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

Abstract

Developing low-emission aero-engines presents a critical step in meeting near-term climate goals. A particular challenge is accurate soot predictions with computational fluid dynamics (CFD), where the integration of advanced thermochemical interaction models is required. The extreme conditions typical of aero-engines—characterized by high temperatures, elevated pressures, and strong transients—demand reliable and accurate modeling to capture the complex pathways of soot formation and oxidation. This study focuses on the soot formation, evolution, and oxidation in a single-sector rich-quench-lean (RQL) aeroengine model combustor, employing high-fidelity numerical simulations validated against experimental data obtained as part of this investigation. Based on the validated simulation results, the high-fidelity large eddy simulations (LES) coupled with the splitbased extended quadrature method of moments (S-EQMOM) soot model are used to examine soot dynamics within the combustor. The LES predictions accurately reproduce experimental trends across a range of operating conditions. By categorizing the combustor flow field into distinct zones—flame, mixing, recirculation, and a transition between flame and mixing—the study provides a detailed quantification of soot behavior. Soot formation and growth are predominantly confined to the flame zone, while oxidation occurs throughout the chamber, reducing the soot volume fraction. High mixing rates corresponding to very low local residence times prevent complete soot oxidation, increasing the probability of soot breakthrough into the lean region. These findings provide critical insights for developing reduced-order models that efficiently predict soot formation. Such models are essential for reducing computational costs and advancing the design of future low-emission aero-engines. (LES) with advanced combustion and soot models. This approach allows for consistent simulations from fuel breakup to soot formation and enables a detailed investigation of the complex interactions between spray dynamics and soot under enginelike conditions. To accurately capture the primary breakup, the fuel spray particle size distribution (PSD) is sampled from SPH simulations and used to initialize Lagrangian spray particles in the LES, where secondary breakup and evaporation are predicted. The objective of this work is to apply these methods to a single-sector aero-engine combustion chamber operated at elevated pressure and high preheating temperatures, with an aeroengine fuel injector geometry, and to investigate the influence of spray dynamics on soot formation. Comparison with experimental data demonstrates that the applied methods accurately capture the overall flow and combustion characteristics. Spray characteristics sampled from SPH simulations significantly improve the accuracy of mixing and soot formation predictions compared to conventional spray representation approaches. Furthermore, an extended analysis across various operating ranges demonstrates that spray initializations tailored to the respective conditions are essential for achieving accurate pollutant predictions.