Design and Simulation of Two Stroke Engines

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1 Chapter 8 - Reduction of Noise Emission from Two-Stroke Engines The box B, a diffusing silencer, has 16-mm-diameter pipes entering and leaving, each pipe being re-entrant by 20 mm. The section length, Lb, is 200 mm. The transmission loss is quite broad-banded, but the most important frequency of suppression is at 850 Hz, this lesson being the principal one learned from the work of Coates [8.3] with his SYSTEM 2 and discussed in Sec. 8.5.1. The first pass-band is also of direct interest, and it is seen to exist at 1300 Hz. If further design of this silencing system was left at this point, and the removal of the pass-band hole assigned to the absorption silencer segment, there would exist the strong possibility that this could turn out to be rather noisy at this frequency. With the first two boxes, A and B, there is a good transmission loss for the silencer up to 1300 Hz, and the evidence from Sec. 8.5.1 is that the pass-band hole at that frequency would exist. Thus, a third small box of the side-resonant type, box C, is added and is targeted to have high attenuation at that specific frequency. It can be seen that a short box, just 50 mm long, with 16 holes of 2.6 mm diameter in the 16-mm-diameter through-pipe with a 1.5-mm-thick wall, has a transmission loss which peaks at 1275 Hz. The addition of this third box, C, making three silencing segments before the absorption silencer portion, would provide strong attenuation of the noise up to about 3500 Hz, with no visible pass-band holes in that transmission loss. The absorption silencer can then be designed to remove the remainder of the high-frequency content, either in the conventional manner or by using the annular flow system recommended in Sec. 8.5.4. You should recall the discussion regarding the sound radiation possibilities from the outside surface of silencer and pipe walls and, in a real design situation, ensure that the wall is double-skinned or suitably damped acoustically along the entire length of the system. 8.7 Concluding remarks on noise reduction The principal concepts which the designer or developer has to retain at the forefront of the thought process when silencing the two-stroke engine, or indeed any reciprocating engine, are: (i) Identify the principal source of noise from the engine, be it mechanical, induction or exhaust noise, and suppress that as a first priority. The other sources of noise could be completely eliminated and the total noise from the engine would be virtually unaffected if the single noisiest source remains unmuffled. (ii) Within any given noise source, the technique for suppressing it is to determine the frequency spectrum of that noise and to tackle, as a first priority, the frequency band with the highest noise content. Should that remain unmuffled, then the other frequency bands could be completely silenced and the total noise content would virtually remain at the original level. (iii) In the identification of noise sources, it is useful to remember that noise level, or loudness, is a function of the square of the distance from any given source [8.3] to the microphone recording that noise level. Thus placing the microphone close to the inlet tract end, or the exhaust pipe end, or a gearbox, in a manner which differentially distances the other sources, permits an initial and approximate identification of the relative contributions of the several sources of noise to the total noise output. 583
Design and Simulation of Two-Stroke Engines References for Chapter 8 8.1 G.P. Blair, J.A. Spechko, "Sound Pressure Levels Generated by Internal Combustion Engine Exhaust Systems," SAE Paper No. 720155, Society of Automotive Engineers, Warrendale, Pa., 1972. 8.2 G.P. Blair, S.W. Coates, "Noise Produced by Unsteady Exhaust Efflux from an Internal Combustion Engine," SAE Paper No. 730160, Society of Automotive Engineers, Warrendale, Pa., 1973. 8.3 S.W. Coates, G.P. Blair, "Further Studies of Noise Characteristics of Internal Combustion Engines," SAE Paper No. 740713, Society of Automotive Engineers, Warrendale, Pa., 1974. 8.4 D.D. Davis, G.M. Stokes, D. Moore, G.L. Stevens, "Theoretical and Experimental Investigation of Mufflers," NACA Report No. 1192, 1954. 8.5 P.O.A.L. Davies, R.J. Alfredson, "The Radiation of Sound from an Engine Exhaust," J.Sound Vib., Vol 13, p389, 1970. 8.6 P.O.A.L. Davies, "The Design of Silencers for Internal Combustion Engines, "J.Sound Vib., Vol l,pl85, 1964. 8.7 P.O.A.L. Davies, "The Design of Silencers for Internal Combustion Engine Exhaust Systems," Conference on Vibration and Noise in Motor Vehicles, Proc.I.Mech.E., 1972. 8.8 G.H. Trengrouse, F.K. Bannister, "The Reduction of Noise Generated by Pressures Waves of Finite AmplitudeAttenuation due to Rows of Holes in Pipes," University of Birmingham, Research Report No. 40, 1964. 8.9 M. Fukuda, H. Izumi, "Kuudougata Shouonki no Tokusei ni Kansuru Kenkyuu," Trans.Japan Soc.Mech.E, Vol 34, No 263, pi294, 1968. 8.10 P.M. Nelson, "Some Aspects of Motorcycle Noise and Annoyance," SAE Paper No. 850982, Society of Automotive Engineers, Warrendale, Pa., 1985. 8.11 R. Taylor, Noise. Penguin, London, 1975. 8.12 CM. Harris, Handbook of Noise Control. McGraw-Hill, New York, 1957. 8.13 L.L. Beranek, Noise Reduction. McGraw-Hill, New York, 1960. 8.14 M.B. Johnston, "Exhaust Port Shapes for Sound and Power," SAE Paper No. 730815, Society of Automotive Engineers, Warrendale, Pa., 1973. 8.15 K. Groth, N. Kania, "Modifications on the Intake Ports with the Aim to Reduce the Noise of a Two-Stroke Crankcase-Scavenged Engine," SAE Paper No. 821069, Society of Automotive Engineers, Warrendale, Pa., 1982. 8.16 SAE Noise Standards, Society of Automotive Engineers, Warrendale, Pa.: SAE J47—Maximum Sound Level Potential for Motorcycles SAE J331a—Sound Levels for Motorcycles SAE J192—Exterior Sound Level Measurement for Snowmobiles SAE J986—Light Vehicle Noise Test Procedures SAE Jl 174—Operator Ear Sound Level Measurement Procedure for Small Engine Powered Equipment SAE J 1046a—Exterior Sound Level Measurement Procedure for Small Engine Powered Equipment 584
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Design and Simulation of Two-Stroke
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A Second Mulled Toast When as a stu
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Acknowledgments As explained in the
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Table of Contents Nomenclature xv C
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Table of Contents 2.10.1 Flow at pi
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Table of Contents 3.5.3.1 The use o
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Table of Contents 6.1.3 The effect
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Nomenclature NAME SYMBOL UNIT (SI)
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speed of rotation speed of rotation
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attenuation or transmission loss wa
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Design and Simulation ofTwo-Stroke
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Design and Simulation ofTwo'Stroke
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Chapter 4 Combustion in Two-Stroke
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Chapter 4 - Combustion in Two-Strok
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a stratilpl o tions to ivior. If m
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CD 30 -, W 20 - LU CO iS _J LU OC 1
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181 also x3 = — = 0.905 x6 = 2.17
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to be cur .3.20) .3.21) .3.22) for
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3.23) com- :on is hhas has a /eng-
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stroke .3.29) mean me to 3land ssio
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a LU z: en 3 CO a LU z EC D m O ho
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CD 1.2 -i 1.0 - di „„ LU 0.8 cc
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CO —> 111" cc LU < LU _J LU CC £
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Combustion in compression-ignition
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stroke ari more often lseful lental
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lat the ssi ;tribu- ELEVATION VIEWS
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CYLINDER HEAD TYPE IS CENTRAL BORE,
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CO E 50 40 - O O _i Hi > I CO 30 Z)
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CURRENT INPUT DATA FOR 2-STROKE 'SP
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Cylin- PP £ Pa- tics of Paper Chap
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vfitro- ;titi >tants 1970. i(In- Ch
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£2 = Pi P2 I Pi J Chapter 4 - Comb
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CHAINSAW AT 9600 rpm. Chapter 4- Co
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LLI •z. O N -z. 0.21 -, 0.20 DC 0
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Chapter 7 Reduction of Fuel Consump
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Chapter 7 • Reduction of Fuel Con
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Chapter 7 - Reduction of Fuel Consu
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0.35 • 0.34 LU ° 0.33 - c 03 DC
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§ 2000
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y, ,6 Chapter 7 - Reduction of Fuel
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Chapter 7- Reduction of Fuel Consum
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INLET FOR r AIR AND FUEL Chapter 7
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o Q_ Ld < CD 15-, 10- Chapter 7 - R
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Page 608 and 609: Active radical (AR) combustion and
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Page 626 and 627: I PISTON POSITION (computer program
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Page 634 and 635: Scavenging (continued) scavenging e
Page 636 and 637: Simulation, engine See Computer mod
Page 638 and 639: temperature vs. crankshaft angle (c
Page 640 and 641: work per thermodynamic (Otto) cycle
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Design and Simulation of Two Stroke Engines

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