Study on In-situ Capacitive Sensor for Monitoring Engine Lubricant Oil Debris

Transcription

1 8th Euopean Wokshop On Stuctual Health Monitoing (EWSHM 016), 5-8 July 016, Spain, Bilbao Study on In-situ Capacitive Senso fo Monitoing Engine Lubicant Oil Debis Moe info about this aticle: Yishou WANG, Zhibin HAN, Dong LIANG, Xinlin QING School of Aeospace Engineeing, Xiamen Univesity, Xiamen Key wods: Debis monitoing, Lubicant oil, Engine, Capacitive senso. Abstact Monitoing of lubicant oil quality plays an impotant ole in assessment of aicaft engine health condition. Geneally, sensos attached to the lubicant pipeline ae used to detect the wea debis in lubicant and detemine the health condition of aicaft engine. Howeve, the most cuent debis detection methods ae off-line and equie a complex set-up. Theefoe, it is ugently necessay to develop eliable online monitoing methods to effectively detect wea debis. Capacitive senso has some advantages such as high esolution and high accuacy fo pecision measuement, small size and designability fo in-situ monitoing. Based on the capacitive theoy, this study focuses on designing a cylindical capacitance senso installed on lubicant pipeline in ode to monito lubicant oil debis in aicaft engine. The pinciple of the cylindical capacitance senso is based on the pemittivity of the lubicant oil. When the debis entes into the lubicant, the elative pemittivity of the debis mateial change the capacitance of the senso, which causes the vaiation o fluctuation of the collected signals. Thee key issues on designing the cylindical capacitance senso ae discussed in this pape. The fist issue involves with how to integate the cylindical senso with the lubicant pipeline. The second issue concens how to design a senso with bette pefomance. The pocess of numeical simulation is pefomed to detemine the optimal paametes of senso stuctue. The last issue is how to build an expeiment system to illustate the effectiveness of the poposed cylindical capacitive senso fo in-situ monitoing the debis in lubicant. 1 INTRODUCTION Aicaft engine, as a coe component, is diectly elated to the pefomance of aicaft and the safety of cew [1]. The continuous online health monitoing of engine is an impotant way to ensue its stability and eliability in the sevice. Lubicant oil monitoing is a key to engine health monitoing []. The continued flowing lubicant oil is used to not only educe the tempeatue, but also tanspot the debis poduced by mechanical wea. The debis not only affects the pefomance of lubicant oil, but also indicates some faults of the mechanical system in the engine. It is an impotant eseach to monito the oil debis in the engine. Two methods fo monitoing engine lubicant oil can be divided into two kinds: off-line and on-line. Off-line oil monitoing includes Feogaphy [3], Spectoscopy [4], Gey taget theoy patten ecognition [5], Fuzzy logic model [6], Sediment test and wea metal analysis [7] and so on. Off-line oil monitoing has been widely used in the ealy stage. With the inceasing equiement in engine health monitoing, the on-line oil monitoing has become a hot eseach field.

2 On-line oil monitoing methods include mico senso [8], electomagnetic senso [9], ultasonic paticle monitoing [10] and so on. Each method has its advantages and disadvantages. The mico senso method has less influence on the popeties of the aicaft engine itself, but its pocessing is complex and costs too much. The electomagnetic senso is used to monito the debis in the magnetic field, but it is easy to be affected by the aibone electical system. Ultasonic paticles method has bette monitoing function fo small size debis, but the lage size debis may be ignoed, and once lage size debis appeaed, it usually will have a moe seious impact on the engine [10]. Based on the above, this study puts fowad a kind of capacitance senso to monito the debis. Capacitive senso has been widely used because of its good tempeatue stability, simple stuctue, stong adaptability, good dynamic esponse, noncontact measuement and othe advantages. Thee ae many types of capacitive sensos, such as vaiable dielectic constant, vaiable distance, and vaiable aea. This pape focuses on the study of the capacitive senso with vaiable dielectic constant. The basic pinciple is that the debis gets into the oil and esult the change of the dielectic constant of oil, which will lead to the change of capacitance. Hence, we can use the change in capacitance to chaacteize whethe the oil contains debis o not. Cuently, some basic eseach on the capacitive senso with vaiable dielectic constant have been pefomed [11,1]. Howeve, thee is no wok involved with pipe-like capacitance senso used in aicaft engine, especially on the mechanism and sensitivity of capacitive senso. This study develops a cylindical capacitive senso that is suitable fo the lubicant oil pipeline of aicaft engine, and discusses its mechanism and sensitivity by numeical simulation and pinciple expeiments. THEORETICAL MODEL OF CAPACITIVE SENSOR Consideing that the lubicant oil pipeline is small in diamete, this study designs a coaxial capacitive senso composed of two coes, as shown in Figue 1. The novelty is that the oute coe is the existing unchaged oil pipeline, while the inne coe is new fine chaged ods, such that the inne coe is easily integated with the oute coe by joint. The joint can be designed as a connecting flange o a nut of a two pipe line (detailed design in section 3). Lubicant oil flows though an annula space between the oute coe and the inne coe. If thee is no debis in the oil, the dielectic constant between two poles is stable in value. That is to say that the measued capacitance will not change. When the oil contains debis, the value of the dielectic constant between two poles is changed, which will esult in capacitance change. Figue 1: Schematic diagam of capacitance senso model In ode to establish a capacitive sensing model as shown in Figue 1, this pape fist assumes that the inne coe is simplified as a long unifom chaged od and the analysis of electic field in the senso is equal to that of the field distibution in a unifomly chaged thin od. Take any point O in a thin od as the coodinate oigin to establish coodinate system, set

3 any point outside the od as Q (the pedal point of is ), whose distance to the thin od is d, and the angles between the x axis along inne coe and two lines fom fom Q to two ends of the thin od ae illustated by a 1 and a, espectively. Finally, the linea chage density is set as.the mathematical model is shown in Figue. e Figue : Reduced mathematical model of capacitive senso Take a line element dx whose chage is dq dx at the distance x fom the oigin. The intensity of the electic field geneated by dq in Q point is defined as Fomula (1). 1 dq e dx de e 0 0 The line element dq in diffeent positions of the thin od will poduce diffeent element field de in position Q. Accoding to Figue, thee ae some elationships among x,, a, i.e. d sin and x dcot. We can get diffeential equation dx d sin d. The electic field intensity poduced by each line element at x axis and y axis can be expessed as equation (3) and (4). 1 edx e e Ex dex cos cos d sin 1 sin 4 4 d 4 d y edx e e y sin sin cos 1 cos d d E de d Accoding to the equation (3) and (4), we can calculate E x and E y. If we change the values of two paametes d and l, the entie field distibution will be diffeent. Thee ae two cases to be discussed. (a) When d<<l, the thin od can be abitaily long, that is, 1 0,. Futhe, we combine it with equation () and (3), and get E x =0, E y =η e /(πε 0 d). (b) When d>>l, thee will be anothe condition, and get E x =0, E y =η e /(πε 0 d )=q/(4πε 0 d ). In this study, the diamete of oil pipeline is small, so the physical model of the cylindical capacitance senso is much moe close to the fist case. In the above analysis, 0 is epesented as the vacuum dielectic constant, but in the actual situation, the capacitance between the two electodes is often not a vacuum. Theefoe, this study intoduces a paamete defined as elative dielectic constant. Then the actual dielectic constant can be fomulated as 0. Hence, the fomula can be futhe ewiten as follows. 3

4 e q 1 E 0 0 l 4 In (4), q is the quantity of the electic chage of the cylinde, l is the length of cylinde. q Then e. The cylinde capacito is made of two coaxial metal cylindes A and B with l adiuses R 1 and R espectively. The length of cylindes l is much longe than R 1. The is dielectic constant between two cylindes. As is shown in Figue 1, the diection of the electic field is pependicula to the axis of the cylinde. Then the electic potential diffeence between two sufaces of two cylindes can be obtained by the fomula (5). V AB R q d q R E d ln (5) 1 0 l l R 0 l R1 The capacitance is calculated by the following equation (6). q 0 l C (6) V R AB ln R we can see that C is a function of l,,and ln(r /R 1 ). Theefoe, if l and ln(r /R 1 ) ae constant, C is just a function of. When thee is a debis paticle passing though the senso, this debis paticle can be seen as an electic dipole. So, the poblem can be simplified as the polaization of the dielectic unde an extenal electic field E 0. The polaization chage appeas on the suface of the dielectic and geneate an additional electic field E, so the field intensity E of any point in the space is the vectoial sum of E 0 and E,i.e. E E0 E. Based on above analysis, those debis into the cylindical capacitive senso can change the oiginal electic field and capacitance. 3 NUMERICAL SIMULATION EXPERIMENT As discussed in Section, the capacitance senso is a kind of capacito with vaiable paametes [13]. When the inne coe length and the distance between two poles ae constant, the vaiation in the dielectic between the plates will change the capacitance value. In ode to design a capacitance senso, it is necessay to undestand the influence of the length and the distance on the senso pefomance. The numeical expeiments ae simulated by the Ansys finite element softwae. Intelligent gid contol method is adopted in the simulation, and the accuacy of the gid is adjusted by "size smat". 3.1 Paametic analysis of capacitive senso without debis in lubicant oil In the basis of simulation, we mainly focus on the senso's length, the distance between the two poles, the voltage between the two poles. Accoding to the fomula (11), we can know that the length of the senso has no influence on the electic field in the senso. If the distance and the voltage between the two poles ae applied as the contol vaiables, the electic field in the senso will be changed obviously. The simulations ae caied out with diffeent values of the distance and voltage between two poles. The expeiments set R 1 =1mm, l=40mm as constant. The distance is set mm, 3mm and 4mm while keep V=V; The voltage is set 0.5V,1V and V while keep the distance =3mm. Afte dividing the gid, thee ae 37 nodes, units. The simulation esults ae shown in Figue 3 and Figue

5 (a) Distance =mm (b) Distance =3mm (c) Distance =4mm Figue 3: The electic field distibution with diffeent distances between two poles (a) Voltage =0.5V (b) Voltage =1V (c) Voltage =V Figue 4: The electic field distibution with diffeent voltages It is not easy to see the change in electic field accoding to Figue 3 and Figue 4. We extact the simulation data and deal with it though fitting method. The fitting esult is shown in Figue 5(a) and (b). Figue 5 (a) coesponds to the fitting cuves of diffeent distances between electodes, and figue 5(b) coesponds to the fitting of the applied voltage at diffeent poles. With the fitting esult, we can intuitively found that the electic field intensity deceases with the incease of the distance between the two electodes. The geate the voltage applied between the two electodes, the electic field stength of the senso will be inceased. Taking into account the effect of signal to noise atio and the flow eduction, we decide the distance between two electodes is 3mm and the applied voltage is V. (a) Diffeent distances (b) Diffeent voltages Figue 5: The fitting esult of diffeent paametes 3. Simulation in electic field vaiation of oil with debis Unde the existing conditions, we can detemine the paametes of the senso model, the inne coe is 1mm, the distance between the two electodes is 3mm, the length is 40, and the 5

6 applied voltage is V. Using the physical model, we simulate the debis into the senso, and the simulation esults ae shown in Figue 6(a) and (b). Figue 6(a) is the simulation of a single debis coming into the senso, Figue 6(b) is a numbe of debis coming into the senso. Fom the simulation esult, we can notice that the electic field distibution will occu obvious change when debis come into the senso. (a) One debis (b) Fou debis Figue 6: The electic field distibution with diffeent numbes of debis In ode to be moe intuitive to see the changes in the case of debis and no debis and calculate the sensitivity of the simulation, we put the simulation data into Matlab. The solution esult is shown in Figue 7. It's appaent to notice that a lage tough occus in the place whee debis exist. It's easy to calculate that the simulation sensitivity is about 30%. 4 EXPERIMENTS 4.1 Expeiment Design Figue 7: The smooth cuve of the data unde the condition of debis and no debis. The coesponding expeiments ae designed to veify the pesented theoical and numeical model. The inne and oute coe mateial of the capacitive senso is coppe, the length is 40mm, the inne coe adius is 1mm, the distance between the two electodes is 3mm. The object is shown as Figue 8 (a) and (b). In ode to make the senso easie to expeiment, we design a plastic coaxial flange to connect two coes. And fom the oute wall of flange to the inne coe, we install a small hole. The small hole can be povided with a metal conductive od, and the extenal voltage is applied to the inne coe. The flange is shown as Figue 8(c). The expeiment system is shown as Figue 8(d), whee the capacitantce is measued by the instument LCR(LCR-8110G) that diectly apply voltage to the senso. 6

7 (a) The inne coe (b) The oute coe (c) The flange (d) The expeiment system Figue 8: Thee components of the developed capacitance senso 4. Fequency selection The simulation in the second section has confimed that the voltage used in the expeiment is V, but the voltage fequency still needs to be futhe detemined. In this section, the fequency of 100Hz, 10Hz, 150Hz, 00Hz, 400Hz, 600Hz, 800Hz, 1000Hz will be egaded as vaiables. It is found that the measued senso capacitances change with the fequency, when the medium is ai, wate, oil, espectively. The expeiment data ae shown in Table 1. The coesponding cuve of Table 1 is shown in Figue 10(a), (b) and (c). Fequency(Hz) Capacitance(pF)/ai Capacitance (pf)/wate Capacitance (pf)/oil e e e e e e e e Table 1: The change of the capacitance with the fequency when the medium is ai, wate and oil It can be seen fom Table 1 that the capacitance value of the senso showed a tend of gadually deceasing with the incease of fequency. In actual measuement, the geate fequency is, the geate fluctuation of the capacitance value is. Theefoe, take a numbe of fluctuations in the value of the capacitance (thee times in this pape), and take the aveage value as the final capacitance. Fom Figue 9, we can see that when the medium is ai o wate, the decline tend of the capacitance is oughly the same, but when the oil is the medium, the tend is opposite. We speculate that the diffeence in the viscosity of the medium can lead to the diffeence in the tend of the capacitance with fequency. In ode to gain a stable value, the fequency 100Hz is selected as the final value. (a) Ai (b) Wate (c) Oil Figue 9: The cuve of the change of the capacitance with the fequency in ai, wate and oil 7

8 4.3 Debis monitoing expeiments On the basis of detemining the applied voltage is V, the voltage fequency is 100Hz, a seies of expeiments on monitoing debis ae caied out. Due to the limited expeimental conditions, we design these debis is in fee fall in the simulation of flowing medium. Test esults show that the viscosity of ai is too low. The time that debis ente the senso in fee fall is too shot, which is only 0.16s. LCR eaction speed is not enough. So, in this section, the test is only concened about wate and oil. The expeimental data ae shown in Table. Numbe Capacitance (pf)/wate Capacitance (pf)/oil e e e e e e e e e e6 Table : The change of capacitance value with the numbe of debis in wate o oil. means no capacitance value. It can be seen fom Table that when the medium is wate, the capacitance is much lage than the medium is oil due to the good conductivity of wate. With the incease of the numbe of debis, the capacitance value inceases with the incease of debis whethe the medium is wate o oil. The tend can be seen fom Figue 10. It is shown that the capacitance value has a bette change tend with the incease of the numbe of debis, the tend is oughly linea. We infe that the capacitance has a good sensitivity to the numbe of debis, which can eflect the numbe of debis in the medium. (a) Wate (b) Oil Figue 10: The cuves of the capacitance value with the numbe of debis in wate o oil 5 CONCLUSIONS Lubicant oil monitoing is an impotant pat of aicaft engine health monitoing. The health state of engine can be chaacteized by means of the oil debis monitoing. This pape 8

9 pesents a cylinde capacitive senso suitable fo in-situ monitoing of engine oil debis. The coaxial cylinde senso is designed based on the vaiable dielectic constant, and the woking mechanism model of capacitive senso monitoing chip is established. The electic field in the pesented senso is simulated by ANSYS softwae. Finally, a test platfom is built to veify the pesented model. Expeimental esults show that the capacitance values incease almost linealy when the numbe and size of debis incease. Howeve, thee ae lots of futhe wok to apply the pesented method into the application. Especially, it is necessay to conside seveal factos influence on monitoing esults. These factos include the flow ate of the lubicant oil, tempeatue, and vibation. ACKNOWLEDGMENT The authos would like to acknowledge the financial suppot of the National Natual Science Foundation of China (Gants No , ) and the suppot of and the Fundamental Reseach Funds fo the Cental Univesities ( , ). REFERENCES [1] Z. Wu, H. Zuo, T. Zhang. Peliminay study on emote diagnosis system of civil aviation engine based on WEB. Poceedings of the Tenth Confeence on stuctual stength and vibation of aicaft engines, , 000. [] L. C. Jaw. Recent advancements in aicaft engine health management (EHM) technologies and ecommendations fo the next step. ASME Tubo Expo 005: Powe fo Land, Sea, and Ai, Ameican Society of Mechanical Enginees, , 005. [3] W. Holzhaue, S.F. Muay. Continuous wea measuement by on-line feogaphy. Wea, 90(1), 11-19, [4] K.R. Januszkiewicz, G. Bekmesian, H.H. Sulek. UV-fluoescence spectoscopic method fo monitoing tamp oil contamination in hot olling emulsions. II: Application of fluoescent taces. Lubication engineeing, 48(1), 56-61, 199. [5] S. Chen, Z. Li, Q. Xu. Gey taget theoy based equipment condition monitoing and wea mode ecognition. Wea, 60(4), , 006. [6] Z. Peng, N. Kessissoglou. An integated appoach to fault diagnosis of machiney using wea debis and vibation analysis. Wea, 55(7), 11-13, 003. [7] L.O. Leugne. Use of sediment tests and wea metals analyses to monito hydaulic system condition. Lubication engineeing, 43(5), , [8] H.-S. Lee, S. S Wang, D. J Smolenski, et al. In situ monitoing of high-tempeatue degaded engine oil condition with micosensos. Sensos and Actuatos B: Chemical, 0(1), 49-54, [9] H. Zhan, Y. Song, H. Zhao, et al. Study of the Senso fo On-line Lubicating Oil Debis Monitoing. Sensos & Tansduces, 175(7), , 014. [10] M. A. Saangi, Doctoal Thesis: Oil Debis Detection Using Capacitance and Ultasonic Measuements. Univesity of Akon, 007. [11] R. Minasamudam, P. Agawal, P. Venkateswaan. Simulation of a Capacitive Senso fo Wea Metal Analysis of Industial Oils. Poceedings of the 013 COMSOL Confeence, in Bangaloe, 013 [1] S. Raadnui, S. Kleesuwan. Low-cost condition monitoing senso fo used oil analysis. Wea, 59(7), , 005. [13] X. Huang, X. Zheng, Pinciple and application of senso. Pess of Univesity of Electonic Science and Technology. 39-4(1999). 9