Abstract
In order to increase the reliability and service life of piston in a heavy-duty diesel engine, the geometric structure of piston was optimized based on its maximum temperature and maximum coupling stress. To begin with, the boundary conditions of thermal and stress fields are calculated, which include the heat produced by the combustion in cylinder, the friction-induced heat, and the heat transferred to cooling system. Then, the finite element model was established to calculate and analyse the temperature and thermal-mechanical coupling stress fields of the piston. By combining this simulation model with orthogonal experimental design methods, computations and analyses were performed to determine how the five geometric parameters (depth of intake and exhaust valve grooves, radius of valve grooves transition, radius of top of valve grooves, height of first piston ring groove, and depth of piston ring groove) influence the two evaluation indicators (maximum temperature and maximum stress of piston). Subsequently, using the proposed ABC-OED- FE (artificial bee colony, orthogonal experiment design, and fitting equations) method, the fitting equations between the geometric parameters and evaluation indicators were determined. Taking the minimum values of two evaluation indicators of piston as optimization objectives, artificial bee colony method was run to determine the values of parameters. At last, the two evaluation indicators of the optimized piston were computed. The results indicate that, after optimization, the maximum temperature of piston decreases to be 16.05 K and the maximum stress decreases to be 13.54 MPa. Both temperature and stress conditions of the optimized piston had been improved, which demonstrates the effectiveness of the optimization and the validity of the algorithm.
Highlights
With development of science and technology, the power density of diesel engine increases continuously
Suggestions for optimized piston with optimal temperature and stress state were provided through the above analysis: height hg of intake and exhaust valve grooves decreased to 5.82 mm; smooth transition was added to groove bottom and radius of curvature rb set to 2.65 mm; smooth transition was added to groove top and radius of curvature rt set to 2.25 mm; height hr of piston ring groove decreased to 2.47 mm, and depth dr of piston ring grooves increased to 6.15 mm
Temperature field and thermal-mechanical coupling stress field of piston in diesel engine were calculated and analysed by finite element method, orthogonal experimental design method, and artificial bee colony algorithm. 5 parameters of the piston’s geometric structure were optimized to decrease thermal and mechanical load exerted on piston
Summary
With development of science and technology, the power density of diesel engine increases continuously. The thermal load and mechanical load exerted on high temperature components in engine’s cylinders, especially pistons, have been increased. Coupling effect of fatigue and creep would drastically shorten the service life of piston and other high temperature components and severely influence the reliability of the entire engine. Combustion condition in cylinder can provide the boundary conditions to calculate the thermal stress field and the thermal-mechanical coupling stress field of piston. It is necessary to analyse the combustion before studying the piston temperature field. Wang et al [3] studied the relationship between compression ratio and ignition type of diesel. To improve the quality of combustion, the ignition time should be advanced and that flammability limits should be extended. Yuan et al [4] established a coupling model to simulate the combustion character of a free piston
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