Acoustics – Sound-modifying means – Muffler – fluid conducting type
Patent
1997-01-23
1998-10-20
Dang, Khanh
Acoustics
Sound-modifying means
Muffler, fluid conducting type
181235, 181260, F01N 708
Patent
active
058249702
DESCRIPTION:
BRIEF SUMMARY
This invention relates to exhaust silencers for internal combustion engines and in particular relates to the silencing of marine and other installations where water is injected into the silencer.
An exhaust system for an internal combustion engine will comprise a pipe connected by a manifold to the exhaust ports of the engine and will have one or more silencers positioned along its length. The silencers reduce the velocity of the exhaust gases and reduce the noise emitted. At the same time, the exhaust gas pressure (known as the back pressure) is increased within the exhaust pipe.
A silencer typically comprises a box which is 3 to 5 times the diameter of the exhaust pipe. Inside each silencer box there is an arrangement of baffle elements positioned to confront the exhaust gas flow and reduce the speed of this flow. Such arrangements may increase the back pressure to the point where engine efficiency is prejudiced. To enable back pressures to be maintained at appropriate levels, the silencers may need to be quite large and as such may intrude into the engine compartment. The silencer housing has to be securely fixed to the hull, e.g. in order to prevent reverberation, and the necessary fixing stays require additional space. In the case of marine engines, in particular, engine cooling water is often injected into the exhaust gases which produces a decrease in gaseous volume and further reduces the gas velocity.
An object of the invention is to provide an effective silencing system having compact dimensions and which is of such a size that it can be contained in the exhaust pipe from the engine.
A further object of the invention is to provide a silencing system which produces a substantial reduction in exhaust noise while maintaining exhaust back pressure within acceptable limits.
In accordance with the invention there is provided an exhaust silencer having a high ratio of internal surface area to cross-sectional area.
In one form of the invention the silencer comprises at least one baffle element situated within a cylinder, wherein the baffle element is inclined towards the axis of the cylinder and wherein the baffle element has a number of apertures therethrough.
According to a more preferred aspect there is provided a silencer for a water-cooled exhaust gas system which comprises a tubular silencer element located within an exhaust duct, said silencer element comprising a baffle having apertured surfaces inclined to the flow of exhaust gas in the duct.
In a preferred embodiment the silencer has a tubular, tapering shape and may, for example, comprise a conical arrangement (including a truncated conical shape) wherein an axis of the cone lies in the direction of the exhaust gas flow. Where the silencer has a tapering, tubular shape, the taper may be continuous or stepped. Along the surface of the cone are arranged apertures which provide a baffle arrangement but, by virtue of the angled conical surface, the back pressure is maintained within acceptable levels.
In another aspect of the invention there is provided a silencer baffle of a shallow V section configuration in longitudinal section, wherein the surfaces of the baffle have a number of apertures of varying sizes.
Preferably, the apertures are larger in size or total area towards the top of the body of the silencer. This tends to cause the water in the exhaust gases to pass more readily through the silencer. The desired degree of back pressure is achieved by selecting the proportion of open area in the silence body. By `proportion of open area` is meant the sum of the total area of the apertures as a proportion of the total surface area of the silencer surface. Generally, a proportion of 10 to 40%, preferably 25 to 35% is employed for most engines.
In order to further improve the mixing of exhaust gases and water and promote the escape of water through the silencer apertures, one or more weir plates can be fitted to the silencer. A weir plate typically extends generally axially to the tubular body of the silencer. An additional, substantially radial p
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patent: 4825652 (1989-05-01), Curran
patent: 5123501 (1992-06-01), Rothman et al.
patent: 5661272 (1997-08-01), Iannetti
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