Pub Date : 2026-01-01Epub Date: 2026-05-28DOI: 10.1016/j.proci.2026.105991
{"title":"The Papers in This Volume Were","authors":"","doi":"10.1016/j.proci.2026.105991","DOIUrl":"10.1016/j.proci.2026.105991","url":null,"abstract":"","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"42 ","pages":"Article 105991"},"PeriodicalIF":5.2,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148170669","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 : 2026-01-01Epub Date: 2026-06-25DOI: 10.1016/j.proci.2026.106037
Daniya Zhumabayeva , Frederick Young , Umair Ahmed , Robert Stewart Cant
Compressible direct numerical simulations with multi-step chemistry were performed to investigate the temporal characteristics of entropy generation in two-dimensional laminar premixed hydrogen–air flames at equivalence ratios of 0.4 and 0.7, subjected to acoustic forcing over a range of frequencies (50–500 kHz) and sound pressure levels (SPL of 110–130 dB). A monopole-type acoustic source located at the inflow boundary generated pressure waves, thereby wrinkling an initially planar flame front. Higher SPL was associated with an earlier increase in entropy generation in both mixtures. Entropy generation rate was found to mark the transition from an initial linear to a non-linear regime of flame development. Beyond this transition point in the non-linear developed phase, the overall entropy evolution was relatively insensitive to variations in acoustic forcing. A stability analysis based on non-equilibrium thermodynamics suggested that all cases with the same equivalence ratio shared similar instability characteristics, indicating that the developed flame behaviour in the non-linear regime is governed primarily by inherent chemical properties, rather than by specific perturbation conditions.
Novelty and significance statement
As hydrogen and hydrogen-enriched fuels become increasingly important for future energy systems, flame instabilities, including intrinsic and acoustic types, remain a central topic in fundamental combustion research due to their strong influence on flame dynamics and stability. Advancing the understanding of their temporal evolution is essential for predictive combustion theory. Conventional approaches to identifying the transition between the linear and non-linear development regimes of intrinsic flame instabilities rely on amplitude evolution or Fourier-mode analysis and are limited by ambiguities in flame-front definitions and non-unique, wavelength-dependent transition times. This study introduces a novel entropy-based marker that provides a single temporal threshold for regime separation, enabling a more precise characterisation of flame dynamics. Unlike conventional methods restricted to planar flames, this marker is also applicable to complex flame configurations. In addition, stability theory from non-equilibrium thermodynamics is applied to assess the entropy-based stability criteria in numerical simulations of acoustically forced flames.
{"title":"Entropy generation rates in acoustically perturbed hydrogen flames","authors":"Daniya Zhumabayeva , Frederick Young , Umair Ahmed , Robert Stewart Cant","doi":"10.1016/j.proci.2026.106037","DOIUrl":"10.1016/j.proci.2026.106037","url":null,"abstract":"<div><div>Compressible direct numerical simulations with multi-step chemistry were performed to investigate the temporal characteristics of entropy generation in two-dimensional laminar premixed hydrogen–air flames at equivalence ratios of 0.4 and 0.7, subjected to acoustic forcing over a range of frequencies (50–500 kHz) and sound pressure levels (SPL of 110–130 dB). A monopole-type acoustic source located at the inflow boundary generated pressure waves, thereby wrinkling an initially planar flame front. Higher SPL was associated with an earlier increase in entropy generation in both mixtures. Entropy generation rate was found to mark the transition from an initial linear to a non-linear regime of flame development. Beyond this transition point in the non-linear developed phase, the overall entropy evolution was relatively insensitive to variations in acoustic forcing. A stability analysis based on non-equilibrium thermodynamics suggested that all cases with the same equivalence ratio shared similar instability characteristics, indicating that the developed flame behaviour in the non-linear regime is governed primarily by inherent chemical properties, rather than by specific perturbation conditions.</div><div><strong>Novelty and significance statement</strong></div><div>As hydrogen and hydrogen-enriched fuels become increasingly important for future energy systems, flame instabilities, including intrinsic and acoustic types, remain a central topic in fundamental combustion research due to their strong influence on flame dynamics and stability. Advancing the understanding of their temporal evolution is essential for predictive combustion theory. Conventional approaches to identifying the transition between the linear and non-linear development regimes of intrinsic flame instabilities rely on amplitude evolution or Fourier-mode analysis and are limited by ambiguities in flame-front definitions and non-unique, wavelength-dependent transition times. This study introduces a novel entropy-based marker that provides a single temporal threshold for regime separation, enabling a more precise characterisation of flame dynamics. Unlike conventional methods restricted to planar flames, this marker is also applicable to complex flame configurations. In addition, stability theory from non-equilibrium thermodynamics is applied to assess the entropy-based stability criteria in numerical simulations of acoustically forced flames.</div></div>","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"42 ","pages":"Article 106037"},"PeriodicalIF":4.6,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148409484","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 : 2026-01-01Epub Date: 2026-06-24DOI: 10.1016/j.proci.2026.106054
M.C. Restrepo-Cadavid, H. Watanabe, V. Rodriguez, O. Dounia, A. Chinnayya
<div><div>Investigations were conducted on the Shock-to-Detonation Transition (SDT) in a stoichiometric hydrogen–oxygen mixture using a rectangular shock tube with repeated obstacles at an initial pressure of 15<!--> <!-->kPa. High-speed shadowgraphy and quantitative analysis of reflected-shock conditions were used to characterize ignition dynamics. Two classical ignition regimes were identified: weak and strong. Within the weak regime, three distinct manifestations were observed: classical weak ignition, weak bifurcation ignition, and the newly identified <em>flame acceleration induced by shock–obstacle interaction (FA-SOI)</em> weak ignition. Quantitative transition limits were established. Isolated cases of strong ignition were observed at reflected-shock temperatures <span><math><mrow><msub><mrow><mi>T</mi></mrow><mrow><mn>5</mn></mrow></msub><mo>≈</mo><mn>1250</mn><mspace></mspace><mstyle><mi>K</mi></mstyle></mrow></math></span>, while the regime became predominantly strong for 1300<!--> <!-->K to 1350<!--> <!-->K and <span><math><mrow><msub><mrow><mi>M</mi></mrow><mrow><mi>s</mi></mrow></msub><mo>=</mo><mn>2</mn><mo>.</mo><mn>91</mn><mo>∼</mo><mn>3</mn><mo>.</mo><mn>10</mn></mrow></math></span>. Classical weak ignition was observed for <span><math><mrow><msub><mrow><mi>T</mi></mrow><mrow><mn>5</mn></mrow></msub><mo>=</mo><mn>1150</mn><mspace></mspace><mstyle><mi>K</mi></mstyle><mspace></mspace><mtext>to</mtext><mspace></mspace><mn>1220</mn><mspace></mspace><mstyle><mi>K</mi></mstyle></mrow></math></span> and <span><math><mrow><msub><mrow><mi>M</mi></mrow><mrow><mi>s</mi></mrow></msub><mo>=</mo><mn>2</mn><mo>.</mo><mn>78</mn><mo>−</mo><mn>2</mn><mo>.</mo><mn>90</mn></mrow></math></span>, while the FA-SOI weak ignition was identified for <span><math><mrow><mn>2</mn><mo>.</mo><mn>63</mn><mo>≤</mo><msub><mrow><mi>M</mi></mrow><mrow><mi>s</mi></mrow></msub><mo>≤</mo><mn>2</mn><mo>.</mo><mn>88</mn></mrow></math></span>. The crossover temperature, corresponding to <span><math><mrow><msub><mrow><mi>T</mi></mrow><mrow><mn>5</mn></mrow></msub><mo>=</mo><mn>1150</mn><mspace></mspace><mstyle><mi>K</mi></mstyle></mrow></math></span>, marked the onset of classical weak ignition. The induction-time sensitivity framework was extended to repeated-obstacle configurations, with classical weak ignition associated with <span><math><mrow><mo>−</mo><mn>2</mn><mo>.</mo><mn>0</mn><mspace></mspace><mstyle><mi>µ</mi><mi>s</mi></mstyle><mo>/</mo><mstyle><mi>K</mi></mstyle></mrow></math></span> to <span><math><mrow><mo>−</mo><mn>0</mn><mo>.</mo><mn>01</mn><mspace></mspace><mstyle><mi>µ</mi><mi>s</mi></mstyle><mo>/</mo><mstyle><mi>K</mi></mstyle></mrow></math></span> and strong ignition predominantly above <span><math><mrow><mo>−</mo><mn>0</mn><mo>.</mo><mn>01</mn><mspace></mspace><mstyle><mi>µ</mi><mi>s</mi></mstyle><mo>/</mo><mstyle><mi>K</mi></mstyle></mrow></math></span>. Above Thomas’ criterion, the mitigation properties of the repeated obstacles were also characte
{"title":"Experimental investigation of Shock-to-Detonation Transition in stoichiometric H2–O2 with repeated obstacles","authors":"M.C. Restrepo-Cadavid, H. Watanabe, V. Rodriguez, O. Dounia, A. Chinnayya","doi":"10.1016/j.proci.2026.106054","DOIUrl":"10.1016/j.proci.2026.106054","url":null,"abstract":"<div><div>Investigations were conducted on the Shock-to-Detonation Transition (SDT) in a stoichiometric hydrogen–oxygen mixture using a rectangular shock tube with repeated obstacles at an initial pressure of 15<!--> <!-->kPa. High-speed shadowgraphy and quantitative analysis of reflected-shock conditions were used to characterize ignition dynamics. Two classical ignition regimes were identified: weak and strong. Within the weak regime, three distinct manifestations were observed: classical weak ignition, weak bifurcation ignition, and the newly identified <em>flame acceleration induced by shock–obstacle interaction (FA-SOI)</em> weak ignition. Quantitative transition limits were established. Isolated cases of strong ignition were observed at reflected-shock temperatures <span><math><mrow><msub><mrow><mi>T</mi></mrow><mrow><mn>5</mn></mrow></msub><mo>≈</mo><mn>1250</mn><mspace></mspace><mstyle><mi>K</mi></mstyle></mrow></math></span>, while the regime became predominantly strong for 1300<!--> <!-->K to 1350<!--> <!-->K and <span><math><mrow><msub><mrow><mi>M</mi></mrow><mrow><mi>s</mi></mrow></msub><mo>=</mo><mn>2</mn><mo>.</mo><mn>91</mn><mo>∼</mo><mn>3</mn><mo>.</mo><mn>10</mn></mrow></math></span>. Classical weak ignition was observed for <span><math><mrow><msub><mrow><mi>T</mi></mrow><mrow><mn>5</mn></mrow></msub><mo>=</mo><mn>1150</mn><mspace></mspace><mstyle><mi>K</mi></mstyle><mspace></mspace><mtext>to</mtext><mspace></mspace><mn>1220</mn><mspace></mspace><mstyle><mi>K</mi></mstyle></mrow></math></span> and <span><math><mrow><msub><mrow><mi>M</mi></mrow><mrow><mi>s</mi></mrow></msub><mo>=</mo><mn>2</mn><mo>.</mo><mn>78</mn><mo>−</mo><mn>2</mn><mo>.</mo><mn>90</mn></mrow></math></span>, while the FA-SOI weak ignition was identified for <span><math><mrow><mn>2</mn><mo>.</mo><mn>63</mn><mo>≤</mo><msub><mrow><mi>M</mi></mrow><mrow><mi>s</mi></mrow></msub><mo>≤</mo><mn>2</mn><mo>.</mo><mn>88</mn></mrow></math></span>. The crossover temperature, corresponding to <span><math><mrow><msub><mrow><mi>T</mi></mrow><mrow><mn>5</mn></mrow></msub><mo>=</mo><mn>1150</mn><mspace></mspace><mstyle><mi>K</mi></mstyle></mrow></math></span>, marked the onset of classical weak ignition. The induction-time sensitivity framework was extended to repeated-obstacle configurations, with classical weak ignition associated with <span><math><mrow><mo>−</mo><mn>2</mn><mo>.</mo><mn>0</mn><mspace></mspace><mstyle><mi>µ</mi><mi>s</mi></mstyle><mo>/</mo><mstyle><mi>K</mi></mstyle></mrow></math></span> to <span><math><mrow><mo>−</mo><mn>0</mn><mo>.</mo><mn>01</mn><mspace></mspace><mstyle><mi>µ</mi><mi>s</mi></mstyle><mo>/</mo><mstyle><mi>K</mi></mstyle></mrow></math></span> and strong ignition predominantly above <span><math><mrow><mo>−</mo><mn>0</mn><mo>.</mo><mn>01</mn><mspace></mspace><mstyle><mi>µ</mi><mi>s</mi></mstyle><mo>/</mo><mstyle><mi>K</mi></mstyle></mrow></math></span>. Above Thomas’ criterion, the mitigation properties of the repeated obstacles were also characte","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"42 ","pages":"Article 106054"},"PeriodicalIF":4.6,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148567305","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}
<div><div>Hydrogen flames exhibit multiple intrinsic instabilities. The low molar masses of H and H<sub>2</sub> lead to significant Soret diffusion near the flame front; however, its influence on hydrogen flame instabilities remains to be quantified. This study investigates the effect of Soret diffusion on instability evolution dynamics via one-dimensional counterflow analysis and two-dimensional, high-fidelity direct numerical simulations covering both the linear growth regime and the fully developed nonlinear regime over a wide range of equivalence ratios (<span><math><mi>ϕ</mi></math></span>). In the linear regime, Soret diffusion increases the perturbation growth rate at <span><math><mrow><mi>ϕ</mi><mo><</mo><mn>1</mn><mo>.</mo><mn>7</mn></mrow></math></span>, especially under lean conditions, but reduces the growth rate at <span><math><mrow><mi>ϕ</mi><mo>></mo><mn>1</mn><mo>.</mo><mn>7</mn></mrow></math></span>. A similar sensitivity reversal is observed in the Markstein length (<span><math><mi>L</mi></math></span>) across the critical equivalence ratio <span><math><mrow><msub><mrow><mi>ϕ</mi></mrow><mrow><mi>c</mi></mrow></msub><mo>=</mo><mn>1</mn><mo>.</mo><mn>7</mn></mrow></math></span>, which coincides with the peak equivalence ratio of unstretched laminar flame speed. In the nonlinear regime, Soret diffusion accelerates the formation of small-scale wrinkles in lean hydrogen flames and reduces the characteristic size of large-scale finger-like structure by one-third. An interesting observation is that, although Soret diffusion promotes preferential diffusion and increases the local flame displacement speed, the global fuel consumption rate decreases due to a substantial reduction in the overall flame surface area. In addition, curvature-based flame segment analysis reveals a synergistic effect between Soret diffusion and Fickian diffusion that enhances/reduces the local equivalence ratio in positively/negatively curved regions of the flame front. The probability distributions of the Karlovitz number (<span><math><mrow><mi>K</mi><mi>a</mi></mrow></math></span>) and the density-weighted displacement speed (<span><math><msubsup><mrow><mi>S</mi></mrow><mrow><mi>d</mi></mrow><mrow><mo>∗</mo></mrow></msubsup></math></span>) are also analyzed; results suggest that, for lean hydrogen flames, Soret diffusion broadens the distributions for both parameters, particularly on the positive side. These findings promise to improve the understanding of hydrogen flame dynamics under complex differential transport across an extended range of equivalence ratios and through different regimes of instability evolution.</div><div><em>Novelty and Significance Statement</em>: This study addresses an important gap regarding the effect of Soret diffusion on hydrogen flame instability, particularly in the nonlinear regime of flame evolution. It extends beyond conventional linear stability theory and quantifies how Soret diffusion influences the probability dist
{"title":"Effects of Soret diffusion on the intrinsic instability of premixed hydrogen/air flames","authors":"Qizhe Wen, Yan Wang, Linlin Yang, Youhi Morii, Thorsten Zirwes, Shengkai Wang, Zheng Chen","doi":"10.1016/j.proci.2026.106065","DOIUrl":"10.1016/j.proci.2026.106065","url":null,"abstract":"<div><div>Hydrogen flames exhibit multiple intrinsic instabilities. The low molar masses of H and H<sub>2</sub> lead to significant Soret diffusion near the flame front; however, its influence on hydrogen flame instabilities remains to be quantified. This study investigates the effect of Soret diffusion on instability evolution dynamics via one-dimensional counterflow analysis and two-dimensional, high-fidelity direct numerical simulations covering both the linear growth regime and the fully developed nonlinear regime over a wide range of equivalence ratios (<span><math><mi>ϕ</mi></math></span>). In the linear regime, Soret diffusion increases the perturbation growth rate at <span><math><mrow><mi>ϕ</mi><mo><</mo><mn>1</mn><mo>.</mo><mn>7</mn></mrow></math></span>, especially under lean conditions, but reduces the growth rate at <span><math><mrow><mi>ϕ</mi><mo>></mo><mn>1</mn><mo>.</mo><mn>7</mn></mrow></math></span>. A similar sensitivity reversal is observed in the Markstein length (<span><math><mi>L</mi></math></span>) across the critical equivalence ratio <span><math><mrow><msub><mrow><mi>ϕ</mi></mrow><mrow><mi>c</mi></mrow></msub><mo>=</mo><mn>1</mn><mo>.</mo><mn>7</mn></mrow></math></span>, which coincides with the peak equivalence ratio of unstretched laminar flame speed. In the nonlinear regime, Soret diffusion accelerates the formation of small-scale wrinkles in lean hydrogen flames and reduces the characteristic size of large-scale finger-like structure by one-third. An interesting observation is that, although Soret diffusion promotes preferential diffusion and increases the local flame displacement speed, the global fuel consumption rate decreases due to a substantial reduction in the overall flame surface area. In addition, curvature-based flame segment analysis reveals a synergistic effect between Soret diffusion and Fickian diffusion that enhances/reduces the local equivalence ratio in positively/negatively curved regions of the flame front. The probability distributions of the Karlovitz number (<span><math><mrow><mi>K</mi><mi>a</mi></mrow></math></span>) and the density-weighted displacement speed (<span><math><msubsup><mrow><mi>S</mi></mrow><mrow><mi>d</mi></mrow><mrow><mo>∗</mo></mrow></msubsup></math></span>) are also analyzed; results suggest that, for lean hydrogen flames, Soret diffusion broadens the distributions for both parameters, particularly on the positive side. These findings promise to improve the understanding of hydrogen flame dynamics under complex differential transport across an extended range of equivalence ratios and through different regimes of instability evolution.</div><div><em>Novelty and Significance Statement</em>: This study addresses an important gap regarding the effect of Soret diffusion on hydrogen flame instability, particularly in the nonlinear regime of flame evolution. It extends beyond conventional linear stability theory and quantifies how Soret diffusion influences the probability dist","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"42 ","pages":"Article 106065"},"PeriodicalIF":4.6,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148567407","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}
<div><div>Detonation initiation by a hypersonic ramp holds requirements in both energy deposition and chemical kinetics, known as the energetic and kinetic limits, respectively. If the post-shock ignition delay time exceeds the flow residence time on the ramp (the kinetic limit being unsatisfied), detonation cannot be formed since autoignition does not occur behind the shock. This work aims to evaluate the feasibility and conditions under which an additional ignition kernel can enable the transition from a ramp-induced inert shock to a stabilized detonation despite the kinetic limit being unmet. To this end, numerical simulations incorporating detailed chemistry are performed for hypersonic ramp flows, with and without extra ignition kernels, across varying freestream Mach numbers and pressures. Baseline simulations without extra ignition kernels reveal three combustion regimes, <em>i.e.</em>, detonation, shock-induced combustion, and inert shock. These numerical results align well with the theoretical predictions by the energetic and kinetic limits. Upon introducing the ignition kernels, three distinctive combustion regimes are identified: failed initiation, stabilized detonation, and destabilized detonation. Results show that whether detonation can be triggered by the ignition kernel or not is jointly influenced by the freestream Mach number and pressure. The boundary separating the detonatable and undetonatable regions aligns well with the theoretical energetic limit, confirming the feasibility of using an extra ignition kernel to facilitate detonation initiation. Nevertheless, stabilization of the triggered detonation is found to be strongly correlated to the formation of a normal detonation wave behind the ramp-induced shock. A third criterion called the standing limit is hence proposed to characterize this nature by defining a nondimensional parameter <em>V</em><sub>S</sub> = <em>V</em><sub>2</sub>/<em>D</em><sub>CJ2</sub> (where <em>V</em><sub>2</sub> and <em>D</em><sub>CJ2</sub> denote the post-shock flow and Chapman–Jouguet velocity). Detonation stabilizes only if <em>V</em><sub>S</sub> is smaller than or approximates unity, with a prompt pattern for <em>V</em><sub>S</sub> < 1 and a delayed pattern for <em>V</em><sub>S</sub> ⪆ 1.</div></div><div><h3>Novelty and significance statement</h3><div>The problem of shock-induced autoignition and its transition to detonation in hypersonic ramp flows has been extensively studied previously. However, little attention was paid to detonation initiation in scenarios where autoignition cannot occur. In this work, we numerically investigate the feasibility of using an additional ignition kernel with low ignition energy to facilitate detonation initiation in hypersonic ramp flows. For the first time, we reveal the specific conditions under which a single ignition kernel can enable the transition from an inert ramp-induced shock to a stabilized detonation and propose quantitative detonation initiation
{"title":"Stabilized detonation triggered by a single ignition kernel in hypersonic ramp flow","authors":"Xinke Shao, Lisong Shi, Ziqi Jiang, Zijian Zhang, Honghui Teng, Chih-Yung Wen","doi":"10.1016/j.proci.2026.106005","DOIUrl":"10.1016/j.proci.2026.106005","url":null,"abstract":"<div><div>Detonation initiation by a hypersonic ramp holds requirements in both energy deposition and chemical kinetics, known as the energetic and kinetic limits, respectively. If the post-shock ignition delay time exceeds the flow residence time on the ramp (the kinetic limit being unsatisfied), detonation cannot be formed since autoignition does not occur behind the shock. This work aims to evaluate the feasibility and conditions under which an additional ignition kernel can enable the transition from a ramp-induced inert shock to a stabilized detonation despite the kinetic limit being unmet. To this end, numerical simulations incorporating detailed chemistry are performed for hypersonic ramp flows, with and without extra ignition kernels, across varying freestream Mach numbers and pressures. Baseline simulations without extra ignition kernels reveal three combustion regimes, <em>i.e.</em>, detonation, shock-induced combustion, and inert shock. These numerical results align well with the theoretical predictions by the energetic and kinetic limits. Upon introducing the ignition kernels, three distinctive combustion regimes are identified: failed initiation, stabilized detonation, and destabilized detonation. Results show that whether detonation can be triggered by the ignition kernel or not is jointly influenced by the freestream Mach number and pressure. The boundary separating the detonatable and undetonatable regions aligns well with the theoretical energetic limit, confirming the feasibility of using an extra ignition kernel to facilitate detonation initiation. Nevertheless, stabilization of the triggered detonation is found to be strongly correlated to the formation of a normal detonation wave behind the ramp-induced shock. A third criterion called the standing limit is hence proposed to characterize this nature by defining a nondimensional parameter <em>V</em><sub>S</sub> = <em>V</em><sub>2</sub>/<em>D</em><sub>CJ2</sub> (where <em>V</em><sub>2</sub> and <em>D</em><sub>CJ2</sub> denote the post-shock flow and Chapman–Jouguet velocity). Detonation stabilizes only if <em>V</em><sub>S</sub> is smaller than or approximates unity, with a prompt pattern for <em>V</em><sub>S</sub> < 1 and a delayed pattern for <em>V</em><sub>S</sub> ⪆ 1.</div></div><div><h3>Novelty and significance statement</h3><div>The problem of shock-induced autoignition and its transition to detonation in hypersonic ramp flows has been extensively studied previously. However, little attention was paid to detonation initiation in scenarios where autoignition cannot occur. In this work, we numerically investigate the feasibility of using an additional ignition kernel with low ignition energy to facilitate detonation initiation in hypersonic ramp flows. For the first time, we reveal the specific conditions under which a single ignition kernel can enable the transition from an inert ramp-induced shock to a stabilized detonation and propose quantitative detonation initiation ","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"42 ","pages":"Article 106005"},"PeriodicalIF":4.6,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148567575","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 : 2026-01-01Epub Date: 2026-06-25DOI: 10.1016/j.proci.2026.106040
Seif Zitouni, Gongrui Huang, Olfa Mechergui, Guillaume Dayma, Philippe Dagaut, Christian Chauveau, Oskar Haidn, Fabien Halter
<div><div>Achieving carbon neutrality will require the integration of renewable, carbon-free fuels, with ammonia (NH₃) emerging as a promising hydrogen carrier. However, its low laminar flame speed (S<sub>L</sub><sup>0</sup> < 10 cm/s at 298 K, 1 bar) limits stable combustion, motivating the use of methane (CH<sub>4</sub>) blending and oxygen enrichment to enhance reactivity. In this work, laminar flame speeds of NH<sub>3</sub>/CH<sub>4</sub>/O<sub>2</sub>/N<sub>2</sub> mixtures were measured under isochoric conditions in a constant-volume spherical chamber over pressures of 2–5 bar, temperatures of 365–470 K, and oxygen mole fractions of 21–40%. A detailed kinetic mechanism incorporating 112 species and 1058 reactions was developed and evaluated against the measurements. Flame speed increased strongly with oxygen enrichment, with 40% O<sub>2</sub> resulting in flame speeds five times the values measured at 21% O<sub>2</sub>. Kinetic analyses showed that oxygen enrichment accelerates H-abstraction in both NH<sub>3</sub> and CH<sub>4</sub> oxidation, strengthens N-C coupled pathways, and promotes conversion of intermediates toward N<sub>2</sub>, CO<sub>2</sub>, and H<sub>2</sub>O, whereas increasing pressure redistributes the reaction fluxes and reduces the relative importance of the most reactive radical-mediated channels. A thermal/chemical contribution analysis further showed that CH<sub>4</sub> promotes NH<sub>3</sub> flame propagation through both effects, with the relative chemical contribution decreasing during isochoric evolution, primarily because of pressure rise. The pressure exponent <em>β</em> captures this competition, shifting toward zero with oxygen enrichment but remaining strongly dependent on equivalence ratio for NH<sub>3</sub>-rich flames. These results provide new insight into the coupled effects of oxygen enrichment, pressure, and blend composition on NH<sub>3</sub>/CH<sub>4</sub> flame propagation under isochoric conditions, and supply useful validation targets for kinetic model development in high-pressure, oxygen-enriched combustion systems.</div></div><div><h3>Novelty and significance statement</h3><div>Available laminar flame-speed data for NH<sub>3</sub>/CH<sub>4</sub> mixtures remain largely confined to near-ambient, air-based conditions, leaving the combined effects of oxygen enrichment, elevated pressure, elevated temperature, and isochoric flame evolution insufficiently documented. The present work addresses this gap by providing laminar flame-speed measurements for NH<sub>3</sub>/CH<sub>4</sub>/O<sub>2</sub>/N<sub>2</sub> mixtures at pressures up to about 5 bar, temperatures up to about 470 K, and oxygen mole fractions from 21 to 40%, obtained in a spherical constant-volume chamber with full optical access. A detailed NH<sub>3</sub>/CH<sub>4</sub> kinetic mechanism comprising 112 species and 1058 reactions is further developed and assessed against the measurements.</div><div>The significance of the work lies no
{"title":"High pressure and temperature premixed laminar NH3/CH4 oxygenated flames: from experiments to kinetic models","authors":"Seif Zitouni, Gongrui Huang, Olfa Mechergui, Guillaume Dayma, Philippe Dagaut, Christian Chauveau, Oskar Haidn, Fabien Halter","doi":"10.1016/j.proci.2026.106040","DOIUrl":"10.1016/j.proci.2026.106040","url":null,"abstract":"<div><div>Achieving carbon neutrality will require the integration of renewable, carbon-free fuels, with ammonia (NH₃) emerging as a promising hydrogen carrier. However, its low laminar flame speed (S<sub>L</sub><sup>0</sup> < 10 cm/s at 298 K, 1 bar) limits stable combustion, motivating the use of methane (CH<sub>4</sub>) blending and oxygen enrichment to enhance reactivity. In this work, laminar flame speeds of NH<sub>3</sub>/CH<sub>4</sub>/O<sub>2</sub>/N<sub>2</sub> mixtures were measured under isochoric conditions in a constant-volume spherical chamber over pressures of 2–5 bar, temperatures of 365–470 K, and oxygen mole fractions of 21–40%. A detailed kinetic mechanism incorporating 112 species and 1058 reactions was developed and evaluated against the measurements. Flame speed increased strongly with oxygen enrichment, with 40% O<sub>2</sub> resulting in flame speeds five times the values measured at 21% O<sub>2</sub>. Kinetic analyses showed that oxygen enrichment accelerates H-abstraction in both NH<sub>3</sub> and CH<sub>4</sub> oxidation, strengthens N-C coupled pathways, and promotes conversion of intermediates toward N<sub>2</sub>, CO<sub>2</sub>, and H<sub>2</sub>O, whereas increasing pressure redistributes the reaction fluxes and reduces the relative importance of the most reactive radical-mediated channels. A thermal/chemical contribution analysis further showed that CH<sub>4</sub> promotes NH<sub>3</sub> flame propagation through both effects, with the relative chemical contribution decreasing during isochoric evolution, primarily because of pressure rise. The pressure exponent <em>β</em> captures this competition, shifting toward zero with oxygen enrichment but remaining strongly dependent on equivalence ratio for NH<sub>3</sub>-rich flames. These results provide new insight into the coupled effects of oxygen enrichment, pressure, and blend composition on NH<sub>3</sub>/CH<sub>4</sub> flame propagation under isochoric conditions, and supply useful validation targets for kinetic model development in high-pressure, oxygen-enriched combustion systems.</div></div><div><h3>Novelty and significance statement</h3><div>Available laminar flame-speed data for NH<sub>3</sub>/CH<sub>4</sub> mixtures remain largely confined to near-ambient, air-based conditions, leaving the combined effects of oxygen enrichment, elevated pressure, elevated temperature, and isochoric flame evolution insufficiently documented. The present work addresses this gap by providing laminar flame-speed measurements for NH<sub>3</sub>/CH<sub>4</sub>/O<sub>2</sub>/N<sub>2</sub> mixtures at pressures up to about 5 bar, temperatures up to about 470 K, and oxygen mole fractions from 21 to 40%, obtained in a spherical constant-volume chamber with full optical access. A detailed NH<sub>3</sub>/CH<sub>4</sub> kinetic mechanism comprising 112 species and 1058 reactions is further developed and assessed against the measurements.</div><div>The significance of the work lies no","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"42 ","pages":"Article 106040"},"PeriodicalIF":4.6,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148567257","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 : 2026-01-01Epub Date: 2026-06-16DOI: 10.1016/j.proci.2026.105995
Pablo E. Pinto, Maria Thomsen, James L. Urban, Xiuqi Xi
<div><div>Understanding the heat transfer mechanisms that govern the interaction between the flame and the solid fuel surface is essential for predicting and modeling flame spread. This work presents a novel technique to spatially resolve the convective heat transfer during horizontal concurrent flame spread over polymethyl methacrylate (PMMA) sheets. The experiments are conducted in a bench-scale flow duct under three inlet flow velocities. A side-wall radiometer (<span><math><msub><mrow><mi>s</mi></mrow><mrow><mn>1</mn></mrow></msub></math></span>) and a dual heat flux gauge positioned downstream and adjacent to the fuel surface (<span><math><msub><mrow><mi>s</mi></mrow><mrow><mn>2</mn></mrow></msub></math></span> and <span><math><msub><mrow><mi>s</mi></mrow><mrow><mn>3</mn></mrow></msub></math></span>) are used to separate the radiative contribution from the total heat flux. The temperature at the dual heat flux gauge <span><math><mrow><mo>(</mo><msub><mrow><mi>s</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>)</mo></mrow></math></span> is also measured, and then a convective heat transfer coefficient is determined locally through an empirical Nusselt number correlation. A previously introduced non-dimensional total heat flux correlation is employed, demonstrating a collapse of all data across the experimental conditions. The local contributions of the heat-transfer mechanisms were quantified, showing that radiation is larger over most of the heated-zone domain, while convection becomes larger in the region of the heated zone nearest the pyrolysis front as the flame approaches the heated zone target (<span><math><msub><mrow><mi>s</mi></mrow><mrow><mn>2</mn></mrow></msub></math></span> location). The flame spread rate is obtained experimentally and predicted using the heat transfer contributions. The results exhibit excellent agreement between experiments and model predictions, highlighting that the methodology provides an accurate and consistent framework to predict flame spread behavior under concurrent flow conditions.</div><div><em>Novelty and significance statement</em>: This work presents a novel technique to spatially resolve convective heat transfer during horizontal concurrent flame spread over PMMA. Using heat flux measurements and fundamental analysis, the contributions of convection and radiation to the fuel surface are each resolved. An empirical local Nusselt number correlation is proposed allowing for estimation of the local convective heat transfer coefficient. The thermal response of the fuel during flame spread is assessed using the local Biot number to identify thermally thin or thick behavior.</div><div>This study provides quantitative insight into the coupled radiative and convective heat transfer mechanisms that control horizontal flame spread, key processes in solid-fuel combustion and fire growth. The results offer a transferable framework for model validation and development in material flammability research, and potentia
{"title":"Local convective heat fluxes in concurrent flame spread","authors":"Pablo E. Pinto, Maria Thomsen, James L. Urban, Xiuqi Xi","doi":"10.1016/j.proci.2026.105995","DOIUrl":"10.1016/j.proci.2026.105995","url":null,"abstract":"<div><div>Understanding the heat transfer mechanisms that govern the interaction between the flame and the solid fuel surface is essential for predicting and modeling flame spread. This work presents a novel technique to spatially resolve the convective heat transfer during horizontal concurrent flame spread over polymethyl methacrylate (PMMA) sheets. The experiments are conducted in a bench-scale flow duct under three inlet flow velocities. A side-wall radiometer (<span><math><msub><mrow><mi>s</mi></mrow><mrow><mn>1</mn></mrow></msub></math></span>) and a dual heat flux gauge positioned downstream and adjacent to the fuel surface (<span><math><msub><mrow><mi>s</mi></mrow><mrow><mn>2</mn></mrow></msub></math></span> and <span><math><msub><mrow><mi>s</mi></mrow><mrow><mn>3</mn></mrow></msub></math></span>) are used to separate the radiative contribution from the total heat flux. The temperature at the dual heat flux gauge <span><math><mrow><mo>(</mo><msub><mrow><mi>s</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>)</mo></mrow></math></span> is also measured, and then a convective heat transfer coefficient is determined locally through an empirical Nusselt number correlation. A previously introduced non-dimensional total heat flux correlation is employed, demonstrating a collapse of all data across the experimental conditions. The local contributions of the heat-transfer mechanisms were quantified, showing that radiation is larger over most of the heated-zone domain, while convection becomes larger in the region of the heated zone nearest the pyrolysis front as the flame approaches the heated zone target (<span><math><msub><mrow><mi>s</mi></mrow><mrow><mn>2</mn></mrow></msub></math></span> location). The flame spread rate is obtained experimentally and predicted using the heat transfer contributions. The results exhibit excellent agreement between experiments and model predictions, highlighting that the methodology provides an accurate and consistent framework to predict flame spread behavior under concurrent flow conditions.</div><div><em>Novelty and significance statement</em>: This work presents a novel technique to spatially resolve convective heat transfer during horizontal concurrent flame spread over PMMA. Using heat flux measurements and fundamental analysis, the contributions of convection and radiation to the fuel surface are each resolved. An empirical local Nusselt number correlation is proposed allowing for estimation of the local convective heat transfer coefficient. The thermal response of the fuel during flame spread is assessed using the local Biot number to identify thermally thin or thick behavior.</div><div>This study provides quantitative insight into the coupled radiative and convective heat transfer mechanisms that control horizontal flame spread, key processes in solid-fuel combustion and fire growth. The results offer a transferable framework for model validation and development in material flammability research, and potentia","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"42 ","pages":"Article 105995"},"PeriodicalIF":4.6,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148567518","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-01Epub Date: 2026-06-27DOI: 10.1016/j.proci.2026.106096
Sina Kazemi, Aryan Nobakht, M. Reza Kholghy, Ahmet E. Karataş
The role of hydrogen addition in soot formation remains unclear, particularly for methane flames at elevated pressures. In this study, we combine radially resolved LED-based diagnostics (three-wavelength line-of-sight attenuation and spectral soot emission) with fully coupled two-dimensional gas- and solid-phase CFD simulations to investigate the sooting behavior of hydrogen-diluted methane coflow diffusion flames at pressures up to 20 atm. For the first time, a monodisperse population balance model is integrated into the 2D framework to describe soot dynamics. While simulations qualitatively capture all major trends, they overpredict absolute soot volume fraction values and pressure sensitivity. Experiments and simulations consistently show that increasing pressure strongly promotes soot formation, primarily due to increased mixture density and enhanced air entrainment, which accelerate fuel decomposition and advance soot inception. Hydrogen addition suppresses soot across the entire pressure range, with the inhibiting effect becoming more pronounced at higher dilution ratios. Detailed numerical analysis indicates that H2 inhibits soot formation primarily by reducing H-radical concentration, thereby decreasing the availability of dehydrogenated surface sites (lowering HACA surface growth rates) and limiting PAH formation, which delays inception and reduces PAH adsorption. Numerical results further indicate that soot formation pathways exhibit different sensitivities to H2 dilution, with inception being less affected while surface or PAH growth by HACA remains highly sensitive across pressures.
Novelty and significance statement: The novelty of this research is that, for the first time, the effect of hydrogen dilution on soot formation in methane diffusion flames is investigated at elevated pressures up to 20 atm using both experiments and simulations. It also introduces the first integration of a monodisperse population balance model into a two-dimensional CFD framework. The study provides new mechanistic insights into how hydrogen addition influences soot formation at high pressure, which is directly relevant to high-pressure industrial combustors such as gas turbine combustors and internal combustion engines. These findings contribute to the broader effort of developing cleaner combustion strategies by improving the fundamental understanding of soot mitigation through fuel modification, and support the advancement of predictive tools for the design of low-emission combustion technologies.
{"title":"Understanding the impact of hydrogen on soot formation in high-pressure methane diffusion flames","authors":"Sina Kazemi, Aryan Nobakht, M. Reza Kholghy, Ahmet E. Karataş","doi":"10.1016/j.proci.2026.106096","DOIUrl":"10.1016/j.proci.2026.106096","url":null,"abstract":"<div><div>The role of hydrogen addition in soot formation remains unclear, particularly for methane flames at elevated pressures. In this study, we combine radially resolved LED-based diagnostics (three-wavelength line-of-sight attenuation and spectral soot emission) with fully coupled two-dimensional gas- and solid-phase CFD simulations to investigate the sooting behavior of hydrogen-diluted methane coflow diffusion flames at pressures up to 20 atm. For the first time, a monodisperse population balance model is integrated into the 2D framework to describe soot dynamics. While simulations qualitatively capture all major trends, they overpredict absolute soot volume fraction values and pressure sensitivity. Experiments and simulations consistently show that increasing pressure strongly promotes soot formation, primarily due to increased mixture density and enhanced air entrainment, which accelerate fuel decomposition and advance soot inception. Hydrogen addition suppresses soot across the entire pressure range, with the inhibiting effect becoming more pronounced at higher dilution ratios. Detailed numerical analysis indicates that H<sub>2</sub> inhibits soot formation primarily by reducing H-radical concentration, thereby decreasing the availability of dehydrogenated surface sites (lowering HACA surface growth rates) and limiting PAH formation, which delays inception and reduces PAH adsorption. Numerical results further indicate that soot formation pathways exhibit different sensitivities to H<sub>2</sub> dilution, with inception being less affected while surface or PAH growth by HACA remains highly sensitive across pressures.</div><div><em>Novelty and significance statement:</em> The novelty of this research is that, for the first time, the effect of hydrogen dilution on soot formation in methane diffusion flames is investigated at elevated pressures up to 20 atm using both experiments and simulations. It also introduces the first integration of a monodisperse population balance model into a two-dimensional CFD framework. The study provides new mechanistic insights into how hydrogen addition influences soot formation at high pressure, which is directly relevant to high-pressure industrial combustors such as gas turbine combustors and internal combustion engines. These findings contribute to the broader effort of developing cleaner combustion strategies by improving the fundamental understanding of soot mitigation through fuel modification, and support the advancement of predictive tools for the design of low-emission combustion technologies.</div></div>","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"42 ","pages":"Article 106096"},"PeriodicalIF":4.6,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148567531","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 : 2026-01-01Epub Date: 2026-07-02DOI: 10.1016/j.proci.2026.106146
Hanzhang Cao, Wang Han, Yihao Tang, Lijun Yang
While hypergolic propellants (e.g., monomethylhydrazine (MMH)/dinitrogen tetroxide (NTO)), which are capable of spontaneous ignition upon contact, are widely used in rockets and spacecraft, the hypergolic ignition processes remain incompletely understood. To this end, numerical simulations of the hypergolic ignition of MMH/NTO are performed in this work using a detailed chemistry, with particular attention to the effects of flow strain. It is found that there are four distinct ignition stages: cold reaction, nitric acid reaction, edge flame, and final multilayer flame. Increasing the strain rate can advance all stages, thin the flame front, and increase the peak heat release rate. Furthermore, budget and flame displacement speed analyses indicate that the edge-flame stage exhibits a more source-dominated character and faster propagation than the multilayer stage. These results clarify the stage-wise evolution and strain-controlled propagation of MMH/NTO hypergolic ignition.
Novelty and significance statement: This work builds on the MMH/NTO counterflow benchmark of Hayashi et al. and provides a mechanism-resolved description of the transient gas-phase route by which hypergolic ignition develops from low-temperature contact reactions to the multilayer flame structure reported in that prior study. Its novelty lies in combining homogeneous reactor analysis with fully resolved two-dimensional simulations to identify practical stage markers and a physically interpretable four-stage ignition sequence. The study further links the stage transitions to the evolving thermochemical structure of the reaction zone and examines how strain rate modifies stage transitions, heat release, flame front propagation, transport budgets, and displacement speed behaviors. These analyses clarify the transient formation pathway and strain-dependent propagation characteristics of MMH/NTO hypergolic ignition, thereby informing reduced models, ignition criteria, and safety-related simulations of hypergolic propulsion systems.
{"title":"A numerical study of strain effects on hypergolic ignition of MMH/NTO","authors":"Hanzhang Cao, Wang Han, Yihao Tang, Lijun Yang","doi":"10.1016/j.proci.2026.106146","DOIUrl":"10.1016/j.proci.2026.106146","url":null,"abstract":"<div><div>While hypergolic propellants (e.g., monomethylhydrazine (MMH)/dinitrogen tetroxide (NTO)), which are capable of spontaneous ignition upon contact, are widely used in rockets and spacecraft, the hypergolic ignition processes remain incompletely understood. To this end, numerical simulations of the hypergolic ignition of MMH/NTO are performed in this work using a detailed chemistry, with particular attention to the effects of flow strain. It is found that there are four distinct ignition stages: cold reaction, nitric acid reaction, edge flame, and final multilayer flame. Increasing the strain rate can advance all stages, thin the flame front, and increase the peak heat release rate. Furthermore, budget and flame displacement speed analyses indicate that the edge-flame stage exhibits a more source-dominated character and faster propagation than the multilayer stage. These results clarify the stage-wise evolution and strain-controlled propagation of MMH/NTO hypergolic ignition.</div><div><em>Novelty and significance statement:</em> This work builds on the MMH/NTO counterflow benchmark of Hayashi et al. and provides a mechanism-resolved description of the transient gas-phase route by which hypergolic ignition develops from low-temperature contact reactions to the multilayer flame structure reported in that prior study. Its novelty lies in combining homogeneous reactor analysis with fully resolved two-dimensional simulations to identify practical stage markers and a physically interpretable four-stage ignition sequence. The study further links the stage transitions to the evolving thermochemical structure of the reaction zone and examines how strain rate modifies stage transitions, heat release, flame front propagation, transport budgets, and displacement speed behaviors. These analyses clarify the transient formation pathway and strain-dependent propagation characteristics of MMH/NTO hypergolic ignition, thereby informing reduced models, ignition criteria, and safety-related simulations of hypergolic propulsion systems.</div></div>","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"42 ","pages":"Article 106146"},"PeriodicalIF":4.6,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148587494","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 : 2026-01-01Epub Date: 2026-07-04DOI: 10.1016/j.proci.2026.106128
Yudong Wang, Fang Wang, Jie Jin, Dasheng Wei
Accurate closure of the micro-mixing term in probability density function (PDF) transport equations remains critical for predictive combustor simulations. This work introduces a Turbulence-Chemistry Recursive (TCR) mixing model for Eulerian Stochastic Field (ESF) methods that quantifies local turbulence-chemistry interactions through partitioned reactors. The approach abstracts computational cells into partitioned zones representing distinct mixing states, eliminating the need for localness modeling in micro-mixing closures. By unifying mixing mode and timescale through scalar variance evolution, the TCR model correctly predicts concurrent increases in mixing frequency and scalar variance in flamelet regimes. Crucially, the model recursively utilizes information obtained during PDF transport equation solution for micro-mixing closure, circumventing contentious timescale modeling in traditional partitioned approaches and avoiding additional model parameters. A priori analysis confirms the TCR model in ESF produces variance distributions aligning more closely with Direct Numerical Simulation data, reducing PDF variance prediction errors to 3.43%–20.49% compared to IEM. Validation on Sandia Flame-D demonstrates enhanced prediction accuracy for temperature and species mass fractions versus standard IEM in ESF, evidenced by mean CO error reduction from 17.65% to 6.58%. By dynamically adapting mixing through turbulence-driven homogenization and chemistry-driven differentiation via real-time target updating, the TCR model enhances ESF applicability for engineering combustor simulations across diverse combustion regimes.
Novelty and significance statement: This paper proposes the TCR model to resolve a fundamental limitation of ESF methods, i.e., their inability to incorporate localness-based micro-mixing models such as EMST. The ESF method avoids explicit localness modeling in Eulerian fields while implicitly capturing localness effects through turbulence-chemistry interactions, a capability that traditional IEM models lack. This partition unifies mixing mode and timescale through scalar variance evolution, thereby correctly predicting increased mixing frequency and enhanced scalar variance in flamelet regimes, e.g., when reaction zones thin and gradients steepen. Such behavior cannot be captured by adjusting timescale alone. The recursive closure utilizes filtered and reference reaction rates from PDF solutions, enabling dynamic parameter determination without empirical calibration. This establishes a robust framework for high-fidelity PDF-based simulations applicable across diverse combustion regimes.
{"title":"Recursive micro-mixing modeling incorporating a multi-layer partitioned approach","authors":"Yudong Wang, Fang Wang, Jie Jin, Dasheng Wei","doi":"10.1016/j.proci.2026.106128","DOIUrl":"10.1016/j.proci.2026.106128","url":null,"abstract":"<div><div>Accurate closure of the micro-mixing term in probability density function (PDF) transport equations remains critical for predictive combustor simulations. This work introduces a Turbulence-Chemistry Recursive (TCR) mixing model for Eulerian Stochastic Field (ESF) methods that quantifies local turbulence-chemistry interactions through partitioned reactors. The approach abstracts computational cells into partitioned zones representing distinct mixing states, eliminating the need for localness modeling in micro-mixing closures. By unifying mixing mode and timescale through scalar variance evolution, the TCR model correctly predicts concurrent increases in mixing frequency and scalar variance in flamelet regimes. Crucially, the model recursively utilizes information obtained during PDF transport equation solution for micro-mixing closure, circumventing contentious timescale modeling in traditional partitioned approaches and avoiding additional model parameters. A priori analysis confirms the TCR model in ESF produces variance distributions aligning more closely with Direct Numerical Simulation data, reducing PDF variance prediction errors to 3.43%–20.49% compared to IEM. Validation on Sandia Flame-D demonstrates enhanced prediction accuracy for temperature and species mass fractions versus standard IEM in ESF, evidenced by mean CO error reduction from 17.65% to 6.58%. By dynamically adapting mixing through turbulence-driven homogenization and chemistry-driven differentiation via real-time target updating, the TCR model enhances ESF applicability for engineering combustor simulations across diverse combustion regimes.</div><div><em>Novelty and significance statement:</em> This paper proposes the TCR model to resolve a fundamental limitation of ESF methods, i.e., their inability to incorporate localness-based micro-mixing models such as EMST. The ESF method avoids explicit localness modeling in Eulerian fields while implicitly capturing localness effects through turbulence-chemistry interactions, a capability that traditional IEM models lack. This partition unifies mixing mode and timescale through scalar variance evolution, thereby correctly predicting increased mixing frequency and enhanced scalar variance in flamelet regimes, e.g., when reaction zones thin and gradients steepen. Such behavior cannot be captured by adjusting timescale alone. The recursive closure utilizes filtered and reference reaction rates from PDF solutions, enabling dynamic parameter determination without empirical calibration. This establishes a robust framework for high-fidelity PDF-based simulations applicable across diverse combustion regimes.</div></div>","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"42 ","pages":"Article 106128"},"PeriodicalIF":4.6,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148582376","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}
扫码关注我们
求助内容：
应助结果提醒方式：
京公网安备 11010802042870号