Hakan KALELI, Levent YUKSEK, Huseyin HACIKADIROGLU

Transcription

1 The 3 rd International Conference on DIAGNOSIS AND PREDICTION IN MECHANICAL ENGINEERING SYSTEMS DIPRE 12 CONDITION MONITORING OF PHOSPHORUS CONTAINING AND NPNA (NON-PHOSPHORUS & NON-ASH) ENGINE OILS AND THEIR EFFECT ON THREE-WAY CATALYST FOR TWO COMMERCIAL VEHICLES DURING OIL DRAIN PERIOD Hakan KALELI, Levent YUKSEK, Huseyin HACIKADIROGLU Yildiz Technical University,Faculty of Mechanical Engineering, Mechanical Engineering Department, Automotive Division, Besiktas-Yildiz, Istanbul, TURKEY kaleli@yildiz.edu.tr, kalelih@yahoo.com ABSTRACT In this study, performance of NPNA (non-phosphorous & non-ash) engine oil was investigated experimentally. A field test conducted with two identical, SI engine powered commercial taxi vehicles. A conventional, P containing SAE 5W-40 synthetic engine oil and NPNA SAE 5W-40 synthetic engine oil used for evaluation. Vehicles operated during a single oil drain period which was predefined as trip length 15,000 km by the manufacturer and the engine oil samples were taken every 2,500 km. Three-way-catalysts dismantled from the vehicles and analyzed individually at the end of the test. Elements on the washcoat surface of catalyst were investigated by using electron probe micro analyzer (EPMA). According to elemental analysis on the catalyst surfaces, P containing engine oil revealed higher levels of Ca, Zn and P than NPNA engine oil. Results of used oil analyses showed that, the total acid and base number (TAN-TBN) data of NPNA oil were not satisfying in conventional standard whilst the wear metals, viscosity, insoluble composition and water content were in acceptable limits at the end of the test. This shows that NPNA oil is in use and did not terminate the level what the driver should change oil. Keywords: Three-way catalyst poisoning, Non-phosphorus engine oil, Non-Ash engine oil, Catalyst surface analysis 1. INTRODUCTION Modern engine oils must have various functions: such as wear and corrosion protection, friction reduction, good heat conductivity to assist in cooling the engine, etc. All of these qualities should be maintained over the drain period to succeed longer lifetime benefit of the engine. A three-way catalyst (TWC) and a Diesel oxidation catalyst (DOC) are used to meet increasingly stringent restrictions on the emissions of certain polluting gases, which are emitting as combustion products by automotive internal combustion engines. A catalyst has an oxidizing function to transform chemically the carbon monoxide (CO) in carbon dioxide (CO 2 ) and the hydrocarbons (HC) to CO 2 and water (H 2 O). A catalytic converter can also has a reducing function by accelerating the reaction of hydrogen (H 2 ) and CO with nitrogen oxides (NO x ) to produce nitrogen (N 2 ) and CO 2. Platinum and palladium promote oxidation of CO and HC whereas the rhodium promotes the reaction of NO x.[1] Lifetime of a TWC or a DOC depends on deactivation mechanisms. Mechanisms of catalyst deactivation are many, but the causes of deactivation are basically three fold: chemical, mechanical and thermal.[2]considering the automotive catalysts the main causes of deactivation can be detailed as thermal deactivation and poisoning. Thermal 1

2 deactivation is the loss of catalytic surface are or loss of support area or the chemical transformations of catalytic phases to non-catalytic phases.[3] The major deactivation mechanisms that reduce the catalyst lifetime are the poisoning. One of the element that induce the poisoning is sulphur: which primarily comes from both fuel and engine oil is presents in hot exhaust gas as sulphur dioxide (SO 2 ) and significantly reduces the efficiency of the catalyst [4]. Zinc dialkyldithiophosphates (ZnDTP), which have been using widely as an antiwear and an antioxidant additive, are manufactured by reaction of alcohols, phosphorus pentasulphide and zinc salts [5]. It is a highly effective antiwear agent and combines the dual function of powerful antioxidancy. It is simply the most performance effective and cost effective additive used in the lubricant industry today. The volatilization and the combustion of engine oil in the cylinder can result in deposition of phosphorus, zinc and calcium compounds on the surface of the catalyst. It has been suggested that phosphorus, sulphur and metal elements such as Ca, Mg and Zn in engine oil deteriorate the catalyst performance; main source of phosphorus is ZnDTP, hence accumulation of ZnDTP in washcoat layer deteriorates the performance of catalyst by poisoning. Deactivation mechanisms, interactions with catalyst surface elements and developed measurement methodologies are well documented in literature [6-9]. Protection of environment is the main concept while designing the vehicle, to maintain the catalyst efficiency over the life of the vehicle is of great importance. In order to reduce poisoning effect of phosphorus and alkali metals, ILSAC-GF-5 as an industry standard: mandates lower levels of phosphorus and sulphur in engine oils. At this stage, the new type of environmental friendly additives which must have comparable antiwear and antioxidant performance are required as a substitute for ZnDTP. Alternatives which must satisfy above described qualifications are available in literature [10-12]. In this study, performance and the effect of phosphorus-free engine oil on TWC was investigated experimentally and compared to phosphorus containing engine oil. A field test conducted with two identical, spark ignition (SI) engine powered commercial taxi vehicles. Catalysts of vehicles removed and replaced with unused original ones at the beginning of the test. Duration of the test was a single oil drain period which pre-defined by the manufacturer of vehicles. Oil samples were taken 2 during the test with equal intervals then analyzed. After the end of the test three-way-catalysts dismantled from the vehicles and analyzed individually. 2. EXPERIMENTS 2.1 Tested Oils A conventional, ZnDTP containing SAE 5W-40 Synthetic Engine Oil (PC) and a specially formulated Non-phosphorus and non-ash containing SAE 5W-40 Synthetic Engine Oil (NPNA) were used for the tests. Details of the formulation of NPNA oil and additive substitute for ZDDP were published in previous studies. [12] Detailed specifications of the test oils are listed in table 1. Table 1. Specifications of the test oils Specification Unit PC NPNA Appearance - clear clear Density@15 C g/cm Kinematic mm 2 /s viscosity@40 C Kinematic mm 2 /s viscosity@100 C Viscosity index Acid number mgkoh/g Base number mgkoh/g Flash p. C Water content mass% Sulfated ash mass% Volatility@250 C mass% Field Test Taxi service comprises harsh environment for engine wear and catalyst operation, higher traffic conditions in metropolis was the main reason for the selection of this type of test. Test vehicles were selected as equal mileage and same specification, which are listed in Table 2. Test duration selected as km according to manufacturer directive and oil samples were taken at every 2500 km interval. In preparation for field testing, both of engines were flushed twice, and filled with oil to the full mark according to the level gauge. To more clearly observe the effects of prolonged use, vehicles received no replenishment when oil samples were taken.

3 Table 2. Specifications of the test vehicles Vehicle Body 4 Door Saloon Kerb weight 1133 kg Overall Height 1470 mm Overall Length 4280 mm Overall Width 1695 mm Engine Cylinder configuration In-line Number of cylinder 4 Valves per cylinder 4 Aspiration Naturally aspirated Bore x Stroke 75.5 x 78.1 mm Compression ratio 10 Displacement 1399 cc Fuel type LPG Fuel System Multi point injection Max. Power RPM Max. Torque RPM 2.3. Measurements and Analysis performances respectively, so these are expected to be worse when they are eliminated from conventional engine oil. A sulfur-based candidate additive which was developed and tested in previous studies can be a possible alternative to maintain sufficient antiwear performance without ZnDTP and calcium detergents [12]. NPNA oil does not contain Phosphorus, Zinc and Calcium based variations of these elements, as is shown from used oil analysis in Figs In spite of flashing, the residual levels of above mentioned elements are remained in the oil; this is an inevitable situation. Fig. 1. Change of Phosphorus respect to mileage Measurements consist of sampled oil s analysis. Measurements divide into two main types of which are catalyst surface analysis and used oil analysis. Ca, Zn, P and S elements on the catalyst washcoat surface detected with using electron probe micro analyzer (EPMA). With applying oil sample analysis, evaluation of wear elements, insolubles, viscosity, total base number (TBN) and total acid number (TAN) are determined. Measurements were done by according to the listed standards in table 3. Table 3. Used engine oil analysis methods Measured quantity Method Fig. 2. Change of Zinc respect to mileage. Viscosity@40 C ASTM D 445 Viscosity@100 C ASTM D 446 Acid number ASTM D 664 Base number ASTM D 2896 Water content ASTM D 4928 Wear Metal analysis ASTM D RESULTS & DISCUSSION 3.1. Used Oil Analysis Results Metal detergent and ZnDTP are usually formulated to satisfy engine detergency and antiwear Fig. 3. Change of Calcium respect to mileage 3

4 According to our fleet test, kinematic viscosity trends of test oils were similar, as shown in Fig. 1. After km, higher rate of decrease obtained for both of oils. Fuel dilution can be eliminated in a LPG fuelled vehicle; at this situation water content in the oil is the possible cause of the reduction of viscosity. As shown in Fig. 2, almost equal quantity of water condensed in both of the test engines this can be related to harshness of taxi service, which comprises cold starts and lower averaged drive speed when compared to normal driving conditions. Fig. 6. Change of TAN with respect to mileage. Fig. 4. Change of kinematic viscosity respect to mileage Fig. 7. Change of TBN with respect to mileage The concentration of the metallic elements in the oil samples is also analyzed. The metallic element values are considered an indicator of the amount of wear to sliding parts inside an engine. The results of elemental analysis are shown in Figs Fig. 5. Change of water content of oils respect to mileage Figures 3 and 4 indicate the change of acid number and base number. Total acid number of the test oils increased significantly at the end of the test. Trend of TAN in PC oil kept constant but a rapid increase was found in NPNA oil after 10,000 km. On the other hand, base number of NPNA constantly decreased and reached almost zero; therefore the rapid TAN increase is due to the loss of alkalinity. Fig. 8. Change of Fe with respect to mileage. 4

5 PC NPNA Fig. 9. Change of Cu with respect to mileage Fig. 11. Preparation of the catalyst patterns The surface analysis by EPMA was conducted to investigate the effect of lubricant s composition on the catalyst performance. EPMA analysis results are shown in Fig. 12, blue colour on the catalyst surface refers the weak accumulation of the indicated element while the red colour indicates strong one. Fig. 10. Change of Al with respect to mileage. Copper levels in NPNA oil samples are higher than PC oil but still in comparable levels and indicate acceptable levels of bearing wear. Also, absence of aluminium and chromium wear element indicates sufficient lubrication provided for piston-liner surface. On the contrary, iron wear of NPNA oiled engine at least three times greater than PC oiled one. According to Fig. 8, NPNA oil anti-wear performance decreased significantly after km which is the start of the rapid increase in TAN value. From the perspective of wear elements, NPNA oil s performance is already in acceptable levels Catalyst Surface Analysis Results At the beginning of the test, catalysts of the vehicles replaced with original unused ones to distinguish the amount of poison element accumulation on the surface. At the end of the test, aged catalysts removed from the test vehicles and analyzed individually. First, the honeycomb structure of catalyst was removed from the exhaust pipe assembly than cut into half and the patterns was obtained from the centre of the catalyst as 1cm square blocks, whole process depicted in Fig. 11. Fig. 12. Results of EPMA surface analysis Distinguishable amount of Ca, P and Zn detected with PC oil and little quantity of poison element 5

6 accumulated with NPNA oil, which did not originally come from its chemical structure. The results are in harmony with used oil analysis; NPNA oil eliminated the Ca, Zn and P accumulation. Therefore, it can be expected to maintain a good catalyst performance. 4. CONCLUSIONS In this study, performance and the effect of phosphorus-free engine oil (NPNA) on engine wear was experimentally investigated and compared to phosphorus containing (PC) engine oil. A field test conducted with two identical, spark ignition (SI) engine powered commercial taxi vehicles. A single oil drain period was considered and oil samples were taken at equal intervals. With applying oil sample analysis, the evaluation of wear elements, insolubles, viscosity, the total base number (TBN) and the total acid number (TAN) are determined. According to the results of fleet test, the obtained conclusions are listed as: a- Viscosities are decreased with similar trend for test oils, after 10,000 km, higher rate of decrease obtained for both of oils. b- A rapid increase was found in TAN levels with NPNA oil after km when compared to PC engine oil. c- Depending upon trace metal analysis,copper levels in NPNA oil samples are higher than PC oil but still in comparable levels and indicates acceptable rates of bearing wear. d- Aluminium and chromium wear results are significantly low for both of test oils; hence these results indicate that sufficient lubrication provided for piston-liner surface. e- Iron wear of NPNA oiled engine is greater than PC oiled engine, but still in acceptable levels. ACKNOWLEDGMENTS This work was supported by Idemitsu Kosan Co. Ltd. and the authors would like to thank Dr. Hiroshi Fujita for his contributions throughout this study. REFERENCES 1. Sideris M., 1998, Methods for monitoring and diagnosing the efficiency of catalytic converters - A patentoriented survey - Introduction., Stud Surf Sci Catal., Bartholomew C.H., 2001, Mechanisms of catalyst deactivation. Appl Catal a-gen. 212, pp Nova I., Acqua L.D., Lietti L., Giamello E., Forzatti P., 2001, Study of thermal deactivation of a de- NOx commercial catalyst. Appl Catal B-Environ, 35, pp Arakawa K., Matsuda S., Kinoshita H., 1997, SOx poisoning mechanism of NOx selective reduction catalysts. Appl Surf Sci., 121, pp Barnes A.M., Bartle K.D., Thibon V.R.A., 2001, A review of zinc dialkyldithiophosphates (ZDDPS): characterisation and role in the lubricating oil, Tribol Int. 34, pp Eaton S.J., Bunting B.G., Toops T.J., Nguyen K., 2009, The Roles of Phosphorus and Soot on the Deactivation of Diesel Oxidation Catalysts. In: SAE International, Eaton S.J., Nguyen K., 2006, Deactivation of Diesel Oxidation Catalysts by Oil-Derived Phosphorus, SAE International, Forzatti P., Lietti L., 1999, Catalyst deactivation. Catal Today, 52, pp Twigg M.V., Collins N.R., Morris D., O Connell T.J., Ball I.K., 2004, The Effect of Phosphorus and Boron Lubricant Oil Additives on Catalyst and Engine Durability, SAE International, Bardasz E., Schiferl E., Curtis T., 2010, Controlling Lubricant Derived Phosphorous Deactivation of the Three Way Catalysts Part 1: Assessments of Various Testing Methodologies, SAE International, Bardasz E., Schiferl E.A., Vilardo J.S., Curtis T.T., 2010, Controlling Lubricant-Derived Phosphorous Deactivation of the Three-Way Catalysts Part 2: Positive Environmental Impact of Novel ZDP Technology, SAE International, Katafuchi T., Shimizu N., 2007, Evaluation of the antiwear and friction reduction characteristics of mercaptocarboxylate derivatives as novel phosphorous-free additives, Tribol Int., 40, pp