Design and Simulation of Two Stroke Engines

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
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