Exhaust cleaning system for marine propulsion engine

Abstract

An exhaust cleaning system for a marine propulsion engine that includes a catalyst positioned within a tube that communicates with an expansion chamber. A cooling jacket extends around at least a portion of the exhaust system and the liquid coolant is discharged into the exhaust system for flow with the exhaust gases. A number of different arrangements are shown for precluding the coolant from flowing back into the exhaust system and contacting the catalyst bed either when the watercraft is inverted and righted or in the event the engine is stopped and restarted.

We claim:  
     
       1. An exhaust system for a watercraft comprised of a hull containing an internal combustion engine mounted within said hull and having at least one exhaust port, said exhaust system being comprised of an exhaust conduit having an inlet end communicating with said exhaust port for receiving exhaust gases therefrom and an outlet end exiting through said hull for discharging the exhaust gases to the atmosphere in proximity to the body of water in which the watercraft is operating in at least some conditions of said watercraft, said exhaust conduit including means defining an expansion chamber and a tube containing a catalyst bed contained within said expansion chamber and through which exhaust gases must pass, and means for precluding water in said exhaust conduit from entering said tube end. 
     
     
       2. An exhaust system for a watercraft as set forth in  claim 1  wherein the means for precluding water from entering the tube end comprises baffle means. 
     
     
       3. An exhaust system for a watercraft as set forth in  claim 2  wherein the baffle means is positioned in the expansion chamber in confronting relationship to the tube end. 
     
     
       4. An exhaust system for a watercraft as set forth in  claim 2  wherein the baffle means is disposed downstream of the expansion chamber in the exhaust conduit. 
     
     
       5. An exhaust system for a watercraft as set forth in  claim 1  wherein the means for precluding water in the exhaust conduit from entering the tube end comprises valve means. 
     
     
       6. An exhaust system for a watercraft as set forth in  claim 5  wherein the valve means is positioned downstream of the expansion chamber. 
     
     
       7. An exhaust system for a watercraft as set forth in  claim 6  wherein the valve means is moveable between an open position and a closed position and is biased to one of said positions. 
     
     
       8. An exhaust system for a watercraft as set forth in  claim 7  wherein the valve means is biased to its closed position and is opened by the pressure of the exhaust gases when the engine is running. 
     
     
       9. An exhaust system for a watercraft as set forth in  claim 7  wherein the valve means is biased to its opened position and is closed in response to inversion of the watercraft. 
     
     
       10. An exhaust system for a watercraft as set forth in  claim 1  wherein the means for precluding water in the exhaust conduit from entering the tube end comprises a further expansion chamber disposed downstream in the exhaust conduit from the first mentioned expansion chamber. 
     
     
       11. An exhaust system for a watercraft as set forth in  claim 10  wherein the first expansion chamber communicates with the second expansion chamber through a first pipe section and the second expansion chamber communicates with the downstream end of the exhaust conduit with a second pipe section and wherein the first and second pipe sections are offset relative to each other. 
     
     
       12. An exhaust system for a watercraft as set forth in  claim 10  wherein there is provided baffle means in the further expansion chamber for precluding water from impending  impinging on the catalyst bed. 
     
     
       13. An exhaust system for a watercraft as set forth in  claim 12  wherein the first expansion chamber communicates with the second expansion chamber through a first pipe section and the second expansion chamber communicates with the downstream end of the exhaust conduit with a second pipe section and wherein the first and second pipe sections are offset relative to each other. 
     
     
       14. An exhaust system for a watercraft as set forth in  claim 13  further including valve means for controlling the flow through one of the pipe sections. 
     
     
       15. An exhaust system for a watercraft as set forth in  claim 14  wherein the valve means is disposed in the first pipe section. 
     
     
       16. An exhaust system for a watercraft as set forth in  claim 15  wherein the valve means is moveable between an open position and a closed position and is biased to one of said positions. 
     
     
       17. An exhaust system for a watercraft as set forth in  claim 16  wherein the valve means is biased to its closed position and is opened by the pressure of the exhaust gases when the engine is running. 
     
     
       18. An exhaust system for a watercraft as set forth in  claim 16  wherein the valve means is biased to its opened position and is closed in response to inversion of the watercraft. 
     
     
       19. An exhaust system for a watercraft as set forth in  claim 10  further including means in the expansion chamber to form a well in which water may accumulate. 
     
     
       20. An exhaust system for a watercraft as set forth in  claim 19  wherein the expansion chamber includes a pipe section around which the well is formed. 
     
     
       21. An exhaust system for a watercraft as set forth in  claim 20  further including means in the additional expansion chamber for forming a further well in which water may accumulate to a level higher than that of the pipe section. 
     
     
       22. An exhaust system for a watercraft as set forth in  claim 1  wherein the tub  tube divides the expansion chamber into two expansion chamber sections. 
     
     
       23. An exhaust system for a watercraft as set forth in  claim 22  wherein both sections of the expansion chamber are formed in a common housing. 
     
     
       24. An exhaust system for a watercraft as set forth in  claim 23  further including means defining a cooling jacket around the expansion chamber. 
     
     
       25. An exhaust system for a watercraft as set forth in  claim 24  wherein the cooling jacket further encircles the pipe. 
     
     
       26. An exhaust system for a watercraft as set forth in  claim 24  wherein the means for precluding water from entering the tube end comprises baffle means. 
     
     
       27. An exhaust system for a watercraft as set forth in  claim 26  wherein the baffle means is positioned in the expansion chamber in confronting relationship to the tube end. 
     
     
       28. An exhaust system for a watercraft as set forth in  claim 26  wherein the baffle means is disposed downstream of the expansion chamber in the exhaust conduit. 
     
     
       29. An exhaust system for a watercraft as set forth in  claim 24  wherein the means for precluding water in the exhaust conduit from entering the tube end comprises valve means. 
     
     
       30. An exhaust system for a watercraft as set forth in  claim 29  wherein the valve means is positioned downstream of the expansion chamber. 
     
     
       31. An exhaust system for a watercraft as set forth in  claim 30  wherein the valve means is moveable between an open position and a closed position and is biased to one of said positions. 
     
     
       32. An exhaust system for a watercraft as set forth in  claim 31  wherein the valve means is biased to its closed position and is opened by the pressure of the exhaust gases when the engine is running. 
     
     
       33. An exhaust system for a watercraft as set forth in  claim 31  wherein the valve means is biased to its opened position and is closed in response to inversion of the watercraft. 
     
     
       34. An exhaust system for a watercraft as set forth in  claim 24  wherein the means for precluding water in the exhaust conduit from entering the tube end comprises a further expansion chamber disposed downstream in the exhaust conduit from the first mentioned expansion chamber. 
     
     
       35. An exhaust system for a watercraft as set forth in  claim 34  wherein the first expansion chamber communicates with the second expansion chamber through a first pipe section and the second expansion chamber communicates with the downstream end of the exhaust conduit with a second pipe section and wherein the first and second pipe sections are offset relative to each other. 
     
     
       36. An exhaust system for a watercraft as set forth in  claim 34  wherein there is provided baffle means in the further expansion chamber for precluding water from impending on the catalyst bed. 
     
     
       37. An exhaust system for a watercraft as set forth in  claim 36  wherein the first expansion chamber communicates with the second expansion chamber through a first pipe section and the second expansion chamber communicates with the downstream end of the exhaust conduit with a second pipe section and wherein the first and second pipe sections are offset relative to each other. 
     
     
       38. An exhaust system for a watercraft as set forth in  claim 37  further including valve means for controlling the flow through one of the pipe sections. 
     
     
       39. An exhaust system for a watercraft as set forth in  claim 38  wherein the valve means is disposed in the first pipe section. 
     
     
       40. An exhaust system for a watercraft as set forth in  claim 39  wherein the valve means is moveable between an open position and a closed position and is biased to one of said positions. 
     
     
       41. An exhaust system for a watercraft as set forth in  claim 40  wherein the valve means is biased to its closed position and is opened by the pressure of the exhaust gases when the engine is running. 
     
     
       42. An exhaust system for a watercraft as set forth in  claim 40  wherein the valve means is biased to its opened position and is closed in response to inversion of the watercraft. 
     
     
       43. An exhaust system for a watercraft as set forth in  claim 34  further including means in the expansion chamber to form a well in which water may accumulate. 
     
     
       44. An exhaust system for a watercraft as set forth in  claim 43  wherein the expansion chamber includes a pipe section around which the well is formed. 
     
     
       45. An exhaust system for a watercraft as set forth in  claim 44  further including means in the additional expansion chamber for forming a further well in which water may accumulate to a level higher than that of the pipe section. 
     
     
       46. An exhaust system for a watercraft as set forth in  claim 1  additionally comprising at least one upstanding pipe section being positioned downstream of the catalyst bed.  
     
     
       47. An exhaust system for a watercraft as set forth in  claim 46  additionally comprising a water trap device which is positioned between the upstanding pipe section and the outlet end.  
     
     
       48. An exhaust system for a watercraft as set forth in  claim 47  additionally comprising another upstanding pipe section arranged between the water trap device and the outlet end.  
     
     
       49. An exhaust system for a watercraft as set forth in  claim 48 , wherein the pipe section, which is positioned between the water trap device and the outlet end, has a transversely extending section that is connected to the upstanding pipe section, and a downwardly extending section that is connected to the transversely extending section such that the pipe section has a gooseneck- like shape.    
     
     
       50. A small watercraft comprising a hull defining a rider's area toward an aft end of the watercraft and including a centrally- located, straddle - type seat that extends generally along the longitudinal axis of the watercraft hull, an internal combustion engine driving a propulsion device to propel the watercraft, said internal combustion engine being mounted within the hull and having at least one exhaust port, and an exhaust system including an inlet end communicating with the exhaust port of the engine for receiving exhaust gases therefrom, and an outlet end exiting through the hull for discharging the exhaust gases to the atmosphere in proximity to the body of water in which the watercraft is operating in at least some conditions of the watercraft, at least a portion of the exhaust system extending beneath the rider's area, a tube through which exhaust gases must flow containing a catalyst bed for treating exhaust gases before discharge through the outlet end, the tube being positioned within an expansion chamber, a water trap device arranged within the exhaust system between the outlet end and the catalyst bed, an exhaust passage communicating with the chamber downstream of the catalyst bed and delivering exhaust gases to the water trap device, and a coolant jacket extending at least along a portion of the chamber, the coolant jacket communicating with the exhaust passage at a point between the catalyst bed and the water trap device so as to introduce at least a portion of the coolant flowing through the coolant jacket into an exhaust gas stream flowing through the exhaust passage.    
     
     
       51. A small watercraft as in  claim 50 , wherein the exhaust passage includes an upstanding section.  
     
     
       52. A small watercraft as in  claim 50  additionally comprising an exhaust pipe extending between the water trap device and the outlet end, the exhaust pipe having an upstanding section and a transversely extending section.  
     
     
       53. A small watercraft as in  claim 50  additionally comprising a baffle disposed within the exhaust passage.  
     
     
       54. A small watercraft as in  claim 50  additionally comprising a valve disposed within the exhaust passage.  
     
     
       55. A small watercraft as in  claim 50  further comprising a second expansion chamber positioned along the exhaust system upstream of the catalyst.  
     
     
       56. A small watercraft as in  claim 50  further comprising a second expansion chamber positioned along the exhaust system upstream of the expansion chamber containing the catalyst.  
     
     
       57. A small watercraft comprising a hull defining a rider's area toward an aft end of the watercraft and including a centrally- located, straddle - type seat that extends generally along the longitudinal axis of the watercraft hull, an internal combustion engine driving a propulsion device to propel the watercraft, said internal combustion engine mounted within said hull and having at least one exhaust port, and an exhaust system including an inlet end for communicating with said exhaust port of the engine for receiving exhaust gases therefrom, and an outlet end exiting through the hull for discharging the exhaust gases to the atmosphere in proximity to the body of water in which the watercraft is operating in at least some operating conditions of the watercraft, said exhaust system extending through the hull between the inlet and the outlet ends with at least a portion of the exhaust system being disposed beneath the rider's area, a catalyst bed positioned in the exhaust system, the catalyst bed being positioned within a tube through which exhaust gases must flow, the tube being disposed within an expansion chamber, a water trap device arranged within the exhaust system between the outlet end and the catalyst bed to receive a flow of mixed exhaust gases and liquid coolant, an exhaust passage delivering exhaust gases to the water trap device, a first exhaust pipe extending between the catalyst bed and the water trap device and a second exhaust pipe extending between the water trap device and the outlet end, the first and second pipes each having a vertically upstanding portion which inhibits water from entering the catalyst bed.    
     
     
       58. A small watercraft as in  claim 57  additionally comprising a cooling jacket that is juxtaposed with at least a portion of the exhaust system and through which the liquid coolant flows, the cooling jacket communicating with the first exhaust pipe downstream of the catalyst bed to discharge the liquid coolant into the exhaust pipe for flow with the exhaust gases.  
     
     
       59. A small watercraft as in  claim 57 , wherein the second exhaust pipe has an upstanding section and a transversely extending section.  
     
     
       60. A small watercraft as in  claim 57  additionally comprising a baffle disposed within the first exhaust pipe.  
     
     
       61. A small watercraft as in  claim 57  additionally comprising a valve disposed within the first exhaust pipe.  
     
     
       62. A small watercraft as in  claim 57  further comprising a second expansion chamber positioned along the exhaust system upstream of the catalyst.  
     
     
       63. A small watercraft as in  claim 57  further comprising a second expansion chamber positioned along the exhaust system upstream of the expansion chamber containing the catalyst.  
     
     
       64. A small watercraft comprised of a hull containing an internal combustion engine mounted within the hull and having at least one exhaust port, said hull having a longitudinal axis extending between fore and aft ends of the watercraft, and an exhaust system including an inlet end communicating with the exhaust port of the engine for receiving exhaust gases therefrom, and an outlet end exiting through the hull for discharging the exhaust gases to the atmosphere in proximity to the body of water in which the watercraft is operating in at least some conditions of the watercraft, a section of the exhaust system housing a catalyst bed for treating exhaust gases before discharge through the outlet end, the section of the exhaust system comprising an expansion chamber, the catalyst bed being positioned within a tube through which exhaust gases must flow that is disposed within the expansion chamber, a water trap device arranged within the exhaust system between the outlet end and the catalyst bed, an exhaust passage communicating with the section of the exhaust system downstream of the catalyst bed and delivering exhaust gases to the water trap device, and a coolant jacket communicating with the exhaust passage at a point between the catalyst bed and the water trap device so as to introduce at least a portion of the coolant flowing through the coolant jacket into an exhaust gas stream flowing through the exhaust passage, said water trap device being positioned within the exhaust system behind an aft end of the engine.  
     
     
       65. A small watercraft as in  claim 64 , wherein the exhaust passage includes an upstanding section.  
     
     
       66. A small watercraft as in  claim 64  additionally comprising an exhaust pipe extending between the water trap device and the outlet end, the exhaust pipe having an upstanding section and a transversely extending section.  
     
     
       67. A small watercraft as in  claim 64  additionally comprising a baffle disposed within the exhaust passage.  
     
     
       68. A small watercraft as in  claim 64  additionally comprising a valve disposed within the exhaust passage.  
     
     
       69. A small watercraft as in  claim 64 , wherein said hull defines a rider's area toward an aft end of the watercraft and includes a centrally- located, straddle - type seat that extends generally along the longitudinal axis of the watercraft, and at least a portion of the exhaust system extends beneath the rider's area.    
     
     
       70. A small watercraft as in  claim 64  further comprising a second expansion chamber positioned along the exhaust system upstream of the catalyst.  
     
     
       71. A small watercraft as in  claim 64  further comprising a second expansion chamber positioned along the exhaust system upstream of the expansion chamber containing the catalyst.  
     
     
       72. A personal watercraft having a hull defining a rider's area sized to accommodate at least one rider, the hull defining an engine compartment containing an internal combustion engine having at least one exhaust port and an output shaft, the engine including a cooling system, a propulsion device carried by the hull on the underside thereof and being driven by the output shaft to propel the watercraft, an exhaust system that extends through at least a portion of the engine compartment to convey exhaust gases from the engine exhaust port to the atmosphere, a catalyzer in the exhaust system to treat exhaust gases before discharge to the atmosphere and a cooling jacket juxtaposing at least a portion of the exhaust system, the cooling jacket discharging at least a portion of the coolant flowing through the cooling jacket to the body of water in which the watercraft is operated through the exhaust system, the catalyzer being located upstream of a point at which the cooling jacket introduces coolant into the exhaust system and downstream of a manifold of the exhaust system, the catalyzer comprising a catalyst bed positioned within a tube through which exhaust gases must flow, the tube being positioned within an expansion chamber of the exhaust system.  
     
     
       73. A personal watercraft as in  claim 72 , wherein at least a portion of the catalyzer is located behind a front end of the engine.  
     
     
       74. A small watercraft as in  claim 72  further comprising a second expansion chamber positioned along the exhaust system upstream of the catalyst.  
     
     
       75. A small watercraft as in  claim 72  further comprising a second expansion chamber positioned along the exhaust system upstream of the expansion chamber containing the catalyst.  
     
     
       76. A personal watercraft having a hull defining a rider's area so as to accommodate at least one rider, the hull defining an engine compartment containing an internal combustion engine having at least one exhaust port and an output shaft, the engine including a cooling system, a propulsion device carried by the hull on the underside thereof and being driven by the output shaft to propel the watercraft, an exhaust system that extends through at least a portion of the engine compartment to convey exhaust gases from the engine exhaust port to the atmosphere, a catalyzer in the exhaust system to treat the exhaust gases before discharge to the atmosphere, a cooling jacket extending along at least a portion of the exhaust system and releasing at least a portion of coolant flowing in the cooling jacket into the exhaust system, and a discharge conduit connected to the cooling jacket, the discharge conduit being formed separate from the exhaust system, the catalyzer comprising a catalyst bed positioned within a tube through which exhaust gases must flow, the tube being positioned within an expansion chamber of the exhaust system.  
     
     
       77. A personal watercraft as in  claim 76 , wherein the cooling jacket communicates with the cooling system of the engine.  
     
     
       78. A personal watercraft as in  claim 76 , wherein the discharge conduit is arranged to discharge a portion of water flowing through the cooling jacket independent of the exhaust system.  
     
     
       79. A personal watercraft as in  claim 76 , wherein the discharge conduit is attached to the cooling jacket downstream of the catalyzer.  
     
     
       80. A personal watercraft as in  claim 76 , wherein the cooling jacket is configured to discharge at least a portion of the coolant flowing through the cooling jacket into the body of water in which the watercraft is operated through the exhaust system.  
     
     
       81. A small watercraft as in  claim 76  further comprising a second expansion chamber positioned along the exhaust system upstream of the catalyst.  
     
     
       82. A small watercraft as in  claim 76  further comprising a second expansion chamber positioned along the exhaust system upstream of the expansion chamber containing the catalyst.  
     
     
       83. A personal watercraft having a hull defining a rider's area sized to accommodate at least one rider, the hull defining an engine compartment containing an internal combustion engine having a cylinder block, at least one exhaust port and an output shaft, the engine also including a cooling system, a propulsion device carried by the hull on the underside thereof and being driven by the output shaft to propel the watercraft, an exhaust system that is connected to the cylinder block and that extends through at least a portion of the engine compartment to convey exhaust gases from the engine exhaust port to the atmosphere, a catalyzer in the exhaust system to treat exhaust gases before discharge to the atmosphere and a cooling jacket juxtaposing at least a portion of the exhaust system, the cooling jacket discharging at least a portion of the coolant flowing through the cooling jacket to the body of water in which the watercraft is operated through the exhaust system, the catalyzer being located upstream of a point at which the cooling jacket introduces coolant into the exhaust system and apart from the cylinder block, the catalyzer comprising a catalyst bed positioned within a tube through which exhaust gases must flow, the tube being positioned within an expansion chamber of the exhaust system.  
     
     
       84. A personal watercraft as in  claim 83 , wherein at least a portion of the catalyzer is located behind a front end of the engine.  
     
     
       85. A personal watercraft as in  claim 83  further comprising a discharge conduit formed separately from the exhaust system, a portion of the coolant flowing through the cooling jacket being diverted from the coolant flow into the discharge conduit prior to the coolant being discharged into the body of water in which the watercraft is operating through the exhaust system.  
     
     
       86. A small watercraft as in  claim 83  further comprising a second expansion chamber positioned along the exhaust system upstream of the catalyst.  
     
     
       87. A small watercraft as in  claim 83  further comprising a second expansion chamber positioned along the exhaust system upstream of the expansion chamber containing the catalyst.  
     
     
       88. A personal watercraft having a hull defining a rider's area sized to accommodate at least one rider, the hull defining an engine compartment containing an internal combustion engine having at least one exhaust port and an output shaft, the engine including a cooling system capable of drawing water from a body of water in which the watercraft is being operated, a propulsion device carried by the hull on the underside thereof and being driven by the output shaft to propel the watercraft, an exhaust system that extends through at least a portion of the engine compartment to convey exhaust gases from the engine exhaust port to the atmosphere, a catalyzer in the exhaust system to treat exhaust gases before discharge to the atmosphere, the cooling system communicating with the exhaust system such that at least a portion of the water is discharged through the exhaust system to the body of water in which the watercraft is being operated, the catalyzer being located upstream of a point at which the water is introduced into the exhaust system and downstream of a manifold of the exhaust system, the catalyzer comprising a catalyst bed positioned within a tube through which exhaust gases must flow, the tube being positioned within an expansion chamber of the exhaust system.  
     
     
       89. A personal watercraft as in  claim 88 , wherein at least a portion of the catalyzer is located behind a front end of the engine.  
     
     
       90. A personal watercraft as in  claim 88 , wherein the water is introduced from a portion of a cooling jacket that extends along at least a portion of the exhaust system.  
     
     
       91. A small watercraft as in  claim 88  further comprising a second expansion chamber positioned along the exhaust system upstream of the catalyst.  
     
     
       92. A small watercraft as in  claim 88  further comprising a second expansion chamber positioned along the exhaust system upstream of the expansion chamber containing the catalyst.  
     
     
       93. A personal watercraft having a hull defining a rider's area so as to accommodate at least one rider, the hull defining an engine compartment containing an internal combustion engine having at least one exhaust port and an output shaft, the engine including a cooling system, a propulsion device carried by the hull on the underside thereof and being driven by the output shaft to propel the watercraft, the cooling system receiving water from the propulsion device, an exhaust system that extends through at least a portion of the engine compartment to convey exhaust gases from the engine exhaust port to the atmosphere, a catalyzer in the exhaust system to treat the exhaust gases before discharge to the atmosphere, the cooling system communicating with the exhaust system such that a portion of the water is introduced into the exhaust system and a portion of the water is expelled separate from the exhaust system through a discharge conduit, the catalyzer comprising a catalyst bed positioned within a tube through which exhaust gases must flow, the tube being positioned within an expansion chamber of the exhaust system.  
     
     
       94. A small watercraft as in  claim 93  further comprising a second expansion chamber positioned along the exhaust system upstream of the catalyst.  
     
     
       95. A small watercraft as in  claim 93  further comprising a second expansion chamber positioned along the exhaust system upstream of the expansion chamber containing the catalyst.  
     
     
       96. A personal watercraft having a hull defining a rider's area sized to accommodate at least one rider, the hull defining an engine compartment containing an internal combustion engine having a cylinder block, at least one exhaust port and an output shaft, the engine also including a cooling system, a propulsion device carried by the hull on the underside thereof and being driven by the output shaft to propel the watercraft, the cooling system receiving water from a body of water in which the watercraft is being operated, an exhaust system that is connected to the cylinder block and that extends through at least a portion of the engine compartment to convey exhaust gases from the engine exhaust port to the atmosphere, a catalyzer in the exhaust system to treat exhaust gases before discharge to the atmosphere and the cooling system communicating with the exhaust system such that at least a portion of the water is introduced into the exhaust system and expelled into the body of water in which the watercraft is being operated through the exhaust system, the catalyzer being located upstream of a point at which the water is introduced into the exhaust system and apart from the cylinder block, the catalyzer comprising a catalyst bed positioned within a tube through which exhaust gases must flow, the tube being positioned within an expansion chamber of the exhaust system.  
     
     
       97. A personal watercraft as in  claim 96 , wherein at least a portion of the catalyzer is located behind a front end of the engine.  
     
     
       98. A personal watercraft as in  claim 96  further comprising a cooling jacket that extends along at least a portion of the exhaust system, a discharge conduit being formed separately from the exhaust system, and a portion of the coolant flowing through the cooling jacket being diverted from the coolant flow into the discharge conduit prior to the coolant being discharged into the body of water in which the watercraft is operating through the exhaust system.  
     
     
       99. A small watercraft as in  claim 96  further comprising a second expansion chamber positioned along the exhaust system upstream of the catalyst.  
     
     
       100. A small watercraft as in  claim 96  further comprising a second expansion chamber positioned along the exhaust system upstream of the expansion chamber containing the catalyst.