Thermal Reliability Design Theory And Application Research For Cylinder Head Of Combustion Enhanced Diesel Engine

Combustion intensification is an important method for diesel engine energy saving and emission reduction.The combustion intensification of diesel engine increases the thermal and mechanical load of heated‐stressed components such as cylinder head,which is challenging the reliability design.On one hand,it takes a lot of time and expense to verified diesel engine product reliability while adopting fatigue life as criteria,and it is hard to meet the actual project development schedule and cost control requirements.On the other hand,numerical simulation method has been widely adopted in multiple designing schemes comparison and optimization for diesel engine.However,due to the limited product information for enchanced diesel engine reliability design,and the systematic theoretical research was not deep enough,the comcept design or innovative desigh of domestic high‐level diesel engine product still relies on cousulting companies.With the rapid development of domestic diesel engine industry,the reliability design problem mentioned above is becoming more and more prominent.There is an urgent need to establish a design theory based on reliability objective,which can guide conceptual or innovative design and can be easily adopted and tested in the engineering application.Taking cylinder head of diesel engine as the object,this paper aims at the thermal reliability design problem of combustion‐enhanced diesel engine.In order to establish the reliability evaluation theory that is convenient for testing in engineering appliacation and based on design parameters,this paper study the the thermal diagnostic parameters model based on fatigue theory.On this basis,the effect of combustion intensity,cooling organization and water jacket structure on thermal parameters of cylinder head were researched systematically,and thermal parameters prediction model based on design parameters is established.In addition,the thermal diagnostic parameters model and prediction model are combined and applied in engines of different combustion intensities.The main research contents and conclusions are as follows:1.Study on cylinder head thermal diagnostic parameters model based on fatigue theory.By theoretically deducing the relationship between thermal fatigue life in the danger region of failure and the temperature distribution of cylinder head,this paper had extracted the critical regional temperature difference parameters representing the fatigure life of cylinder head,and establish the cylinder head thermal diagnostic parameters model based on fatigue theory.The temperature field,stress field and fatigue life of cylinder head are obtained by fluid‐solid thermal coupling analysis and thermo‐mechanical coupling simulation analysis.According to the simulation results,the cylinder head thermal diagnostic parameters model is verified and corrected,and the comprehensive temperature difference parameters are established,which can reflect the fatigue life of cylinder head.2.Study on effect of combustion intensity on thermal state of cylinder head.By adopting thermal dynamic model,this paper research the effect of power density on in‐cylidner heat transfer intensity and explosive pressure.On this basis,the almost‐linear variation of peak temperature and critical regional temperature difference of cylinder head is revealed with heat transfer intensity and fire‐deck thickness increased,while power density is in the range of 29⁵3 kW/L.3.Study on effect of cooling organization and water jacket structure on thermal state of cylinder head.The fluid‐solid thermal coupled model is adopted to research the effect of cooling organization and structures on thermal parameters of cylinder head.The results showed that:there is a logarithmic relationship between the coolant flux and the thermal parameters of cylinder head.Optimizing the critical up‐hole is beneficial to reduce the peak temperature of cylinder head.The combination of split cooling and top‐down cooling can reduce the peak temperature of the cylinder head,and reduce the frictional power consumption and thermal dissipation of coolant.The results of effect research of double water jacket showed that,the application of double water jacket reduce the thermal parameters of cylinder head,and improve the LCF life and HCF safety coefficient.4.Establishment and verification of thermal parameters prediction model of cylinder head based on design parameters.Response surface method（RSM）was applied to establish the coupling effect model of double water jacket structure parameters on the thermal parameters of cylinder head.The model showed that,the effect of dimensionless height and diameter of lower water jacket on the themal parameters of cylinder head is interactive.RSM was applied to establish the coupling effect model of coolant flux and double water jacket structure parameters while split cooling and top‐down cooling is adopted.The model showed that,water jacket dimensionless height?has most significant impact on_???and?????.Combining the above RSM model and effect results,this paper established thermal parameters prediction model of cylinder head based on design parameters.The accuracy of this prediction model is verified by the cylinder head temperature data of a diesel engine before and after combustion intensifying5.Integrated application research of the thermal diagnostic parameters model and prediction model of cylinder head.A cooling organization and water jacket structure design method for combustion‐enhanced diesel engine cylinder head is established based on the thermal diagnostic parameters model and prediction model,and it is applied in diesel engine of various power densities.The results showed that,the prediction model has high accuracy,and the cylinder head LCF life requirements are met while appling the cooling organization and water jacket structure scheme,which means the thermal diagnostic parameters model is accurate.While appling thermal diagnostic parameters model and prediction model in the cylinder head cooling design,the time cost significantly reduced.