[0001] The invention relates to a method for attenuating sound of exhaust gases of an engine, the method comprising leading the exhaust gases of the engine through an inlet duct to a sound attenuation space separated from the surroundings and further through an outlet duct out of the sound attenuation space. The invention also relates to an apparatus for attenuating sound of exhaust gases of an engine.

[0002] Different engines, such as internal combustion engines and turbine engines, produce exhaust gases during operation. Simultaneously sound is produced, the amount of which rises to an unacceptable level. The level of sound produced by an engine is quite strictly limited by different regulations and laws. A long-term trend has also been towards stricter and stricter limits.

[0003] For the above mentioned reasons, a plurality of solutions related to sound attenuation of engines have been developed. The great number of presented solutions shows that it is technically difficult to attenuate sound in an engine.

[0004] Examples of solutions known in the field include solutions described in US patent publications 7 383 919 B2 and 5 962 822 and PCT publications WO 02/053884 A2 and WO 2006/120709 A1 .

[0005] A problem with the previously known solutions has been, for instance, increased fuel consumption and diminished engine performance. It is assumed that the above mentioned facts result from, for instance, an increase in the back pressure of exhaust gases caused by a sound attenuation arrangement. A disadvantage of some previously known solutions has also been their complexity and large size. A large size often causes problems when the sound attenuation solution is installed in its place in connection with an engine. Still, a space intended for the sound attenuation arrangement is sometimes quite limited, and in practical situations there are often problems, which are difficult to solve.

[0006] The object of the invention is to provide a method and an apparatus by which the prior art disadvantages can be eliminated. This is achieved by a method and apparatus of the invention. The method of the invention is characterized by providing the sound attenuation space separated from the surroundings with an ejection space, to which the exhaust gases coming from the engine and led through the inlet duct are directed, and keeping a part of the engine's exhaust gas flow led to the sound attenuation space in continuous circulation in the sound attenuation space in such a manner that the recirculated part of the exhaust gas flow is accommodated by means of an ejector effect to the exhaust gas flow coming from the engine and directed to the ejection space. The apparatus of the invention, for its part, is characterized in that the sound attenuation space formed by the casing part is provided with an ejection space, to which the exhaust gases from the engine are arranged to be directed, and a recirculation space, whereby a part of the exhaust gas flow directed to the ejection space is arranged to flow to the recirculation space and stay in continuous circulation in such a manner that the recirculated part of the exhaust gas flow is accommodated by means of an ejector effect to the exhaust gas flow coming from the engine and directed to the ejection space.

[0007] A particular advantage of the invention is that, in the invention, sound attenuation according to the present standards can be achieved with a very simple solution without increasing the engine's fuel consumption or diminishing its performance. Compared to the previously known solutions, another advantage of the solution according to the invention is its small size, which makes it possible to eliminate the space-related problems that were found in connection with the prior art solutions.

[0008] The invention will be explained in the following in more detail by means of examples described in the attached drawing, in which

Figure 1 shows a schematic perspective section of a first embodiment of an apparatus according to the invention, and

Figure 2 shows a schematic perspective section of a second embodiment of the apparatus according to the invention.

[0009] Figure 1 shows a first embodiment of an apparatus of the invention. Figure 1 shows the apparatus in section in such a manner that the structure of the inner parts of the apparatus is visible. In reality, the structure of the apparatus is closed, which means that the structures of the inner parts of the apparatus cannot be seen from the outside.

[0010] Reference numeral 1 denotes a casing part, which constitutes a sound attenuation space separated from the surroundings. Reference numeral 2 refers to an inlet duct, through which exhaust gases of an engine are led to the sound attenuation space. Reference numeral 3 in Figure 1 refers to an outlet duct, through which the exhaust gases of the engine are led out of the sound attenuation space. In Figure 1 , arrows 4 indicate flow of exhaust gases of the engine through the inlet duct to the sound attenuation space. Arrows 5 in Figure 1 indicate flow of exhaust gases through the outlet duct 3 out of the sound attenuation space.

[0011] As described above, Figure 1 is a sectional view. The sectional view is provided in such a manner that the apparatus has been split in the direction of the exhaust gas inlet, thus showing, for instance, the inlet duct 2 as a trough-shaped part and the casing part 1 , respectively, as a part having one open side. In reality, the inlet duct 2 is a tubular element and the casing part 1 , respectively, a closed element, etc.

[0012] The casing part 1 is connected to a duct of the exhaust gas side of the engine by means of the inlet duct 2 in such a manner that exhaust gases from the engine are able to flow into the casing part via the inlet duct. The outlet duct 3, for its part, is connected to an exhaust gas tube, through which the exhaust gases are exhausted. The engine may be any engine, for instance an engine of a ship, such as an internal combustion engine or turbine engine.

[0013] For a person skilled in the art, this is fully conventional technology, wherefore it is not explained in greater detail herein.

[0014] According to the essential idea of the invention, an ejection space 6 is provided in the sound attenuation space separated from the surroundings. The ejection space 6 is formed by means of partitions 7. The exhaust gases coming from the engine and led through the inlet duct 1 are directed to the ejection space as indicated by the arrows 4. A part of the exhaust gases directed to the ejection space 6 are directed to flow to a recirculation space 8 and kept in continuous circulation inside the sound attenuation space. The recirculated exhaust gas part is illustrated in Figure 1 by means of arrows 9. The recirculated part of the exhaust gas flow is accommodated by means of an ejector effect to the exhaust gas flow coming from the engine and directed to the ejection space 6. Direction of the recirculated exhaust gas part according to the exhaust gas flow directed from the engine to the ejection space 6, achieved by means of the ejector effect, is shown schematically by arrows 10.

[0015] The exhaust gas flow exhausted from the sound attenuation space, referred to in Figure 1 by the arrows 5, has released part of its sound and pressure wave energy to the exhaust gas part directed to the recirculation, which is illustrated in Figure 1 by means of the arrows 9. Thus, the basic idea of the invention is that by keeping a part of the exhaust gas flow in continuous circulation inside the sound attenuation space formed by the casing part 1 without allowing it to exit the sound attenuation space, it itself serves as an efficient absorber of both sound energy and, in particular, pressure strokes typical for exhaust gases of internal combustion engines. The recirculation space 8 also serves as a sound absorbing space in the invention.

[0016] Figure 1 shows an example of the invention, wherein the sound attenuation space formed by the casing part 1 is provided with an ejection space 6 by using two partitions 7 and a recirculation space 8 next to the ejection space on its both sides. However, this is not the only feasible solution, but the invention may also be applied by using another kind of structure.

[0017] Figure 2 shows a second embodiment of the invention. In Figure 2, the same reference numerals as in Figure 1 are used at corresponding points. A difference between the embodiment of Figure 2 and the embodiment of Figure 1 is that the embodiment of Figure 2 comprises one recirculation space 8, which is located on the other side of the ejection space 6 next to the ejection space 6. Thus, the embodiment of Figure 2 is in a sense asymmetrical. The embodiment of Figure 1 , for its part, comprises two recirculation spaces 8 located on both sides of the ejection space 6 next to the ejection space 6. Thus, the embodiment of Figure 1 is in a sense a symmetrical solution.

[0018] The embodiment of Figure 2 has the same operating principle as the embodiment of Figure 1 . The part of the exhaust gas flow coming from the engine and indicated by the arrow 9 is directed to the recirculation space 8 and kept in continuous circulation inside the sound attenuation space formed by the casing part 1 . The above mentioned continuous circulation of the part of the exhaust gas flow directed to the recirculation space 8 is achieved by accommodating this part of the exhaust gas flow by means of the ejector effect to the exhaust gas flow coming from the engine and directed to the ejection space 6, as indicated by the arrow 10 in Figure 2.

[0019] The invention is described above by means of two different examples. However, the invention is not restricted in any way to the above- mentioned examples only but may be freely modified within the scope of the accompanying claims. Consequently, different details of the invention may also differ from those shown in the figures. For instance, the ejection space may be formed by using one or more partitions, etc.