Atul.S.Shah, Dr.D.V.Bhatt

Transcription

1 Experimental Approach to Investigate Friction Contribution of Each Element in PRA System under Different Variables on Multicylinder Motorized Test Rig - A Case Study Abstract The understanding of tribology is more important in reducing friction of an Internal Combustion Engine i.e. piston ring assembly (PRA). Piston Ring Assembly is the heart of the Internal Combustion Engine. The knowledge of tribological factors is important to reduce frictional losses, emission level and also to improve the fuel economy in an I.C. engine. The frictional losses are in the PRA vary from approximately 40 to 50% of the total mechanical losses as reported in the literature. There are many different types of four stroke multi cylinder petrol engine automotives are available in different capacity in the market with a fuel efficiency of 10 km/lit to 25 km/lit. Experiments are done at laboratory scale to measure PRA friction on multi cylinder 800 cc engine test rig by measurement of power consumption under different operating parameters i.e. speed, lubricants and PRA system elements. The authors have put efforts to find out Frictional power loss variation under individual piston ring under different speed and lubricants. From experimental results it is observed that without 1 st or 2 nd piston ring individually, the power consumption is less than the power consumption under standard assembly condition. The role of piston oil ring is observed critical in PRA system. Index Terms PRA, Piston Ring, Tribology. I. INTRODUCTION IC engine was invented two centuries back. In these two centuries more and more improvements were carried out and this process is still continuing. Referring to present scenario of energy crisis and environment pollution it has become a need, to check possibilities for improving fuel efficiency by decreasing losses, to make more environment friendly vehicle by decreasing pollutants and to check other options means alternative fuels to run an engine. Around 13 to 18% frictional losses are observed in automotive vehicles. Approximately 40 to 50 % losses of total losses are contributed by only PRA system. If this losses are reduced even by in turn of 1% it may results in saving of scare petroleum fuels due to vigorous market growth of automotive products for this efforts should be put in study the Tribological behavior of the PRA system. There are many types of four stroke multi cylinder automotive petrol engines are available in market with fuel efficiency of 10 Km/lt to 25 Km/lt. 800c.c vehicle enjoys the market share more than 50% and there for it is preferable to select engine system for the study. The research study is mainly focused on experimental work. Authors have put efforts in this experimental work to find out the friction losses in various elements and for this the Motored engine friction test Atul.S.Shah, Dr.D.V.Bhatt 93 method (strip method) [10] is used. It is generally adopted to get the first impressions about frictional losses of multi cylinder engine (unfired) and also the frictional losses of various components. II. PREVIOUS RESEARCH WORK Nautiyal et. al.,[1] studied friction and wear process in piston rings and friction co-efficient were investigated on a modified Bowden-Leben machine using actual segments of piston ring and cylinder liner. Experiments were carried out with an objective to study the friction characteristics and the lubricant failure mechanism under simulated conditions as existing neat the TDC of the top piston ring. Co-efficient of friction remains more or less constant with increase in oil temperature but sudden stiff rise observed as soon as lubricating oil losses its viscosity to sustain operating load that 400 K. Large part of top piston ring wear of an I.C. Engine takes place during boundary lubrication around TDC position. The surface temperature, peak-combustion pressure and physical property of material are the responsible factor for wear. Hoshi [2] has experimented on 1300cc 4-cylinder petrol engine and identified various friction loss contributing systems individually in an engine at 2000 rpm without load and at 5000 rpm with full load by using lubricating oil as SAE 10W30 oil at constant temperature 800C and concluded that Friction losses in piston system were reduced by 23% that amounted to % of total frictional losses by changing the piston shape and reducing cross section. 3% of total frictional losses reduced by reducing slightly diameters and width of bearing on crankshaft and connecting rod. Estimated total % frictional losses were observed at 2000 rpm without load and at 5000 rpm with full load were 21% and 17% respectively Ting [3] have used test bench for measurements and found that PRA friction force was increased linearly with the piston speed and observed that use of low viscosity oil cause sudden increase in wear at TDC and BDC. Wakuri T. [4] studied the frictional behaviors by varying no. of piston rings 5-nos., (3 comp. +2 oil) and 3 nos. (2 comp. +2 oil) and concluded that it is effective to decrease the number of piston rings. They have performed computations of piston ring friction in I. C. engines as the friction between the piston ring and cylinder liner significantly contributes to the mechanical power loss of the engine. Tateishi [5] has experimented to reduce piston ring friction losses by applying two-ring package instead of the standard three ring packages and by developing low

2 viscosity engine oil, reduction in piston mass, piston ring width and piston ring tension. Reduction of piston ring tension and using two ring packages are effective in reducing piston ring friction and reduction of piston ring friction can contribute to reducing the fuel consumption by several percentages. C.M. Taylor [6] focused on the major frictional components of the automobile engine, that is, the bearings, the valve train and the piston ring assembly. Noorman [7] measured friction by motoring of an engine by an electric dynamometer and found that motoring friction was increase with increase in speed. D.V.Bhatt, Mistry [8] have experimented on motorized piston-cylinder system with an application of different lubricants SAE-15, SAE-20, SAE-30 & 2T along with the different piston ring geometry at a RPM range from 500 to 1850 and found that ring geometry also response differently in case of same lubricant. One side chamfering on TDC side has offered the minimum friction. Peter Anderson [9] and many others measured the electrical resistance between the piston ring and cylinder liner to determine the oil film thickness. Oil film breakdown was indicated by abrupt fall of resistance near the end of stroke (TDC/BDC). Sharma [10] has experimentally studied the various parameters of the engine Tribology and experimented with various application of the piston ring geometry at low profile at the piston ring edge and offered a co-relation in the form of equations with a different constant of system. He concluded that oil film thickness doesn t depend on ring thickness but is highly dependent on the ring curvature Taylor [11] suggested a procedure to calculate PRA friction loss by solving Reynolds equation. The calculation of oil film thickness under the piston rings involves solving Reynolds equation, using the appropriate piston ring profile and taking into account the variable speed of the piston ring as the piston moves from BDC to TDC. It is also necessary to know the gas pressure on either side of the piston ring, the piston ring temperature and the liner temperature at the piston ring position. If all these parameters are known, then the oil film thickness and friction force of the piston ring may be calculated. Bolander etal.,[12] have developed the numerical model to investigate the effects of surface modifications on the lubrication condition and frictional loss at the interface between a piston ring and cylinder liner and observed that the modified cylinder liner was shown to reduce the cycle-average friction coefficient by 55-65%, while total energy loss per cycle was reduced by 20-40%. Victor W. Wong (2005) [13] have done experiments and found that the PRA friction force was found to increase linearly with the piston speed, decrease with increasing oil film temperature and slightly increase with gas pressure. Riaz A. Mufti and Martin Priest [14] have measured the piston assembly friction losses under fired condition on a single cylinder Ricardo Hydra Gasoline Car engine using the IMEP method and with the help of data logger system. The test was carried out under fired condition with lubricant inlet temperature of 24 C, 40 C, 60 C and 80 C. The piston assembly friction was measured at engine speeds of 800 rpm with 25% load; rpm with 50% load and at 2000 rpm with 50% loading, SAE0W20 lubricant without friction modifier was used. Piston assembly friction force found approximately double during power stroke and compression stroke in comparison to exhaust and suction stroke in an engine cycle at all different speeds and lubricant inlet temperature. Piston ring friction losses (both rings) also observed about 30-35% of total piston assembly power losses at different experimented speeds. Power loss by first compression ring is always found more than second ring at all different speeds. Power loss by first ring is found approximately 33% higher than that of second ring at all different operating conditions. Experimental power loss in piston assembly friction is found less than the theoretical predicted total friction. Zheng M A, Naeim A. Henein, Walter Bryzik [15] has developed a onedimensional elstohydrodynamic mixed lubrication wear and friction model. The model can predict the effects of surface roughness, asperity contact, and temperature pressureviscosity on wear, lubrication, and friction of the piston rings and cylinder liner. Wear is predicted based on the surface asperity contact pressure. The cylinder bore wear and the ring pack friction during an engine break-in are simulated and compared with the experimental results. The influence of cylinder wall temperature and surface roughness on friction and wear is investigated. The ring pack friction due to oil viscous shearing and asperity contact is found to reach its minimum at a certain oil temperature and observations are made George A. Livanos, Nikolaos P. Kyrtatos 16] A general-purpose engine piston assembly friction model to study and developed for predicting the frictional losses of each piston assembly component (piston rings, piston skirts and gudgeon pin) independently. He experimented on a four stroke medium-speed marine diesel engine in laboratory of Marine Engineering test-bed and variables are engine speed and engine load on predicted piston assembly friction losses was examined and compared with results obtained from other semi-empirical FMEP models. It was found that the new model follows the trends of the existing models, having at the same time the advantage of detailed simulation of lubrication conditions prevailing on piston assembly. E. Abu-Nada, l. Al- Hinti, A. Al- Sakhi, B. Akash [17] has presented thermodynamic analysis of piston friction in spark-ignition internal combustion engines. The effect of piston friction on engine performance was examined during cold starting and normal working conditions. A parametric study was performed covering wide range of dependent variables such as engine speed, taking into consideration piston friction combined with the variation of the specific heat with temperature, and heat loss from the cylinder. The results are presented for skirt friction only, and then for total piston friction (skirt and rings). The effect of oil viscosity is investigated over a wide range of engine speeds and oil temperatures. He observed that oils with higher viscosities result in lower efficiency values. Using high viscosity oil can reduce the efficiency by more than 50% at cold oil temperatures. Efficiency maps for SAE 10, SAE 30, and SAE 50 are reported. The effect of

3 different piston ring configurations on the efficiency is also presented. The oil film thickness on the engine performance is studied in this paper. Riaz A. Muftil and Martin Priest [18] has discussed about the three main tribological components responsible for the frictional losses in an engine are the piston assembly, Valve train, Bearings. There are two main types of frictional losses associated with these parts: shear loss and metal to metal friction. Thick oil in an engine will reduced the boundary friction but will increase shear losses. The thin oil in an engine will reduce the shear friction but will increase boundary friction and wear. They describe how engine operating conditions affect the distribution of power loss at component level. P S Dellis [19] efficient engine operation is combined with effective lubrication in the ring/cylinder interface. This study is focused on parametric friction force measurements, their appearance close to the dead centers of the stroke, and how load, speed, and temperature affect the friction maxima. An approach is also attempted to the role of high-temperature, high-shear viscosity for a group of CASTROL lubricants. Piston rings with different curvatures were also tested, and friction power losses for each testing case are presented. The friction force maxima appear close to the piston stroke dead centres, but not exactly at the dead centres (i.e. 180 and360 ).The friction force peak sand the slight shift are due to the squeeze film effect between the liner surface and the piston ring, which forces the lubricant flow to delay compared with the mechanical movement of the crank III. EXPERIMENTAL SETUP The fabricated test rig, 800-CC multi cylinder internal combustion engine system with crank mechanism, piston cylinder head, engine lubrication system, and engine cooling system, without gear box is used. Crank shaft is coupled with induction motor to drive the engine. For varying the speed of test rig, the A.C. motor drive /variable frequency drive is used. The multi functional watt meter is used to measure the performance in terms of power consumption. (Refer Block diagram) A. Specification Table 1 Engine Specification TYPE 4 Stroke Cycle, Water Cooled No. Cylinder 3 Lubrication System Piston Displacement Wet pump High Pressure and Splash system kg/cm 2 at 3000 rpm. 796 C.C Compression Ratio 8.7 : 1 Table2 Motor Specification 3 ph 440V Induction Motor 7.5 k W rpm Table 3 A.C. Motor Drive Specifications (Variable Frequency Drive) Model Number VFD-XXXB,DELTA Electronics Inc. Applicable Motor Output Max. 7.5 (kw) Rated Output Capacity (kva) 13.4 Rated Output Current (A) 13.5 Rated Input Current (A) 13.8 Output Frequency (Hz) Hz B. Variables Lubricants: 20W40-Castrol GTX (A), Gulf (B), Maruti Genuine oil (Servo) (C) Speed (rpm): 600, 900, 1200, 1800, 2100, and 2400 Table 4 Sets of Experiment 1. Power consumption to run in original condition With standard coolant (3piston with standard ring) 2. Power consumption to run in original condition without Top ring. 3. Power consumption to run in original condition without 2 nd ring. 4. Power consumption to run in original condition with oil ring only. 5. Power consumption to run with piston only. 6. Power consumption to run Crank shaft only. Fig.1. Block Diagram of Test Rig IV. EXPERIMENTS METHODOLOGY The experimental work is carried out on developed multi cylinder I.C. engine test rig under different variables i.e. speed, different lubricant. In this experimental work the strip method is used to find out the friction of individual element of engine system. The test sequences to conduct experiments are as under. 1. First of all select coolant and lubricating oil and prepare the engine. 2. Check all electrical connection of test rig including VFD and watt meter etc. 3. Switch on the power supply and set the frequency on VFD to required rpm. 4. Initially the system is to be run for at lest 5 to 10 minutes, so that the system get stabilize & the lubricating oil can reach properly up to the surface of piston rings and cylinder liner. 95

4 Power (kw) Power (kw) Power (kw) ISSN: After getting the stable condition of the system, record the rpm of the system and also the power consumption. 6. Now for the next measurement, change the frequency on VFD to change the rpm of the system and allow time to stabilize. 7. Now repeat the same procedure for another measurement. 8. Like vise different 18 set of experiments as per the table are taken and record all the measurements plotted in graphical form V. RESULTS AND OBSERVATIONS Speed v/s Power (Oil-A) Sid W/O Top ring W/O 2nd Ring With Oil ring With Piston only With Crank Shaft only Engine Speed (rpm) Fig. 2. Speed V/S Power (Oil-A) From fig.2 PRA set without 1 st ring the power consumption is lesser in comparison to standard operating condition at all observed speed. The variation in the power reduction varies between 4 to 13.5% in comparison to power consumption value under standard operating conditions. PRA set without 2 nd ring power consumption is lesser in comparison to standard operating condition at all observed speed. The variation in the power reduction varies between 4.3 to 19.4% in comparison to power consumption value under standard operating conditions. PRA set without both piston rings, except at 600 rpm, the power consumption is higher than the standard power consumption value at all rpm with stiff rise. PRA set with piston only except at 600 rpm, the power consumption is higher than the standard power consumption value at all rpm with stiff rise. Maximum power consumption at all speeds except at 600 rpm in comparison to all different test results shown and with crank shaft only power consumption is increases with speed linearly Speed v/s Power ( Oil- B) Std W/O Top ring W/O 2nd ring With Oil ring With Pistin only With Crank Shaft only Engine Speed (rpm) Fig. 3. Speed v/s Power (Oil-B) 96 From fig. 3 PRA set without 1 st ring the power consumption is lesser in comparison to standard operating condition at all observed speed. The variation in the power reduction varies between 5.3 to 12.2% in comparison to power consumption value under standard operating conditions. PRA Set without 2 nd ring power consumption is lesser in comparison to standard operating condition at all observed speed. The variation in the power reduction varies between 4.3 to 16.4% in comparison to power consumption value under standard operating conditions. PRA set without both piston rings except at 600 rpm, the power consumption is higher than the standard power consumption value at all rpm with stiff rise. PRA set with piston only except at 600 rpm, the power consumption is higher than the standard power consumption value at all rpm with stiff rise. Maximum power consumption at all speeds except at 600 rpm in comparison to all different test results shown and with crank shaft only power consumption is increases with speed linearly Speed v/s Power (Oil-C) Std. W/O Top ring W/O 2 nd ring With Oil ring With Piston only With Crank Shaft only Engine Speed (rpm) Fig. 4. Speed v/s Power (Oil-C) From fig. 4 PRA set without 1 st ring the power consumption is lesser in comparison to standard operating condition at all observed speed? The variation in the power reduction varies between 5.2 to 11.6% in comparison to power consumption value under standard operating conditions.pra Set without 2 nd ring power consumption is lesser in comparison to standard operating condition at all observed speed. The variation in the power reduction varies between 4.5 to 13.9% in comparison to power consumption value under standard operating conditions.pra set without both piston rings except at 600 rpm, the power consumption is higher than the standard power consumption value at all rpm with stiff rise. PRA set with piston only except at 600 rpm, the power consumption is higher than the standard power consumption value at all rpm with stiff rise. Maximum power consumption at all speeds except at 600 rpm in comparison to all different test results shown and with crank shaft only the power consumption is increases with speed linearly. VI. DISCUSSION From fig it is observed that variation in PRA friction having without 1 st ring the power consumption is less at all observed speed. The variation in the power

5 reduction varies between 4 to 13.5% in comparison to power consumption value under standard operating conditions. The result gives a further research scope above the location of the piston ring with respect to crank centre because the similar observation without 2 nd ring found increase in power reduction variation between 4.3 to 19.4 %, thus it can be said that there is a scope of alternative location of 2 nd ring to study power reduction variation. However the results are in good arrangement with published literature. The frictional power reduction variation contributed by 1 st ring is more effective than with 2 nd ring application. (Without 1 st ring) Friction losses by oil ring observed comparatively significant without 1 st and 2 nd ring but along with one of the (1st or 2 nd ) it has observed significant reduction in power loss indicates the key role of oil ring in PRA system. The nature of curve with oil ring and with one of the piston ring is similar to the striback cure while without 1 st and 2 nd ring the nature of curve does not follow the striback cure nature but offers liner relationship power v/s engine speed. It proves that there is a need of piston ring combination for effective results. The effectiveness of lubricants is not significantly found however viscosity v/s Temperature calibration observed between room temperature to 60 0 C temperature. Same specified lubricants under different manufacturer shows variation in viscosity in fig. 5 calibrated chart and oil C has offers the best results among used three same specified oil. After 70 0 C viscosity variation is more or less same. Thus the results are useful for understanding the lubrication processes during low speed of the engine during start up of the cold engine. This method of frictional power loss measurement closely follows the defined strip method referred in literature review [10] Fig.5 Temp V/S Viscosity VII. CONCLUSION 1. Both piston rings do not offer equal friction as individual application st piston ring offers less friction than 2 nd piston ring in all cases. 3. Location of 1 st piston ring plays vital role and there is a scope of improvement. 4. Oil-ring friction is observed maximum at all speed while along with 1 st or 2 nd ring it is reduced significant. So role of oil ring is critical. 5. Same specified lubricants under different brand offers variation in PRA friction. REFERANCES [1] Nautiyal, P. C., Singhal, S., Sharma J. P., Friction and Wear Processes in Piston Rings, Tribology International, pp , [2] Hoshi, M., Reducing Friction Losses in Automobile Engines, Tribology International, Vol.17, No.4, pp , August [3] Ting, L. L., A Review of Present Information on Piston Ring Tribology, SAE paper , [4] Hamatake, Wakuri T., Soejima, M., Kitahare, T. Piston Ring Friction in I.C. Engine, Tribology International, Vol.25, No.5, pp , [5] Tateishi, Y., Tribological Issues in Reducing Piston Ring Friction Losses, Tribology International, Vol.27, [6] C. M. Taylor, Automobile Engine Tribology Design Considerations for Efficiency and Durability, Tribology International Wear 221, pp.1 8, 1998 [7] Noorman, M. T., Overview Techniques for Measuring Friction using Bench Tests and Fired Engines, SAE International, pp. 1-11, June 2000 [8] D.V. Bhatt, Mistry K. N., Friction Measurement in Reciprocating System A Case Study, IPROMM, 2000, Workshop, Nagpur pp.19-20, Jan [9] Peter Anderson and etc., Piston ring tribology-a literature survey, VTT Tiedotteita, 105 pages, Espoo [10] Sharma, R. P., Technical Advisor, Mahindra and Mahindra. Practical Consideration in Engine Tribology, Proceedings of Workshops in Current Trends in I.C. Engine Development, Hyderabad. April, [11] Taylor, R. I., Lubricant, Tribology and Motor sport, Shell Globe Solutions (UK), , PP 1-16 ASME Journal of Tribology, Vol.127,pp. 1-22, October [12] Bolander, N. W., Steenwyk B.D., Sadeghi F, Gerber G. R., Lubrication Regime Transitions at the Piston Ring Cylinder Liner Interface, Journal of Engineering Tribology, Proc. ImechE Vol. 219, Part J, pp ,2005. [13] Wong, V. W. (Principal Investigator, MIT), Low Engine Friction Tribology for Advanced Natural Gas Reciprocating Engines, Advanced University Reciprocating Engine Program (AUREP), Annual Review Meeting, Argonne, IL, pp. 1-62, July 12, [14] Mufti, R. A. and Priest, M., Experimental Evaluation of Piston Assembly Friction under Motored and Fired Conditions in a Gasoline Engine, ASME Journal of Tribology, Vol.127, pp.1-22, October [15] Zheng MA, Naeim A. Henein, Walter Bryzik A Model for Wear and Friction in Cylinders and Piston Tribological Transactions, 49, pp , [16] George A. Livanos, Nikolaos P. Kyrtatos Friction model of a marine diesel engine piston assembly Tribology International 40, pp ,2007. [17] E. Abu-Nada, l. Al-Hint, A. Al-Sakhi, B. Akash "Effect of Piston Friction on the Performance of S.I Engine, A New Thermodynamic Approach" Journal of Engineering for Gas Turbines and power, Vol March

6 [18] Mufti R. A., Priest M Effect of Engine operating conditions and Lubricant Rheology on the Distribution of Losses in an Internal Combustion Engine Journal of Tribology, Vol. 131/ , October [19] P S Dellis Effect of friction force between piston rings and liner: a parametric study of speed, load, temperature, pistonring curvature, and high-temperature, high-shear viscosity J. Engineering Tribology.IMechE Vol. 224 Part J, January [20] Nagar, P., Miers, S., "Friction between Piston and Cylinder of an IC Engine: a Review," SAE Technical Paper , 2011 [21] Liao, K., Chen, H.,Tian, T., "The Study of Friction between Piston Ring and Different Cylinder Liners using Floating Liner Engine - Part 1," SAE Technical Paper , [22] D.V. Bhatt, PhD thesis Performance study of Tribological parameters of a Single Cylinder 2 stroke petrol engine S. G. University, [23] A.S.Shah, M.Tech thesis Development of PRA Friction Measurement Test Rig for Multi Cylinder Engine System and Experimental Study of Tribological Parameters SVNIT, AUTHORS PROFILE Atul S.Shah is Senior Lecturer in Mechanical Engineering Department, Government polytechnic, Waghai, and Gujarat, India. He has completed his M.TECH (Mechanical) from S.V.National Institute of Technology; Surat. He is Associate Dean of Gujarat Technological University, Gujarat, India. His area of Research Work is in Engine Tribology.. Dr D.V.Bhatt is Professor in Mechanical Engineering Department & Dean (Alumni and Resource Generation). He is Professor In charge of E.D. cell & Member Secretary Incubation Center, S.V.National Institute of Technology, Surat, and Gujarat, India 98