Browsing by Author "Kuschke, Jonathan"

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Open Access
Systematic investigation of fuel efficiency restoration during engine overhaul
(2015) Kuschke, Jonathan; Staudacher, Stephan (Prof. Dr.-Ing.)
The increased importance of fuel consumption in the books of aircraft operators has led to a raised focus on the aspect of performance recovery for the engine overhaul process. It follows thus the need for a method to systematically and cost-efficiently investigate the impact of single workscope elements on engine efficiency. A survey of existing studies and methods unearths recently developed methods for a comprehensive maintenance planning. These methods do not yet incorporate the aspect of performance recovery in spite of the high effort made to adapt engine specific workscope for observed hardware conditions. This is due to a lack of a systematic approach to establish a model correlating workscope and performance recovery. Research linking the two has so far been focused on predicting workscope-induced performance recovery based on pre-defined models and comparing the results with measured performance changes. No method for an adaptive model, based on available field data, has yet been established. Furthermore, any conceptual reflections to use field data to assess workscope impact on performance recovery are focused on the use of test cell data, rather than on-wing data recorded during engine operation. To close this existing gap a new methodology is developed, correlating the engine overhaul's workscope and its effect. The workscope is therein defined by the degree of restoration which quantifies the percentage of parts for which a given feature is restored, either by repair or use of new parts. In order for the correlation model's extend to be manageable, the degree of restoration is defined for clusters comprising multiple stages. The workscope effect, in terms of performance recovery, can be analysed using test cell or on-wing data both of which are subject to uncertainty induced by measurements and the engine model. It is demonstrated that the latter leads to lower analysis uncertainty for the high pressure components who are the primary lever for improvements on SFC and EGT-margin. This is explained by the improved accuracy achieved with averaging multiple snapshots. It is demonstrated that using an average of 50 filtered snapshots is a valid approach, since the engine components may be considered to be a system of constant state during the operation time frame. Furthermore, the importance of the proper choice of the core flow analysis method is demonstrated, as well as the potential for analysis accuracy improvement using a more detailed engine model. It is shown that these measures have the potential of improving the analysis accuracy of HPC and HPT by a factor of 1.4 and 3.4 respectively. Analysis of recovered performance of fan and LPT is demonstrated to be more sensitive to installation effects. For these components, better accuracy can be achieved using test cell data, provided a performance test run is carried out prior to the overhaul. In order to correlate workscope and performance recovery, a general functional relation is established to serve as the principal model. The model is then adapted to optimally fit available field data from past engine overhauls through implementation within an appropriate optimisation algorithm. An application to the high pressure components provides plausible results indicating clear distinctions between the leverage that different workscope elements provide for recovering performance. A cross validation using the leave one out algorithm shows the results of the correlation to be sensible. The potential for further improvement, for example by using measured dimension changes of the different features for the workscope description, is discussed. With this investigation, it is understood for the first time what the feasibilities and limitations in correlating workscope and performance recovery are. The established approach provides a basis for systems aimed at systematically planning engine workscopes with respect to performance restoration.