Because of a pressing demand for emissions reduction, very ambitious future NOx reduction targets have been set of 80% by 2020. Existing design rules for conventional combustion systems cannot be applied for lean low-emission combustors. It is therefore important to define new design rules quickly, so that the new technology can be incorporated faster into future products.
The objective of this project was to develop a design methodology for lean burn, low-emission combustors to achieve a sufficient operability over the entire range of operating conditions whilst maintaining a low NOx emission capability. A knowledge-based design system will form the framework to capture existing combustor design knowledge and knowledge generated in this project.
The aim is to create the first building blocks of an integrated combustor design system. The system will incorporate 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 developed. These guidelines will be incorporated 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 airflow 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 a highly efficient cooling design will be performed. An assessment of generated knowledge and implementation in the knowledge-based system took place.
The project consisted of seven work packages (WPs), as follows:
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.
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 technolog
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).