SELECTION OF LUBRICATING OIL AIMED AT REDUCTION OF IC ENGINE FRICTION LOSSES

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Barbara Janiszewska
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1 Journal of KONES Internal Combustion Engines 003, vol. 0, No 3-4 SELECTION OF LUBRICATING OIL AIMED AT REDUCTION OF IC ENGINE FRICTION LOSSES Anna Krzymień, Piotr Krzymień Institute of Combustion Engines and Fundamentals of Machinery Design Poznań University of Technology ul. Piotrowo 3, Poznań Phone: +48(6) , Fax: +48(6) Abstract Rheological properties of lubricating oil decisively affect the engine internal power loss. An increase in engine mechanical efficiency can be achieved through the reduction in engine s power loss caused by friction. The paper will present some results of an experiment carried out on a SI engine lubricated with three types of lubricating oil. The achieved results allow to formulate conclusions relating to the reduction of friction loss thanks to the use of proper oil. MOŻLIWOŚCI OBNIŻENIA STRAT TARCIA SILNIKA O ZAPŁONIE ISKROWYM W ZALEZNOŚCI OD RODZAJU ZASTOSOWANEGO OLEJU Streszczenie Właściwości reologiczne oleju smarującego w zasadniczy sposób wpływają na wartość oporów wewnętrznych silnika. Zwiększenie sprawności mechanicznej można uzyskać m. in. przez zmniejszenie strat tarcia potrzebnych na pokonanie oporów własnych silnika spalinowego. W pracy zostaną przedstawione wyniki badań mocy tarcia silnika o zapłonie iskrowym do smarowania którego zastosowano trzy rodzaje oleju. Uzyskane wyniki pozwalają na sformułowanie wniosków odnośnie zmniejszenia oporów tarcia w wyniku zastosowania odpowiedniego oleju smarującego.. Introduction Following kinds of efficiency serve as indicators of engine run: theoretical (η t ), indicated (η i ), thermal (η c ), mechanical (η m ) and total efficiency (η o ). Hence, the last is the product of all efficiencies: η o = η η c m = η η η t i m In spite of constant efforts on engine modernization and development, the IC engine total efficiency is still quite low and equals η = [7]. Therefore the constructors attention is focused on each of constituent efficiencies. The mechanical efficiency constitutes the measure of engine parts production and lubrication quality as well as the volume of energy consumed as a result of auxiliaries operation. Energy loss result from: friction, gas exchange, auxiliaries drive, ventilation,

2 blower or mechanical supercharger drive. The engine mechanical efficiency can be increased thanks to modern manufacturing of cooperating parts, e.g. journals and shells or elements of the crank mechanism as well as improvement of lubricating media like lubricating oil. The analysis of mechanical loss proved that the decisive role play friction losses in crank mechanism, which constitute as much as 65% of the total mechanical loss. Other losses result from the drive of such mechanisms as cooling water pump, lubricating oil pump, fan, alternator, compressor or hydraulic pumps. The rheological properties of lubricating oil affect the engine inner resistance, which eventually manifest in increased fuel consumption and toxic emissions [3]. This makes that lubricating oil should reduce the wear of rubbing surfaces when engine runs. As to achieve this, the oil should be viscous in order to build up a continuous oil film between cooperating surfaces and at the same time should be liquid for quick distribution over the lubricated area. Because of those requirements the most wanted oils are those which possess low viscosity, but a high viscosity index, i.e. those of viscosity relatively stable with changes in temperature.. Test bed investigations Tests have been carried out in order to prove a relation between the type of lubricating oil and friction loss in an IC engine. They were performed on a typical test bed furnished with a 4-stroke gasoline engine ((N e = 55. kw at 500 rpm, M o = 4.7 Nm at 300 rpm). LOTOS lubricating oils (synthetic, semi-synthetic and mineral one) have been used for lubrication. The properties of each lubricating oil have been presented in Table. Table. List of LOTOS lubricating oils properties No oil type Syntetic Semisyntetic API Quality API Quality Parameter SJ/CF/EC SAE 5W/40 SG/CD SAE 0W/40 Density at 0 O C [g/ml] Mineral API Quality SG/CD SAE 5W/40 Kinematic Viscosity at O C [mm /s] 3 Viscosity Index 65 (55, min.) 50 (40, min.) 35 (30, min.) 4 Dynamic Viscosity at O C [mpa s] (3500, max.)) (3500, max.)) (3500, max.) 5 Dynamic Viscosity at O C [mpa s] 6 HT/HS Viscosity [mpa s] Flash Point Contents of volatile parts, Noack method [%} (0, max.) (3, max.) (55, max.) 9 Water [%] no no no The research methodology consisted in application of two methods of engine friction power determination: method of external drive the IC engine is driven by an electric motor with swinging stator, which allowed reading the value of torque necessary for maintain the engine run at applied speed, and measured at the IC Engine Laboratory of PUT as above

3 method of subsequent cylinder exclusion where reading of the torque value is carried out after exclusion of ignition in consecutive cylinders. Details of both methods can be found in [6]. Measurements of friction power performed according to the first method have been carried out for three values of rotational speed at engine run temperature (75±5 o C, measured in oil sump). The results are presented in Table. Table. Results of test-bed investigation friction power determined according to the external drive method for LOTOS oils Oil type Mineral oil Semisynthetic oil Synthetic oil Oil temperature t o [ o C] Rotational speed Torque M o [Nm] Friction power N t [kw] The measurements of engine mechanical efficiency followed the introductory tests of mechanical loss of the external drive, i.e. electrical motor with an articulated shaft and gear box. Relation between external drive unit mechanical loss and rotational speed were presented in Fig.. 5,00 N t [kw] 4,00 3,00,00,00 0,00 Fig.. Mechanical loss of external drive vs. rotational speed η m 0,80 0,78 0,76 0,74 0,7 0,70 0,68 3 0,66 0,64 0,6 0,60 Fig.. Mechanical efficiency vs. speed determined according to the successive cylinders switch off method for three types of lubricating oil: synthetic (), semisynthetic () and mineral one (3) at the temperature of engine run (oil sump temperature 75±5 o C).

4 The next figure presents the comparison of mechanical loss determined according to the external drive method for three types of lubricating oil and different speeds at the temperature of engine run (oil sump temperature 75±5 o C). 3. Result analysis Figs. 3 and 4 present the comparison of mechanical loss determined according to the external drive method and the successive cylinders switch-off method, respectively, for three types of lubricating oil: mineral (), semisynthetic () and synthetic one (3) at the temperature of engine run (oil sump temperature 75±5 o C). 4 Nt [kw] Fig. 3. Comparison of mechanical loss determined according to the external drive method for three types of lubricating oil: mineral (), semisynthetic () and synthetic one (3) at the temperature of engine run (oil sump temperature 75±5 o C). 8,00 N t [kw] 7,00 6,00 5,00 4,00 3,00,00,00 3 0,00 Fig. 4. Comparison of mechanical loss determined according to the successive cylinders switch-off method for three types of lubricating oil: mineral (), semisynthetic () and synthetic one (3) at the temperature of engine run (oil sump temperature 75±5 o C). Comparing the values of friction loss determined according to both methods mentioned one should notice that the method of external drive gives results higher than those obtained using the other method. The difference results from the mechanical power loss generated by the drive unit (see Fig. ). Taking it into account the results achieved are almost identical, what proves the accuracy of measurements. Friction loss increase with speed almost linearly for all types of lubricating oil used in the tested engine. In the case of mineral oil they are the highest for the entire range of rotational speed. For semisynthetic and syntetic oil the friction losses are about the same in the speed range 000 to 3000 rpm (see Fig. 4).

5 4. Conclusions The tests carried out on a test bed allow to formulate the following observations: in running engine the lowest friction power loss has been encountered for synthetic oil, a little bit higher for the semisynthetic oil, the same values of friction losses achieved using both methods prove the accuracy of measurements (at the same test conditions), in order to verify the obtained results it seems to be useful to carry out similar examination, but for a modern engine lubricated with synthetic oil of new generation. References [] Krzymień A.: Wyznaczenie strat tarcia w węzłach ciernych silnika spalinowego. Zagadnienia Eksploatacji Maszyn.. Z. (06), Vol.3/996. PWN Warszawa 996, [] Krzymień A., Krzymień P.: Wpływ rodzaju oleju na straty tarcia pierścieni tłokowych w czterosuwowym silniku samochodowym w warunkach rozruchu. Eksploatacja silników spalinowych, Zeszyt Nr 6 Problemy Rozruchu silników spalinowych, Szczecin 00. [3] Krzymień A., Krzymień P.: Badania stanowiskowe wpływu rodzaju oleju smarującego na straty tarcia w czterosuwowym silniku spalinowym o zapłonie iskrowym. Nr pracy 5-89/00/DS (praca niepublikowana). [4] Merkisz J.: Ekologiczne problemy silników spalinowych Tom., Wydawnictwo Politechniki Poznańskiej, Poznań 999. [5] Serdecki W.: Wpływ wybranych parametrów pracy silnika na straty tarcia w układzie tłokowo-cylindrowym. KONMOT 996 [6] Serdecki W.: Badania silników spalinowych. Laboratorium. Wydawnictwo Politechniki Poznańskiej, Poznań 00.

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