Abstract:
The invention relates to a marine wet exhaust system and a method for treating the exhaust from a marine engine. The system comprises a first conduit for receiving an exhaust flow including gaseous, liquid and particulate solid components, a separator for separating the liquid and particulate components from gaseous component, and a second conduit for expelling the gaseous component. A third conduit is provided for receiving from the separator the liquid and particulate solid components, which then pass to a filter for separating the particulate solid component from the liquid component, and the liquid component is discharged via a fourth conduit.

Description:
PRIOR PROVISIONAL APPLICATION 
     Applicant claims the benefit of the filing date of Provisional Application Ser. No. 60/055,115, filed Aug. 8, 1997. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention pertains to exhaust systems for water craft, and more particularly to improved marine wet exhaust systems for reducing the emission of particulate materials in the exhaust flows of marine engines. 
     2. Description of the Related Art 
     The internal combustion engines commonly used to power watercraft generate power through the rapid combustion of organic fuels and the expansion of the combustion products against pistons coupled to a drive shaft. The combustion products typically include particulate materials capable of polluting the surrounding air or water when released. The periodic combustion, expansion and discharge of the combustion products also produces undesirable heat and noise in the exhaust flow from the engine. 
     Internal combustion engines utilized in watercraft typically use the water supporting the craft for cooling purposes. The water is drawn into the craft and circulated through an engine cooling jacket or engine coolant heat exchanger. The water is then commonly injected into the exhaust system to cool the combustion products so that they might be safely discharged through the hull of the craft without presenting a fire hazard. Accordingly, a marine wet exhaust system must handle not only exhaust gases, but also the waste cooling fluid or water which is injected into the exhaust system. 
     In addition to safely handling exhaust gases and waste cooling water, a marine wet exhaust system should muffle or attenuate the exhaust noise generated by operation of the marine engine. Muffling of exhaust noise from marine engines has been handled in a number of ways. For example, the exhaust may be discharged below the water level. In outboard engines and in inboard/outdrive installations the exhaust is sometimes routed through the drive unit so that the exhaust gas and waste cooling water are discharged through or adjacent the propeller driving the craft. An exhaust system including a water separator for use in outboard drive units with exhaust routed through the propeller under the water line is disclosed in North et al., U.S. Pat. No. 3,759,041. 
     Mufflers are often placed along the exhaust conduit running between the engine and the exhaust discharge to attenuate the exhaust noise. One such example is shown in Harbert, U.S. Pat. No. 5,022,877. 
     Often, marine muffler designs are closely akin to the mufflers used on automobiles, but are constructed of materials such as fiberglass which can better tolerate the marine environment. While such mufflers are popular in the boating industry, many do not provide good attenuation of the noise generated by marine engines. 
     Furthermore, such mufflers often do not adequately separate water from the exhaust gas, even if they are designed to perform any water separation at all. The engine and muffler are often mounted amidship and located as far as 30 ft. to 40 ft. from the discharge. At these lengths it is difficult to maintain an overall downward grade necessary to drain the waste coolant water separated from the exhaust flow. In practice, the exhaust conduit leading from the muffler to the discharge may curl up-and-down as it crosses various sections of the boat, creating traps where water may accumulate and constrict the exhaust flow. 
     Even among those devices which do separate cooling water from the exhaust flow, it does not appear that any provision has been made to separate particulate materials from either the cooling water or the exhaust flow before the cooling water and exhaust are discharged into the surrounding water and the atmosphere. 
     Catalytic converters have been used in land vehicles to adsorb or otherwise remove pollutants from automotive exhaust flows. Such devices are less practical in marine craft, however, inasmuch as the very high temperatures necessary to the reduction processes in the converters cannot be tolerated in the less efficiently ventilated engine spaces in water craft. 
     Consequently, there remains a need for a marine wet exhaust system capable of both attenuating exhaust noise and separating particulate material before the cooling water and the exhaust are discharged. 
     SUMMARY OF THE INVENTION 
     This need is addressed by means of the marine wet exhaust system of the present invention. The marine wet exhaust system of the present invention includes a centrifugal water separator having a cooling water outlet in series with a filter for removing particulate materials. 
     The structure of the centrifugal separator is not critical to the present invention. Nonetheless, a preferred centrifugal water separator is a combined muffler/water separator of the type described in U.S. Provisional Application No. 60/003,073, filed Aug. 31, 1995, and U.S. patent application Ser. No. 08/703,346, filed Aug. 26, 1996, the disclosures of which are incorporated by reference. The preferred combined muffler/water separator comprises a generally cylindrical housing having an inlet structure for inducing the exhaust flow to rotate about a longitudinal axis of an interior of the housing. A first outlet positioned along the axis conducts dried exhaust gas from the housing while a second outlet spaced from the first outlet drains water (and the entrained particulate materials) from the housing. Preferred inlet structures include tangential inlets and inlets near which baffle or vane structures are mounted for deflecting the exhaust flow along an inner wall of the housing. 
     The structure of the filter is not critical to the present invention. Nonetheless, the preferred filter is a conventional fibrous-type filter for separating and retaining particulate materials larger than a pre-selected mesh size. The preferred filter includes a removable filter cartridge and a holding tank for retaining the particulate materials. The preferred holding tank includes means such as an opening for access to the removable filter and to the stored particulate materials. 
     The marine wet exhaust system is designed so as to separate the particulate materials from the exhaust flow with the waste cooling water and then filter the particulate materials out of the cooling water as the cooling water flows toward a water drain below the water line. The preferred muffler/water separator is designed such that cooling water and particulate materials are removed near the inner wall of the separator housing. The particulate materials entrained in the separated cooling water flow downwardly into the filter, in which the particulates larger than the pre-selected mesh size are separated and retained for later disposal. Ideally, no significant quantity of particulate materials larger than the pre-selected mesh size will be released into the environment with the exhaust gas or cooling water. 
     In an especially preferred form, the marine wet exhaust system of the present invention also comprises a first exhaust conduit for conducting exhaust gas from the marine engine to the muffler/water separator; a water injector for injecting droplets of water into the first exhaust conduit; a second exhaust conduit for receiving dried exhaust gas from the muffler/water separator and expelling the exhaust gas to the environment; a cooling water conduit for conducting the separated cooling water and the entrained particulate materials to the filter; and a water drain for discharging the filtered cooling water, preferably below the water line. 
    
    
     Therefore, it is one object of the present invention to provide a marine wet exhaust system capable of separating particulate materials from the exhaust flow. The invention will be further described in conjunction with the appended drawings and following detailed description. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view of the marine wet exhaust system of the invention; 
     FIG. 2 is a side sectional view of a first embodiment of a preferred combined marine wet muffler and water separator for the marine wet exhaust system; 
     FIG. 3 is a top sectional view of the preferred combined marine wet muffler and water separator of FIG. 2; 
     FIG. 4 is a side sectional view of a second embodiment of a preferred combined marine wet muffler and water separator for the marine wet exhaust system of FIG. 1; 
     FIG. 5 is a top sectional view of a third embodiment of the preferred combined marine wet muffler and water separator for the marine wet exhaust system of FIG. 1; 
     FIG. 6 is a side sectional view of the preferred combined marine wet muffler and water separator of FIG. 5; and 
     FIG. 7 is a schematic side view of a preferred filter for the marine wet exhaust system of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring initially to FIG. 1 of the drawings, an engine  10  for rotating a drive shaft  12  (shown partially in phantom) is provided with a marine wet exhaust system  14  for treating and expelling exhaust gas generated by the engine  10 . The marine wet exhaust system  14  includes a first exhaust conduit or first conduit  16  for receiving exhaust gas from an engine exhaust manifold  18 ; a water injection tube  20  (shown partially in phantom) for injecting waste coolant water from the engine  10  into the first exhaust conduit  16  to cool the exhaust gas; a combined marine wet muffler and water separator (also referred to as a “muffler/water separator”)  22  for attenuating exhaust noise and separating the waste coolant water from the exhaust flow; a second exhaust conduit or second conduit  24  (shown partially in phantom) for expelling the exhaust gas; a coolant water conduit or third conduit  26  for conducting waste cooling water (and entrained particulate materials) away from the muffler/water separator  22 ; a filter  28  for removing particulate materials from the cooling water received from the coolant water conduit  26 ; and a water drain or fourth conduit  30  for expelling filtered waste coolant water. 
     Since the preferred muffler/water separator  22  efficiently separates the waste coolant water from the exhaust gas, the path and grade of the second exhaust conduit  24  are not critical and the second exhaust conduit  24  may discharge the exhaust either above the water line  32  (as shown in FIG. 1) or below. The efficiency of the preferred muffler/water separator  22  reduces the likelihood that water will collect at bends in the second exhaust conduit  24 , thereby blocking or partially blocking the exhaust flow through the conduit  24 . 
     Preferably, the water drain  26  discharges the waste cooling water below the water line  32 . In an especially preferred embodiment, the cooling water conduit  26 , the filter  28  and the water drain  30  are positioned so as to maintain a uniformly sloping downward grade to promote the drainage of the cooling water from the marine wet exhaust system  14 . If additional force is required to propel the cooling water through the filter  28 , a holding tank and pump  27  is positioned across the cooling water conduit  26  upstream of the filter  28 . 
     While the muffler/water separator  22  also attenuates the exhaust noise, a secondary muffler  34  (shown in phantom) may be positioned across the second exhaust conduit  24  to provide additional attenuation. The secondary muffler  34  may be any one of those that are commercially available, including so-called “dry mufflers.” Exemplary mufflers are disclosed in U.S. Pat. Nos. 5,196,655 to Woods and 4,713,029 to Ford, the disclosures of which are incorporated by reference. 
     As best shown in FIGS. 2 and 3, a first embodiment of the preferred muffler/water separator  22  includes a generally cylindrical housing  40  made up from a cylindrical wall  42  and a pair of end caps  44  and  46  (FIG. 2) affixed to the cylindrical wall  42 . As shown in FIG. 2, a transverse or calming baffle  48  is positioned across the interior of the housing  40  so as to divide the housing interior into a first chamber  50  adjacent the cap  44  and a second chamber  52  adjacent the cap  46 . The cap  44  defines a first outlet  54  leading from the first chamber  50  while the cap  46  defines a second outlet  56  leading from the second chamber  52 . A first pipe  58  is secured through the first outlet  54  so that the first pipe  58  opens through a mouth  60  into the first chamber  50 . A second pipe  62  is secured adjacent the second outlet  56 . 
     As shown in FIG. 3, an inlet structure  70  is provided in communication with an inlet pipe  72 . The inlet structure  70  comprises an outer wall or wall member  74 ; an inner wall or wall member  75 ; and an angled baffle or baffle structure  76 . 
     The outer wall  74  and the inner wall  75  of the inlet structure  70  are spaced in parallel relation to each other relative to an inlet longitudinal axis  77  and define a channel therebetween. The angled baffle  76  is contiguous with the inner wall  75  and has a trailing edge  83  (FIG. 2) which extends toward the outer wall  74  to define an orifice opening  81 . The angular disposition of the baffle  76  relative to the outer wall  74  and the restricted opening  81  help to increase the velocity of the exhaust gas (and of the entrained water droplets and particulate materials) as it enters the separator  22 . This increased velocity facilitates a swirling pattern to this suspension so as to induce centrifugal separation of the cooling water and the particulate materials from the exhaust gas. 
     As shown in FIG. 2, the trailing edge  83  of the baffle  76  has an inwardly curving, parabolic shape which also has been found helpful in imparting the desired swirling pattern to the fluid mixture admitted through inlet pipe  72 . 
     In use, exhaust gas, entrained water droplets and entrained particulate materials enter the housing through the inlet structure  70  and spiral downwardly about a housing longitudinal axis  90  toward the calming baffle  48 . As the exhaust flow spirals, the relatively heavy water droplets and particulate materials spiral away from the axis  90  toward the cylindrical wall  42 . 
     The exhaust gas enters the mouth  60  of the first pipe  58  near the axis  90  and flows out of the housing  40  through the first outlet  54 . Meanwhile, the cooling water and entrained particulate materials move downwardly through apertures  92 ,  94 ,  96 ,  98  (FIG. 3) that are provided in the transverse or calming baffle  48 . The number and arrangement of the apertures may, of course, be varied provided that adequate area is provided for communication of the first chamber with the second chamber  52 . The separated cooling water and entrained particulate materials exit the housing  40  through the second pipe  62  disposed in the second chamber. Preferably, the cooling water pools over the second outlet  56  to prevent exhaust gas from entering the second pipe  62 . 
     A second embodiment of the water separator  22 ′ is shown in FIG.  4 . Here, water separator  22 ′ includes housing  40 ′ made up from a cylindrical wall  42 ′, an end cap  44 ′ and a bottom flange  46 ′. As with the embodiment  22  of FIGS. 2 and 3, a transverse or calming baffle  48 ′ is welded across the interior of the housing  40 ′ so as to divide the interior into a first chamber  50 ′ adjacent the cap  44 ′ and a second chamber  52 ′ adjacent the flange  46 ′. Unlike the embodiment shown in FIGS. 2 and 3, the flange  46 ′ of the separator  22 ′ includes first and second outlets  54 ′ and  56 ′ leading from the second chamber  52 ′. A first pipe  58 ′ is welded through the first outlet  54 ′ so that the first pipe  58 ′ passes through the transverse baffle  48 ′ and opens through a mouth  60 ′ into the first chamber  50 ′. A second pipe  62 ′ is welded adjacent the second outlet  56 ′ radially outwardly from the first pipe  58 ′ and the first outlet  54 ′. 
     The housing  40 ′ of the FIG. 4 embodiment has an inlet structure  70 ′ similar in structure to the inlet structure  70  of the embodiment of FIGS. 2 and 3. In use, exhaust gas, entrained water droplets and entrained particulate materials enter the housing  40 ′ through the inlet structure  70 ′ and rotate about the longitudinal axis  90 ′ of the housing  40 ′ toward the calming baffle  48 ′. As the exhaust flow rotates, the relatively heavy water droplets and particulate materials spiral away from the axis  90 ′ (FIG. 2) toward the cylindrical wall  42 ′. 
     The exhaust gas enters the mouth  60 ′ of the first pipe  58 ′ near the axis  90 ′ and below cap  44 ′ and flows downwardly out of the housing  40 ′ through the first outlet  54 ′. Meanwhile, the cooling water and the particulate materials move downwardly through apertures (not shown) in the transverse baffle  48 ′ into the second chamber  52 ′, from which they exit the housing  40 ′ through the second pipe  62 ′. 
     A third embodiment of the preferred muffler/water separator  122  which is preferably positioned horizontally in a wet marine exhaust system such as that shown at  14  (FIG. 1) is shown in FIGS. 5 and 6. The muffler/water separator  122  comprises a housing  140  including a cylindrical wall  142  and a pair of end caps  144  and  146  (FIG. 6) attached to the cylindrical wall  142 . As shown in FIG. 6, inlet structure  170  is provided in communication with an inlet pipe  172  and is concentric with a housing-longitudinal axis  190 . The inlet structure  170  includes the end cap  144 , a vane structure  147  and a calming shield  148 . 
     The end cap  144  is substantially formed of a truncated cone diverging outwardly from the inlet pipe  172  toward the cylindrical wall  142 . The end cap  146  includes a first outlet  154  leading from within the housing  140 . A first pipe  158  is attached through the first outlet  154  coaxial to the housing longitudinal axis  190  and opens through a mouth  160  into the housing  140 . A second outlet  156  leading from within the housing  140  is located in the cylindrical wall  142  adjacent the end cap  146  such that the second outlet  156  may be positioned at the lowest point of the housing  140  when the muffler/water separator  122  is installed. A second pipe  162  is vertically disposed and attached to the cylindrical wall  142  adjacent the second outlet  156  below the first pipe  158  and the first outlet  154 . 
     As shown in FIG. 5, the vane structure  147  is attached to the end cap  144  and preferably includes a series of blades  202 ,  204 ,  206  and  208  extending radially outwardly from the housing longitudinal axis  190 . The span of each blade extends parallel to a center axis  212 ,  214 ,  216  and  218  oblique to the housing longitudinal axis  190 . 
     Each blade  212 ,  214 ,  216 ,  218  preferably has a finite angle of attack to facilitate a swirling pattern in the exhaust flow entering the muffler/water separator  122  to induce centrifugal separation of the exhaust gas from the cooling water and particulate materials. The number and arrangement of the blades  212 ,  214 ,  216 ,  218 , as well as the blade profiles, may be varied provided that adequate swirling motion is imparted to the exhaust flow. 
     As shown in FIG. 6, the calming shield  148  is substantially conical, having first and second ends  220 ,  222  spaced coaxially along the housing longitudinal axis  190 . The first end  220  is supported by the vane structure  147  while the second end  222  rests adjacent the mouth  160 . The diameter of the second end  222  is at least as large as the inner diameter of the mouth  160  so as to prevent direct fluid flow from the inlet structure  170  to the mouth  160 . 
     In operation, the exhaust gas, entrained water droplets and entrained particulate materials enter the housing through the inlet structure  170 . The vane structure  147  imparts a swirling motion to the exhaust flow. As the exhaust flow spirals along the inner wall of the housing  140 , the relatively heavy water droplets and particulate materials spiral away from the housing longitudinal axis  190  toward the cylinder wall  142 . 
     The exhaust gas exits the muffler/water separator  122  through the first outlet  154  and the first pipe  158 . The extracted water (and the entrained particulate materials) drops toward the bottom of the housing  140  and exit the muffler/water separator  122  through the second outlet  156  and the second pipe  162 . 
     In each of the three embodiments  22 ,  22 ′ and  122 , the tortuous flow paths combined with the effects of the water droplets in the exhaust gas serve to attenuate exhaust noise. It is believed that the housings  40 ,  40 ′ and  140  may be “tuned” to further attenuate the exhaust noise. 
     As shown in FIG. 7, the preferred filter  28  is a fibrous-type filter including a filter housing  200  at least partially surrounding a removable filter cartridge  202 . A filter inlet pipe  204  communicates with cooling water conduit  26  while a filter outlet pipe  206  communicates with the water drain  30 . An access opening  210  in the housing  200  provides access to the filter cartridge  202  for cleaning or replacement of the cartridge  202 . 
     In use, the separated cooling water and the entrained particulate materials flow into the filter housing  200  through the filter inlet pipe  204 . The particulate materials are retained by the filter cartridge  202 . The cooling water itself flows through the filter cartridge  202  and enters the water drain  30  through the filter outlet pipe  206 . The filter cartridge  202  is periodically cleaned or replaced so that the accumulated particulate materials do not obstruct the flow of cooling water toward the water drain  30 . 
     As suggested by the foregoing, the marine wet exhaust system  14  of the present invention serves to separate and collect particulate materials from the exhaust flow, thereby inhibiting the release of these particulate materials to the environment. Particulate materials entrained in the exhaust gas entering the marine wet exhaust system  14  through the first exhaust conduit  16  are separated with the waste cooling water in a centrifugal separator such as the muffler/water separator  22 . The particulate materials exiting the muffler/water separator  22  with the separated waste cooling water are themselves separated and collected in the filter  28 . The filtered cooling water is discharged through the water drain  30  while the separated exhaust gas is expelled through the second exhaust conduit  24 . The particulate materials collected in the filter  28  may be disposed of in an environmentally acceptable manner. 
     In theory, the same result could be achieved by interposing a filter (not shown) across the exhaust system upstream of the water separator. In the current state of technology, however, this arrangement is not believed to be commercially practical. A filtering system capable of handling the flow volume of the suspension of water droplets in the exhaust upstream of the water separator would be too large to be easily accommodated in the limited space available in a watercraft. In addition, a filtering system of the necessary size may inhibit the efficient operation of the marine engine  10 . 
     Having described the invention in detail and by reference to preferred embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the appended claims.