Design and Simulation of Two Stroke Engines

Chapter 8 - Reduction of Noise Emission from Two-Stroke Engines
8.7 and in this section. However, the input data are in the more conventional length dimensions
in mm units and temperature in Celsius values; they are converted within the program to
strict SI units before being entered into the programmed equations for the attenuation of a
diffusing silencer according to Fukuda [8.9], Eqs. 8.5.3-8.5.5. You can check the input dimensions
of SYSTEM 2 and SYSTEM 3 from Fig. 8.2.
The measured noise characteristics of SYTEM 2 are shown in Fig. 8.4. The attenuation of
SYSTEM 2, as predicted by the theory of Fukuda and shown in Fig. 8.12, has a first major
attenuation of 14 dB at 320 Hz and the first two pass-band frequencies are at 550 and 1100
Hz. If you examine the measured noise frequency spectrum in Fig. 8.4, you will find that an
attenuation hole of 12 dB is created at a frequency of 400 Hz. Thus the correspondence with
the theory of Fukuda, with regard to this primary criterion, is quite good and gives some
confidence in its application for this particular function. There is also some evidence of the
narrow pass-band at 550 Hz and there is no doubt about the considerable pass-band frequency
at 1100 Hz in the measured spectra. There is no sign of the predicted attenuation, nor the passband
holes, at frequencies above 1.5 kHz in the measured spectrum. There is also no evidence
from the empirical solution of the reason for the attenuation in the measured spectrum of the
fundamental pulsation frequency of 133 Hz, as commented on in Sec. 8.4.2. The general
conclusion as far as SYSTEM 2 is concerned is that Prog.8.1 is a useful empirical design
calculation method for a diffusing silencer up to a frequency of 1.5 kHz.
The measured noise characteristics of SYTEM 3 are shown in Fig. 8.5. The attenuation of
SYSTEM 3, as predicted by the theory of Fukuda and shown in Fig. 8.13, has a first major
A
T
T 40
E
N
U
A 30
T
!
0
N 20
dB
10
50 DESIGN FOR A DIFFUSING SILENCER
0
CALCULATION BY Prog.8.1
DATA FROM Coates/Blair SYSTEM 2
1000
FREQUENCY, Hz
INPUT DATA
LB= 305
DSB= 76
DS1= 28.6
DS2= 28.6
L1= 0
L2= 0
LT= 152
T2C= 10
3650
I
i—i—i—r"i—|
4000
Fig. 8.12 Calculation by Prog.8.1 for the silencing characteristics of SYSTEM 2.
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