Novel Fuel-Flexible ultra-Low Emissions Combustion systems for Sustainable aviation

Project Information

FFLECS

Grant agreement ID: 101096436

DOI

10.3030/101096436

EC signature date 9 October 2023

Start date 1 December 2023

End date 30 November 2026

Funded under

• Climate, Energy and Mobility

Total cost

€ 1 905 741,25

EU contribution

€ 1 905 741,00

Coordinated by

UNIVERSITA DEGLI STUDI DI FIRENZE
Italy

Periodic Reporting for period 1 - FFLECS (Novel Fuel-Flexible ultra-Low Emissions Combustion systems for Sustainable aviation)

Reporting period: 2023-12-01 to 2025-05-31

Summary of the context and overall objectives of the project

Improving Local Air Quality at airports while at the same time decarbonising aviation can be achieved by switching to sustainable aviation fuels (SAFs) and hydrogen, as confirmed by recent engine development programs. However, both these fuels require significant developments in the gas-turbine combustor because present technologies not only require to further reduce NOx and PM emissions as expected by long-term standards and objectives, but they also are not normally suitable for 100% direct combustion of hydrogen. In this project, revolutionary combustor architectures will be studied, extending the preliminary results of previous Clean Sky 2 "Innovative NOx Reduction Technologies" projects in terms of scientific scope and TRL. In particular, this project will advance
1) the Lean Azimuthal Flame (LEAFinnox), a novel combustion system based on Flameless Oxidation,
2) the Compact Helically Arranged combustoR (CHAIRlift), a new system which uses interacting lean lifted flames,
3) plasma and electric manipulation of the spray and of the flame stabilisation mechanism.
The fuel flexibility offered by these novel concepts is key to allow for SAF and H2 operations. This unique feature will be exploited to give novel dual-fuel LTO cycle strategies and ultra-low NOx, ultra-low soot, single or dual-fuel use. Experiments on available dedicated rigs and numerical work will be performed to provide knowledge at the fundamental and practical level that will allow TRL3 and higher developments at the end of the project. The project will include new CFD, low-order, and AI models, and novel stabilisation techniques ripe for commercial exploitation.
To achieve its main objectives, the research activities of the project FFLECS are arranged into three main technical work packages. Figure 1 shows a schematic representation of FFLECS WP structure where the interactions and links among tasks are pointed out.
Each WPs is expected to contribute to the main goals of the project. WP2 is focused on the investigation of the fuel-flexible operations of the LEAF and CHAIR concepts so to possibly extend the use of such technologies to low-carbon multi-fuel applications. WP3 will then investigate electromagnetic interactions fuel preparation, flame stabilization and emissions and will develop fundamental understanding to enable transition to electric control of emission performance. The development of numerical models and diagnostic tools for the prediction of engine emissions and their control will be carried out in WP4, with the contribution of all the other WPs.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

On a WP basis, the main results achieved in the first reporting period can be summarized as follows:
WP2 - Fuel flexible combustion systems
A first test campaign at ambient pressure was carried out at ETH to investigate LEAF combustor for fuel-flex operations with jet A-1/H2, and transition of jet A-1 to 100% H2. Figure 2 shows time-averaged OH* chemiluminescence images showing LEAF topology or L_CC = 60 mm and P_th = 10 kW (left); L_CC = 60 mm and P_th = 35 kW (middle); L_CC = 80 mm and P_th = 35 kW (right). ϕ_global = 0.8 ± 0.01 and ALR-4 are constant for three cases. OH* intensity normalised between 0 and 1.
A new dual-fuel version of the CHAIR burner concept was developed by KIT and UNIFI. A preliminary experiemntal validation was carried out at KIT at ambient pressure, ranging from 100% jetA up to 100% H2. Figure 3 reports time-averaged OH* chemiluminescence images of flame for varying H2/Jet-A1 fuel splits under different configurations: (a, b, e) Config 1, (c, f) Config 2, and (d, g) Config 3., relative pressure drop = 3%, air inlet temperature = 673 K, thermal power=31 kW.
A chemical kinetics scheme has been developed by UNINA starting from literature data. The kinetic mechanism includes the oxidation of a few representative hydrocarbons, which are important components of aviation fuel surrogates. The reaction mechanism is intended to well-represent the individual components as well as a multi-component surrogate for jet fuel made up of these fuel components. The full mechanism also includes reactions for pollutant formation: gaseous and condensed phase compounds, and NOx formation reaction pathways.
UCAM and UNIFI had worked to dual-fuel versions of the CMC and DTFM turbulent combustion models for LES investigations. Models are under validation on the well known Cambridge Swirl flame operated with heptane and hydrogen
WP3 - Electric-fields assisted combustion and fuel preparation
A test rig to investigate plasma assisted combustion on the CHAIR concept is under final development and commissioning at UNILE.
Reactive molecular dynamics (MD) simulations have been used by IC to investigate the effects of an electric field on the reaction dynamics of a fuel representing SAF. Results are detailed in the first journal article published within FFLECS project (https://doi.org/10.1063/5.0264365)
KIT/EBI is involved in the modelling of the atomization process in electro-sprayers within SPH code. First investigations confirmed that the electric charge of the liquid will significantly affect surface tension and may even lead to zero effective surface tension for large droplets thus improving the atomization process. IC has carried out an investigation by the means of CFD calculations (OpenFOAM) to verify the chance of controlling the trajectory of charged fuel droplets in a number of configurations relevant for aviation applications. Also in this case results have been reported in a journal paper (https://doi.org/10.1016/j.ijmultiphaseflow.2025.105289).
WP4 - Integration and emission prediction
With the contribution of all the partners, a set of reference engine cycle thermodynamic conditions has been selected for the investigation of the developed combustion concepts up to full-scale conditions. A small engine cycle (typical turbopropo engine) and a classical high pressure turbofan engine cycle were defined.
Task 4.1.2 has seen the consolidation of the conceptual design of CHAIR and LEAF combustion technologies and related plasma assisted operations. Full details are reported in Deliverable D4.2.
UNINA is currently collaborating with KIT and ETH to use two sensors, one for temperature measurements and the other for particulate matter (PM) measurements, to enable active combustion control.
KIT teams is developing a machine-learning-based digital twin to control flame instabilities in low-emission combustors. As part of this effort, time series data from ion probe sensors are being collected by project partners at KIT/EBI to characterize flame behavior and predict lean blowout (LBO) events.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Promising results have been achieved so far, showing unconventional dual-fuel operations with two different combustion concepts, which are expected to have a significant future impact. Experimental investigations are supported by novel CFD models for dual fuel flames, which are expected to represent a clear improvement with respect to state of the art.
Relevant novelty and progress beyond current knowledge is represented by achieved results on the use of electric fields to control spray atomization.

Figure 1 - WP structure of FFLECS project

Figure 3 - CHAIR burner configurations operated for varying H2/Jet-A1 fuel

Figure 2 - Time-averaged OH* chemiluminescence images showing LEAF topology at different conditions