1,721,538 research outputs found
Interazioni tra fumi e sistemi sprinkler: analisi fluidodinamica durante un incendio
Full text linkGli incendi in galleria costituiscono uno degli scenari incidentali di maggior rischio e sono stati oggetto di ampi studi in letteratura, volti ad indagarne lo sviluppo o l’influenza di vari parametri, come ad esempio l’effetto delle ostruzioni sulla velocità critica di ventilazione. Uno sviluppo minore è invece riscontrabile per quanto riguarda l’utilizzo e gli effetti di impianti di tipo sprinkler per migliorare la sicurezza dei tunnel stradali. Un esempio recente è costituito dallo studio di Zheng e Ingason, in cui l’impiego di sprinkler è stato testato su una riproduzione in scala di una galleria stradale.
Questo studio si propone di indagare l’interazione tra i fumi e i sistemi antincendio fissi ad acqua in galleria, problema che risulta essere tuttora non completamente risolto
THE OPTIMIZATION OF CHEMICAL KINETICS WITH RESPECT TO MILD COMBUSTION
Full text linkThis work has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska- Curie grant agreement No 643134.info:eu-repo/semantics/nonPublishe
Heat Release Rate Markers for the Adelaide Jet in Hot Coflow Flame
No full textIn the present work, the correlation between the Heat Releaser Rate (HRR) and species mole fractions and net reaction rates is studied. The PaSR closure model is employed in a RANS framework to implement a detailed kinetic scheme, including the excited species OH*, used as a HRR marker. The effect of oxygen dilution on the combustion regime is investigated, as it can lead to Moderate or Intense Low-Oxygen Dilution (MILD) conditions. Two cases with different levels of oxygen concentration are analyzed. The results suggest the possibility of combining chemical species to construct an appropriate scalar to achieve better correlation with the HRR. It is found that typical markers such as radicals O, OH, OH* correlate fairly well with the HRR but improved correlations can be achieved with appropriate species mole fractions combinations, particularly for the MILD region of the flame.This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme under grant agreement no. 714605. The author Marco Ferrarotti also wishes to thank Fonds de la Recherche Scientifique FNRS Belgium for financing his research.SCOPUS: ar.jinfo:eu-repo/semantics/publishe
Selection of appropriate constraints for dimension reduction in MILD combustion simulations via RCCE
Full text linkModeling MILD (Moderate or Intense Low-oxygen Dilution) combustion is well known to be computation-
ally demanding due to the need of an accurate description of the chemistry, because the low Damköhler
number. The present work investigates the potentials of Rate-Controlled Constrained Equilibrium for the
dimension reduction of kinetic schemes for a burner fed with a mixture of ethylene and air emulating MILD
combustion conditions. A method based on the Computational Singular Perturbation theory is proposed for
the identification of the species to be retained in the reduced representation of the chemistry. A significant
reduction was achieved by using only 10 species (out of 34 species in the full kinetic scheme) and 3 elements;
the results from the reduced model were in very good agreement with those of the full kinetic scheme. The
sensitivity of predictions to the turbulence and combustion models was also preliminary assessed, indicating
the need of modifying the residence time constant of the Eddy Dissipation Concept for MILD combustion
conditions
Chemistry reduction for modelling flameless combustion of ethylene
Full text linkFlameless combustion is a novel combustion technology able to ensure high combustion efficacies with low pollutant emissions thanks to the dilution of reactants, usually achieved through recirculation of combustion products. The technology has been successfully applied in several processes and has been found to be able to handle a large variety of fuels, including low grade fuels, industrial by-products and hydrogen. Further development of this innovative combustion technology would benefit of Computational Fluid Dynamics (CFD) tools; however, modelling flameless combustion is much more challenging than conventional flames, because of the strong coupling between turbulent mixing and chemical kinetics. In particular the chemical kinetics plays a fundamental role, even though there no common opinion on the degree a mechanism can be reduced. Some useful works may be found on flameless burners fed with methane, but there is lack of information on different fuels. The present work describes the numerical modelling of an ethylene jet flame issuing in a hot coflow burner, emulating flameless combustion and fully characterised in literature, with the scope of investigating the potential for chemistry reduction in the context of flameless combustion. A Principle Component/Variable Analysis is used to investigate the most important species in the chemical mechanism and subsequently a dimension reduction technique based on the Rate-controlled constrained-equilibrium (RCEE) principle is applied to the detailed mechanism to be coupled to the CFD code, in order to make simulations more affordable. Results indicated that the use of Principle Component/Variable Analysis leads to a good choice of the variables to be retained as results with the reduced scheme were found to be consistent with those obtained with the full mechanism.SCOPUS: ar.kinfo:eu-repo/semantics/publishe
Kinetic modeling of soot formation in premixed burner-stabilized stagnation ethylene flames at heavily sooting condition
Full text linkA detailed kinetic mechanism of soot formation and oxidation is revised and extended to include temperature-dependent collision efficiencies. The collision efficiency for various particle size is studied and compared with experimental data and molecular dynamics simulations for the PAH dimerization where the experimental data are not available. This revised kinetic model is validated in comparison with the premixed burner-stabilized stagnation ethylene flames at heavily sooting conditions. The results showed that quasi-one-dimensional numerical simulations can capture the flame structure and predict soot formation quite satisfactorily. The predicted particle size distribution function (PSDF) is in reasonable agreement with experimental results, but the model only partially reproduces the distinct separation between nucleation and coagulation modes observed experimentally. This leads to some discrepancies in the prediction of soot number density, while the predicted soot volume fraction, which is dominated by the large particles of the PSDF, is in generally good agreement with the experimental data. There is an overestimation of the initial soot volume fraction in the flame region close to the burner, which is a consequence of the over-prediction of the amount of young particles. Therefore, the prediction of PAHs formation and their condensation on soot, which controls the nucleation rate, will require further attention. The comparison between the temperature-dependent model and the model neglecting the temperature dependency showed that the temperature-dependent model could improve the prediction of soot number density, which is controlled by small particles
Evaluation of Modeling Approaches for MILD Combustion Systems With Internal Recirculation
No full textNumerical simulations employing two different modeling approaches are performedand validated against experimental results from a moderate or intense low-oxygendilution (MILD) system with internal recirculation. The flamelet-generated manifold (FGM)and partially stirred reactor (PaSR) closures are employed in a Reynolds-averagedNavier–Stokes (RANS) framework to carry out the numerical simulations. The resultsshow that the FGM model strongly overpredicts temperature profiles in the reactiveregion, while yielding better results along the central thermocouple. The PaSR closuresbased on a prescribed mixing time constant, Cmix, of 0.01, 0.1, and 0.5 are compared,showing that a Cmix value of 0.5 is the most appropriate choice for the cases underinvestigation. A PaSR formulation allowing local estimation of the Cmix value is found toprovide improved results for both the lateral and central thermocouples. A flame indexanalysis, used to assess the ability of FGM and PaSR to capture intense mixing of thecyclonic burner, indicates how the FGM model predicts a typical non-premixed regionafter the injection zone, contrary to the experimental observation.info:eu-repo/semantics/publishe
Capturing Extinction and Reignition in Turbulent Flames: a Principal Component Analysis Approach
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