Man L23/30DF, Project Manual

Page: 229 / 392

Internal exhaust gas system
From the exhaust valves, the gas is led to the
exhaust gas receiver where the fluctuating pressure
from the individual cylinders is equalized and the
total volume of gas led further on to the turbo-
charger, at a constant pressure. After the turbo-
charger, the gas is led to the exhaust pipe system.
The exhaust gas receiver is casted sections, one for
each cylinder, connected to each other, by means
of compensators, to prevent excessive stress due
to heat expansion.
After each cylinder a thermosensor for reading the
exhaust gas temperature is fitted.
To avoid excessive thermal loss and to ensure a
reasonably low surface temperature the exhaust
gas receiver is insulated.
External exhaust gas system
The exhaust back-pressure should be kept as low
as possible.
It is therefore of the utmost importance that the
exhaust piping is made as short as possible and
with few and soft bends.
Long, curved, and narrow exhaust pipes result in
higher back-pressure which will affect the engine
combustion. Exhaust back-pressure is a loss of
energy and will cause higher fuel comsumption.
The exhaust back-pressure should not exceed 30
mbar at MCR. An exhaust gas velocity through the
pipe of maximum 35 m/sec is often suitable, but
depends on the actual piping.
During commissioning and maintenance work,
checking of the exhaust gas back pressure by
means of a temporarily connected measuring
device may become necessary. For this purpose, a
measuring socket must be provided approx. 1-2 m
after the exhaust gas outlet of the turbocharger at
an easily accessible place. Usual pressure measur-
ing devices require a measuring socket size of ½".
This measuring socket must be provided to ensure
utilisation without any damage to the exhaust gas
pipe insulation.
MAN Diesel & Turbo will be pleased to assist in
making a calculation of the exhaust back-pressure.
The gas outlet of turbocharger, the expansion bel-
lows, the exhaust pipe, and silencer, (in case of
silencer with spark arrestor care must be taken that
the cleaning parts are accessible), must be insula-
ted with a suitable material.
The insulation should be shielded by a thin plating,
and should comply with the requirements of the
classification society and/or the local authorities.
Exhaust pipe dimensions
It should be noted that concerning the maximum
exhaust gas velocity the pipe dimension after the
expansion bellows should be increased for some of
the engines.
The wall thickness of the external exhaust pipe
should be min. 3 mm.
Exhaust pipe mounting
When the exhaust piping is mounted, the radiation
of noise and heat must be taken into consideration.
Because of thermal fluctuations in the exhaust pipe,
it is necessary to use flexible as well as rigid sus-
pension points.
In order to compensate for thermal expansion in the
longitudinal direction, expansion bellows must be
inserted. The expansion bellows should preferably
be placed at the rigid suspension points.
Note: The exhaust pipe must not exert any force
against the gas outlet on the engine.
One sturdy fixed-point support must be provided
for the expansion bellows on the turbocharger. It
should be positioned, if possible, immediately above
the expansion bellows in order to prevent the trans-
mission of forces, resulting from the weight, thermal
expansion or lateral displacement of the exhaust
piping, to the turbocharger.
The exhaust piping should be mounted with a slope
towards the gas outlet on the engine. It is recom-
mended to have drain facilities in order to be able to
remove condensate or rainwater.
Position of gas outlet on turbocharger
B 16 02 0 shows turning alternatives positions of
the exhaust gas outlet. Before dispatch of the
engine exhaust gas outlet will be turned to the wan-
ted position.
The turbocharger is, as standard, mounted in the
front end.
MAN Diesel & Turbo
1655213-2.6
Page 1 (4)
Exhaust gas system
B 16 00 0
L28/32S, L27/38S, L23/30S, L21/31S, L16/24S, L23/30DF, L28/32DF, L16/24,
L21/31, L23/30H, L27/38, L28/32H
2015.01.14