Research On Thermal Load Of The Cylinder Head And Heat Transfer Enhancement Inside The Cooling Water-Jacket

In order to meet the increasingly stringent requirements for energy saving and emission reduction of engine in the modern society, the engine develops in the direction of high pressure-charging and high compression ratio. However, almost all of high power density engine are faced with the thermal load problem. Fatigue damage easily occurs in such places like bridge zone, injector hole which has higher thermal stress. Therefore, it is of great significance to accurately predict the heat transfer conditions of cooling system and reasonably control the thermal load in the process of modern engine design and optimization. In this paper, a multi-field coupled model considering boiling heat transfer was established for the diesel cylinder head, this model was used to accomplish some research on flow and heat transfer of cooling water-jacket and thermal load of cylinder head. On this basis, optimal design of water-jacket structure was conducted. The following works were completed:First, considering the interaction of physical fields such as flow in cooling water-jacket, combustion in cylinder, intake and exhaust, heat conduction of solid in cylinder head, a coupled model with boiling heat transfer in diesel engine cylinder head was established based on single phase flow boiling flow model. On this basis, taking TBD-226B diesel engine as the research object, the three-dimensional numerical simulation was performed by using the established calculation model, and the temperature both of fire deck and cooling water-jacket wall were measured by using hardness plug and thermocouple on designed and built temperature measurement test platform. The accuracy and applicability of the established calculation model was verified by combination numerical simulation with experimental study.Secondly, the CFD calculation model of a six-cylinder diesel engine with high strength was established to simulate the flow and heat transfer of cooling water-jacket by using Fluent software, and the influence of boiling on coolant heat transfer was analyzed and evaluated based on single phase flow boiling flow model. Then the three-dimensional transient simulation of in-cylinder working process in the diesel engine was carried out. These studies were to establish a multi-field coupled model including the flow heat transfer inside the cooling water-jacket, combustion process inside the cylinder, the heat conduction in the cylinder head, meanwhile, the study of thermal load in the cylinder head was conducted, the effect of boiling heat transfer on thermal load was evaluated. On the basis, the accuracy of the numerical simulation was verified by comparing the simulation results and the experimental results of the temperature on the fire deck, which provided a basis for the optimum design of cylinder head.Finally, nine kinds of optimal design scheme was presented by means of experimental design using orthogonal table, choosing the upper nozzles as the optimal factor. Besides, through the analysis of the comprehensive evaluation of different indexes obtained the best optimization scheme. In the following, it was verified that the optimization scheme effectively enhanced the heat-transfer capability of the coolant and reduced the thermal load of cylinder head by comparing with temperature field within original engine.