Better understanding of engine aging
APOSEM and EVE: Paradigm shift in engine maintenance
Engines are one of the most complex components in any aircraft. And they have to be overhauled regularly. Thanks to the strategic use of modern computer information systems, engines are checked and monitored continuously even in flight. Lufthansa Technik has been monitoring its customers' engines during flight operation since the 1970s using Engine Conditioning Monitoring (ECM) and transmits all relevant engine data for analysis and trend diagnosis continuously to the data center in Frankfurt. Action can therefore be taken immediately in case of irregularities before more serious damage is caused. Moreover, the optimum time for overhauling an engine can be determined in this way – completely independently of the recommended maintenance intervals. A critical aspect in this regard is to also be able to predict future changes in condition on the basis of trends in the ECM and on the actual operating conditions.
New methodology enables more accurate predictions
Of particular importance is the ability to predict aging in engines of customers whose entire fleet is looked after by Lufthansa Technik over a longer period of time. Precise removal planning and intensive fleet management can contribute significantly to optimizing the costs per flight hour and reduce the risks for all parties involved. Despite decades and thousand-fold experience with various engine types, predictions of the operation-dependent aging of engines have not been very exact to date. To change this, Lufthansa Technik is working together with the company ANSYS, the DLR, the University of Stuttgart and the TU Braunschweig to develop a new methodology in the framework of the research project APOSEM (Advanced Prediction Of Severity effects on Engine Maintenance). The objective is for engines to be monitored over their entire lifetime with the aid of physically substantiated models and for advanced predictions to be made concerning the impact of operation on maintenance.
In addition to empirical knowledge, data from inspections carried out in the shops and – if available – specific data from flight operation has been used to date for risk assessment and flat-rate contracts in engine overhaul. But that alone is not enough. Solid underlying data is important and necessary. Integration of big data, in other words all data derived from flight operation, with physically substantiated models is what is needed to make the breakthrough. Over the course of the three-year project phase, from January 2014 to December 2016, such physically substantiated models will on one hand be developed in very detailed form for individual components that are critical for the engine and validated with existing data. On the other hand, a methodology for simulating flight operation and for predicting the aging of the engine will be developed as an overall system. Methods such as for example numeric flow simulation and thermomechanical lifetime consumption analysis are being used for developing models.
Modified test model for deriving additional measurement parameters
In order to be able to validate the aging behavior of engines predicted by the models experimentally under real conditions, a decommissioned engine of the type CFM56-5C was modified to create a test model as part of a separate internal project (EVE, Engine for Validation Experiments) and provided with extensive additional instrumentation. Up to 310 additional measurement parameters can be established using an independent data acquisition system. The engine can now be looked at in detail in the engine test center under different external temperatures, in wet and dry weather conditions, with flown high-pressure compressor blades as well as with simulated power-up, taxiing and start-up after different cooling periods. One of the objectives is to understand the response of the secondary air system and to record its impact on the air flow and aging of the turbine.
With the support of the APOSEM research project funded by the Federal Ministry of Economics and Technology (BMWI) and the EVE project, it will be possible to make long-term predictions regarding the operation-related aging of engines. This will allow reliable prediction of the respective service life and the required depth of intervention, such as for example scrap rates and workscopes. Moreover, the underlying basis will also be created for improved costing in the framework of flat-rate contracts. And the findings derived will help to acquire an increasingly deeper and more comprehensive understanding of the engines.