Pub Date : 2024-08-03DOI: 10.1016/j.proci.2024.105671
Prabakaran Rajamanickam, Joel Daou
The Darrieus–Landau instability of premixed flames propagating in a narrow Hele-Shaw channel in the presence of a strong shear flow is investigated, incorporating also the Rayleigh–Taylor and diffusive-thermal instabilities. The flow induces shear-enhanced diffusion (Taylor dispersion) in the two-dimensional depth averaged equations. Since the diffusion enhancement is in the streamwise direction, but not in the spanwise direction, this leads to anisotropic diffusion and flame propagation. To understand how such anisotropies affect flame stability, two important cases are considered. These correspond to initial unperturbed conditions pertaining to a planar flame propagating in the streamwise or spanwise directions. The analysis is based on a two-dimensional model derived by asymptotic methods and solved numerically. Its numerical solutions comprise the computation of eigenvalues of a linear stability problem as well as time-dependent simulations. These address the influence of the shear-flow strength (or Peclet number ), preferential diffusion (or Lewis number ) and gravity (or Rayleigh number ). Dispersion curves characterising the perturbation growth rate are computed for selected values of , and . Taylor dispersion induced by strong shear flows is found to suppress the Darrieus–Landau instability and to weaken the flame wrinkling when the flame propagates in the streamwise direction. In contrast, when the flame propagates in the spanwise direction, the flame is stabilised in mixtures, but destabilised in mixtures. In the latter case, Taylor dispersion coupled with gas expansion facilitates flame wrinkling in an unusual manner. Specifically, stagnation points and counter-rotating vortices are encountered in the flame close to the unburnt gas side. More generally, an original finding is the demonstration that vorticity can be produced by a curved flame in a Hele-Shaw channel even in the absence of gravity, whenever , and that the vorticity remains confined to the flame preheat and reaction zones.
{"title":"Effect of a shear flow on the Darrieus–Landau instability in a Hele-Shaw channel","authors":"Prabakaran Rajamanickam, Joel Daou","doi":"10.1016/j.proci.2024.105671","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105671","url":null,"abstract":"The Darrieus–Landau instability of premixed flames propagating in a narrow Hele-Shaw channel in the presence of a strong shear flow is investigated, incorporating also the Rayleigh–Taylor and diffusive-thermal instabilities. The flow induces shear-enhanced diffusion (Taylor dispersion) in the two-dimensional depth averaged equations. Since the diffusion enhancement is in the streamwise direction, but not in the spanwise direction, this leads to anisotropic diffusion and flame propagation. To understand how such anisotropies affect flame stability, two important cases are considered. These correspond to initial unperturbed conditions pertaining to a planar flame propagating in the streamwise or spanwise directions. The analysis is based on a two-dimensional model derived by asymptotic methods and solved numerically. Its numerical solutions comprise the computation of eigenvalues of a linear stability problem as well as time-dependent simulations. These address the influence of the shear-flow strength (or Peclet number ), preferential diffusion (or Lewis number ) and gravity (or Rayleigh number ). Dispersion curves characterising the perturbation growth rate are computed for selected values of , and . Taylor dispersion induced by strong shear flows is found to suppress the Darrieus–Landau instability and to weaken the flame wrinkling when the flame propagates in the streamwise direction. In contrast, when the flame propagates in the spanwise direction, the flame is stabilised in mixtures, but destabilised in mixtures. In the latter case, Taylor dispersion coupled with gas expansion facilitates flame wrinkling in an unusual manner. Specifically, stagnation points and counter-rotating vortices are encountered in the flame close to the unburnt gas side. More generally, an original finding is the demonstration that vorticity can be produced by a curved flame in a Hele-Shaw channel even in the absence of gravity, whenever , and that the vorticity remains confined to the flame preheat and reaction zones.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141946243","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 : 2024-08-03DOI: 10.1016/j.proci.2024.105672
Philipp Koob, Hendrik Nicolai, Robert Schmitz, Christian Hasse
Reducing emissions from aero-engines, vital for aviation climate goals, requires accurate prediction of pollutants like soot. In modern rich-quench-lean aero-engine combustion chambers, fresh air is introduced after the primary combustion zone to dilute the rich exhaust gases and to cool the combustor liner walls, which will consequently also lead to the oxidation of soot with O. In this study, a simplified configuration is derived from the actual aero-engine configuration that enables an in-depth analysis of these soot oxidation processes. Detailed chemistry, together with the split-based extended quadrature method of moments soot model, is used for a comprehensive analysis of soot oxidation, focusing on the influence of varying scalar dissipation rates, mixing times, and particle size distributions derived from the real combustor. It is shown that soot oxidation linearly connects to the oxidation time scale represented by the OH residence time, meaning more soot breakthrough with shorter oxidation times. Furthermore, the influence of the soot particle size distribution is investigated. By connecting the oxidation time and the soot particle size, a metric to quantify soot breaking through the mixing zone into the lean regions of the combustion chamber is proposed.
减少航空发动机的排放对实现航空气候目标至关重要，这需要对烟尘等污染物进行准确预测。在现代富-淬-稀航空发动机燃烧室中，在一次燃烧区之后会引入新鲜空气，以稀释富废气并冷却燃烧器衬壁，从而也会导致烟尘与 O 氧化。详细的化学过程，加上基于分裂的扩展正交法矩烟尘模型，被用于烟尘氧化的综合分析，重点是不同的标量耗散率、混合时间和来自实际燃烧器的粒度分布的影响。结果表明，烟尘氧化与 OH 驻留时间所代表的氧化时间尺度呈线性关系，这意味着氧化时间越短，烟尘突破越多。此外，还研究了烟尘粒度分布的影响。通过将氧化时间和烟尘粒度联系起来，提出了一种量化烟尘突破混合区进入燃烧室贫燃区的指标。
{"title":"Analysis of potential soot breakthrough during oxidation at aero-engine relevant conditions","authors":"Philipp Koob, Hendrik Nicolai, Robert Schmitz, Christian Hasse","doi":"10.1016/j.proci.2024.105672","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105672","url":null,"abstract":"Reducing emissions from aero-engines, vital for aviation climate goals, requires accurate prediction of pollutants like soot. In modern rich-quench-lean aero-engine combustion chambers, fresh air is introduced after the primary combustion zone to dilute the rich exhaust gases and to cool the combustor liner walls, which will consequently also lead to the oxidation of soot with O. In this study, a simplified configuration is derived from the actual aero-engine configuration that enables an in-depth analysis of these soot oxidation processes. Detailed chemistry, together with the split-based extended quadrature method of moments soot model, is used for a comprehensive analysis of soot oxidation, focusing on the influence of varying scalar dissipation rates, mixing times, and particle size distributions derived from the real combustor. It is shown that soot oxidation linearly connects to the oxidation time scale represented by the OH residence time, meaning more soot breakthrough with shorter oxidation times. Furthermore, the influence of the soot particle size distribution is investigated. By connecting the oxidation time and the soot particle size, a metric to quantify soot breaking through the mixing zone into the lean regions of the combustion chamber is proposed.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141946239","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 : 2024-08-03DOI: 10.1016/j.proci.2024.105665
Thorsten Zirwes, Feichi Zhang, Thomas L. Kaiser, Kilian Oberleithner, Oliver T. Stein, Henning Bockhorn, Andreas Kronenburg
Hydrogen is quickly becoming one of the most important fuels for combustion applications. However, compared to conventional hydro-carbon flames, the high diffusivity of hydrogen makes lean hydrogen flames prone to form cellular instabilities. In this work, the formation of cellular structures on a lean hydrogen–air flame is studied numerically in a laminar flow with prescribed initial perturbation. The flame is fully resolved and a detailed reaction mechanism as well as detailed diffusion models are utilized. In the literature, most numerical works directly studying cell formation are limited to two-dimensional setups. However, the additional principal curvature direction in three dimensions can have a strong impact on the cell formation and flame propagation. Because of this, simulations are performed both in 2D and 3D to directly quantify the effect of dimensionality on flame propagation. In the 3D simulations, higher local curvatures yield local heat release rates that exceed the ones from 2D simulations by 80%. In addition, simulations with and without thermo or Soret diffusion are carried out. While Soret diffusion leads to a decrease in flame speed for freely propagating flames, it accelerates the formation of thermodiffusively unstable cells as well as increases local heat release rates. This can be explained by an increase of local equivalence ratios in the reaction and post-oxidation zone due to the altered focusing of diffusive fluxes, leading to locally increased heat release rates for positively curved flame segments. The efficiency factor is evaluated to model the effect of the cellular structures on the local burning rate. increases during the formation of primary cells and reaches a quasi-steady value once the secondary structures are formed, which can present an approach for modeling the effect of cellular structures on hydrogen flame dynamics.
{"title":"The role of thermodiffusion and dimensionality in the formation of cellular instabilities in hydrogen flames","authors":"Thorsten Zirwes, Feichi Zhang, Thomas L. Kaiser, Kilian Oberleithner, Oliver T. Stein, Henning Bockhorn, Andreas Kronenburg","doi":"10.1016/j.proci.2024.105665","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105665","url":null,"abstract":"Hydrogen is quickly becoming one of the most important fuels for combustion applications. However, compared to conventional hydro-carbon flames, the high diffusivity of hydrogen makes lean hydrogen flames prone to form cellular instabilities. In this work, the formation of cellular structures on a lean hydrogen–air flame is studied numerically in a laminar flow with prescribed initial perturbation. The flame is fully resolved and a detailed reaction mechanism as well as detailed diffusion models are utilized. In the literature, most numerical works directly studying cell formation are limited to two-dimensional setups. However, the additional principal curvature direction in three dimensions can have a strong impact on the cell formation and flame propagation. Because of this, simulations are performed both in 2D and 3D to directly quantify the effect of dimensionality on flame propagation. In the 3D simulations, higher local curvatures yield local heat release rates that exceed the ones from 2D simulations by 80%. In addition, simulations with and without thermo or Soret diffusion are carried out. While Soret diffusion leads to a decrease in flame speed for freely propagating flames, it accelerates the formation of thermodiffusively unstable cells as well as increases local heat release rates. This can be explained by an increase of local equivalence ratios in the reaction and post-oxidation zone due to the altered focusing of diffusive fluxes, leading to locally increased heat release rates for positively curved flame segments. The efficiency factor is evaluated to model the effect of the cellular structures on the local burning rate. increases during the formation of primary cells and reaches a quasi-steady value once the secondary structures are formed, which can present an approach for modeling the effect of cellular structures on hydrogen flame dynamics.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141946241","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 : 2024-08-03DOI: 10.1016/j.proci.2024.105244
Christopher B. Reuter, Steven G. Tuttle
The interactions between droplets and shock waves have many applications, but few studies have investigated how the distributions of droplet diameters and droplet velocities in a spray are modified after passing through a shock. This study examines the droplet statistics upstream and downstream of shock waves in an underexpanded jet by performing phase Doppler interferometry in combination with Schlieren imaging. A mixture of water and propylene glycol is employed as the liquid. It is observed that, when the spray passes through an oblique shock, the droplet diameters decrease and then increase but the droplet velocities remain steady. When the droplets pass through a weak normal shock, on the other hand, the most probable droplet diameter decreases, some very large droplets appear, and the velocity distribution splits into three distinct regions. However, a strong normal shock causes the mean droplet diameters and the mean droplet velocities to decrease consistently. Reasons for these different behaviors are given, and secondary breakup regimes are estimated in terms of the Weber number. Additionally, droplet probability distribution fits are compared to the measured values for each of the different cases. The droplet statistics presented here can be used to improve computational modeling of spray-shock interactions.
{"title":"Interactions between liquid sprays and shock waves in underexpanded flows","authors":"Christopher B. Reuter, Steven G. Tuttle","doi":"10.1016/j.proci.2024.105244","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105244","url":null,"abstract":"The interactions between droplets and shock waves have many applications, but few studies have investigated how the distributions of droplet diameters and droplet velocities in a spray are modified after passing through a shock. This study examines the droplet statistics upstream and downstream of shock waves in an underexpanded jet by performing phase Doppler interferometry in combination with Schlieren imaging. A mixture of water and propylene glycol is employed as the liquid. It is observed that, when the spray passes through an oblique shock, the droplet diameters decrease and then increase but the droplet velocities remain steady. When the droplets pass through a weak normal shock, on the other hand, the most probable droplet diameter decreases, some very large droplets appear, and the velocity distribution splits into three distinct regions. However, a strong normal shock causes the mean droplet diameters and the mean droplet velocities to decrease consistently. Reasons for these different behaviors are given, and secondary breakup regimes are estimated in terms of the Weber number. Additionally, droplet probability distribution fits are compared to the measured values for each of the different cases. The droplet statistics presented here can be used to improve computational modeling of spray-shock interactions.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141946096","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 : 2024-08-03DOI: 10.1016/j.proci.2024.105579
Sven Eckart, Krishna P. Shrestha, Binod R. Giri, Qilong Fang, Wei Li, Fabian Mauss, Hartmut Krause, Yuyang Li
Diethoxymethane ((CHCHO)CH, DEM) is a promising carbon-neutral fuel. DEM is a diether or acetal with a molecular structure similar to oxymethylene ethers (CHO–(CHO)–CH, OME). Thus, DEM can be expected to have a similar combustion behavior to OMEs, reducing harmful emissions such as NO and particulate matter (PM) in internal combustion engines. From both experimental and kinetic modeling, fundamental studies on DEM are scarce in the literature. More studies are required to gain a detailed insight into the oxidation kinetics of DEM. Laminar burning velocity (LBV) is a critical property that allows a detailed assessment of the potential application of DEM in combustion devices. Unfortunately, the literature on the LBV of DEM is limited. Therefore, in this study we have investigated the LBV of DEM using two reactors for the first time, namely a heat flux burner and a combustion chamber. The experimental data is reported for equivalence ratio between 0.7 and 1.7, initial temperatures of 368–423 K, and initial pressure of 1–5 bar. In addition, we developed a detailed kinetic model extending our recent work of Shrestha et al. () to characterize the combustion behavior of DEM utilizing the new experimental data from this work and the literature data. Our model performs remarkably well in capturing the newly measured LBV experimental data over various experimental conditions. We found that DEM and dimethoxy methane (DMM) have similar values of LBVs (within ±1.5 cm/s) for a given condition, which indicates that intermediate chemistry governs the flame chemistry. Despite DEM being a larger molecule that is expected to have slightly lower LBVs than DMM, its effect on the measured values of LBVs is negligible. Finally, we experimentally measured NO formation in DEM flame for the first time. The stochiometric flame has the highest NO formation. The proposed model predicted the equivalence ratio dependence of NO nicely. However, it overestimates the NO formation for stoichiometric DEM/air mixtures by ∼30 %. The model suggests that the thermal NO formation route is favored at lean and stochiometric conditions. In contrast, the prompt NO formation route is enhanced for rich mixtures.
二乙氧基甲烷（(CHCHO)CH，DEM）是一种很有前途的碳中性燃料。DEM 是一种二醚或缩醛，其分子结构与氧亚甲基醚（CHO-(CHO)-CH，OME）相似。因此，DEM 可望具有与 OME 相似的燃烧行为，从而减少内燃机中的氮氧化物和颗粒物质（PM）等有害排放物。从实验和动力学模型两方面来看，文献中关于 DEM 的基础研究都很少。要详细了解 DEM 的氧化动力学，还需要进行更多的研究。层流燃烧速度（LBV）是一项关键特性，可用于详细评估 DEM 在燃烧装置中的潜在应用。遗憾的是，有关 DEM 层燃速度的文献十分有限。因此，在本研究中，我们首次使用两种反应器（即热通量燃烧器和燃烧室）对 DEM 的 LBV 进行了研究。我们报告了当量比在 0.7 和 1.7 之间、初始温度为 368-423 K 和初始压力为 1-5 bar 时的实验数据。此外，我们还开发了一个详细的动力学模型，扩展了 Shrestha 等人最近的研究成果（），利用这项研究的新实验数据和文献数据来描述 DEM 的燃烧行为。我们的模型在各种实验条件下都能很好地捕捉到新测得的枸杞多糖实验数据。我们发现，在给定条件下，DEM 和二甲氧基甲烷（DMM）的 LBV 值相似（±1.5 厘米/秒以内），这表明中间化学反应控制着火焰化学反应。尽管 DEM 是一种较大的分子，预计其 LBVs 会略低于 DMM，但其对 LBVs 测量值的影响可以忽略不计。最后，我们首次通过实验测量了 DEM 火焰中 NO 的形成。稳态火焰中的 NO 生成量最高。所提出的模型很好地预测了 NO 的等效比依赖性。然而，该模型高估了化学计量 DEM/空气混合物中 NO 的形成，高估幅度达 30%。该模型表明，在贫气和定容条件下，NO 的热形成途径更受青睐。与此相反，在富混合物中，NO 的迅速形成途径得到了加强。
{"title":"Insight into premixed diethoxymethane flames: Laminar burning velocities, temperatures, and emissions behaviour","authors":"Sven Eckart, Krishna P. Shrestha, Binod R. Giri, Qilong Fang, Wei Li, Fabian Mauss, Hartmut Krause, Yuyang Li","doi":"10.1016/j.proci.2024.105579","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105579","url":null,"abstract":"Diethoxymethane ((CHCHO)CH, DEM) is a promising carbon-neutral fuel. DEM is a diether or acetal with a molecular structure similar to oxymethylene ethers (CHO–(CHO)–CH, OME). Thus, DEM can be expected to have a similar combustion behavior to OMEs, reducing harmful emissions such as NO and particulate matter (PM) in internal combustion engines. From both experimental and kinetic modeling, fundamental studies on DEM are scarce in the literature. More studies are required to gain a detailed insight into the oxidation kinetics of DEM. Laminar burning velocity (LBV) is a critical property that allows a detailed assessment of the potential application of DEM in combustion devices. Unfortunately, the literature on the LBV of DEM is limited. Therefore, in this study we have investigated the LBV of DEM using two reactors for the first time, namely a heat flux burner and a combustion chamber. The experimental data is reported for equivalence ratio between 0.7 and 1.7, initial temperatures of 368–423 K, and initial pressure of 1–5 bar. In addition, we developed a detailed kinetic model extending our recent work of Shrestha et al. () to characterize the combustion behavior of DEM utilizing the new experimental data from this work and the literature data. Our model performs remarkably well in capturing the newly measured LBV experimental data over various experimental conditions. We found that DEM and dimethoxy methane (DMM) have similar values of LBVs (within ±1.5 cm/s) for a given condition, which indicates that intermediate chemistry governs the flame chemistry. Despite DEM being a larger molecule that is expected to have slightly lower LBVs than DMM, its effect on the measured values of LBVs is negligible. Finally, we experimentally measured NO formation in DEM flame for the first time. The stochiometric flame has the highest NO formation. The proposed model predicted the equivalence ratio dependence of NO nicely. However, it overestimates the NO formation for stoichiometric DEM/air mixtures by ∼30 %. The model suggests that the thermal NO formation route is favored at lean and stochiometric conditions. In contrast, the prompt NO formation route is enhanced for rich mixtures.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141946244","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 : 2024-08-03DOI: 10.1016/j.proci.2024.105669
Hojin Jung, Jaeyoung Cho, Yeonjoon Kim, Zhanhong Xiang, Sabari Kumar, Piper Barnard, Charles S. McEnally, Lisa D. Pfefferle, Seonah Kim
Substituted aromatics are commonly observed in lignin-based biofuel; however, their high sooting tendency prevents direct utilization in commercial combustors. Recent studies have revealed that oxygenated functional group substitution could effectively suppress the soot emission from aromatic biofuels. This study aims to enhance the understanding of sooting tendencies in aromatic oxygenates with mono-, di-, and tri-substitutions, focusing on various functional groups and their positional isomerism. We established a yield sooting index (YSI) database of 42 single-ring aromatic compounds, including 30 new measurements from the present study. The constructed database was utilized to develop a multivariate linear regression (MLR) model to predict the YSI of substituted aromatic oxygenates based on their structural features. The fitted coefficients of the MLR model indicate vastly different impacts of hydroxyl, formyl, and methoxy functional group, as well as the importance of positional isomerism. To understand the role of oxygenated functional groups, we used substituted vanillin isomers containing hydroxyl, methoxy, and formyl groups as a model system. Comparing the sooting tendencies of these compounds revealed a high sensitivity of YSI to positional isomerism. A further mechanistic study using quantum-mechanical calculations showed that subtle interactions between three oxygenated functional groups in vanillin isomers can alter their thermal decomposition pathway, affecting the sooting tendencies of these aromatic fuels. The present study provides a novel statistical and theoretical explanation of how oxygenated substitution and its positional isomerism influence sooting behaviors, facilitating the rational design of lignin-based biofuels with minimal soot emission.
{"title":"Sooting tendency of substituted aromatic oxygenates: The role of functional groups and positional isomerism in vanillin isomers","authors":"Hojin Jung, Jaeyoung Cho, Yeonjoon Kim, Zhanhong Xiang, Sabari Kumar, Piper Barnard, Charles S. McEnally, Lisa D. Pfefferle, Seonah Kim","doi":"10.1016/j.proci.2024.105669","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105669","url":null,"abstract":"Substituted aromatics are commonly observed in lignin-based biofuel; however, their high sooting tendency prevents direct utilization in commercial combustors. Recent studies have revealed that oxygenated functional group substitution could effectively suppress the soot emission from aromatic biofuels. This study aims to enhance the understanding of sooting tendencies in aromatic oxygenates with mono-, di-, and tri-substitutions, focusing on various functional groups and their positional isomerism. We established a yield sooting index (YSI) database of 42 single-ring aromatic compounds, including 30 new measurements from the present study. The constructed database was utilized to develop a multivariate linear regression (MLR) model to predict the YSI of substituted aromatic oxygenates based on their structural features. The fitted coefficients of the MLR model indicate vastly different impacts of hydroxyl, formyl, and methoxy functional group, as well as the importance of positional isomerism. To understand the role of oxygenated functional groups, we used substituted vanillin isomers containing hydroxyl, methoxy, and formyl groups as a model system. Comparing the sooting tendencies of these compounds revealed a high sensitivity of YSI to positional isomerism. A further mechanistic study using quantum-mechanical calculations showed that subtle interactions between three oxygenated functional groups in vanillin isomers can alter their thermal decomposition pathway, affecting the sooting tendencies of these aromatic fuels. The present study provides a novel statistical and theoretical explanation of how oxygenated substitution and its positional isomerism influence sooting behaviors, facilitating the rational design of lignin-based biofuels with minimal soot emission.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141946246","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 : 2024-08-03DOI: 10.1016/j.proci.2024.105677
Qingyan He, Yuxin Zhou, Xiaoqing You
In this work, we investigated the effect of ferric chloride (FeCl) addition on soot formation during ethylene pyrolysis in a laminar flow reactor by characterizing particles sampled at the reactor outlet. To avoid the interference of oxygen atoms on soot formation, we selected FeCl as an iron-based additive and used a diffusion dryer to absorb water in the FeCl solution. By studying particle size distribution, morphology, and chemical composition, we found that iron-containing particles evolved from iron nuclei to core-shell particles and finally to aggregates. These iron-containing particles, which had an overall higher charge fraction, hindered the agglomeration of iron nuclei but promoted the formation of core-shell particles. In addition, ReaxFF molecular dynamics simulations were performed to study the interaction between FeCl and pyrene molecules in the early stages of soot formation. Simulation results show that FeCl would undergo thermal decomposition to form Fe-C sosoloid as the core of the core-shell particles.
{"title":"Effect of ferric chloride addition on soot formation during ethylene pyrolysis in a laminar flow reactor","authors":"Qingyan He, Yuxin Zhou, Xiaoqing You","doi":"10.1016/j.proci.2024.105677","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105677","url":null,"abstract":"In this work, we investigated the effect of ferric chloride (FeCl) addition on soot formation during ethylene pyrolysis in a laminar flow reactor by characterizing particles sampled at the reactor outlet. To avoid the interference of oxygen atoms on soot formation, we selected FeCl as an iron-based additive and used a diffusion dryer to absorb water in the FeCl solution. By studying particle size distribution, morphology, and chemical composition, we found that iron-containing particles evolved from iron nuclei to core-shell particles and finally to aggregates. These iron-containing particles, which had an overall higher charge fraction, hindered the agglomeration of iron nuclei but promoted the formation of core-shell particles. In addition, ReaxFF molecular dynamics simulations were performed to study the interaction between FeCl and pyrene molecules in the early stages of soot formation. Simulation results show that FeCl would undergo thermal decomposition to form Fe-C sosoloid as the core of the core-shell particles.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141946236","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 : 2024-08-03DOI: 10.1016/j.proci.2024.105675
Bingjie Chen, Huajie Lyu, Peng Liu, Vasilios G. Samaras, Xingcai Lu, Xiang Gao, William L. Roberts, Heinz Pitsch
Nitrogen-containing aromatics, including nitrogen-substituted monocyclic and polycyclic aromatic hydrocarbons (NPAHs), are toxic and a specific type of combustion emissions arising from fuel-nitrogen in coal and protein-rich biomass. However, the formation chemistry of pyridine, the first nitrogen heterocyclic ring in NPAHs, is poorly understood and needs to be enhanced. In this work, we investigated the chemistry of pyridine formation based on experimental measurements and theoretical reaction pathway exploration. Three pyrolysis experiments were performed in a jet stirred reactor with reactants of acetylene, acetylene + acetonitrile, and acetylene + acrylonitrile. The large molecule products were collected offline and analyzed by comprehensive two-dimensional (2D) gas chromatogram with time-of-flight mass spectrometry (GC × GC - ToF - MS) for species identification and measurements. Guided by experimental results, four pyridine formation pathways, CH + CHCN radical, CHCN + CH radical, CHCN + CH radical, and HCN + -CH radical are proposed and investigated. The calculated product yields and reaction rate coefficients determined by the combination of high-level quantum chemistry and RRKM-ME theories, and the simulated mole fractions by kinetic modeling confirmed the importance of the proposed pyridine formation pathways. The unraveled pyridine formation chemistry may help explain how the first nitrogen heterocyclic ring is formed from fuel-nitrogen in biomass gas-phase combustion.
{"title":"On the formation of pyridine, the first nitrogen heterocyclic ring in NPAHs","authors":"Bingjie Chen, Huajie Lyu, Peng Liu, Vasilios G. Samaras, Xingcai Lu, Xiang Gao, William L. Roberts, Heinz Pitsch","doi":"10.1016/j.proci.2024.105675","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105675","url":null,"abstract":"Nitrogen-containing aromatics, including nitrogen-substituted monocyclic and polycyclic aromatic hydrocarbons (NPAHs), are toxic and a specific type of combustion emissions arising from fuel-nitrogen in coal and protein-rich biomass. However, the formation chemistry of pyridine, the first nitrogen heterocyclic ring in NPAHs, is poorly understood and needs to be enhanced. In this work, we investigated the chemistry of pyridine formation based on experimental measurements and theoretical reaction pathway exploration. Three pyrolysis experiments were performed in a jet stirred reactor with reactants of acetylene, acetylene + acetonitrile, and acetylene + acrylonitrile. The large molecule products were collected offline and analyzed by comprehensive two-dimensional (2D) gas chromatogram with time-of-flight mass spectrometry (GC × GC - ToF - MS) for species identification and measurements. Guided by experimental results, four pyridine formation pathways, CH + CHCN radical, CHCN + CH radical, CHCN + CH radical, and HCN + -CH radical are proposed and investigated. The calculated product yields and reaction rate coefficients determined by the combination of high-level quantum chemistry and RRKM-ME theories, and the simulated mole fractions by kinetic modeling confirmed the importance of the proposed pyridine formation pathways. The unraveled pyridine formation chemistry may help explain how the first nitrogen heterocyclic ring is formed from fuel-nitrogen in biomass gas-phase combustion.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141946091","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 : 2024-08-02DOI: 10.1016/j.proci.2024.105650
Bowen Mei, Ziyu Wang, Andy Thawko, Ning Liu, Laura Thompson, Jacques Attinger, Yiguang Ju
Dimethoxymethane (DMM) is a promising renewable fuel with low-carbon intensity and low tendencies for soot and NO emissions, which is drawing increasing attention to meet the carbon-neutral requirements. In this work, DMM oxidation was studied by using a novel supercritical pressure jet-stirred reactor at 10 and 100 atm, with temperatures between 450 and 950 K, and equivalence ratios of 0.27 and 2.0. The experimental results show that the negative temperature coefficient (NTC) behavior becomes much weaker under 100 atm than the case of 10 atm. One reason is the significant shift of the intermediate-temperature HO chemistry to lower temperature at 100 atm and the other one is the increase of multi-oxygen addition reactions at 100 atm. Selected kinetic models in the literature show some discrepancies in comparison to the experimental results in this study. Thus, a new model updated from a previous study was developed to improve the prediction of the experimental data under high pressures. Reaction pathway and sensitivity analyses were performed to identify key reactions in DMM high-pressure oxidation. DMM H-atom abstraction at the primary C site by OH (DMM_1 radical) is found to be the most important reaction to promote oxidation, while the secondary site (DMM_2 radical) shows different sensitivity under different conditions. The reason is that under richer or lower pressure conditions, the decomposition of DMM_2 is favored over O addition, thus inhibits the oxidation process. DMM H-atom abstractions by CHO and HO are found to be important under low- and intermediate-temperature, respectively. Therefore, more efforts in studying these reactions are suggested to further improve the model prediction. In addition, reaction 2HO = 2OH + O, added in this work, is found to be important in promoting DMM oxidation at the early stage and improves model prediction on oxidation onset temperature.
二甲氧基甲烷（DMM）是一种前景广阔的可再生燃料，具有碳强度低、烟尘和氮氧化物排放量低的特点，在满足碳中和要求方面日益受到关注。本研究采用新型超临界压力喷射搅拌反应器，在 10 和 100 atm、450 和 950 K 温度以及 0.27 和 2.0 等效比条件下研究了 DMM 的氧化过程。实验结果表明，负温度系数（NTC）行为在 100 atm 条件下比 10 atm 条件下要弱得多。其中一个原因是中温 HO 化学反应在 100 atm 时明显转向低温，另一个原因是多氧加成反应在 100 atm 时有所增加。文献中选取的动力学模型与本研究的实验结果相比存在一些差异。因此，我们在先前研究的基础上开发了一个新模型，以改进高压下实验数据的预测。通过反应途径和敏感性分析，确定了 DMM 高压氧化过程中的关键反应。发现 DMM H 原子在一级 C 位点被 OH（DMM_1 自由基）抽取是促进氧化的最重要反应，而二级位点（DMM_2 自由基）在不同条件下表现出不同的敏感性。原因是在富氧或低压条件下，DMM_2 的分解比 O 的加入更有利，从而抑制了氧化过程。在低温和中温条件下，发现 CHO 和 HO 对 DMM H 原子的抽取分别非常重要。因此，建议加大对这些反应的研究力度，以进一步改进模型预测。此外，这项工作中加入的反应 2HO = 2OH + O 被发现在早期阶段对促进 DMM 氧化非常重要，并改善了模型对氧化起始温度的预测。
{"title":"Dimethoxymethane low- and intermediate-temperature oxidation up to 100 atm","authors":"Bowen Mei, Ziyu Wang, Andy Thawko, Ning Liu, Laura Thompson, Jacques Attinger, Yiguang Ju","doi":"10.1016/j.proci.2024.105650","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105650","url":null,"abstract":"Dimethoxymethane (DMM) is a promising renewable fuel with low-carbon intensity and low tendencies for soot and NO emissions, which is drawing increasing attention to meet the carbon-neutral requirements. In this work, DMM oxidation was studied by using a novel supercritical pressure jet-stirred reactor at 10 and 100 atm, with temperatures between 450 and 950 K, and equivalence ratios of 0.27 and 2.0. The experimental results show that the negative temperature coefficient (NTC) behavior becomes much weaker under 100 atm than the case of 10 atm. One reason is the significant shift of the intermediate-temperature HO chemistry to lower temperature at 100 atm and the other one is the increase of multi-oxygen addition reactions at 100 atm. Selected kinetic models in the literature show some discrepancies in comparison to the experimental results in this study. Thus, a new model updated from a previous study was developed to improve the prediction of the experimental data under high pressures. Reaction pathway and sensitivity analyses were performed to identify key reactions in DMM high-pressure oxidation. DMM H-atom abstraction at the primary C site by OH (DMM_1 radical) is found to be the most important reaction to promote oxidation, while the secondary site (DMM_2 radical) shows different sensitivity under different conditions. The reason is that under richer or lower pressure conditions, the decomposition of DMM_2 is favored over O addition, thus inhibits the oxidation process. DMM H-atom abstractions by CHO and HO are found to be important under low- and intermediate-temperature, respectively. Therefore, more efforts in studying these reactions are suggested to further improve the model prediction. In addition, reaction 2HO = 2OH + O, added in this work, is found to be important in promoting DMM oxidation at the early stage and improves model prediction on oxidation onset temperature.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-08-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141886570","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 : 2024-08-02DOI: 10.1016/j.proci.2024.105553
D.A. Quan Reyes, Dirk Roekaerts, Jeroen van Oijen
The Argon Power Cycle (APC) is a compression ignition combustion concept that would substantially enhance efficiency by using argon as the working fluid. When used with hydrogen and oxygen, such closed loop system would be free of emissions. Fundamental understanding on the combustion dynamics of such system is needed in order to determine the best injection strategy. A direct numerical simulation of a fully developed turbulent () reacting case which resembles the direct injection of has been performed. Attention was devoted to (1) understanding the influence of preferential diffusion and turbulence on the ignition behavior and development of flame kernels, (2) determining the composition space accessed by the turbulent and laminar analogue, and (3) finding the types of flamelets that could resemble such composition space. It was found that igniting kernels emerge near the stoichiometric mixture fraction in regions convex to the fuel side, and with high scalar dissipation, in contrast to what has been reported for other fuels in the literature. Furthermore, these igniting kernels can extinguish if exposed to high curvature levels due to the enhanced diffusion of radicals out of the kernel. There is good agreement between the composition space accessed by the turbulent flame and the laminar analogue, but better agreement can be reached by using strained and curved flamelets.
{"title":"Direct numerical simulation of igniting non-premixed hydrogen combustion for the Argon Power Cycle","authors":"D.A. Quan Reyes, Dirk Roekaerts, Jeroen van Oijen","doi":"10.1016/j.proci.2024.105553","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105553","url":null,"abstract":"The Argon Power Cycle (APC) is a compression ignition combustion concept that would substantially enhance efficiency by using argon as the working fluid. When used with hydrogen and oxygen, such closed loop system would be free of emissions. Fundamental understanding on the combustion dynamics of such system is needed in order to determine the best injection strategy. A direct numerical simulation of a fully developed turbulent () reacting case which resembles the direct injection of has been performed. Attention was devoted to (1) understanding the influence of preferential diffusion and turbulence on the ignition behavior and development of flame kernels, (2) determining the composition space accessed by the turbulent and laminar analogue, and (3) finding the types of flamelets that could resemble such composition space. It was found that igniting kernels emerge near the stoichiometric mixture fraction in regions convex to the fuel side, and with high scalar dissipation, in contrast to what has been reported for other fuels in the literature. Furthermore, these igniting kernels can extinguish if exposed to high curvature levels due to the enhanced diffusion of radicals out of the kernel. There is good agreement between the composition space accessed by the turbulent flame and the laminar analogue, but better agreement can be reached by using strained and curved flamelets.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-08-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141886573","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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