Geko EISEMANN 250000 ED-S/DEDA Bedienungsanleitung Seite 72

Expansion joints consisting of flexible sealed elements must be inserted in long stretches of exhaust pipe.
When designing the layout of the exhaust system, ensure that the pipes are not located too near the engine air filters in order to prevent the intake of hot air.
All exhaust pipes must nevertheless be insulated to prevent overheating of the generator room and, above all, to prevent accidental contact with hot surfaces.
In multiple set applications, the individual exhaust lines must not be conducted into a single outlet: this situation would create problems; for example, when only one set is operational, the exhaust gases
would tend to flow towards the inactive units.
The back pressure on the engine exhaust greatly influences the power delivered by the engine and its thermal load.
Any excessive back pressure (measured on the outlet side of the exhaust manifold for induction engines and on the turbine outlet side for turbocharged engines) causes a decrease in power, an increase in
the temperature of the exhaust gases, produces smoke, increases fuel consumption and superheats the cooling water, with subsequent deterioration in the lubricant and consequences for other engine parts.
The recommended limits (referring to maximum power delivery conditions under full service operations) on Motors sets are:
- 150 mbar (1500 mm H2O) for induction engines
- 50 mbar (500 mm H2O) for turbocharged engines.
Motors will supply the exhaust gas flow and temperature values of its engines (see tech-
nical data sheets) necessary for the design.
As an example, Figure shows a nomogram for calculating the diameter of an exhaust
pipe. Starting with the length of the pipe and proceeding up through the number of
bends (90º bends with r = 2.5d) and gas flow (in m 3 /h)*, then, assuming a fixed back-
pressure value, it is possible to determine the diameter of the pipe (either insulated or
non-insulated) from the top right scale of the nomogram. Of course, this backpressure
only refers to the pipe length and does not include the effect of the silencer. The need,
therefore, is to perform the exercise so that the total backpressure (pipe plus silencer) is
contained within the above limits for induction or turbocharged engines.
These limits can be respected by suitable sizing of the exhaust system: pipe and silencer.
* The flow of exhaust gas is obtained from the date sheets in kg/h. Initially, this value
can be divided by 0.42 to obtain the flow in m 3 /h.
The exhaust pipes must be as short as possible with the minimum number of bends.
When bends need to be installed, they must be formed with a large radius of curvature
(on average 2.5 to 3 times the diameter of the pipe).
In order to calculate the total length of the exhaust pipe, required for the exhaust back-
pressure calculation, the equivalent length (lo) of the bends must be added to the
straight length. The equivalent lengths are obtainable for various pipe diameters from Figure.
The table shows the various types of bend and their equivalent lengths.
Bends with a radius of curvature of less than 2.5d are more detrimental and should be avoided, or calculated directly.
In all cases, the exhaust pipe should never have a diameter less than that of the engine manifold.
When the diameter of the pipe is greater than the manifold, a reducer of taper angle not greater than 30° must be used to prevent excessive head loss.
It is also worthwhile checking the total backpressure generated by the pipe and silencer experimentally. The measurement is taken near the outlet • ange of the engine manifold (or turbine), if possible
along a straight section of pipe. Motors engines are normally fitted with a screwed socket for fitting the pressure gauge (vacuometer). If this instrument is not available, it is possible to use a simple transpa-
rent plastic tube bent into a U shape and partially filled with water. One end of the tube is inserted in contact with the exhaust gas at the above point, and the other end is held free in the air. The difference
in water level between the two legs of the U is the backpressure value in mm H 2 O.
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