Experiment and Simulation Analysis on Heat load of Heavy-duty Vehicle Diesel Engine 2007-01-2069
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. The studies involve heat load test of complete machine, 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 sixth cylinder water jacket which lies on the most wicked heat transfer condition. The test and simulation results show that overheat of engine results largely from insufficiency of the heat-sinking capacity of water-radiator and shortage of the coolant flux. The unsuitable flow field in cylinder head water jacket, where only 12.22% coolant can cool the bottom of cylinder head, is the main reason causing cylinder head overheat on the bottom side and thermal cracks in the valve bridge region. Based on these tests and simulation, we proposed four protocols to improve the cylinder head's structure. The follow-up numerical simulation and experimental validation identified that in the first protocol the coolant average velocity of bottom side of cylinder increased by 168%, the tiptop temperature within the valve bridge region reduced by 12.2°C. Furthermore, by adopting the optimized structure of cylinder head and raising the rotational speed of cooling water-pump, the temperature within valve-bridge will further reduce, and the heat load of complete machine could decrease significantly.