EXHAUST NOISE ANALYSIS RESEARCH FOR A SINGLE-CYLINDER DIESEL ENGINE AND EVALUATION OF NOISE FILTRATION BY SIMULATION

The paper develops an ana lysis of exhaust noise for a single-cylinder diesel engine tested in laboratory conditions. The acoustic signal at the engine exhaust system, for the speed range 1,300 – 2,700 rpm was measured and recorded. The results of the noise recordings were subjected to a processing from which the variation of the noise level depending on the engine speed was obtained. Next, the physiological effect of acoustic filtrations for noise recordings was analyzed by simulation. This allowed the optimization of the exhaust noise, having identified the areas and the optimal attenuation effect. In the performed simulations, it was found that the low frequencies require the highest attenuation background.

Analysis for effect of pores on acoustic performance of reactive muffler

The major source of noise pollution was an internal combustion engine. Henceforth, the design of the engine exhaust system was a tough challenge for automotive industries. The mufflers have been used to moderate the exhaust noise from the engine to the neighboring atmosphere. So in domestic as well as the industrial application, it is required to reduce noise levels to prevent human hazards. The performance of muffler is measured in terms of transmission loss. The transmission loss of reactive muffler is depending on its geometry. This article describes the effects of pores at the inlet pipe and outlet pipe of the reactive muffler on its performance capacity at a target frequency. It is found that the muffler performance is dependent on the number and position of pores. The single chamber and double chamber reactive mufflers are used for the study. The numerical analysis is performed by COMSOL Multiphysics software. The numerical analysis result of the different models of the muffler is compared with experimental analysis. The purpose of the study is to investigate the effect of pores in inlet and outlet pipe to maximize the TL at the target frequency of reactive muffler.

Calculation of Acoustic Efficiency of Exhaust Silencers for Automotive Internal Combustion Engines

Insertion losses as the main characteristic that mathematically describes the acoustic efficiency of a noise silencer has been considered. This characteristic shows the reduction of noise generated by its source, in particular by the internal combustion engine’s exhaust system, at the control point as a silencer use result. Has been presented a mathematical description of the insertion losses, and have been considered parameters necessary for calculating this characteristic. Has been demonstrated the analytical dependence of impedance for the sound emission by the exhaust system’s end hole from the coefficient of acoustic waves reflection by this hole. The performed analysis of the widely used formulas for calculating the coefficient of sound reflection by the end hole has showed their insufficient accuracy for project designs performing. Have been proposed calculation dependences providing high accuracy for calculations of the reflection coefficient modulus, and the attached length of the channel end hole without a flange in the entire range of the existence of plane waves in it. It has been shown that the end correction of this hole at ka = 0 is 0.6127, and not 0.6133, as it was mistakenly believed until now in world acoustics. Has been proposed a method for calculation the exhaust noise source internal impedance. This method more accurately, in comparison with the already known ones, describes the acoustic processes in the internal combustion engine’s exhaust manifold, thanks to increases the accuracy of calculation the silencer acoustic efficiency, that allows develop the silencer at the early stages of the design of an automotive internal combustion engine.

Exhaust Noise Reduction by Application of Expanded Collecting System in Pneumatic Tools and Machines

In this paper, we demonstrate how to reduce the noise level of expanded air from pneumatic tools. Instead of a muffler, we propose the expanded collecting system, where the air expands through the pneumatic tube and expansion collector. We have elaborated a mathematical model which illustrates the dynamics of the air flow, as well as the acoustic pressure at the end of the tube. The computational results were compared with experimental data to check the air dynamics and sound pressure. Moreover, the study presents the methodology of noise measurement generated in a pneumatic screwdriver in a quiet back room and on a window-fitting stand in a production hall. In addition, we have performed noise measurements for the pneumatic screwdriver and the pneumatic screwdriver on an industrial scale. These measurements prove the noise reduction of the pneumatic tools when the expanded collecting system is used. When the expanded collecting system was applied to the screwdriver, the measured Sound Pressure Level (SPL) decreased from 87 to 80 dB(A).

Application of the Integrated Acoustic Efficiency Indicator to Optimize a Combined Silencer for a Vehicle Exhaust System

A practical solution to the problem of determining the configuration of a combined muffler for exhaust noise of a vehicle with maximum acoustic efficiency for a given volume is presented using an integral indicator of acoustic efficiency. Optimization of the geometric parameters of noise mufflers based on the integral indicator of acoustic efficiency makes it possible to reduce the time spent on the selection of the main spatial parameters and characteristics of the applied sound-absorbing materials before starting numerical calculations.