SOot in TUrbulent Flames: a new look at soot production processes in turbulent flames leading to novel models for predictive large eddy simulations

Project Information

SOTUF

Grant agreement ID: 757912

DOI

10.3030/757912

Project closed

EC signature date 17 November 2017

Start date 1 June 2018

End date 31 May 2024

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 436 330,00

EU contribution

€ 1 436 330,00

Coordinated by

CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE CNRS
France

Periodic Reporting for period 4 - SOTUF (SOot in TUrbulent Flames: a new look at soot production processes in turbulent flames leading to novel models for predictive large eddy simulations)

Reporting period: 2022-12-01 to 2024-05-31

Summary of the context and overall objectives of the project

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 had successfully demonstrated its capacity to represent gaseous turbulent combustion processes, was far from being predictive for soot emission at the beginning of the SOTUF project.
In this context, the goal of the SOTUF project was to provide new insights on the collisional and chemical processes governing soot production in turbulent flames to characterize its specific nature and to develop an high-fidelity numerical framework, encompassing the state-of-art and allowing reliable predictions of soot in turbulent flames. For this, the following objectives have been achieved: (1) the turbulence-flame-nanoparticles coupling has been characterized using advanced space and time-resolved optical diagnostics; (2) a new high-fidelity simulation framework has been developped by combining reduced kinetics, sophisticated methods for the description of the particle size distribution and subgrid models to account for unresolved turbulence effects on nanoparticle evolution; (3) the capability of the developped numerical framework strategy to reproduce soot trends in complex systems was proven. The obtained research developments have the potential to drastically improve the prediction of soot production in industrial configurations, helping the design of new low-emission systems with notably reduced soot levels.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

During the project, a novel strategy has been developped based on the study of TiO2 nanoparticles, which are submitted to the same collisional processes than soot particles to perform complementary investigations without the chemical complexities characterizing soot production. Thus, all along the project, studies on TiO2 production have been performed jointly to activities on sooting flames.
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 complexity were first implemented: laminar diffusion flames with a pre-vaporized injection of liquid precursors, perfectly-premixed turbulent swirled flames, turbulent spray jet flames. Second, various developments on optical diagnostic techniques were provided. The most relevant achievement consists in the extension of the laser induced-incandescence (LII) technique, originally developped for soot particles, to the study of TiO2 production in flames by characterizing its volume fraction, mean primary particle size and absorption function. These configurations have been studied in the second part of the project using the developped advanced optical diagnostics for soot or TiO2 production to characterize turbulence-flame-nanoparticles coupling. Concerning simulations, new detailed chemical models for the production of nanoparticles and simplified models to account for particle size distribution have been developed in a laminar context. These reduced methods allow to reduce the CPU cost of the simulations allowing to perform high-fidelity simulations of turbulent configurations and parameteric studies of model combustors. Besides, new approaches have been proposed to validate in a rigorous way the subgrid models that have been developped based on variance approaches to correctly account for NP ligaments behavior that cannot be resolved on actual simulations grid due to their negligible diffusivity. New paradigms have been proposed to validate a posteriori the developped submodels in a consistent way with experiments or/and reference simulations. The final combined experimental/numerical approach is today available for the engineering study of the effect of the flame environment on soot emission when considering sustainable aviation fuels or renewable synthetic fuels, essential for the engineering design and next generation of ‘zero-emission’ combustors. The developped combined strategy is also of great interest for the optimization of the aerosol technology for the flame synthesis of functionalized nanoparticles, with application in energy storage and conversion, for example.
The results obtained have led to 11 peer-reviewed articles in major international journals, more than 25 oral presentations and 7 invited presentations. A strong science divulgation activity has also been done by the team with, notably, two youtube videos (https://www.youtube.com/watch?v=kNH3WaKcDkk) and (https://www.youtube.com/watch?v=CsgoB8Bbzfc&t=1s) more than 2400 and 25000 views, respectively.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The SOTUF researches have led some major achievements:
1) Advanced optical diagnostics, originally developped for the study of soot production (LII, laser scattering, shadowgraphy, OH* chemiluminescence) have been extended to the study of TiO2 techniques and are today available for the study of flame-made nanoparticle synthesis for the optimization of flame spray pyrolysis systems.
2) A whole high-fidelity formalism for the study of TiO2 flame synthesis has been developped by accounting for a detailed description of gas kinetics, of the particle size distribution and of subgrid turbulence effects on nanoparticle evolution based on mixing subgrid models.
3) By comparing soot formation with TiO2 synthesis with both experiments and numerical simulations in similar reactive configurations, it has been observed that soot presence is a rare event that strongly depends on the local environment and its own history, unlike TiO2. This is due to the fact that long characteristic time scales characterize soot production, requiring the developments of specific experimental and numerical tools that have been proposed in the ERC framework.
4) New approaches have been developped combining high-speed measurements and numerical synthesis of laser signals from simulations to consistently compare experimental and numerical results on soot production.
5) The effect of the flame environement on soot production in a model combustor representative of industrial applications has been characterized experimentally by considering various equivalence ratio, flame power, wall temperature and burner’s geometries. The formalism proposed for the numerical simulation of soot production is capable to reproduce the experimental trends for a low CPU cost.
The proposed approach combining experimental and numerical framework is today ready to be extended to the study of soot emission when using synthetic fuels or energy mix with H2 to guide the design of future ‘zero-emission’ combustion systems, fully satisfying the central objective of the ERC SOTUF project.

Summary of the ERC SOTUF project