Research On The Coolant Flow And Heat Transfer Enhancement In Cylinder Head Of Heavy-duty Vehicle Diesel Engine

With the increasing of the power density of the engine, the cooling system becomes more and more important, which turns to the key problem for further development of the diesel engine.The paper reports an experimental and simulating exploration over a series of problems, such as overheat of the complete machine and thermal cracks in the valve bridge region of cylinder head in YC6M360 series diesel engine. The studies involve heat load test of complete machine, analyzing coolant-flow distribution of each cylinder, measuring the temperature of the bottom part of cylinder head, analyzing coolant-flow distribution of upper nozzles in the bottom side of cylinder head, and three-dimensional numerical simulation on the coolant flow in the water jacket. This paper proposed some schemes to improve the matching of subassembly in the cooling system and optimized the structure within water jacket according to the test and simulation results. The follow-up numerical simulation and experimental validation identified that the temperature within valve-bridge decreased remarkably, and the heat load of complete machine could be improved significantly, by adopting these optimized schemes.Formerly, the results of simulation were always verified by the results of experiment, but there is always a great deal of the cost on the experimental study, then the experiment always hard to be achieved. But if there is no experimental validation, the mistake of numerical simulation will leads to the loss. So the verification method should be updated. In the paper, a new idea, that the results of simulation can be verified by the simulation results of another software package, was reported. In this paper, the experimental study has been done by using FIRE TM and Fluent TM software package. At last, the idea was improved by result of experiment. Results indicate that this new method can be used to verify the numerical simulation data.The disturbed flow and the boiling flow can enhanced the heat transfer of the coolant. The paper also explored the study on the influence of the flow in upper nozzles on the HTC in cylinder head by means of experimental design using orthogonal table, and the influence of boiling flow to the HTC in cylinder head. Using the numerical simulation method, the effects of the different diameter of the upper nozzles 2 and 3 of the new design cooling jacket within the cylinder head on the HTC in cylinder head have been pointed out. Through the contrast, the best scheme of the diameter has been achieved. Subsequently, the flow velocity within the cylinder head can be considered to be the sum of the velocity without the upper nozzles and the effect of the upper nozzles on the flow velocity, and the effects of the upper nozzle on the HTC within the cylinder head include the improving of the coolant flow inside the cylinder head and the effect of turbulent flow of coolant on HTC. Based on these concepts, the effects of turbulent flow of coolant which flow through the different diameter upper nozzles on the HTC within this area have been pointed out. This conclusion can be considered to be important reference for the optimized design of upper nozzle.In the research of flow boiling inside the cylinder head, the contrast of boiling heat transfer coefficient in the valve-bridge zone between taking the boiled coolant into account or not has been achieved. Besides, the contrast of boiling heat transfer coefficient in the valve-bridge zone among different boiling heat transfer models has been achieved. These contrasts can be considered to be the reference for the numerical simulation on the coolant flows and heat transferring which help to optimize the structure of water jacket.At last, the fluid-solid coupling simulation inside the cylinder head has been completed. The temperature field inside the cylinder head has been gotten by the couple simulation between the flow field of coolant and the heat transfer of the cylinder head. In the following, the results of the simulation were verified by the results from the experimental study. The contrast result indicates that the error can be accepted for engineering application. By means of the fluid-solid coupling simulation, the distribution of temperature inside the cylinder head can be acquired in detail during the initial period for the development of new diesel engine. As a result, the structure optimization of cylinder head and water jacket can also be done during this period, and then the design period is shorted significantly.