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1 Thermal Analysis Of Ic Engine Piston Using Finite Element Method Shirisha 1, G.S.Dk.Sravani 2 1 PG Scholar, Pydah College of Engineering, Kakinada, AP, India. 2 Assistant Professor, Pydah College of Engineering, Kakinada, AP, India. ABSTRACT Thermal barrier coatings have been successfully applied to the internal combustion engine, in particular the combustion chamber in order to simulate adiabatic changes. The objectives are not only for reduced in-cylinder heat rejection and thermal fatigue protection of underlying metallic surfaces, but also for possible reduction of engine emissions and brake specific fuel consumption. The application of TBC reduces the heat loss to the engine cooling-jacket through the surface exposed to the heat transfer such as the cylinder head, liner, piston crown and piston rings. The insulation of the combustion chamber with ceramic coating affects the combustion process and, hence, the performance and exhaust emissions characteristics of the engines improve. On the other hand, the desire of increasing the thermal efficiency or reduce fuel consumption of engines leads to the adoption of higher compression ratios, in particular for diesel engines, and reduced in-cylinder heat rejection. Both of these factors cause increased mechanical and thermal stresses of materials used in combustion chamber The application of TBC to the surfaces of these components enhances high temperature durability by reducing the heat transfer and lowering temperature of the underlying metal. Typical TBCs failure is by spalling of the ceramic top coat from the bond coat. There are many factors that influence the overall performance of coatings and cause spalling of the coating. However oxidation and thermal mismatch are identified as two major factors influencing the life of the coating system. The coatings are permeable to the atmospheric gases and liquids resulting in the oxidation of the bond coat and spalling of the coating. The functionally graded coatings were used to reduce the mismatch effect. Therefore the thermal expansion and interfacial stresses are an alternative approach to conventional thermal barrier coatings.in this project, the main emphasis is placed on the study of thermal behaviour of functionally graded coatings obtained by means of using a commercial code, ANSYS on aluminium and steel piston surfaces and the results are verified with numerical and experimental works. INTRODUCTION TO PISTON A piston is a component of reciprocating engines, pumps and gas compressors. It is located in a cylinder and is made gas-tight by piston rings. In an engine, its purpose is to transfer force from expanding gas in the cylinder to the crankshaft via a piston rod and/or connecting rod. In a pump, the function is reversed and force is transferred from the crankshaft to the piston for the purpose of compressing or ejecting the fluid in the cylinder. In some engines, the piston also acts as a valve by covering and uncovering ports in the cylinder wall. INTRODUCTION TO ANSYS 1.1 Description about ANSYS ANSYS is commercial Finite Element Analysis (FEA) software package. Finite Element Analysis is a numerical method of deconstructing a complex system into very small pieces (of user designated size) called elements. The software implements equations that govern the behavior of these elements and solves them all; creating a comprehensive explanation of how the system acts as a whole. These results then can be presented in tabulated or graphical forms. This type of analysis is typically used for the design and optimization of a system far too complex to solve analytically. Systems that may fit into this category are too complex due to their geometry, scale, or governing equations. 1.2 Structural Figure 1: Structural Analysis Structural analysis is probably the most common application of the finite element method as it Page 200

2 implies bridges and buildings, naval, aeronautical, and mechanical structures such as ship hulls, aircraft bodies, and machine housings, as well as mechanical components such as pistons, machine parts, and tools. Static Analysis: Static analysis is performed to determine displacements, stresses, etc. under static loading conditions. ANSYS can compute both linear and nonlinear static analyses. Nonlinearities can include plasticity, stress stiffening, large deflection, large strain, hyper elasticity, contact surfaces, and creep. Transient Dynamic Analysis: Transient Dynamic analysis is used to determine the response of a structure to arbitrarily timevarying loads. All nonlinearities mentioned under Static Analysis above are allowed. Buckling Analysis: Buckling Analysis is used to calculate the buckling loads and determine the buckling mode shape. Both linear (Eigen value) buckling and nonlinear buckling analyses are possible. In addition to the above analysis types, several special-purpose features are available such as Fracture mechanics, Composite material analysis and Fatigue analysis. MODELING AND MESHING The geometric modelling can be done with the help of computer aided software s like Ideas, Pro-E, and Catia etc. In this analysis the model is created with the help of Catia V5 and the model is saved as step file or iges file. Iges file is having less data loss when compared to other file formats. Once model is generated in Catia, the file is exported from Catia in the required format for further analysis. Modelling of Piston Design: The piston is designed according to the procedure and specification which are given in machine design and data hand books. The dimensions are calculated in terms of SI Units. The pressure applied on piston head, temperatures of various areas of the piston, heat flow, stresses, strains, length, diameter of piston and hole, thicknesses, etc., parameters are taken into consideration Design Considerations for a Piston In designing a piston for an engine, the following points should be taken into consideration: It should have enormous strength to withstand the high pressure. It should have minimum weight to withstand the inertia forces. It should form effective oil sealing in the cylinder. It should provide sufficient bearing area to prevent undue wear. It should have high speed reciprocation without noise. It should be of sufficient rigid construction to withstand thermal and mechanical distortions. It should have sufficient support for the piston pin. Procedure for Piston Design The procedure for piston designs consists of the following steps: Thickness of piston head (th) Heat flows through the piston head (H) Radial thickness of the ring (t1) Axial thickness of the ring (t2) Width of the top land (b1) Width of other ring lands (b2) The above steps are explained as below: Thickness of Piston Head (th) The piston thickness of piston head calculated using the following Grashoff s formula, Where P= maximum pressure in N/mm² D= cylinder bore/outside diameter of the piston in mm. t=permissible tensile stress for the material of the piston. Here the material is a particular grade of AL-Si alloy whose permissible stress is 50 Mpa- 90Mpa. Before calculating thickness of piston head, the diameter of the piston has to be specified. The piston size that has been considered here has an L*D specified as 152*140. Heat Flow through the Piston Head (H) The heat flow through the piston head is calculated using the formula H = 12.56*tH * K * (Tc-Te) Kj/sec Where K=thermal conductivity of material which is W/mk Tc = temperature at center of piston head in C. Te = temperature at edges of piston head in C. Radial Thickness of Ring (t1) t1 = D 3pw/ t Where D = cylinder bore in mm Pw= pressure of fuel on cylinder wall in N/mm². Its value is limited from 0.025N/mm² to 0.042N/mm². For present material, t is 90Mpa Page 201

3 Axial Thickness of Ring (t2) The thickness of the rings may be taken as t2 = 0.7t1 to t1 Let assume t2 =5mm Minimum axial thickness (t2) = D/( 10*nr ) Where nr = number of rings thickness of the ring (t1) Axial thickness of the ring (t2) 4 Width of the top land (b1) Width of other ring lands (b2) 3 Width of the top land (b1) The width of the top land varies from b1 = th to 1.2 th MODELING PROCEDURAL STEPS IN CATIA Width of other lands (b2) Width of other ring lands varies from b2 = 0.75t2 to t2 Maximum Thickness of Barrel (t3) t3 = 0.03*D + b mm Where b = Radial depth of piston ring groove Thus, the dimensions for the piston are calculated and these are used for modelling the piston in CATIA. In the above procedure the ribs in the piston are not taken into consideration, so as make the piston model simple in its design. In modelling a piston considering all factors will become tedious process. Thus, a symmetric model is developed using the above dimensions. DESIGN1 PARAMETERS: Size S No Design1 - Dimensions in mm 1 Length of the Piston(L) 152 Cylinder bore/outside 2 diameter of the piston(d) Thickness of piston head (th) Radial thickness of the ring (t1) Axial thickness of the ring (t2) 5 6 Width of the top land (b1) Width of other ring lands (b2) 4 DESIGN2 PARAMETERS: S No Design 2 -Dimensions Size in mm Length of the 1 Piston(L) 152 Cylinder bore/outside diameter of the 2 piston(d) Thickness of piston head (th) Radial 4 By properly setting the global element edge length, the volume is free meshed with the help of the meshing tool. The generated Finite element Model is shown as follows. ANALYSIS RESULTS & DISCUSSIONS Analysis is the process of breaking a complex topic or substance into smaller parts to gain a better understanding of it. The current model is undergone Thermal Analysis and followed by Static Analysis, together called as Coupled Filed Analysis. The Steps Page 202

4 involved in the thermal analysis is explained as below. THERMAL ANALYSIS The basis for thermal analysis in ANSYS is a heat balance equation obtained from the principle of conservation of energy. The finite element solution performed is via ANSYS which calculates nodal temperatures, and then uses the nodal temperatures to obtain the other thermal quantities. Only the ANSYS Multi physics, ANSYS Mechanical, ANSYS Professional, and ANSYS FLOTRAN programs support thermal analyses. The ANSYS program handles all three primary modes of heat transfer: conduction, convection, and radiation. CONVECTION MODE OF HEAT TRANSFER The convection is specified as a surface load on conducting solid elements or shell elements. The convection film coefficient and the bulk fluid temperature at a surface; ANSYS then calculates the appropriate heat transfer across that surface. If the film coefficient depends upon temperature, a table of temperatures is specified along with the corresponding values of film coefficient at each temperature. For use in finite element models with conducting bar elements (which do not allow a convection surface load), or in cases where the bulk fluid temperature is not known in advance, ANSYS offers a convection element named LINK34. In addition, you can use the FLOTRAN CFD elements to simulate details of the convection process, such as fluid velocities, local values of film coefficient and heat flux, and temperature distributions in both fluid and solid regions. RADIATION MODE OF HEAT TRANSFER ANSYS can solve radiation problems, which are nonlinear, in four ways: By using the radiation link element, LINK31 By using surface effect elements with the radiation option (SURF151 in 2-D modelling or SURF152 in 3-D modelling) by generating a radiation matrix in AUX12 and using it as a super element in a thermal analysis. TYPES OF THERMAL ANALYSIS ANSYS supports two types of thermal analysis for analyzing the component with the influence of temperature: Steady-state thermal analysis A steady-state thermal analysis determines the temperature distribution and other thermal quantities under steady-state loading conditions. A steady-state loading condition is a situation where heat storage effects varying over a period of time can be ignored The ANSYS Multiphysics, ANSYS Mechanical, ANSYS FLOTRAN, and ANSYS Professional products support steady-state thermal analysis. A steady-state thermal analysis calculates the effects of steady thermal loads on a system or component. Engineer/analysts often perform a steady-state analysis before doing a transient thermal analysis, to help establish initial conditions. A steady-state analysis also can be the last step of a transient thermal analysis; performed after all transient effects have diminished. Steady-state thermal analysis is used to determine temperatures, thermal gradients, heat flow rates, and heat fluxes in an object that are caused by thermal loads that do not vary over time. Such loads include the following: Convections Radiation Heat flow rates Heat fluxes (heat flow per unit area) Heat generation rates (heat flow per unit volume) Constant temperature boundaries A steady-state thermal analysis may be either linear, with constant material properties; or nonlinear, with material properties that depend on temperature. The thermal properties of most material do vary with temperature, so the analysis usually is nonlinear. Including radiation effects also makes the analysis nonlinear. Transient thermal analysis A transient thermal analysis determines the temperature distribution and other thermal quantities under conditions that vary over a period of time. The ANSYS Multi physics, ANSYS Mechanical, ANSYS Professional, and ANSYS FLOTRAN products support transient thermal analysis. Transient thermal analysis determines temperatures and other thermal quantities that vary over time. Engineers commonly use temperatures that a transient thermal analysis calculates as input to structural analyses for thermal stress evaluations. Many heat transfer applications - heat treatment problems, nozzles, engine blocks, piping systems, pressure vessels, etc. - involve transient thermal analyses. A transient thermal analysis follows basically the same procedures as a steady-state thermal analysis. The main difference is that most applied loads in a transient analysis are functions of time. To specify time-dependent loads, you can either use the Page 203

5 Function Tool to define an equation or function describing the curve or then apply the function as a boundary condition, or you can divide the loadversus-time curve into load steps. For each load step, you need to specify both load values and time values, along with other load step options such as stepped or ramped loads automatic time stepping, etc. You then write each load step to a file and solve all load steps together. To get a better understanding of how load and time stepping work, see the example casting analysis scenario in this chapter. Coupled-field analysis Some types of coupled-field analyses, such as thermal-structural and magnetic-thermal analyses, can represent thermal effects coupled with other phenomena. A coupled-field analysis can use matrix-coupled ANSYS elements, or sequential load-vector coupling between separate simulations of each phenomenon. For more information on coupled-field analysis, A coupled-field analysis is a combination of analyses from different engineering disciplines (physics fields) that interact to solve a global engineering problem; hence, we often refer to a coupled-field analysis as a multi physics analysis. When the input of one field analysis depends on the results from another analysis, the analyses are coupled. Some analyses can have one-way coupling. For example, in a thermal stress problem, the temperature field introduces thermal strains in the structural field, but the structural strains generally do not affect the temperature distribution. Thus, there is no need to iterate between the two field solutions. More complicated cases involve two-way coupling. A piezoelectric analysis, for example, handles the interaction between the structural and electric fields: it solves for the voltage distribution due to applied displacements, or vice versa. In a fluid-structure interaction problem, the fluid pressure causes the structure to deform, which in turn causes the fluid solution to change. This problem requires iterations between the two physics fields for convergence. The coupling between the fields can be accomplished by either direct coupling (matrix coupling) or sequential coupling (load vector coupling). Load transfer can take place across surfaces or volumes. Coupling across fields can be complicated because different fields may be solving for different types of analyses during a simulation. For example, in an induction heating problem, a harmonic electromagnetic analysis calculates Joule heating, which is used in a transient thermal analysis to predict a time-dependent temperature solution. The induction heating problem is complicated further by the fact that the material properties in both physics simulations depend highly on temperature. Some of the applications in which coupled-field analysis may be required are pressure vessels (thermal-stress analysis), fluid flow constrictions(fluid-structure analysis),induction heating(magnetic-thermal analysis), ultrasonic transducers (piezoelectric analysis), magnetic forming (magneto -structural analysis), and microelectromechanical systems (MEMS). In this project thermal and structural coupling is done to find out the thermal stress value. ANALYSIS PROCEDUREAL STEPS: The meshed component is analyzed to find the thermal stresses of the piston. The component is subjected to the influence of heat conduction at the top of the piston and heat convection to side lands etc. Design Specification before Optimization-design In this work have thermal stress analysis is being done. For thermal stress analysis, firstly the model is created as described in earlier chapter, following steps should be followed. 1.Define the Type of Element Pre-processor > Element Type > Add/Edit/Delete > Solid 90 2.Define Element Material Properties Pre-processor > Material Props > Material Models > Thermal > Conductivity > Isotropic 3.Define Mesh Size Pre-processor > Meshing > Size Cntrls > Global >Set 4.Mesh Volumes Pre-processor > Meshing > Mesh volume > Tet >Free Mesh >Pick all Page 204

6 The below plot shows the Vonmises Stress plots of the piston, when it is acted upon by the thermal and static loads and boundary conditions. The Maximum Stress obtained is found to be 937 Mpa. This stress can be ignored, because this is spurious stress due fixed constraints at the constraining region. 5.Define Analysis type Solution > Analysis Type >New Analysis > Type of Analysis > Thermal Analysis > Ok 6. Obtaining Solution Solution >Solve >Current Ls >ok Deformation Plots for Coated Zirconium Piston for Design1: in X-direction, when it is acted upon by the thermal Maximum displacement in the X direction is found to be 0.80 mm. in Z-direction, when it is acted upon by the thermal Maximum displacement in the Z direction is found to be mm. in Y-direction, when it is acted upon by the thermal Maximum displacement in the Y direction is found to be 1.20 mm. in Resultant direction, when it is acted upon by the thermal and static loads and boundary conditions. The Maximum displacement in the x direction is found to be mm. in Z-direction, when it is acted upon by the thermal Maximum displacement in the Z direction is found to be 1.17 mm. in Resultant direction, when it is acted upon by the Page 205

7 thermal and static loads and boundary conditions. The Maximum displacement is found to be 1.45 mm. The below plot shows the Vonmises Stress plots of the piston, when it is acted upon by the thermal and static loads and boundary conditions. The Maximum Stress obtained is found to be 1876 Mpa. This stress can be ignored, because this is spurious stress due fixed constraints at the constraining region. in Resultant direction, when it is acted upon by the thermal and static loads and boundary conditions. The Maximum displacement in the x direction is found to be 0.68 mm. Deformation Plots for Uncoated Aluminium Piston for Design2: in X-direction, when it is acted upon by the thermal be 0.61 mm. S No Design 2 -Dimensions Size in mm 1 Length of the Piston(L) 152 Cylinder bore/outside 2 diameter of the piston(d) Thickness of piston head (th) Radial thickness of the ring (t1) 4 5 Axial thickness of the ring (t2) 4 6 Width of the top land (b1) Width of other ring lands (b2) 3 in Y-direction, when it is acted upon by the thermal be 0.62 mm. The below plot shows the Vonmises Stress plots of the piston, when it is acted upon by the thermal and static loads and boundary conditions. The Maximum Stress obtained is found to be 592 Mpa. This stress can be ignored, because this is spurious stress due fixed constraints at the constraining region. in Z-direction, when it is acted upon by the thermal be mm. Page 206

8 The fringe plot is adjusted to estimate the obtained stress levels, it can be found that, Vonmises stress away the blocking zone, which is not spurious is found to be 295 Mpa. This value is useful for the assessment of the Piston under given loading conditions. in Resultant direction, when it is acted upon by the thermal and static loads and boundary conditions. The Maximum displacement in the x direction is found to be mm. Deformation Plots for Coated Zirconium Piston for Design2: in X-direction, when it is acted upon by the thermal be 0.44 mm. The below plot shows the Vonmises Stress plots of the piston, when it is acted upon by the thermal and static loads and boundary conditions. The Maximum Stress obtained is found to be 856 Mpa. This stress can be ignored, because this is spurious stress due fixed constraints at the constraining region. in Y-direction, when it is acted upon by the thermal be 0.39 mm. The fringe plot is adjusted to estimate the obtained stress levels, it can be found that, Vonmises stress away the blocking zone, which is not spurious is found to be 295 Mpa. This value is useful for the assessment of the Piston under given loading conditions. Results from analysis in Z-direction, when it is acted upon by the thermal be 0.41 mm. The coated and uncoated pistons are analyzed in ANSYS and the thermal stresses are obtained. Page 207

9 Comparing between the coated and uncoated stress results, the maximum thermal stress is low in coated piston, resulting in less transfer of heat to the piston. As only less amount of heat is lost, combustion process should be increased. Vonmises Stress when compared to the Uncoated AL Piston. Vonmises Stress comparison for Ring Land for Uncoated and Coated Piston for Design1: CONCLUSIONS A finite element model of the piston without and with coating layer is created in ANSYS and analyzed in the influence of thermal load on the top surface of the piston. The results are analyzed and concluded as follows Resultant Displacement comparison for Top Land for Uncoated and Coated Piston for Design1: From the above graph it can be concluded that coated zirconium piston has more resultant Vonmises Stress when compared to the Uncoated AL Piston. Resultant Displacement comparison for Top Land for Uncoated and Coated Piston for Design2: From the above graph it can be concluded that coated zirconium piston has more resultant displacement when compared to the Uncoated AL Piston. Resultant Displacement comparison for Ring Land for Uncoated and Coated Piston for Design1: When compared to Design1, optimized design 2 has better resultant displacement for the coated Zr piston, when compared with the uncoated with the Aluminium Piston. Resultant Displacement comparison for Ring Land for Uncoated and Coated Piston for Design2: From the above graph it can be concluded that coated zirconium piston has more resultant displacement when compared to the Uncoated AL Piston. Vonmises Stress comparison for Top Land for Uncoated and Coated Piston for Design1: When compared to Design1, optimized design 2 has better resultant displacement for the coated Zr piston, when compared with the uncoated with the Aluminium Piston. Vonmises Stress comparison for Top Land for Uncoated and Coated Piston for Design2: From the above graph it can be concluded that coated zirconium piston has more resultant Page 208

10 Vonmises Stress comparison for Ring Land for Uncoated and Coated Piston for Design2: 6. Zhang T, Xu L, Xiong W, et al. Experimental research on the thermal contact resistance between Cu-Cu in vacuum and low temperature. Cryogenics, ANSYS manual guide Functionally Graded Materials (FM) and Their Production Methods. The thermal stresses of both coated and uncoated pistons are obtained and compared. The maximum thermal stress of Zirconium is low as compared to the maximum thermal stress obtained by the uncoated aluminium piston. The Contour plots for the deformations and as well as for stresses already shown in the earlier chapter. As the thermal stresses are reduced, the heat transfer in the piston is also reduced resulting in increased combustion which should result with the increase in engine power. FUTURE SCOPE OF THE WORK Piston Design models are simulated on iteration based. Needs more number of iterations to check whether design is safe or not and to validate the models with the allowable. Instead of above process, DOE Design of Experiments concept can be used to optimize the design within short time and to get better optimized parameters. DOE should be carried in Ansys workbench. In Ansys workbench modelling can be done from Catia or Design Modeller using parametric model options. DP stands for design points, optimization can be done in workbench based on the required outputs namely deformations and stress with in prescribed limits. REFERENCES 1. Ekrem Buyukkaya, Thermal Analysis of functionally graded coating AlSi alloy and steel pistons, Surface and coatings technology (2007) 2. Reinhold H. Dauskardt, THERMAL BARRIER COATINGS (1999). 3. M. Foy, M. Marchese, G. Jacucci, Engineering plasma spray films by knowledge based simulations proceedings of IFIP conference on, in: Arthur B. Baskin, et al., (Eds.), Cooperative Knowledge Processing for Engineering Design, Kluwer Academic Publishers, The Netherlands, 1999, p J.S. Lee, T. Matsubara, T. Sei, T. Tsuchiya, J. Mater, Preparation and properties of Y2O3-doped ZrO2 thin films by the sol-gelprocess, Surface Coating Technology (1997). 5. J.N.Reddy, An introduction to finite element analysis. Page 209