Microsoft Word - cet-01.docx CHEMICAL ENGINEERING TRANSACTIONS VOL. 46, 2015 A publication of The Italian Association of Chemical Engineering Online at www.aidic.it/cet Guest Editors: Peiyu Ren, Yancang Li, Huiping Song Copyright © 2015, AIDIC Servizi S.r.l., ISBN 978-88-95608-37-2; ISSN 2283-9216 Study on the Life Estimation of Civil Aviation Engine Chungang Qu*, Hongbo Peng College of Aeronautical Engineering, CAUC, Tianjin, 300300, China. pqbird@sina.com The Life Estimation is one of important areas in Engine research. Take-off EGTM is an important parameter to monitor Engine performance. The value of take-off EGTM is influence on Engine life greatly. Reducing EGT will help to extend Engine life on wing (LOW), thereby reducing operating costs. Aiming at aero-Engine condition monitoring, the definition of take-off EGT Margin is given, estimation methods and their application on Engine life estimation are discussed. 1. Introduction EGT (Exhaust Gas Temperature) is one of important engine monitoring performance parameters in Engine cross sections. CFMI (2001) and Pratt & Whintey (2001) published some materials to introduce engine condition monitoring. Engine failure and performance degradation will be shown by EGT rising. Osborn, B. E. et al. (2007) estimated a trend in EGT. Weihua Yang (2000) introduced aero-Engine Modeling and fault Diagnosis in his PhD thesis. Xisen Wen (1997) also reported pattern recognition for engine failure. Engine life depends on take-off EGT Margin commonly. And its improvement will help extending Engine life on wing and reducing airline operating costs. İ Yılmaz. (2009) studied the relationship between EGT and operational parameters in cfm56-7b engines. Mercer C R et al. (2007) published fundamental technology development for gas-turbine Engine health management and Jaw L C (2005) introduced several advancements. Ilbas, M., Turkmen, M. (2012) and Zhifeng Ye, Jianguo Sun (2002) used neural Network to estimate EGT. Jin guang Song, Chunsheng Xu (2003) applied genetic algorithm and BP network for engine replace forecast. Guang- Bin Yu et al. (2013) proposed a support process vector model to predict EGT. 2. The collection of take-off data As the take-off phase is critical in flight safety, the data is often acquired by the automatic data logging system. The collected data used for Engine condition monitoring based on take-off EGT Margin include: 1) Aircraft identification information; 2) Take off parameters in the time of peak EGT: EGT, N1 (or EPR), TAT, etc.; 3) Bleeding air status. Different methods are used for different styles to judge the Peak EGT during take-off, such as CF6-80C2 (installed in the B747-400, B767-200, etc.) uses the record 40s after the flight speed reaches 100 Knots; CFM56-3 (installed in B737-300/400/500) uses records when the aircraft height reaches 90m or 9s after the front wheel leaves ground; CFM56-5C (installed in the A320 series, etc.) is recorded when the EGT reaches the maximum. 3. The definition of take-off EGT margin In order to meet the need of aircraft performance, Engine is usually required to be able to provide a constant thrust at a certain temperature. In the following we take the GE Engine (with N1 reflects the thrust) as an example. In Figure 1, the horizontal axis represents the OAT (outside air temperature), Tcp is the inflection point (corner point) temperature or the flat rating temperature (such as the flat rating temperature of CFM56 Engine is 30 C ). There are three curves in the figure: Thrust, N1 and EGT. We can see from the thrust curve that, when DOI: 10.3303/CET1546182 Please cite this article as: Qu C.G., Peng H.B., 2015, Study on the life estimation of civil aviation engine, Chemical Engineering Transactions, 46, 1087-1092 DOI:10.3303/CET1546182 1087 OAT Tcp Engine can produce a constant thrust, when OAT Tcp , in order to prevent excessive of EGT during take-off, the thrust is usually reduced, Engine won’t produce the full rated thrust. Figure 1: Schematic diagram of Engine flat thrust It can be seen from the N1 Curve that, before a temperature reaches Tcp, with the increasing of OAT, speed N1 (setting value of N1 during take-off) is hoped to increase to keep Engine thrust maintain a constant; at a temperature above Tcp, in order to prevent excessive of EGT, engine will reduce the N1 take off setting, Correspondingly aircraft take-off commercial weight will be affected concerning the decreasing of thrust. It can be seen from the EGT curve that, at a temperature below Tcp, with the increasing of OAT, in order to keep Engine thrust constant, it is needed to increase N1, EGT will increase correspondingly; at a temperature above the Tcp, engine chooses sacrifice thrust to limit EGT. Factors affecting take-off EGT include: the setting of take-off thrust, OAT (outside air temperature), outside air pressure and the Engine bleed air. When the aircraft take-off weight does not reach Maximum take off mass, the airlines usually require less thrust to use, that is don’t let the Engine produce full-rated thrust, thus reduce the take-off EGT and extend Engine life. Definition of Sea level take-off EGT Margin: the distance between EGT and EGT red value when the Engine produces full-rated thrust, at sea level, under flat rating temperature, with normal air-bleeding. As shown in Figure 2. Figure 2: Schematic diagram of take-off EGT Margin Take-off EGT Margin reflects the state of Engine performance. GE Engine also uses OATL (outside air temperature limit) to reflect the Engine performance, as is shown in Figure 2. It indicates that at sea level, when the OAT reaches OATL and the Engine produces full thrust, the EGT will reach EGT red line. Figure 3 shows the effect of performance degradation on EGT Margin and OATL. Curve 1 represents an Engine which just put to use, curves 2 represents an Engine whose performance has degraded. Figure 3 shows that with the degeneration of Engine performance, EGTM reduced, OATL also reduced. So EGTM can reflect the general performance of the Engine. Figure 3: The effect of Engine performance degradation on EGM and OATL 1088 4. The estimate of take-off EGT margin There are a variety of methods for Take-off EGTM estimation, cruise EGT is commonly used to estimate take-off EGTM in Engineering, in particular: 1) Estimate with test-stand EGTM in Engine factory and the change of EGT during cruise phrase, see formula 1; 2) Estimate with the Engine EGT alert during cruise, as shown in Equation 2. ( ) C TESTCELL C I EGTM EGTM EGT EGT    (1) C ALERT C EGTM EGT EGT   (2) In which, C EGTM indicates the current Engine EGTM, TESTCELL EGTM as EGTM in factory units, C EGT as the deviation between current EGT and baseline, I EGT as deviation of the initial installed Engine EGT relative to baseline; ALERT EGT as the alert value of EGT . When the EGTM difference between these two methods is within the range of 5 C , it is thought the basic accuracy of the estimate have acquired. Establishment method of the Engine cruise alert value is shown in Figure 4. Figure 4 indicates the relationship between test-stand EGTM and initial installed deviation I EGT of the PW4056, it can be seen that when EGTM reaches zero, 22EGT C   . Therefore ALERT EGT of PW4056 Engine is defined as 22 C . -5 0 15 40 -20 -10 0 10 20 30 EGTM E H M △ E G T y＝－1.0706x+21.562 5 20 30 40 10 25 35 Figure 4: Determination of the cruise EGT alert value Finally, we must make it clear that the take-off EGTM equals 0 C only means that the Engine EGT will be reach the red line value when the Engine take-off full-thrust in at the sea level and flat rating temperature. If the Engine is arranged to take-off at low temperatures airport, or reduced thrust take off, EGT won’t go over the red line. The Engine users can take the following measures to increase EGT Margin: 1) If possible use reduced thrust take off; 2) Control the aircraft take-off weight, reduce unnecessary carrying fuel and water and use APU to supply air for air condition system to reduce the Engine load during the plane take-off, etc. 3) Cleaning the Engine gas path regularly can get a certain EGT Margin recovery. 4) Plan the route structures reasonably, such as arranging degraded Engine to fly some lines of the cold regions and so on. 5. The engine life estimation using take-off EGT margin Currently, on condition maintenance is widely used for civil aviation Engine. It usually has only a soft limit for the whole Engine, and there are not strict working hours or the number of limit cycles. However, some parts such as turbine disks, shafts and seals, etc. have critical time restrictions, so they are known as LLP (life limited part). Failure of Engine System can usually be solved in the way of repair/replacement. After the failure is removed, the Engine can be used continuity. The Engine whose performance has completely degraded must return to factory to do performance recovery work. Engine performance status is evaluated mainly through condition monitoring, especially monitoring software. In Engineering, usually take-off EGTM is directly used to predict the Engine remaining life, to be outlined below. After Installed in the aircraft, the cruise EGT of Engine will increase gradually, rapidly in the early, slow down later. The rate of Engine EGT decline (i.e., the amount of decline per one thousand circulations) is defined as, 1089  / 1000EGTDecay EGT CSI  (3) CSI represent cycles since installation. The relationship between flight cycles and Engine EGT rate of decline of a PW4000-94 inch Engine is shown in Figure 5. It can be seen that the EGT decline rate falls faster before2000 CSI, while it slows down after 2000CSI. For the remaining life prediction of Engine on the wing, in Engineering, the Engine take-off EGTM is estimated at first, then predicted using the CSI and EGT decline rate. Here we give an example of the residual life prediction of Engine. Figure 5: The relationship between Engine EGT decline rate and the flight cycles for PW4000-94 Example 1: When EGTM is less than EGTDecay Known: the time and cycles of a PW4056 Engine since installation are TSI / CSI = 1200Hrs/494Cycles The EGTM in test-stand before installation 12 TESTCELL EGTM C  The initial value after installation 8 I EGT C   , the current moment 15EGT C   PW4056 Engine 22 ALERT EGT C   1) Estimate EGTM Estimate using test-stand EGTM and cruise EGT increment ( ) 12 (15 8) 5 C TESTCELL C I EGTM EGTM EGT EGT C         Estimate using EGT alert Value 22 15 7 C ALERT C EGTM EGT EGT C       The error of the two estimation method is within the prescribed limits, take the mean value 6 C EGTM C  2) Predict the remaining life The currently CSI of the Engine is only 494Cycs, thus, the decline rate is:    / 1000 7 494 / 1000 14.17( / 1000 )EGTDecay EGT CSI C Cycles     Considering that the current decline rate of EGT is large and EGTM is little, the Engine doesn’t need to be regarded as time-phased process. After investigation, the utilization rate of the aircraft installed with the Engines is 2.12 cycles / day. Thus, the theoretical remaining time before EGTM reaches zero is: Re ( ) 1000 (6 14.17) 1000 423( ) maining C Cycle EGTM EGTDecay Cycles        Re Re 2.12 7 423 2.12 7 28.5( )maining mainingLife Cycle Weeks   Re maining Cycle is the remaining number of cycles, Re mainingLife is the remaining life (unit: week). So the Engine EGTM is expected to reach zero 28.5 weeks later. Authentication: The theoretical zero EGTM remaining cycle of the Engine is 423Cycles. After the Engine is removed, the test-stand EGTM is -1 C , and the total CSI is 935Cycles, thus it was used 935-494 = 441 1090 Cycles after the predicted point. The theoretical zero EGTM remaining cycles and the actual number of cycles of the Engine are basically the same. Example 2: When EGTM of is more than EGTDecay Known: the time and cycles of a PW4056-3 Engine since overhaul are TSO / CSO = 6939H/3241C The EGTM in test-stand before Installation 48 TESTCELL EGTM C  The initial value after installation 6 I EGT C   , the current moment 34EGT C   PW4056-3 Engine 56 ALERT EGT C   1) Estimate EGTM Estimate using test-stand EGTM and cruise EGT increment ( ) 48 (34 6) 20 C TESTCELL C I EGTM EGTM EGT EGT C         Estimate using EGT alert Value 56 34 22 C ALERT C EGTM EGT EGT C C C         The error of two estimation method is within the prescribed limits, take the mean value 21 C EGTM C  2) Estimation the remaining life The average EGT decline rate of the Engine is:    / 1000 28 3241 / 1000 8.64( / 1000 )EGTDecay EGT CSI C Cycles     The Engine CSI has reached 3241Cyces, and EGT Margin is more than EGTDecay, time-phased process should be used. The change of EGT decline rate is as following: 0-1064 cycles:    / 1000 12 1064 / 1000 11.28( / 1000 )EGTDecay EGT CSI C Cycles     1064-2103 cycles:    / 1000 8.6 1039 / 1000 8.28( / 1000 )EGTDecay EGT CSI C Cycles     2103-3241 cycles:    / 1000 7.4 1138 / 1000 6.5( / 1000 )EGTDecay EGT CSI C Cycles     As can be seen from the above data, there is large deviation between the average Engine EGT decline rate and the EGT decline rate during each time stage. It will have a greater error if the average decline rate is used to predict the remaining life. As Engine is normal recession mode, the replace time of the Engine may be thereby be calculated using the decline rate 6.50 / 1000C Cycles after the 3000 cycles. After investigation, the utilization rate of the aircraft installed with the Engines is 2.67 cycles / day. Thus, the theoretical remaining time before Engine EGTM reaches zero is: Re ( ) 1000 (21 6.5) 1000 3231( ) maining C Cycle EGTM EGTDecay Cycles        Re Re 2.12 7 3231 2.67 7 173( )maining mainingLife Cycle Weeks   So, EGTM is expected to reach zero after 173 weeks. The time can only serve as a reference of the Engine replacement time currently. Over time, the calculation should continue with time goes, until the EGTM is less than EGTDecay when the method in example 1 should be used for prediction. 6. Conclusions Take-off EGT Margin has a quite big influence on Engine life. Improvement in take-off EGT Margin will help to extend Engine on-wing time, and to reduce operating costs. Here we have analyzed and discussed the civil aviation Engine life prediction based on take-off EGT Margin. 1091 Associated with relative monitoring software, Engine performance monitoring can, on one hand, help maintenance technician to troubleshoot, on the other hand, Engineers can use long-term changes of Engine performance to manage Engine fleet effectively, such as arranging Engine removal in echelon, planning workscope of Engine overhaul, et.al. Acknowledgements This work was financially supported by Civil Aviation University of China research fund: ZXH2012P007. References GE Aircraft Engine / CFMI, 2001, Engine condition monitoring, USA, GEAE / CFMI. Hao Y., 2004, Engine Take-off EGT Margin Estimates, Aviation Maintenance and Engineering, (2): 39-40. Hao Y., Sun J.G., Bai J., 2003, The status and prospects of aviation gas turbine engine gas path fault diagnosis, Journal of Aerospace Power, 18: 753-760. Ilbas M., & Turkmen M., 2012, Estimation of exhaust gas temperature using artificial neural network in turbofan engines, Isi Bilimi Ve Teknigi Dergisi. Jaw L.C., 2005, Recent advancements in aircraft engine health management technologies and recommendations for the next step, ASME GT 2005 -68625. Mercer C.R., Simon D.L., Hunter G.W., 2007, Fundamental technology development for Gas-Turbine Engine health management, NASA-20070022364. Osborn B.E., Fullington M.D., Herron W.L., Hershey J.E., Dockendorff J.E., Hansen C.H., (2007), System and method for estimating a trend in exhaust gas temperatures in a turbine engine. EP doi: EP1746271 A2. Pratt & Whintey, 2001, Engine health monitoring (EHM) training guide, USA, Pratt & Whintey Customer Training Center. Song J.G., Xu C.S., 2003, Engines replace forecast based on genetic algorithm and BP network, Journal of Aerospace Power, (5): 676-680. Wen X.S., 1997, Pattern Recognition and Status Monitoring [M], Changsha: National University of Defense Technology Press. Xu C.S., 2000, The Reliability of Aviation Engines Concluding Report, Civil Aviation University of China. Yang W.H., 2000, Aero-Engine modeling and fault diagnosis [PhD thesis], Nanjing, Nanjing University of Aeronautics and Astronautics. Ye Z.F., Sun J.G., 2002, Application prospect of using neural network in aircraft engine gas path fault diagnosis, Journal of Propulsion Technology, 01(1): 1-4. Yılmaz I., 2009, Evaluation of the relationship between exhaust gas temperature and operational parameters in cfm56-7b engines. Proceedings of the Institution of Mechanical Engineers Part G Journal of Aerospace Engineering, 223, 433-440. Yu G.B., Ding G., Yao W., Huang L., 2013, Aeroengine exhaust gas temperature prediction using support process vector machine, Electric Machines & Control. 1092