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) Okres sprawozdawczy: 2021-06-01 do 2022-11-30 Podsumowanie kontekstu i ogólnych celów projektu Many practical systems emit soot into the atmosphere as a result of incomplete combustion of hydrocarbons. This pollutant emission is characterized by a distribution of solid carbon particles of different sizes and shapes, which have negative effects on human health and the environment. Controlling such emission represents a societal issue and an industrial challenge that require a deep understanding of the intricate processes underlying soot production in the turbulent flames that generally characterize practical systems. In this context, progress in numerical simulations is essential to the successful design of low-emission combustion systems. Unfortunately, the Large-Eddy Simulations (LES) approach, which has successfully demonstrated its capacity to represent gaseous turbulent combustion processes, is far from being predictive for soot emission. Indeed, soot production in turbulent flames is a complex process that is not easy to be represented with the classical LES strategy: the long time scales and the broad range of length scales place soot processes outside the usual scale ranges of LES subgrid models. In this context, the goal of the present project is to provide new insights on the processes governing soot production in turbulent flames to develop novel LES models, encompassing the state-of-art and allowing reliable predictions of soot in turbulent flames. These objectives will be achieved by: (1) characterizing the turbulence-flame-soot coupling from novel well-controlled experiments employing advanced space and time-resolved optical diagnostics; (2) developing new subgrid models based on information extracted from experiments and high-fidelity simulations; (3) validating and applying the developed LES modeling strategy on complex systems. The research results are expected to drastically improve the prediction of soot production in industrial configurations, helping to design new low-emission systems with notably reduced soot levels. Prace wykonane od początku projektu do końca okresu sprawozdawczego oraz najważniejsze dotychczasowe rezultaty In the first part of the project, most of the experimental and numerical tools to perform the characterization and modeling of turbulence-flame-nanoparticles coupling has been developed. From the experimental point of view, different configurations with increasing have been implemented. The investigations can today be carried on engineered nanoparticles in suspension or produced in flames: laminar diffusion flames with a pre-vaporized injection of liquid precursors, perfectly-premixed turbulent swirled flames, turbulent spray jet flames. These configurations will be studied to prove the feasibility of using advanced space and time-resolved optical diagnostics from sooting flames to the investigation of spray synthesis of nano-particles and to consequently characterize turbulence-flame-nanoparticles coupling. Concerning simulations, new detailed chemical models for the production of nanoparticles have been developed in a laminar context to be used in high-fidelity simulations of turbulence-flame-nanoparticles interactions. Besides, new approaches have been proposed to validate in a rigorous way the subgrid models expected by the end of the project. Innowacyjność oraz oczekiwany potencjalny wpływ (w tym dotychczasowe znaczenie społeczno-gospodarcze i szersze implikacje społeczne projektu) In the first part of the project, some essential progresses have been obtained: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.
