Marine Exhaust System With Catalyst

Abstract

A marine engine exhaust system is provided that utilizes a single catalyst housing through which exhaust gases from multiple heads of an exhaust system flow. A first conduit directs a first exhaust gas from a first engine head or exhaust manifold to the catalyst, and a second conduit directs a second exhaust gas from a second engine head or exhaust manifold to the catalyst. The first and second conduits may be separate or may merge prior to the catalyst. The catalyst includes a housing and at least one substrate to convert the first and second exhaust gases into processed exhaust gas. A third conduit directs the processed exhaust gas away from the catalyst. At least one pre-sensor may be located upstream of the catalyst housing, and at least one post-sensor may be located downstream of the catalyst housing.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to provisional application having U.S. Patent Application Ser. No. 62/129,225, filed on Mar. 6, 2015, the contents of which are incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to a marine engine exhaust system that includes a catalyst for reducing emissions of the exhaust system. More particularly, the present application includes a marine engine exhaust system that may include a single catalyst housing having at least one substrate that receives and processes exhaust from multiple heads of a marine engine.

BACKGROUND

Marine engines used to power watercraft, such as a boat, are susceptible to being damaged through introduction of water. Water injection can occur in a marine engine in several different manners. Although four such manners will be discussed it is to be understood that other types are possible. The first mechanism is through wave action. Here, a surge of water enters the exhaust and proceeds into the engine. The surge of water is produced from an external source such as the wake of a passing boat, inclement weather or turning of the watercraft. Water intrusion may also occur when a boat is put in unusual attitudes, for example a sport fishing boat backing up in heavy seas in which water is forced into the exhaust track in sufficient volume to enter the engine.

The second way in which water can be introduced into the marine engine is through by-products of the combustion process. As the gasoline/air fuel mixture undergoes combustion during the operation of the engine, a chemical reaction takes place that may produce moisture within the engine components, which may negatively affect engine performance.

A third way of introducing water into the marine engine is by way of condensation. In general, condensation may occur in the system due to the temperature differential of a hot engine and ambient air, and can cause engine malfunction. Marine engines must be cooled, such as with water jacketing, to keep the engines from overheating, since they must be safely designed in order to be enclosed in a watercraft. This cooling creates a lower temperature than land based engines. Condensation may occur through dissimilar cooling rates of various components, which may occur during cooling or subsequent to shutting down the engine. Temperature differences between daytime and nighttime may also cause condensation to form in the engine exhaust system. Further, condensation may also result from having too low of an operating temperature of the exhaust system.

The fourth way through which water may be introduced into a marine engine is through reversion. Reversion occurs when the marine engine is idling and, due to camshaft timing overlap, the cooling water from the exhaust manifold/elbow actually migrates or “walks” backward in the exhaust track to the engine. Reversion is the backwards flow of exhaust gases during the time period in which both intake and exhaust valves are simultaneously open, and primarily occurs when the engine runs at idle speed or slightly above idle speed.

Water injected into a marine engine typically damages components, such as exhaust valves, which prevents the cylinder with the damaged exhaust valve from correctly sealing. This damaged cylinder then causes water to be pulled into the engine through the corroded exhaust valve. This water is redistributed to the rest of the engine and causes its ultimate failure. The control of water injection is a primary objective of watercraft and engine manufacturers and is especially challenging considering the environment in which the watercraft is deployed.

Design of marine engine exhaust systems is further complicated by the need to reduce emissions from marine engines as may be required by government regulations. Current marine engine designs typically employ a pair of catalysts that remove or reduce certain impurities or pollutants from the exhaust gas streams emitted from either side of an inboard engine that has two cylinder heads. The engine could include two, four, six, eight, ten cylinders and these cylinders are typically divided so that half are on one side of the engine, and the other half on the other side of the engine. A standard design may include, for example, four runners associated with the individual exhaust ports on each side of the engine that includes a total of eight cylinders. Each side has an engine head, which may have an exhaust manifold that receives the output from the four runners per side, and output from the exhaust manifold on each side is in the form of a single common exhaust outlet on each side of the manifold.

The catalysts in marine engine exhaust systems are typically located downstream from the exhaust outlets on each engine head or exhaust manifold, such that each exhaust manifold from each engine head has its own catalyst. For instance, one catalyst is located downstream from the right side exhaust manifold outlet, and the other catalyst is located downstream from the left side exhaust manifold outlet. The catalysts could be behind the engine, on top of the engine, on the right or left sides of the engine, or at any other location relative to the engine. Water that enters the marine engine exhaust system will also interfere with the proper functioning of the left and right side catalysts and associated sensors because the catalysts and sensors cannot operate correctly if they are wet. Water introduced into the catalysts will cause their eventual failure. Since the catalysts are located downstream from the engine and the exhaust manifolds, they are generally closer to the introduction point of water into the system, thus making the overall system more susceptible to failure.

The use of two catalysts in existing marine exhaust systems requires that two catalyst monitoring systems be employed. The first catalyst will require a first oxygen sensor be located before, or upstream of the first catalyst to measure the exhaust gas before entering the first catalyst, and a second oxygen sensor to be located after, or downstream of the first catalyst to acquire data about the exhaust gas exiting the first catalyst. The second catalyst will likewise require its own pre- and post-oxygen sensors to measure properties of the exhaust gas both entering and exiting the second catalyst, and thus a second catalyst monitoring system may also be needed.

Single catalyst exhaust systems are employed in automotive engines, but these automotive exhaust designs are not readily applicable to marine engines. The manufacture and/or marinization of engines for marine use in watercraft require unique considerations that are not relevant to the automotive industry. For example, inboard marine engines and exhaust systems are encased within the hull of the boat during use, so spatial limitations and overheating issues are primary concerns for marine exhaust system design. Automotive exhaust systems, on the other hand, are open to the air underneath the automobile, and so do not have the same heat concerns. Moreover, automotive exhaust systems are not located in immediate proximity to the engine, but rather extend under the body of the automobile. Marine exhaust systems, on the other hand, must be contained within the same limited space as the engine and transmission, and therefore packaging and interference with other components becomes a critical concern. Finally, marine engines and exhaust systems are intended for use on the water, and so water infiltration is a primary concern in the marine engine field. Automobiles, conversely, are designed for land-based use where water hazards are less extensive. For these and many other reasons, marine and automotive engines and exhaust systems are not interchangeable.

Although current systems are capable of reducing emissions in marine engine exhaust systems, there remains room for variation and improvement within the art.

SUMMARY

The present invention is directed to a marine engine exhaust system for a dual-head or multi-head engine utilizing a single catalyst for processing all of the exhaust gas generated during combustion. Specifically, the present exhaust system includes a first conduit in fluid communication with exhaust gases exiting from a first engine head, and a second conduit in fluid communication with exhaust gases exiting from a second engine head. In at least one embodiment, the exhaust system includes a first exhaust manifold at the first engine head, and a second exhaust manifold at the second engine head. The exhaust manifolds collect exhaust gases from the respective engine heads, and may connect to the first and second conduits, respectively.

A catalyst is also in fluid communication with the first and second exhaust gases, which are directed from the engine heads to the catalyst by the first and second conduits. In some embodiments, the conduits may combine to form a merged conduit before joining with the catalyst. In other embodiments, the first and second conduits each join the catalyst. The conduits may connect to the catalyst at any surface, such as the top, bottom, or sides of the catalyst.

The catalyst has a housing and at least one substrate positioned therein in contacting engagement with the exhaust gases so as to convert the exhaust gases as they pass therethrough for emissions purposes. The catalyst may include one substrate or multiple substrates, but all substrates are located within the same housing.

The system further includes a third conduit in fluid communication with at least one processed gas exiting from the catalyst. Such processed gas is the result of the catalytic conversion reaction performed by the substrate(s) as the exhaust gases pass therethrough. The third conduit conveys the processed gas away from the engine for expulsion from the watercraft. In at least one embodiment, the system may include a third and fourth conduits in fluid communication with the processed gas(es). The third conduit, and fourth conduit in appropriate embodiments, may connect to the catalyst at any surface, such as the top, bottom, or sides of the catalyst, and in at least one embodiment are located opposite of the first and second or merged conduit.

In some embodiments, the present exhaust system includes at least one pre-sensor located in monitoring engagement of the first and second exhaust gases, and may preferably be located upstream of the catalyst. The exhaust system may also include at least one post-sensor located in monitoring engagement of the processed exhaust gases, and may preferably be located downstream of the catalyst. The pre-sensor(s) and post-sensor(s) monitor the performance of the catalyst. Because the present invention includes only one catalyst housing, it is possible to have only one pre-sensor and one post-sensor, thereby providing a more efficient monitoring system.

The present exhaust system also contemplates the use of a water-cooled jacketing system to surround and cool the exhaust manifolds, conduits and catalyst. In such embodiments, the third conduit includes a cooling water introduction point at which water from the cooling system is permitted to mix with the processed exhaust gases. Preferably, this cooling water introduction system is located at a terminal end of the third (and fourth) conduits, and permits mixing with the cooling water just prior to expulsion from the watercraft. This positioning reduces the risk of water infiltration into the exhaust system and engine.

These and other features and advantages of the present invention will become clearer when the drawings and detailed description are taken into consideration.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth more particularly in the remainder of the specification, which makes reference to the appended Figs. in which:

FIG. 1 is a perspective view of one example of a marine engine exhaust system showing a pair of conduits entering the catalyst.

FIG. 2 is a perspective view of another example of a marine engine exhaust system showing a pair of conduits merging before entering the catalyst.

FIG. 3 is a perspective view of an example of a marine engine exhaust system showing the conduits entering the catalyst from the bottom and exiting from the top of the catalyst.

FIG. 4 is a schematic diagram of a marine engine exhaust system with a pair of conduits entering the bottom of the catalyst.

FIG. 5 is a schematic diagram of a marine engine exhaust system with a pair of conduits that merge exhaust gases before entering the bottom of the catalyst.

FIG. 6 is a schematic diagram of a marine engine exhaust system with a pair of conduits that enter the side of the catalyst.

FIG. 7 is schematic diagram of a marine engine exhaust system with a pair of conduits that enter the top of the catalyst.

FIG. 8 is a schematic diagram of a marine engine exhaust system with a pair of conduits that merge exhaust gases before entering the top of the catalyst.

FIG. 9 is a schematic diagram of a marine engine exhaust system with a pair of conduits that enter the side of the catalyst and output of the catalyst out of the bottom of the catalyst.

FIG. 10 is a schematic diagram of a marine engine exhaust system with a pair of conduits entering the side of the catalyst and a pair of conduits exiting the bottom of the catalyst.

FIG. 11 is a schematic diagram of a marine engine exhaust system with a pair of conduits entering the top of the catalyst and a pair of outlet conduits exiting the sides of the catalyst.

FIG. 12 is a cross-sectional schematic diagram of one example of a catalyst showing a single substrate.

FIG. 13 is a cross-sectional schematic diagram of another example of a catalyst showing multiple circular substrates within the housing.

FIG. 14 is a cross-sectional schematic diagram of another example of a catalyst showing multiple rectangular substrates within the housing.

Repeat use of reference characters in the present specification and drawings is intended to represent the same or analogous features or elements of the invention.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, and not meant as a limitation of the invention. For example, features illustrated or described as part of one embodiment can be used with another embodiment to yield still a third embodiment. It is intended that the present invention include these and other modifications and variations.

It is to be understood that the ranges mentioned herein include all ranges located within the prescribed range. As such, all ranges mentioned herein include all sub-ranges included in the mentioned ranges. For instance, a range from 100-200 also includes ranges from 110-150, 170-190, and 153-162. Further, all limits mentioned herein include all other limits included in the mentioned limits. For instance, a limit of up to 7 also includes a limit of up to 5, up to 3, and up to 4.5.

The present invention provides for marine engine exhaust system 10 that includes a catalyst 12 and limits or prevents water from damaging the engine 14 and the catalyst 12. The system 10 includes a single catalyst 12 that processes exhaust gases from multiple different engine heads or exhaust manifolds. The catalyst 12 includes a housing 70 and at least one substrate 72, and the exhaust gases 50, 52 from the first and second manifolds 16, 18 are both be directed through and treated by the substrate(s) 72 of the single catalyst 12 to remove pollutants therefrom. The resulting processed exhaust gas 80 can be subsequently merged with cooling water 46 upon exiting the exhaust system. The various components of the exhaust system 10 and conduits 20, 22, 24 and 26 can be water jacketed for cooling purposes of the system 10.

Accordingly, the present invention provides a more efficient marine exhaust system than previously known. The single catalyst housing 70 through which all the exhaust gases 50, 52 flow provides a single point for emissions processing. This translates to a reduction in the number of pre-sensors and post-sensors needed to monitor the exhaust gas and catalyst operation. The electrical wiring and harnesses are therefore also simplified since fewer sensors and other components are needed. It also simplifies and improves engine calibration and efficiency monitoring, since only one catalyst must be monitored.

Moreover, by cutting the number of catalysts in half, the present exhaust system reduces the chance for exhaust leaks by 50% and reduces the chance for coolant leaks by 50%, thus providing a more safe exhaust system. Having a single catalyst that processes all exhaust gases 50, 52 means that the exhaust manifolds are freed of individual catalysts. In current marine engine exhaust systems, each exhaust manifold typically has its own dedicated catalyst which is attached directly to the exhaust manifold. The attachment of the catalyst to the exhaust manifold creates a moment arm, or cantilever effect, which induces bolt stress on the exhaust manifold, leading to breakage over time. The current invention eliminates this mechanical stress by uncoupling the catalyst from the exhaust manifold and using only a single catalyst for all exhaust gases, regardless from which exhaust manifold they emanate.

The present marine engine exhaust system 10 may be used with any type of marine watercraft engine. For example, the present exhaust system 10 can be used with inboard engines, which are enclosed within the hull of a boat. Other arrangements are possible in which the marine engine exhaust system 10 is used in connection with an outboard engine, which is located external to the hull. The system 10 can also be used with a combination inboard/outboard engine, sometimes known as a stern drive.

For example, in FIG. 1, one embodiment of the exhaust system 10 of the present invention is shown in in conjunction with a marine engine 14. The exhaust system 10 of the present invention may be used with any size or power of engine. For instance, the exhaust system 10 can be utilized with engines having any number of cylinders or pistons, such as 4 cylinder, 6 cylinder, V-6 or V-8 engines. The cylinders may be positioned in any configuration throughout the engine, but most typically are present as equal numbers of cylinders on each side of the engine, which may be arranged vertically or at a slight angle or pitch within the engine block. The engine size can be any displacement, including but not limited to 5.1 liter, 5.7 liter, 6.0 liter, 6.2 liter, 8.1 liter or any other sized engine suitable for marine watercraft, including those intended for towing. The present exhaust system 10 is intended for use with combustion engines, such as gasoline or petrol-based engines, although under certain circumstances diesel engines may be used.

The upper portions of the cylinders on one side of an engine are referred to collectively as an engine head. FIG. 1 shows one embodiment of the system 10 from a perspective illustrating one side of the engine 14, showing a first engine head 86. A second engine head 88 on the opposite side of the engine 14 is also indicated. Exhaust gases from the individual runners of individual exhaust ports at the first engine head 86 are referred to here as a first exhaust gas 50. Similarly, on the other side of the engine, exhaust gases from the individual runners of the individual exhaust ports at the second engine head 88 form the second exhaust gas 52.

In at least one embodiment, as in the Figures, the exhaust system 10 includes a first exhaust manifold 16 that channels and combines the first exhaust gas 50 from the first engine head 86. Similarly, a second exhaust manifold 18 channels and combines the second exhaust gases 52 from the second engine head 88. Any type of exhaust manifold may be employed in the present exhaust system 10, as indicated by their schematic representation in FIGS. 1-3. For instance, the exhaust manifolds 16, 18 may be log manifolds, or may be pyramidal, linear, curved, “banana”, or tubular shaped, or any other configuration as enables the combination of exhaust gases from cylinders of the engine. Further, the exhaust manifolds 16, 18 may be made of any suitable material, including but not limited to metals such as stainless steel, ceramic, or other materials, and may be made by casting from a mold, welding, layering, plating, spray-coating, or other methods of manufacture typical for exhaust manifolds.

The exhaust system 10 includes a first conduit 20 in fluid flow communication with a first exhaust gas 50 exiting from a first engine head 86 such that the first exhaust gas 50 enters the first conduit 20 as it exits from the first engine head 86. Similarly, the system 10 also includes a second conduit 22 in fluid flow communication with a second exhaust gas 52 exiting from the second engine head 88. In some embodiments, the exhaust gases 50, 52 go directly from the cylinder exhaust port at the engine heads 86, 88 into the first or second conduits 20, 22, respectively. In other embodiments, as shown in FIGS. 1-3, the exhaust gases 50, 52 generated at the engine heads 86, 88 are collected in exhaust manifolds 16, 18 before being directed into the first or second conduits 20, 22, respectively.

“Conduit” as used herein means an elongate enclosed structure having two opposite open ends, defining a hollow interior extending through the length between the opposite open ends, so as to receive, convey and deliver fluids from one location to another over a distance. The conduits 20, 22 are preferably tubes, such as pipes, formed of a solid wall defining a hollow interior through which the fluids, such as exhaust gases 50, 52 are conveyed. They may be any length. The conduits 20, 22 may have any cross-sectional shape, such as circular, oval, square, rectangular, or irregular, although circular or oval may be preferable in some embodiments. The conduits 20, 22 may also be symmetrical or asymmetrical in cross-section. The conduits 20, 22 may have any diameter appropriate for the volume of exhaust gas 50, 52 to be transferred or conveyed therethrough. For example, the diameter of the conduit 20, 22 is large enough to allow movement of the volume of exhaust gases 50, 52 generated by the engine at a flow rate sufficient to permit clearance of the gases 50, 52 from the engine heads 86, 88 and catalytic conversion of the exhaust gases 50, 52, as described in greater detail below. Accordingly, the conduits 20, 22 may attach in sealing engagement to the engine heads 86, 88 or exhaust manifolds 16, 18 and may be aligned so that the hollow interior of the conduits 20, 22 meet up with the opening(s) of the engine heads 86, 88 or exhaust manifolds 16,18 for transfer of exhaust gases 50, 52.

The conduits 20, 22 may be made of metals, such as stainless steel or aluminum, or any suitable material for connecting to the engine heads 86, 88 or exhaust manifolds 16, 18 in sealing engagement and transferring the hot exhaust gases therein. Further, in the embodiments of FIGS. 1-3, the conduits 20, 22 may be made of a rigid material.

The conduits 20, 22 may include one or more bends 38, 40 which change the direction of the conduit 20, 22 for fluid flow. A bend may therefore change the shape or configuration of the conduit without changing the diameter or cross-section of the conduit. For instance, a bend may redirect the conduit in any direction within a 360° rotation from the point at which the bend begins, and may provide redirection of an overall acute or obtuse angle. Accordingly, bends 38, 40 may be used to route the conduits 20, 22 from the engine heads 86, 88 or exhaust manifolds 16, 18, around the engine 14 and toward the catalyst 12, as is best illustrated in FIGS. 1-3. Any number of bends 38, 40 is contemplated as may be appropriate to achieve a desired route for the conduits 20, 22 around the other components of the engine 14 or exhaust system 10, which may vary depending on the particular engine used. Therefore, any configuration of exhaust system 10, conduits 20, 22 and bends 38, 40 is contemplated herein.

Moreover, the bends 38, 40 may constitute a sharp or gradual change in direction, although a gradual change is preferable. For example, even when a bend 38, 40 redirects the conduit 20, 22 by 90°, such as in FIG. 1, the change may be sufficiently gradual that the conduit wall remains curved and not angular, and there is not a point or edge defined by the bend 38, 40. In some embodiments, however, points or edges may be formed by the bend 38, 40.

In some embodiments, the conduits 20, 22 and bends 38, 40, respectively, are formed of a single or unitary piece, as may be made by casting, forming or hammering of material. In other embodiments, the bends 38, 40 may be joints combining different sections of conduit 20, 22 together to permit usage of rigid materials and still direct the flow of exhaust gases 50, 52 as needed. In still other embodiments, the conduits 20, 22 are made of flexible or semi-flexible material, such as thermo-resistant plastics or polymers, or pliable metals, which permit changes in direction without the use of bends 38, 40 or joints. Such materials may be bent or hammered in a desired configuration, after which they may remain in their formed shape.

The first and second conduits 20 and 22 may be oriented in a variety of manners with respect to one another. They may be symmetrical with respect to one another such that the conduits 20, 22 are symmetrical about a midline of the engine 14. The conduits 20 and 22 may turn toward the opposite side of the engine 14 so that they directly face one another, or so that they face one another on an angle, which may also extend upwards or downwards. The conduits 20 and 22 need not be symmetrical with one another in other embodiments and can be shaped differently, have different cross-sectional sizes, geometries and/or different lengths.

Continuing with FIGS. 1-3, the conduits 20, 22 direct the exhaust gases 50, 52 from each engine head 86, 88 or exhaust manifold 16, 18 to the catalyst 12 for processing. Accordingly, the catalyst 12 is in fluid flow communication with both of the first and second exhaust gases 50, 52. The catalyst 12 has a single housing 70 containing at least one substrate 72 therein. Exhaust gases 50, 52 from both of the conduits 20, 22 enter the housing 70 of a single catalyst 12. The housing 70 is sufficiently large to accommodate the substrate(s) 72 contained therein, in whatever configuration they may be. For instance, since there is only a single catalyst 12 and must be able to process the exhaust gases coming from two manifolds, in one embodiment the catalyst 12 is twice the size of catalysts currently used on each exhaust manifold in marine engines. However, in other embodiments, such as with increased efficiency in catalytic substrate material and/or configurations, less size may be needed to accomplish the same catalytic conversion process. Therefore, in such embodiments, the catalyst 12, though but a single catalyst, may be the same size as current catalysts, or may even be smaller or more compact. The housing 70, accordingly, is sized to accommodate the substrate(s) 72 that are needed for catalytic conversion. The housing 70 may be made of any suitable material, such as, but not limited to, metals such as stainless steel, aluminum or titanium, ceramic, or other materials.

As the exhaust gases 50, 52 travel through the catalyst 12, they mix with one another and are treated by the catalyst 12, specifically the substrate(s) 72 therein, to convert them for emissions purposes and to remove pollutants. The substrate(s) 72 is disposed or positioned within the housing 70 of the catalyst 12 in contacting communication with the exhaust gases 50, 52 as they pass through the catalyst 12. As the exhaust gases 50, 52 come into contact with the substrate(s) 72, the substrate(s) 72 act on them to perform a chemical reaction, such as oxidation or reduction reactions, or other chemical reactions, converting them into different chemical compounds that are less toxic to the environment. Pollutants may also be removed. These are commonly known processes that occur in catalysts and catalytic converters already well known. For instance, substrate(s) 72 may include any commonly known catalytic substrate materials, including precious metals such as platinum, palladium, rhodium. These materials may also be heat tolerant at temperatures generated in the engines and exhaust systems. For example, the catalyst 12 and substrate(s) 72 therein can withstand temperatures in the range of 400°-1600° Fahrenheit. In a preferred embodiment, the temperatures are optimal at 1200°-1600° F., and most preferably at 1400° F. It should be understood that the temperature increases with more pollutants, and so the catalyst 12 may withstand even the higher range of temperatures.

Moreover, the substrate(s) 72 may be present in any configuration or arrangement within the housing 70 as permits contacting engagement with the exhaust gases 50, 52 and chemical conversion thereof. For instance, the substrate(s) 72 may have a honeycomb structure or pattern as is known for catalytic substrates, such as in monoliths. The cell density of the honeycomb structure may be any as allows for a sufficient air flow rate and contacting engagement with the exhaust gases to perform catalytic conversion. For example, an air to fuel ratio of 14.7:1 is considered optimal for catalytic conversion performance. In at least one embodiment, the substrate(s) 72 comprise a cell density of 400 holes per square inch. In another embodiment, the substrate(s) 72 has a cell density of thousands of holes per square inch. The number and size of substrate(s) 72 included in the catalyst 12, and the size and number of cells or holes therein, will depend on the size and demand of the engine, and the volume and rate of exhaust gases 50, 52 generated. Generally speaking, the larger the engine, or the more cylinders in the engine, the larger and/or more substrate(s) 72 will be used in the catalyst 12, and will have larger sized holes for air flow through the substrate(s) 72. Moreover, while a honeycomb pattern is common, other patterns are also contemplated. For instance, rod structures may also be used. Multiple substrate(s) 72 or materials therein may be disposed in layers with relation to each other, which may be offset from one another to increase surface area for contacting engagement with exhaust gases 50, 52. These are just a few non-limiting examples for illustrative purposes.

FIGS. 12-14 depict various schematic embodiments of the housing 70 and substrate(s) 72 configurations therein of the catalyst 12 of the present exhaust system. For instance, in the embodiment of FIG. 12, the housing 70 includes a single substrate 72 which fills up substantially the entire interior of the housing 70. This configuration may maximize contact between the substrate 72 and exhaust gases 50, 52 for processing and chemical conversion. In the embodiment of FIG. 13, the housing 70 may include two substrates 72, such as when catalysts from two exhaust manifolds are combined into a single catalyst 12. They may include a first substrate 73 and a second substrate 74, which may vary from one another in composition, configuration, cell density, or other characteristic. In other embodiments, first and second substrates 73, 74 may be the same as each other in all relevant characteristics except position within the housing 70. In the embodiment of FIG. 14, three substrates 72 are present and aligned in such a way as to maximize contacting engagement with the exhaust gases 50, 52 passing through. It should be appreciated from these examples that any number of substrates 72 may be present in the catalyst 12, so long as they are all present in the same single housing 70. Moreover, the substrates 72 may comprise any shape or dimension as permits chemical conversion of the exhaust gases 50, 52, such as circular, rod-shaped, rectangular, square, or other shapes. Similarly, the housing 70 may be any shape or dimension as accommodates the desired substrate(s) 72 in the desired configuration.

As noted above, as the exhaust gases 50, 52 pass through the catalyst 12 and make contact with the substrate(s) 72 therein, they undergo chemical processes that convert them to other compounds. The gases that have been converted are now processed exhaust gases 80. In a preferred embodiment, the catalyst 12 converts the first and second exhaust gases 50, 52 into at least one processed exhaust gas 80, which may include a plurality of gases. These processed exhaust gases 80 may be consistent with the emissions requirements for combustion engines in a particular state or country.

Returning to FIGS. 1-3, the marine exhaust engine system 10 also includes a third conduit 24 in fluid communication with the processed gas(es) 80 exiting from the catalyst 12. For example, the third conduit 24 connects to the catalyst housing 70 in fluid flow communication with the processed gas(es) 80 to route them away from the catalyst 12 and out of the exhaust system 10. Accordingly, the third conduit 24 may be attached in sealing engagement to the catalyst housing 70. As with the first and second conduits 20, 22, the third conduit 24 can be rigid and made of a metal such as aluminum, or may be a flexible member in yet other embodiments. The third conduit 24 may be made of the same material as the first and second conduits 20, 22 described above, and may further include one or more bends or other device to chance the direction of the third conduit 24 for routing purposes. In a preferred embodiment, the third conduit 24 routes the processed gases 80 to the back of the boat or watercraft for exiting the boat, although the third conduit 24 may route the processed gases 80 in any direction.

Marine engines require additional considerations unique to watercraft, such as protecting the engine and other components from water infiltration and heat concerns from compact space limitations and conformations, often known as packaging. Accordingly, the exhaust manifolds 16, 18, catalyst 12 and the various conduits 20, 22, 23, 24 and 26 described herein may be surrounded by water jackets through which cooling water 46 runs to act as a heat sink and keep the temperature of the components from climbing too high and overheating. This water jacket system is preferably carried throughout the various components of the exhaust system 10. The water-cooled jacketing system may be a closed-loop system in which at least a portion of the cooling water 46 is recirculated through cooling system. In other embodiments, the water-cooled jacketing system is open-ended, such that cooling water traveling through the system exits the cooling system at the same terminal end of the exhaust system 10. Cooling water 46 may be fresh water or salt water, and may be supplied from a reservoir or pumped directly from the body of water in which the watercraft is at least partially submerged.

Cooling water 46 may exit from the water jacketing system and may be mixed with the processed exhaust gases 80 at a cooling water introduction point 36. Once the cooling water 46 is added, a combined processed exhaust gas and cooling water stream 48 is created and is subsequently transferred out of the marine engine exhaust system 10 into the body of water in which the boat 44 is located. For the catalyst 12 to function properly, no cooling water 46 should be present within the exhaust gas 50, 52 entering the catalyst 12. The chemical reactions necessary for removing contaminants from the gas stream will not work, or will not function as well, if cooling water 46 is mixed with the exhaust gas affected by the catalyst for contaminant removal. As such, cooling water 46 may be missing from the gas stream at all points upstream from point 36 all the way back through to the engine 14.

Therefore, in at least one embodiment, the cooling water introduction point 36 is located as far downstream (at the end of the exhaust system 10) as possible from the catalyst 12, such as at the terminal end of the third conduit 24, to provide maximum distance between the catalyst 12 and limit water infiltration into the exhaust system 10. In another embodiment, the third conduit 24 includes at least one bend, such as described above in relation to the first and second conduits 20, 22, to create a more convoluted route for the processed gas 80 before the cooling water introduction point 36. In such an embodiment, the bends in the third conduit 24 may function as obstacles to inhibit water infiltration from the cooling water introduction point 36. The third conduit 24 may include any number of bends between the catalyst 12 and the cooling water introduction point 36 to achieve this purpose. In another embodiment, the cooling water 46 exits the water jacketing system at the cooling water introduction point 36 as a mist, thereby reducing the amount of water that could potentially back up into the exhaust system 10.

FIGS. 4-11 illustrate various configurations for the third conduit 24 and cooling water introduction point 36.

In at least one embodiment, the first and second conduits 20, 22 are directed toward each other from opposite sides of the engine and connect to the catalyst 12 at the top. For instance, the first and second conduits 20, 22 connect individually to the catalyst 12, as in the embodiments of FIGS. 1 and 7. In these embodiments, the first exhaust gas 50 coming from the first engine head 86 or exhaust manifold 16 and the second exhaust gas 52 coming from the second engine head 88 or exhaust manifold 18 are kept separate and do not co-mingle until they are within the catalyst 12. In other embodiments, as in FIGS. 2 and 8, the first and second conduits 20, 22 merge upstream of the catalyst 12, forming a merged conduit 23. In the merged conduit 23, the first and second exhaust gases 50, 52 co-mingle to form a combined exhaust gas 54. The merged conduit 23 connects to the catalyst 12, and the combined exhaust gas 54 enters the catalyst 12.

In these embodiments, the first and second exhaust gases 50, 52 enter the catalyst 12 from the top 60. In other embodiments, the exhaust gases 50, 52, 54 enter the catalyst 12 from the bottom. For instance, FIGS. 3 and 4 show embodiments in which the first conduit 20 and second conduit 22 connect to the catalyst 12 at the bottom separately. In FIG. 5, the first and second conduits 20, 22 may merge upstream of the catalyst 12 to form a merged conduit 23 which subsequently connects to the catalyst 12 from the bottom.

As can be appreciated from the Figures, the merged conduit 23 may be a separate component or a part of either the first or second conduits 20, 22, and may be at any angle with relation to either the first or second conduits 20, 22. For instance, the merged conduit 23 may be a separate section of conduit from the first and second conduits 20, 22, as in FIG. 5. It may be positioned at a 90° angle in relation to the first and second conduits 20, 22, as in FIG. 5, or may be at an angle less than or greater than 90° to the conduits 20, 22. In other embodiments, the merged conduit 23 may be a portion of the first and/or second conduits 20, 22, which may even be shared in common, as in FIG. 2.

Further, the third conduit 24 which directs processed exhaust gas 80 away from the catalyst 12 may connect to the top, bottom, or sides of the catalyst 12. In at least one embodiment, the third conduit 24 connects to the catalyst 12 opposite of the first and second conduits 20, 22 or merged conduit 23. For instance, the third conduit 24 may connect to the bottom 62 of the catalyst 12, as in FIGS. 1, 2 and 7-9. In some embodiments, the third conduit 24 connects opposite of the first and second conduits 20, 22, as in FIGS. 1, 2, 7 and 8. In other embodiments, the third conduit 24 is not opposite of the first and second conduits 20, 22, such as in FIG. 9 where the first and second conduits 20, 22 enter the catalyst 12 from opposite sides of the catalyst 12, and the third conduit 24 connects to the bottom 62 of the catalyst 12. In other embodiments, as in FIGS. 3 and 4-6, the third conduit 24 connects to the top 60 of the catalyst 12. It should therefore be appreciated that the first and second conduits 20, 22 or merged conduit 23 directing the exhaust gases 50, 52, 54 into the catalyst 12 and the third conduit 24 directing the processed exhaust gases 80 out of the catalyst 12 may connect to any side or surface of the catalyst 12 as would permit flow of the gases through the catalyst 12.

While it may be preferable to have a single conduit conveying the processed gases 80 away from the catalyst and out of the boat, so as to simplify manufacturing, packaging and housing considerations, there may be more than one such conduit in certain embodiments. For example, as seen in FIGS. 10 and 11, the exhaust system 10 may include not only a third conduit 24 in fluid communication with a processed gas exiting from the catalyst 12, but also a fourth conduit 26 in fluid communication with a processed gas exiting from the catalyst 12. In some embodiments, both the third and fourth conduits 24, 26 receive and direct the same processed exhaust gas 80 away from the catalyst 12. In other embodiments, the third conduit 24 may receive a first processed exhaust gas 82 from the catalyst 12, and the fourth conduit 26 receives a second processed exhaust gas 84 from the catalyst 12. In such embodiments, the first and second processed exhaust gases 82, 84 may comprise the same composition of gases, but one may be from a first substrate 73 within the catalyst 12 and the other may be from a second substrate 74 within the catalyst 12. Examples of this are illustrated in FIGS. 10 and 11. In other embodiments, the first and second processed gases 82, 84 may comprise difference compositions.

FIG. 13 shows an example of the inside of a catalyst 12 having a first and second substrate 73, 74 that may be used to separately process exhaust gases 50, 52, and optionally may direct the resulting processed exhaust gases 82, 84 into a third and fourth conduit 24, 26. In this example, the first substrate 73 may be in contacting engagement with a first exhaust gas 50 which comes from a first engine head 86 or manifold 16, and results in a first processed exhaust gas 82. A second substrate 74 may be in contacting engagement with a second exhaust gas 52 coming from a second engine head 88 or exhaust manifold 18, resulting in a second processed exhaust gas 84.

The present exhaust system 10 also includes at least one pre-sensor 28 in contacting engagement with the first and second exhaust gases 50, 52, and at least one post-sensor 32 in contacting engagement with the processed exhaust gas(es) 80 to measure the performance of the catalyst 12. For instance, as seen in FIG. 4, the first exhaust gas 50 travels through the first conduit 20 and a first pre-sensor 28 acquires data about the first exhaust gas 50 before or as it enters the catalyst 12. The second conduit 22 can also include a pre-sensor 28 that acquires data about the second exhaust gas 52 before it enters the catalyst 12. The pre-sensor(s) 28 can sense any type of property or properties associated with the exhaust gas streams 50 and 52, such as, but not limited to, carbon dioxide, carbon monoxide, nitrogen oxides, temperature, pressure, and air flow rate. In a preferred embodiment, the pre-sensor 28 is an oxygen sensor.

The first pre-sensor 28 can be located at the conduits 20, 22 at any point along the length of the conduit 20, 22. For example, in one embodiment, the pre-sensor 28 may be located at the point where the conduit 20, 22 meets the engine head 86, 88 or exhaust manifold 16, 18. In another embodiment, the pre-sensor 28 may be located in the wall of the conduit 20, 22 just downstream of where the conduit 20, 22 meets the engine head 86, 88 or exhaust manifold 16, 18. In still other embodiments, the pre-sensor 28 may be located at the point where the conduit 20, 22 meets the catalyst housing 70. The pre-sensor 28 may also be located at the conduit 20, 22 just prior to the point of joining with the catalyst housing 70. In other embodiments, the pre-sensor 28 may be located upstream of a bend(s) 38, 40 in the conduit 20, 22. The pre-sensor 28 may also be located downstream of a bend(s) 38, 40 in the conduit 20, 22. In still other embodiments, the pre-sensor 28 may be located in the catalyst housing 70 at or near the point where the conduit 20, 22 joins the housing 70. In some embodiments, there are multiple pre-sensors 28 along the conduit 20, 22, which may be disposed anywhere along the length of the conduit 20, 22 and/or the catalyst housing 70.

In other embodiments, as in FIG. 2, the pre-sensor 28 may be located in the merged conduit 23, so that the exhaust gases 54 are monitored before entering the catalyst 12. In still other embodiments, as in FIGS. 1 and 3, the pre-sensor may be located in the catalyst 12 itself, such as at a point near the entry of the first and second exhaust gases 50, 52, so as to measure the gases prior to catalytic processing.

The catalyst 12 receives the first and second exhaust gas streams 50, 52 and functions to remove pollutants therefrom as described above. The catalyst 12 can be any type of catalyst used with engine exhaust systems. The catalyst 12 may work best if the first and second exhaust gas streams 50, 52 are both hot and dry. The exhaust gases 50, 52 are likewise mixed within the catalyst 12 along with being treated by the catalyst 12 to remove pollutants. This mixing may occur while the catalyst 12 is removing contaminants, or may be done before the catalyst 12 removes contaminants or even after removal of the contaminants, or any combination of the aforementioned sequences. As such, the catalyst 12 may function to both mix the exhaust gases 50, 52 in addition to treating the exhaust gases 50, 52 for contaminant removal. The single catalyst 12 may be included such that a second catalyst 12 is not necessary as all of the exhaust gas 50, 52 is treated by the single catalyst 12. As such, all of the exhaust of the engine 14 may flow through this single catalyst 12, even though this exhaust may come from opposite sides of the engine 14.

At least one post-sensor 32 is provided after the catalytic processing to measure certain properties of the processed exhaust gas(es) 80, so the performance of the catalyst 12 can be monitored and the efficiency determined. As with the pre-sensor(s) 28, the post-sensor(s) 32 may measure and/or monitor properties be such as, but not limited to, oxygen levels, carbon dioxide levels, carbon monoxide levels, nitrogen oxides levels, temperature, pressure, and air flow rate. The post-sensor(s) 32 also be used to determine if the catalyst 12 has stopped working, or if there is a leak in the system.

The post-sensor 32 may be located anywhere downstream of the catalyst 12. In some examples, as in FIGS. 1-4 and 7, the post-sensor 32 is located at the third conduit 24 and measures one or more properties of the processed exhaust gas 80 flowing through the third conduit 24. In other embodiments, such as in FIGS. 10 and 11, the third and fourth conduits 24, 26 each include a post-sensor 32 to monitor the properties of the processed exhaust gases 82, 84 flowing through each, respectively. The post-sensor 32 may be located anywhere along the conduits 24, 26, such as at or just after their connection point with the catalyst 70, or anywhere along their length between the catalyst 12 and the cooling water introduction point 36 so that monitoring is not impeded by potential water infiltration. In at least one preferred embodiment, the post-sensor 32 is located within the conduit(s) 24, 26 as far away from the cooling water introduction point 36 as is possible. In embodiments in which the third or fourth conduits 24, 26 include at least one bend, the post-sensor 32 may be located before or after any one of the bends along the conduit 24, 26. In still other embodiments, the post-sensor 32 may be located in the catalyst 12, but at a point that is downstream of the catalyst conversion processes occurring in the substrate(s) 72, such as at the point of exit of the catalyst 12.

The various arrangements of the marine engine exhaust system 10 discussed herein are all similar in that they utilize a single catalyst 12 for cleaning all of the exhaust gases 50, 52 from engine heads 86, 88 or exhaust manifolds 16, 18 generated by the combustion process in the engine 14. For example, the arrangement of FIG. 5 is different than that of FIG. 4 in that the first conduit 20 and the second conduit 22 merge with one another such that the first exhaust gas 50 and the second exhaust gas 52 also merge with one another prior to the catalyst 12. The conduits 20, 22 are in communication with one another at a merge point from which the merged conduit 23 extends. The pre-sensor 28 is located in the merged conduit 23 and the combined first and second exhaust gas 54 travels through the merged conduit 23 and into the catalyst 12 through the bottom of the catalyst 12. The exhaust gas stream 54 does not need to be mixed in the catalyst 12 since it is already mixed, but the catalyst 12 still treats the exhaust gas stream 54. The third conduit 24 exits through the top surface 60 of the catalyst 12 and the processed exhaust gas 80 is measured at a post sensor 32 in the third conduit 24.

The arrangement of FIG. 6 is the same as that previously discussed with respect to the system 10 of FIG. 4 except that the first and second conduits 20 and 22 enter the catalyst 12 through the side surface 58 of the catalyst 12 instead of through the bottom surface 62. The catalyst 12 may be cylindrical in shape such that it has a cylindrical shaped outer surface 58, and the conduits 20, 22 can enter through opposite sides of the outer surface 58. In other embodiments, the catalyst 12 can be variously shaped and need not be cylindrical. Likewise, instead of exiting the top surface 60, the third conduit 24 having the processed exhaust gas 80 may exit through the bottom surface 62 or the side surface 58 in other exemplary embodiments.

FIG. 7 shows another embodiment of the system 10 in which a pair of gas streams 50 and 52 enter the catalyst 12 and are mixed therein and treated. The system 10 of FIG. 7 is similar to that of FIG. 4 except that the first and second conduits 20, 22 terminate at the upper surface 60 of the catalyst 12 instead of the lower surface 62. After the exhaust gas streams 50 and 52 mix and are treated in the catalyst 12, they exit the catalyst 12 through the bottom surface 62. The processed exhaust gases 80 are measured by the post-sensor 32 in the third conduit 24, and the processed exhaust gases 80 are eventually mixed with cooling water 46 at point 36. The system 10 employs three sensors 28, 32 that are measured by a catalyst 12 monitoring system of the system 10. The sensors 28, 32 provide information as to how the catalyst 12 is functioning and as to the emissions being removed from the combined gases 54.

FIG. 8 shows an alternate arrangement of the system 10 in which the first and second conduits 20, 22 merge with one another to form a merged conduit 23 before the catalyst 12. The first and second gases 50, 52 merge into the combined stream 54 in the merged conduit 23, and are measured by the pre-sensor 28. There is some amount of conduit 23 that extends from the merge point of the first and second conduits 20, 22 to the top surface 60. The pre-sensor 28 may be located at merged conduit 23. With this arrangement, only one pre-sensor 28 may be needed since the gases 50, 52 merge before entering the catalyst 12.

The third conduit 24 extends from the bottom surface 62, and the processed exhaust gases 80 are measured by the post-sensor 32 after being treated by the catalyst 12. In other arrangements, the third conduit 24 can exit from the side surface 58 or the top surface 60 of the catalyst 12. The processed exhaust gases 80 are transferred through the third conduit 24 to such a point 36 in which cooling water 46 is mixed therewith to form the combined gas and cooling water stream 48. In other arrangements, the processed exhaust gases 80 may not mix with cooling water 46 in the third conduit 24 or at any point in the system 10.

The arrangement in FIG. 8 employs only two sensors 28, 32 and does not need to have three sensors in the catalyst 12 monitoring of the system 10. Also, as only a single catalyst 12 is used, a second catalyst with its associated weight, size, positioning, and catalyst monitoring system is not needed.

FIG. 9 shows another arrangement of the marine engine exhaust system 10 that is similar to that previously discussed with respect to the system of FIG. 7. However, the system 10 in FIG. 9 is different in that the first and second conduits 20, 22 enter the side surface 58 of the catalyst 12 instead of the top surface 60. The third conduit 24 exits the bottom surface 62, and sensors 28, 32 are employed along with the single catalyst 12.

The marine engine exhaust system 10 may be configured so that only a single exhaust outlet, for example the third conduit 24, leaves the engine 14 and includes the combined exhaust gas and cooling water stream 48, as in FIGS. 1-9. However, in other embodiments, twin exhaust gas/cooling water conduit streams can be provided in the design. For example, FIG. 10 is an alternative exemplary embodiment of the system 10 in which the first and second exhaust gases 50, 52 enter the catalyst 12 through the side surface 58 and mix therein and are treated therein for the removal of pollutants. A pair of outlets composed of a third conduit 24 and a fourth conduit 26 exit the bottom surface 62, and combined exhaust gases 54 flow out of the catalyst 12 and into both of the conduits 24 and 26. The third conduit 24 is equipped with a first post-sensor 32 to measure the processed exhaust gases 82 in the third conduit 24. The fourth conduit 26 has a second post-sensor 34 that measures a property or properties of the processed exhaust gases 84 in the fourth conduit 26. Each of the conduits 24, 26 has a water merge point 36 in which cooling water 46 is merged with the processed exhaust gases 82, 84 to form the combined cooling water and exhaust gas streams 48.

The pair of exhaust conduits 24, 26 allow for the provision of a dual exhaust arrangement of the system 10 with the use of but a single catalyst 12. There are two pre-sensors 28 and two post-sensors 32 present in the system 10 for the measurement of the gases and proper control of the emission reduction. Although shown as exiting the bottom surface 62, the various conduits 24, 26 can exit on any of the surfaces 58, 60 and 62 in accordance with other arrangements.

FIG. 11 shows another alternative exemplary embodiment of the system 10 that is similar to the system 10 of FIG. 10 in which the conduits 20 and 22 enter the catalyst 12 through the top surface 60. Also, the third and fourth conduits extend from the side surface 58 of the catalyst 12 instead of the bottom surface 62. As previously mentioned, the system 10 includes various arrangements in which the various conduits 20, 22, 24 and 26 can engage the catalyst 12 at any combination or one of the sides 58, 60 and 62, and it is to be understood that the examples specifically illustrated herein are only exemplary and that others are possible.

The exhaust gases 50 and 52 are mixed with one another in the catalyst 12 in certain embodiments, and there is only one catalyst 12. The system 10 may utilize a single catalyst monitoring system, since only a single catalyst 12 is employed. A single catalyst 12 and monitoring system may decrease the size of the system 10 and give more space for other components of the boat. Fewer components would be required and thus a savings on cooling hoses and materials would result. Also, as certain embodiments may require reduced sensors 28, 32, the wiring harness of the system 10 may be simplified. Engine 14 calibration may be improved because combined exhaust from each engine head 86, 88 or exhaust manifold 16, 18 allows the catalyst 12 to run more consistent temperature and pressure gradients due to the steady flow of exhaust gases 50, 52. The combined exhaust gases in some arrangements allow for only a pair of sensors 28 and 32 to be required. The combined exhaust arrangement allows the catalyst 12 to maintain light off temperature even at engine 14 idle conditions via the use of a closed loop cooling system. However, open loop cooling systems are used in other arrangements. Also, a single exhaust design may allow the boat to be more easily serviced and affords greater flexibility in boat design.

Additional information associated with portions of the marine engine exhaust system 10 such as water jacketing, conduit arrangements, sensors, catalyst monitoring, and the prevention of water through the system 10 and into the engine 14 may be provided as described in U.S. Pat. No. 6,644,024 to Powers et al; U.S. Pat. No. 7,803,026 to McKinney; and U.S. Pat. No. 3,206,836 to Schlussler the entire contents of which are incorporated by reference herein in their entireties for all purposes. Still further, the catalyst and catalyst monitoring system and other components associated with the catalyst may be provided as described in U.S. Pat. No. 7,314,044 to Westerbeke, the entire contents of which are incorporated by reference herein in their entirety for all purposes.

While the present invention has been described in connection with certain preferred embodiments, it is to be understood that the subject matter encompassed by way of the present invention is not to be limited to those specific embodiments. On the contrary, it is intended for the subject matter of the invention to include all alternatives, modifications and equivalents as can be included within the spirit and scope of the following claims.

Claims

1. A marine engine exhaust system, comprising:

a first conduit in fluid communication with a first exhaust gas exiting from a first engine head;

a second conduit in fluid communication with a second exhaust gas exiting from a second engine head;

a catalyst in fluid communication with both said first and second exhaust gases having a housing and at least one substrate positioned within said housing in contacting engagement with said first and second exhaust gases to convert said first and second exhaust gases into at least one processed exhaust gas; and

a third conduit in fluid communication with said at least one processed exhaust gas exiting from said catalyst.

2. The marine engine exhaust system as recited in claim 1, further comprising a first exhaust manifold interposed in fluid communication between said first engine head and said first conduit, and a second exhaust manifold interposed in fluid communication between said second engine head and said second conduit.

3. The marine engine exhaust system as recited in claim 1, wherein said catalyst includes a first substrate in contacting engagement of said first exhaust gas to produce a first processed exhaust gas, and a second substrate in contacting engagement of said second exhaust gas to produce a second processed exhaust gas.

4. The marine engine exhaust system as recited in claim 3, wherein each of said first and second conduits is in fluid communication with said catalyst housing.

5. The marine engine exhaust system as recited in claim 3, wherein said third conduit is in fluid communication with said first processed gas exiting from said catalyst, and further comprising a fourth conduit in fluid communication with said second processed exhaust gas exiting from said catalyst.

6. The marine engine exhaust system as recited in claim 1, wherein said first and second conduits join to form a merged conduit upstream of said catalyst, and wherein said merged conduit is in fluid communication between said first and second conduits and said catalyst housing.

7. The marine engine exhaust system as recited in claim 1, wherein each of said first and second conduits are in fluid communication with said catalyst housing.

8. The marine engine exhaust system as recited in claim 1, further comprising at least one pre-sensor in contacting engagement with said first and second exhaust gases.

9. The marine engine exhaust system as recited in claim 8, wherein said catalyst includes said at least one pre-sensor.

10. The marine engine exhaust system as recited in claim 8, wherein at least one of said first and second conduits includes said at least one pre-sensor.

11. The marine engine exhaust system as recited in claim 8, wherein said first and second conduits join to form a merged conduit upstream of said catalyst, and wherein said merged conduit includes said at least one pre-sensor.

12. The marine engine exhaust system as recited in claim 1, further comprising at least one post-sensor in contacting engagement with said at least one processed exhaust gas.

13. The marine engine exhaust system as recited in claim 12, wherein said catalyst includes said at least one post-sensor.

14. The marine engine exhaust system as recited in claim 12, wherein said third conduit includes said at least one post-sensor.

15. The marine engine exhaust system as recited in claim 1, wherein said first and second engine heads are located on opposite sides of an engine.

16. A marine engine exhaust system consisting essentially of:

a first conduit in fluid communication with a first exhaust gas exiting from a first engine manifold;

a second conduit in fluid communication with a second exhaust gas exiting from a second engine manifold;

a catalyst in fluid communication with both said first and second exhaust gases having a housing and a substrate positioned within said housing in contacting engagement with said first and second exhaust gases to convert said first and second exhaust gases into processed exhaust gas;

a third conduit in fluid communication with said processed exhaust gas exiting from said catalyst;

a first pre-sensor in contacting engagement with said first exhaust gas located upstream of said substrate;

a second pre-sensor in contacting engagement with said second exhaust gas located upstream of said substrate; and

a post-sensor in contacting engagement with said processed exhaust gas located downstream of said substrate.

17. The marine engine exhaust system as recited in claim 16, wherein said first and second conduits join to form a merged conduit upstream of said catalyst, and wherein said merged conduit is in fluid communication between said first and second conduits and said catalyst housing.

18. The marine engine exhaust system as recited in claim 17, wherein said merged conduit includes a pre-sensor in contacting engagement with said first and second exhaust gases located upstream of said substrate.