Pub Date : 2024-10-05DOI: 10.1016/j.combustflame.2024.113784
Sayop Kim , Tonghun Lee , Kenneth S. Kim , Chol-Bum M. Kweon , Je Ir Ryu
This study delves into ignition and flame dynamics involving a cylindrical hot surface impact. Previous studies have focused on the flat-wall hot surface interacting with fuel spray, leaving gaps in understanding the effects of cylindrical hot surfaces on fuel-air mixing and ignition. Using high-fidelity large-eddy simulations (LES), this study investigates how fluid elements, upon contacting an electronically activated glow plug structure, exhibit mixing and thermochemical properties. The analysis examines how this type of structure enhances fuel-air mixing and subsequently influences the thermochemistry behavior in conjunction with the fuel-specific combustion behavior. The study includes scenarios with free spray and non-thermal deposit cases to assess their mixing impact, alongside testing five different electric voltage inputs to study the thermally assisted ignition process. Results demonstrate that the cylindrical structure hinders flow, reducing its inertia and increasing flow residence time. Moreover, a significant Coandă effect due to the circular wall structure is identified, potentially serving as a mechanism for enhancing flame-holding. Furthermore, varying the input voltage notably affects ignition timing, revealing a non-monotonic ignition delay pattern with lower voltages. Detailed analysis highlights the critical role of negative temperature coefficient (NTC)-driven low-temperature chemistry (LTC) in the ignition process.
{"title":"Physiochemical View of Fuel Jet Impingement and Ignition Upon Contact with a Cylindrical Hot Surface","authors":"Sayop Kim , Tonghun Lee , Kenneth S. Kim , Chol-Bum M. Kweon , Je Ir Ryu","doi":"10.1016/j.combustflame.2024.113784","DOIUrl":"10.1016/j.combustflame.2024.113784","url":null,"abstract":"<div><div>This study delves into ignition and flame dynamics involving a cylindrical hot surface impact. Previous studies have focused on the flat-wall hot surface interacting with fuel spray, leaving gaps in understanding the effects of cylindrical hot surfaces on fuel-air mixing and ignition. Using high-fidelity large-eddy simulations (LES), this study investigates how fluid elements, upon contacting an electronically activated glow plug structure, exhibit mixing and thermochemical properties. The analysis examines how this type of structure enhances fuel-air mixing and subsequently influences the thermochemistry behavior in conjunction with the fuel-specific combustion behavior. The study includes scenarios with free spray and non-thermal deposit cases to assess their mixing impact, alongside testing five different electric voltage inputs to study the thermally assisted ignition process. Results demonstrate that the cylindrical structure hinders flow, reducing its inertia and increasing flow residence time. Moreover, a significant Coandă effect due to the circular wall structure is identified, potentially serving as a mechanism for enhancing flame-holding. Furthermore, varying the input voltage notably affects ignition timing, revealing a non-monotonic ignition delay pattern with lower voltages. Detailed analysis highlights the critical role of negative temperature coefficient (NTC)-driven low-temperature chemistry (LTC) in the ignition process.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"270 ","pages":"Article 113784"},"PeriodicalIF":5.8,"publicationDate":"2024-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142423829","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 : 2024-10-04DOI: 10.1016/j.combustflame.2024.113786
Taylor Brown, Rachel Hytovick, Anthony Morales, Joshua Berson, Sheikh Salauddin, Khaoula Chougag, Kareem Ahmed
The structures and mechanisms of aerosolized liquid-fuel cloud detonations are studied in a detonation facility using simultaneous high-speed optical diagnostics. The characteristic length scale of the droplet lifetime in liquid fuel detonations is not well predicted by established breakup and evaporation models, whereas it captured by calculations of the evaporation time of the droplet cloud.
Novelty and significance statement
Detonation research has mostly focused on gaseous fuels with limited investigations of purely liquid fueled detonations. This research explores the characteristic length scales of aerosolized liquid fuel droplets’ lifetime showing it does not scale with established breakup and evaporation models. It scales well with the evaporation time of child droplet clouds, highlighting the significance.
{"title":"Liquid fuel cloud detonation and droplet lifetime","authors":"Taylor Brown, Rachel Hytovick, Anthony Morales, Joshua Berson, Sheikh Salauddin, Khaoula Chougag, Kareem Ahmed","doi":"10.1016/j.combustflame.2024.113786","DOIUrl":"10.1016/j.combustflame.2024.113786","url":null,"abstract":"<div><div>The structures and mechanisms of aerosolized liquid-fuel cloud detonations are studied in a detonation facility using simultaneous high-speed optical diagnostics. The characteristic length scale of the droplet lifetime in liquid fuel detonations is not well predicted by established breakup and evaporation models, whereas it captured by calculations of the evaporation time of the droplet cloud.</div></div><div><h3>Novelty and significance statement</h3><div>Detonation research has mostly focused on gaseous fuels with limited investigations of purely liquid fueled detonations. This research explores the characteristic length scales of aerosolized liquid fuel droplets’ lifetime showing it does not scale with established breakup and evaporation models. It scales well with the evaporation time of child droplet clouds, highlighting the significance.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"270 ","pages":"Article 113786"},"PeriodicalIF":5.8,"publicationDate":"2024-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142423830","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 : 2024-10-04DOI: 10.1016/j.combustflame.2024.113759
Yiqing Wang , Chao Xu , Cheng Chi , Zheng Chen
<div><div>The cool flame dynamics, especially in turbulent flows, is of great interest for both practical application and fundamental research. In this study, a series of direct numerical simulations of turbulent premixed <em>n</em>-C<span><math><msub><mrow></mrow><mrow><mn>7</mn></mrow></msub></math></span>H<sub>16</sub>/O<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span>/O<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span>/N<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> cool flames are performed, with the focus on the influence of turbulence intensity (<span><math><mrow><msup><mrow><mi>u</mi></mrow><mrow><mo>′</mo></mrow></msup><mo>/</mo><msub><mrow><mi>S</mi></mrow><mrow><mi>L</mi></mrow></msub></mrow></math></span>, where <span><math><msub><mrow><mi>S</mi></mrow><mrow><mi>L</mi></mrow></msub></math></span> is the laminar flame speed) on the flame structure as well as the global and local cool flame dynamics. It is found that the cool flame front is considerably wrinkled by turbulence at high <span><math><mrow><msup><mrow><mi>u</mi></mrow><mrow><mo>′</mo></mrow></msup><mo>/</mo><msub><mrow><mi>S</mi></mrow><mrow><mi>L</mi></mrow></msub></mrow></math></span>, leading to significantly thickened turbulent cool flame brush and largely altered local reactivity compared with the reference laminar flame. However, the turbulent flame structure in the temperature space is found to be insensitive to <span><math><mrow><msup><mrow><mi>u</mi></mrow><mrow><mo>′</mo></mrow></msup><mo>/</mo><msub><mrow><mi>S</mi></mrow><mrow><mi>L</mi></mrow></msub></mrow></math></span>. Besides, with increasing <span><math><mrow><msup><mrow><mi>u</mi></mrow><mrow><mo>′</mo></mrow></msup><mo>/</mo><msub><mrow><mi>S</mi></mrow><mrow><mi>L</mi></mrow></msub></mrow></math></span>, the normalized turbulent cool flame speed (<span><math><mrow><msub><mrow><mi>S</mi></mrow><mrow><mi>T</mi></mrow></msub><mo>/</mo><msub><mrow><mi>S</mi></mrow><mrow><mi>L</mi></mrow></msub></mrow></math></span>) is monotonically increased, attributed to substantial augmentation on the flame surface area (<span><math><mrow><msub><mrow><mi>A</mi></mrow><mrow><mi>T</mi></mrow></msub><mo>/</mo><msub><mrow><mi>A</mi></mrow><mrow><mi>L</mi></mrow></msub></mrow></math></span>), while the stretching factor (<span><math><msub><mrow><mi>I</mi></mrow><mrow><mn>0</mn></mrow></msub></math></span>) remains almost constant and is smaller than 1. The underlying mechanisms for such variations are revealed through local flame dynamics analysis. Specifically, the local flame displacement speed <span><math><msub><mrow><mi>S</mi></mrow><mrow><mi>d</mi></mrow></msub></math></span> is found to be strongly negatively correlated with flame curvature; meanwhile, such negative correlation and the probability distribution function (PDF) of flame curvature are barely influenced by <span><math><mrow><msup><mrow><mi>u</mi></mrow><mrow><mo>′</mo></mrow></ms
{"title":"Direct numerical simulations of turbulent premixed cool flames: Global and local flame dynamics analysis","authors":"Yiqing Wang , Chao Xu , Cheng Chi , Zheng Chen","doi":"10.1016/j.combustflame.2024.113759","DOIUrl":"10.1016/j.combustflame.2024.113759","url":null,"abstract":"<div><div>The cool flame dynamics, especially in turbulent flows, is of great interest for both practical application and fundamental research. In this study, a series of direct numerical simulations of turbulent premixed <em>n</em>-C<span><math><msub><mrow></mrow><mrow><mn>7</mn></mrow></msub></math></span>H<sub>16</sub>/O<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span>/O<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span>/N<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> cool flames are performed, with the focus on the influence of turbulence intensity (<span><math><mrow><msup><mrow><mi>u</mi></mrow><mrow><mo>′</mo></mrow></msup><mo>/</mo><msub><mrow><mi>S</mi></mrow><mrow><mi>L</mi></mrow></msub></mrow></math></span>, where <span><math><msub><mrow><mi>S</mi></mrow><mrow><mi>L</mi></mrow></msub></math></span> is the laminar flame speed) on the flame structure as well as the global and local cool flame dynamics. It is found that the cool flame front is considerably wrinkled by turbulence at high <span><math><mrow><msup><mrow><mi>u</mi></mrow><mrow><mo>′</mo></mrow></msup><mo>/</mo><msub><mrow><mi>S</mi></mrow><mrow><mi>L</mi></mrow></msub></mrow></math></span>, leading to significantly thickened turbulent cool flame brush and largely altered local reactivity compared with the reference laminar flame. However, the turbulent flame structure in the temperature space is found to be insensitive to <span><math><mrow><msup><mrow><mi>u</mi></mrow><mrow><mo>′</mo></mrow></msup><mo>/</mo><msub><mrow><mi>S</mi></mrow><mrow><mi>L</mi></mrow></msub></mrow></math></span>. Besides, with increasing <span><math><mrow><msup><mrow><mi>u</mi></mrow><mrow><mo>′</mo></mrow></msup><mo>/</mo><msub><mrow><mi>S</mi></mrow><mrow><mi>L</mi></mrow></msub></mrow></math></span>, the normalized turbulent cool flame speed (<span><math><mrow><msub><mrow><mi>S</mi></mrow><mrow><mi>T</mi></mrow></msub><mo>/</mo><msub><mrow><mi>S</mi></mrow><mrow><mi>L</mi></mrow></msub></mrow></math></span>) is monotonically increased, attributed to substantial augmentation on the flame surface area (<span><math><mrow><msub><mrow><mi>A</mi></mrow><mrow><mi>T</mi></mrow></msub><mo>/</mo><msub><mrow><mi>A</mi></mrow><mrow><mi>L</mi></mrow></msub></mrow></math></span>), while the stretching factor (<span><math><msub><mrow><mi>I</mi></mrow><mrow><mn>0</mn></mrow></msub></math></span>) remains almost constant and is smaller than 1. The underlying mechanisms for such variations are revealed through local flame dynamics analysis. Specifically, the local flame displacement speed <span><math><msub><mrow><mi>S</mi></mrow><mrow><mi>d</mi></mrow></msub></math></span> is found to be strongly negatively correlated with flame curvature; meanwhile, such negative correlation and the probability distribution function (PDF) of flame curvature are barely influenced by <span><math><mrow><msup><mrow><mi>u</mi></mrow><mrow><mo>′</mo></mrow></ms","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"270 ","pages":"Article 113759"},"PeriodicalIF":5.8,"publicationDate":"2024-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142423851","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 : 2024-10-04DOI: 10.1016/j.combustflame.2024.113757
Qiang Xiao , Qibin Zhang , Ashwin Chinnayya
The present communication proposes a new scaling approach to unify the dynamics of gaseous detonations subject to wall losses in both the narrow channels and small tubes, by compiling the published experimental data of detonations in 23 different mixtures with a very large range of cellular instabilities. A kinetic induction length can be determined from the detonation velocity deficit and detailed chemistry. In order to take into account the sensitivity of the latter length to post-shock temperature fluctuations (through the reduced activation energy ), which is a partial and indirect marker of the cellular structure, and to bring out energetics (through the Chapman–Jouguet detonation Mach number ), an effective kinetic length of was built and has been shown to collapse the different detonation dynamics of various gaseous mixtures, subjected to wall losses, into a single universal curve for detonation velocity deficits.
Novelty and Significance: Scaling analysis of large sets of published data of gaseous detonation experiments in narrow channels and small tubes has been made for 23 different mixtures with varied cellular instabilities and activation energies. The universal dynamics of gaseous detonations subject to wall losses in different mixtures has been achieved, for the first time, by adopting an effective kinetic length by taking into account the effect of both the activation energy and the energetics.
{"title":"The universal gaseous detonation dynamics","authors":"Qiang Xiao , Qibin Zhang , Ashwin Chinnayya","doi":"10.1016/j.combustflame.2024.113757","DOIUrl":"10.1016/j.combustflame.2024.113757","url":null,"abstract":"<div><div>The present communication proposes a new scaling approach to unify the dynamics of gaseous detonations subject to wall losses in both the narrow channels and small tubes, by compiling the published experimental data of detonations in 23 different mixtures with a very large range of cellular instabilities. A kinetic induction length <span><math><msub><mrow><mi>Δ</mi></mrow><mrow><mi>i</mi><mo>,</mo><mi>l</mi><mi>o</mi><mi>s</mi><mi>s</mi></mrow></msub></math></span> can be determined from the detonation velocity deficit and detailed chemistry. In order to take into account the sensitivity of the latter length to post-shock temperature fluctuations (through the reduced activation energy <span><math><mi>θ</mi></math></span>), which is a partial and indirect marker of the cellular structure, and to bring out energetics (through the Chapman–Jouguet detonation Mach number <span><math><msub><mrow><mi>M</mi></mrow><mrow><mi>C</mi><mi>J</mi></mrow></msub></math></span>), an effective kinetic length of <span><math><mrow><msub><mrow><mi>Δ</mi></mrow><mrow><mi>i</mi><mo>,</mo><mi>l</mi><mi>o</mi><mi>s</mi><mi>s</mi></mrow></msub><mspace></mspace><mrow><mo>(</mo><msubsup><mrow><mi>M</mi></mrow><mrow><mi>C</mi><mi>J</mi></mrow><mrow><mn>4</mn></mrow></msubsup><mo>/</mo><msup><mrow><mi>θ</mi></mrow><mrow><mn>3</mn></mrow></msup><mo>)</mo></mrow></mrow></math></span> was built and has been shown to collapse the different detonation dynamics of various gaseous mixtures, subjected to wall losses, into a single universal curve for detonation velocity deficits.</div><div><strong>Novelty and Significance:</strong> Scaling analysis of large sets of published data of gaseous detonation experiments in narrow channels and small tubes has been made for 23 different mixtures with varied cellular instabilities and activation energies. The universal dynamics of gaseous detonations subject to wall losses in different mixtures has been achieved, for the first time, by adopting an effective kinetic length by taking into account the effect of both the activation energy and the energetics.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"270 ","pages":"Article 113757"},"PeriodicalIF":5.8,"publicationDate":"2024-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142423811","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 : 2024-10-03DOI: 10.1016/j.combustflame.2024.113778
Yilun Liang , Xuantong Liu , Mo Yang , Xin Hui , Juan Wang
A rapid transition from conventional jet fuels to sustainable aviation fuels (SAFs) is imperative in order to reduce carbon emissions. Hydro-processed esters and fatty acids synthetic paraffinic kerosene (HEFA-SPK), as a type of SAF, exhibits broad applications. In this study, a new HEFA-SPK named ZH-HEFA was investigated. The fuel comprises 14% n-alkanes, 85% iso-alkanes and only 1% cycloalkanes by weight, with the majority of alkanes ranging from C9 to C17. Oxidation experiments of the fuel were conducted using an atmospheric pressure flow reactor at temperatures ranging from 550 K to 1075 K under three equivalence ratios (0.5, 1.0 and 1.5). Species mole fraction profiles were measured by an on-line gas chromatographic (GC). For comparison purposes, an experiment was also performed on RP-3, a conventional jet fuel commonly used in China, under the equivalence of 0.5. Compared to RP-3, ZH-HEFA exhibited significantly stronger low temperature reactivity and higher combustion conversion rates while demonstrating considerably lower yields of aromatics at high temperatures. The kinetic simulation of ZH-HEFA was achieved by proposing two surrogates and their corresponding kinetic models. Surrogate S-1 consisted solely of n-dodecane, while S-2 comprised 35% n-dodecane and 65% 2,6,10-trimethyl dodecane by weight. Both surrogate models were validated by the experimental data. S-1 exhibited a closer resemblance to the global oxidation characteristics of ZH-HEFA, whereas S-2 demonstrated improved accuracy in predicting the formation of small hydrocarbon intermediates during the fuel oxidation. Rate of production analysis revealed that the branched alkane component in S-2 possessed more pathways and greater capability than S-1 in generating C3 intermediates, which are important for the generation of aromatics. Furthermore, both models displayed good predictive performance for the auto-ignition properties of HEFA-SPK fuels.-
{"title":"Investigating the oxidation characteristic of a hydro-processed bio-jet fuel: Experimental and modeling study","authors":"Yilun Liang , Xuantong Liu , Mo Yang , Xin Hui , Juan Wang","doi":"10.1016/j.combustflame.2024.113778","DOIUrl":"10.1016/j.combustflame.2024.113778","url":null,"abstract":"<div><div>A rapid transition from conventional jet fuels to sustainable aviation fuels (SAFs) is imperative in order to reduce carbon emissions. Hydro-processed esters and fatty acids synthetic paraffinic kerosene (HEFA-SPK), as a type of SAF, exhibits broad applications. In this study, a new HEFA-SPK named ZH-HEFA was investigated. The fuel comprises 14% n-alkanes, 85% iso-alkanes and only 1% cycloalkanes by weight, with the majority of alkanes ranging from C<sub>9</sub> to C<sub>17</sub>. Oxidation experiments of the fuel were conducted using an atmospheric pressure flow reactor at temperatures ranging from 550 K to 1075 K under three equivalence ratios (0.5, 1.0 and 1.5). Species mole fraction profiles were measured by an on-line gas chromatographic (GC). For comparison purposes, an experiment was also performed on RP-3, a conventional jet fuel commonly used in China, under the equivalence of 0.5. Compared to RP-3, ZH-HEFA exhibited significantly stronger low temperature reactivity and higher combustion conversion rates while demonstrating considerably lower yields of aromatics at high temperatures. The kinetic simulation of ZH-HEFA was achieved by proposing two surrogates and their corresponding kinetic models. Surrogate S-1 consisted solely of n-dodecane, while S-2 comprised 35% n-dodecane and 65% 2,6,10-trimethyl dodecane by weight. Both surrogate models were validated by the experimental data. S-1 exhibited a closer resemblance to the global oxidation characteristics of ZH-HEFA, whereas S-2 demonstrated improved accuracy in predicting the formation of small hydrocarbon intermediates during the fuel oxidation. Rate of production analysis revealed that the branched alkane component in S-2 possessed more pathways and greater capability than S-1 in generating C<sub>3</sub> intermediates, which are important for the generation of aromatics. Furthermore, both models displayed good predictive performance for the auto-ignition properties of HEFA-SPK fuels.-</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"270 ","pages":"Article 113778"},"PeriodicalIF":5.8,"publicationDate":"2024-10-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142423828","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 : 2024-10-03DOI: 10.1016/j.combustflame.2024.113774
Kai Zhang , Yishu Xu , Ronghao Yu , Hui Wu , Xiaowei Liu , Xiaobei Cheng
The reactive force field molecular dynamics (ReaxFF MD) simulations are performed to depict the whole process including fuel pyrolysis, the formation and growth of PAHs/NPAHs and soot formation in the pyrolysis of C2H4 and C2H4/NH3 mixtures. NH3 doping increases the concentration of H radicals through the decomposition of NH3. These H radicals then promote the consumption of C2H4 by participating in H-abstraction reactions. The formation of C-N species (mainly HCN, H2CN, C2N, CH3CN, NCCN, and HC3N) removes the C atoms participating in the formation of PAHs and soot, thus inhibiting the formation of soot. And such inhibitory effect is strengthened with increasing temperature due to the promoted formation of C-N species. Most importantly, the structure, formation and evolution paths of N-containing PAHs (NPAHs) are identified based on the experimental and simulation results for the first time, revealing that N atoms in the NPAHs are almost always present in the carbon chains attached to the aromatic rings while barely enter the rings to form heterocyclic structure. The simulations further reveal that when the temperature is less than 2500 K, the first N-containing aromatic ring is formed through the reaction of phenyl with small C-N species (such as HCN and CN radicals), followed by the increase of new rings primarily via the HACA mechanism. At temperatures greater than 2500 K, the formation and growth of NPAHs are dominated by the continuous attachment of N-containing carbon chains and cyclic polycondensation-cyclization reactions. The identification of new C-N species especially NPAHs would help improve the kinetic mechanisms for ammonia blending combustion.
反应力场分子动力学（ReaxFF MD）模拟描述了 C2H4 和 C2H4/NH3 混合物热解的整个过程，包括燃料热解、多环芳烃/NPAHs 的形成和增长以及烟尘的形成。掺入 NH3 会通过分解 NH3 增加 H 自由基的浓度。然后，这些 H 自由基通过参与 H-萃取反应促进 C2H4 的消耗。C-N 物种（主要是 HCN、H2CN、C2N、CH3CN、NCCN 和 HC3N）的形成会清除参与多环芳烃和烟尘形成的 C 原子，从而抑制烟尘的形成。由于促进了 C-N 物种的形成，这种抑制作用会随着温度的升高而加强。最重要的是，根据实验和模拟结果首次确定了含 N 多环芳烃（NPAHs）的结构、形成和演化路径，揭示了 NPAHs 中的 N 原子几乎总是存在于附着在芳香环上的碳链中，而几乎不进入环中形成杂环结构。模拟进一步发现，当温度小于 2500 K 时，第一个含 N 的芳香环是通过苯基与小的 C-N 物种（如 HCN 和 CN 自由基）反应形成的，随后主要通过 HACA 机理增加新环。在温度高于 2500 K 时，NPAH 的形成和增长主要是通过含 N 碳链的连续附着和循环缩聚-环化反应进行的。识别新的 C-N 物种，尤其是 NPAHs，将有助于改进氨混合燃烧的动力学机制。
{"title":"ReaxFF molecular dynamics study of N-containing PAHs formation in the pyrolysis of C2H4/NH3 mixtures","authors":"Kai Zhang , Yishu Xu , Ronghao Yu , Hui Wu , Xiaowei Liu , Xiaobei Cheng","doi":"10.1016/j.combustflame.2024.113774","DOIUrl":"10.1016/j.combustflame.2024.113774","url":null,"abstract":"<div><div>The reactive force field molecular dynamics (ReaxFF MD) simulations are performed to depict the whole process including fuel pyrolysis, the formation and growth of PAHs/NPAHs and soot formation in the pyrolysis of C<sub>2</sub>H<sub>4</sub> and C<sub>2</sub>H<sub>4</sub>/NH<sub>3</sub> mixtures. NH<sub>3</sub> doping increases the concentration of H radicals through the decomposition of NH<sub>3</sub>. These H radicals then promote the consumption of C<sub>2</sub>H<sub>4</sub> by participating in H-abstraction reactions. The formation of C-N species (mainly HCN, H<sub>2</sub>CN, C<sub>2</sub>N, CH<sub>3</sub>CN, NCCN, and HC<sub>3</sub>N) removes the C atoms participating in the formation of PAHs and soot, thus inhibiting the formation of soot. And such inhibitory effect is strengthened with increasing temperature due to the promoted formation of C-N species. Most importantly, the structure, formation and evolution paths of N-containing PAHs (NPAHs) are identified based on the experimental and simulation results for the first time, revealing that N atoms in the NPAHs are almost always present in the carbon chains attached to the aromatic rings while barely enter the rings to form heterocyclic structure. The simulations further reveal that when the temperature is less than 2500 K, the first N-containing aromatic ring is formed through the reaction of phenyl with small C-N species (such as HCN and CN radicals), followed by the increase of new rings primarily via the HACA mechanism. At temperatures greater than 2500 K, the formation and growth of NPAHs are dominated by the continuous attachment of N-containing carbon chains and cyclic polycondensation-cyclization reactions. The identification of new C-N species especially NPAHs would help improve the kinetic mechanisms for ammonia blending combustion.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"270 ","pages":"Article 113774"},"PeriodicalIF":5.8,"publicationDate":"2024-10-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142423831","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 : 2024-10-01DOI: 10.1016/j.combustflame.2024.113755
Anastasia Moroshkina, Evgeniy Sereshchenko, Vladimir Mislavskii, Vladimir Gubernov, Sergey Minaev
<div><div>In this work, the spatial distribution and spectral characteristics of the chemiluminescence of chemically excited species, OH<span><math><msup><mrow></mrow><mrow><mo>∗</mo></mrow></msup></math></span> and CH<span><math><msup><mrow></mrow><mrow><mo>∗</mo></mrow></msup></math></span>, are experimentally and numerically studied by using a stationary premixed methane–air flame stabilized on the surface of a flat porous burner for various equivalence ratio and normal pressure. Numerical simulations are carried out using detailed reaction mechanisms, and the experimental study includes high-resolution spatial and spectral optical measurements. Despite the data reported in the literature, it is found that (i) the rotational degrees of freedom of OH<span><math><msup><mrow></mrow><mrow><mo>∗</mo></mrow></msup></math></span> and CH<span><math><msup><mrow></mrow><mrow><mo>∗</mo></mrow></msup></math></span> are not in thermal equilibrium with the surrounding gas and therefore cannot be used to measure flame temperature; (ii) there is no direct correlation between the heat release rate and the distribution of OH<span><math><msup><mrow></mrow><mrow><mo>∗</mo></mrow></msup></math></span> and CH<span><math><msup><mrow></mrow><mrow><mo>∗</mo></mrow></msup></math></span>; (iii) the detailed reaction mechanisms not only quantitatively, and also qualitatively differ in description of the OH<span><math><msup><mrow></mrow><mrow><mo>∗</mo></mrow></msup></math></span> and CH<span><math><msup><mrow></mrow><mrow><mo>∗</mo></mrow></msup></math></span> concentrations. Since the chemically excited species are well localized in a direction normal to the flame surface, they are demonstrated to be a very accurate markers of flame location. The shape of the combustion front can be reconstructed and resolved up to the accuracy of tens of microns, which is very important for estimation of blow-off critical parameters and measurement of the laminar burning velocity.</div><div><strong>Novelty and significance statement</strong></div><div>Currently, there is a growing interest in the development of sensors for combustion control systems, including active control and suppression of instabilities, in combustion chambers of various devices and engines based on chemiluminescence of excited reaction species. The possibility of non-invasive determination of parameters such as flame temperature, stoichiometry, heat release rate location, etc. using this technique is discussed. We have found that most of these parameters cannot be estimated either due to fundamental limitations or insufficient knowledge of the reaction kinetics involved in the production of these species. Nevertheless, since OH* and CH* are well localized in the direction normal to the flame surface, they can be used as very accurate markers of flame shape and position, allowing us to reconstruct the flame surface to within tens of microns resolution, which is very important for estimating blow-off critical parame
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Pub Date : 2024-10-01DOI: 10.1016/j.combustflame.2024.113780
Adam Kotler , Anthony Morales , Sheikh Salauddin , Daniel Rosato , Mason Thornton , Hardeo M. Chin , Zachary White , Kareem Ahmed
A standing normal detonation mode of combustion consisting of a normal shock coupled with heat release is realized in an experimental high-speed reacting-flow facility. The normal detonation is stabilized using a 2D ramp where the high-enthalpy freestream Mach number and reactant composition is equivalently matched to the Chapman-Jouguet (CJ) consumption speed of the detonation, at M∞/MCJ = 1.06. High resolution optical measurements of OH* chemiluminescence and density gradients from schlieren clearly show the close-coupling between the normal shock and the heat release of the standing detonation. A ZND analysis have been conducted using the boundary conditions where the induction length is found to closely matches the experimentally measured induction length. The agreement between the induction length scales and the freestream Mach number to detonation CJ Mach number confirm the realization of a standing detonation mode of combustion.
在实验性高速反应流设备中实现了由正常冲击和热释放组成的常态爆燃模式。正常爆燃通过二维斜坡来稳定，其中高焓自由流马赫数和反应物成分与爆燃的查普曼-朱盖特（CJ）消耗速度（M∞/MCJ = 1.06）等效匹配。OH* 化学发光的高分辨率光学测量和来自裂片的密度梯度清楚地表明了正常冲击与立爆热量释放之间的密切联系。利用边界条件进行了 ZND 分析，发现感应长度与实验测量的感应长度非常接近。感应长度尺度与自由流马赫数到起爆 CJ 马赫数之间的一致性证实了驻留起爆燃烧模式的实现。
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Pub Date : 2024-09-30DOI: 10.1016/j.combustflame.2024.113731
F.C. Destro, R. Fournet, R. Bounaceur, V. Warth, P.A. Glaude, B. Sirjean
Estimation of kinetic parameters is a key aspect of chemical combustion modeling and several approaches were developed to approximate unknown data. In this work, a code in Python was developed to build tables of transition state (TS) models automatically for intramolecular H-shift reactions in alkyl radicals. The code generates the kinetic rules for all the possible combinations of methyl-substituted reactions based on the structures of the minimal, non-substituted, reactant, TS, and product. The code is able to create and differentiate multiple transition state configurations, considering the axial and equatorial positions for the cyclic substituents and including all the possible pathways for the reactions, which is shown to be an important feature in performing accurate automatic kinetic calculations. Each structure is automatically submitted to geometry optimization and electronic energy calculations, as well as the relaxed scans of the torsional modes identified by the code. From the results of electronic calculations, the rate constants for each pathway are obtained automatically by the application of the transition state theory with tunneling corrections, in a defined temperature range. The kinetic coefficients, as well as the modified Arrhenius parameters, are then assembled and organized to create a final table that connects the kinetic data with TS structure characteristics. These tables can be directly applied as a kinetic data source for reaction mechanism development. The ability of the code to generate reliable rate constants was tested for 1,3-H-shift reactions and the results were compared with theoretical data manually produced, and showed a good agreement. In particular, the code was able to create all the transition state configurations, with an exhaustive description of all possible reaction pathways, using a rigorous and systematic counting based on symmetry, stereocenters, and diastereomers. The proposed method leads to more accurate results on these aspects, compared to repetitive hand calculations of dozens of rate constants.
动力学参数估计是化学燃烧建模的一个关键方面，人们开发了多种方法来近似未知数据。在这项工作中，我们用 Python 开发了一套代码，用于为烷基自由基分子内 H 移位反应自动建立过渡态（TS）模型表。该代码根据最小、非取代、反应物、TS 和产物的结构，为甲基取代反应的所有可能组合生成动力学规则。该代码能够创建和区分多种过渡态构型，考虑环状取代基的轴向和赤道位置，并包括反应的所有可能路径，这已被证明是进行精确自动动力学计算的重要特征。每个结构都会自动进行几何优化和电子能量计算，并对代码确定的扭转模式进行松弛扫描。根据电子计算的结果，在规定的温度范围内，应用带有隧道修正的过渡态理论，自动获得每种途径的速率常数。然后，对动力学系数和修正的阿伦尼斯参数进行组合和组织，创建一个最终表格，将动力学数据与 TS 结构特征联系起来。这些表格可直接用作反应机理开发的动力学数据源。该代码生成可靠速率常数的能力已在 1,3-H-转变反应中进行了测试，测试结果与人工生成的理论数据进行了比较，结果显示两者具有良好的一致性。特别是，该代码能够创建所有的过渡态构型，并通过基于对称性、立体中心和非对映异构体的严格而系统的计算，详尽地描述了所有可能的反应途径。与重复手工计算几十个速率常数相比，所提出的方法在这些方面得出的结果更为精确。
{"title":"Automatization of theoretical kinetic data generation for tabulated TS models building - Part 1: Application to 1,3-H-shift reactions","authors":"F.C. Destro, R. Fournet, R. Bounaceur, V. Warth, P.A. Glaude, B. Sirjean","doi":"10.1016/j.combustflame.2024.113731","DOIUrl":"10.1016/j.combustflame.2024.113731","url":null,"abstract":"<div><div>Estimation of kinetic parameters is a key aspect of chemical combustion modeling and several approaches were developed to approximate unknown data. In this work, a code in Python was developed to build tables of transition state (TS) models automatically for intramolecular H-shift reactions in alkyl radicals. The code generates the kinetic rules for all the possible combinations of methyl-substituted reactions based on the structures of the minimal, non-substituted, reactant, TS, and product. The code is able to create and differentiate multiple transition state configurations, considering the axial and equatorial positions for the cyclic substituents and including all the possible pathways for the reactions, which is shown to be an important feature in performing accurate automatic kinetic calculations. Each structure is automatically submitted to geometry optimization and electronic energy calculations, as well as the relaxed scans of the torsional modes identified by the code. From the results of electronic calculations, the rate constants for each pathway are obtained automatically by the application of the transition state theory with tunneling corrections, in a defined temperature range. The kinetic coefficients, as well as the modified Arrhenius parameters, are then assembled and organized to create a final table that connects the kinetic data with TS structure characteristics. These tables can be directly applied as a kinetic data source for reaction mechanism development. The ability of the code to generate reliable rate constants was tested for 1,3-H-shift reactions and the results were compared with theoretical data manually produced, and showed a good agreement. In particular, the code was able to create all the transition state configurations, with an exhaustive description of all possible reaction pathways, using a rigorous and systematic counting based on symmetry, stereocenters, and diastereomers. The proposed method leads to more accurate results on these aspects, compared to repetitive hand calculations of dozens of rate constants.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"270 ","pages":"Article 113731"},"PeriodicalIF":5.8,"publicationDate":"2024-09-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142358702","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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