Marine exhaust with dual cooling

[0002] The features and advantages of the present invention will become apparent from the following detailed description of the invention when read with the accompanying drawing in which a watercraft is illustrated as having an exhaust pipe having connections to a first supply of water and to a second supply of water.

[0003] The FIGURE illustrates a watercraft 10 having a hull 12 with an internal combustion engine 14 disposed within the hull. The engine 14 has an exhaust pipe 16 passing through a transom 18 to the exterior of the hull 12. The engine 14 is connected to a stern drive 20 as is known in the art of inboard/outboard marine craft. Although illustrated herein as embodied as an inboard/outboard powered watercraft, the present invention may be embodied in any style of watercraft, including inboard, outboard and inboard/outboard applications.

[0004] Watercraft 10 is equipped with an engine cooling apparatus 22 which includes a pump 24 and associated water jacket 23 and piping 25. Engine cooling apparatus 22 is operable to draw water from a body of water 42 exterior to the hull 12, to circulate the water through various engine cooling passages (not shown) and water jacket 23 to remove heat from the engine 14, and to return the heated water to the exterior of hull 12. Engine cooling apparatus 22 is an active apparatus in the sense that pump 24 provides the motive force for the circulation of coolant through the cooling apparatus 22. As used herein, the term “active apparatus” is meant to include only those components or collection of components which generate their own movement to accomplish their intended design function. Engine cooling apparatus 22 is an active apparatus because pump 24 must be operated in order to circulate coolant there through. As used herein, the term “passive apparatus” is meant to include only those components or groups of components which can perform their intended design function without self generated motion. In addition to providing an engine cooling function, engine cooling apparatus 22 is connected to the exhaust pipe 16 by a first fluid connection such as conduit 26. Conduit 26 is operable to direct a first flow of water 28 from the engine cooling apparatus 22 into exhaust pipe 16 to cool exhaust gas 30 and downstream portions of pipe 16.

[0005] The FIGURE also illustrates an auxiliary water supply 32 operable to provide a second flow of water 34 into the exhaust pipe 16 upstream of muffler 54. As illustrated in the figure, the auxiliary water supply 32 includes a tube 38 having a funnel shaped opening 36 disposed on a forward facing surface of the stern drive 20. As the watercraft 10 is moved forward through body of water 42, tube 38 functions as a Pitot tube operable to force water through conduit 40 and into exhaust pipe 16. The auxiliary water supply 32 is a passive apparatus since its functioning to deliver cooling water 34 to exhaust pipe 16 does not require the self generated movement of any of the components of the water supply 32. The second flow of water 34 augments the cooling capability of the first flow of water 28 to further reduce the temperature of the exhaust gas 30. Opening 36 is preferably funnel shaped in order to increase the flow of water through conduit 40 as the watercraft is moved through the body of water 42. One may appreciate that the opening 36 of tube 38 may be disposed on any forward facing surface of watercraft 10 as long as it is located at a point below the water line 44 during the operation of the watercraft 10. In order to prevent exhaust gas from flowing out of opening 36 when engine 14 is running but watercraft 10 is stationary or moving very slowly, a check valve 46 may be connected in conduit 40 in order to pass fluid flowing into the exhaust pipe 16 but to block fluid from flowing out of exhaust pipe 16 into tube 38. In order to further increase the volume of the second flow of water 34, a plurality of openings 36 may be provided at different locations on the exterior of watercraft 10 below waterline 44. It is desirable that the connections of both conduit 26 and conduit 40 are located on an upstream portion of exhaust pipe 16 in order to minimize the uncooled length of exhaust pipe 16. In one embodiment the outlet 48 of conduit 40 is disposed on the exhaust pipe 16 at a location proximate the outlet 50 of the conduit 26. Such proximate locations may include, for example, the outlets 48, 50 being located on a single flanged insert 52 which is adapted to be installed as part of exhaust pipe 16. By using such an insert 52, one can envisioned the auxiliary water supply 32 being installed as a back-fit kit on an existing watercraft that is already equipped with a connection between the engine water jacket 23 and the exhaust pipe 16.

[0006] A method of cooling the exhaust pipe 16 of a watercraft 10 includes the steps of directing a first flow of water 28 from an engine cooling apparatus 22 into the exhaust pipe 16 of an engine 14. A second flow of water 34 may then be. directed from an auxiliary water supply 32 into the exhaust pipe 16. The means for directing the second flow of water 34, such as auxiliary water supply 32, is preferable a passive apparatus which is operable independent of the means for directing the first flow of water 28, such as engine cooling apparatus 22. By disposing the inlet end 36 of a conduit 40 below a waterline 44 of the watercraft 10, a flow of water 34 will be forced through conduit 40 as the watercraft 10 is moved through a body of water 42. Thus even upon failure of an engine cooling apparatus 22, a continued source of cooling water 34 will be supplied to exhaust pipe 16, thereby preventing damage to the exhaust pipe 16 and associated downstream components such as muffler 54. Furthermore, the risk of injury to an occupant of the watercraft 10 during periods of continued engine operation following the failure of cooling apparatus 22 is significantly reduced.

[0007] In one embodiment, engine coolant apparatus 22 may be designed to provide a flow rate of 30 gpm of water through conduit 26 into exhaust pipe 16 at full throttle operation. With no other cooling flow,this amount of water will cool the. exhaust gas from approximately 1,400 degrees Fahrenheit to 160 degrees Fahrenheit. Auxiliary water supply 32 may be designed to provide a flow rate of 10 gpm of water through conduit 40 into exhaust pipe 16 at full throttle speed. With no cooling flow 28 from the engine cooling apparatus 22, this auxiliary water supply 32 will cool the exhaust gas to approximately 200 degrees Fahreheit, which is sufficiently low to protect downstream components such as muffler 54. With both systems operating, the exhaust gas will be cooled to approximately 130 degrees Fahrenheit. While less than optimal for long term operation of engine 12, the flow of cooling water 34 provided by the auxiliary source of cooling water 32 is adequate to prevent component damage and dangerously high exhaust pipe temperatures for short periods of operation of engine 12 without exhaust cooling flow 26. A higher flow rate may be provided through the auxiliary water supply 32 by increasing the size of the conduit 40, and the specific component sizes and resulting temperatures may be selected on an application specific basis using analytical or empirical techniques known in the art.

[0008] While the preferred embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions will occur to those of skill in the art without departing from the invention herein. Accordingly it is intended that the invention be limited only by the spirit and scope of the appended claims.