A Finite Element Thermo-Mechanical Stress Analysis of IC Engine Piston

Transcription

1 A Finite Element Termo-Mecanical Stress Analysis of IC Engine Piston Manis Kumar M.Tec., Dept. of Mecanical Engineering HBTI Kanpur, India *** Abstract - A piston is a component of reciprocating engines, pumps and gas compressors. It is located in a cylinder and is made gas-tigt by piston rings. Engine pistons are one of te most complex components among all automotive or oter industry field components. Piston and connecting rod are connected by te piston pin at one end of connecting rod and oter big end of connecting rod tan connected to cranksaft. Pistons are subjected to forces generated by ot burned gases on fuel combustion and in ig temperature combustion camber. Tese two causes result in termal and mecanical stresses. Mecanical stresses appear due to gas force and termal stresses due to ig temperature of combustion. In te present work, te termal boundary conditions are obtained to calculate te temperature distribution and termal stress in piston. Te analysis is carried out to identify te maximum and minimum stress location in piston. Te modeling of piston is carried out in CATIA software wereas ANSYS workbenc is used for te Finite Element Analysis. Von Mises stresses criterion is used in Finite element analysis. Key Words: Piston, Termo-mecanical, Stress, Temperature, Heat Transfer Coefficient 1. Introduction Pistons are subjected to forces generated by ot burned gases on fuel combustion and in ig temperature combustion camber. Tese two causes result in termal and mecanical stresses. Mecanical stresses appear due to gas force and termal stresses due to ig temperature of combustion; terefore, a piston must be capable of transmitting te kinetic energy of ig gas pressure and temperature. Te piston is subjected to te varying pressure and temperature by te gases and inertia forces due to te acceleration/retardation in a cycle. Te piston beaviour affected by termal-mecanical stresses penomenon due to cyclic termal and mecanical loadings. Te objective of present work is to predict te temperature distribution and stresses due to termal and mecanical loadings for te conventional pistons. Te analyses are carried out to identify te critical location of stresses and deformations. 1.1 Literature Review analytically of an S.I. engine. Douglas M. Baker et al. discussed about a metodology for a coupled termodynamic and eat transfer analysis for diesel engine wit 1-D and 2-D eat flow finite element models to find te piston and liner temperatures and eat transfer rate [4]. Madi Hamzeei et al. measured te temperature of piston and cylinder ead in a 4-cylinder gasoline engine at actual process [6]. Krisztina Uzuneanu et al. modeled te eat transfer in te piston ead of a spark ignition engine supplied wit etanol-gasoline blend using simple termal networks to multidimensional differential equation modeling [7]. Yanxia Wang et al. investigated te termomecanical coupling of piston using ANSYS software to find te temperature and stress distribution [8]. Dr. Amed beiruti et al. discussed te analytical study on te termal effects on te diesel engine piston and its compression rings during te contact between te piston and rings wit tree dimensional finite element metod using ANSYS software [9]. P. Gudimetal et al. analyzed te finite element analysis of reverse engineered internal combustion engine piston using ANSYS package [10]. 1.2 Temperature Field and Stress Locations Te piston is used to take te load from te combustion gases and transfer it to cranksaft troug connecting rod for te rotational motion in an engine, It sould be strong enoug to remain rigid under loading, and also be ligt enoug to reduce te inertia forces wic are produced wen te connecting rod and piston stop, cange directions and start again at te end of eac stroke. Piston is under te ig termal load and mecanical load. Tus te stresses in te piston are found greatly near te piston pin areas. [1] C.S. Wang et al. discussed a eat transfer model tat used quasi-steady eat flux relations to calculate te eat transfer from combustion gases troug cylinder wall to te coolant in an internal combustion engine to calculate te components temperature distribution [2].T. Morel et al. sowed te temperature and eat flow distribution Figure 1: Te piston stress locations 2017, IRJET Impact Factor value: ISO 9001:2008 Certified Journal Page 1976

2 2. Engine Heat Transfer Heat transfer analysis of engine is carried out using convection eat transfer, to calculate te eat transfer coefficient and ambience temperature on piston boundaries. A teoretical model is taken for te study wit engine specifications as sown in Table 1. Table 1: Engine specifications Bore Stroke 80 mm 110 mm Te conditions at coolant side [11], wall tickness, wall termal conductivity, molar mass and density of combustion gases are given in Table 2. Te average eat transfer coefficient at te gas side is calculated wit assumption Nusselt, Reynolds and Prandtl number relationsip for turbulent flow in pipes and over flat plates [5]: Nu = a Re m Pr n In present work, te mean eat transfer coefficient is calculated from empirical relationsip of Nusselt s equation [12] at mean pressure and bulk gas temperature P Tg ( C ) m m Connecting Rod 234 mm Table 2: Pysical & Termal properties of materials Compression Ratio 16.5 Rated Power SFC RPM 245 g / kw Te eat in engine is generated on combustion of fuel. Heat is transferred by all tree modes. Heat is transferred by conduction troug te cylinder ead, cylinder walls, and piston; troug te piston rings to te cylinder wall; troug te engine block and manifolds. Heat is transferred by forced convection between te in-cylinder gases and te cylinder ead, valves, cylinder walls, and piston. Heat excange by radiation occurs troug te emission and absorption of electromagnetic waves. Only convection eat transfer is taken into account in present work to obtain piston termal boundary conditions to predict temperature witin te piston to calculate te termal stresses. A typical eat transfer pat [5] is sown in Figure 2. Figure 2: Convection eat transfer from gas to coolant Parameter Value Bulk gas temperature, T gm 1162 K Gas eat transfer coefficient, m 293 W/m 2 K Cylinder wall temperature, T wg C Wall termal conductivity, k 46 W/mK Wall tickness, t w 6 mm Water temperature, T cm 80 o C Water eat transfer coefficient, c 1400 W/m 2 K Molar mass of combustion gas, M 29 kg/kmole Combustion gas density kg/m Termal Boundary Conditions In tis work, finite element termal analysis is carried out to calculate te piston temperature wit te elp of tird kind boundary condition as below [13]: T k ( T Tf ) n Were, T is te surface temperature, n is te exterior normal vector for te object boundary, is te convection eat transfer coefficient, k is te termal conductivity of object and T f is te ambience temperature at te boundary of te object. Te piston gets eat at crown from combustion wit convection mode and transfers tis eat to te wole piston in conduction mode and from warm piston to coolant; eat is transferred in convection mode of eat transfer. Hence, te convection eat transfer takes place at te boundary of te piston. Te piston is distinguised in many surfaces as sown in Figure 3 wit different ambience temperature and eat transfer coefficient. 2.1 Steady state eat transfer modeling Gas temperature is a function of crank angle in an engine and varies wit crank angle. So, for steady state termal analysis in tis work te following relationsip to obtain mean gas temperature at mean gas pressure [5], T gm = 2017, IRJET Impact Factor value: ISO 9001:2008 Certified Journal Page 1977

3 R R 3 4 ln( r / r ), conductive resistance of te liner Lk 3 liner 1, convective resistance between te liner A water s and te cooling water Figure 3: Surfaces of te eat excange of te piston Te boundary conditions are calculated of piston surfaces from literature wit numerical means of surfaces from A to H as figure 3, At piston crown face, A: Ambience Temperature is bulk gas temperature and gas side eat transfer coefficient. Ring land surface, B: Since tere is a small gap between piston crown and te liner, te captured gas temperature is te mean temperature of te crevice surfaces [14]. Terefore, te eat is conducted troug te gas wit te convective eat transfer coefficient: k Were is crevice clearance, 0.5 mm for te present work, for k = W/ m K It gives, = 94 W/ m 2 K, and te ambience temperature at tis face is taken as te wall temperature. Ring groove face, C: te rings are placed to make a tigt seal for gases. Te eat transfer modeling in tis region is obtained troug ring resistance approac. Te oil film resistance R 2 is neglected in tis face. Te eat transfer in rings is sown in Figure 4: Were, r 1, r 2, r 3 and r 4 are inner radius of ring, outer radius of ring, bore radius and inner radius of water-jacket, respectively. L 1, L 2 and L 3 are te widts of te eat transfer pats, respectively. Te effective eat transfer coefficient is obtained from, eff 1 R A Were, A eff is te piston surface in contact wit te ring and R tot is te total resistance. Oter ring land D and E: te eat transfer coefficient at tis face is taken as te one tird of te gas eat transfer coefficient and te ambience temperature is te 69.5 % and 66.5% of te first ring land temperature for D and E respectively [15]. Skirt F; Te eat transfer at tis face troug convection wit low coefficient [16]. Piston underside eat transfer G and H: te piston underside is divided into two regions: Region G and H, te crown underside is cooled by splas cooling type. Te ambience temperature is taken in tis region te oil temperature [15]. Te value of convective eat transfer coefficient is calculated from te following equations, H RPM tot eff G RPM Te surface boundary conditions, eat transfer coefficient and gas temperature ambience to te piston surface for given Figure 3 are calculated as given in Table 3 below: Table 3: Piston termal boundary conditions Figure 4: Termal circuit of eat transfer resistances in te region of te rings Were, R 1: conductive resistance of te ring, R 2: conductive resistance of te oil film is negligible, R 3: conductive resistance of te liner, R 4: convective resistance between te liner and te cooling water. Te resistances are: R ln( r / r) 2 1 1, conductive resistance of te ring 2 L1 kring Termal boundary Ambience temperature [ 0 C] Heat transfer coefficient[w/m 2 K] Piston crown, A Crevice surface, B Rings, C Ring land, D Ring land, E Skirt, F Underskirt, G Under crown, H , IRJET Impact Factor value: ISO 9001:2008 Certified Journal Page 1978

4 3. Mecanical Loading on Piston Te stress, strain and deformations are te most serious wen te explosive pressure of te fuel gas acieves maximum under te condition of stable rotational speed. Terefore, te researc of te stable stress under te maximum explosive pressure is very important [17] and te inertia- forces at te maximum acceleration at te condition of maximum gas pressure at TDC teoretically. 3.1 Gas Pressure Model Te gas pressure model is described witout te effect of temperature acting on te piston crown, combustion camber surface, field of fire, ring grooves and so on as sown in Figure 5. gravity. Te maximum reciprocating inertial force can be calculated as: 2 P m (1 R j j In ANSYS, te inertial force is not loaded directly, but acceleration is loaded in it. Software calculates te inertial force automatically wit take te mass of piston into account. Te acceleration is obtained as: ar 2 (cos cos 2 ) Among tem, is te crank angle: = RPM / 30 is te link rod ratio: = R/L 3.3 Constraint Conditions for Mecanical Loading Tree freedom degrees of te piston pin are restrained to let te piston in a static condition to eliminate te revolving of te piston around te piston pin. Te selection of te displacement boundary condition is very important to te finite element analysis. If te selection is not correct, it will affect te calculation precision. On te moment of te maximum gas pressure, te pin contacted to te surface of te pin ole [18]. 4. Finite Element Analysis Figure 5: Variation of gas pressure along cylinder axis Te maximum explosive pressure is taken as 10 times of mean effective pressure. Te maximum gas pressure P is 5.5 MPa for pressure loading on piston top wic is te 10 times of mean effective pressure approximately. Te values of gas load on te piston are given in Table 4 [18]. Table 4: Gas pressure variation on piston Boundary field Load Value [MPa] Piston crown P 5.5 Bottom of first groove P 76% 4.18 Bottom of te second groove P 30% 1.65 Bottom of te tird groove P 20% Inertia Force Model Because te piston does te reciprocating motion in te cylinder, according to te Dynamics of Engine, tis process can produce te reciprocating inertial force P j. Its value is proportion to te acceleration of te piston [18]. Te mass of te piston is supposed to be concentrated in its centre of In tis section FE based stress analysis piston is carried out using ANSYS Workbenc software. Te ANSYS software is very important tool for te stress analysis, use to solve te problem related to te structure analysis wit complex structure and loading conditions, eat flow analysis, fluid flow analysis and design optimization. In tis present work te Steady State Termal and Static Structural tools of ANSYS software are used to analyze te Termal and Mecanical stresses. Te piston material properties are given in Table 5[15]. Table 5: Material properties of piston Materials Young s Modulus(GPa) 71 AlSi Alloy Density (kg/m 3 ) 2770 Poisson s Ratio 0.33 Termal Conductivity (W/m 0 C) 155 Specific Heat (J/kg 0 C) 875 Termal Expansion ( /K) 23 Te next stage is to generate te mes in 3D piston model 4- node tetraedron element as sown in Figure , IRJET Impact Factor value: ISO 9001:2008 Certified Journal Page 1979

5 Figure 6: Finite element mes model of piston (a) 5. Results and Discussion 5.1 Piston Temperature Distribution Te piston temperature distribution as in Figure 7 canges between C to C wit te maximum temperature at te piston top and minimum temperature at te lower part of te piston skirt. At te piston ring land, temperatures are distributed uniformly along te piston in te radial direction. Te piston temperature canges uniformly from te piston top to te bottom, witout any sarp cange penomenon. Te eat absorbed from te gas by te piston crown is generally takes up 2-4 % of te total eat of fuel burning [19]. Te eat transfer for piston crown for present work is calculated from kw to kw. (b) (c) Figure 8: (a) Equivalent Von-Mises Stress, (b) strain, and (c) deformations of piston Figure 7: Surface Temperature field of te piston 5.2 Aluminium Alloy Piston Mecanical Stresses Te gas pressure model and inertial forces model given to ANSYS workbenc, Displacement constraints are given at te piston pin oles to avoid te motion of te piston. Te value of equivalent von-mises stress for te Aluminium alloy piston is 199 MPa maximum and 0.11 MPa is minimum value. Te maximum stress is on te piston pin ole and greater stress is found on te above portion of piston pin ole. At te piston crown te stress value is nearly 28 MPa. Te maximum value of strain and total deformation are mm/mm, and mm respectively. 5.3 Coupling Stress in Piston In tis section, te coupling stresses on aluminium alloy piston are calculated. Te termal and mecanical boundary conditions are given into ANSYS work benc. Te maximum value of stress near piston pin ole is found 661 MPa maximum at piston pin ole, strain near piston pin ole mm/mm, and total deformation is mm. 2017, IRJET Impact Factor value: ISO 9001:2008 Certified Journal Page 1980 (a)

6 (b) (c) Figure 9: (a) Stress, (b) strain, and (c) deformations of piston Conclusions Te maximum temperature is obtained for piston is C to C wit te maximum temperature at te piston top and minimum temperature at te lower part of te piston skirt. Te eat flux on piston crown is W/m. 2 Te stresses obtained by action of gas pressure and inertia forces; te maximum value of equivalent stresses on conventional piston is MPa at near region of piston pin ole and total deformation is mm. Te coupled stresses in piston by temperature, pressure and inertia forces are calculated. Coupled stress for aluminium alloy piston near piston pin ole region is MPa. Te total deformations are mm near te piston crown face radially. References [1] F.S. Silva Fatigue on engine pistons-a compendium of case studies, Engine failure analysis 13(2006), pp , doi: /j.engfailanal [2] C.S. Wang, G F Berry, Heat transfer in internal combustion engines,1985,te American society of mecanical engineers. [3] R. Nicole, Title of paper wit only first word capitalized, J. Name Stand. Abbrev., in press. [4] Douglas M Baker, A metodology for coupled termodynamic and eat transfer analysis of a diesel engine,1994,applied matematical modeling, vol 18, November, butterwort Heinemann [5] J.B. Heywood, Internal combustion engine fundamentals, ISBN: X, 1998, McGraw Hill Inc. [6] Madi Hamzeei, Manocer Rasidi, 2006, Determination of piston and cylinder ead temperature distribution in a 4-cylinder gasoline engine at actual process, proceedings conf. on Heat transfer engineering and environment, Elounda, Greece, August 21-23,2006, pp [7] Krisztina Uzuneanu, Modeling te eat transfer in te piston ead of a spark ignition engine supplied wit etanol-gasoline blend,cofret 08, Jun 11-13,2008, France [8] Yanxia wang, Simulation investigation on te termomecanical coupling of te QT 300 piston, Second international conference on information and computing science, pp [9] Dr. Aamed, termal effects on diesel engine piston and piston compression rings,2009, Eng & tec journal, vol 27, No. 8, 2007, pp [10] Gudimetal P, Gopinat C V, Finite element analysis of reverse engineered internal combustion engine piston,2009, AIJSTPME (4), pp [11] Imdat Taymaz, An analysis of residual stresses in termal barrier coatings: A FE performance assessment, 2009, WILEY-Verlag Gmb & Co [12] Tosio Sudo, Applicability of eat transfer equations to ydrogen combustion, JSAE review, Vol 23 No pp [13] Hongyuan Zang, Jian Xing, Temperature field analysis to gasoline engine piston and structure optimization, ISSN: , JATIT Feb 2013, pp [14] Ekrem Buyukkaya, Termal analysis of functionally graded coating AlSi alloy and steel pistons, 2008, Elsevier Ltd., pp [15] V. Esfaanian, A. Javaeri, Termal analysis of an SI engine piston using different combustion boundary condition treatments, 2005, Elsevier Ltd., 2006, pp [16] Hongyuan Zang, Jian Xing, Temperature field analysis to gasoline engine piston and structure optimization, ISSN: , JATIT Feb 2013, pp [17] Hongyuan Zang An analysis to termal load and mecanical load coupling of a gasoline engine piston ISSN: , Journal of teoretical and applied information tecnology, Vol 48, no. 2, Feb 2013, pp [18] Yanxia Wang, Haiyan Si, Simulation and analysis of termo-mecanical coupling load and mecanical dynamic load for a piston, 2010 IEEE, pp [19] Vinay V. Kuppast et al. Study on influence of temperature on IC engine vibration-a finite element approac, ISSN: , IJERA, Vol 1, Issue 4, pp , IRJET Impact Factor value: ISO 9001:2008 Certified Journal Page 1981