressure gain combustion community to move beyond proxy definitions, which facilitates integration of measurements with reduced-order models, (2) it eliminates the need for both a reference equilibrium state and a time-resolved pressure measurement when interpreting measured state quantities, and (3) it is applicable across the full operating range of RDEs. In addition, the measurements in this work are the first publicly available combustion efficiency dataset obtained across a range of operating conditions using laser absorption spectroscopy at acquisition rates exceeding 50 kHz. The method and dataset provide a foundation for quantitatively assessing energy conversion processes and performance deficits in detonation-based engines.
{"title":"Quantifying combustion efficiency in rotating detonation engines using MHz-rate scanned-wavelength-modulation spectroscopy","authors":"Jose I. Guerrero, Mirko Gamba","doi":"10.1016/j.combustflame.2025.114744","DOIUrl":"10.1016/j.combustflame.2025.114744","url":null,"abstract":"<div><div>This work presents a framework to obtain reference-free combustion efficiency measurements in rotating detonation engines using a chemical balance model and a time-averaged H<sub>2</sub>O mole fraction. Because a time-resolved pressure measurement was not available, a new post-processing method was developed to estimate a time-averaged H<sub>2</sub>O mole fraction directly from time-resolved partial pressure measurements. The approach is demonstrated in an RDE with a 50% converging exit nozzle. Temperature and <span><math><mi>P</mi></math></span> <sub>H<sub>2</sub>O</sub> were measured <em>in-situ</em> at 1 MHz using a single-ended scanned-wavelength-modulation spectroscopy sensor. Results across a range of equivalence ratios (<span><math><mrow><mi>Φ</mi><mo>≈</mo><mn>0</mn><mo>.</mo><mn>55</mn></mrow></math></span>–1.5) and mass flowrates (150–350 g/s) showed combustion efficiencies of 50%–65%, with uncertainties between 14%–16% for most cases. Clear trends were identified between combustion efficiency, equivalence ratio, and wave speed ratios (<span><math><mrow><mi>D</mi><mo>/</mo><mi>D</mi></mrow></math></span> <sub>CJ</sub>). This framework enables accurate characterization of energy conversion losses in RDEs and supports future performance optimization.</div><div><strong>Novelty and Significance Statement</strong></div><div>This work involves the development and application of a novel method for measuring the combustion efficiency of H<sub>2</sub>-air rotating detonation engines (RDEs) using a chemical balance model and measurable state quantities. The approach is innovative for three reasons: (1) it defines combustion efficiency based on a conserved quantity (mass), allowing the pressure gain combustion community to move beyond proxy definitions, which facilitates integration of measurements with reduced-order models, (2) it eliminates the need for both a reference equilibrium state and a time-resolved pressure measurement when interpreting measured state quantities, and (3) it is applicable across the full operating range of RDEs. In addition, the measurements in this work are the first publicly available combustion efficiency dataset obtained across a range of operating conditions using laser absorption spectroscopy at acquisition rates exceeding 50 kHz. The method and dataset provide a foundation for quantitatively assessing energy conversion processes and performance deficits in detonation-based engines.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"285 ","pages":"Article 114744"},"PeriodicalIF":6.2,"publicationDate":"2025-12-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145881341","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}
Pub Date : 2025-12-29DOI: 10.1016/j.combustflame.2025.114731
Vigneshwaran Sankar , Xiangrong Huang , Karl P. Chatelain , Rémy Mével , Deanna A. Lacoste
<div><div>This study examines the impact of reaction rate uncertainties by performing a series of two-dimensional simulations of detonation propagating in a weakly unstable mixture 2H<sub>2</sub>+O<sub>2</sub>+3.76Ar at 20 kPa and 295<!--> <!-->K. Several chemical models, namely, FFCM-2, Hong 2011, Mével 2014, and San Diego 2016, were employed, while the experimental targets used for quantifying the impact of uncertainties correspond to the cell width (<span><math><mi>λ</mi></math></span>), its distribution (<span><math><mrow><mn>2</mn><mi>σ</mi><mo>/</mo><mi>λ</mi></mrow></math></span>), the induction zone length (<span><math><msub><mrow><mi>Δ</mi></mrow><mrow><mi>i</mi></mrow></msub></math></span>), and the normalized shock speed (<span><math><mrow><mi>D</mi><mo>/</mo><msub><mrow><mi>D</mi></mrow><mrow><mi>CJ</mi></mrow></msub></mrow></math></span>) dynamics within a cell cycle. Two extreme versions of each model, either maximizing or minimizing <span><math><msub><mrow><mi>Δ</mi></mrow><mrow><mi>i</mi></mrow></msub></math></span>, are created by perturbing the five most sensitive reactions within their (1<span><math><mi>σ</mi></math></span>) uncertainty limit: denoted by <span><math><msub><mrow></mrow><mrow><mo>±</mo><mn>1</mn><mi>σ</mi></mrow></msub></math></span>. Depending on the reaction model, the <span><math><msub><mrow><mi>λ</mi></mrow><mrow><mtext>mean</mtext></mrow></msub></math></span> predictions may be strongly influenced by the initial kinetic model and rate perturbations. The variability of the cell size (<span><math><mrow><mn>2</mn><mi>σ</mi><mo>/</mo><mi>λ</mi></mrow></math></span>) differs by factors of 1.2 to 8 when perturbed reaction models are used, with some models transitioning from a regular to an irregular cellular structure. FFCM-2<span><math><msub><mrow></mrow><mrow><mo>−</mo><mn>1</mn><mi>σ</mi></mrow></msub></math></span> shows the closest agreement with experimental <span><math><msub><mrow><mi>λ</mi></mrow><mrow><mtext>mean</mtext></mrow></msub></math></span> and <span><math><mrow><mn>2</mn><mi>σ</mi><mo>/</mo><mi>λ</mi></mrow></math></span>. While <span><math><msub><mrow><mi>Δ</mi></mrow><mrow><mi>i</mi></mrow></msub></math></span> predictions improve with FFCM-2<span><math><msub><mrow></mrow><mrow><mo>−</mo><mn>1</mn><mi>σ</mi></mrow></msub></math></span>, the slope of <span><math><mrow><msub><mrow><mi>Δ</mi></mrow><mrow><mi>i</mi></mrow></msub><mo>=</mo><mi>f</mi><mrow><mo>(</mo><mi>D</mi><mo>/</mo><msub><mrow><mi>D</mi></mrow><mrow><mi>CJ</mi></mrow></msub><mo>)</mo></mrow></mrow></math></span> remains largely unaffected by reaction rate uncertainty. Similarly, the evolution of <span><math><msub><mrow><mi>Δ</mi></mrow><mrow><mi>i</mi></mrow></msub></math></span> as a function of the relative cell length, or as a function of the distance between consecutive triple points <span><math><mrow><mo>(</mo><msub><mrow><mi>d</mi></mrow><mrow><mtext>TP</mtext></mrow></msub><mo>)</mo></mrow></math></span>, is the closest fo
本研究通过对2H2+O2+3.76Ar弱不稳定混合物在20 kPa和295 K下的爆轰传播进行一系列二维模拟，考察了反应速率不确定性的影响。本文采用了FFCM-2、Hong 2011、m录影带2014和San Diego 2016等化学模型，而用于量化不确定性影响的实验目标分别为细胞宽度（λ）、细胞宽度分布（2σ/λ）、诱导区长度（Δi）和细胞周期内的归一化激波速度（D/DCJ）动态。每个模型的两个极端版本，要么最大化要么最小化Δi，是通过在（1σ）不确定性极限内扰动五个最敏感的反应来创建的：用±1σ表示。根据反应模型的不同，λ均值预测可能受到初始动力学模型和速率扰动的强烈影响。当使用微扰反应模型时，细胞大小的可变性（2σ/λ）相差1.2至8倍，一些模型从规则细胞结构过渡到不规则细胞结构。FFCM-2−1σ与实验λ均值和2σ/λ最接近。虽然使用FFCM-2−1σ可以改善Δi的预测，但Δi=f（D/DCJ）的斜率在很大程度上不受反应速率不确定性的影响。同样，对于FFCM-2−1σ， Δi作为相对细胞长度的函数，或作为连续三点之间的距离（dTP）的函数的演化最接近，但与实验结果仍然存在一些差异。在爆轰模拟中观察到的典型的实验-数值差异不能仅仅归因于反应速率的不确定性。化学模型性能、三维效应、振动非平衡或它们的非线性相互作用中的其他因素也必须对差异负责。未来的爆轰模拟应系统地评估其1σ反应速率不确定性的重要性，因为反应模型对这些不确定性的敏感性不能先验地估计。新颖性和意义声明：本研究利用四种氢氧化动力学模型对二维爆轰模拟中的反应速率不确定性提供了一种新的综合定量评估方法。通过在不确定性（±1σ）范围内系统地干扰最敏感的反应速率，本研究分离了模型选择和速率不确定性对关键爆轰指标（即细胞大小、细胞变异性和诱导区长度动力学）的各自贡献。这项工作的意义在于证明了反应速率的不确定性不能单独解释典型的实验-数值差异。此外，本研究强调需要将±1σ不确定性分析作为未来多维爆炸模拟的标准实践。本文的结论得到了12个二维爆轰模拟的综合分析的支持。
{"title":"Role of reaction rate uncertainties on the dynamics of two-dimensional detonation","authors":"Vigneshwaran Sankar , Xiangrong Huang , Karl P. Chatelain , Rémy Mével , Deanna A. Lacoste","doi":"10.1016/j.combustflame.2025.114731","DOIUrl":"10.1016/j.combustflame.2025.114731","url":null,"abstract":"<div><div>This study examines the impact of reaction rate uncertainties by performing a series of two-dimensional simulations of detonation propagating in a weakly unstable mixture 2H<sub>2</sub>+O<sub>2</sub>+3.76Ar at 20 kPa and 295<!--> <!-->K. Several chemical models, namely, FFCM-2, Hong 2011, Mével 2014, and San Diego 2016, were employed, while the experimental targets used for quantifying the impact of uncertainties correspond to the cell width (<span><math><mi>λ</mi></math></span>), its distribution (<span><math><mrow><mn>2</mn><mi>σ</mi><mo>/</mo><mi>λ</mi></mrow></math></span>), the induction zone length (<span><math><msub><mrow><mi>Δ</mi></mrow><mrow><mi>i</mi></mrow></msub></math></span>), and the normalized shock speed (<span><math><mrow><mi>D</mi><mo>/</mo><msub><mrow><mi>D</mi></mrow><mrow><mi>CJ</mi></mrow></msub></mrow></math></span>) dynamics within a cell cycle. Two extreme versions of each model, either maximizing or minimizing <span><math><msub><mrow><mi>Δ</mi></mrow><mrow><mi>i</mi></mrow></msub></math></span>, are created by perturbing the five most sensitive reactions within their (1<span><math><mi>σ</mi></math></span>) uncertainty limit: denoted by <span><math><msub><mrow></mrow><mrow><mo>±</mo><mn>1</mn><mi>σ</mi></mrow></msub></math></span>. Depending on the reaction model, the <span><math><msub><mrow><mi>λ</mi></mrow><mrow><mtext>mean</mtext></mrow></msub></math></span> predictions may be strongly influenced by the initial kinetic model and rate perturbations. The variability of the cell size (<span><math><mrow><mn>2</mn><mi>σ</mi><mo>/</mo><mi>λ</mi></mrow></math></span>) differs by factors of 1.2 to 8 when perturbed reaction models are used, with some models transitioning from a regular to an irregular cellular structure. FFCM-2<span><math><msub><mrow></mrow><mrow><mo>−</mo><mn>1</mn><mi>σ</mi></mrow></msub></math></span> shows the closest agreement with experimental <span><math><msub><mrow><mi>λ</mi></mrow><mrow><mtext>mean</mtext></mrow></msub></math></span> and <span><math><mrow><mn>2</mn><mi>σ</mi><mo>/</mo><mi>λ</mi></mrow></math></span>. While <span><math><msub><mrow><mi>Δ</mi></mrow><mrow><mi>i</mi></mrow></msub></math></span> predictions improve with FFCM-2<span><math><msub><mrow></mrow><mrow><mo>−</mo><mn>1</mn><mi>σ</mi></mrow></msub></math></span>, the slope of <span><math><mrow><msub><mrow><mi>Δ</mi></mrow><mrow><mi>i</mi></mrow></msub><mo>=</mo><mi>f</mi><mrow><mo>(</mo><mi>D</mi><mo>/</mo><msub><mrow><mi>D</mi></mrow><mrow><mi>CJ</mi></mrow></msub><mo>)</mo></mrow></mrow></math></span> remains largely unaffected by reaction rate uncertainty. Similarly, the evolution of <span><math><msub><mrow><mi>Δ</mi></mrow><mrow><mi>i</mi></mrow></msub></math></span> as a function of the relative cell length, or as a function of the distance between consecutive triple points <span><math><mrow><mo>(</mo><msub><mrow><mi>d</mi></mrow><mrow><mtext>TP</mtext></mrow></msub><mo>)</mo></mrow></math></span>, is the closest fo","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"285 ","pages":"Article 114731"},"PeriodicalIF":6.2,"publicationDate":"2025-12-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145881335","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}
Pub Date : 2025-12-28DOI: 10.1016/j.combustflame.2025.114743
Jiaxin Xie , Mengmeng Jia , Frederick Nii Ofei Bruce , Chong-Wen Zhou , Henry Curran , Taufiq Yap Yun Hin , Song Cheng , Ce Sun , Fei Qin , Yang Li
2-Ethylhexyl nitrate (EHN) has attracted attention for its high reactivity, making it a promising candidate for use in propellants and as a combustion-enhancing fuel additive. To gain a fundamental understanding of its combustion behavior and support its practical application in advanced propulsion systems, it is essential to develop an accurate and reliable chemical kinetic model. In this study, ignition delay times (IDTs) of EHN/O₂/N₂ mixtures were systematically measured using a high-pressure shock tube. Experiments were conducted over a temperature range of 900–2000 K, at pressures of 5 and 10 bar, and under equivalence ratios of 0.5 and 1.0. The results clearly demonstrate the characteristic two-stage ignition behavior of EHN. Moreover, the IDTs were found to be highly sensitive to changes in both equivalence ratio and pressure. In the theoretical investigation, the initial decomposition pathways of EHN were systematically explored using high-level quantum chemical calculations at the QCISD(T)/CBS//M06–2X/6–311++G (d,p) level. The results indicate that cleavage of the O–N bond is the dominant reaction channel. A detailed kinetic model for EHN was developed based on the C3MechV3.3 reaction mechanism. The model predictions show good agreement with experimentally measured IDT. Furthermore, based on the current kinetic model, sensitivity, flux, and OH radical rate of production analyses were performed to identify key controlling steps and characterize radical-driven kinetics. The results show that in the first stage of ignition, over 90% of EHN is consumed via O–N bond cleavage, producing the 2-ethylhexoxy radical (EHO) and NO₂, which spontaneously initiate the NO₂–NO catalytic cycle and significantly enhance the system’s initial reactivity. In contrast, during the second stage, the chain-branching reaction H + O₂ → O + OH becomes dominant and serves as the primary driving force behind the rapid acceleration of system reactivity.
{"title":"An experimental and kinetic modeling study of the autoignition mechanism of 2-ethylhexyl nitrate combustion","authors":"Jiaxin Xie , Mengmeng Jia , Frederick Nii Ofei Bruce , Chong-Wen Zhou , Henry Curran , Taufiq Yap Yun Hin , Song Cheng , Ce Sun , Fei Qin , Yang Li","doi":"10.1016/j.combustflame.2025.114743","DOIUrl":"10.1016/j.combustflame.2025.114743","url":null,"abstract":"<div><div>2-Ethylhexyl nitrate (EHN) has attracted attention for its high reactivity, making it a promising candidate for use in propellants and as a combustion-enhancing fuel additive. To gain a fundamental understanding of its combustion behavior and support its practical application in advanced propulsion systems, it is essential to develop an accurate and reliable chemical kinetic model. In this study, ignition delay times (IDTs) of EHN/O₂/N₂ mixtures were systematically measured using a high-pressure shock tube. Experiments were conducted over a temperature range of 900–2000 K, at pressures of 5 and 10 bar, and under equivalence ratios of 0.5 and 1.0. The results clearly demonstrate the characteristic two-stage ignition behavior of EHN. Moreover, the IDTs were found to be highly sensitive to changes in both equivalence ratio and pressure. In the theoretical investigation, the initial decomposition pathways of EHN were systematically explored using high-level quantum chemical calculations at the QCISD(T)/CBS//M06–2X/6–311++<em>G</em> (d,p) level. The results indicate that cleavage of the O–N bond is the dominant reaction channel. A detailed kinetic model for EHN was developed based on the C3MechV3.3 reaction mechanism. The model predictions show good agreement with experimentally measured IDT. Furthermore, based on the current kinetic model, sensitivity, flux, and OH radical rate of production analyses were performed to identify key controlling steps and characterize radical-driven kinetics. The results show that in the first stage of ignition, over 90% of EHN is consumed via O–N bond cleavage, producing the 2-ethylhexoxy radical (EHO) and NO₂, which spontaneously initiate the NO₂–NO catalytic cycle and significantly enhance the system’s initial reactivity. In contrast, during the second stage, the chain-branching reaction <em>H</em> + <em>O</em>₂ → <em>O</em> + OH becomes dominant and serves as the primary driving force behind the rapid acceleration of system reactivity.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"285 ","pages":"Article 114743"},"PeriodicalIF":6.2,"publicationDate":"2025-12-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145881340","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}
The current study investigates NH3/H2 non-premixed flames stabilized on a Jet-in-Hot-Co-flow (JHC) burner, with a focus on identifying the conditions that enable transition to the MILD regime. Experiments were conducted at a fixed co-flow temperature of 1180 K, with co-flow oxygen concentrations in H2/N2/O2 combustion products ranging from 3 % to 9 % by mass, and hydrogen dilution in the fuel varied between 0 % and 15 % by volume. Flame structure and radical distribution were characterized using simultaneous planar laser-induced fluorescence (PLIF) imaging of NH and OH radicals, in combination with temperature measurements. The results show that a small amount of hydrogen (1 % vol) effectively reduces the local auto-ignition temperature below the co-flow temperature, independent of the oxygen concentration. This implies that minor initial dissociation of ammonia can help in the transition to the MILD combustion regime. At 9 % oxygen concentration, three distinct combustion regimes were observed as hydrogen dilution increases from 0 % to 15%: no visible reaction, a stable visible reaction zone, and a standard turbulent flame. In contrast, such regime transitions were absent at 3 % oxygen, highlighting the essential role of oxidizer reactivity in enabling MILD combustion. Despite meeting the temperature-based criteria for MILD combustion, NO emissions remained relatively high and consistent (∼800 ppm) at 250 mm downstream of the jet across all MILD cases. N2O exhibited strong sensitivity to hydrogen dilution, increasing from 90 ppm to 780 ppm as the hydrogen dilution rose from 3 % to 15 %. These findings highlight the need for revised and more comprehensive criteria to define MILD combustion in NH₃-fueled environments.
{"title":"Ammonia/hydrogen non-premixed turbulent jet flames stabilized on a hot and diluted co-flow burner","authors":"Lele Ren , Adamu Alfazazi , Aurora Maffei , Sonu Kumar , Heinz Pitsch , Bassam Dally","doi":"10.1016/j.combustflame.2025.114741","DOIUrl":"10.1016/j.combustflame.2025.114741","url":null,"abstract":"<div><div>The current study investigates NH<sub>3</sub>/H<sub>2</sub> non-premixed flames stabilized on a Jet-in-Hot-Co-flow (JHC) burner, with a focus on identifying the conditions that enable transition to the MILD regime. Experiments were conducted at a fixed co-flow temperature of 1180 K, with co-flow oxygen concentrations in H<sub>2</sub>/N<sub>2</sub>/O<sub>2</sub> combustion products ranging from 3 % to 9 % by mass, and hydrogen dilution in the fuel varied between 0 % and 15 % by volume. Flame structure and radical distribution were characterized using simultaneous planar laser-induced fluorescence (PLIF) imaging of NH and OH radicals, in combination with temperature measurements. The results show that a small amount of hydrogen (1 % vol) effectively reduces the local auto-ignition temperature below the co-flow temperature, independent of the oxygen concentration. This implies that minor initial dissociation of ammonia can help in the transition to the MILD combustion regime. At 9 % oxygen concentration, three distinct combustion regimes were observed as hydrogen dilution increases from 0 % to 15%: no visible reaction, a stable visible reaction zone, and a standard turbulent flame. In contrast, such regime transitions were absent at 3 % oxygen, highlighting the essential role of oxidizer reactivity in enabling MILD combustion. Despite meeting the temperature-based criteria for MILD combustion, NO emissions remained relatively high and consistent (∼800 ppm) at 250 mm downstream of the jet across all MILD cases. N<sub>2</sub>O exhibited strong sensitivity to hydrogen dilution, increasing from 90 ppm to 780 ppm as the hydrogen dilution rose from 3 % to 15 %. These findings highlight the need for revised and more comprehensive criteria to define MILD combustion in NH₃-fueled environments.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"285 ","pages":"Article 114741"},"PeriodicalIF":6.2,"publicationDate":"2025-12-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145881342","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}
Pub Date : 2025-12-27DOI: 10.1016/j.combustflame.2025.114755
Aryan Nobakht, Ahmet E. Karataş
This study investigates the influence of pressure on synergistic soot formation in co-flow laminar diffusion flames of ethylene/propane mixtures (1–6 atm). Radially resolved fields of soot volume fraction, temperature, and the soot absorption function, , were obtained using three-color line-of-sight attenuation and spectral soot emission techniques. Synergistic promotion of soot formation was observed at all pressures, but its strength varied with pressure: at 1 atm, the peak soot volume fraction increased from 1.24 ppm in neat ethylene to 1.52 ppm with 5% carbon from propane, whereas at 6 atm it increased only marginally from 86.4 ppm to 90.3 ppm. Normalized soot yield revealed the strongest nonlinearity at 2 atm, followed by 3 atm, then 1 atm, 4 atm, 5 atm, and 6 atm. Temperatures for different mixtures at a given pressure were similar and primarily controlled by soot loading and associated radiative losses. The measurements show that varies both spectrally and spatially; values are notably lower than the commonly assumed 0.26 in nascent soot regions near the flame base and higher elsewhere. This variation demonstrates that a constant can misestimate soot volume fraction depending on location and wavelength. Despite substantial differences in soot concentration among mixtures, soot maturity distributions were broadly similar. These results provide high-fidelity data for model validation and emphasize the need to account for wavelength-dependent optical properties when quantifying soot at elevated pressures.
Novelty and significance statement
This study provides the first multi-parameter characterization of synergistic soot formation in ethylene/propane diffusion flames at elevated pressures. By introducing a wavelength-dependent absorption function, , it captures spatial variation in soot maturity and improves quantification. The results demonstrate persistent synergistic effects across pressures and yield novel mechanistic insights, including rate-limiting steps, with direct relevance to predictive soot models for high-pressure combustion systems using blended fuels.
{"title":"Pressure dependence of synergistic soot formation in ethylene/propane co-flow diffusion flames","authors":"Aryan Nobakht, Ahmet E. Karataş","doi":"10.1016/j.combustflame.2025.114755","DOIUrl":"10.1016/j.combustflame.2025.114755","url":null,"abstract":"<div><div>This study investigates the influence of pressure on synergistic soot formation in co-flow laminar diffusion flames of ethylene/propane mixtures (1–6 atm). Radially resolved fields of soot volume fraction, temperature, and the soot absorption function, <span><math><mrow><mi>E</mi><mrow><mo>(</mo><mi>m</mi><mo>)</mo></mrow></mrow></math></span>, were obtained using three-color line-of-sight attenuation and spectral soot emission techniques. Synergistic promotion of soot formation was observed at all pressures, but its strength varied with pressure: at 1 atm, the peak soot volume fraction increased from 1.24 ppm in neat ethylene to 1.52 ppm with 5% carbon from propane, whereas at 6 atm it increased only marginally from 86.4 ppm to 90.3 ppm. Normalized soot yield revealed the strongest nonlinearity at 2 atm, followed by 3 atm, then 1 atm, 4 atm, 5 atm, and 6 atm. Temperatures for different mixtures at a given pressure were similar and primarily controlled by soot loading and associated radiative losses. The measurements show that <span><math><mrow><mi>E</mi><mrow><mo>(</mo><mi>m</mi><mo>)</mo></mrow></mrow></math></span> varies both spectrally and spatially; values are notably lower than the commonly assumed 0.26 in nascent soot regions near the flame base and higher elsewhere. This variation demonstrates that a constant <span><math><mrow><mi>E</mi><mrow><mo>(</mo><mi>m</mi><mo>)</mo></mrow></mrow></math></span> can misestimate soot volume fraction depending on location and wavelength. Despite substantial differences in soot concentration among mixtures, soot maturity distributions were broadly similar. These results provide high-fidelity data for model validation and emphasize the need to account for wavelength-dependent optical properties when quantifying soot at elevated pressures.</div><div><strong>Novelty and significance statement</strong></div><div>This study provides the first multi-parameter characterization of synergistic soot formation in ethylene/propane diffusion flames at elevated pressures. By introducing a wavelength-dependent absorption function, <span><math><mrow><mi>E</mi><mrow><mo>(</mo><mi>m</mi><mo>)</mo></mrow></mrow></math></span>, it captures spatial variation in soot maturity and improves quantification. The results demonstrate persistent synergistic effects across pressures and yield novel mechanistic insights, including rate-limiting steps, with direct relevance to predictive soot models for high-pressure combustion systems using blended fuels.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"285 ","pages":"Article 114755"},"PeriodicalIF":6.2,"publicationDate":"2025-12-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145881343","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}
Pub Date : 2025-12-27DOI: 10.1016/j.combustflame.2025.114736
Xinyu Ma , Baisheng Nie , Weili Wang , Yushu Zhang , Dan Zhao , Li Chang , Xianfeng Liu
The efficient utilization of flue gas has strategic value in alleviating environmental pressure and promoting sustainable development. This study investigated the explosion characteristics of hydrogen under inert conditions and analyzed the difference in inerting effects between single gas dilution (CO₂, N₂) and multi-component synergistic control (flue gas)using a 20 L spherical explosion test system. The Chemkin simulation software was applied to reveal the microscopic reaction mechanism of different inert gases in hydrogen explosions. The findings indicate that the addition of inert gases lowers the flame temperature of hydrogen explosion and thus the Pmax, (dP/dt)max and KG, while tb and tc raise parabolically. The critical inhibition concentrations of the three diluents are 50 % flue gas, 40 % N2 and 30 % CO2. For a given dilution ratio, the KG of N2 and flue gas in suppressing hydrogen explosion are higher than those for CO2. The explosion suppression effect of flue gas is not a linear superposition of single CO2 and N2. The different heat capacities of the inert gases and the regulation mechanism on the chain reactions fundamentally determine the severity of hydrogen explosion. Sensitivity analysis reveals that free radicals are primarily sensitive to the intermediate reaction R26 (forward direction) and R15 (reverse direction). The research results provide a scientific basis for improving disaster prevention systems and developing efficient explosion suppressants.
{"title":"Flue gas to mitigate explosions: The diluting effect and mechanism of inert gases on hydrogen explosion in confined space","authors":"Xinyu Ma , Baisheng Nie , Weili Wang , Yushu Zhang , Dan Zhao , Li Chang , Xianfeng Liu","doi":"10.1016/j.combustflame.2025.114736","DOIUrl":"10.1016/j.combustflame.2025.114736","url":null,"abstract":"<div><div>The efficient utilization of flue gas has strategic value in alleviating environmental pressure and promoting sustainable development. This study investigated the explosion characteristics of hydrogen under inert conditions and analyzed the difference in inerting effects between single gas dilution (CO₂, N₂) and multi-component synergistic control (flue gas)using a 20 L spherical explosion test system. The Chemkin simulation software was applied to reveal the microscopic reaction mechanism of different inert gases in hydrogen explosions. The findings indicate that the addition of inert gases lowers the flame temperature of hydrogen explosion and thus the P<sub>max</sub>, (dP/dt)<sub>max</sub> and K<sub>G</sub>, while t<sub>b</sub> and t<sub>c</sub> raise parabolically. The critical inhibition concentrations of the three diluents are 50 % flue gas, 40 % N<sub>2</sub> and 30 % CO<sub>2</sub>. For a given dilution ratio, the K<sub>G</sub> of N<sub>2</sub> and flue gas in suppressing hydrogen explosion are higher than those for CO<sub>2</sub>. The explosion suppression effect of flue gas is not a linear superposition of single CO<sub>2</sub> and N<sub>2</sub>. The different heat capacities of the inert gases and the regulation mechanism on the chain reactions fundamentally determine the severity of hydrogen explosion. Sensitivity analysis reveals that free radicals are primarily sensitive to the intermediate reaction R26 (forward direction) and R15 (reverse direction). The research results provide a scientific basis for improving disaster prevention systems and developing efficient explosion suppressants.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"285 ","pages":"Article 114736"},"PeriodicalIF":6.2,"publicationDate":"2025-12-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145837864","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}
This study investigates a low-carbon combustion method based on powder-gas “hybrid” flames, in which ultra-lean methane–air mixtures are assisted by biomass powder (Lycopodium spores) to achieve continuous “weak explosions”. This approach offers a solution to achieving stable combustion of low-calorific gaseous fuels with a small amount of combustible powder. In this hybrid fuel, both the powder concentration and the gas-phase equivalence ratio are below their respective flammability limits. A stagnation-point flame was employed, and the burning velocity was determined from particle image velocimetry (PIV) measurements. The results showed that an increase in powder loading rate leads to an increase in burning velocity. A qualitative analysis was conducted to assess the mechanisms controlling the burning velocity; namely, effects of pyrolysis-induced increases in the equivalence ratio and flame surface area, as well as the influence of radiative preheating on the burning velocity. This work offers a new pathway for the combustion of low-calorific gaseous fuels and biomass-based wastes, contributing to carbon neutrality through the utilization of renewable solid fuels. It may represent a promising direction for future developments in sustainable combustion technologies.
{"title":"Study on powder–gas “hybrid” combustion: Its mechanism to achieve variable burning velocities","authors":"Yuyang Jiang, Ryoki Okada, Akito Tayama, Daiki Matsugi, Yuji Nakamura","doi":"10.1016/j.combustflame.2025.114730","DOIUrl":"10.1016/j.combustflame.2025.114730","url":null,"abstract":"<div><div>This study investigates a low-carbon combustion method based on powder-gas “hybrid” flames, in which ultra-lean methane–air mixtures are assisted by biomass powder (Lycopodium spores) to achieve continuous “weak explosions”. This approach offers a solution to achieving stable combustion of low-calorific gaseous fuels with a small amount of combustible powder. In this hybrid fuel, both the powder concentration and the gas-phase equivalence ratio are below their respective flammability limits. A stagnation-point flame was employed, and the burning velocity was determined from particle image velocimetry (PIV) measurements. The results showed that an increase in powder loading rate leads to an increase in burning velocity. A qualitative analysis was conducted to assess the mechanisms controlling the burning velocity; namely, effects of pyrolysis-induced increases in the equivalence ratio and flame surface area, as well as the influence of radiative preheating on the burning velocity. This work offers a new pathway for the combustion of low-calorific gaseous fuels and biomass-based wastes, contributing to carbon neutrality through the utilization of renewable solid fuels. It may represent a promising direction for future developments in sustainable combustion technologies.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"285 ","pages":"Article 114730"},"PeriodicalIF":6.2,"publicationDate":"2025-12-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145837865","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}
Steam-diluted hydrogen-oxygen combustion is a key technology for future hydrogen utilization. Steam dilution significantly affects heat release and mixing, altering flame characteristics. Normal diffusion flames (NDFs) and inverse diffusion flames (IDFs) in coaxial jets exhibit distinct flame evolution patterns under steam influence. To elucidate the coupling between combustion mode and steam dilution, this study combines experiments and numerical simulations to clarify the distinct mechanisms of steam dilution on NDFs and IDFs. Static characterization shows that steam dilution significantly alters the unfiltered broadband flame emission structure and OH* distribution near the flame root in NDFs. When the steam dilution exceeds 40 %, the emission peak shifts downstream, while the spatial distribution in IDFs remains stable. Dynamic analysis demonstrates that steam dilution intensifies transient flame front wrinkling and shortens the OH* oscillation period in NDFs. In contrast, IDFs dynamics are less sensitive to dilution, with minimal disruption to the transient flame front structure. Multiphysics analysis of combustion reveals that near-field vortex evolution in NDFs is governed by viscous diffusion, vortex stretching and tilting, volume expansion, and baroclinic torque, with viscous diffusion dominating downstream. In IDFs, viscous diffusion controls near-field dynamics, while vortex stretching and tilting, volume expansion, and viscous diffusion jointly influence the downstream region. Steam dilution enhances the misalignment between density and pressure gradients within the flame, thereby amplifying the baroclinic torque effect in NDFs. Conversely, the baroclinic torque mechanism is negligible in IDFs.
{"title":"Effects of steam dilution on flame characteristics and vortex field mechanisms in normal and inverse diffusion Hydrogen-Oxygen flames","authors":"Jinqi Zhu, Xiaopeng Jiang, Yu Zhang, Wenda Zhang, Penghua Qiu, Yijun Zhao","doi":"10.1016/j.combustflame.2025.114722","DOIUrl":"10.1016/j.combustflame.2025.114722","url":null,"abstract":"<div><div>Steam-diluted hydrogen-oxygen combustion is a key technology for future hydrogen utilization. Steam dilution significantly affects heat release and mixing, altering flame characteristics. Normal diffusion flames (NDFs) and inverse diffusion flames (IDFs) in coaxial jets exhibit distinct flame evolution patterns under steam influence. To elucidate the coupling between combustion mode and steam dilution, this study combines experiments and numerical simulations to clarify the distinct mechanisms of steam dilution on NDFs and IDFs. Static characterization shows that steam dilution significantly alters the unfiltered broadband flame emission structure and OH* distribution near the flame root in NDFs. When the steam dilution exceeds 40 %, the emission peak shifts downstream, while the spatial distribution in IDFs remains stable. Dynamic analysis demonstrates that steam dilution intensifies transient flame front wrinkling and shortens the OH* oscillation period in NDFs. In contrast, IDFs dynamics are less sensitive to dilution, with minimal disruption to the transient flame front structure. Multiphysics analysis of combustion reveals that near-field vortex evolution in NDFs is governed by viscous diffusion, vortex stretching and tilting, volume expansion, and baroclinic torque, with viscous diffusion dominating downstream. In IDFs, viscous diffusion controls near-field dynamics, while vortex stretching and tilting, volume expansion, and viscous diffusion jointly influence the downstream region. Steam dilution enhances the misalignment between density and pressure gradients within the flame, thereby amplifying the baroclinic torque effect in NDFs. Conversely, the baroclinic torque mechanism is negligible in IDFs.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"285 ","pages":"Article 114722"},"PeriodicalIF":6.2,"publicationDate":"2025-12-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145837901","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}
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