Pub Date : 2024-06-12DOI: 10.1016/j.combustflame.2024.113489
Congjie Hong , Yilong Ao , Yuyang Zhang , Wuchuan Sun , Zemin Tian , Yingwen Yan , Zuohua Huang , Yingjia Zhang
n-Dodecane is commonly employed as a surrogate for investigating the combustion characteristics of jet and diesel fuels. Enhancing comprehension of its combustion behavior and developing accurate chemical kinetics models for simulating combustion is of paramount importance in engine development. This study focuses on a detailed exploration of n-dodecane oxidation kinetics under low-temperature conditions and presents a novel dataset concerning the first-stage ignition delay time. A broad spectrum of experimental conditions is investigated, encompassing a range of temperature (600 ∼ 1350 K), pressure (5 ∼ 20 atm), equivalence ratios (0.5 ∼ 1.0), and dilution gases (N2 and Ar). Additionally, combustion experiments in a pure oxygen environment are performed, contributing valuable data to existing research. To enhance the precision of the chemical reaction kinetics model of n-dodecane, this study integrates updated rate coefficients obtained from the latest theoretical calculations for specific reaction classes. The improved rate rule provides a more accurate reference for the construction of the chemical reaction kinetics model of long straight alkane. The resulting improved model excels in accurately predicting both the first-stage ignition delay time and the total ignition delay time under a wide range of operational conditions. Additionally, the model performance is rigorously evaluated through a comprehensive assessment against a diverse array of datasets gathered from various literature references. The results show that, in contrast to the previously proposed model, this enhanced model provides highly reliable predictions over a broad range of parameters.
{"title":"Exploring the first-stage ignition and model optimization in the comprehensive study of n-dodecane oxidation","authors":"Congjie Hong , Yilong Ao , Yuyang Zhang , Wuchuan Sun , Zemin Tian , Yingwen Yan , Zuohua Huang , Yingjia Zhang","doi":"10.1016/j.combustflame.2024.113489","DOIUrl":"https://doi.org/10.1016/j.combustflame.2024.113489","url":null,"abstract":"<div><p><em>n</em>-Dodecane is commonly employed as a surrogate for investigating the combustion characteristics of jet and diesel fuels. Enhancing comprehension of its combustion behavior and developing accurate chemical kinetics models for simulating combustion is of paramount importance in engine development. <em>This study</em> focuses on a detailed exploration of <em>n</em>-dodecane oxidation kinetics under low-temperature conditions and presents a novel dataset concerning the first-stage ignition delay time. A broad spectrum of experimental conditions is investigated, encompassing a range of temperature (600 ∼ 1350 K), pressure (5 ∼ 20 atm), equivalence ratios (0.5 ∼ 1.0), and dilution gases (N<sub>2</sub> and Ar). Additionally, combustion experiments in a pure oxygen environment are performed, contributing valuable data to existing research. To enhance the precision of the chemical reaction kinetics model of <em>n</em>-dodecane, <em>this study</em> integrates updated rate coefficients obtained from the latest theoretical calculations for specific reaction classes. The improved rate rule provides a more accurate reference for the construction of the chemical reaction kinetics model of long straight alkane. The resulting improved model excels in accurately predicting both the first-stage ignition delay time and the total ignition delay time under a wide range of operational conditions. Additionally, the model performance is rigorously evaluated through a comprehensive assessment against a diverse array of datasets gathered from various literature references. The results show that, in contrast to the previously proposed model, this enhanced model provides highly reliable predictions over a broad range of parameters.</p></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":null,"pages":null},"PeriodicalIF":4.4,"publicationDate":"2024-06-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141315120","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 : 2024-06-11DOI: 10.1016/j.combustflame.2024.113553
Mhedine Alicherif, Samir B. Rojas Chavez, Karl P. Chatelain, Thibault F. Guiberti, Deanna A. Lacoste
The detonation front’s unstable structure leads to an unsteady and three-dimensional (3D) phenomenon that renders the study of the cell cycle challenging. Traditionally, fundamental studies are carried out in narrow channels where the detonation behavior is very peculiar (quasi two-dimensional with velocity deficit). In this study, we propose a fully experimental approach to study the cell cycle in the case of multicellular detonations. The cell cycle is characterized through three techniques: systematic and statistical analysis of soot foil, planar laser-induced fluorescence on nitric oxide, and Rayleigh scattering. These techniques provide measurements for cell size, local induction length, and local shock speed, respectively. The work is carried out in the 2-O-3.76Ar and the 2-O-3.76N mixtures at 293 K, and 20 kPa and 25 kPa, respectively. These conditions ensure that the cell pattern is considered being between regular and weakly irregular, thus, a shot-to-shot reconstruction of the cell cycle is possible. The cell widths follow a normal distribution, from which a quantitative parameter (2/) is proposed to assess the cell regularity, experimentally. The evolution of the speed and the local induction length are reconstructed along the cell cycle. The results agree with the available data for narrow channels and constitute the first of their kind for 3D detonation (i.e., multicellular in the transverse dimension). Two methods are proposed to analyze the local induction length and compare it to the available literature (experimental and numerical studies). The technique can be applied to mixtures where the mean cell width is a meaningful parameter from highly regular to irregular mixtures.
Novelty and Significance statement
For the first time, combined soot-foils, NO-PLIF, and Rayleigh scattering measurements were used to reconstruct and characterize the cellular cycle of multicellular detonations using a 2-O-3.76Ar and 2-O-3.76N mixtures at 293 K, and 20 kPa and 25 kPa, respecti
{"title":"Experimental characterization of the cell cycle for multicellular detonations","authors":"Mhedine Alicherif, Samir B. Rojas Chavez, Karl P. Chatelain, Thibault F. Guiberti, Deanna A. Lacoste","doi":"10.1016/j.combustflame.2024.113553","DOIUrl":"https://doi.org/10.1016/j.combustflame.2024.113553","url":null,"abstract":"<div><p>The detonation front’s unstable structure leads to an unsteady and three-dimensional (3D) phenomenon that renders the study of the cell cycle challenging. Traditionally, fundamental studies are carried out in narrow channels where the detonation behavior is very peculiar (quasi two-dimensional with velocity deficit). In this study, we propose a fully experimental approach to study the cell cycle in the case of multicellular detonations. The cell cycle is characterized through three techniques: systematic and statistical analysis of soot foil, planar laser-induced fluorescence on nitric oxide, and Rayleigh scattering. These techniques provide measurements for cell size, local induction length, and local shock speed, respectively. The work is carried out in the 2<span><math><msub><mrow><mi>H</mi></mrow><mrow><mn>2</mn></mrow></msub></math></span>-O<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span>-3.76Ar and the 2<span><math><msub><mrow><mi>H</mi></mrow><mrow><mn>2</mn></mrow></msub></math></span>-O<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span>-3.76N<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> mixtures at 293 K, and 20 kPa and 25 kPa, respectively. These conditions ensure that the cell pattern is considered being between regular and weakly irregular, thus, a shot-to-shot reconstruction of the cell cycle is possible. The cell widths follow a normal distribution, from which a quantitative parameter (2<span><math><mi>σ</mi></math></span>/<span><math><mi>λ</mi></math></span>) is proposed to assess the cell regularity, experimentally. The evolution of the speed and the local induction length are reconstructed along the cell cycle. The results agree with the available data for narrow channels and constitute the first of their kind for 3D detonation (i.e., multicellular in the transverse dimension). Two methods are proposed to analyze the local induction length <span><math><msub><mrow><mi>δ</mi></mrow><mrow><mi>i</mi></mrow></msub></math></span> and compare it to the available literature (experimental and numerical studies). The technique can be applied to mixtures where the mean cell width is a meaningful parameter from highly regular to irregular mixtures.</p><p><strong>Novelty and Significance statement</strong></p><p>For the first time, combined soot-foils, NO-PLIF, and Rayleigh scattering measurements were used to reconstruct and characterize the cellular cycle of multicellular detonations using a 2<span><math><msub><mrow><mi>H</mi></mrow><mrow><mn>2</mn></mrow></msub></math></span>-O<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span>-3.76Ar and 2<span><math><msub><mrow><mi>H</mi></mrow><mrow><mn>2</mn></mrow></msub></math></span>-O<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span>-3.76N<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> mixtures at 293 K, and 20 kPa and 25 kPa, respecti","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":null,"pages":null},"PeriodicalIF":4.4,"publicationDate":"2024-06-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141303751","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 : 2024-06-11DOI: 10.1016/j.combustflame.2024.113554
Jiabo Zhang , Minh Bau Luong , Hong G. Im
The effects of heat diffusion and turbulence on the detonation propensity of a stoichiometric hydrogen/air mixture under representative low- and high-temperature conditions in internal combustion engines are investigated using two- and three-dimensional direct numerical simulations (DNS) with detailed chemistry. Parametric studies are performed by varying the root-mean-square temperature fluctuation, , the most energetic length scale of the temperature and velocity fluctuation, and , and the turbulent velocity fluctuation, . Two non-dimensional parameters, namely the resonance parameter and the reactivity parameter , are employed to identify ignition modes. The results reveal that the gradient of the temperature field experiences a rapid dissipation prior to the main ignition due to the pronounced effect of heat diffusion, leading to a decrease of the mean and an increase of the mean , especially at lower initial temperature having a long ignition delay time. Due to the decreased and the increased , these cases have a weaker detonation propensity — their ignition mode shifts from deflagration to detonation transition (DDT) to spontaneous auto-ignition. Moreover, turbulence with faster mixing time scales, characterized by the ratio of ignition delay time to eddy-turnover time, , and larger length scales of enhances the effect of heat dissipation, which in turn effectively decreases the temperature gradient level, and thus the detonation propensity. These effects of heat diffusion and turbulence on the ignition mode are well-characterized by the newly proposed turbulent Damköhler number, Da, considering the turbulence intensity characterized by both
{"title":"Effects of heat diffusion and turbulence on detonation development of hydrogen/air mixtures under engine-relevant conditions","authors":"Jiabo Zhang , Minh Bau Luong , Hong G. Im","doi":"10.1016/j.combustflame.2024.113554","DOIUrl":"https://doi.org/10.1016/j.combustflame.2024.113554","url":null,"abstract":"<div><p>The effects of heat diffusion and turbulence on the detonation propensity of a stoichiometric hydrogen/air mixture under representative low- and high-temperature conditions in internal combustion engines are investigated using two- and three-dimensional direct numerical simulations (DNS) with detailed chemistry. Parametric studies are performed by varying the root-mean-square temperature fluctuation, <span><math><msup><mrow><mi>T</mi></mrow><mrow><mo>′</mo></mrow></msup></math></span>, the most energetic length scale of the temperature and velocity fluctuation, <span><math><msub><mrow><mi>l</mi></mrow><mrow><mi>T</mi></mrow></msub></math></span> and <span><math><msub><mrow><mi>l</mi></mrow><mrow><mi>e</mi></mrow></msub></math></span>, and the turbulent velocity fluctuation, <span><math><msup><mrow><mi>u</mi></mrow><mrow><mo>′</mo></mrow></msup></math></span>. Two non-dimensional parameters, namely the <em>resonance paramete</em>r <span><math><mi>ξ</mi></math></span> and the <em>reactivity parameter</em> <span><math><mi>ɛ</mi></math></span>, are employed to identify ignition modes. The results reveal that the gradient of the temperature field experiences a rapid dissipation prior to the main ignition due to the pronounced effect of heat diffusion, leading to a decrease of the mean <span><math><mover><mrow><mi>ξ</mi></mrow><mo>¯</mo></mover></math></span> and an increase of the mean <span><math><mover><mrow><mi>ɛ</mi></mrow><mo>¯</mo></mover></math></span>, especially at lower initial temperature having a long ignition delay time. Due to the decreased <span><math><mover><mrow><mi>ξ</mi></mrow><mo>¯</mo></mover></math></span> and the increased <span><math><mover><mrow><mi>ɛ</mi></mrow><mo>¯</mo></mover></math></span>, these cases have a weaker detonation propensity — their ignition mode shifts from deflagration to detonation transition (DDT) to spontaneous auto-ignition. Moreover, turbulence with faster mixing time scales, characterized by the ratio of ignition delay time to eddy-turnover time, <span><math><mrow><msub><mrow><mi>τ</mi></mrow><mrow><mi>i</mi><mi>g</mi></mrow></msub><mo>/</mo><msub><mrow><mi>τ</mi></mrow><mrow><mi>t</mi></mrow></msub></mrow></math></span>, and larger length scales of <span><math><mrow><msub><mrow><mi>l</mi></mrow><mrow><mi>e</mi></mrow></msub><mo>/</mo><msub><mrow><mi>l</mi></mrow><mrow><mi>T</mi></mrow></msub></mrow></math></span> enhances the effect of heat dissipation, which in turn effectively decreases the temperature gradient level, and thus the detonation propensity. These effects of heat diffusion and turbulence on the ignition mode are well-characterized by the newly proposed turbulent Damköhler number, Da<span><math><msub><mrow></mrow><mrow><mi>t</mi></mrow></msub></math></span>, considering the turbulence intensity characterized by both <span><math><mrow><msub><mrow><mi>τ</mi></mrow><mrow><mi>i</mi><mi>g</mi></mrow></msub><mo>/</mo><msub><mrow><mi>τ</mi></mrow><mrow><mi>t</mi></mrow></msub></mrow></m","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":null,"pages":null},"PeriodicalIF":4.4,"publicationDate":"2024-06-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141308174","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 : 2024-06-10DOI: 10.1016/j.combustflame.2024.113555
Chong Li , Yangyang Luo , Haixin Deng , Zihao Zhou , Hongbo Ning , Yanlei Shang , Sheng-Nian Luo
Ammonia (NH) is a promising carbon-free and alternative fuel, but its applications are hindered by high auto-ignition temperature and low burning velocity. A common approach to overcome such drawbacks is to blend NH with a high-reactivity fuel. In this study, a heated shock tube is employed to measure ignition delay time of NH blended with methyl hexanoate (MHX). The experiments are conducted at 6 atm, equivalence ratios of 0.5–2.0, temperatures of 1168–2115 K, and MHX blending ratios of 0, 20%, 50%, 70%, and 100%. Ignition delay time of the binary mixtures decreases monotonically with the addition of MHX. Compared with pure NH, the reactivity of the binary mixtures increases significantly with the addition of only 20% MHX, leading to a 10 times faster ignition delay time at around 1500 K and 6 atm. The reactivity of the fuel-lean and stoichiometric ratio mixtures is similar, and higher than the fuel-rich mixtures. The promotion effect of ignition delay time decreases with increasing blending ratio and pressure, and decreasing temperature. The influence of equivalence ratio on the promotion effect of ignition delay time is less significant than that of blending ratio, temperature and pressure. A detailed NH/MHX kinetic model is developed by updating the interaction reactions between MHX and NH/NO/NO radicals, and the NH and MHX sub-mechanism. The present kinetic model can reproduce satisfactorily the ignition delay time of pure MHX and NH, and the NH/MHX mixtures in the whole experimental conditions explored here. The kinetic analyses reveal that the interaction reactions between MHX and NH radical have a significant impact on the ignition of the binary mixtures. Moreover, the important intermediate NH is more prone to forming NH rather than NNH in the presence of MHX, different from the production of NNH in pure NH
{"title":"Shock tube and kinetic modeling study on high-temperature ignition of ammonia blended with methyl hexanoate","authors":"Chong Li , Yangyang Luo , Haixin Deng , Zihao Zhou , Hongbo Ning , Yanlei Shang , Sheng-Nian Luo","doi":"10.1016/j.combustflame.2024.113555","DOIUrl":"https://doi.org/10.1016/j.combustflame.2024.113555","url":null,"abstract":"<div><p>Ammonia (NH<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span>) is a promising carbon-free and alternative fuel, but its applications are hindered by high auto-ignition temperature and low burning velocity. A common approach to overcome such drawbacks is to blend NH<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span> with a high-reactivity fuel. In this study, a heated shock tube is employed to measure ignition delay time of NH<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span> blended with methyl hexanoate (MHX). The experiments are conducted at 6 atm, equivalence ratios of 0.5–2.0, temperatures of 1168–2115 K, and MHX blending ratios of 0, 20%, 50%, 70%, and 100%. Ignition delay time of the binary mixtures decreases monotonically with the addition of MHX. Compared with pure NH<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span>, the reactivity of the binary mixtures increases significantly with the addition of only 20% MHX, leading to a 10 times faster ignition delay time at around 1500 K and 6 atm. The reactivity of the fuel-lean and stoichiometric ratio mixtures is similar, and higher than the fuel-rich mixtures. The promotion effect of ignition delay time decreases with increasing blending ratio and pressure, and decreasing temperature. The influence of equivalence ratio on the promotion effect of ignition delay time is less significant than that of blending ratio, temperature and pressure. A detailed NH<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span>/MHX kinetic model is developed by updating the interaction reactions between MHX and NH<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span>/NO<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span>/NO radicals, and the NH<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span> and MHX sub-mechanism. The present kinetic model can reproduce satisfactorily the ignition delay time of pure MHX and NH<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span>, and the NH<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span>/MHX mixtures in the whole experimental conditions explored here. The kinetic analyses reveal that the interaction reactions between MHX and NH<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> radical have a significant impact on the ignition of the binary mixtures. Moreover, the important intermediate N<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span>H<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> is more prone to forming N<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span>H<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span> rather than NNH in the presence of MHX, different from the production of NNH in pure NH<span><math><msub><m","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":null,"pages":null},"PeriodicalIF":4.4,"publicationDate":"2024-06-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141303750","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 : 2024-06-08DOI: 10.1016/j.combustflame.2024.113539
Lingzhi Zheng, Miguel Figueroa-Labastida, Jesse W. Streicher, Alison M. Ferris, Ronald K. Hanson
The flame speeds of premixed stoichiometric n-heptane/21% O2-79% Ar (so-called “airgon”) flames with different extents of pre-flame auto-ignition chemistry were experimentally investigated using an extended test-time, side-wall-imaging shock tube. n-Heptane/airgon mixtures were impulsively heated by reflected shock waves to a temperature of 703 ± 8 K and pressure of 1.55 ± 0.05 atm, exhibiting first-stage auto-ignition at 20.1 ± 0.6 ms. Flames were spark-ignited using a laser from 0.45 ms to 39 ms after reflected-shock heating, thus probing the augmentation of flame speeds with variable extents of pre-flame auto-ignition chemistry. The fixed-initial-temperature experiments displayed multiple distinctive flame speed regimes across first-stage auto-ignition. A burned-gas flame speed () increase of 6% was first observed with spark-ignition at 7 ms after reflected-shock heating. At spark-ignition timing very close to the first-stage auto-ignition, displayed a sharp 24% rise, which then gradually declined to 10% above the reference value where pre-flame chemistry is negligible. Experiments were additionally performed at 1.55 ± 0.05 atm using two fixed spark-ignition timings (0.45 ms and 25 ms after reflected-shock heating) for initial temperatures between 641 K and 771 K. In the experiments with variable initial temperatures, a non-monotonic dependence on initial temperature was observed for the 25-ms experiments, which showed a maximum increase of 14% relative to the 0.45-ms experiments. To provide modeling comparisons, the thermochemical time history of the reacting gas was first simulated; the species profiles and the temperature at a given residence time were then used to obtain the flame speed from 1D steady-state simulations. The multi-regime flame speed behavior was not observed in fixed-initial-temperature simulations, which predicted a single rise in flame speed only near the first-stage auto-ignition time. The simulations with variable initial temperatures qualitatively recovered the non-monotonic flame speed trend, but generally showed underprediction of flame speeds relative to experimental results. These new experiments provide insight into the effect of pre-flame chemistry on flame propagation and offer targets for improving flame modeling, potentially aiding the development of next-generation engine concepts.
{"title":"Experimental measurements of n-heptane flame speeds behind reflected shock waves with variable extents of pre-flame auto-ignition chemistry","authors":"Lingzhi Zheng, Miguel Figueroa-Labastida, Jesse W. Streicher, Alison M. Ferris, Ronald K. Hanson","doi":"10.1016/j.combustflame.2024.113539","DOIUrl":"https://doi.org/10.1016/j.combustflame.2024.113539","url":null,"abstract":"<div><p>The flame speeds of premixed stoichiometric <em>n</em>-heptane/21% O<sub>2</sub>-79% Ar (so-called “airgon”) flames with different extents of pre-flame auto-ignition chemistry were experimentally investigated using an extended test-time, side-wall-imaging shock tube. <em>n</em>-Heptane/airgon mixtures were impulsively heated by reflected shock waves to a temperature of 703 ± 8 K and pressure of 1.55 ± 0.05 atm, exhibiting first-stage auto-ignition at 20.1 ± 0.6 ms. Flames were spark-ignited using a laser from 0.45 ms to 39 ms after reflected-shock heating, thus probing the augmentation of flame speeds with variable extents of pre-flame auto-ignition chemistry. The fixed-initial-temperature experiments displayed multiple distinctive flame speed regimes across first-stage auto-ignition. A burned-gas flame speed (<span><math><msubsup><mrow><mi>S</mi></mrow><mrow><mi>b</mi></mrow><mrow><mn>0</mn></mrow></msubsup></math></span>) increase of 6% was first observed with spark-ignition at <span><math><mo>∼</mo></math></span>7 ms after reflected-shock heating. At spark-ignition timing very close to the first-stage auto-ignition, <span><math><msubsup><mrow><mi>S</mi></mrow><mrow><mi>b</mi></mrow><mrow><mn>0</mn></mrow></msubsup></math></span> displayed a sharp 24% rise, which then gradually declined to <span><math><mo>∼</mo></math></span>10% above the reference value where pre-flame chemistry is negligible. Experiments were additionally performed at 1.55 ± 0.05 atm using two fixed spark-ignition timings (0.45 ms and 25 ms after reflected-shock heating) for initial temperatures between 641 K and 771 K. In the experiments with variable initial temperatures, a non-monotonic <span><math><msubsup><mrow><mi>S</mi></mrow><mrow><mi>b</mi></mrow><mrow><mn>0</mn></mrow></msubsup></math></span> dependence on initial temperature was observed for the 25-ms experiments, which showed a maximum <span><math><msubsup><mrow><mi>S</mi></mrow><mrow><mi>b</mi></mrow><mrow><mn>0</mn></mrow></msubsup></math></span> increase of 14% relative to the 0.45-ms experiments. To provide modeling comparisons, the thermochemical time history of the reacting gas was first simulated; the species profiles and the temperature at a given residence time were then used to obtain the flame speed from 1D steady-state simulations. The multi-regime flame speed behavior was not observed in fixed-initial-temperature simulations, which predicted a single rise in flame speed only near the first-stage auto-ignition time. The simulations with variable initial temperatures qualitatively recovered the non-monotonic flame speed trend, but generally showed underprediction of flame speeds relative to experimental results. These new experiments provide insight into the effect of pre-flame chemistry on flame propagation and offer targets for improving flame modeling, potentially aiding the development of next-generation engine concepts.</p></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":null,"pages":null},"PeriodicalIF":4.4,"publicationDate":"2024-06-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141290997","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 : 2024-06-08DOI: 10.1016/j.combustflame.2024.113540
Yuki Murakami, Takuya Tezuka, Hisashi Nakamura
The extinction limits of non-premixed counterflow flames of methane (CH4)/ammonia (NH3)/nitrogen (N2) versus high-temperature air (TAir = 700 K and 1000 K) were investigated both experimentally and numerically. Extinction stretch rates of non-premixed counterflow flames of CH4/NH3 mixtures decreased greatly as the ammonia mixing ratio increased. Recent chemical kinetic models could well predict measured extinction limits of non-premixed counterflow flames of CH4/NH3 mixtures, especially for TAir = 1000 K. Chemical kinetic analyses indicated that the nature of NH3 consuming active radicals but not regenerating them through its oxidation is the primary reason for the drastic decreases in extinction stretch rates of non-premixed counterflow flames of CH4/NH3 mixtures. Furthermore, the combined metric of the transport weighted enthalpy (TWE) and the radical index (RI) is introduced for non-premixed counterflow flames of CH4/NH3 mixtures. The OH-radical index (RIOH), previously used in the combined metric for extinction limits of non-premixed counterflow flames of large hydrocarbons, expresses linear relationships with extinction limits for both TAir conditions. According to further investigations on heat releases from individual reactions, the contribution to heat releases from a reaction involving O radicals, i.e., CH3 + O ⇄ CH2O + H, becomes large in addition to reactions involving OH radicals, i.e., CO + OH ⇄ CO2 + H and H2 + OH ⇄ H + H2O. Based on the analyses, a new radical index based on the combination of OH and O radicals (RIOH&O) is proposed. The RIOH&O better expresses the linear relationship between extinction limits and the combined metric of RIOH&O and TWE.
通过实验和数值计算研究了甲烷（CH4）/氨（NH3）/氮（N2）与高温空气（TAir = 700 K 和 1000 K）非预混逆流火焰的消光极限。随着氨气混合比的增加，CH4/NH3 混合物的非预混合逆流火焰的熄灭伸展率大大降低。最新的化学动力学模型可以很好地预测 CH4/NH3 混合物非预混合逆流火焰的消光极限，特别是在 TAir = 1000 K 的情况下。化学动力学分析表明，NH3 消耗活性自由基而不是通过其氧化作用再生活性自由基的性质是 CH4/NH3 混合物非预混合逆流火焰消光伸展率急剧下降的主要原因。此外，还针对 CH4/NH3 混合物的非预混合逆流火焰引入了传输加权焓（TWE）和自由基指数（RI）的组合指标。之前用于大碳氢化合物非预混逆流火焰消光极限的组合指标中的羟基-自由基指数（RIOH）与 TAir 两种条件下的消光极限均呈线性关系。根据对单个反应释放热量的进一步研究，除了涉及 OH 自由基的反应（即 CO + OH ⇄ CO2 + H 和 H2 + OH ⇄ H + H2O）外，涉及 O 自由基的反应（即 CH3 + O ⇄ CH2O + H）对释放热量的贡献也变得很大。根据分析结果，提出了一种基于 OH 和 O 自由基组合的新自由基指数（RIOH&O）。RIOH&O 更好地表达了消光极限与 RIOH&O 和 TWE 组合指标之间的线性关系。
{"title":"The extinction limits and the radical index of non-premixed counterflow flames of methane/ammonia/nitrogen versus high-temperature air","authors":"Yuki Murakami, Takuya Tezuka, Hisashi Nakamura","doi":"10.1016/j.combustflame.2024.113540","DOIUrl":"https://doi.org/10.1016/j.combustflame.2024.113540","url":null,"abstract":"<div><p>The extinction limits of non-premixed counterflow flames of methane (CH<sub>4</sub>)/ammonia (NH<sub>3</sub>)/nitrogen (N<sub>2</sub>) versus high-temperature air (<em>T</em><sub>Air</sub> = 700 K and 1000 K) were investigated both experimentally and numerically. Extinction stretch rates of non-premixed counterflow flames of CH<sub>4</sub>/NH<sub>3</sub> mixtures decreased greatly as the ammonia mixing ratio increased. Recent chemical kinetic models could well predict measured extinction limits of non-premixed counterflow flames of CH<sub>4</sub>/NH<sub>3</sub> mixtures, especially for <em>T</em><sub>Air</sub> = 1000 K. Chemical kinetic analyses indicated that the nature of NH<sub>3</sub> consuming active radicals but not regenerating them through its oxidation is the primary reason for the drastic decreases in extinction stretch rates of non-premixed counterflow flames of CH<sub>4</sub>/NH<sub>3</sub> mixtures. Furthermore, the combined metric of the transport weighted enthalpy (<em>TWE</em>) and the radical index (<em>RI</em>) is introduced for non-premixed counterflow flames of CH<sub>4</sub>/NH<sub>3</sub> mixtures. The OH-radical index (<em>RI</em><sub>OH</sub>), previously used in the combined metric for extinction limits of non-premixed counterflow flames of large hydrocarbons, expresses linear relationships with extinction limits for both <em>T</em><sub>Air</sub> conditions. According to further investigations on heat releases from individual reactions, the contribution to heat releases from a reaction involving O radicals, i.e., CH<sub>3</sub> + O ⇄ CH<sub>2</sub>O + H, becomes large in addition to reactions involving OH radicals, i.e., CO + OH ⇄ CO<sub>2</sub> + H and H<sub>2</sub> + OH ⇄ H + H<sub>2</sub>O. Based on the analyses, a new radical index based on the combination of OH and O radicals (<em>RI</em><sub>OH&O</sub>) is proposed. The <em>RI</em><sub>OH&O</sub> better expresses the linear relationship between extinction limits and the combined metric of <em>RI</em><sub>OH&O</sub> and <em>TWE</em>.</p></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":null,"pages":null},"PeriodicalIF":4.4,"publicationDate":"2024-06-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0010218024002499/pdfft?md5=30f6fc89999ac63b449dd015a6b0b595&pid=1-s2.0-S0010218024002499-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141290143","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 : 2024-06-08DOI: 10.1016/j.combustflame.2024.113530
Chong Li , Yangyang Luo , Yanlei Shang , Hongbo Ning , S.N. Luo
Biodiesel is a renewable and promising alternative to diesel with similar physicochemical properties. To explore the feasibility of biodiesel in improving the combustion performance of ammonia (NH), this work investigates the autoignition characteristics of NH blended with a medium-size unsaturated biodiesel surrogate (trans-methyl-3-hexenoate, MHX3D), using a heated shock tube. The experiments are conducted at 1108–2097 K with different pressures (2.9–6.2 atm), equivalence ratios (0.5–2.0), and MHX3D blending ratios (0–100%). Ignition delay times of NH/MHX3D mixtures decrease with increasing pressure and MHX3D blending ratio and decreasing equivalence ratio. A small addition of MHX3D dramatically reduces the ignition delay time and ignition temperature of NH, and this promotion effect is slightly more significant than that of its saturated structure. Using the advanced kinetic theory, the rate constants of the important cross-coupling reactions between MHX3D and NH radicals are accurately determined, where the dual-level multi-structural torsional (MS-T) method is applied to characterize the MS-T anharmonicity. Based on our calculations and literature data, a detailed combustion model is proposed to reveal the combustion mechanism of NH/MHX3D mixtures. The kinetic analyses demonstrate that the degeneration of MHX3D in the initial stage yields the reactive radicals that perturb the system to accelerate the consumption of NH by H-abstraction reactions. The cross-coupling reactions between NH radicals and C-containing species and the related subsequent reactions of produced cross-coupling intermediates are crucial in controlling the ignition process of NH/MHX3D mixtures.
Novelty and Significance statement: This work investigates the autoignition characteristics of NH blended with a medium-size unsaturated biodiesel surrogate, trans-methyl-3-hexenoate (MHX3D), under a wide range of experimental conditions. The rate constants of important cross-coupling reactions between MHX3D and NH radical are calculated using the canonical variational transition-state theory and the small-curvature tunnelin
{"title":"Experimental and kinetic studies on autoignition characteristics of ammonia/methyl 3-hexenoate mixture","authors":"Chong Li , Yangyang Luo , Yanlei Shang , Hongbo Ning , S.N. Luo","doi":"10.1016/j.combustflame.2024.113530","DOIUrl":"https://doi.org/10.1016/j.combustflame.2024.113530","url":null,"abstract":"<div><p>Biodiesel is a renewable and promising alternative to diesel with similar physicochemical properties. To explore the feasibility of biodiesel in improving the combustion performance of ammonia (NH<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span>), this work investigates the autoignition characteristics of NH<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span> blended with a medium-size unsaturated biodiesel surrogate (<em>trans</em>-methyl-3-hexenoate, MHX3D), using a heated shock tube. The experiments are conducted at 1108–2097 K with different pressures (2.9–6.2 atm), equivalence ratios (0.5–2.0), and MHX3D blending ratios (0–100%). Ignition delay times of NH<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span>/MHX3D mixtures decrease with increasing pressure and MHX3D blending ratio and decreasing equivalence ratio. A small addition of MHX3D dramatically reduces the ignition delay time and ignition temperature of NH<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span>, and this promotion effect is slightly more significant than that of its saturated structure. Using the advanced kinetic theory, the rate constants of the important cross-coupling reactions between MHX3D and NH<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> radicals are accurately determined, where the dual-level multi-structural torsional (MS-T) method is applied to characterize the MS-T anharmonicity. Based on our calculations and literature data, a detailed combustion model is proposed to reveal the combustion mechanism of NH<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span>/MHX3D mixtures. The kinetic analyses demonstrate that the degeneration of MHX3D in the initial stage yields the reactive radicals that perturb the system to accelerate the consumption of NH<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span> by H-abstraction reactions. The cross-coupling reactions between NH<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> radicals and C-containing species and the related subsequent reactions of produced cross-coupling intermediates are crucial in controlling the ignition process of NH<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span>/MHX3D mixtures.</p><p><strong>Novelty and Significance statement:</strong> This work investigates the autoignition characteristics of NH<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span> blended with a medium-size unsaturated biodiesel surrogate, <em>trans</em>-methyl-3-hexenoate (MHX3D), under a wide range of experimental conditions. The rate constants of important cross-coupling reactions between MHX3D and NH<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> radical are calculated using the canonical variational transition-state theory and the small-curvature tunnelin","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":null,"pages":null},"PeriodicalIF":4.4,"publicationDate":"2024-06-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141290998","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 : 2024-06-08DOI: 10.1016/j.combustflame.2024.113543
Hao Zhao , Chao Yan , Guohui Song , Ziyu Wang , Ahren W. Jasper , Stephen J. Klippenstein , Yiguang Ju
The oxidation of H2 diluted in N2 with and without 10 % H2O or 20 % CO2 additions are studied at fuel-lean conditions at 100 atm and 500–1000 K in a supercritical-pressure jet-stirred reactor. The mole fractions of H2 and O2 are quantified by using micro-gas chromatography (µ-GC). Experiment shows that H2 oxidation is inhibited at lower temperatures (850–950 K) while it is promoted at higher temperatures (950–1050 K) with 10 % H2O additions or 20 % CO2 additions. In addition, the effect of H2O is more significant than that of CO2. Five models are employed in simulations of the observables. Unfortunately, all of these models fail to capture the effect of H2O and CO2 additions on H2 oxidation. Pathway and sensitivity analyses of H2 show that the reactions of H + O2 + (M) = HO2 + (M) and H2O2 + (M) = 2OH + (M) dominate the radical production (HO2 and OH) and H2 oxidation at 100 atm. A further perturbation of pre-exponential coefficients and collisional factors of these reactions indicates that collisional factors of H2O and CO2 have small effect under the experimental conditions, while a smaller reaction rate for H2O2 + (M) = 2OH + (M) may explain the inhibiting effect of H2O and CO2 additions at lower temperatures. Real-fluid corrections on intermolecular interactions and mixing rules should be further investigated to explain the effect of H2O and CO2 additions.
在超临界压力喷射搅拌反应器中，在 100 atm 和 500-1000 K 的燃料稀释条件下，研究了添加或不添加 10 % H2O 或 20 % CO2 的 N2 中稀释的 H2 的氧化过程。采用微气相色谱法（µ-GC）对 H2 和 O2 的摩尔分数进行了量化。实验表明，在较低温度（850-950 K）下，H2 的氧化作用会受到抑制，而在较高温度（950-1050 K）下，添加 10% 的 H2O 或 20% 的 CO2 会促进 H2 的氧化作用。此外，H2O 的影响比 CO2 的影响更为显著。在模拟观测数据时采用了五个模型。遗憾的是，所有这些模型都未能捕捉到添加 H2O 和 CO2 对 H2 氧化的影响。对 H2 的途径和敏感性分析表明，在 100 atm 时，H+O2+（M）=HO2+（M）和 H2O2+（M）=2OH+（M）反应在自由基生成（HO2 和 OH）和 H2 氧化中占主导地位。对这些反应的预指数系数和碰撞因子的进一步扰动表明，在实验条件下，H2O 和 CO2 的碰撞因子影响较小，而 H2O2 + (M) = 2OH + (M) 的反应速率较小，这可能解释了在较低温度下 H2O 和 CO2 的添加具有抑制作用。应进一步研究分子间相互作用和混合规则的实际流体修正，以解释 H2O 和 CO2 添加的影响。
{"title":"High-pressure oxidation of hydrogen diluted in N2 with added H2O or CO2 at 100 atm in a supercritical-pressure jet-stirred reactor","authors":"Hao Zhao , Chao Yan , Guohui Song , Ziyu Wang , Ahren W. Jasper , Stephen J. Klippenstein , Yiguang Ju","doi":"10.1016/j.combustflame.2024.113543","DOIUrl":"https://doi.org/10.1016/j.combustflame.2024.113543","url":null,"abstract":"<div><p>The oxidation of H<sub>2</sub> diluted in N<sub>2</sub> with and without 10 % H<sub>2</sub>O or 20 % CO<sub>2</sub> additions are studied at fuel-lean conditions at 100 atm and 500–1000 K in a supercritical-pressure jet-stirred reactor. The mole fractions of H<sub>2</sub> and O<sub>2</sub> are quantified by using micro-gas chromatography (µ-GC). Experiment shows that H<sub>2</sub> oxidation is inhibited at lower temperatures (850–950 K) while it is promoted at higher temperatures (950–1050 K) with 10 % H<sub>2</sub>O additions or 20 % CO<sub>2</sub> additions. In addition, the effect of H<sub>2</sub>O is more significant than that of CO<sub>2</sub>. Five models are employed in simulations of the observables. Unfortunately, all of these models fail to capture the effect of H<sub>2</sub>O and CO<sub>2</sub> additions on H<sub>2</sub> oxidation. Pathway and sensitivity analyses of H<sub>2</sub> show that the reactions of H + O<sub>2</sub> + (M) = HO<sub>2</sub> + (M) and H<sub>2</sub>O<sub>2</sub> + (M) = 2OH + (M) dominate the radical production (HO<sub>2</sub> and OH) and H<sub>2</sub> oxidation at 100 atm. A further perturbation of pre-exponential coefficients and collisional factors of these reactions indicates that collisional factors of H<sub>2</sub>O and CO<sub>2</sub> have small effect under the experimental conditions, while a smaller reaction rate for H<sub>2</sub>O<sub>2</sub> + (M) = 2OH + (M) may explain the inhibiting effect of H<sub>2</sub>O and CO<sub>2</sub> additions at lower temperatures. Real-fluid corrections on intermolecular interactions and mixing rules should be further investigated to explain the effect of H<sub>2</sub>O and CO<sub>2</sub> additions.</p></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":null,"pages":null},"PeriodicalIF":4.4,"publicationDate":"2024-06-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141290142","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 : 2024-06-08DOI: 10.1016/j.combustflame.2024.113528
Shumeng Xie , Huangwei Zhang
Recently, a two-stage ignition phenomenon of NH3/H2 mixtures was experimentally observed in a rapid compression machine, which is closely linked to the concept of flame bifurcations and cool flames. One interesting question may arise: do similar flame bifurcations exist in NH3/H2 mixtures? To answer this, this study employs the premixed counterflow configuration and examines the potential bifurcations of the NH3/H2/air flame with one-dimensional simulations. For the first time, a novel weak combustion mode of NH3/H2 mixtures is observed and termed as the weak flame in the following. Unlike the conventional hot flame, the weak flame exhibits significantly lower flame temperatures (1300–1500 K) and a mere 1 % of the heat release rate (∼109 J/m3/s) associated with hot flames. Within the weak flame, H2 is entirely oxidized to H2O, whereas only a portion of NH3 is partially oxidized, resulting in the formation of H2O, N2, N2O, and NO. Further reaction path analyses reveal that the NH3 (+OH) → NH2 (+NO2) → H2NO (+NH2, +HO2, +O2, +NO2) → HNO (+O2) → NO (+HO2) → NO2 → N2O pathway is the primary oxidation route of ammonia in the weak flame. Furthermore, the effects of pressure, hydrogen content, and equivalence ratio are systematically assessed to explore the operation conditions of the ammonia/hydrogen weak flame. The study reveals that the weak flame is promoted at elevated pressures, and exists with a moderate hydrogen addition, i.e., = 0.02–0.4. A regime diagram is further proposed to summarize the combined influences of hydrogen molar fraction and equivalence ratio. In the end, the impacts of chemical mechanisms are tested and the dominant ammonia oxidization path in the weak flame persists for models capable of predicting weak flames.
{"title":"Existence and chemistry of stretched ammonia/hydrogen weak flames at elevated pressures","authors":"Shumeng Xie , Huangwei Zhang","doi":"10.1016/j.combustflame.2024.113528","DOIUrl":"https://doi.org/10.1016/j.combustflame.2024.113528","url":null,"abstract":"<div><p>Recently, a two-stage ignition phenomenon of NH<sub>3</sub>/H<sub>2</sub> mixtures was experimentally observed in a rapid compression machine, which is closely linked to the concept of flame bifurcations and cool flames. One interesting question may arise: do similar flame bifurcations exist in NH<sub>3</sub>/H<sub>2</sub> mixtures? To answer this, this study employs the premixed counterflow configuration and examines the potential bifurcations of the NH<sub>3</sub>/H<sub>2</sub>/air flame with one-dimensional simulations. For the first time, a novel weak combustion mode of NH<sub>3</sub>/H<sub>2</sub> mixtures is observed and termed as the weak flame in the following. Unlike the conventional hot flame, the weak flame exhibits significantly lower flame temperatures (1300–1500 K) and a mere 1 % of the heat release rate (∼10<sup>9</sup> J/m<sup>3</sup>/s) associated with hot flames. Within the weak flame, H<sub>2</sub> is entirely oxidized to H<sub>2</sub>O, whereas only a portion of NH<sub>3</sub> is partially oxidized, resulting in the formation of H<sub>2</sub>O, N<sub>2</sub>, N<sub>2</sub>O, and NO. Further reaction path analyses reveal that the NH<sub>3</sub> (+OH) → NH<sub>2</sub> (+NO<sub>2</sub>) → H<sub>2</sub>NO (+NH<sub>2</sub>, +HO<sub>2</sub>, +O<sub>2</sub>, +NO<sub>2</sub>) → HNO (+O<sub>2</sub>) → NO (+HO<sub>2</sub>) → NO<sub>2</sub> → N<sub>2</sub>O pathway is the primary oxidation route of ammonia in the weak flame. Furthermore, the effects of pressure, hydrogen content, and equivalence ratio are systematically assessed to explore the operation conditions of the ammonia/hydrogen weak flame. The study reveals that the weak flame is promoted at elevated pressures, and exists with a moderate hydrogen addition, i.e., <span><math><msub><mi>x</mi><mrow><mi>H</mi><mn>2</mn></mrow></msub></math></span> = 0.02–0.4. A regime diagram is further proposed to summarize the combined influences of hydrogen molar fraction and equivalence ratio. In the end, the impacts of chemical mechanisms are tested and the dominant ammonia oxidization path in the weak flame persists for models capable of predicting weak flames.</p></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":null,"pages":null},"PeriodicalIF":4.4,"publicationDate":"2024-06-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141290995","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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