Numerical Simulation And Optimization Of Structure Of Water Jacket Of Diesel Engine

Cooling system is an important part of diesel engine. In order to make diesel engine work under fitting temperature, reasonable design of cooling system should be made by researchers. Water jacket plays an important role in cooling system. On the one hand good structure of the water jacket can strengthen flow and heat transfer and reduce thermal load on the high-temperature zones. It can effectively improve durability and reliability of diesel engine, appropriately lessen intake air temperature and increase charging efficiency .It can improve fuel consumption and exhaust gas emission .On the other hand it can reduce flow resistance of water jacket and power consumption of cooling components (example:water pump ,cooling fan). It can be beneficial to the dynamics of diesel engine. As the more compact design and output power is applied in diesel engine, capacity of water jacket should be higher than before.The research method of water jacket includes flow test and numerical simulation. As far as test method is concerned, coolant flow velocity and pressure should be measured in the water jacket. Researchers can obtain macro information about coolant flow. Although this method can provide relevant data of coolant flow and estimate cooling capacity of water jacket , because of complexity of structure and internal flow of water jacket, it is not sufficient to obtain generally real flow of water jacket. So this method has some flaws .Another research method is numerical simulation. It bases on computational fluid dynamics theory and uses relevant CFD software to analyze water jacket. It can provide detailed distribution of pressure ,velocity and heat transfer coefficient of water jacket .It can become an important supplement for test method.The 3-D simulation software FLUENT that uses finite volume method is applied to analyze water jacket of 498 diesel engine which includescomputational model with water pump and without one, and perfect computational model of water jacket and optimize the structure of water jacket in this thesis.Firstly 3-D CAD software PRO/E is used to build the geometric structure of 498 diesel engine which includes engine block ,cylinder head ,lumen of water pump and oil-cooler .Because the structure of water jacket is very complicated ,it is difficult to build complete geometric model according to the real entity. We should simplify the origin geometric structure of water jacket under the premise that does not produce big impact.Grid is a basis of simulating computation .Its density and quality will decide CFD precision and efficiency. The principle of meshing grid is to maintain coherence between the computational field and the real flow domain. On the premise of maintaining computational precision ,the size and type of grid shall be adjusted and the number of grid shall be reduced for increasing the computational efficiency. According to the complicated structure of water jacket ,unstructured grid Tetra and Prism are used to mesh water jacket. The total grid number is about 2.4 million. Simulating computation uses steady state model, water is cooling medium , incompressible viscous turbulent flow ,turbulent model isκ-εstandard equation .The wall function is used to simulate distribution of velocity and pressure that is near the boundary layer. Because we need to make numerical simulation about water jacket with water pump and without water pump, there are two sorts of boundary condition:With water pump boundary condition Water temperature : 368K/293K; Inlet of engine block : pressure inlet , 101325 Pa; Inlet of oil cooler : pressure inlet , 101325 Pa; Outlet of cylinder head: velocity outlet , 0.815m/s;Without water pump boundary condition Water temperature : 368K/293K; Lumen inlet of water pump ,velocity inlet ,local cylindrical coordinate system,round velocity 9.08m/s, radial velocity 0.71m/s; Cylinder head outlet : outflow;The main work content:1.Computational work:Calculating water jacket model with water pump and without water pump at rated power of 498 diesel engine and comparing computational result and test result. Building perfect water jacket model with water pump;Analyzing the finally computational result of model with water pump ,and evaluating the cooling capacity of water jacket;On the basis of computational analysis ,three different improvement cases are applied for the baseline water jacket, calculating the improvement models and confirming the more ideal optimizing scheme.2.Test work:LDA system is used to test water velocity of the critical region of 498 diesel;Pressure test system is used to attain pressure parameter about the critical regions of 498 diesel engine; The main computational conclusion:Attaining evaluation parameter of water jacket of rated power and peak torque condition;Traditional water jacket model does not include water pump, in fact the internal flow field of water pump has an important impact on the whole water jacket. The computational result with water pump is more precise , and the computational model is more coherent to the real work condition by the comparison between the computation and test result;Cooling capacity of engine block is not sufficient .Because bumping phenomenon exists at the intake side of engine block ,which leads tostagnant regions. The water flow distribution is not even between the intake side and exhaust one. The velocity is a little bit low at the exhaust side of the 4th cylinder.;By comparing these three improvement cases with the baseline one ,the effect of case2 and case3 are ideal, structure alteration is little, and those can be put into practical projects.