Non-linear static coupled field analysis of a piston in a...

Non-linear static coupled field analysis of a piston in a four-stroke single cylinder diesel

engine using ANSYSB. Praveena

PG Student, Dept. of Mechanical EngineeringNova College of Engineering and Technology, India

Y.Suresh KumarAsst Professor, Dept. of Mechanical Engineering

Nova College of Engineering and Technology, India

Kalapal PrasadAsst Professor, Dept. of Mechanical Engineering

Jawaharlal Nehru technological University Kakinada, India

Abstract: The component piston in an internal combustion engine plays an important role in transforming the thermal energy developed during the combustion in to mechanical energy. During this process, the piston is subject to heat, and pressures developed in the combustion as well as variations in pressures during various strokes of the engine. Hence, there is a need to study the behavior of the piston to the loads acting on it. In this work, the distributions of stress and temperatures in the piston are found using finite element analysis package, ANSYS UNDER two loading conditions i.e. only gas pressure, and combination of thermal load and gas pressure. Design of the piston has been carried out using standard procedures available in the literature. Later, uniaxial tension test has been performed on an Aluminum specimen and the values from the stress-strain diagram are imported to ANSYS to define the non-linear behavior of the material. CAD model is generated in the ANSYS and static couple field analysis (Non-linear structural and thermal) is performed by applying various loads (thermal and combustion pressure) on the piston. The stress and temperature distributions on the piston are studied and the conclusions are drawn.

Keywords: Piston, Uniaxial tension test, Combined loading, Non-linear analysis, ANSYS

I. INTRODUCTION

The objective of a design engineer is to design the components according to the need of the customer. This requires lot of experience and consideration of effect of various factors governing the design like environmental effects, various loads acting like forces, pressures and temperatures, rate of wear and tear, and the unbalance of the forces in the assembly. Under the action of various loads on the structural components, the response may change tending to decrease the strength of the component and lifetime. At the same time, incorporating all these practical conditions in the design makes the process more complex. Hence, there is a need to study the effect of all these factors independently or in combination of these. This reveals the level of failure and the maximum values of stresses and deflections, shape deformations, temperature distributions and their locations. In turn, it helps to design the component with best optimum dimensions and by this; the life of the component is increased.

Lot of research work has been carried out in the area of stress analysis as well as thermal analysis of the internal combustion engine components, analytically, theoretically and experimentally. Hongyuan Zhang et. Al [3] had performed thermal analysis of gasoline engine pistons y considering the variable thermal loading on the piston and found that the maximum temperature is occurring at the location of first ring. They have optimized the piston structure by incorporating a cooling chamber which resulted in the decrease of maximum temperature thereby increasing its life. Yanxia Wang et. al [4] studied the behavior of piston by performing the thermo-mechanical analysis using finite element analysis software Ansys and mechanical dynamic analysis subjected to fatigue loading and calculated the fatigue life span of the piston. They found that the maximum value of stress is obtained at the upper end of the piston pin boss inner hole and also that the design of the piston is reliable.

Jadhav rajendra and Vikhe Patil [5] developed a program in visual basic to study the kinematic, static and dynamic behavior of a four stroke single cylinder internal combustion engine under the action of forces

International Journal of Innovations in Engineering and Technology (IJIET)

Volume 4 Issue 4 December 2014 79 ISSN: 2319 – 1058

developed during the entire cycle and for every crank interval. Yanxia Wang et. al [6] performed thermo-mechanical analysis of the QT300 marine diesel engine using Ansys and found that the maximum stress is developed at the inner surface of the piston pin boss and maximum deflection is observed at the piston top surface. Vinay V. Kuppast [7] studied the influence of temperature and pressure on the dynamic behavior of the piston using multibody dynamics (MBD). Three dimensional model of the piston used in a four stroke single cylinder kirloskar diesel engine is designed in Catia and later analysis is performed in the design softwares Ansys and Hypermesh. They had observed that the effect of temperature and pressure played a major role in the development of lateral deflections and vibrations. In addition, they also observed that the noise caused in the engine is because of the stresses developed in the engine parts.M. R. Ayatollahi et. al. [8] developed a macro in the Ansys APDL to find the high cycle fatigue safety factor (HCF) and low cycle fatigue (LCF) life for the piston subjected to multiaxial loading. They have identified three regions around the piston; oil inlet hole in the piston skirt and piston and the piston pin contact region as the most critical regions where maximum fatigue stresses will be developed due to the cyclic thermal and mechanical loads. Vinod Junju et. al. [9] analyzed the behavior of the piston by forming a ceramic layer over the piston crown and a layer of ceramic reinforced fiber strip is introduced between the ceramic crown and the piston skirt. They had observed that this arrangement decreased the level of stress developed in the piston when compared with the stresses developed without the ceramic layer.

In this research work, the effect of combined loading (gas pressure and thermal load) on the piston is studied, by performing the non-linear static coupled analysis using ANSYS. In the section-2, the design procedure adopted in this work is presented and in the section-3, the finite element analysis of the piston and the methodology adopted in this work is explained with the representation of the elements used in the analysis. In addition, various boundary conditions applied on the piston and the loading conditions are also discussed. In section-4, the discussion of the results obtained from the present analysis, are presented in detail. In section-5, the scope for the future work is presented.

II. DESIGN PROCEDURE FOR THE PISTON

The nomenclature of the piston is presented in the fig. 1.

Fig. 1 Details of the piston

The design procedure adopted in this work is presented below and the results are tabulated:

2.1 Piston Head:-

Thickness of piston head is determined on basis of strength as well as on heat dissipation

316H

t

Pt D= (1) Cross-sectional Area, 2

4D

ÕA = (2)

Indicated Power, .60LR AN

I R = (3)

P = Pm= indicated mean effective pressure.Brake Power, . . * mechBR = I R

Heat flow through piston head, * . * * .vC C mH = H BR (4)



2.2 Radial Ribs:-

Radial ribs may be four in number the thickness of the ribs varies from 3ht to

2ht

2.3 Piston Rings:-Out of four rings, three are compression rings and one is oil ring

· Radial thickness of the piston rings , 1

(3 )

t

t DR

= (5)

· Axial thickness of piston rings, 2 110.7t t to t= (6)

· Distance from the top of piston to first ring groove i.e.,

· Width of the top land, 1 1.2 Hb t= (7)

· Width of other ring land, 2 2 20 .7 5b t to t= (8)

2.4 Piston Barrel:-Radial depth of piston ring grooves (b) is 0.4mm more than radial thickness of piston (t1).

1 0 .4b t= + (9)

Maximum thickness of barrel, 3 0.03 4.5t D b mm= + + (10)

Piston wall thickness towards the open end, 4 3 30.25t t to t= (11)

2.5 Piston Skirt:-

Maximum gas load = 2max4

DÕ

R (12)

Length of the piston, L = Length of skirt + Length of ring section + Top land

2 2 1(4 3 )L l t b b= + + + (13)

2.6 Piston Pin:-Load on the pin due to bearing pressure = Bearing pressure * Bearing ratio * Bearing area

= 1 0 1bp d L´ ´ 1( 0.45 )L D= (14)

Maximum load on the piston due to Gas pressure = 2

4D p

P´ ´ (15)

Dimensions of the piston are calculated using the above equations and are presented in table: 1.

Table. 1 Calculated Design valuesS. No

Parameter Value (mm)1 Thickness of piston head (tH) 8.82

2 Radial thickness of piston rings(t )

2.333 Axial thickness of piston

rings(t )1.76

4 Width of top land(b1) 8.82

5 Width of other land(b2) 1.32

6 Radial depth of piston grooves(b)

2.74

7 Piston wall thickness towards the open end(t )

2.578 Length of piston (L) 65.68

9 Diameter of piston(D) 70.56

10 Diameter of piston pin(d0) 31.75



III. FINITE ELEMENT ANALYSIS USING ANSYS

Finite element analysis is a powerful tool, which can be used to study the behavior of any structural member subjected to any type of load. Even though the results are approximate, it predicts the chances of failure with more accuracy. Hence, in most of the engineering analysis, it is mostly preferred. After calculating the dimensions, 3-d model of the piston is modeled in the ANSYS environment itself which is presented in fig. 2.

Fig. 2 CAD Model of the Piston

The version of ANSYS used in this work is ANSYS 12.0. In this work, for performing the coupled field analysis, initially, the meshing is performed by defining the thermal element and the thermal properties in the thermal environment and then, the element and properties related to the structural analysis are defined. The detailed analysis procedure carried out in this work is discussed in the next sections.

3.1 Thermal analysisThermal properties of the Aluminum are presented in the table. 2.

Table. 2 Thermal properties of Aluminum

Property Value

Thermal conductivity(k) 206 w/m-k

Den 2707 kg/m3

Specific heat (cp) 986 J/kg-k

Table.3 Structural properties of Aluminum

Property Value

Young’s modulus (E) 70GPa

Poisson ratio(µ) 0.33Coefficient of linear 23x10-6m/m0c

The element type used for thermal analysis is 20 node 90.It is a higher order 3-D thermal element. The element has 20 nodes with a single degree of freedom, temperature, at each node. These elements have compatible temperature shapes and are well suited to model curved boundaries. It has 4 element shapes, which are presented in fig. 3.

Fig. 3 Element shapes of 20 node 90 – Thermal Element [1]

· 10 node tetrahedron with one degree of freedom at each node· 13 node quadrilateral pyramid with one degree of freedom at each node



· 15 node triangular prism with one degree of freedom at each node· 20 node quadrilateral prism with one degree of freedom at each node

In this work, we are using 10-node tetrahedron having one degree of freedom. Because of irregularity in the shape with curved edges, 10-node tetrahedron is more preferred in this work. In addition, geometric non-linearity is also included in the analysis. The meshed view of the piston is presented in fig. 4.

Fig. 4 Meshed view of the Piston

During meshing, 22,165 nodes and 12,316 elements are generated.

Later the steady state thermal analysis is performed by applying the convective boundary conditions and temperature as the working load at the respective locations, as presented in table.4 [4].

Table. 4 Heat transfer coefficients at various locations on the piston surface [4]

DescriptionNot-ation

Heat transfer coefficient

(w/m2k)

Temp-erature

°C

Piston junk h1 145 150

Top edge of the first circular groove

h2 456 150

Inner edge of the first circular groove

h3 375 150

Bottom edge of first circular groove

h4 2331 150

Top edge of second circular groove

h5 389 130

Inner edge of the second circular groove

h6 244 130

Bottom edge of the second circular groove

h7 389 130

Top edge of the third circular groove

h8 387 120

Inner edge of the third circular groove

h9 244 120

Bottom edge of third circular groove

h10 387 130



Bottom ring land of first ring

h11 145 130

Bottom ring land of second ring

h12 145 110

Piston skirt h13 532 110Bottom of piston crown

h14 1000 110

Inner surface of piston skirt

h15 1000 110

Half mid way between the piston pin boss

h16 500 110

Piston pin boss h17 400 110

Piston crown h18 474.58 1369.19

top edge of the fourth circular groove

h19 389 120

Inner edge of fourth circular groove

h20 244 120

Bottom edge of fourth circular groove

h21 387 120

The variable boundary conditions are applied because the rate of heat transfer is different at different locations on the surface of the piston. The obtained temperature distribution and heat flux distribution in radial and axial directions are presented in fig. 5, 6 & 7 respectively. Analysis of these results is discussed in section-5 of this article.

Fig.5 Temperature distribution over the Fig. 6 Heat flux distribution over the Fig. 7 Heat flux distribution overpiston surface piston surface in radial direction the piston surface in axial direction

a. Structural analysis

The element type used for structural analysis is 20 node 186.It is a higher order 3-D 20 node element that exhibits quadratic displacement behavior. The element is defined by 20 nodes having three degree of freedom per node: translation in the nodal X, Y, and Z directions. The element supports the plasticity and it is a 3-d element having 20 nodes and is a higher order element having 3 distinct element behaviors. It has three degrees of freedom. The element behaviors are as shown in fig. 8.



Fig. 8 Element shapes of 20 node186 –Structural Element [1]

· 10 node tetrahedron with 3 degree of freedom at each node· 13 node quadrilateral pyramid with 3 degree of freedom at each node· 15 node triangular prism with 3 degree of freedom at each node· 20 node quadrilateral prism with 3 degree of freedom at each node

This element is compatible for structural analysis when 20 node90 is opted for thermal analysis, when coupled field analysis is performed. For both the elements, 10 node tetrahedron shape is opted having 4 nodes at 4 corners and 6 nodes at the midpoints of the edges of the tetrahedron. This element also supports the non-linearity in the analysis.

After the completion of thermal analysis, the structural environment is switched on and the gas pressure [4] is applied on the surface of the piston along with the temperature distribution obtained in thermal analysis. Here the material non-linearity is considered and it is included in the analysis by giving the values of stress and strain from the load-deflection curve obtained from the uniaxial tension test as input. These values are presented in table. 2.

Table 5 Stress – strain values given as input in ANSYS

Points Stress(MPa) Strain1 079.00 0.022

2 173.70 0.025

3 194.90 0.014

4 444.62 0.0310

5 462.00 0.0416 645.00 0.068

7 651.70 0.138

The obtained load-deflection curve is presented in fig. 9.

Load - Deflection curve for Aluminum

Deflection (mm)

5 10 15 20 25 30

10

15

20

25

30

Load (kN) vs Deflection (mm)

Fig. 9 Load deflection curve for Aluminum specimen



The values of gas pressures applied on the surface of piston are presented in table. 5.

Table. 6 Pressure distributions over the Piston surface [4]

Location Value Pressure (Mpa)

Piston round, crown, top of first groove

Pz 5

Bottom of first groove

Pz x76%

3.8

Top and bottom of second groove

Pz x 25%

1.25

Top and bottom of third groove

Pz x 20%

1

Top of fourth groove Pz x 15%

0.75

Bottom of fourth groove

Pz x 10%

0.50

All degrees of freedom are arrested at the inner surface of the piston pin boss, to avoid the displacement of piston in the radial direction and rotation about the piston pin axis. After the analysis, the obtained thermal stress distribution is presented in the fig. 10 & 11.

Fig. 10 Distribution of first principal stress Fig. 11 Distribution of second principal stress

(Thermal stresses) (thermal stresses)

The same non-linear analysis of the piston is carried under the action of only gas pressure using the same materials and element and the corresponding stress distributions are presented in fig. 12, 13 & 14.



Fig. 12 First Principal stress distribution Fig. 13 Second principal stress distribution Fig. 14 Third Principal stress

under only gas pressure under gas pressure distribution under gas pressure

The obtained maximum and minimum values of the stresses with and without thermal loading are presented intable 7 for comparison. In addition, the maximum and minimum temperature values at the piston surface are also presented in table 7.

Final conclusions of this work are presented in detail in section-4.

Table. 7 Maximum and minimum values of various parameters

S.NO

ParameterOnly

mechanical Thermal stresses

Maximum

Minimum

Maximum

Minimum

1Principal stress - 1

66.4 Mpa

-7.83 Mpa

625 Mpa

-239 Mpa

2Principal stress - 2

29.7 Mpa

-29.3 Mpa

130 Mpa

-565 Mpa

3Principal stress –3

13.7 Mpa

-29.5 Mpa

117 Mpa

-96.6 Mpa

Maximum Minimum

4Temperat

ure 188.47°C 134.158°C

5Heat flux

– axial189876 W/m2

= 0.19MW/m2-542108 W/m2 = -0.542 MW/m2

6Heat flux - radial

312855 W/m2

= 0.313 MW/m2

-302363 W/m2 = -0.302 MW/m2

IV. CONCLUSION

1. From the analysis, it has been observed that under the action of only gas pressure, the stresses induced in the piston are very less and are within the elastic limit. The obtained principal stresses are far less than the thermal stresses induced due to the combined loading.

2. From the results of thermal analysis, fig. 10 it has been observed that maximum temperature is observed at the top of the piston i.e. at piston crown and the minimum temperature is observed at the bottom end of the piston i.e. at half way below the piston pin boss on the piston skirt. In addition, by comparing the fig. 5 and 6, the results shows that the heat flux flowing out of the piston in axial direction is found to be maximum than in the radial direction. This indicates that more amount of heat is lost to the surroundings along the length of the piston. This increases the thermal load on the piston pin boss, thereby increasing damage to the piston.

3. At the piston ring land, temperatures are distributed uniformly along the piston in the radial direction. We can see clearly that the temperature of the piston skirt along the piston pin hole is higher than that



perpendicular to the pin hole, thus causing the thermal deformation of the piston in the direction of the piston pin is greater.

4. The piston temperature changes uniformly from the piston top to the bottom, without any sharp change phenomenon. The piston maximum temperature is at the piston top surface with the temperature of about 188.47°C and the temperature of the upper surface of the first circular groove being about 176.437°C.

5. To assess the thermal condition of the piston, we should first pay attention to the maximum temperature of the piston top and the temperature of the first circular groove. The allowable average temperature of the aluminum piston top is 300°C to 350°C and the allowable average temperature of the first circular groove is 180°C to 220°C. [1]

6. This standard indicates that, in the present work, except the temperature of the first circular groove (nearer to the lower limit of above-mentioned range), the overall temperature of this piston is within the allowable average temperature, but the thermal load is severe. In high temperature, the material intensity will decrease and the high-temperature creep will occur. In the uneven temperature field, the piston in operation will cause great thermal stress, which will easily cause the piston cracked after long-time operation. The over-high temperature of the first circular groove will not only decrease the intensity of some materials of the circular groove, speed up the circular groove wearing, and influence the gaseous ring tightness, but also easily cause the piston ring cemented.

7. In the coupled field analysis, combined gas pressure and thermal load (convection effect by the hot combustion gases) is applied on the piston. It has been observed that the effect of gas temperature is significant and the stresses obtained are very high, indicating that the material is in plastic state. The stress distribution indicates no visible separation of the material i.e. the fracture on the piston at any location even though the material is exhibiting plastic behavior. Hence, to avoid the fracture, the design of the piston is to be modified by changing the dimensions at the required location.

The results of thermal stresses obtained from the coupled field analysis supports the comments written above because of higher average temperature at the top surface of first piston ring. Therefore, it is necessary to take measures to carry out optimization of design for the piston, to decrease the thermal load of the piston.However, based on the coupled-field analysis only, we cannot judge the behavior. Because the piston is subject to cyclic loads, which are mentioned below:

· Repeated pressure variations acting on it, high during the combustion process and less during the suction process

· High temperature during the combustion and low temperature during the suction process· In addition, the piston loses its heat to the surrounding cooling media by conduction, convection, and

radiation phenomenon.· Even the presence of oil holes is also to be considered while performing the analysis, which is not

included.These effects are also to be included in the analysis for studying the accurate behavior of the piston throughout its working cycle.

V. SCOPE FOR THE FUTURE WORK

The present work can be extended further as mentioned below, to assess the behavior of the piston much more accurately.

1. By changing the design of piston crown (various types of combustion chamber design), we can find in which design the thermal load will be minimum.

2. By using the composite material having the better properties than the ordinary metals in general use (Aluminum, Cast iron, forged steel) for piston, we can reduce the damage by thermal load.

3. For different loads on the engine like no load, 20% full load, 40% full load, 60% full load, 80% full load and 100% full load· Thermal analysis can be performed on the piston to study the temperature and heat flux

distributions· Structural analysis can be performed on the piston to study the variation of stresses in the piston

4. Fatigue analysis (structural) can be performed by considering the cyclic pressure variations occurring in the engine for various loading conditions.

5. CFD analysis can be performed to study the convection effect of the hot gases on the piston for various loading conditions (mentioned in point-3) as well as injection pressures.

REFERENCES

[1] Element Reference – ANSYS 12.0[2] Heat transfer data book by C. P. Kothandaraman



[3] Hongyuan Zhang, Zhaoxun Lin, Iian Xing,Temperature field analysis to gasoline engine Piston and structure optimization, 37, Vol. 48 No.2, Journal of Theoretical and Applied Information Technology

[4] Yanxia Wang, Yongqi Liu, Haiyan Shi, Simulation And Analysis Of Thermo-Mechanical Coupling Load And Mechanical Dynamic Load For A Piston, Second International Conference on Computer Modeling And Simulation, 2010, IEEE.

[5] Er.Jadhav Rajendra B, Dr. G. J. Vikhe Pati, Computer Aided Design and Analysis of Piston Mechanism of Four Stroke S.I. Engine, 2010 IEEE

[6] Yanxia Wang, Yuzhen Dong, Yongqi Liu, Simulation Investigation on the Thermo-mechanical Coupling of the QT 300 Piston, 2009 Second International Conference on Information and Computing Science, IEEE

[7] Vinay V. Kuppast, S. N.Kurbet, Aravind Yadawad, Basavaraj Kambale, Study on Influence of Temperature on I C Engine Vibration-A Finite Element Approach, International Journal of Engineering Research and Applications (IJERA), Vol. 1, Issue 4, pp.1893-1897.

[8] M.R.Ayatollahi, F.Mohammadi and H. R. Chamani, Thermo-Mechanical Fatigue Life Assessment of a Diesel Engine Piston International Journal of Automotive Engineering Vol. 1, Number 4, October 2011

[9] Vinod Junju, M.V. Mallikarjun and Venkata Ramesh Mamilla,Thermo mechanica l analysis of diesel engine piston using ceramic crown, International Journal of Emerging Trends In Engineering And Development (IJETD), issue 2, vol.5 (July 2012).



Non-linear static coupled field analysis of a piston in a...

Documents

Transcript of Non-linear static coupled field analysis of a piston in a...