Design and Simulation of Two Stroke Engines

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Chapter 8 - Reduction of Noise Emission from Two-Stroke Engines «-oC IOOO RPM aooo Fig. 8.5 One-third noise spectrogram from SYSTEM 3. flow rate calculation over a complete cycle determine the noisiest frequency to be tackled by the silencer. Of direct interest is the silencing effect of the various silencer elements attached to the exhaust pipe by Coates, SYSTEMS 2-4, the noise spectra for which are shown in Figs. 8.4- 8.6. The SYSTEM 2, a simple diffusing silencer without re-entrant pipes, can be seen to reduce the noise level of the fundamental frequency at 133 Hz from 116 dB to 104 dB, an attenuation of 12 dB. From the discussion in Sec. 8.1.2, an attenuation of 12 dB is a considerable level of noise reduction. It will also be observed that a large "hole," or strong attenuation, has been created in the noise spectra of SYSTEM 2 at a frequency of 400 Hz. In Sec. 8.5.1 this will be a source of further comment when an empirical frequency analysis is attempted for this particular design. The noise spectra for SYSTEM 3, a diffusing silencer with re-entrant pipes, is shown in Fig. 8.5. The noise level of the fundamental frequency of 133 Hz has been reduced further to 98 dB. The "hole" of high attenuation is now at 300 Hz and deeper than that recorded by SYSTEM 2. 553
Design and Simulation of Two-Stroke Engines I20t e-o" 70 1 25 0-30- I20 IOOO RPM i i i i f i • i i i i i i i i i i i i i i i i IOO IOOO Hi- 10.000 —i—i—I—r- I I I I I IOOO Hi— 10,000 IO.OOO 25 IOO IOOO Hi— 10,000 Fig. 8.6 One-third noise spectrogram from SYSTEM 4. The noise spectra for SYSTEM 4 is shown in Fig. 8.6. This is a side-resonant silencer. The noise level of the fundamental frequency of 133 Hz is nearly as quiet as SYSTEM 2, but a new attenuation hole has appeared at a higher frequency, about 500 Hz. This, too, will be commented on in Sec. 8.5.2 when an empirical acoustic analysis is presented for this type of silencer. It can also be seen that the noise level at higher frequencies, i.e., above 1000 Hz, is reduced considerably from the unsilenced SYSTEM 1. The most important conclusion from this work by Coates is that the noise propagation into space from a pipe system, with or without silencing elements, can be predicted by a theoretical calculation based on the motion of finite amplitude waves propagating within the pipe system to the pipe termination to the atmosphere. In other words, designers do not have to rely on empirically based acoustic equations for the design of silencers, be they for the intake or the exhaust system, for internal-combustion engines. 8.4.3 Future work for the prediction of silencer behavior It has always seemed to me that this pioneering work of Coates [8.3, 8.17] has never received the recognition it deserves. Worse, it has tended to be ignored [8.25], due in part to 554
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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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^ s C£ Q 2^ E Q. Q_ z' o ISSI HCEM
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o > z~ Q w CO UJ w g x O z o z o m
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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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Page 608 and 609: Active radical (AR) combustion and
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in crankcase heat transfer analysis
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Mercury Marine air-assisted fuel in
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I PISTON POSITION (computer program
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Pressure wave reflection (in pipes)
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local acoustic velocity, 60 local M
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Roots blower in turbocharged/superc
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Scavenging (continued) scavenging e
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Simulation, engine See Computer mod
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temperature vs. crankshaft angle (c
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work per thermodynamic (Otto) cycle
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Design and Simulation of Two Stroke Engines

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