Vibration diagnostics of common rail injectors

Transcription

1 Journal of Marine Engineering & Technology ISSN: (Print) (Online) Journal homepage: Vibration diagnostics of common rail injectors Marcin Kluczyk & Andrzej Grządziela To cite this article: Marcin Kluczyk & Andrzej Grządziela (2017): Vibration diagnostics of common rail injectors, Journal of Marine Engineering & Technology, DOI: / To link to this article: Published online: 11 Oct Submit your article to this journal Article views: 10 View related articles View Crossmark data Full Terms & Conditions of access and use can be found at Download by: [Gothenburg University Library] Date: 25 November 2017, At: 16:06

2 JOURNAL OF MARINE ENGINEERING & TECHNOLOGY, Vibration diagnostics of common rail injectors Marcin Kluczyk and Andrzej Grządziela Faculty of Mechanical Electrical Engineering, Polish Naval Academy, Gdynia, Poland ABSTRACT This article presents the possibility of evaluating the technical condition of common rail fuel systems injectors using the vibration method. The other most successful methods of diagnosing the common rail injectors were described. Marine diesel engine common rail injection installations had been characterised. Results of tests obtained during vibration measurements were presented as well. The results confirm the possibility of determining the technical condition of modern diesel engines injectors without the need of engine stopping. The results are especially important for marine engines without indicating cocks or thermoelements allowing measurements of exhaust gases temperature on each cylinder. Introduction According to strict emission standards set out in Annex VI to Marpol 73/78 and other IMO documents, marine engine design engineers are now required to develop solutions allowing control of the combustion process in engines. One such solution is the use of common rail injection system (MAN). The fundamental difference comparing to mechanical injection equipment is the use of one pump producing a high fuel pressure of approximately 200 MPa and feeding all electronically controlled injectors from one rail. Despite the advantages of such construction, its biggest disadvantage is the relatively high failure rate of electronically controlled injectors. Currently two types of injectors are used, piezoelectric and electromagnetic injectors. In the first type, the opening of the injector is caused by a change in the volume of the piezoelectric stack. The second one, which will be the subject of further consideration, is characterised by electromagnetic induction in the coil. Operational problems arising from the use of electronically controlled common rail injectors are mainly due to the high precision of their components. Secondly, those injectors are much more complicated than the mechanically controlled injectors. The best solution to evaluate the technical state of common rail injectors are tests on a test bench under laboratory conditions, while in stand conditions their diagnosis is limited in practice to measuring the volume of fuel flowing out from individual injectors (Busz and Walaszyk 2012; Knefel 2012). It ARTICLE HISTORY Received 6 July 2017 Accepted 27 September 2017 followsthatthepersonnelservicingtheengineonboard have very limited possibilities to determine the injector s technical condition. This leads to a decision of replacing all engines injectors in most cases. Unfortunately, costs associated with unplanned downtime and potential loss of profit are serious financial problems for the shipowner. The lack of proper diagnostic tools on board can also bring the situation in which a faulty injector is allowed to continue operating. Consequently, it might cause a loss of power and even serious damage to the engine. Construction of solenoid-valve-controlled injectors The solenoid-valve-controlled injectors are commonly used in marine applications. Structurally and functionally they are similar to injectors operating on the same principle used in the automotive industry. However, the similarity applies only to fuel installations of high-speed marine engine. Comparison of the construction of the MTU high-speed marine engine injector and the Bosh injector from car engines is presented in Figure 1 (Kuiken 2008). According to medium- and low-speed engines powered by heavy fuel oil, there are significant differences in the construction of common rail injectors. The fundamental difference in the construction of two presented injectors is different methods of adjusting the initial tension of the control valve spring. Polish Navy uses for CONTACT Marcin Kluczyk m.kluczyk@amw.gdynia.pl Faculty of Mechanical Electrical Engineering, Polish Naval Academy, Śmidowicza 69 st., Gdynia , Poland 2017 Institute of Marine Engineering, Science & Technology

3 2 M. KLUCZYK AND A. GRZĄDZIELA Figure 1. Comparison of the construction for the MTU highspeed marine engine injector (Kuiken 2008) and the Bosh injector from car engines. 1 electrical connection, 2 coil, 3 valve spring, 4 valve control chamber, 5 valve control plunger, 6 needle spring, 7 nozzle, 8 atomiser, 9 fuel return, 10 high-pressure fuel inlet. propulsion purposes only light fuel oil, which suggests that injectors in new engines introducing on boards of Polish warships will be similar in design to those from theautomotiveindustry.despitethedifferencesinthe construction of common rail injectors and mechanical injectors, in both cases the main source of their vibrations is the accompanying rise and fall of the injector needle associated with the opening and closing of the injector. For the mathematical description of the needle movement, it was assumed that the pressure p II equals to the pressure from the common rail. The F cr force generated by the coil in the injection process outweighs the value of the spring pressure of the control valve allowing the control valve to open. As a result, the pressure in the control chamber (point 4 in Figure 1)becomeslowerthaninthe injection chamber and the fuel injection process starts. The equation describing the dynamics of the common rail injector needle is as follows (Marčič et al. 2015): m i d 2 h i dt 2 + (c + c 1 + c 2 ) dh i dt + (k + k 1 + k 2 )h i = F tr F 0 F cr + p II (A II A III ) + p II (A III A IV ) + p IV A IV, (1) Figure 2. Distribution of individual pressures in the injector s nozzle. where m i is the needle mass; c is the needle motion viscous damping coefficient; c 1 is the upper needle seat damping coefficient; c 2 is the lower needle seat damping coefficient; k isthespringcoefficientfornozzlevalve spring; k 1 is the spring coefficient for upper nozzle valve seat; k 2 isthespringcoefficientforlowernozzlevalveseat; F cr is the coil force; F tr is the friction force between nozzle body and needle; F 0 is the initial spring tension for needle; p II, p IV are pressures acting on needle presented in Figure 2; A II istheareaofneedleincrosssectionii;a III is the area of needle in cross section III; A IV is the area of needle in cross section IV. Taking into consideration the right side of Equation (1) and the construction of common rail injectors, it can be stated that mechanical damage will result in pressure changes in the different parts of the injector nozzle. Mechanicaldamagetothecontrolvalvewillresultin a drop of pressure in the control chamber. As a consequence, changes in the technical condition of the injector must alter to the parameters of the needle s movement, whichinturnwillaffectaschangesofdynamicparameters recorded on the injector body. Changes in the initial spring tension for the needle on the right side of Equation (1) result in stiffness changes in the left side of the

4 JOURNAL OF MARINE ENGINEERING & TECHNOLOGY 3 equation. This implies a reduction of energy dissipation assuming a constant efficiency of the device. Analysing the structure of the dissipated energy can be assumed injector vibroactivity reduction. The most popular common rail injectors defects According to available literature, fuel injectors (Gűnther 2009;StoeckandOsipowicz2015;Mazuruk2013)arethe most breakdown components of the fuel supply system of today s self-ignition engines. Injectors defects might be divided into three main groups: (1) Defects of electrical and electronic components that are relatively easy to detect even without the need to removetheinjectorfromtheengine. (2) Failures to the injector hull and its external components, which are usually detectable after dismantling injectors from engine and thoroughly cleaning in complete condition before inspection. (3) The last group of damage are damages to their internal components. In most cases, detectable only in repair workshop. According to data provided by Stoeck et al. (2014), the most usual damage of common rail injectors are all kinds of control valve failures involving leakage of couple valve and its seat. This results in a change of the fuel injection process characteristics. The most common cause of such damage is the poor fuel quality, especially the presence of water or mechanical impurities. The next group are damages to the valve control plunger, mainly involving the formation of cracks and corrosion on its surface caused by the presence of solid or water in the marine fuel. Failures also affects to the nozzle mainly due to difficult working conditions connected with high temperature in the engine combustion chamber. The last group of damages significant from diagnostic point of view is damages to the injector s needle by its erosion, corrosionormashing.inthiscasealso,thepoorqualityoffuelisthemainreasonoffailures.inconclusion, the most common cause of common rail system damages is poor fuel quality. This issue is extremely important according to the operating conditions of engines on board of warships where they are endangered to work withcontaminatedfuel.itshouldbeemphasisedthatthe most common contamination of marine fuel (NATO F- 75 type fuel) is water which accumulates in the consumption and storage tanks. This is due to the high humidity and high air temperature in marine power plant environment. After the air has been cooled below the dew point, the condensation of water from air in fuel tanks starts. Injector technical condition control There are few methods of controlling the technical condition of common rail fuel injectors. The simplest test that does not require the injector to be dismantled from the engine is to verify the injector electrical control signals. It is necessary to use an oscilloscope or a dedicated diagnostic device for specific engine brand. In this approach, the volume of fuel injected to the engine combustion chamber might be approximately calculated (Gűnter 2010). Another test is to measure the volume of fuel from fuel return pipe. It allows pre-evaluating the technical stateofpaircontrolvalve valveseat(osipowiczetal. 2015; Koniecznyetal.2015).Thebestandusuallyreliable method is to dismantle the injectors from engine, wash them in ultrasonic cleaners, and test on special test benches (Karpiuk et al., 2016). Such test stands checks injectors in selected operating states. Investigated injectors had been tested on a dedicated device the NT 816C injectors tester. Tester is shown in Figure 3. It allows one to test most manufacturers injectors. Tested injectors were four common rail injectors from the AR 32,501 engine. There are type injectors cooperating with the Bosch EDC 15C-5,8 controller. In order to determine the value of vibration parameters of injectors working properly, vibration acceleration measurements were already made in the first stage of the test. Piezoelectric accelerometer was mounted on the hull of individual injectors. The location of the transducer is shown in Figure 3. The measurement gives the possibility to record injector vibrations without interference from the remaining injectors. Due to another method of assembling the injectorsontestbed,theresultsobtainedduringsuch measurements may be misinterpreted. Checking the technical state of common rail injector on the test bench is carried out in five stages: Figure 3. One of the investigated injectors in the test bench with the accelerometer mounting location.

5 4 M. KLUCZYK AND A. GRZĄDZIELA Table 1. Resultsofinjectorstests. Leak Full load Medium load Idle Pilot Injector number 35 ± 35 mm 3 /t 45.7 ± 4.2 mm 3 /t 35 ± 35 mm 3 /t 17.9 ± 3mm 3 /t 2.8 ± 1.3 mm 3 /t 2.1 ± 1.3 mm 3 /t (4) measurements of injected fuel volume for idle (25 MPa) (5) pilot dose measurement performed at 80 MPa rail pressure. Figure 4. Investigated injectors with accelerometers mounted on a test bench. (1) measuring the leakage of the injector at maximum pressure in the feed rail (for the tested type equal 140 MPa) (2) measurements of injected fuel volume and overflowed fuel from the injector in full load condition (135 MPa) (3) measurements of injected fuel volume for medium load (80 MPa) The test results of four injectors are summarised in Table 1. Measured values were expressed in units [mm 3 /t], which is the volume of fuel measured during the whole stage test time. For tested injectors, the test lasts for 30 s. Duration time of tests and its parameters vary with the manufacturer and type of tested injectors. Crew on board is most likely to perform only overflow tests, but they do not provide full information on the technical condition of the tested injectors. Analysing the results presented in Table 1, all injectors would meet the condition specified for the overflow test. However, after careful analysis, it appears that the efficiency of the injectors at full and partial load is too small. This results in a natural wear of the investigated injectors which are dismantled and serve for didactic purposes. Figure 5. Functional diagram of common rail engine control station.

6 JOURNAL OF MARINE ENGINEERING & TECHNOLOGY 5 Figure 6. Amplitude frequency spectra of vibrations accelerations for injector 1 bad condition (signal 2) and 3 (signal 4). Figure 7. Amplitude frequency spectra of vibrations accelerations for injector 2 bad condition (signal 3) and 4 (signal 4). Summarising, injectors 1 and 2 are in a worse technical condition than the injectors 3 and 4. As far as the technical condition of the injectors had been known, further research was carried out to determine the relationship betweenthetypeandvaluesofthevibrationparameters and the technical condition of the tested components. Measurements of vibration parameters during injectors operation The next stage of the research was installation of alreadytested injectors at the common rail engine control station manufactured by Mechatronika company. Stand

7 6 M. KLUCZYK AND A. GRZĄDZIELA Table 2. Results of vibration parameters analyses rpm 50 MPa 1500 rpm 80 Mpa 2000 rpm 50 Mpa 2000 rpm 80 Mpa Injector number III h mm/s 2 8k-20 khz m/s khz mm/s III h mm/s 2 8k-20 khz m/s khz mm/s III h mm/s 2 8k-20 khz m/s khz mm/s III h mm/s 2 8k-20 khz m/s khz mm/s Figure 8. Results of the injectors technical condition test. is located at the Laboratory of Marine Power Plants Operation of the Polish Naval Academy. The stand enables to present common rail system operation principles. It allows one to control correct operation of its components, with particular emphasis on the highpressure pump and injectors. The method of transducers installationontheinjectorhullsisshowninfigure4. Figure 5 presents the functional diagram of the considered station. The characteristic feature of this station is the ability to control the injection system by an independent controllersothatitispossibletochangetheparametersof the injection and make them independent to the original engine map. During the measurements, the test stand was cooperating with electronic control unit (ECU). It allowed one to reproduce the natural parameters of the injectors work, of course without the effect of high temperatures. Tests were conducted at two rotational speeds of power shaft (1500 and 2000 rpm) and two different common rail pressures (50 and 80 MPa). The maximum pressure of the tested common rail system was 140 MPa (first generation of common rail). Such high pressures occuronlywhenengineloadisincreased.duringthe measurements, the acceleration of vibration was measured with a sampling frequency of 65,536 khz and a measuring range of 25.6 khz. Results of measurements Accelerations of vibrations recorded in time domain were analysed with the Pulse Reflex software. Sample of frequency amplitude spectra for all injectors is presented in Figures 6 and 7. Spectra present four waveforms corresponding to acceleration of vibration in frequency domain recorded on individual injectors working with a common rail pressure of 50 MPa and an engine shaft speed of 2000 rpm. The velocity of vibration spectra was also analysed. The results are summarised in Table 2 and shown in Figure 9. Graph 8 presents results from Table 1. It allows one to compare the technical condition of the injectors with their results obtained during vibration measurements. Preliminary analysis of the spectral components showed a great similarity between vibration parameters of all observed injectors, working in the same conditions. However, it was possible to pre-select for further analysis three quantities that could give unambiguous information about the technical condition of the tested injectors. Velocity of vibrations values connected with third harmonic of crankshaft rotational speed, i.e. 25 Hz at 1500 rpm and 33 Hz at 2000 rpm, was controlled. Another controlled parameter was accelerations of vibrations average value (a rms ) in the frequency range from 8

8 JOURNAL OF MARINE ENGINEERING & TECHNOLOGY 7 Figure 9. Vibrations of accelerations for individual injectors in operational conditions (rotational speed of crankshaft and pressure in common rail). to 20 khz. The initial analysis of the sample graph shown in Figure 6 indicates the differences in the band. A comparison of average vibration velocities (v rms )intherange of Hz was also performed. Analysis of values presented in Tables 1 and 2 gives information about the connection between the technical state of investigated injectors and chosen vibration parameters. Further graphs do not represent velocity of vibrations values, but they also change according to the technical state of injectors. Considering results of all tests shown in Figure 8, it is clear that injectors 3 and 4 are characterised by the highest fuel injection rates, with the smallest values of fuel discharged to the overflow. This proves that they are better than the other two injectors technical condition. Figure 9 presents results related to the accelerations measurement. During measurements of vibration parameters, all transducers were mounted in the same way and at the same location. Conclusions Analysis of the obtained results indicates certain dependencies between the technical condition of common rail injectors determined on the test bench and their vibration parameters. It has been found that injectors 3 and 4 in the normal technical condition are characterised by standard, repeatable vibroactivity values in amplitude analysis. This especially applies to the average vibration acceleration (a rms ) in the frequency range from 8 to 20 khz. In the case of injectors 1 and 2 in the technical condition below the operating parameters, the vibration parameters indicate a significant reduction in the vibroactivity values below the finger prints level of the correct injector. Analysing the right side of Equation (1), it could be found that this is justified. In efficient injectors, the injection process is more dynamic. This is due to the correct tightness and co-operation of the precision pairs. Moreover, all springs and controls have proper characteristics. In order to implement the method of determining the technical condition of common rail injectors on board of Polish Navy ships, it is still necessary to carry out many tests on engines equipped with different types of injectors in different but known technical conditions. On this basis, it will be possible to accurately determine the vibrational symptoms that give information about the technical condition of marine diesel engines equipped with the common rail fuel installation. After conducting a preliminary series of tests, it can be stated that the symptom of injector s precision pairs deterioration is reduction of the root mean square value for the accelerations of vibrations in the range from 8 to 20 khz. Future researches will be carried out by the authors, mainly for the analysis of these values. Final result of future research will be methodology of vibration test on the common rail fuel system which will allow one to determine the technical condition of injectors. The obtained test results indicate the need to prepare

9 8 M. KLUCZYK AND A. GRZĄDZIELA a fingerprints vibration database of different types of injectors for common rail installations. Disclosure statement No potential conflict of interest was reported by the authors. References Busz W, Walaszyk A Optymalizacja procesu testowania wtryskiwaczy paliwa Common Rail [Optimization of common rail injectors testing process]. Combust Engines. 3/2015: Polish. Gűnter H Diagnozowanie silników wysokoprężnych [Diagnosing of internal combustion engines]. 3rd ed. Warsaw: Transport and Communication Publishers. Polish. Gűnter H Układy wtryskowe Common Rail w praktyce warsztatowej, Budowa, sprawdzanie, diagnostyka [Common rail injection systems in workshop practice, construction, checking, diagnostics]. 1st ed. Warsaw: Transport and Communication Publishers. Polish. Karpiuk W, Bor M, Smolec R Possibilitiesofanalysis of condition and repair of common-rail system injectors. J KONES Powertrain Transp. 23:4. Knefel T Technical assessment of Common Rail injectors on the ground of overflow bench tests. Maint Reliab. 14(1): Polish. Konieczny Ł, Adamczyk B, Adamczyk G Diagnostyka i regeneracja wtryskiwaczy CR [Diagnosis and regeneration of CR injectors]. Sci J Silesian Univ Technol Ser Transp. 86(1926): Polish. Kuiken K Diesel engines for ship propulsion and power plants part I. Target Global Energy Training. Marčič S, Marčič M, Praunseis Z Mathematicalmodel for the injector of a common rail fuel-injection system. Engineering. 7: Mazuruk P Diagnostyka zasobnikowych układów paliwowych na podstawie fazowości procesu wtrysku [Diagnosis of fuel common rail systems based on injection phase phasing]. [disssertation]. Mechanical Department of Szczecin Maritime University (PhD Thesis). Polish. Osipowicz T, Abramek KF, Stoeck T Testing of modern common rail fuel injectors. Combust Engines. 162(3): Stoeck T, Osipowicz T Usterki mechaniczne wtryskiwaczy układów Common Rail [Mechanical faults of common rail injectors]. Buses. 6/2015: Polish. Stoeck T, Osipowicz T, Abramek KF Methodologyfor the repair of Denso common rail solenoid injectors. Maint Reliab. 16(2):

10 本文献由 学霸图书馆 - 文献云下载 收集自网络, 仅供学习交流使用 学霸图书馆 ( 是一个 整合众多图书馆数据库资源, 提供一站式文献检索和下载服务 的 24 小时在线不限 IP 图书馆 图书馆致力于便利 促进学习与科研, 提供最强文献下载服务 图书馆导航 : 图书馆首页文献云下载图书馆入口外文数据库大全疑难文献辅助工具