The Simulation Research On Exhaust System's Performance Of Marine Sequential Turbocharging Diesel

Diesel engine is the most widely used power machines,and the exhaust turbocharging technology is an effective way to improve these engines' performance.On the marine diesel engines,the exhaust turbocharging systems are almost necessary systems currently.To the turbocharging diesel engines,the exhaust systems are not only the outflow passages,but also affecting the using of exhausting gas energy and the engines' performance.So it is quite important to select different exhaust systems for different diesel engines.Firstly,in this paper,the performance of exhaust systems will be studied by simulation,based on two different type diesel engines,the V12 high-speed diedel engine and the V16-STC medium-and-high speed diesel engine.Secondly,establish the V12-STC simulation model,and run the model based on the propeller characteristics,then compare the calculated result of engine performance with the original engine.By studying on the influence of exhaust connecting pipe on the engine performance,confirm that closing the exhaust connecting pipe valve make engine performance better.Run the model of V16-STC diesel engine based on the propeller characteristics and analyze the calculated result which shows that the exhaust tempreture of the second cylinder closed to the end of the exhaust manifold is much higher than other cylinders.By analyzing this problem,confirm that the reason of quite higher tempreture is the uneven scavenging of different cylinders.Then define the conception of scavenging unevenness.Then change the pulse turbocharging exhaust system of the V12-STC engine to the MPC system,and calculate the scavenging unevenness of above-mentioned two engines.Under the 100% load condition,the scavenging unevenness of the V12MPC-STC engine is 8.65,while this value of the V16-STC engine is 39.00.This result shows that there is no storng scanving disturbance between the cylinders of the V12MPC-STC engine,and the MPC system is appropriate for this engine.Then optimize the key structure parameters of the MPC system,make the performance of the engine equipped contraction branch MPC system is equal to original engine with simpler structure.According to the low scavenging unevenness of the V12MPC-STC engine,try to apply the expansion exhaust branch MPC system,and optimize the key structure parameters.Finally,make the engine performance better than the engine equipped contraction branch MPC system.Thirdly,for the high scavenging unevenness V16-STC diesel engine,design an improved exhaust system.The calculated result shows that the improved exhaust system could control the high exhaust tempretrue effectively while improving the scavenging unevenness of different cylinders.On the other hand,the structure of the exhaust system is simple and the performance of the engine equipped with improved exhaust system is equal to the original engine.Finally,for intuitively analyzing the working principle of the improved exhaust system,establish the geometry model of the improved and original exhaust system of the V16-STC diesel engine with Solid Works software,and finish meshing with ICEM software.By using the calculated results of GT-Power software as boundry conditions,make the 3D numerical simulation of the exhaust system with the Fluent software.