Engine Exhaust Noise Research Articles

Optimisation of Exhaust Emissions, Vibration, and Noise of Unmodified Diesel Engine Fuelled with Canola Biodiesel-Diesel Blends with Natural Gas Addition by Using Response Surface Methodology

The paper presents methods to determine the optimum input parameters of CNG addition, biodiesel blend ratio, and engine speed to improve engine responses in terms of exhaust emissions, vibration, and noise of CNG-biodiesel-diesel fuelled engine. Box-Behnken based on response surface methodology was used to predict and optimise input parameters. Variance analysis was applied to determine the significant relationship between the input parameters and engine responses. At optimum input parameters (CNG addition=9.24 L/min, biodiesel blend ratio=40%, engine speed=1524.24 rpm), the optimum engine responses of NOx, CO, CO2, O2, engine vibration acceleration, and noise were 93.77 ppm, 438.05 ppm, 1.47%, 18.59%, 37.17 m/s2 and 91.34 dB[A], respectively. In terms of coefficient determination of R2, the values were 99.11%, 99.22%, 99.41%, 99.70%, 98.65%, and 98.60% respectively. The correlation between the optimised result and the engine test result showed an acceptable error limit for NOx, CO, CO2, O2, engine vibration acceleration, and noise as 4.2%, 3.8%, 4.9%, 0.25%, 4.12%, and 0.17%, respectively.

Case study: Noise attenuating performance of perforated corrugated lined straight-through perforated pipe-resistant muffler

Noise of internal combustion engine is the main source of noise pollution, and mufflers are the main means to reduce exhaust noise of internal combustion engine. In the process of improving the acoustic performance of the exhaust muffler based on the three-dimensional numerical method, the influence of the high speed and high temperature airflow discharged by the engine in the actual working process on the acoustic performance of the exhaust muffler is often ignored, which leads to the obvious deviation between the predicted results and the actual situation. In this paper, based on the structural optimization design of the straight-through perforated pipe resistance muffler, the noise characteristics of the straight-through perforated pipe resistance muffler with perforated corrugated lining was analyzed considering the airflow velocity and temperature inside the muffler. The influence of temperature and velocity fields on the acoustic performance of muffler was studied by using numerical simulation method, which takes the solution results inside muffler as boundary conditions of sound field analysis. The influence of changing the internal structure of muffler on the aerodynamic performance of muffler was discussed, and the pressure loss is analyzed. The research has shown that adding perforated corrugated lining inside muffler could effectively improve the transmission loss of muffler and the noise reduction performance of prototype straight-through perforated pipe-resistant muffler.

State of the art of rational design of efficient mufflers

An efficient exhaust muffler needs to satisfy the rather conflicting requirements of adequate insertion loss (IL) with limited back pressure, weight, size and cost. The unmuffled exhaust noise of an internal combustion engine peaks at the engine firing frequency and the first few harmonics thereof. Designing the muffler (a wide-band low pass acoustical filter) for such low frequencies is quite a challenge. Therefore, design of efficient mufflers has remained an art as well as science. During the last two decades or so, however, (a) multi-hole cross-flow perforates, (b) multiply connected perforated pipes and baffles, and (c) the double-tuned, grazing-flow concentric tube resonators have emerged as promising constituent elements. In this paper, elements (a) and (c) have been combined ingeniously to synthesize efficient muffler configuration for diesel generator (DG) sets as well as automotive engines. Relatively simpler lumped parameter approximation for perforates opening into cavities, electro-acoustic analogies, and the simple expansion chamber equivalence of the double-tuned concentric tube resonator have been used to develop a rational design methodology. A novel feature of this methodology is incorporation of the given back-pressure limit into the acoustic design process. The resulting muffler configurations are robust and can be scaled up (and down) easily for IL as well as back pressure.

Acoustic performance of a heat exchange silencer for marine diesel engine

For the noise contribution of a marine diesel engine, exhaust noise plays an important role, especially considering its low frequency characteristics. The marine exhaust silencer is an effective device to attenuate the engine exhaust noise. Expansion chamber or resonators have been the backbone of almost all marine exhaust silencers, but issue of bulkiness remains. It is well known that the passband for an expansion chamber is related to its geometric length. For a fixed firing frequency, if the exhaust gas is cooled, then the wavelength of the firing frequency can be reduced. Inspired by this principle, the heat exchanger and silencer are combined to improve the low frequency effect of the device. Various reactive configurations are tried to get a well-balanced silencing effect. The effectiveness-number of transfer unit method and acoustic finite element method are adopted to calculate the noise reduction effect with or without exhaust gas cooling. It is concluded that that the heat exchange silencer has satisfactory cooling effect on the exhaust gas, but its contribution to noise attenuation is very limited. Since the reduction of the exhaust gas temperature, low-frequency performance of the silencer is enhanced.

Control of noise and temperature using radial air injection inside engine silencer

Silencer is a device mainly used for attenuation of the engine exhaust noise. Several modifications were attempted to improve the performance of a silencer. In this paper experimental and simulation study was carried out to determine the effect of radial air injection on the temperature and sound pressure level. The radial air injection is introduced in the form of jets inside the silencer. The design of available silencer was studied, and the 3D model was prepared using CATIA software. Simulation study was carried out using ANSYS Fluent, to determine the temperature distribution inside the silencer with and without modification. The radial jets at different pressure were introduced inside the silencer at three different locations. To acquire sound pressure level and temperatures at different locations, Lab View software and FFT analyser were used. The performance of silencer is analysed by comparing temperature of exhaust gases and sound pressure level at constant speed of 3000 rpm. With radial air jets of 2 bar reservoir pressure at three different location Overall Sound Pressure Level reduces by 6 dB and 42 K reduction in temperature of exhaust gases.

Active Control of Diesel Engine Exhaust Noise Incorporating Widrow-hoff LMS Algorithm

Active Control of Diesel Engine Exhaust Noise Incorporating Widrow-hoff LMS Algorithm

Optimization of exhaust emissions, vibration, and noise of a hydrogen enriched fuelled diesel engine

In this study, the effects of various input parameters are examined on exhaust emissions, vibration, and noise of an unmodified diesel engine. The primary aim of this study is to optimize the vibration, noise, and exhaust emissions of the engine to get optimal configuration parameters. Experiments were carried out on a four-stroke, four-cylinder, diesel engine fuelled with diesel-biodiesel-hydrogen blends. To minimize the number of experiments Box-Behnken design (BBD) has been adopted. Optimum desirability is found as 0.862 with hydrogen addition of 4.63 L/min, fuel blend of 26.8% and 1500 rpm engine speed for the diesel engine. When the diesel engine is operated at 1500 rpm engine speed and fuelled with 4.63 L/min hydrogen addition and 26.8% biodiesel blend ratio; the optimum responses of CO, CO2, NOx, vibration, and noise are established as 214 ppm, 1.35%, 90.4 ppm, 38.6 m/s2, and 91.3 dB[A], respectively. The predicted values were confirmed experimentally and the errors in predicted values are found in a limit range.

SOFTWARE DEVELOPMENT FOR ESTIMATION OF LOW FREQUENCY SOUND PROPAGATION IN GAS GUIDES OF POWER PLANTS TAKING TO ACCOUNT ACTIVE SOUND SOURCES

This paper is devoted to the problems of modelling and calculation of propagation of low frequency sound in gas guides of power plants taking to account active sound sources. The structure of software for prediction and calculation of low-frequency sound propagation in gas guides have described. Software uses four-pole method and takes to account radiation from additional (active) sound course. By using software it is possible to estimate sound source parameters to provide efficient sound attenuation. Examples of software application to calculation of intake and exhaust noise of internal combustion engine are described. The results of calculations show the possibilities of four-pole method software using to design acoustically the parameters of gas guides and mufflers for the different fields of applications.

Assessment of tractor noise level during spraying operation while using a tractor mounted aero blast sprayer

Tractor noise consists of engine noise, exhaust, intake fan and mechanical noise created by combustion, gears, cams, bearings and pumps, etc. Its noise spectra cover the entire audible range from 20 Hz to 20 kHz.The severity associated with noisy tractor may be annoying to varying degrees, lack of concentration, fatigue, rhythm disturbance and damage to hearing. In this paper noise of the tractor (John Deere (5103)) at the operator’s ear level and for bystander position was measured during no load (NL) and spraying operation using an areo blast sprayer at different engine speeds. The results showed that noise level during spraying operation higher than during NL condition. It is found that the effect of engine speed was significant at the 5 percent level of significance. It is observed that noise at a tractor operator’s ear level during spraying operation using an areo blast sprayer was higher than the permissible level (85 dB (A)) which was given by Occupational Safety and Health Administration (OSHA) and National Institute for Occupational Safety and Health (NIOSH).

Development of a Lumped Parameter Model for an Aeronautic Hybrid Electric Propulsion System

This paper describes a case study for applying a hybrid electric propulsion system for general aviation aircraft. The work was performed by a joint team from the Centro Italiano Ricerche Aerospaziali (CIRA) and the Department of Industrial Engineering of the University of Naples Federico II. The use of electric and hybrid electric propulsion for aircraft has gained widespread and significant attention over the past decade. The driver of industry interest has principally been the need to reduce the emissions of combustion engine exhaust products and noise; however, studies have revealed the potential for overall improvement in the energy efficiency and mission flexibility of new aircraft types. The goal of the present study was to demonstrate the feasibility of aeronautic parallel hybrid electric propulsion for light aircraft, varying mission profiles and electric configurations. Through the creation and application of a global model with AMESim® software, in which every aspect of the components chosen by the industrial partners can be represented, some interesting studies were carried out. The numerical model used was more complete and more accurate compared to some others available in the literature. In particular, it was confirmed that, for particular missions, integrating state-of-the-art technologies provides notable advantages for aircraft hybrid electric propulsion for light aircraft.

Exhaust noise, performance and emission characteristics of spark ignition engine fuelled with pure gasoline and hydrous ethanol gasoline blends

The exhaust noise, performance and emission characteristics of a gasoline engine fuelled by hydrous ethanol gasoline with 10%, 20% hydrous ethanol by volume (E10W and E20W) and pure gasoline (E0) were experimentally investigated. The tests were performed at full load and different engine speeds varying from 1500 rpm to 5000 rpm. The results showed that compared with E0, E10W and E20W had much lower exhaust noise at low engine speeds. With the increase of engine speed, E0 showed an advantage in low exhaust noise. However, engine fuelled with three fuels displayed comparable noise emissions at high speed. In addition, better thermal efficiency, significantly decreased CO and HC emissions were achieved by hydrous ethanol gasoline at all tested operating conditions. However, significant NOx emission and slight BSFC were observed for E10W and E20W. Compared with E20W, E10W showed decreased BSFC, HC and NOx emissions with the increase of engine speed, while CO emission was only slightly increased. Hydrous ethanol gasoline was capable of realizing comparable torque and power with E0 at all operating conditions. From the results above, hydrous ethanol gasoline could be considered as a promising alternative for SI engine. What's more, E10W exhibits enhanced performance.

Linearized Navier–Stokes equations for aeroacoustics using stabilized finite elements: Boundary conditions and industrial application to aft-fan noise propagation

In this paper, a numerical method for solving the linearized Navier-Stokes equations is presented for aeroacoustic sound propagation problem. The Navier–Stokes equations are linearized in the frequency domain. The fan noise of jet engine is emitted nearly selectively at certain frequencies, which depend on the rotation velocity of the fan. A frequency domain approach is highly suitable for this kind of problem, instead of a costly time-dependent simulation which can handle a large range of frequencies depending on the time step and the mesh.The calculations presented here were all made using Aether, a Navier–Stokes code which uses finite elements stabilized with SUPG (Streamline Upwind Galerkin). Automatic code differentiation was used to linearize this code. Entropy variables bring interesting mathematical properties to the numerical scheme, but also prevent the easy implementation of boundary conditions. For instance, the pressure is a non-linear combination of the entropy variables. Imposing a pressure variation needs a linearization of this relation which is detailed herein. The performance of different types of boundary conditions used to impose the acoustic pressure variation inside the engine is studied in detail. Finally, a very surprising effect of the SUPG scheme was to transform a homogeneous Dirichlet boundary condition on all variables to a transparent one which is able to let only outgoing waves pass through with no incoming wave. A one-dimensional toy model is given to explain how SUPG brings about this transformation.The last part of the article is dedicated to an industrial test case. The geometry of a model turbine from the Clean Sky European project was used for sound propagation of the fan exhaust noise of a jet engine. Computations on several modes with increasing complexities were done and the results compared to a boundary element method which served as a reference when no mean flow is present. Results of a computation with a mean flow are shown.

Hybrid Electric Aircraft Propulsion Case Study for Skydiving Mission

This paper describes a case study for applying innovative architectures related to electrified propulsion for aircraft. Electric and hybrid electric propulsion for aircraft has gained widespread and significant attention over the past decade. The driver for industry interest has principally been the need to reduce emissions of combustion engine exhaust products and noise, but increasingly studies revealed potential for overall improvement in energy efficiency and mission flexibility of new aircraft types. In this work, a conceptual new type for a skydiver lift mission aircraft is examined. The opportunities which electric hybridisation offers for this role is analysed in comparison with conventional legacy type propulsion systems. For a conventional commercial skydiving mission, an all-electric propulsion system is shown as viable, and a hybrid-electric system is shown to reduce aircraft fuel costs and CO2 emissions whilst maintaining conventional aero-engine operational benefits. The new paradigm for aircraft development which hybrid electric propulsion enables has highlighted significant issues with aircraft certification practices as they exist today. The advancement of aircraft design and production to harness the value of new propulsion systems may require adaption and development of certification standards to cater for these new technologies.

IC-engine acoustic source characterization in-situ with capsule tube method

Typically, a component level approach is used in control of internal combustion engine (IC-engine) exhaust noise. This has enabled the development of new, cost-efficient silencers, for example. However, prediction of sound emission from a tailpipe or insertion loss of a silencer requires a more extensive, system level approach. Therefore, valid IC-engine source characteristics and a valid model of the whole transmission path are needed. When characterizing an IC-engine as a source with the commonly used in-duct multi-load method, the requirements for load impedance variation must be fulfilled. It is fairly easy to vary the load in automotive cases, whereas new methods must be developed for large IC-engines, used e.g. in power plants. In this study, the source data determination process is investigated in detail, a novel “capsule tube method” is developed further and used for experimental acoustic source data determination of medium speed IC-engine exhaust system in harsh environment. With suitable filtration and statistical outlier rejection methods presented in this paper, the source data of a test IC-engine exhaust system was derived with success.

Robustness of the extended delayed-X harmonics synthesizer algorithm applied to engine exhaust noise control

Exhaust noise of a combustion engine contains several harmonic components of the fundamental frequency that depends on the engine speed. Active noise cancellation (ANC) in the exhaust line of a diesel-electric drive faces serious challenges such as high temperature, high sound pressure levels, standing waves phenomena, a time-varying environment, and slightly varying disturbance frequencies. In the case of a non-acoustic reference sensor, also an offset or a mismatch in the estimation of the disturbance frequencies negatively affects the performance. The extended delayed-X harmonics synthesizer (DXHS) is known from several researches to be appropriate for control of periodic noise with multiple harmonic components. The algorithm is robust against observation noise and fluctuation of the plant under control. In this paper, the extended DXHS is implemented in an ANC-system for a diesel-electric drive and experimentally investigated in laboratory experiments. A modified update rule, a convergence factor regu...

Experimental and Simulation Study to Reduce Engine Noise

The silencer or muffler is used to reduce the engine exhaust noise and also to reduce the exhaust flue gas temperature. To achieve this, a proper design of silencer is very important. The aim of this study is to find the effect of radial jets at the upstream of muffler on temperature and acoustic pressure. The radial jets were introduced at different reservoir pressure at the downstream of muffler. The simulation study has been carried out to determine the temperature and pressure distribution inside the silencer with and without radial jets and experiments were carried out to validate the result. It is observed that around 10 dB reduction in OASPL with interaction of jets in cross flow. These jets also reduces the exhaust gas temperature by 80 0C for engine speed 4000 rpm with jets at 2 bar reservoir pressure. Thus, this study concludes that the technique is effective to reduce the temperature of exhaust and noise. This technique can be applied easily to all vehicle mufflers where air at higher pressure is readily available as well as stationary engine mufflers using high pressure from small compressor.

Optimal design of compact multi-partition MPP silenders for I.C. engines noise control

Engine exhaust noise is always characterized as the major source of automotive noise especially in the urban areas which can be reduced using the passive mufflers. Muffler performance is controlled by using complex geometries or by adding porous materials inside the chamber. However, when a clean absorbent system is desirable or when the muffler must support high air flux, it is not possible to add fibrous materials. The use of micro-perforated panels (MPP) as another alternative to improve the acoustic performance becomes important. Different constraints such as muffler size and cost as well as back pressure present the major challenge in muffler design. The purpose of this work is to optimize the acoustic performance of low-cost simple geometry mufflers using MPP and to find the best shape design under a limited space constraint aiming at improving the acoustic performance of automotive engines. On the basis of linear plane wave theory, the four-pole matrix for two wave guides coupled via an MPP tube is derived and used to compute the transmission loss. Two different procedures to optimize the muffler performance, the internal design and wall damping methods, are used. The muffler internal structure is firstly chosen using the acoustically based method and then numerically optimized by maximizing its transmission loss. Different methods to improve the MPP wall impedance via its geometry and the back cavity dimension are also presented and compared using the 3-D FEM. A new optimized muffler is proposed and experimentally used to study the acoustic performance of a four-cylinder diesel engine and its performance compared to the existing straight through resonator muffler. It is shown that the new optimized muffler reduces the A-weighted engine noise by 5 dB and also reduces the brake specific fuel consumption by 6% at the same operating conditions.

Experimental Investigation on Exhaust Noise Reduction Using Particulate Trap in Direct Injection (DI) Diesel Engine

Excessive pollution caused by engine emission has led to serious environmental degradation in the past three to five decades. Researchers worldwide are striving hard for reducing the emission from the engine. But the uses of dieselpowered vehicles are increasing day-by-day. The diesel engines have acquired much wider application than ever because of their main advantages of higher power and lower cost of the fuel. Although diesel exhaust is relatively clean with respect to unburnt hydrocarbons and carbon monoxide, it contains pollutants like particulate matter and oxides of nitrogen with greater exhaust noise. The paper reports on the control of the engine exhaust noise by a particulate trap for DI diesel engine. The experimental work comprises of design and development of the particulate trap for the given engine to control the exhaust noise level. The noise level reduction is also studiedusing a muffler. The reduction in noise level using particulate trap and muffler is experimentally investigated and compared. The noise level without particulate trap and muffler is 132 dB, with trap 116 dB, with muffler 125 dB. The percentage reduction in noise level is 12.5% with trap and is 9% with muffler.

Source identification of gasoline engine noise based on continuous wavelet transform and EEMD–RobustICA

In order to separate noise source of gasoline engine, ensemble empirical mode decomposition (EEMD), robust independent component analysis (RobustICA) and continuous wavelet transform (CWT) are applied to study the blind source separation and noise source identification of gasoline engine. After the signal is decomposed with EEMD into a set of intrinsic mode function (IMFs), RobustICA has been applied to extract independent sources. The combined technique alleviates the problem of mode mixing in EMD and overcomes the problem that the number of sensors must be larger than or equal to the number of separated components. At the same time, RobustICA’s cost efficiency and robustness are particularly remarkable for short sample length in the absence of pre-whiten. CWT using the Complex Morlet Wavelet (CMW) is used for its better time–frequency localization features to analyze time–frequency characteristics of the ICA results. Combining the time–frequency results with different noise sources frequency spectrums, the corresponding relation of the different noise sources of gasoline engine and the independent components is determined. It turns out that these independent components correspond to the exhaust, combustion and piston slap noise of the gasoline engine respectively.

Design and test research on semi-active muffler system based on the H-Q tube

In this paper, one type of semi-active muffler system is designed to reduce diesel engine exhaust noise, especially the low frequency noise. The muffler is based on the principle of Herschel-Quincke tube. Different from other mufflers, this one can change the control fundamental frequency with valves. In the certain control frequency interval between two adjacent fundamental frequencies, it can meet the resonance condition by the stepper motor automatically. Both the valves and the stepper motor are under command of the designed controller. Transmission loss and insertion loss experiments of the muffler have been conducted. Experimental results show that the semi-active muffler has a substantial noise reduction: from 35 to 100 Hz. The maximum TL of the muffler is approaching 35 dB. The IL has an average of 11 dB attenuation in the entire range of 35 to 100 Hz.