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.
For their application in a multisector combustor, several laser-based measurement techniques underwent further development to generate useful results in the demanding environment of highly luminous flames under elevated pressures. The techniques were applied to two burner configurations and the results were used to explain their respective behavior. Multisector combustors at elevated pressure present formidable difficulties to the operation of laser based techniques, as the optical path length is longer than for a single sector while the optical density of the flowing medium can be quite high. Hence, the techniques have to be set up to perform under low signal to noise levels. Nevertheless for a validation exercise geared at multidimensional simulation, quantitative results are requested. Here the modification of standard Laser Induced Incandescence as a means to measure soot concentrations with higher dynamic range is described. For situations where the optical density is too high for the application of imaging techniques, laser absorption was used and its application in the multisector combustor is presented. Since combustion and soot formation is closely coupled to flowfield and mixing, velocity measurements are highly desired for comparison with computed flowfields. Although with Laser-Doppler Anemometry a well-established technique is at hand, the high operating costs of a multisector combustor cannot be supported for the needed time of operation. Therefore an effort was made to make the Particle Imaging Velocimetry technique operable in highly luminous flames by using a second camera. The two-camera system and its operation are described in the paper. Finally the application on two different burner configurations is reported together with chemiluminescence as a tracer for heat release, and differences in soot production are related to the measured flow field.
An experimental investigation of a nonreacting multiple jet mixing with a confined crossflow has been conducted. Flow and geometric conditions were varied in order to examine favorable parameters for mixing. The requirement for a rapid and intense mixing process originates from combustion applications, especially the RQL-combustion concept. Thus, the jets were perpendicularly injected out of one opposed row of circular orifices into a heated crossflow in a rectangular duct. Spacing and hole size were varied within the ranges referring to combustor applications. The results presented are restricted to an in-line orientation of opposed jet axis. Temperature distribution, mixing rate, and standard deviation were determined at discrete downstream locations. Best, i.e., uniform mixing can be observed strongly depending on momentum flux ratio. For all geometries investigated, an optimum momentum flux ratio yields to a homogeneous temperature distribution in the flow field downstream of the injection plane. Overly high ratios deteriorate the mixing process due to the mutual impact of the opposed entraining jets along with a thermal stratification of the flowfield. Correlations are introduced describing the dependency of optimum momentum flux ratio on mixing hole geometry. They allow the optimization of jet-in-crossflow mixing processes in respect to uniform mixing.
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