Insertion Loss Measurement And Calculation Of Reactive Muffler With Complex Structures

Large-scale projects across the country have started because of the changing of national policy. More and more projects require large machines following by the strong development of the construction machinery industry. The noise impact on the environment increases with bigger and bigger power of construction machinery used. The noise from engine is the main part of the engine exhaust noise of the construction machinery. Mounting muffler is the most effective way to reduce engine exhaust noise. For construction machinery, the most widely used is reactive muffler, which is not easy to be blocked by engine exhaust soot, grease and can be maintained easily.This paper discusses the muffler principles and evaluation in detail, and then introduces the reactive muffler test equipments and system components, including acoustic measurement, air flow measurement, pressure measurement and insertion loss measurement. At the same time, the principles and methods of test are introduced, as well as the insertion loss measurement.The signals at speed970r/min-2200r/min was measured, by which1/3octave spectrum was plotted. By analyzing the noise spectrum, we explore the relationship of muffler performance, structural arrangement, and the airflow. Without the pressure loss considered, the expansion ratio and insert pipe affect performance mostly.In this paper, the semi-empirical formula is presented based on the formulas for expansion chamber mufflers and perforated pipe mufflers which consider the noise generated by flow air. The calculation method is to separate multi-chamber mufflers into one or two cavities alone, and finally get the superposition of the calculated results. Compared with the data of test, the results of computations are very close at part of the band. Values calculated by the internal combustion engine ignition frequency are close to the insertion loss values obtained from experimental measurements. The error is less than5%, so that we can use the calculated value of this frequency to estimate the attenuation performance. The estimation can be used to reduce the blindness of the initial design, and shorten the design cycle.