The Calculation And Analysis Of The Cylinder Head Thermal-mechanical Stress And Low Cycle Fatigue Life In The Process Of Cold Start

To study the temperature and stress variation of the cylinder head in the process of cold start, temperature, stress and fatigue life were calculated under different ambient temperatures using numerical method. Comparative analyses of the changing process of the temperature and stress were made. The temperature-time curve peak and the stress-time curve peak in the process of cold start were found for the first time. Under different ambient temperatures, the fatigue life calculations of cylinder head in the steady state and transient state were made and compared. The optimization scheme based on the coolant temperature was put forward finally.The main research contents and conclusions are:(1) Three dimensional diesel engine model was made and the boundary conditions were acquired. Fluid-solid coupled numerical simulations were made. The temperature field calculation results of the cylinder head were compared with the test results. It was shown that the maximum relative error is within 5%, the numerical model could satisfy the requirement of engineering application.(2) The cylinder head temperature field, stress field and the low cycle fatigue life calculations in the steady state were made under different ambient temperatures. It was found that the ambient temperature has little influence on the cylinder head temperatue field, stress field and the fatigue life in the steady state.(3) The cylinder head temperature calculations in the transient state were made under different ambient temperatures. It was found that the peak value appeared in the temperature-time curve of some areas on the flame deck during cold start. And the peak gradually reduced or even disappeared with the falling of the ambient temperature.(4) The cylinder head stress field and the low cycle fatigue life calculations in the transient state were made under different ambient temperatures. It was found that the peak value appeared in the stress-time curve of some areas on the flame deck during cold start. And the peak gradually reduced with the falling of the ambient temperature. The fatigue life calculated in the transient state was lower than that in the steady state.(5) An optimization scheme was put forward. The initial coolant temperature was changed to 0 ℃ when the ambient temperature is-25 ℃. The results showed that the temperature peak value and the stress peak value in the curves were significantly reduced and optimization effect was obvious.