Thermo-mechanical coupling strength analysis of a diesel engine piston based on finite element method

ABSTRACT

   Due to improvements in diesel engine power and performance, the piston in the combustion chamber is subjected increasingly higher thermal and mechanical loads. The cyclic changes in thermal and mechanical stresses seriously affect the piston fatigue life. Therefore, it is necessary to analyze the strength of the piston in the design process. In this paper, the finite element analysis of piston under thermal, mechanical and thermo-mechanical loads coupling is carried out by using the ANSYS software. By analyzing the heat and force distributions on the piston, the stress and strain distributions on the piston can be obtained, so as to determine the maximum stress concentration areas and check whether the piston strength meets the requirements. Results indicate that the highest temperature on the piston appears at the top of the combustion chamber bulge, where the deformations of the piston and combustion chamber are the most serious. There is a large stress concentration in the contact between the piston pin seat, the piston pin hole and the piston. The minimum number of piston cycles is 1.2×10⁶ times, which meets the piston cycle number from starting, running, and to stopping process. Thus the strength of the diesel engine piston meets the requirements.

KEYWORDS:

• Diesel engine piston
• Finite element analysis
• Temperature and stress field
• Thermo-mechanical coupling

Disclosure statement

No potential conflict of interest was reported by the author(s).

Nomenclature

$a$	=	clearance between piston and cylinder
$b$	=	thickness of cylinder liner
$c$	=	clearance of top side
$C_m$	=	the average speed of the piston
$d$	=	distance between two midpoints $d=\sqrt{{\left(\frac{\mathrm{h}}{2}\right)}^2+{\left(\frac{l}{2}\right)}^2}$
$D$	=	diameter of cylinder
$e$	=	clearance of back side
$F_g$	=	the force on the piston top
$F_j$	=	the reciprocating inertia force of the piston
$F_{N_1}$	=	the reaction force acting on piston pin seat
$F_{N_2}$	=	the lateral pressure on the piston skirt
$\mathrm{h}$	=	height of piston ring
$h$	=	the equivalent heat transfer coefficient
$h_w$	=	heat transfer coefficient of cooling water
$K_{\theta }$	=	constant the value is 7.799
$l$	=	radial height of ring
$n$	=	rotation speed
$P_g$	=	the instantaneous pressure of fuel gas
$S$	=	piston stroke
$t_{oil}$	=	oil mist temperature under piston cavit
$t_{w1}$	=	piston crown temperature
$t_{w2}$	=	piston chamber temperature
$T_g$	=	the instantaneous temperature of fuel gas
$T_{gm}$	=	the average gas temperature at the top of the piston
$T_{res}$	=	the boundary temperature
$\beta$	=	the gas heat transfer coefficient
${\beta }_m$	=	the average heat release coefficient at the top of the piston
λ	=	heat conductivity
λ1	=	heat conductivity of gas
λ2	=	heat conductivity of cylinder
λ3	=	heat conductivity of piston rings
λ0	=	heat conductivity of cooling oil
λp	=	the thermal conductivity of piston material
δp	=	piston crown thickness

Additional information

Funding

The work was supported by the Jiangsu University of Science and Technology .