KIGAS Vol. 12, No. 4, December, 2008 (Journal of the Korean Institute of Gas) l x CNG» v m s w ½ Á y w» œw (2008 9 30, 2008 12 10, 2008 12 10 k) Numerical Analysis for Temperature Distribution and Thermal Stresses in a Turbocharged Large CNG Engine Piston Yang Sul Kim Su Chul An Department of Mechano-Informatics & Design Engineering Hongik University (Received 30. September. 2008, Revised 10. December. 2008, Accepted 10. December. 2008) 6»m ƒ v m w 3 ww k s x dwš,» w m mw v m w w» wš w. w þƒ l v m w e w sƒw» w þƒ y v m s s š x w. v m š j ùkûš, v m j w w. Abstract The purpose of this paper is to establish a standard finite element analysis model of a piston by carrying out three dimensional modeling of a series six-cylindered CNG engine's piston to forecast temperature distribution at stationary state and the following thermal stress and variation, and cross checking it with existing analysis. Also, in order to evaluate the affects of the cooling system to the piston s heat load, the paper analyzed piston's temperature and thermal stress distribution according to the cooling water temperature changes and the following variations. As a result, the maximum temperature was found at the center of the crown in the piston and the maximum thermal stress occurred from the lower part of the piston. Key words : finite element method, CNG engine, temperature distribution, thermal stress and deformation, heat transfer coefficient I. š» wd ƒš. p, x»»ƒ w»» w. x wƒ w w» w wù ƒ (CNG) wù.» w w š, p x ƒ (CNG) w»ƒ w d w. e :kimys@hongik.ac.kr Fig. 1. 3-Dimensional FE-model of a piston. 58
l x CNG» v m s w ü x ww ƒ (CNG) y w w, v w t v m w y w [5,7]. Fig. 1 v m 3 ww k s x dwš,» w m mw v m w w» wš w [6,9]. w g ADINA(Automatic Dynamic Incremental Nonlinear Analysis, R&D, Inc., 1999) w s w w. II. v m w 2.1. v m v m y, š v m fp w p ww» w v m d x w w. ù» w x l l[1] v m y wš y Ì w z š x [2] w z w w. w w x w w v m ƒ Fig. 2. Table 1. Material properties of aluminum alloy. Elastic modulus, E [GPa] 6.66 10 10 Poisson s ratio, ν 0.33 Density, ρ [kg/m 3 ] 2.75 10 3 Coef. of thermal exp, β [1/K] 2.1 10 5 Table 2. Maximum and minimum temperatures in the piston ( o C). Tc Min. temperature Max. temperature Difference 60 148.2 444.1 295.9 70 151.2 446.2 295.0 80 157.1 450.2 293.1 90 162.9 454.3 291.4 100 168.8 458.3 289.5 Fig. 2. Thermal circuit method of resulted boundary conditions of the piston. Fig. 3. Temperature distribution of the piston. 59 w ƒ wz 12«4y 2008 12
½ Á 2.2. v m w w w 3 v m w s w ww. w x CNG» v m ( w ) e(300 o C) Table 1 [4,10]. v m s w k þƒ v m þƒ l v m w e w sƒw» w þƒ y v m s w w š w. w þƒ ƒ» 80 o C» 10 o C, 20 o C j û ù ƒ w w. þƒ w s Fig. 3 ùkü. Table 2 þƒ ƒ v m š ƒ, š w ùkû. w, Fig. 3 š j sw š, fp w w. III. v m w v m w. w w w 3 2.2 w w w ww. Fig. 4 v m Stress Strain ùkü. j w 66.69 MPa w š, p p (Thrust side) 0.009493 mmƒ w. IV. 4.1. v m s v m ü s w xk s v m (Bowl) ùkù x» ew. Fig. 5 š x[3] d w ƒ e w w mw w. e ƒ ù, w š w x w w š w Fig. 4. Thermal stress and strain distribution of a piston. Fig. 5. Comparison with temperature results of the piston for analysis and experiment. KIGAS Vol. 12, No. 4, December, 2008 60
터보과급 대형 CNG기관 피스톤의 온도분포와 열응력 해석 Fig. 6. Position temperature distribution of the piston. 적 만족한 결과를 도출하였다. 피스톤의 각 부위별 온도 분포는 Fig. 6과 같다. 피스톤의 열응력분포 열전달 해석을 통해 구한 각 절점에서의 온도를 입 한국가스학회지 제12권 제4호 2008년 12월 4.2. 61
½ Á Table 3. Summary of results thermal stress of the piston. Tc ( o C) Max. stress (MPa) Max. displacement (mm) 060 66.69 0.009190 070 66.05 0.009234 080 65.07 0.009319 090 63.43 0.009408 100 62.84 0.009493 s w. s Fig. 4 j w š w. w, v m þƒ l v m w e w sƒw» w þƒ y v m s w w. Table 3 þƒ ƒ v m û ùkû. þƒ ƒ v m û þƒ ƒ v m š (Temperature gradient)ƒ» q. VI. CNG v m w s w ww. v m ƒ e w v m s w š, w s w v m w w. (1) v m j v m fp ƒ w w ùkþš, š j ùkû. (2) v m s wù v m j w w š, v m vy w., v m» j w w š ƒ v m ƒ š q. (3) x v m j ó w j v m w w w j, x ƒ š q. 2008w y w w w. š x [1] Li, K.S. Study on Heat Transfer and Thermal Behavior Characteristics of a Naturally Aspirated Diesel Engine, w w, (1997) [2] Li, C.H. Piston Thermal Deformation and Friction Considerations, SAE 820086, (1982) [3], l v m w w, w œwz, 2(9), 92-98, (2001) [4],, x, x, ü» v m w w w w, w» wz, 12(3), 528-533, (1988) [5] Overbye, E.A. Unsteady Heat Transfer in Engines, SAE Translation, 69(461), 461-494, (1961) [6] Bertodo, R. and T.J. Carter, Stress Analysis of Diesel- Engine Cylinder Heads, Journal of Strain Analysis, 6(1), (1971) [7] Pattas, K. Thermische Belastung des Zylinderkopfes von Hochleistungs Dieselmotoren, MTZ, 35(10), 314-318, (1974) [8] Garro, A. and V. Vullo, Some Consideration on the Evaluation of Thermal Stress in Combustion Engine, SAE 780664, (1978) [9] Hohenberg, G.F. Advanced Approaches for Heat Transfer Calculations, SAE 790858, (1979) [10] Assanis, D.N. and E. Badillo, Transient Heat Conduction in Low-Heat Rejection Engine Combustion Chambers, SAE 870156, 156-163, (1987) KIGAS Vol. 12, No. 4, December, 2008 62