Study on Decrease of Heat Load of Six-Cylinder Vehicle Diesel Engine

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.