【摘要】 针对某车用6缸柴油机整机热负荷过高,气缸盖鼻梁区出现热裂等问题,进行了整机热负荷、气缸盖底部温度测量、气缸盖底面上水孔水流分布等试验研究和水套内三维数值模拟分析。结果表明:水散热器散热能力不足和冷却水流量偏小是导致该型柴油机热负荷过高的主要原因;气缸盖水套内水流不合理,仅有约12.22%的冷却水对气缸盖底部进行了有效的冷却,是气缸盖底部热负荷过高造成鼻梁区热裂的主要原因。基于此,提出了4种气缸盖结构改进方案,通过数值模拟和试验验证得出,改进方案一能使气缸盖底部流速提高1.68倍,气缸盖鼻梁区最高温度降低12.2℃。采用气缸盖改进方案在同时提高冷却水泵转速、改善水散热器能力,不仅可进一步改善气缸盖热负荷,使鼻梁区温度降低,而且还可较好地解决整机热负荷问题。更多还原

【Abstract】 With the increase of the power density of vehicle diesel engine,a series of problems such as the engine overheat and the occurrence of crazes at the valve bridge of the cylinder head should be solved.Experimental studies on heat load of a six-cylinder vehicle diesel engine,temperature measuring of cylinder head bottom,and coolant flow distribution of inlet holes of cylinder head bottom were carried out,and the CFD simulation of coolant flow in water jacket were performed.Based on the results of these experiments and simulations,it can be concluded that the main causes resulting in the engine overheat are insufficient heat-sinking capability of the water-radiator and the less coolant flow rate.The unsuitable coolant flow in cylinder head,where only 12.22% coolant can be used to cool the bottom of cylinder head,is the main cause resulting the cylinder head overheat and occurrence of thermal crazes at the valve-bridge.Four optimized structures of water jacket have been presented.The follow-up numerical simulation and experimental validation showed that the coolant flow velocity at bottom side of cylinder head was increased by 168%,the temperature at the valve bridge region was reduced by 12.2℃.Furthermore,by using the optimized structure of cylinder head and raising the speed of water pump,the heat load of cylinder head and the temperature at valve-bridge can be further reduced,thus,the heat load of the engine can be decreased significantly.更多还原