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Item type:Publication, Soot modeling in turbulent diffusion flames: review and prospects(Springer Science and Business Media Deutschland GmbH, 2021-04-01)This work reviews the state of the art of the main soot modeling approaches used in turbulent diffusion flames. Accordingly, after a short introduction about the subject addressed here, the main soot formation mechanisms are described next. This description provides the basis for the discussions about the different soot modeling techniques employed nowadays for soot predictions. Since combustion and radiation models have a significant impact on soot predictions, as a consequence of the strong coupling between chemistry, turbulence and soot formation, a general overview about these models is also provided. For the sake of clarity, the main soot formation models reviewed in this work are classified as semiempirical soot precursor models and detailed ones. Both advantages and disadvantages of the referred soot modeling approaches are properly discussed. In the last part of this review, comparative results obtained using some of the main soot models currently available are presented along with a discussion about the prospects for soot modeling in turbulent flames. Finally, some conclusions and references are provided. Overall, based on the literature reviewed, it is concluded that there is yet a long path to be followed before understanding first and having then a soot model able to properly describe the formation of this critical pollutant for a variety of situations of industrial interest. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Computational assessment of soot models in ethylene/air laminar diffusion flames(Taylor and Francis Ltd., 2024-01-01)To improve the accuracy of soot formation and evolution predictions, several physical and chemical models have been developed over the last decades. These models include (i) detailed chemical kinetic mechanisms describing both gas-phase chemistry related to combustion processes and reaction pathways leading to large-sized aromatic molecules, which are needed for modelling soot formation, and (ii) soot models providing a comprehensive description of soot particle dynamics and interactions with gas-phase chemical species. Accordingly, in this work, two detailed soot models, the method of moments (MOM) and the discrete sectional method (DSM), are evaluated in ethylene/air laminar diffusion flames, and their corresponding results are compared with experimental measurements. Furthermore, the NBP and KM2 chemical kinetic mechanisms are assessed and compared with each other by examining key chemical species related to soot formation and evolution. To compute gas mixture’s radiative properties, the weighted sum of grey gases model considering a grey medium is also utilised. Finally, the contributions of the soot precursors known as PAH (polycyclic aromatic hydrocarbon) to soot formation are also analysed. The main results show that the discrepancies in PAH concentrations obtained with different chemical kinetic mechanisms can be significant. In addition, compared to MOM ones, DSM results obtained here show a better agreement with experimental data. Finally, the analysis of PAH shows that those with two (A2) to four (A4) aromatic rings impact the most on soot modelling. Specifically, contributions of A4 were found to be more significant at lower heights above the burner, whereas A2 was found to be more impactful downstream as the flame develops. Maximum contributions of A2 and A4 to the soot inception rate were 66% and 85%, respectively, whereas the maximum summed contribution of PAH with five (A4R5) to seven (A7) aromatic rings accounted for only 13% of the inception rate. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Soot evolution in turbulent non-premixed bluff body flames: Assessment of detailed soot formation models using large eddy simulation(Centre National de la Recherche Scientifique, 2024-01-26)Exploring the complexities of soot formation in combustion systems implies recognizing the intricate interplay among turbulence, chemical kinetics, radiation, and soot particle dynamics. Achieving accurate predictions of soot levels in turbulent flames entails a meticulous representation of all stages of soot formation and oxidation, which prompts the development and use of detailed soot formation models. This work delves into three detailed soot models-Method of Moments with Interpolative Closure (MOMIC), Hybrid Method of Moments (HMOM), and Discrete Sectional Method (DSM)-integrated into the open-source computational tool OpenFOAM. Both the combustion process and the formation of soot precursors in the gas phase are characterized using the Flamelet Progress Variable combustion model along with the detailed ABF chemical kinetic mechanism. Turbulence is addressed through a Large Eddy Simulation based approach, and the computational results are compared with experimental data from the Adelaide ENB1 Bluff Body Flame. Specifically, the analysis extends to detailing flow velocities and their fluctuations, along with fields and profiles depicting soot volume fraction. In order to obtain quantitatively correct soot volume fractions, the nucleation sticking factor was adjusted. The comparative assessments of the soot formation models carried out provide a unique perspective on soot formation, highlighting different effects of each soot source terms and specific model limitations. HMOM described the measured soot volume fraction with greatest accuracy followed by DSM and MOMIC. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Soot formation models assessment in turbulent diffusion jet flames: A RANS-based comparison(Centre National de la Recherche Scientifique, 2024-10-02)A RANS-based Comparison Due to the intricate interaction between turbulence, chemical kinetics, radiation, and soot particle dynamics, modelling soot formation processes in flames is a challenging task. To predict the level of soot formed, it is essential to accurately capture all stages of soot formation and oxidation. Using a RANS approach, this study focuses on the implementation, within the computational open-source tool OpenFOAM, and comparison of three detailed soot formation models, (i) the Interpolative Closure Method of Moments (MOMIC), (ii) the Hybrid Method of Moments (HMOM), and (iii) the Discrete Sectional Method (DSM), as well as a semi-empirical two-equation model. Both the combustion process and the formation of soot precursors in the gas phase are described using the Steady Laminar Flamelet model and a detailed chemical kinetic mechanism. Radiation effects are modelled using the optically thin method. The computational results obtained here are compared with the experimental data characterizing the Adelaide ENH1 jet flame and other past numerical results. The results reveal significant differences in soot formation source terms among the models and for each of the soot formation stages. DSM best matches the experimental peak soot position, which is attributed to its modelling of condensation and surface growth occurring downstream compared to MOMIC and HMOM. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Computational assessment of detailed soot formation models in ethylene/air laminar diffusion flames(Centre National de la Recherche Scientifique, 2024-01-26)To improve the accuracy of soot formation and evolution predictions, several physical and chemical models have been developed over the last decades.These models include (i) detailed chemical kinetic mechanisms describing both gas-phase chemistry related to combustion processes and reaction pathways leading to large-sized aromatic molecules, which are needed for modeling soot formation, and (ii) soot models providing a comprehensive description of soot particle dynamics and interactions with gas-phase chemical species.Accordingly, in this work, two detailed soot models, the method of moments (MOM) and the discrete sectional method (DSM), are evaluated in ethylene/air laminar diffusion flames, and their corresponding results are compared with experimental measurements.Furthermore, the NBP and KM2 chemical kinetic mechanisms are assessed and compared with each other by examining key chemical species related to soot formation and evolution.To compute gas mixture's radiative properties, the weighted sum of gray gases model considering a gray medium is also utilized.Finally, the contributions of the soot precursors known as PAH (polycyclic aromatic hydrocarbon) to soot formation are also analyzed.The main results show that the discrepancies in PAH concentrations obtained with different chemical kinetic mechanisms can be significant.In addition, compared to MOM ones, DSM results obtained here show a better agreement with experimental data.Finally, the analysis of PAH shows that those with two (A2) to four (A4) aromatic rings impact the most on soot modeling.Specifically, contributions of A4 were found to be more significant at lower heights above the burner, whereas A2 was found to be more impactful downstream as the flame develops.Maximum contributions of A2 and A4 to the soot inception rate were 66% and 85%, respectively, whereas the maximum summed contribution of PAH with five (A4R5) to seven (A7) aromatic rings accounted for only 13% of the inception rate. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Numerical Simulation of Bluff Body Turbulent Flows Using Hybrid RANS/LES Turbulence Models(Springer Science and Business Media Deutschland GmbH, 2023-04-01)Many engineering applications involve turbulent flows around bluff bodies. Because of their intrinsically unsteady dynamics, bluff body characteristic flows feature unique turbulence-related phenomena, which makes their numerical modeling challenging. Accordingly, accounting for a circular bluff body flow configuration, three different turbulence modeling approaches are investigated in this work, (i) Reynolds-averaged Navier–Stokes (RANS), (ii) large eddy simulation (LES), and (iii) hybrid RANS/LES. Regarding the hybrid approaches, two variants of the detached eddy simulation (DES) one, delayed DES (DDES) and improved delayed DES (IDDES), are studied. As RANS model, the k - ωSST is utilized here. This RANS model is also used as the background one for both DDES and IDDES. Wall-adaptive local eddy viscosity (WALE) is used in turn as the sub-grid scale (SGS) model for LES. The velocity two-point correlation function is used to assess the mesh size requirements. When compared to experimental data, the obtained numerical results indicate that RANS overestimates the recirculating bubble length by over 18% and is not capable of describing the turbulent kinetic energy and the flow anisotropy in agreement with the experimental data. In contrast, LES, DDES, and IDDES are all within 1% of the recirculating bubble length while predicting both the Reynolds stress tensor components and the corresponding flow anisotropy in agreement with the measurements. Besides, normalized anisotropy tensor invariants maxima in the shear layer were reproduced by all scale resolving models studied here, but they failed to yield the local extrema measured within the wake recirculation region. A comparative analysis of the anisotropic Reynolds stress tensor invariances underscores the adequacy of the scale resolving models.