Volvo D11 series, Installation Manual

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Exhaust system
28
Expansion (reactive) silencers
These work on the principle of reflecting and thus
containing sound within the silencer. There are in-
ternal baffle plates fitted to divide the silencer into
sections, which can be individually tuned to a specific
frequency. A reactive silencer creates a relatively high
backpressure due to the torturous gas flow path, i.e.
through the baffle plates, which reverses flow.
Volvo Penta HD silencers combine reactive and ab-
sorptive type of silencing.
Silencer location
The reactive silencer is fitted as close to the exhaust
manifold as is practical to prevent noise break-out
through pipe work.
Insulation of long lines will affect the exhaust back-
pressure and therefore the exhaust pipe diameter
must be increased.
Silencer
There are generally two types of silencers described
as either absorptive or reactive.
Absorptive type
These work on the principle of absorbing noise by
means of an absorbent lining inside the silencer and
normally provide attenuation over a broad frequency
range.
An absorptive silencer is generally designed as a
straight through and would only create a marginally
greater backpressure than similar length of straight
pipe.
Exhaust line
. Compensator
2. Flexible exhaust hose
3. Three point fixture
4. Insulation (mineral wool)
5. Silencer
6. Flexible attachment
7. Glass fibre fabric
3
2
4
6
7
5
Calculation of HD silencer backpressure
To calculate the backpressure for Volvo Penta HD silencers use the following formulas:
See
Sales Guide Marine Propulsion Diesel Engines Technical Data.
Bore velocity = (m/s)
Backpressure = (mm Wc)
T = engine exhaust temperature (°C), mm Wc = 0.0098 kPa
Exhust gas flow (m
3
/min)
Area of pipe (m²) x 60
Resistance from graph (mm Wc) x 673
T + 273