Ultrasonic Measurements of Kinematic Viscosity for Analize of Engine Oil Parameters

Transcription

1 th European Conference on Non-Destructive Testing (ECNDT 04), October 6-0, 04, Prague, Czech Repubic More Info at Open Access Database Utrasonic Measurements of Kinematic Viscosity for Anaize of Engine Oi Parameters Vadimir A. CHUPRIN cientific-industria Company UCH C; Moscow, Russia; Phone/Fax: ; E-mai: Abstract It is noted that the oi anaysis has been widey used as a suitabe too for condition monitoring of equipments, in order to reduce ones expenditure and to improve reiabiity and productivity. On-ine measurements of kinematic viscosity by means of utrasonic have been discussed. The utrasonic sensor has been described. It has consisted of two thick pates (waveguides), in which the norma acoustic pate waves, namey, the owest symmetrica and horizonta-poarized waves have propagated. These waves have been excited and received with the utrasonic wedge transducer. The frequency range of the norma waves from.0 to.5 MHz, the pate thickness of 0. mm and ength of 00 mm have been investigated. Immersing a part of the waveguide surface in an investigated iquid, the wave attenuation coefficient has been measured. The possibiity has been showed, to cacuate a iquid kinematic viscosity using utrasonic datum. Comparisons of measured and tabe vaues of the kinematic viscosity have been presented. Keywords: utrasonic measurement, symmetrica pate wave, horizonta-poarized norma pate wave, waveguide, iquid kinematic viscosity.. Introduction ubricating oi contains a good dea of information about a triboogica interactions of engine surfaces between which it circuates. Therefore, oi anaysis has been widey used as a suitabe too for condition monitoring of equipments, in order to reduce the expenditure and to improve reiabiity and productivity. The kinematic viscosity is one of the most important iquid parameters permitting to describe ubricating oi since its variations (sma increases or decreases) have been indicated different processes which oi is undergroing during use. It is obvious that contro observations of the machine oi viscosity are to be often carried out in harsh environments and resuts have to eave unbroken. In these cases appications of utrasonic measurement technoogies certainy have advantages on condition that they provide the necessary accuracy of measurements. As the resut of many utrasonic impedance measurement technoogies are the ongitudina = ρ c and shear = ρ η ω / impedances of investigated iquids ( ρ, c, η are density, ongitudina wave veocity, shear viscosity of a iquid, ω is the utrasonic frequency). Therefore, if the both impedances of the investigated iquid are measured, kinematic/shear viscosities are to be cacuated. The advantages and disadvantages of conventiona suitabe acoustica impedance measurements have been we studied [-5]. They have been based on measurements of wave refection coefficients from the soid/a waveguide investigated iquid interface or the veocity and the attenuation of the fundamenta ongitudina and torsiona modes in waveguides immersed in a iquid. This discussion showed that the compatibiity and the verification of the necessary accuracy and sensibiity of different methods have met defe difficuties. The high accuracy of refection based measurements is difficuty reaizabe owing to weak infuence of iquids on refection coefficient change since the numerica vaues of both impedances of iquids and soids are typicay very different.

2 As to measurements of the fundamenta ongitudina and torsiona modes in cyindrica/rectanguar waveguides, they theoreticay permit to reaize higher sensibe and precise measurements. However, pubished experimenta resuts have not aowed to estimate the accuracy and sensibiity of these kinematic viscosity measurements (see for exampe [5]).. Using of norma waves Another utrasonic technoogy giving the possibiity, to achieve a very good sensibiity, has been described here. This technoogy based on the measurement of the both acoustica impedances of an investigated iquid by using the norma acoustic pate waves, namey, the owest symmetrica and horizonta-poarized waves. aveguides are the main part of the utrasonic sensor and are consisted of thin pates of rectanguar form for each type of waves. The waves are generated and received by piezoeectric transducers which have been mounted on one end surface of the waveguide out of iquids (see figure ). One part of each waveguide/pate has been immersed in a iquid. Each nu-mode of norma waves has been generated and has been received with the own wedge transducer after the refection from the free pate end. Figure. The acoustica bock structure Eectrica channes of waves are independent. Apart from the generator and the ampifier there is the caibrated attenuator that has been joined between the transducer and the receiver entrance. The signa ampitude has been maintained constanty by means of this attenuator. The accuracy of attenuator gradation was ±0.dB. After the ampification the signa has been observed with the digita oscioscope. According to the theory [6-8] the both impedances of an investigated iquid can be found if the infuence of a iquid on the propagation of norma waves in the waveguide has been measured. Physica causes due to this infuence of iquids on and horizonta-poarized norma (H) waves have differed from each other. The horizonta-poarized norma wave obsesses ony dispacements which are parae to the waveguide surface. Therefore, the cause of energy osses of a propagation wave is the friction between the osciating waveguide surface and the contacting iquid. If an investigated iquid

3 can be considered as a Newton one, the measured attenuation coefficient to the reation / [7]: = ρ c is the waveguide shear impedance, ρ is proportiona = χ, () and c are its density and shear sound χ of Newton iquid is / d ( d veocity. Theoretica vaue of the proportiona coefficient is the waveguide thickness). Unike horizonta-poarized waves, waves create dispacements of the waveguide surface ying in the vertica pane. urface dispacements have the both norma component and component directed aong the propagation direction. The dispersion equation for waves propagating in a waveguide immersed in viscous Newton iquid had been got in [9]. Using this equation, one can show that two items give main contributions in the attenuation coefficient with an accuracy of not ess than 5% if a viscosity of a iquid does not exceed Poise = + () () () The first one is caused by the radiation of the wave eastic energy in the contacting iquid. The () attenuation coefficient due to radiation is proportiona with the coefficient χ to the reation / : () () () = χ. (3) ( c / c ) In this case c and c are veocities of the symmetrica nu-mode and ongitudina wave in the iquid. The atter veocity has to be measured in addition to impedances. The attenuation contribution of another dispacement component is anaogous to earier considered attenuation coefficient of horizonta-poarized norma waves. It can be presented with the proportiona coefficient χ in form: () () () () χ = χ =. (4) χ According to the theory [9], a proportiona coefficients do not depend on viscosity and density. It is understood that a proportiona coefficients can be theoreticay cacuated. At the same time, the theory had been buit, supposing that a waves are pane, and boundary condition do not change on the wave propagation way. These preconditions were not reaized in the experiment and therefore the resuts of parameter cacuation possess possibe errors which vaues depend on how far as the rea wave is cose to the pate of the or horizonta-poarized waves. Therefore, it is meaningfu to find these coefficients from a caibration procedure. For exampe, one can use two types of iquids which viscosities and densities are known and one cacuates their acoustica impedances. Then, one immerses waveguides consecutivey in each iquids and measures the attenuation coefficients of the both waves. Further, one cacuates a three proportiona coefficients from equaities () (4). If a proportiona coefficients are known, the kinematic viscosity ν has been found:

4 () ( c ) χ ( c ) = ( ) ( ) () ω χ χ ν = ω. (5) 3. Resuts of kinematic viscosity measurements As noted earier, a change of an ia kinematic viscosity has been of interest as the information source of triboogica interactions between rubbing engine arrangements. It means that ia vaue of the kinematic viscosity has to be remembered by a measurement arrangement. Then, the sensor has to observe and to measure its eventua change. In view of the ratio (5) the observation over engine triboogica interactions consists in measurements of the both impedances and ongitudina veocity in iquid, the cacuation of actua kinematic viscosity and the comparison of the both actua and ia vaues. The possibiity of a high sensitivity was checked experimentay. It is necessary to note that the theory and our experiment have showed that the changes of the propagation veocity of both wave types due to contact with iquid aways remain very ow. Consequenty, diffraction effects remain constant, if iquid parameters change and accuracies of the both impedance measurements have to be determined by errors of ampitude measurements ony. The measurements were performed in the frequency range from to.5 MHz, using the straightforward auminium waveguide, which thickness d and the ength were 0. and 00 mm correspondenty (/d=000). uch waveguide ength has been caused by the fact that the shear impedance vaues have aways been very ow in comparison with the waveguide ones. For exampe, a iquid with the shear viscosity of Poise has the shear impedance at the 3 frequency MHz 4 0 g / cm s and, accordingy, for auminium waveguide in water 3 / 5 0 whie / 0. χ. Therefore, the waveguide has to possess a sufficient contact ength in order to ensure the high sensitivity of shear viscosity/kinematic viscosity measurements. This circumstance can put obstaces in the way of the integration of the sensor and the equipment. To avoid this probem, the waveguide can be manufactured in the form of an accordion. This form can be seen in figure. Our measurements have showed that the infuence of this bend on a signa ampitude has been absent ti a bend radius R has been above 8 0 mm.

5 Figure. The waveguide form Measurements of numerica vaues of ampitude sensibiity of each wave type have been carried out in our investigations in the foowing way. At first measurements have been carried out in a iquid, which parameters have been accepted as ia. The short waveguide part 0 (3 mm) had been immersed in an investigated iquid. The rest of the waveguide ength was in the air. The ampitude A 0 and propagation time t 0 of the signa, refected from the waveguide end, have been measured. Then the ength of immersed waveguide part has been consecutivey increased by and the new ampitude A has been measured. An ia attenuation coefficient is equa = 0g( A / A0 ). (6) ( ) 0 Then, waveguides have been immersed in another iquid, which parameters have simuated changed ones of engine iquid. Measurement procedures have been repeated. At first vaue A 0 new has estabished at immersing of 3 mm waveguide part. Then, a new vaue A has measured, and a new attenuation coefficient has cacuated as the sum of ia one and its change vaue: new = + 0g( Anew / A ). (7) ( ) 0 As the contacting iquid has been used gycero-water mixtures in which gycero concentrations have been varied in the range of 0 to 00%. This gives the possibiity to estabish the necessary physica properties of the investigated iquid in a wide range. As investigated iquids have been chosen water soutions with concentrations of 60 to 90% gycero that have permitted to vary ia vaues of kinematic viscosity of 9.0 to 50 ct. Utrasonic veocities for each concentration have been measured by the standard echo-impuse method. For this aim an additiona utrasonic sensor has been used. It (see fig.) has consisted of ongitudina transducer mounted on a round waveguide. Another waveguide end has been

6 immersed in investigated iquids. The ongitudina waves have propagated aong waveguide in iquid and then they have come back, refected from a refector. It s easy to see, in according to the reation (7), the sensibiity to kinematic viscosity changes is determined by accuracy of ampitude measurements. Our experiments showed that it is approximatey equa ( 3) 0 mv/t in the viscosity range of (0. ) 0 t. Comparisons of kinematic viscosity vaues, measured by utrasonic, with tabe ones [0] have been presented in figure 3. In this case, kinematic viscosity vaues have been potted against the tabe ones (soid curve). The dashed curve has been corresponded the situation, when the both vaues do not differ. It has been seen that differences of the both vaues do not exceed 0 5%. 4. Concusion - idea dependence, - experimenta vaues. Figure 3. The reationship between the tabuated and cacuated vaues of ν. Experimenta resuts have estabished the possibiity to measure on-ine a kinematic viscosity of oi-ike iquids with accuracy suitabe for practica using. As to a difference of the both experimenta and tabe kinematic viscosity vaues, one can suppose that it is caused by gradients of temperature into investigated iquids since specia measures weren't taken in order to eiminate this infuence.. It is necessary to note that theoretica reations () (5) have been suitabe ony for Newton iquids. However, how it is known, Newton's equation can be unsuitabe for the description of rheoogy of very viscous iquids, especiay in case of using it in measurement on high frequencies. The suitabiity of Newton's equation has to be checked experimentay, for exampe, by comparison of measured frequency dependences of both impedances. References. P. Hauptmann, N. Hope, A. Püttmer, Appication of Utrasonic ensors in the Process Industry, Meas. ci. Techno., Vo. 3, pp. R73-R83, 00.

7 ..C. ynnworth, Utrasonic Measurements for Process Contro, Academic Press, Boston, p. 59, G. Harrison, A.J. Barow, Methods of Experimenta Physics, Vo. 9, pp , H. heen, H.T. Chein, A.C. Rapits, Measurement of hear Impedance of Viscoeastic Fuids, IEEE Utrasonic ymposium Proceedings, Vo., IEEE, p. 453, T.K. Vogt, M.J.. owe, P. Cawey, Measurements of the Materia Properties of Viscous iquids using Utrasonic Guided aves, IEEE Transaction on utrasonics, ferroeectrics and frequency contro, Vo. 5, 6, pp , M.B.Gitis, Procedures and Equipment to the Quaity Contro of Technica Onecomponent and Muti-component iquids by Means of Utrasound in-ine Measurements of its Viscosity, Density, Compessibiity and Voume Viscosity, Germany Patent 0, 006, 003, 649, M. B. Gitis, V. A. Chuprin, Appication of urface and Norma Utrasonic aves for Measuring the Parameters of Technica Fuids: I. hear Viscosity measurements, Technica physics, Vo. 57, 5, pp , M. B. Gitis, V. A. Chuprin, Appication of urface and Norma Utrasonic aves for Measuring the Parameters of Technica Fuids: I. Density Measurements, Technica physics, Vo. 57, 5, pp , hu, J. u, The Propagation of aves in a Pate Boarded with a Viscous iquid, JAA, Vo. 98, Pt, pp , J.B. egur, H. Oberstar, Viscosity of Gycero and its Aqueous outions, Ind. & Eng. Chem., Vo. 43, pp. 7-0, 95.