Session: 04-22 Combustion - Emissions II

Submission Number: 177276

Large Eddy Simulation Study of Fuel Sensitivity in a Realistic Aeroengine Combustor 

While relying on fossil-based jet fuels, aviation contributes around 3% of global CO₂ emissions and 5% of global warming, also emitting NO_X, soot, and producing contrails. Sustainable Aviation Fuels (SAF) offer a near-term drop-in solution, and can potentially reduce life cycle emissions by up to 35% depending on the production pathway. While SAF must meet ASTM standard thermophysical requirements, their distinct chemical makeup can drastically affect spray, evaporation, and combustion behaviors under aeroengine-relevant conditions. For instance, modern jet engine combustors are compact, high-performance systems operating under tight spatial and thermal constraints. Efficient combustion, minimal pressure loss, NO_X reduction and outlet temperature are critical, involving flow deceleration, flame stabilization, staged air injection, and complex cooling strategies. Hence, SAF's unique properties necessitate detailed evaluation in such environments. In this context, the EU-funded project MYTHOS aims to develop a flexi-fuel aeroengine architecture capable of operating with various SAF blends. A multi-fidelity methodology is employed, combining zero-dimensional (0D) thermodynamic models for engine cycle simulations, three-dimensional (3D) Finite Rate Chemistry (FRC) Large Eddy Simulations (LES), and experimental validation.

Component-level geometry and dimensions were derived from 0D engine cycle simulations, ensuring coherence with the parallel development of compressor and turbine sections. A modern annular combustor was designed, featuring a downscaled academic triple swirler injector, previously investigated numerically and experimentally, a dump-type pre-diffuser and a Rich-burn Quick-mix Lean-burn (RQL) strategy with staged air injection (primary, mixing, dilution holes). The design comprises 18 burner heads and uses film cooling and a front heat shield, similar to the Rolls-Royce Z-Ring. This integrated approach, linking thermodynamic simulation with combustor geometry generation, lays the groundwork for subsequent high-fidelity combustion simulations and fuel-sensitivity studies. In particular, in the present work, unsteady, reactive flow LES are performed following a state-of-the-art methodology employed in similar works, with ideal gas equation of state, constant Prandtl and Schmidt numbers, and the Localized Dynamic k-equation model for subgrid turbulence closure. Finite-rate chemistry is computed with Arrhenius kinetics, coupled to the LES-Partially Stirred Reactor combustion model, using the compact Z79 reaction mechanisms for Jet A and for one SAF candidate, referred to as Alcohol-to-Jet C1 (ATJ C1). Additionally, a 19-step NO_X scheme is employed, and the liquid fuel injection is treated via Lagrangian Particle Tracking.

This work presents the modelling of a single sector of the Mythos aeroengine combustor under Jet A and SAF operation. The study focuses on the use of (Alcohol to Jet) ATJ C1, in comparison with conventional Jet A, and investigates the effects of the fuel at both cruise and take-off conditions. Another parallel study focuses more on the virtual certification of the developed design across various mission points, solely using Jet A, and includes a detailed mesh sensitivity study on the on-design condition, i.e., cruise operation. One main objective of this study is to gain insight into the fuel effects on the flame dynamics, heat release rate in the chamber, species formation, temperature distribution across the flame tube and on the liners, pattern factor at the combustor exhaust, as well as potential thermoacoustic coupling mechanisms. The results will be used to identify which features should be modified to achieve a compromise design that responds as robustly as possible to variations in fuel. This particularly addresses how the combustion chamber manages varying fuel-air ratios with different fuel compositions or different fuel mass flows under the same operating conditions, as well as the resulting effects on flame tube cooling. In summary, the overarching objective is to identify major discrepancies between conventional and alternative jet fuel operation on a realistic aeroengine platform and to inform potential design optimization pathways aimed at fuel-flexibility and SAF integration.

Presenting Author: Pierre Vauquelin Lund University

Presenting Author Biography: Mr. Pierre VAUQUELIN graduated with a Mechanical Engineering degree from the French National Institute of Applied Sciences in 2022. He worked within MTU Aero Engines in Munich, Germany, where he focused on combustion CFD simulations of aeroengines combustors and completed a one-year research degree with his French university. Since October 2023, Mr. VAUQUELIN is a PhD student at Lund University, Sweden. He mainly performs high-fidelity simulations of swirl-stabilized flames, typically used in aircraft gas turbine combustors, to evaluate the combustion dynamics of sustainable aviation fuels. He also investigates grouping and mapping approaches to improve the efficiency of finite-rate chemistry LES.

Authors:

Pierre Vauquelin Lund University
Jan Donndorf Ruhr-University Bochum
Federico Lo Presti Ruhr-University Bochum
Francesca Di Mare Ruhr-University Bochum
Xue-Song Bai Lund University
Christer Fureby Lund University