Marine engine silencer

Details Marine engine silencer Marine engine silencer

2001-04-27

2003-07-15

Dang, Khanh (Department: 2837)

Acoustics

Sound-modifying means

Muffler, fluid conducting type

C181S262000, C181S272000

Reexamination Certificate

active

06591939

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to devices and methods for silencing engines. More particularly, the invention relates to devices and methods for silencing marine engines. Still more particularly, the invention relates to devices and methods for silencing marine engine wet exhaust gas using water separation techniques.
BACKGROUND OF THE INVENTION
The present invention belongs to the general class of internal combustion engine exhaust silencers or mufflers that may be characterized as attempting to achieve a “cold, wet/dry” condition, as contrasted with a “cold, wet” or “hot, dry” conditions, for extracting acoustic energy from exhaust gas. A “cold, wet/dry” condition is one in which a liquid coolant, typically water, first has been added to the exhaust gas of an engine, typically a marine engine, in order to reduce the temperature of the exhaust gas (the “cold, wet” stage), and then the water has been separated from the gas (the “dry” stage) in preparation for further reduction of the acoustic energy of the “dry” gas. The reduction in temperature is desireable for two reasons. First, the lower temperature reduces the acoustic velocity in the gas, that is, the speed at which sound propagates through the gas. The lower the acoustic velocity, the smaller the chamber that may be used to achieve a given reduction in acoustic energy, or noise. Alternatively, greater noise reduction can be achieved in a given space. Second, as the exhaust gas cools, it becomes denser. Thus, the dynamic pressure of the gas passing through a tube of a given size is reduced, resulting in a reduction in the pressure drop through the tube, and, consequently, a smaller “back pressure” effect. Back pressure is undesireable because it may interfere with the efficient operation of the engine or may damage it.
One undesireable attribute of cold, wet marine-exhaust silencers is that the reduction in back pressure achieved by water cooling, as just described, is offset as a consequence of the presence of water mixed with the gas. The denser net mass of the inhomogeneous water-gas mixture, as compared to a cold, wet/dry system in which the water has been removed, or as compared to a hot, dry system in which water was never added, results in an increase in back pressure. In order to avoid excessive back pressure, water-gas velocities in cold, wet exhaust systems are generally held to a range of 20 to 50 feet per second (fps). This velocity restriction places requirements on the sizes of pipes, which in some cases makes the silencers larger or less effective than desirable. Moreover, whereas in a “dry” gas silencer, i.e., either a “hot, dry” or “cold, wet/dry” silencer, the “dry gas” may be conducted to a remote discharge point using a routing of both upward and downward pitched piping, such routing is often impracticable in a “wet” silencer because of an unacceptably large increase in back pressure for upward pitches and for corners. Because the appropriate discharge of exhaust gas from the vessel may be an important safety and convenience consideration, the limitation on discharge-pipe routing imposed by mixed water and gas discharge can impose a serious design problem or constraint.
In general, prior art marine-exhaust silencers have not optimally balanced the benefits of water cooling with the need to reduce back pressure while minimizing the size of the silencer. More specifically, some prior art marine-exhaust silencers attempt to operate in a “cold, wet/dry” condition but fail to achieve sufficient separation of the water from the gas. Other designs improve on such separation at the expense of large size and reduced flexibility of configuration.
For example, U.S. Pat. Nos. 5,022,877 and 4,019,456 to Harbert rely on gravitational effects and condensation to separate the exhaust gas from the water coolant, thus only partially achieving a “cold, wet/dry” condition. Greater separation using these means could be achieved, but at the expense of increasing the size of the silencer; i.e., by providing a larger free surface of the gas-water mixture through which the gas could rise, or at the expense of increased back pressure due to elaborate flow control. U.S. Pat. No. 4,917,640 to Miles employs such an approach by providing a more complex configuration of tubular separation chambers. Another approach, disclosed in U.S. Pat. No. 5,588,888 to Maghurious, is to agitate the wet mixture of exhaust gas and water in order to atomize the water droplets in the mixture and thereby increase the absorption of acoustic energy by the water mass. This approach is a variation of a cold, wet design in that it relies upon reduction in the acoustic energy of the exhaust gas before it is fully separated from the water, thereby incurring the penalties associated with cold, wet systems already noted.
Other techniques use waterlift silencers such as that described in U.S. Pat. No. 3,296,997 to Hoiby et al. In the Hoiby device, the mixture of cooling water and exhaust gas is introduced into a chamber through an inlet pipe. An exit tube extends vertically through the top of the chamber. The bottom of the exit tube is spaced from the bottom of the chamber so that the mixture may enter the bottom of the tube and be expelled. As described by Hoiby, the gas separates from the water in the chamber and, when the dynamic pressure in the chamber is such as to force water up the outlet tube, the level of the water surface in the chamber reduces to an extent allowing direct expulsion of gas through the tube. The kinetic energy of the gas escaping through the tube partially atomizes the water, according to Hoiby, and entrains the atomized liquid particles. The entrained liquid is thus carried, along with the exhaust gas, up through the exit tube. A similar design is shown in U.S. Pat. No. 5,554,058 to LeQuire. U.S. Pat. No. 2,360,429 to Leadbetter is one type of silencer that uses water to silence exhaust gas and includes multiple chambers.
U.S. Pat. No. 6,024,617 to Smullin et al., incorporated herein by reference in its entirety, discloses a silencer wherein a fluid mixture enters a separation chamber having an in-flow port for receiving the fluid mixture, and an out-flow port for the separated exhaust gas, and a liquid-coolant out-flow port. The separation chamber contains a separation plate having at least one dynamic separator for separating the exhaust gas from the liquid coolant by inertial or frictional effects, or both, using a series of vanes or a mesh pad.
Also, U.S. patent application Ser. No. 09/349,871 is incorporated herein by reference in its entirety. This application discloses using multiple lifting tubes, the height of the bottoms of different tubes can be differentially set, to allow the flow to be sequentially enabled in the different tubes for the purpose of generating sound attenuating benefits.
SUMMARY OF THE INVENTION
In one aspect of the invention, a silencer is disclosed that reduces the acoustic energy of a fluid mixture of a liquid coolant and of exhaust gas from an engine. The engine may be a marine engine. The silencer according to this aspect includes a receiving chamber that receives the fluid mixture, at least one lifting conduit; and a separation chamber. The lifting conduit has a receiving portion with a first opening and an expelling portion with a second opening. The receiving portion is fluidly coupled with the receiving chamber so that the fluid mixture enters the first opening from the receiving chamber and is lifted through the lifting conduit to the expelling portion. This lifting may be accomplished, at least in part, by dynamic effects. The separation chamber is fluidly coupled with the second opening of the lifting conduit, and has at least one interior surface. The at least one interior surface may include an extending member. The expelling portion of the lifting conduit is disposed so that fluid mixture expelled from the second opening is directed toward the at least one interior surface of the separation chamber. The at least one interior surface may be configured and arranged to dynamica

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