Fly with SAFs for a safe environment – FlySAFe

Aeronautics has set ambitious goals in its fight against climate change that aim at increasing fuel efficiency and reducing greenhouse gas emissions. A promising mid-term path relies on drop-in Sustainable Aviation Fuels (SAFs) using the same engines and fuel distribution infrastructure while avoiding injection of carbon in the biosphere. To enhance the environmental benefit, SAFs can be used with the lean burn architectures, a disruptive technology able to reach the target of NOx reduction while limiting CO formation. But liquid fuels by their complex composition and impact on atomization and evaporation can change the combustion dynamics of the system. It is then important to examine the nonlinear processes susceptible to induce combustion/acoustic resonant coupling. This may lead to large amplitudes oscillations of pressure, velocity and heat release rate that are most dangerous when they involve azimuthal modes. To deal with the complexity of SAF’s composition, the FlySAFe project proposes to use surrogates which emulate properties of the target SAFs derived from biomass. It aims at responding to the following issues: (1) What are the dynamical features of swirling spray flames fed with a binary liquid surrogate with components having different evaporation rates when combustion interacts with longitudinal and azimuthal/transverse acoustic modes? (2) What are the effects of collective interactions of multiple injectors on the combustion dynamics of the system when neighboring injectors are fed with multicomponent liquid fuels? To deal with the complexity of these issues, laboratories CORIA, EM2C and CERFACS propose to combine advanced experimentation, modeling and high-performance simulations working with the same sets of injectors. Experiments will be performed by means of 4 original setups: an annular combustor MICCA-Spray comprising 16 swirling spray-flames, potentially unstable to acoustic longitudinal and azimuthal modes and 2 chambers, SICCA (single injection) and TICCA (3-injection), forced by longitudinal waves (EM2C laboratory); a linear 5-flame array combustor TACC-Spray, simulating an unfolded sector of the annular combustor, forced by transverse waves (CORIA laboratory). The large eddy simulation of flames formed by multi-component fuel developed by CERFACS for SAFs will serve to simulate the spray-acoustics coupling and the combustion-acoustics coupling, especially in multiple flame injectors. FlySAFe, organized in 4 main scientific tasks strengthened by exchanges between laboratories, will use the elements obtained from this combined research to advance low order models describing the acoustic response of annular combustors, and within the Helmholtz solver AVSP developed by CERFACS to calculate the system dynamics and combustion instabilities coupled by azimuthal modes. This project aims at facilitating the prediction of thermo-acoustic instabilities and thus avoiding dynamical phenomena that reduce the engine operability ranges, induce vibrations and cyclic fatigue possibly leading to the mechanical degradation of the combustion chamber. The methodological advances of this project can both provide answers to fundamental questions in the field of combustion dynamics and keys for the use of SAFs as a replacement for kerosene. The objectives are in line with goals set by engine manufacturers (like Safran) and with the stakes of the scientific axis H.9: A sustainable, clean, safe and efficient energy, and with those of the SDG no. 7: ``affordable and clean energy’’ defined by the UN 2030 Agenda.