D. Design Proposal ......................................................................... Error! Bookmark not defined
VII. Recommendations and Future Work
The complexity of operation and analysis of the exhaust provides a wide scope. This research has attempted to provide the basic foundations of exhaust and silencer design and analysis however in doing so, depth of research has been sacrificed for breadth. As a result continued work should hope to explore more specialised techniques of exhaust design and analysis to extend upon the basic concepts presented herein. Some topics of interest would stem from tuning interactions assumed constant within this study. For instance, the simultaneous tuning of the exhaust and intake as well as valve timing is documented as a significant method of engine performance optimisation. In addition, tuning methods identified herein suggests potential for innovative integrated designs that combine the use of inertial scavenging and wave tuning in a synergistic manner that may be worthy of investigation. For a single cylinder engine there is limited further work that could be undertaken in the way of exhaust tuning via pipe design. However a hypothesis was formed during the course of this study that specialised exhaust components such as Helmholtz chambers have been used within industry to not only provide a means of targeted silencing but also to enhance wave tuning effects via wave interaction. The implementation of such a component in this way would be expected to enhance performance as well as to justify a lighter silencer and therefore it seems worthy to recommend an investigation into the feasibility of the idea.
Furthermore, commercial products such as those in Fig.(39) incorporate components that are unexplained by this study but may offer extra performance benefit and therefore may represent another opportunity for further work.
It was found during the course of this research, that a range of studies into silencer design used other forms of silencer concepts as the basis of a design optimisation. In particular a text by Munjal entitled ‗Acoustics of ducts and mufflers with application to exhaust and ventilation system design‘ was used by a number of studies who were concerned with the implementation of reactive silencers. Ideally, future work conducted by the ADFA FSAE team would be able to identify whether a reactive silencer concept would be able to surpass the current proposed design in terms of attenuation, back pressure and weight.
Finally, much literature is available as to the implementation of coupled 1D/3D analyses within this topic area. WAVE openly admits to enhanced inaccuracy when dealing with complex components and the development of this capability within any aspect of exhaust design would represent a powerful design tool.
Figure39. Commercial exhaust system with novel components labelled ‘Powerbomb’ and ‘Megabomb’
Acknowledgements
The author would like to gratefully thank a variety of important individuals that helped throughout the course of this study. Thanks goes to thesis supervisor, Dr Warren Smith for providing much needed guidance during the course of what always seemed to be a grossly under defined problem. To Mr Alan Fien, for your willingness to offer your vast technical insight. To Mrs Marion Burgess for your patience and understanding despite the tribulations of this project. Much thanks goes to SEIT workshop staff particularly Doug Collier and Marcos De Almeida for their assistance throughout the design and manufacturing process. Thanks to members of the FSAE team and fellow engineers whose support was invaluable and who at times managed to make this project an enjoyable process. Finally, to my girlfriend who showed amazing patience over the course of a very long year of work as well as offering much needed support over the course of this degree. Thanks to my family who are well deserving of official recognition of all their support over the many years.
References
[1] SAE, "FSAE Inspection Sheet," ed: SAE, 2011.
[2] SAE-Australiasia. (2011, 07 May). Competition Overview [Internet Web Page]. Available:
http://www.saea.com.au/formula-sae-a/competition-overview
[3] G. P. Blair, "Design and Simulation of Engines: A Centruy of Progress," SAE International1999.
[4] G. P. Blair. (1999). Design and Simulationof Four-Stroke Engines.
[5] J. Robinson. (1994). Motorcycle tuning
[6] Smith and Morrison, Scientific Design of Exhaust & Intake Systems, 2009.
[7] A. G. Bell. (2001). Four Stroke Performance Tuning.
[8] D. Winterbone and. R. Pearson, Design Techniques for Engine Manifolds - Wave action methods for IC engines.
London and Bury St Edmunds, UK: Professional Engineering Publlishing Limited, 1999.
[9] M. Ashe, G.Blair, G.Chatfield, D.Mackey, "Exhaust Tuning on Four-Stroke Engine: Experimentation and Simulation," The Queen's Univeristy of Belfast; OPTIMUM Power Technology2001.
[10] Yunquig Li, Jincheng Wang and Peng He, "Study on the exhaust system parameters of a small gasoline engine,"
Beihang University 2008.
[11] G. Sammut and. A. Alkidas, "Relative Contributions of Intake and Exhaust - Tuning on SI Engine Breathing - A Computational Study," Oakland University 2007.
[12] J.D. Irwin and E.R. Graf, Industrial Noise and Vibration Control. New Jersey: Prentice-Hall 1979.
[13] J. Pang et al. "Flow Excited Noise Analysis of Exhaust," Ford Motor Company; Gates Coporation2005.
[14] A. Jauer, J. Brand and D. Wiemeler, "Flow Noise Level Prediction Methods of Exhaust System Tailpipe Noise,"
Tenneco, Germany 2008.
[15] S. W. Coates, "The Prediction of Exhaust Noise Characteristics of Internal Combustion Engines ", The Queen's University of Belfast, 1974.
[16] Muthukumar Yadav, Kiran, Tandon and Raju, "Optimized Design of Silencer - An Integrated Approach," The Automotive Research Association of India, Pune, India 2007.
[17] Silvestri, Morel, Goerg and Jebasinski, "Modeling of Engine Exhaust Acoustics," Gamma Technologies, BMW AG, J. Eberspacher, GmbH & Co.1999.
[18] Wrtz and Mazzoni, "Application of WAVE in Motorcylce Prototyping," Ducati Motor S.p.A,, Bologna, Italy.
[19] Honda et al, "Honda, Kodama, Wakabayashi,Nakayama, Morimoto and Ueda," Kokushikan University, Japan 2005.
[20] Rose, Marshland and Law, "Optimisation of the Gas-Exchange System of Combustion Engines by Genetic Algorithm," in 4th International Conference on Autonomous Robots and Agents, Wellington, New Zealand, 2009.
[21] Massey, Williamson and Chuter, "Modelling Exhaust Systems Using One-Dimensional Methods," Flowmaster (UK) Ltd. ; ArvinMeritor 2002.
[22] Montenegro and Onorati, "A Coupled 1D-multiD Nonlinear Simulation of I.C. Engine Silencers with Perforates and Sound Absorbing Material," Politecnico di Milano 2009.
[23] Montenegro and Onorati, "Modeling of Silencer for I.C. Engine Intake and Exhaust Systems by Means of an Integrated 1D-multiD Approach," Dipartimento di Energetica - Politecnico di Milano2008.
[24] Zhang and Romzek, "Computational Fluid Dynamics Applications in Vehicel Exhaust System," Eberspaecher North America, Inc.2008.
[25] J. Middleberg, T. Barber, S. Leong, E. Leonardi and K. Byrne, "Determining the Acoustic Performanec of a Simple Reactive Muffler using Computational Fluid Dynamics," presented at the The Eight Western Pacific Acoustics Conference, Melbourne, Australia, 2003.
[26] Shah, Kuppili, Hatti and Thombare, "A Practical Approach towards Muffler Design, Developement and Prototype Validation," 2010.
[27] S. Sen, "Predction of Flow and Acoustical Performance of an Automotive Exhaust System using 3D CFD," TATA Technologies Ltd.2011.
[28] J. Caradonna, "Advanced Computational Aero-Acoustic Simulation of Complex Automotive Exhaust Systems,"
Faurecia Emissions Control Technologies2011.
[29] Lu Lirong, Jin Xiaoxiong, Peng Wei and He Wei, "Application of Flow Field Simulation Technique to the Study of Exhaust Noise of Car," presented at the IEEE Vehicle Power and Propulsion Conference, Harbin, China, 2008.
[30] W. Y. Fowlkes a. C. M. Creveling, Engineering Methods for Robust Product Design- Using Taguchi Methods in Technology and Product Developement. Reading, Massachusetts: Addison Wesley, 1954.
[31] Bureau of Meteorology. (05 Nov 11). Sound Attenuation Calculator. Available:
http://www.csgnetwork.com/atmossndabsorbcalc.html
[32] Bureau of Meteorology. Humiditiy Calculator. Available: http://www.bom.gov.au/lam/humiditycalc.shtml
[33] T. J. Schultz, "Acoustical Uses for Perforated Metals: Principles and Applications," I. P. Association, Ed., ed:
Industrial Perforates Association Inc, 1986.
[34] N. Huff, "Materials for Absorptive Silencer Systems," Owens Cornering Automotive Solutions2001.
Annex A Summary of Acoustic Theory for Automotive Silencers
1. Absorptive/Side-Resonant Silencer
The absorptive and side-resonant silencers operate under the principles established for the use of perforated metals in acoustic treatments. These principals differentiate between the design parameters of the perforated materials utilised within the design, which in turn specify if the action of the silencer to be through the resonant action of the perforated material or via viscous dissipation within sound absorbing material placed behind.
Parameters such as the Transparency Index [33] in Eq.(A1) or otherwise Blair‘s empirical relations [4] in Eq.(A2) and Eq.(A3) may be used to distinguish between these types of silencer which are concerned with perforation pattern of the material used. However, since the transparency index measure is only capable of distinguishing between these variations of silencer beyond 10 kHz, being a frequency fairly well beyond the significant spectrum present in an exhaust, it is not predominantly used for this purpose within this application.
Aonversely, Blair‘s relations were developed specifically for automotive silencers and are therefore much more relevant.
An absorption silencer utilises perforated material that shows negligible preference to the transmission of any region of the frequency spectrum through the material and into the side chamber, otherwise known as the
‗transparency approach‘ [33]. By permitting acoustic wave energy within the side chamber it is made to reflect from the outer shell and constructively interfere with sound waves entering the chamber. This interference then establishes standing waves characterised by increased amplitude of particle oscillation, within the region between the perforated pipe and the silencer housing. As seen in Fig.(A1), sound absorbing material fills this region where wave superposition is predicted to occur.
Consequently, viscous dissipation of sound is achieved as particle kinetic energy is converted to thermal energy via interaction with the sound absorbing material. As per Fig.(A2), correlation is shown between the radial distance between the silencer shell and perforated pipe and the largest wavelength capable of superposition within the thickness of the sound absorbing material.
Consequently, this figure shows that for an increase in thickness of the sound absorbing material, a significant increase in attenuation is achieved for noise of longer wavelength.
The Transparency Index can however be informative through the evaluation of the Access Factor, which represents a measure of the perforated metal‘s ability to obstruct the entry of acoustic waves and has the effect of scaling the absorption factor of the silencer[33] (The absorption factor is defined as the transmission loss expressed as a fraction of the incident sound energy).
Figure A1. Schematic of absorption silencer
Annex A Summary of Acoustic Theory for Automotive Silencers This is therefore a measure of the degradation in the ability of the silencer to attenuate acoustic energy as a result of perforation parameters. As per Fig.(A3), perforated metals with a transparency index of less than 6500 begin to have a noticeable effect on the attenuation achieved at frequencies below 2000 Hz (frequencies up to this point are considered significant sources of vehicle noise).
Literature provides additional design consideration relevant to the manufacture and implementation of an absorption silencer are proposed which include the following:
It is recommended that the perforated pipe be manufactured with stabbed holes rather than blind holes as seen in Fig.(A4). This has the effect of increasing the discharge coefficient for flow into the side chamber from the central pipe and reducing turbulent eddies produced by gas flowing over the sharp edges of blind holes. [4]
While taking the transparency approach, it is also important to consider that an excessive perforated area of a tube may enable violent exhaust flow through the silencer to degrade the sound absorbing material and even attempt to rip it from the side chamber. It is therefore attenuating high frequency noise. Therefore this component is recommended to be one of the last within the exhaust system such that turbulent flow preceding the absorption silencer has limited opportunity to build up this high frequency component.
The choice of sound absorbing material as well as the density of the packing will lead to variation in the achieved transmission loss as per Fig.(A5) [34]. This data reiterates that the maximum wavelength absorbed increases with thickness of sound absorbing material. In addition, an increase in the material density from 100g/L to 200g/L is seen to accompany a reduction in absorption achieved. This highlights that a density too high will restrict the entry of acoustic waves into the side chamber, while a density too low is also acknowledged to become less effective in achieving viscous dissipation of acoustic energy.
In contrast a side-resonant silencer, whilst sharing a similar form as the absorption silencer, does not utilise packing material and instead provides attenuation over a relatively narrow band of frequencies as per Fig.(A6). This is achieved through the resonance of the side cavity at its natural frequency. The design of this type of silencing component is governed by Eq.(A4) to Eq.(A7). The design variables, seen in Fig.(A7), are shown to dictate the resonant frequency of the component as well as the attenuation achieved at the resonant frequency [4].
Figure A2. Variation in attenuation with frequency for thickness of absorption silencer
Figure A3. Access Factor vs frequency and Transmission Index of perforated sheet metal
Figure A4. Schematic of perforated pipe showing standard blind holes and stabbed
Annex A Summary of Acoustic Theory for Automotive Silencers
√ (A4)
(A5)
( ) (A6)
√ ⁄
(A7)
hole conductivity
Figure A5. Variation in attenuation with density of sound absorbing material
Figure A6. Attenuation predicted for a side-resonant silencer
Figure A7. Design parameters of side-resonant silencer element
Annex A Summary of Acoustic Theory for Automotive Silencers
2. Diffusing Silencer/Expansion Chamber
The expansion chamber as seen in Fig.(A8), is designed to absorb acoustic wavelengths equivalent to the natural frequency of the chamber. The transmission loss of an expansion chamber is given by Eq.(A8) to Eq.(A11).
[ ( )] (A8)
( ) ( ( ) ( ) ( )) (A9)
(A10)
(A11)
As per Fig.(A9) [12], the attenuation is seen to be periodic with frequency. In addition, the maximum attenuation is seen to increase with area ratio of the chamber (m). These relations have been experimentally determined to have value up to a frequency of 1500 Hz. In practical terms, Fig.(A9) suggests that a longer chamber will offer increased attenuation at lower frequency, hence why this component is employed within silencers to address low frequency noise corresponding to the engine firing rate.
Figure A8. Schematic of diffusing silencer/ expansion chamber
Figure A9. Plot of theoretical attenuation of expansion chamber with design parameters
Annex A Summary of Acoustic Theory for Automotive Silencers
3.
Hershel-Quincke TubeAs seen in Fig.(A10), the Hershel-Quincke tube is a device in which sound waves from a common source travel through two tubes of different lengths and recombine, producing reinforcement or cancellation of sound depending on the difference in path length. Unfortunately, no further description can be provided as this concept is poorly documented with regards to acoustic attenuation.
4. Helmholtz Resonance Silencer
A Helmholtz chamber is seen in Fig.(A11) attached to the header pipe of an aftermarket Akrapovic exhaust system. It is an acoustic filter element that operates under the principles of a spring-mass system where the equivalent mass and spring force components are defined by the structural parameters of the chamber seen in Fig.(A12).
The Helmholtz silencer is classified as a band-stop filter which offers attenuation at a specified frequency defined by Eq.(A12) and Eq.(A13).
√ (A12)
(A13)
The acoustic power transmission coefficient is then defined by Eq.(A14) and shown in Fig.(A13) for a specified chamber.
( ( ⁄ ⁄ ⁄ ) ) (A14) Figure A10. Example of a Hershel Quincke tube silencing component
Figure A11. Helmholtz chamber
Figure A12. Schematic of Helmholtz chamber
Annex A Summary of Acoustic Theory for Automotive Silencers
Figure A13. Acoustic power transmission coefficient for an example Helmholtz chamber
Annex B WAVE model validation data -WR450 Power curves
Figure B1. WR450 power curve generated with developed WAVE model
Figure B2. WR450 power curves provided by Cal Poly FSAE team
10000 2000 3000 4000 5000 6000 7000 8000 9000 10000
5 10 15 20 25 30 35 40
RPM
Engine Power(hp)
WAVE Model Power Curve
Annex C Muffler Parameter Study - Experimental Data
Figure C1
SPL Magnitude at Position A with Engine Speed for Parameter Variations and Commercial WR450 Muffler
SPL Magnitude at Position B with Engine Speed for Parameter Variations, Unsilenced and Commercial WR450 Muffler
Design 1
Annex C Muffler Parameter Study - Experimental Data
Figure C3
Annex C Muffler Parameter Study - Experimental Data
40
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SPL (dB)
Frequency (Hz)
SPL with Frequency at 3000 rpm at position B
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SPL (dB)
Frequency (Hz)
SPL with Frequency at 7000 rpm at position B
Design 1
Annex C Muffler Parameter Study - Experimental Data
-20
Annex C Muffler Parameter Study - Experimental Data
Figure F7
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0
Variation in transmission loss with silencer design at 3000 rpm
Design 1
Variation in transmission loss with silencer design at 3000 rpm
Design 1
Annex C Muffler Parameter Study - Experimental Data
Figure C11
Figure C12
Annex C Muffler Parameter Study - Experimental Data
Figure C13
Figure C14
Annex C Muffler Parameter Study - Experimental Data
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Annex C Muffler Parameter Study - Experimental Data
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Annex C Muffler Parameter Study - Experimental Data
Figure C19
SPL with Frequency at 3000 rpm at position C
Series1
SPL with Frequency at 7000 rpm at position C
Series1 Series2 Series3 Series4 Series5
Annex D WAVE Parameter Study – Exhaust Design for Scavenging Performance
Figure D1
Figure D2
Annex D WAVE Parameter Study – Exhaust Design for Scavenging Performance
Figure D3
Figure D4
Annex D WAVE Parameter Study – Exhaust Design for Scavenging Performance
Figure D5
Figure D6
Annex D WAVE Parameter Study – Exhaust Design for Scavenging Performance
Figure D7
Figure D8
Annex D WAVE Parameter Study – Exhaust Design for Scavenging Performance
Figure D9
Figure D10
0 0.5 1 1.5
400 500 600 700 800 900 1000 1100
Spatial Temperature and Speed of Sound in stepped pipe- Design 1
Position (m)
Speed of Sound (m/s) / Temperature (K)
Pipe step 1 Pipe step 2
0 0.5 1 1.5
400 500 600 700 800 900 1000 1100
Spatial Temperature and Speed of Sound in stepped pipe- Design 2
Position (m)
Speed of Sound (m/s) / Temperature (K)
Pipe step 1 Pipe step 2
Annex D WAVE Parameter Study – Exhaust Design for Scavenging Performance
Figure D11
Figure D12
Annex D WAVE Parameter Study – Exhaust Design for Scavenging Performance
Figure D13
Annex D WAVE Parameter Study – Exhaust Design for Scavenging Performance
Figure D14
Annex D WAVE Parameter Study – Exhaust Design for Scavenging Performance
Figure D15
Annex D WAVE Parameter Study – Exhaust Design for Scavenging Performance
Figure D16
Figure D17
Annex D WAVE Parameter Study – Exhaust Design for Scavenging Performance
Figure D18
Figure D19
Annex D WAVE Parameter Study – Exhaust Design for Scavenging Performance
Figure D20
Figure D21
Annex D WAVE Parameter Study – Exhaust Design for Scavenging Performance
Figure D22
Figure D23
Annex D WAVE Parameter Study – Exhaust Design for Scavenging Performance
Figure D24
Figure D25
Annex E WAVE Parameter Study – Exhaust Design for Scavenging Performance
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Annex E WAVE Parameter Study – Exhaust Design for Scavenging Performance
Figure E2
Figure E3
Annex E WAVE Parameter Study – Exhaust Design for Scavenging Performance
Figure E4
Figure E5 0
0.5 1 1.5 2 2.5 3 3.5 4
0.00E+00 2.00E+00 4.00E+00 6.00E+00 8.00E+00 1.00E+01 1.20E+01
Ratio increase in Transmission Loss
Ratio increase in weight
Comparison of Transmission Loss to Weight of Absorption Silencer
Diameter Length
Annex E WAVE Parameter Study – Exhaust Design for Scavenging Performance
Figure E6
Figure E7
Annex E WAVE Parameter Study – Exhaust Design for Scavenging Performance
Figure E8
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Annex E WAVE Parameter Study – Exhaust Design for Scavenging Performance
Figure E9
Figure E10
Annex E WAVE Parameter Study – Exhaust Design for Scavenging Performance
Figure E11
Figure E12
Annex E WAVE Parameter Study – Exhaust Design for Scavenging Performance
Figure E13
Figure E14
Annex E WAVE Parameter Study – Exhaust Design for Scavenging Performance
Figure E15
Figure E16
Annex E WAVE Parameter Study – Exhaust Design for Scavenging Performance
Figure E17
Figure E18
Annex E WAVE Parameter Study – Exhaust Design for Scavenging Performance
Figure E19
Figure E20
Annex E WAVE Parameter Study – Exhaust Design for Scavenging Performance
Figure E21