Thermo Mechanical Analysis of Piston

National FEAST- Users / Developers Meet 2017

THERMO MECHANICAL ANALYSIS OF PISTON 1

Thermo Mechanical Analysis of Piston 1Shubham K. Chaudhari (SVR Infotech)

2Aniket H. Bhelsaikar (SVR Infotech)

3Vinod Atpadkar (SVR Infotech)

1. Abstract:

Engine is a heart of vehicle, it converts the heat generated by the combustion fuel into kinetic

energy at end of the crankshaft which again transferred to gear box latter to wheel for propulsion

action of vehicle. The piston is driving member in engine and subjected to various loading during

the four stroke i.e. suction, compression, power and exhaust. During power stroke, combustion of

Fuel – Air Mixture causes tremendous amount of heat generated on the surface of piston. The

temperature & pressure of power stroke results in generation of thermal expansion along with

mechanical stresses. So it is very important to determine such factor which causes failure of piston

during working of engine. Also while designing piston it is necessary to calculate or simulate such

factor before manufacturing. The paper discussed on piston which is modeled in CATIA V5 and

then discretized in HyperMesh software and analyzed in VSSC/ISRO FEAST software. Various

boundary condition and material has been used to determine effect of temperature and pressure on

piston.

Key Words: Piston, Thermal stresses, Combined Loading, CATIA V5 and FEASTsmt.

2. 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 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.

3. Design Procedure for Piston.

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

3.1 Piston Head Thickness: -

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

𝑡𝐻 = 𝐷√3𝑃

16𝜎𝑡− − − − − − − − − (1)



Fig 1: Details of piston.

Where,

D = Cylinder bore diameter. (mm)

P = Maximum gas pressure or explosion pressure. (Mpa)

𝜎𝑡 = Permissible bending stress (N/mm2)

The piston head absorbs the heat during combustion of fuel and transmits it to the cylinder wall. It

should have sufficient thickness to quickly transfer the heat to the cylinder wall. On the basis of

heat dissipation, the thickness of piston head is given by,

𝑡ℎ = [𝐻

12.56𝑘(𝑇𝑐 − 𝑇𝑒)] × 103 − − − − − − − −(2)

Where,

H = amount of heat conducted through piston head. (W)

K = thermal conductivity factor. (W/m/ºC)

Tc = temperature at center of piston head. (ºC)

Te = temperature at edge of piston head. (ºC)



3.2 Piston ribs and cup.

When the thickness of piston head is 6mm or less, no ribs are required. The no. of ribs are

varies from 4 to 6 and thickness of ribs are given by:

𝑡𝑅 = (𝑡ℎ

3) 𝑡𝑜 (

𝑡ℎ

2) − − − − − − − −(3)

When the ratio of stroke length to bore is up to 1.5, a cup is required on the top of the

piston. The radius of cup is given by:

𝑅𝑎𝑑𝑖𝑢𝑠 𝑜𝑓 𝑐𝑢𝑝 = 0.7𝐷 − − − − − −(4)

3.3 Piston Rings.

The radial width of ring is given by:

𝑏 = 𝐷√3𝑃𝑤

𝜎𝑡− − − − − − − − − − − (5)

The axial thickness of piston ring is given by:

ℎ = 0.7𝑏 𝑡𝑜 𝑏 − − − − − − − − − (6)

The distance from the top of the piston to the first ring groove is called top land which is

given by:

ℎ1 = (𝑡ℎ) 𝑡𝑜 (1.2𝑡ℎ) − − − − − − − (7)

The distance between two consecutive ring grooves is called the width of the ring groove

and is given by:

ℎ2 = 0.75 ℎ 𝑡𝑜 ℎ − − − − − − − − − (8)

3.4 Piston Barrel.

The thickness of piston barrel at the top end is given by,

𝑡3 = (0.03𝐷 + 𝑏 + 4.9) − − − − − −(9)

The thickness of piston barrel at the lower or open end is given by:

𝑡4 = (0.25𝑡3) 𝑡𝑜 (0.35𝑡3) − − − − − (10)

3.5 Piston skirt.

Maximum gas force on piston head is given by equation:



𝐺𝑎𝑠 𝑓𝑜𝑟𝑐𝑒 = (𝜋𝐷2

4) 𝑃𝑚𝑎𝑥 − − − − − −(11)

The total length of piston is given by,

𝐿 = 𝑡𝑜𝑝 𝑙𝑎𝑛𝑑 + 𝑙𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑟𝑖𝑛𝑔 𝑠𝑒𝑐𝑡𝑖𝑜𝑛 + 𝑙𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑠𝑘𝑖𝑟𝑡 − − − (12)

3.6 Piston Pin.

The piston pin is partly in contact with piston bosses and partly with the bush of the

connecting rod. The bearing area of the piston pin is approximately divided between the piston

bosses and the connecting rod bush. The outer diameter of piston pin is determined by equating

the force acting on the piston and the resisting bearing force offered by piston pin:

𝐹𝑜𝑟𝑐𝑒 𝑜𝑛 𝑝𝑖𝑠𝑡𝑜𝑛 = (𝜋𝐷2

4) 𝑃𝑚𝑎𝑥

𝑅𝑒𝑠𝑖𝑠𝑡𝑖𝑛𝑔 𝑓𝑜𝑟𝑐𝑒 = (𝑃𝑏)1 × 𝑑𝑜 × 𝑙1 − − − − − − − (13)

Dimensions of piston according to above empirical relation are calculated and presented in Table

1.

Sr. No. Parameter Value

(mm)

1 Thickness of piston head 13

2 Thickness of ribs, tR 5.4

3 Radial width of piston ring 3

4 Axial width of piston ring 2.5

5 Top land length 14.3

6 Distance between two rings 2

7 Thickness of piston barrel at

top

11

8 Thickness of piston barrel at

open end

3

9 Length of skirt 67.36

10 Length of ring section 16

11 Length of piston 98

12 Outer diameter of piston pin 30

Table 1: Calculated design value.



4. Modeling and discretization:

The finite element analysis requires a geometry on which load and boundary condition are going

to act. Finite element solver is great tool to determine the physical parameter on the complicated

geometries. The model is prepared after calculating design data in modeling software CATIA V5.

Fig 2: Piston CAD part.

Discretization is one of main aspect in finite element method. To convert infinite degrees of

freedom to finite degrees of freedom geometry needed to be divide in multiple sets of elements.

The boundary condition and constraint which are acting on the body are totally taken on the

elements and nodes in model. The element used for discretization of model are tetra element. The

tetra element are efficient and cover the model easily. The tetrahedral element have three degree

of freedom which is required for calculating stresses in all direction respective of heat generation.

For discretization HyperMesh software is used. It is industry based software for only meshing.

Fig 3: 10 Node tetrahedral element.

https://www.google.co.in/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwj1-NClx-DXAhXDrI8KHcalCucQjRwIBw&url=https://andreweib.wordpress.com/2010/12/10/basic-fea-process/&psig=AOvVaw0MFl9j6UBmQwyI01eXY67R&ust=1511934011078024



Fig 4: Discretized Model of Piston In Hypermesh.

5. Material and Boundary Condition.

Piston is made of mostly different type of material according to the application. Cast iron piston

are used for moderately rated engines with piston speed below 6 m/s. Aluminum alloy pistons are

used for highly rated engines with piston speeds above 6 m/s. The material properties for cast iron

which are required for thermo mechanical analysis are given in Table 2.

Sr. No. Parameter Value Units

1 Thermal conductivity (k) 83 W/m-k

2 Density (ρ) 7200 Kg/m3

3 Specific Heat (Cp) 460 J/Kg-K.

4 Young’s Modulus (E) 1.1 GPa

5 Poisson Ratio (µ) 0.33

6 Tensile ultimate strength 240 Mpa.

Table 2: Thermal and Mechanical Properties of Cast Iron.

The aluminum alloy are mostly use for high speed cars because of their higher heat dissipation

properties. An aluminum alloy piston has less variation in temperature from the crown to the piston

rings. The density of aluminum alloy is about one third of cast iron. This results in light weight

construction and reduces inertia forces. The properties for aluminum alloys are given in Table 3.



Sr. No. Parameter Value Units

1 Thermal conductivity (k) 206 W/m-k

2 Density (ρ) 2707 Kg/m3

3 Specific Heat (Cp) 986 J/Kg-K.

4 Young’s Modulus (E) 70 GPa

5 Poisson Ratio (µ) 0.33

6 Tensile ultimate strength 310 Mpa.

Table 3: Thermal and Mechanical Properties of Aluminum alloy.

The boundary condition for thermal analysis for different material are different. The cast iron

piston reach up to temperature of 450 to 500ºC and aluminum alloys piston reaches up to 700 to

850ºC. At this value the temperature distribution is find out. This data is then fed to mechanical

structural analysis under which maximum gas pressure is applied on the top surface piston which

is generated by combustion of gases. The pressure is taken as 5Mpa as the piston is design for that

pressure value.

6. Results and Discussion.

6.1 Thermal analysis of Piston

Fig 5: Temperature distribution for Cast iron & Aluminum alloys respectively.

From the above two figures it is clearly seen that the thermal conductivity of aluminum alloy is

more than that of the cast iron. Which makes aluminum alloy more reliable for high speed engine

use because it will dissipate heat at higher rate.

6.2 Thermo-Mechanical Analysis.

The results obtained from the thermal analysis are then imported as input file for mechanical static

analysis. The static analysis consist of applied pressure caused by combustion of air-fuel mixture

at the top surface of piston. Basically the piston are design as per the force acting on it. This force



is calculated by the gas pressure applied on it. The resistance to the gas pressure is applied to the

piston pin section which is under high stress.

Fig 6: Displacement for Cast iron & Aluminum alloy respectively.

Fig 7: Stresses for Cast iron & Aluminum alloy respectively.

From displacement point of view the strength of cast iron is more which result minimum expansion

of material rather than aluminum. The stresses on the aluminum are also more than that of the cast

iron. The results of FEAST software are compared with ANSYS software for validation of results.

Fig 8: Displacement for Cast iron & aluminum alloy in ANSYS software.



6.3 Static Structure analysis.

The result of static structure analysis for both cast iron and aluminum are presented below.

Fig 9: Displacement for Cast iron & aluminum alloys respectively.

Fig 10: Stresses in Cast iron & aluminum alloy respectively.

7. Conclusion:

1. From the analysis it is clear that under the action of only gas pressure the stresses developed

in the piston are way too different as compare to thermo structure analysis. The stress for

static analysis is around 27 Mpa and for thermo-mechanical analysis it is around 138 Mpa

for aluminum alloy and 128 Mpa for cast iron.

2. The temperature distribution for thermal analysis shows that aluminum alloy is transferring

maximum heat to cylinder wall. So it is necessary to provide more gap between piston and

cylinder wall for expansion.

3. The displacement cause due to thermo-mechanical analysis in cast iron is 0.19 mm and for

aluminum it is 0.45 mm. From this two value it is clearly understand that cast iron has more

strength as compare to that of aluminum, so cast iron can be used in most moderately rated

engines.



4. The displacement of piston in static structure analysis is 0.015 mm for cast iron and 0.023

mm for aluminum alloys which are less as compare to thermo-mechanical analysis. This

results provide information that thermal expansion of piston is common phenomenon

happening inside engine.

5. 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 effect are also to be included in the analysis for studying the accurate behavior of

the piston throughout its working cycle.

8. 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 Patil, 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 mechanical analysis of

diesel engine piston using ceramic crown, International Journal of Emerging Trends In

Engineering And Development (IJETD), issue 2, vol.5 (July 2012).

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Thermo Mechanical Analysis of Piston