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Thermal stress analysis of the cylinder head C28 engine

Ing. Miloš Moravec Supervisor: Doc. Ing. Miroslav Španiel, CSc.

Abstract

This paper deals with complete FEM (finite element method) heat transfer analysis of the

cylinder head assembly of the C28 series engine and its cooling system. More specifically the

paper analyzes modeling of the temperature fields by FEM and 1D fluid flow in structures

with cooling. It brings a brief overview on current heat transfer simulation possibilities and

uses FEM as the fundamental approach. Furthermore, the paper includes basic information

about weighted residual methods and describes in detail the Petrov-Galerkin method that is

used to solve convection/diffusion problems. With the theoretical information, principles and

basic methods considered a special model solving the cooling system was created and verified

in the FEM software program ABAQUS.

Key words

MKP PG FORMULACE, MKP; PETROV GALERKINOVA METODA; TEPLOTNÍ

NAPJATOST; 1D PROUDĚNÍ; MKP CHLAZENÍ;

1. Introduciton

This paper deals with the numerical simulation of cooling for thermal strain parts, concretely

it focuses on liquid medium cooling with forced circulation. The main object was to design

and to verify computational procedure based on combination of one-dimensional model of

liquid flow in the system of the cooling tubes and on spatial finite element model of cooling

system. The heat problem of the finite element model which includes forced convection given

by medium velocity field is solved by using the special elements using Petrov-Galerkin

formulation of shape functions. The verification of the proposed method is based on

numerical solution of the 6C28DSG series engine (originally designed by ČKD MOTORY,

a.s. Hradec Králové company) cooling system. This paper considers thermal decrease of

conduction/forced convection in the system of the cooling tubes round the exhaust valves.

Figure 1 – Engine head 6C28DSG

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2. Description of the engine and problem specification

This combustion engine that is cooled by water is four-stroke turbocharged engine with

direct fuel injection and is used in power generating units. It is composed by two suction and

two exhaust valves and central injector. The valves are placed in molded slide rails. The

engine is started by compressed air. Basic technical parameters of the engine are shown in

the table 1.

Drilling 275 [mm]

Stroke 330 [mm]

Rotation speed 750 [min-1

]

Cylindrical power 240 [kW]

Effective press 19,6 [bar]

Table 1 – Basic technical parameters of the engine

Heat and thermal analysis performed in this paper is solved in terms of steady-state running.

The seats around the exhaust valves are cooled by water circulating in water channels in the

cylinder head of the engine. (See figure 2). The bottom of the cylinder head is cooled by

special drilled channels, as is evident from figures 2 and 3.

Figure 2 and figure 3 – Cooling channels in the cylinder head

3. Stacionary flow of viscous liquid in pipeline

The one dimensional type of the flow which is described by Bernoulli expanded equation (1).

zevp

hgvp

hg 2

.2

.2

22

22

2

11

11

(1)

A special algorithm for the cooling system determining velocity field in the whole system

and solving friction hydraulic losses and local hydraulic losses was designed. This algorithm

uses standard hydrodynamic criteria numbers and equations to solve the heat transfer

coefficients on the heat transfer surfaces in the cooling tubes.

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Figure 4 and figure 5 – Cooling system of channels

The utility in Matlab was created for calculation of the flow in the cooling system. The

acquired data are later used for thermal analysis. The program structure is outlined in

figure 6.

Figure 6 – Scheme utility in Matlab

The calculation of the criterial equations went through simplification. Kinematic viscosity is

a function of temperature which will be considered only at its value of 20 °C. It was

necessary to make the conversion to mass flow rates. These are used as a boundary condition

for determining the “Mass flow rate” in an environment of ABAQUS.

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4. Basic FE model

The main objective of this model was to examine all the problematic parts, which the general

description of the cooling system brings. Mainly it means to relate the individual parts of the

cooling liquid into one single unit. Figure 4 shows geometry model of the cooling system. It

consists of five models of liquid and of a cooled solid into which the cooling liquid flows.

The individual liquid models are linked to each other by using coupling equations. In

addition to the described objects, it was necessary to create a system of points – known as

„cutpoints‟ that can simulate (using the coupling equation) junction and the bend flow.

Figure 4 shows this basic model.

Figure 7 – Basic model geometry of the cooling system

The calculation of the finite element simplified model of the flowing was formulated as

transient thermal analysis. The time of the circulation took 10 seconds and the results show

large heat taken away and decreasing temperature around the cooling tubes. The temperature

of the liquid increases only a little because of high velocities.

Figure 8 – Temperature distribution in the basic model

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5. FE model of cylinder head of the engine C28

The FE mesh of the model was adopted from previous calculations. In the final model of the

cylinder head C28 a model of cooling liquid was created. The geometry is shown in figure 9.

Figure 9 – Scheme of cooling system

The main calculation was formulated as a stationary analysis of thermal field so the time of

the calculation was much shorter than if it would be in the case of transient thermal analysis.

The highest temperature was detected in the area of the exhausted valves. The temperature of

the cooling liquid increased by 60 K in this place. If the flowing of liquid is reflected it is

possible to compute the heat transfer coefficients and they don„t have to be determinated by

experiments or experience.

Figure 10 – Temperature field of exhaust seat, valve and direction

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Figure 11 – Section of cooling channels

6. Conclusion

The analysis of the temperature field in the model of engine cylinder head C28 with cooling

around the seats and cooling in the drilled channels brings new sight on problematic of

cooling. Due to universal Bernoulli equations the application of this method can be used for a

great variety of cooling systems. This method is a reasonable compromise between using the

full 3D flowing liquid model and the description of 1D flowing liquid by using Bernoulli

equations. The suggested solution was verified in the latest edition of ABAQUS, which

contains a superstructure CFD, where a similar method for flowing was used.

References

[1] Idelchic I.E., Handbook of Hydraulic Resistance, Begell House Publishers; 3rd edition (June 1, 2001)

[2] Španiel M., Tichánek R., Macek J.,Polášek M.: Výpočet oběhu motorů 6C28 a stanovení okrajových

podmínek pro pevnostní a a deformační výpočet hlavy válce. Výpočet teplotního pole, deformace a stavu

napjatosti hlavy válce, ČVUT Praha 2008

[3] Fletcher C.A.J: Computational Galerkin methods, Springer-Verlag, New York, 1984

[4] McAssey, E.V. – Kandlikar, S.G.:Convective heat transfer of binary mixtures under flow boiling conditions,

Villanova University, Villanova, PA USA