International Colloquium Tribology
ict
expert verlag Tübingen
125
2022
231
Enhanced engine lifetime by use of premium fuel
125
2022
Marcella Frauscher
Adam Agoes
Thomas Wopelka
Andjelka Ristic
Florian Holub
Wolfgang Payer
In order to evaluate the impact of premium fuels containing elevated levels of friction modifier (FM) additives regarding wear, engine test bench investigations were performed with a conventional fuel and with a premium fuel containing FM. All tests utilised an artificially aged engine oil that simulated the condition of a reference used oil after 25,000 km of operation. Thus, a large-scale artificial ageing of 180 L engine oil was carried out with oil condition monitoring by means of conventional parameters and high-resolution mass spectrometry. Oil analysis confirmed a comparable condition of the
artificially aged oil with the reference used oil. Additionally, SRV® tribometer experiments with the artificially aged oil proved a significantly higher coefficient of friction compared to the fresh oil but similar tribological performance compared to the reference used oil. During the engine bench tests, wear was monitored via wear particle concentration in the oil by means of optical emission spectroscopy as well as by radio isotope concentration method with activated piston rings. Both analytical methods found a significantly lower wear in the engine bench test operated with premium fuel with FM compared to tests with conventional fuel. Moreover, subsequent used oil analysis from bench test oil samples by mass spectrometry showed a transfer of the FM from the fuel into the engine oil. In particular, an increase in FM with proceeding engine operation time was observed. Hence, the usage of premium fuels may lead to enhanced engine lifetime.
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23rd International Colloquium Tribology - January 2022 105 Enhanced engine lifetime by use of premium fuel Marcella Frauscher AC 2 T research GmbH, Wiener Neustadt, Austria Adam Agocs AC 2 T research GmbH, Wiener Neustadt, Austria Thomas Wopelka AC 2 T research GmbH, Wiener Neustadt, Austria Andjelka Ristic AC 2 T research GmbH, Wiener Neustadt, Austria Florian Holub OMV Downstream GmbH, Vienna, Austria Wolfgang Payer OMV Downstream GmbH, Vienna, Austria Summary In order to evaluate the impact of premium fuels containing elevated levels of friction modifier (FM) additives regarding wear, engine test bench investigations were performed with a conventional fuel and with a premium fuel containing FM. All tests utilised an artificially aged engine oil that simulated the condition of a reference used oil after 25,000 km of operation. Thus, a large-scale artificial ageing of 180 L engine oil was carried out with oil condition monitoring by means of conventional parameters and high-resolution mass spectrometry. Oil analysis confirmed a comparable condition of the artificially aged oil with the reference used oil. Additionally, SRV ® tribometer experiments with the artificially aged oil proved a significantly higher coefficient of friction compared to the fresh oil but similar tribological performance compared to the reference used oil. During the engine bench tests, wear was monitored via wear particle concentration in the oil by means of optical emission spectroscopy as well as by radio isotope concentration method with activated piston rings. Both analytical methods found a significantly lower wear in the engine bench test operated with premium fuel with FM compared to tests with conventional fuel. Moreover, subsequent used oil analysis from bench test oil samples by mass spectrometry showed a transfer of the FM from the fuel into the engine oil. In particular, an increase in FM with proceeding engine operation time was observed. Hence, the usage of premium fuels may lead to enhanced engine lifetime. 1. Introduction In times of high claims towards sustainability the possibility to enhance lifetime of combustion engines by boosting aged engine oil via high-quality fuels with elevated levels of additives such as FM is a topic of high interest in the automotive and fuel sector. Within this study, a comprehensive approach was chosen comprising the artificial generation of an engine oil commercially available but in a well-defined condition comparable to an oil towards its end of lifetime, engine test rig runs with basic and premium fuels, and high-resolution wear measurement as well as mass spectrometry. The results revealed a significant impact of the fuel quality on the engine oil as well as on the occurring wear in the engine. 2. Materials and methods A reference used oil after 25,000 km of operation was characterised by conventional parameters such as oxidation or viscosity, and high-resolution MS to identify the residual FM content. According to this condition a largescale artificially oil alteration similar as described in [1] using elevated temperature, synthetic air and shear stress was conducted. This resulted in 180 L aged oil with the same characteristics as the reference used oil, and almost fully degraded FM. 106 23rd International Colloquium Tribology - January 2022 Enhanced engine lifetime by use of premium fuel The similarity was not only shown by analytical results, but also with SRV ® tribometer experiments. Experiments were carried out with following parameters: 100Cr6 polished plate 100Cr6 standard ball, 50 N, 1 mm and 30 Hz. Aliquots of the fresh, the artificially aged and the reference used oil were tested. As top compression rings in the engine test rig, standard X90CrMoV18 rings were used for the engine bench test. For the wear measurement with the radio-isotope concentration (RIC) method the piston rings were activated in a cyclotron facility, which means that a known amount of radioactive tracer isotopes was produced within a surface layer of the piston rings with a few micrometres thickness. As tracer isotope Co57 was used. The RIC method mainly consists of a gamma radiation detector, which detects the emitted gamma activity of the tracer isotopes. The amount of wear can be derived with two methods: 1) by measuring the activities of each piston ring before and after the bench test. The difference of the measured activities can be converted to a wear volume or wear height, and 2) by measuring the activity of the lubricant which transports the wear particles containing the tracer isotopes to the radiation detector in a closed lubricant circuit [2]. The latter method can be used as continuous wear measurement during a test run, which was not done in this study. Engine test rig experiments with artificially aged oil without noteworthy residual FM content were performed with commercially available basic and premium fuel, whereas the premium fuel contained an additive package including a higher dose of FM. At the beginning, during the experiment and at the end of the test rig runs (120 h in total) oil sample aliquots were taken to monitor the FM content via MS. Additionally, the activated piston rings were measured by RIC and wear was determined after the test runs. For the determination of the piston ring wear the piston ring activities were measured before and after the engine bench test in a well-defined position. These measurements were repeated thirty times for statistical reasons to reduce the uncertainties. The wear volume or average wear height were calculated from the differences of the activities before and after the engine bench test. 3. Results 3.1 Artificial oil ageing in large scale In accordance to the reference used oil (25,000 km) the artificially aged oil was produced with an oxidation of 18 A/ cm, fully consumed anti-wear additive and partially consumed antioxidants within 55 hours in a large-scale alteration device (see figure 1). Figure 1: An increasing oxidation while partially to fully depletion of additives was detected during large scale artificial ageing. A viscosity index decrease, which indicates the decomposition of the oil by the applied shear stress during the entire time, and an oxidation increase was monitored during the entire ageing process. The FM depletion was determined in the end sample by MS. It was confirmed that in the desired end condition of the aged oil, the antiwear additive as well as the FM were fully depleted (see figure 1). To show the similarity in performance with the reference used oil from the field SRV ® tribometer experiments were performed. Both, the artificially aged oil as well as the reference used oil showed similar results regarding coefficient of friction and friction curve, while the fresh oil was performing significantly better. 3.2 Piston ring wear with RIC Table 1 shows the results of the RIC wear measurements of the piston rings for test runs carried out with basic fuel without FM and premium fuel containing FM. The wear volume is the total wear volume worn off throughout the whole test and the wear height is meant to be the average wear height over the whole running surface calculated by dividing the wear volume by this surface area. The results are given as relative values comparing the premium with the basic fuel. Table 1: piston ring wear volume and average wear height for engine bench tests without (basic fuel) and with (premium fuel) friction modifier (FM) relative to each other Test specification Piston ring wear volume Piston ring wear height Basic fuel 100 % 100 % Premium fuel 23,69 % 23,77 % The results show a significant reduction in wear volume for the premium fuel compared to the basic fuel by more than a factor of 4. 23rd International Colloquium Tribology - January 2022 107 Enhanced engine lifetime by use of premium fuel 3.3 Characterisation of used engine oil with MS During both engine test rig experiments, with basic and premium fuel, engine oil aliquots were taken, and elemental analysis and MS measurement were conducted. The elemental analysis revealed a faster and slightly higher increase of iron in the oil with increasing running time for the test with basic fuel not containing any friction modifier. The MS explains this observation by revealing significant differences in the engine oil samples. While for both engine oil series only a slight decrease of antiwear additives and phenolic antioxidants was found there was a significant change regarding the FM content and the aminic antioxidants. The samples from the experiment with basic fuel did not only show no FM increase, but also a higher degree of aminic antioxidant depletion, further increasing with longer operation time. For the engine test rig performed with premium fuel a considerable amount of FM was detected in the oil samples. This content was increasing over the operation time, and at the same time degradation products were built up. Compared with the content in the premium fuel itself, a remarkably higher amount of FM was found in the engine oil after 120 h of operation time than in the pure premium fuel. This indicates a transfer from the fuel to the engine oil, and an accumulation of the FM over time as depicted in figure 2. Figure 2: Mass spectra of the premium fuel containing FM, engine oil samples after large-scale ageing with fully depleted FM, and samples after an operation time from 15 - 120 h. 4. Summary and conclusion By using the large-scale ageing device with selected and pre-defined conditions, the generation of a test oil similar to a reference used oil regarding the desired oil parameters was enabled. The degradation of the FM was detected by high-resolution MS in both oils, the reference used oil as well as the artificially aged oil and their similar performance was confirmed by SRV ® tests. Engine test rig experiments with activated piston rings were performed using a basic fuel without FM and a premium fuel including a FM additive package. RIC measurements of the piston rings revealed a considerably higher wear when using the basic fuel compared to test runs with premium fuel. MS measurements of engine oil samples were able to explain this effect, as an accumulation of FM additive in the oil when using premium fuels was observed. A transfer from fuels containing FM additives in certain amount takes place, and an improvement in wear behaviour is achieved. This effect was additionally observed with piston rings already showing wear from previous test runs. Hence, an enhanced lifetime by wear reduction when a premium fuel is used regularly can be concluded. 5. Acknowledgements The work presented was funded by the Austrian COMET program (Project InTribology, Nr. 872176) and carried out at the “Excellence Centre of Tribology” (AC 2 T research GmbH). References [1] Besser C., Agocs A., Ronai B., Ristic A., Repka M., Jankes E., McAleese C., Dörr N.: Generation of engine oils with defined degree of degradation by means of a large scale artificial alteration method, Tribol. Int., Vol 132, p 39-49, Elsevier B.V., ISSN 0301-679X, DOI 10.1016/ j.triboint.2018.12.003, 2018 [2] Jech, M. (2012): Wear Measurement at Nanoscopic Scale by means of Radioactive Isotopes. Vienna University of Technology.
