Design And Performance Analysis Of Reactive Muffler On Construction Machinery Based On CFD

Engine exhaust noise is a main source for construction machinery noise,and it has a very significant impact on the level of construction machinery noise.Raising the level of muffler design has an important significance in upgrading the whole machine quality of China's construction machinery.Insertion loss and pressure loss are two very important evaluation criteria for evaluating the muffler's noise attenuation performance and aerodynamic performance.In the current international environment of energy-saving and emission-reduction,under the premise of enough noise elimination, the researches on influence of mufflers on the engine power performance are becoming more and more involved.That is to say,under the premise of enough noise elimination, pressure loss should be reduced as much as possible in an appropriate range.Advanced muffler technology can get rid of disadvantage of dependence on imports for some mufflers,improve the competitiveness of domestic muffler products,so there are good social and economic benefits.In this paper,based on studying the impact of muffler unit structure and the entrance flow velocity on the pressure loss of muffler,the designing and improving process for mufflers of complicated structures is studied systematically.The elimination structures and entrance boundary conditions have very significant impacts on the pressure loss for mufflers.By computational fluid dynamics method, through geometric modeling,grid meshing,solution model selecting,boundary conditions setting,and other steps,the internal flow field in basic muffler units,which are expanding chamber,insert-pipe and perforated pipe,are simulated and computed. The influence laws of the basic muffler unit structure,such as,lengths and diameters of expanding chamber,lengths and positions of insert-pipes,perforation rates and diameters of direct/cross-flow perforated pipe,upon velocity field,pressure field and temperature field of airflow are studied.The change law of pressure loss of muffler unit under the conditions of different entrance flow velocities is discussed.All above provide a certain amount of design basis for designing mufflers of complicated structures.Through simulating and analyzing the velocity field of airflow internal the complicated muffler of typical structure,expanding chamber,insert-pipe and perforated pipe,the role and impact of basic muffler units upon pressure loss of complicated mufflers are studied.It is found that the velocity field distribution of airflow internal the muffler is similar to that of pressure and temperature field.Under the conditions of a particular entrance velocity,comparative analysis of simulation and experimental results of pressure loss for three typical structured mufflers is carried out,so their difference between each other is studied,and the reason for difference is also explained,all above which further certified the validity of computational fluid dynamics method for analyzing the aero dynamics of muffler.By analyzing the inlet/output pressure and pressure loss for three typical reactive mufflers under different inlet velocities,a kind of mathematical relation among above three parameters is initially found.Referring to relative conclusions about muffler units,combining practical engineering design experience,and utilizing reliable empirical formulas,a complicated reactive muffler is designed and improved for practical appointed excavator.The reason and structure of yielding bigger pressure loss for designed muffler is discovered,and the improved muffler design is put forward.The manifold and line of airflow in important region of muffler are analyzed by airflow traces from improved muffler inlet.It is found that,compared to the entrance velocity and other factors,the impact of inlet temperature on pressure loss is very small,which can be ignored in some degree,and then the muffler research in some particular conditions is furthermore simplified.At different engine working conditions,contrastive analysis of simulation and experiment results for improved muffler's pressure loss is carried out,and it is proved that on the premise of experiment error and manufacturing precision for muffler,the two results are relatively consistent.At the same time,the practical impact test of inlet velocity of airflow on pressure loss for improved muffler also deeply certified that for typical reactive muffler based on expanding chamber,insert-pipe,and perforated pipe,the mathematical relation among the four parameters,which are inlet/outlet velocity,pressure loss and inlet velocity,is correct.That is,under two kinds of inlet velocities,whose value is not equal to zero,their inlet/outlet pressure ratio and pressure loss ratio are all close to the square ratio of the two inlet velocities.Comprehensive performance of improved muffler is evaluated according to the practical experiment of pressure loss and insertion loss for improved muffler.Measuring results shows that the improved muffler has bigger insertion loss and lower pressure loss,both of which has satisfied the requirements limits of some relevant standards,So the improved muffler scheme has been adopted for final designing determined muffler. The general designing process for mufflers of complicated structures is summarized.In the new muffler design process,there has been great improvement for traditional design patterns.Most muffler design work is transferred onto the computer,which will greatly shorten the product development cycle for muffler,and apparently improve the efficiency of designing muffler.The proposed muffler design process is of good economy,and it has certain significance for improving our country's level of designing muffler.This project is supported by Sci-Tech Development Research Projects of Shandong Province,China with name of Design and Performance Improved for Reactive Muffler on Construction Machinery under Grant No 2007GG3WZ04017.