Design and Simulation of Two Stroke Engines

Design and Simulation of Two-Stroke Engines
A
T
T
E
N
U
A
T
I
0
N
50
40
30"
20
dB
10
1275 Hz
0 T i i r -T-1—I—I—\—l—I 'I' I—t—i—i—i—i i i—i—i—r
1000 2000
FREQUENCY, Hz
BOX A BOXC
ONE OFF 5
08 HOLE
16 OFF
0 2.6 HOLES
ABSORPTION
SILENCER
BOX A BOX B BOX C
INPUT DATA INPUT DATA INPUT DATA
LB= 150
LB= 50
DSB= 80
DSB= 80
DS3= 16
DS3= 16
TH= 1.5
TH= 1.5
NH= 1
NH= 16
D5H= 6
D5H= 2.6
T2C= 400
T2C= 400
r~| 1 I I 1—1 1 1—T"
3000 4000
Fig. 8.28 Silencer design for a small motorcycle engine using Progs. 8.1 and 8.2.
The box A, a side-resonant silencer, has a single 8-mm-diameter hole in the 16 mm pipe
with a 1.5-mm-thick wall. The exhaust temperature is assumed to be 400°C. Note that, if the
real box has sloping walls as in the sketch, then the computed box volume may not ultimately
agree with the actual box volume, in which case a modified length, Lb, should be inserted as
data so that the calculation operates with a realistic box volume. You will understand the
importance of that statement more fully if the relevant acoustic theory is re-examined in Sec.
8.5.2 and Eqs. 8.5.6-8.5.16. That comment aside, the computed acoustic transmission loss is
seen to peak at 475 Hz, which is sufficiently close to the target frequency of 500 Hz for
maximum suppression.
582