Periodic Reporting for period 3 - SOTUF (SOot in TUrbulent Flames: a new look at soot production processes in turbulent flames leading to novel models for predictive large eddy simulations)
Periodo di rendicontazione: 2021-06-01 al 2022-11-30
1) The development of a detailed chemical model for the description of TiO2 including both oxidation and hydrolysis of TiCl4. The detailed kinetics available in the literature have not been validated in flames and only account for oxidation. However, when considering nanoparticles production in flames, hydrolysis can greatly contribute to TiO2 production due to the presence of vapor H2O. In particular, we proved that it has to be accounted for by the kinetics to retrieve numerically the high conversion rates that are experimentally observed. Reproducing such trends in laminar flames is essential to perform high-fidelity simulations of the interactions between turbulence, flame, and nanoparticles.
2) The characterization of the effect of the flame characteristics on soot and nano-particle productions. In particular, it has been observed that a small modification of the injector can greatly modify the stabilization of the flame, consequently reducing soot production. Similarly, by modifying the mixture composition of the dispersion gas of the liquid atomizer the pilot flame characteristics can be changed, enhancing or reducing nanoparticle production. Understanding the role of flame and flow characteristics on nanoparticle production can lead to the optimization of combustion systems and aerosol technology.
3) The development of a consistent ‘forward’ approach for the validation of numerical predictions of the primary particle size with the experimental data based on the numerical synthetization of the signals. This strategy allows reducing the errors and uncertainties introduced by the postprocessing of the experimental signals.
4) The development of an ‘a posteriori’ strategy to clearly quantify the role of a subgrid model in LES of nanoparticle production in turbulent flames, essential for the validation of the models developed in the second part of the project.
Thanks to these essential achievements, in the second part of the project it will be possible to:
1) Identifying which advanced space and time-resolved optical diagnostics from sooting flames can be used for the investigation of spray synthesis of nano-particles and applied them to the characterization of turbulence-flame-nanoparticles interactions and, more generally, to flame synthesis.
2) Extensively characterizing the coupling between turbulence, flame, and soot. In particular, we will identify some universal behaviors at small scales necessary to the development of general subgrid LES models. This will be possible by using identified advanced optical diagnostics and by performing high-fidelity simulations based on the developed detailed kinetics.
3) Developing general subgrid LES model for soot production and validating them with additional numerical simulations and comparison with the created experimental data.
Once validated, the subgrid LES models could be used for the optimization of burners and validation of new designs, allowing for a reduction of soot emission. Also, the understanding of the effect of turbulence on nano-particle synthesis is of great relevance since flame synthesis is a promising technique to produce nanoparticles with well-defined characteristics in terms of particle size, morphology, and properties, which can be potentially optimized by perfectly controlling the flame and the flow.