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Final Report Summary - INTELLECT D.M. (Integrated lean low emission combustor design methodology)

The objective of the INTELLECT D.M. project was to develop a design methodology for lean burn low emission combustors and to achieve a sufficient operability over the entire range of operating conditions whilst maintaining low NOx emission capability. A knowledge-based design system forms the framework to capture existing combustor design knowledge and knowledge generated in this project.

Through pressing demand for emission reduction, very ambitious future NOx reduction targets of 80 % by 2020 have been set. Existing design rules, for conventional combustion systems, cannot be applied for lean low emission combustors. It is, therefore, important to embody new design rules quickly, so that the new technology can be incorporated faster into future products.

The aim was to create the first building blocks of such an integrated combustor design system. The system incorporates preliminary design tools to make first estimates of the arrangement for lean burn combustion, which meets operability, external aero-dynamics, cooling and emissions needs.

Guidelines for the design of lean low NOx combustors for reliable and safe operation were derived. There was an incorporation of these guidelines for lean low NOx combustion in the knowledge based combustor engineering tool in order to strengthen European competitiveness by reducing development costs and time.

Lean blow out limit, ignition and altitude relight were investigated. The air flow distribution and the aero-design of pre-diffusers for lean low NOx combustion with up to 70 % air consumption were optimised. Wall temperature prediction and testing for highly efficient cooling design were performed. An assessment of generated knowledge and implementation in the knowledge based system has taken place.

The project consisted of seven work packages (WPs), as follows:

WP1: Management
The project was implemented according to plan although two extensions had become necessary due to technical issues with highly complex test facilities. All partners have completed the entire technical project work as planned successfully.

WP2: Knowledge-based combustor
The knowledge-based engineering (KBE) tool developed under this WP by Rolls Royce and Rolls Royce Deutschland is the corner stone for capture and application of future lean low NOx design methodology.

Key design parameters and the models to be integrated have been identified, as well as the way they fit into the preliminary design process. All major data-flows driving the preliminary design have also been captured. Work has been done to identify the combustion system module's interface. A one-dimensional (1D) combustor aerodynamical model has been integrated into the system as well as an export into Unigraphics for automated meshing and an automatic tool for the simplification of technological details. This integration has been performed on the Technosoft platform and is based on AML language.

In parallel, a parametric injector has been added to the combustor CAD model by the University of the Bundeswehr in Munich and linked to the Excel database. The mesh generation in ICEM-CFD is automated via a replay file, which is generated and exported by the Excel database after every calculation. Computational fluid dynamics (CFD) simulations are performed automatically. The CFD results are judged by an experienced design engineer and input parameters are changed within the Excel spreadsheet if necessary.

ONERA developed an optimisation method based on response surface model and applied it on the two-phase flow optimisation of a Turbomeca lean premixed prevaporised (LPP) injector. Because optimisation requires a lot of computations, the basic idea was to define a surrogate model reproducing the behaviour of the complex system with a short restitution time.

This response surface model (a multilayer perceptron neural network) was used in the optimisation process instead of the two-phase flow code to decrease CPU time. This chain was applied on a Turbomeca LPP injector optimisation computed in axisymmetrical two-dimensional (2D). The results obtained have been exploited by Turbomeca to enhance the performances of low NOx injection technologies for small gas turbines applications. CERFACS developed a fully automated optimisation loop based on the coupling device PALM. The main optimisation strategy adopted consists of a surrogate-based method. It allows treatment of mono and multi-objective problems with reduced clock time. This strategy was tested on simple 2D cases and then applied to the three-dimensional (3D) optimisation of a Turbomeca combustor radial exit temperature profile.

WP3: Ignition capability
The implementation of a Monte Carlo code for the simulation of the LEPDF spray equation was concluded by M14. The code is capable of simulating the large eddy behaviour of a gas flow in which a spray is injected. The LES equations for the gas-vapour mixture phase are coupled with a probabilistic description of the spray. A Monte Carlo integrator code for particles dynamics has been incorporated into the LES Boffin solver. The implementation includes droplet transport, droplet heating and vaporization, droplet break-up and a special treatment for injector boundary conditions. The implementation allows both one-way and complete two-way coupling between the droplet and gas phases. It has been demonstrated that small droplets typically present in a spray may enhance the rotational strength of coherent structures. As a consequence these structures, which are the major cause of droplet dispersion, are responsible for droplet concentration and vapour fields that are highly discontinuous. These findings may be of use in combustion chamber design; atomiser diameter and fuel inflow directions may be tailored to minimise segregation effects and thus non-vaporised and un-burnt liquid fuel.

WP4: Stability and extinction
The development of lean burn technology for single annular combustor architecture has been pursued. The emissions performance of the LP(P)5, the LPX1, the LPX2 and the LN2B have been investigated. Two configurations of the LN2B fuel injector have been investigated for their emission performance. The HPSS investigations were carried out applying an effusion cooled combustor liner, which was inserted in the test rig for the determination of realistic combustion efficiency.

They feature V-shroud flame stabilisers for improved weak extinction capability, airfoil guide vanes for aerodynamic quality and effective area. The NOx emission performance demonstrated in the HPSS test rig was the best of all injectors investigated. The C13 configuration achieved a NOx reduction of 77 % (as measured) relative to the CAEP/2 emission certification standard. The C22 configuration achieved 74 % NOx reduction. The cruise efficiency of 99.2 % is lower than required.

For the first time ever, a Fischer-Tropsch GTL has been investigated for its NOx performance and compared with emissions from conventional petroleum based Jet-A1 kerosine. The investigated GTL contained special molecules.

In the context of the emissions results, it has to be noted that this fuel is just one example and is probably not representative for all GTL fuels available at the present time. It is recommended to gather more experience with the emissions performance of fully and semi-synthetic fuels in conjunction with lean burn modules. However, the data which summarised the NOx performance, showed that the NOx emissions in terms of DP NOx,c / Foo increase by 18 %. The cruise NOx is increased by 11 %. Although there are virtually no aromatics in the GTL, the soot / particulate matter emissions seem to increase slightly for fuel staged conditions (i.e. +5 % for cruise). For fuel rich pilot burner operation (e.g. 7 % and 30 % thrust parameters) soot has been found to be 40 to 50 % reduced compared to petroleum Jet-A1. The combustion efficiency of GTL at cruise was 0.2 %-points down compared to petroleum Jet-A1.

WP5: Technology assessment
The main objective of WP5 was to carry out an assessment of the technology improvements achieved within the physics-based work packages (WP3, WP4, WP6, WP7) with a view to formulating new design guidelines where possible. Considering the diversity of the combustion-related topics worked on within Intellect DM, WP5 aimed to collate the various contributions, highlight the progress made and identify remaining gaps.

According to plan, the assessment focused on three different topics: evaluation of progress with respect to:
- the state of the art of the emissions achievable with piloted lean burn design concepts;
- evaluation of progress made on the development of diffuser technology for lean burn; and
- evaluation of effective calculation methods for cooling.
The delay affecting some of these deliverables simply reflected the need to wait for the physics-based tasks to complete before the assessment could be carried out.

WP6: External aerodynamics

WP7: Combustor cooling design
The assessment of combustor cooling aspects for lean burn systems was the key point of the activities carried out in this WP. The exploitation of results from other European projects has been done, as well as the validation of conjugate design procedure against experimental results and anisotropic CFD turbulence modelling implementation (University of Florence, SNECMA and CNRS). The simulation of effusion cooling devices with RANS-CFD has been carried out by SNECMA. In the same task CERFCAS developed and validated a LES based strategy to simulate an effusion cooling system in an isolated and controlled environment for a suitable generation of a numerical database from which models can be obtained to simulate such systems in real CFD-RANS solvers (experimental results were provided by Turbomeca).

The achievements were: the definition of a number of cooling devices, the evaluation of possible coupled solutions (impingement-pin fin, impingement- ribs), the evaluation of innovative effusion cooling geometries, the selection of innovative cooling devices for experimental studies (AVIO, University of Florence).