Barcelona, 13 June 2022 - After the first three years of the project, ESTiMatE researchers have developed a set of advanced tools to obtain further understanding of the process of soot formation in aeroengines. The ambitious objectives of the European Union to reach net-zero emissions by 2050 have strongly urged research on developing new combustion technologies for ultra-low emissions aircrafts. One of the most harmful pollutants produced in aeroengines is soot, a conglomeration of carbon atoms of a wide range of sizes that deteriorate air quality and cause respiratory problems. The great concern about its impact on human health and the environment has triggered intense research in the aeronautical community. Despite the significant advances made in this field, there are still many open questions about the mechanisms governing soot in practical conditions. Soot formation is a highly complex physicochemical process that is originated in the gas phase by the formation of PAHs (Polycyclic Aromatic Hydrocarbons) that are eventually converted into solid particles through the process of nucleation. The processes of soot formation and growth involve nucleation, coagulation, agglomeration, and oxidation, and many of them are still not fully understood. Besides, a complex interaction exists between all these processes with the turbulent flow field. Appropriate numerical tools are required to describe the physics at all the scales. Along this line, the ESTiMatE researchers focused on the development of advanced soot models based on first principles that can be integrated into Computational Fluid Dynamics (CFD) codes.
A new reaction mechanism for Jet-A1 fuels including soot chemistry was derived to describe the chemistry of the fuel oxidation. A great effort was put into the chemistry of the PAHs (Polycyclic Aromatic Hydrocarbons) like benzene, naphthalene, etc., up to pyrene. PAHs play a fundamental role during soot nucleation and accurate chemistry models are required to correctly represent the inception process. that. A wide range of conditions were tested, and large datasets with detailed information of the thermochemical states were generated. These experimental datasets, which are shared with ESTiMatE´s industrial partner Rolls Royce, will enable future model developments of soot oxidation chemistry and also assessment of CFD models for sooting flames. This chemistry is integrated into the CFD codes Alya, OpenFoam and PRECISE-UNS to evaluate the influence of the combustion model and the treatment of turbulence-chemistry interactions on the predicting capabilities of the soot models. Two different strategies to describe the soot particle distributions are compared, which are based on the method of moments, and the discrete sectional method. As fuel atomization plays a fundamental role in fuel/air mixing, and consequently in pollutant formation, especially soot, dedicated effort is given to develop spray breakup models that can be integrated in Lagrangian simulations to represent complex breakup events at reduced cost.
“After achieving this milestone, we are now working on the application of soot models we recently developed with Large Eddy Simulations to predict soot formation in two new combustion test rigs with high instrumentation,” said Daniel Mira, BSC senior researcher and ESTiMatE coordinator. “This investigation will help us to obtain better understanding on the mechanisms of soot formation and develop higher fidelity models.”
These methodologies have been validated in laminar test rigs, and now they are extended to LES to investigate soot formation in more representative conditions. Two test rigs with increased level of complexity were selected to evaluate the different approaches. The first configuration is a turbulent counterflow flame that allows the study of the influence of the combustion model and turbulence-chemistry interactions on soot formation, while the second is a spray flame of an aeroengine-model injector of an airblast atomizer.
ESTiMatE is an European project, funded by the European Commission under the Clean Sky program, composed of seven European leading institutions in combustion science: the Barcelona Supercomputing Centre (BSC), the Technische Universität Berlin (TUB), the Universitat Politècnica de València (UPV), the Technische Universiteit Eindhoven (TUE), the Technische Universität Darmstadt (TUD), the Karlsruher Institut für Technologie (KIT) and the Universität Stuttgart (USTUT) in collaboration with Rolls Royce (RR). The project establishes a strong collaboration between industry and academia to develop advanced simulation technology that can be used to generate cleaner and more efficient propulsion systems. ESTiMatE proposes a multidisciplinary approach involving chemical kinetics development, application of optical and laser diagnostics, development of soot models, coupling soot models with CFD codes, and the use of High-Performance Computing (HPC) to increase the computational performance of the methods. Different disciplines are combined in ESTiMatE with the aim of developing predictive models for aircraft emissions.