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Technology Enhancements for Clean Combustion

Tags: Air

State of the Art - Background

Over the next 20 years, air traffic is expected to grow annually by 3% for passengers and 9-10% for freight volume (ACARE 'average' scenario). This traffic growth will continue to affect the environment with:

- increased greenhouse effects (CO2 emissions);

- degradation of local air quality (NOx, but also particulates and CO emissions as well as UHCs - un-burnt hydrocarbons).

The engine emissions issue is addressed by the evolution of the corresponding international regulations (e.g. ICAO CAEP standards) and by ambitious technological objectives agreed by the European aeronautics industry, as described in Vision 2020 and the second version of the ACARE Strategic Research Agenda.

The availability of clean engines would not only have a huge environmental impact, but has also become a vital stake for every manufacturer to remain as a player within the world competition for sustainable growth of aviation transport. Developing combustion technologies for clean engines is consequently mandatory to comply with the ambitious ACARE 2020 targets and future ICAO standards, to gain new markets and to remain competitive.

Despite several ambitious R&T projects addressing engine emissions over the years, these technologies have not yet been brought to the level required for introduction into service with the necessary reliability, safety and proven economical viability.


The scientific and technological objectives are:

1. To solve the main limitations identified during past and ongoing projects which appear when lean combustion is pushed toward its maximum potential regarding NOx emission reductions. In particular the targets are:

- to provide full combustor operability in terms of ignition, altitude relight and weak extinction performance;

- to suppress the occurrence of thermo-acoustic instabilities by reducing the combustor sensitivity to unsteady features to such a level that instabilities will not happen;

- to ensure injection system robustness with respect to coking that can appear during transient operations of the engine;

- to develop, demonstrate and validate design rules, CFD capabilities and scaling laws;

- to provide knowledge for global optimisation of the multiplicity of combustion parameters of lean combustion systems to achieve lower flame temperatures and thus lower thermal NOx formation (e.g. homogeneous fuel-air mixtures, cooling and unsteady behaviour optimisation).

2. To look even further ahead and to overcome the complexity issues inherent in staged lean combustors. The TECC-AE project will also aim to design and assess an innovative, compact, lighter and simplified lean combustion combustor concept, and to develop a compact Ultra Low NOx (ULN) injection system.

Description of Work

To achieve an 80% reduction in NOx emissions for a commercial engine by 2020 without compromising operability and CO/UHC emissions it is also necessary to address in parallel the industrialisation of the system. This means there is a need to take into account weight, simplification and cost issues to deliver a solution that is easy to produce and then maintain.

The TECC-AE approach will be worked in parallel:

1. the development of the technology to guarantee an 80% reduction in NOx emissions;

2. the overall design of the combustor and injection system to achieve a simpler, lighter and more economic lean combustion system.

TECC-AE has been divided into four main technical work packages:

- Enhanced operability for staged injection systems;

- Thermal management;

- Sensitivity to unsteady features;

- Innovative technologies.

Three additional work packages are included: the first will be dedicated to the management of the project, and the last two to the exploitation and the dissemination. Regarding the exploitation, the complete synthesis and assessment of lean combustion regarding the ACARE 2020 objectives will be done by taking into account the results of previous projects as well as the TECC-AE outputs. The strategy and the main principles on how to design the best combustor, taking into account all the available knowledge, will then be established.

Expected Results

TECC-AE will have a major impact on short and long-term engine manufacturer competitiveness as it will provide:

- an acceleration towards the entry into service for lean technologies based on internally staged injection systems;

- knowledge and material for optimising the relevance of the technological strategy developed during the R&T phase to gain excellent performance (both operational and environmental) while maintaining exploitation costs at market acceptance levels;

- an increase of the technology robustness regarding some vital trade-off (NOx emissions reduction/combustor durability, transient operations/coking, CO-UHC emissions/NOx emissions);

- knowledge and multi-physics CFD methodology for scaling technology and for carrying out performance optimisation for the whole combustion system, ensuring that the product will have optimal environmental and operational performance;

- an extension of the acquired knowledge to the problem of lean combustion and its embodiment into a more or less automatic system, (which is of vital importance for ensuring that the combustion system will be designed within the shortest possible time, and will fully meet its operational and environmental objective performance).