Design and Simulation of Two Stroke Engines

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Chapter 8 • Reduction of Noise Emission from Two-Stroke Engines
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PERFORATED
SECTION
PLAIN HOLES
EQUAL SPACING
5 ROWS OF HOLES
8 HOLES PER ROW
EACH HOLE $3.18
Fig. 8.2 Various exhaust systems and silencers used by Blair and Coates [8.3].
are four spectrograms on any given figure: the one at the top is where the measuring microphone
is placed directly in line with the pipe end and the directivity angle is declared as zero,
and the others are at angles of 30°, 60° and 90°. The solid line on any diagram is the measured
noise spectra and the dashed line is that emanating from the theoretical solution outlined in
Sec. 8.4.1. It can be seen that there is a very high degree of correlation between the calculated
and measured noise spectra, particularly at frequency levels below 2000 Hz.
Perhaps the most important conclusion to be drawn from these results is that the designer
of silencing systems, having the muffling of the noisiest frequency as a first priority, can use
an unsteady gas-dynamic simulation program as a means of prediction of the mass flow rate
at the pipe termination to atmosphere, be it the inlet or the exhaust system, and from that mass
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