Lean-burn combustion technology is identified to be the key technology for aero-engine combustion systems to achieve future legislative requirements for NOx. The lean-burn low NOx combustor development at Rolls-Royce Deutschland RRD for the upcoming generation of aero-engines is presented, which has been supported by the German aeronautical research programme. The down selection process of different injector concepts is described in detail to develop lean-burn fuel injection technology up to a technology level for engine application. Initial concept validation with testing on single sector combustion rigs applying advanced laser measurement techniques is followed by high power single sector emission tests to prove low emission characteristics. Climbing the level of technology readiness, which is in each phase substantiated by intense CFD simulations, the most promising low emissions design concepts have been investigated for unrestricted combustor operability compared to conventional rich burn systems. Altitude relight, weak extinction margins, fuel staging optimisation and combustion efficiency in the vicinity of staging points have been optimised on different sub-atmospheric, atmospheric, medium and high-pressure test vehicles. The validation process concludes with sub-atmospheric and high-pressure testing within a fully annular test environment before the final lean-burn fuel injector configuration has been selected for core engine testing to prove emission performance and operability of the fuel-staged combustion system. Two fuel injector configurations were successfully tested in a high-pressure fully annular rig. The combustor module and both injector standards have been cleared for core engine operation.

Engine 3E is the aero engine part of the German Aeronautics Research Program under which Rolls-Royce Deutschland developed key technologies for an all new core engine that incorporates major advances with regard to environmental friendliness, efficiency and economy. The derived E3E core engine will serve as a scalable baseline for the future two-shaft engine family in the medium take-off thrust range between 12 – 40 klb. The core consists of a highly loaded 9-stage HPC, a lean burn combustion chamber with internal fuel staging and a 2-stage shroudless HPT. On the basis of its high specific power, low NOx combustion and low manufacturing cost, it will enable significant improvements in SFC, emissions, unit cost and weight. The related technology demonstrator is currently in the final build and instrumentation phase for testing in an altitude test facility in first quarter 2008.

For lean burn combustor development in low emission aero-engines, the pilot stage of the fuel injector plays a key role with respect to stability, operability, NOj¡ emissions, and smoke production. Therefore it is of considerable interest to characterize the pilot module in terms of pilot zone mixing, fuel placement, flow field, and interaction with the main stage. This contribution focuses on the investigation of soot formation during pilotonly operation. Optical test methods were applied in an optically accessible single sector rig at engine idle conditions. Using planar laser-induced incandescence (LII), the distribution of soot and its dependence on air/fuel ratio, as well as geometric injector parameters, was studied. The data shows that below a certain air/fuel ratio, an increase of soot production occurs. This is in agreement with smoke number measurements in a standard single sector flame tube rig without optical access. Reaction zones were identified using chemiiuminescence of OH radicals. In addition, the injector flow field was investigated with PIV. A hypothesis regarding the mechanism of pilot smoke formation was made based on these findings. This along with further investigations will form the basis for developing strategies for smoke improvement at elevated pilot-only conditions.

For lean burn combustor development in low emission aero-engines, the pilot stage of the fuel injector plays a key role with respect to stability, operability, NOx emissions, and smoke production. Therefore it is of considerable interest to characterize the pilot module in terms of pilot zone mixing, fuel placement, flow field and interaction with the main stage. This contribution focusses on the investigation of soot formation during pilot-only operation. Optical test methods were applied in an optically accessible single sector rig at engine idle conditions. Using planar laser-induced incandescence (LII), the distribution of soot and its dependence on air/fuel ratio, as well as geometric injector parameters, was studied. The data shows that below a certain air/fuel ratio, an increase of soot production occurs. This is in agreement with smoke number measurements in a standard single sector flame tube rig without optical access. Reaction zones were identified using chemiluminescence of OH radicals. In addition, the injector flow field was investigated with PIV. A hypothesis regarding the mechanism of pilot smoke formation was made based on these findings. This along with further investigations will form the basis for developing strategies for smoke improvement at elevated pilot only conditions.