Session: 04-40: Emissions III

Paper Number: 153105

Exploring Soot Pathways: High-Fidelity LES Investigation of Soot Formation and Oxidation in RQL Combustion Systems Under Real Conditions 

Reducing emissions is a key challenge in developing next-generation aircraft engines. Effective optimization requires a comprehensive understanding of the underlying physical and chemical processes.  Accurately predicting soot formation, evolution and oxidation remains particularly challenging due to the complex thermo-chemical processes involved. While previous studies have mostly investigated soot formation in simplified configurations, detailed numerical investigations under realistic operating conditions remain scarce.

Accurate soot predictions using computational fluid dynamics (CFD) require detailed descriptions of the gas-phase chemistry and advanced soot models that account for the various formation and evolution pathways. However, existing detailed soot models typically require increased computation costs, limiting their application in design optimization, where multiple configurations must be analyzed in relatively short times. Hence, detailed knowledge of soot development pathways under technically relevant conditions is essential to design new reduced order soot models.

This study presents a detailed analysis of the pathways of soot evolution under engine-relevant conditions, including elevated pressure and high preheating temperatures, using high-fidelity and massively parallel CFD simulations. Soot formation is investigated in a single-sector rich-quench-lean (RQL) aero-engine model combustor using highly-resolved large eddy simulation (LES) coupled with the split-based extended quadrature method of moments (S-EQMOM) soot model, which provides detailed, pointwise information on the soot particle size distribution (PSD). This model captures soot formation, growth, evolution and oxidation, making it an ideal tool for examining soot behavior across the RQL combustor zones.

Simulation results are compared to available measurement data. The high-fidelity LES setup used for this work enables a detailed analysis of soot evolution mechanisms in distinct regions of the combustion chamber and their interaction with the local gas phase chemistry. While average trends provide a broad understanding, local transient effects are crucial for a complete characterization of the involved mechanisms, such as soot breakthrough into lean regions of the combustor, especially under high load conditions. To gain further insight, particular attention is placed on the role of soot oxidation and its sensitivity to varying operating conditions and local flow dynamics. Results show that soot oxidation is significantly influenced in the near-wall region and in the quenching zone due to increased scalar dissipation rates and rapidly decreasing temperatures, leading to reduced oxidation timescales and higher soot emissions. These findings are quantified and compared to recently published correlations from the literature.

Overall, this study enhances the understanding of soot formation pathways and their spatial distribution in RQL combustion. It highlights the important role of local flow dynamics on soot formation mechanisms, providing valuable insights for optimizing combustion systems. This knowledge  is crucial for the development of advanced reduced order models that can accurately predict soot formation with decreased computational costs used in the design of next-generation sustainable aero-engines.

Presenting Author: Philipp Koob Technical University of Darmstadt

Presenting Author Biography: Philipp Koob obtained his M.S. at the Technical University of Berlin in Engineering Science. Since 2021 he is a research associate at the Institute for Simulation of reactive Thermo-Fluid Systems at the Technical University of Darmstadt. He works in the field of emission modeling in gas turbine engines using numerical methods.

Authors:

Philipp Koob Technical University of Darmstadt
Federica Ferraro Technische Universität Braunschweig
Eggert Magens German Aerospace Center
Johannes Heinze German Aerospace Center
Thomas Soworka German Aerospace Center
Thomas Behrendt German Aerospace Center
Ruud Eggels Rolls-Royce Deutschland Ltd & CO KG
Christian Hasse Technical University of Darmstadt
Hendrik Nicolai Technical University of Darmstadt