Combined silencer and spark arrester

This invention relates to a silencer for silencing exhaust gases that enables the entrapment of burning carbon particles or sparks carried in the exhaust gases, particularly for use in internal combustion engine applications where fire hazards exist.

When internal combustion engines are operated in locations requiring the removal of sparks from exhaust gases, such as in power generating sets, it can be necessary to provide a spark arrester. Conventional spark arresters work by providing an angular rotation to the flow of exhaust gases through a spark arrester chamber by means of fixed blades, thereby causing the sparks to move to the outer perimeter of the chamber. A carbon trap is generally provided at the outer wall of the chamber and traps the carbon particles and sparks. The remaining exhaust gas then passes through the exhaust gas silencer to the atmosphere.

The provision of a spark arrester to an exhaust gas silencer system can add significant cost to the system. Moreover conventional separate spark arresters are bulky and take up additional space in or near the engine. The present invention provides a silencer with an integral spark arrester, which allows a separate spark arrester to be omitted where conditions permit.

The present invention provides a silencer for silencing exhaust gases comprising an exhaust gas inlet, an exhaust gas outlet, a first chamber and a first passage having first and second ends. The first chamber and first passage are arranged between the exhaust gas inlet and the exhaust gas outlet such that exhaust gases passing from the exhaust gas inlet to the exhaust gas outlet pass from the first end to the second end of the first passage and hence through the first chamber. The second end of the first passage communicates with the first chamber. The silencer further includes at least one acoustic resonator chamber connected by a connecting passage to the first chamber. The connecting passage is positioned proximate the second end of said first passage.

From another aspect, the invention provides a method of arresting sparks in a silencer comprising the steps of:

causing exhaust gases to flow from an exhaust gas inlet to an exhaust gas outlet via a first chamber,

providing an acoustic resonator chamber connected by a connecting passage to said first chamber, and

directing the flow of exhaust gases through said first chamber such that sparks in said exhaust gases are caused to enter the acoustic resonator chamber and become trapped therein.

Other features and aspects of this invention will become apparent from the following description and the accompanying drawings.

FIG. 1 is an isometric view of a silencer forming one embodiment of the invention;

FIG. 2 is an isometric view of the silencer of FIG. 1 with the outer casing and inner lining omitted for clarity;

FIG. 3 is a cross-sectional view taken on the line III—III of FIG. 1 ; and

FIG. 4 is a schematic view of the silencer of FIG. 1 .

One embodiment of the invention will now be described with reference to the drawings, by way of example. FIG. 1 shows a silencer 10 that is mounted to an engine (not shown) or other supporting structure by mounting brackets 12 , 14 . The silencer 10 includes an exhaust gas inlet 20 on a stub pipe 22 and an exhaust gas outlet 30 on an outlet pipe 32 . The stub pipe 22 enters an outer casing 40 divided into a number of chambers, defined by two end caps 44 , 46 , two baffle plates 48 , 50 , a low frequency resonator plate 54 and the outer casing 40 itself, together with an inner lining 42 fixed inside the outer casing 40 .

The inlet chamber 64 is defined by the inner lining 42 , a first end cap 44 and a first baffle plate 48 . A first end 58 of a bridge pipe or first passage 56 forming a first passage is in communication with the inlet chamber 64 . A second end 60 of the bridge pipe or first passage 56 extends into and is in communication with a first chamber 66 , which is defined by the inner lining 42 , the low frequency resonator plate 54 and baffle plate 50 .

The low frequency resonator plate 54 forms part of an acoustic resonator chamber 52 , which may be of the sort commonly referred to as a Helmholtz resonator, which communicates with the first chamber 66 by means of a resonator neck pipe or connecting passage 62 . The connecting passage 62 is preferably tubular and is axially aligned with the bridge pipe 56 , as can be seen most clearly in FIG. 3 . The entrance to the connecting passage 62 is adjacent to and directly opposite the second end 60 of the bridge pipe 56 . In the illustrated embodiment the low frequency resonator plate 54 forms a boundary wall between the first chamber 66 and the acoustic resonator chamber 52 .

A second chamber 68 is defined by the inner lining 42 , the first baffle plate 48 and a second baffle plate 50 . This second chamber 68 communicates with the first chamber 66 by means of a return pipe or return passage 70 . The outlet pipe 32 also communicates with the second chamber 68 by means of a plurality of perforations 35 in a perforated portion 34 of the outlet pipe 32 . The outlet pipe 32 has an absorbent pod 36 of conventional design mounted therein.

The mode of operation of the silencer will most readily be understood by reference to FIG. 4 , which shows the flow of exhaust gases through the silencer 10 by means of arrows 72 . The exhaust gases enter the silencer 10 through the exhaust gas inlet 20 and enter the inlet chamber 64 . From here the gases pass along the first passage 56 to the first chamber 66 , which is adjacent to the acoustic resonator chamber 52 . The acoustic resonator chamber 52 provides a silencing function, as will be understood by those skilled in the art. The size, materials and other parameters of the low frequency resonator plate 54 and other components of the resonator chamber 52 are selected by the engine designer in accordance with the requirements of the particular engine with which the silencer 10 is to be used, in a manner understood by those skilled in the art.

The first chamber 66 serves to reverse the flow of the exhaust gases, which enter in a first direction 76 through the first passage 56 , are deflected through 90° in a second direction 78 and leave in a direction opposite to the first direction 76 through the return passage 70 . However, any burning carbon particles or sparks 74 carried by the exhaust gases continue under their own momentum in a substantially straight line through the connecting passage 62 and into the acoustic resonator chamber 52 . Because the acoustic resonator chamber 52 is a closed chamber having only one inlet 62 , there is not a substantial flow of exhaust gases into or out of the resonator chamber 52 , so that the carbon particles 74 remain in the chamber 52 . The resonator chamber 52 may be provided with an access cover (not shown) to allow periodic removal of accumulated carbon particles 74 during operation of the silencer. For best results the connecting passage 62 should be positioned proximate the second end 60 of the first passage 56 . It has been found that particularly good results are obtained when the connecting passage 62 is substantially axially aligned with the second end 60 of the first passage 56 .

As described above, the exhaust gases leave the first chamber 66 by means of the return passage 70 . They then enter the second chamber 68 , and pass through the perforations 35 in the perforated portion 34 of the outlet pipe 32 before exiting to the atmosphere through the exhaust gas outlet 30 . The operation of perforated pipes in silencers is well known to those skilled in the art, and is not described further here.

The invention provides a silencer in which the flow of exhaust gases is directed through a chamber 66 in the silencer 10 such that sparks in the exhaust gases are caused to enter the acoustic resonator chamber 52 and become trapped therein. The silencer according to the invention combines a spark arrester with a silencer, so that it is not necessary to provide a separate spark arrester for exhaust gases to flow through either before or after the silencer. This makes possible cost and assembly time savings, as well as saving space within the engine. The invention has particular benefit in power generating sets, where regulations may require spark control. In the engines associated with such power generating sets a single silencer according to the invention can replace a silencer and a separate spark arrester, offering significant cost savings.

It is to be understood that the particular arrangement of passages and chambers shown in the illustrated embodiment is by way of example only, and other arrangements of passages and chambers are envisaged. For example the first chamber 66 may be arranged to redirect the flow of exhaust gases by an angle other than 180° or by a series of intermediate angles, and the silencer may contain a greater or smaller number of passages and chambers in total. Although the illustrated embodiment shows only one acoustic resonator chamber 52 , there may be more than one such chamber. The acoustic resonator chamber 52 may take a form other than that illustrated in the Figures, and is not limited to a Helmholtz resonator. Other modifications to the invention are possible within the scope of the appended claims.