JP3469725B2 - Exhaust cooling structure of ship propulsion device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust system in which water is directly injected into exhaust gas introduced from an internal combustion engine through an exhaust passage of an exhaust pipe. The present invention relates to an exhaust cooling structure of a marine vessel propulsion device that cools a boat. [0002] The exhaust cooling structure of the marine propulsion device includes:
Conventionally, there is the one configured as follows. [0003] That is, an internal combustion engine is mounted on a hull floating on water such as the sea, and an exhaust pipe extending from the internal combustion engine is provided, and an inner hole of the exhaust pipe guides exhaust gas from the internal combustion engine. It has been. A water outlet opening toward the exhaust passage is formed in the exhaust pipe, and the water is injected into the exhaust passage through the water outlet. When the internal combustion engine is driven and the exhaust gas discharged from the internal combustion engine is guided through the exhaust passage,
Water is injected into the exhaust passage to cool the exhaust,
Thereafter, the exhaust gas and the water that has cooled the exhaust gas are discharged from the extended end of the exhaust pipe to the outside of the hull through the exhaust passage. [0005] In the above-mentioned prior art, the water injection port is opened in the direction toward the downstream side along the flow of the exhaust gas in the exhaust passage. However, the water injected from the water injection port into the exhaust passage is not dispersed throughout the exhaust passage, but tends to be supplied to a part of the exhaust flowing therethrough, so that there is an uneven cooling of the exhaust. Thus, the cooling may be insufficient. SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and is intended to make the water injected from the water injection port toward the exhaust passage more evenly supplied to each part of the exhaust. Accordingly, it is an object to sufficiently cool the exhaust gas. Another object is to achieve the above object with a simple configuration. [0008] The exhaust cooling structure of the boat propulsion device of the present invention for achieving the above object is as follows. The "means for solving the problem"
In the section, the terms in parentheses described below correspond to the terms in the claims. According to the first aspect of the present invention, an internal combustion engine 13 is mounted on a hull 3 floating on water 2, and a first exhaust pipe (exhaust pipe) 19 extending from the internal combustion engine 13 is provided. (Exhaust pipe) The inner hole of the exhaust pipe 19 serves as an exhaust passage 55 that guides exhaust 60 from the internal combustion engine 13, and the first exhaust pipe (exhaust pipe)
Pipe (tube) 19 is connected to each cylinder of the internal combustion engine 13
An exhaust pipe body 69 extending from the manifold 18;
The middle part of the exhaust pipe body 69 in the longitudinal direction is fitted to each other.
An inner cylinder 71 and an outer cylinder 72 are provided.
1 between the outer cylinder 72 and the fourth cooling water jacket (cooling water
And the fourth cooling water jacket.
(Cooling water jacket) 73
So as to supply, the exhaust passage 55 water injection port 80 that opens toward the forming in the first exhaust pipe (exhaust pipe) 19, the exhaust passage 5 the water 2 through the water injection port 80
5 between the downstream ends of the inner cylinder 71 and the outer cylinder 72.
A sealing material 74 is interposed, and the downstream end of the inner cylinder 71 is
A protrusion is formed in a direction along the exhaust 60 flowing through the exhaust passage 55.
78 are integrally protruded, and the fourth cooling
Water jacket (cooling water jacket) 73
Second water passage communicating with the exhaust passage 55 in the downstream portion of the body 69
A passage (water passage) 79 is formed, and the second water passage (water passage) is formed.
The downstream end of the water injection port 79 is defined as the water injection port 80.
0 is formed at the protruding end of the projection 78 and the water injection port 8 is formed.
0 is located near the inner surface 69a on the downstream side of the exhaust pipe main body 69 and faces the inner surface 69a. Embodiments of the present invention will be described below with reference to the drawings. In FIGS. 2 and 3, reference numeral 1 denotes a straddle-type (in other words, a saddle-ride type) small boat, which floats on water 2. An arrow Fr indicates the front of the boat 1 in the traveling direction. The hull 3 of the boat 1 is made of fiber reinforced resin (FRP), the lower part of which is a hull 4 and the upper part is a deck 5.
The joint between the hull 4 and the deck 5 is
It is. The interior of the hull 3 is divided into a front room 9 and a rear room 10.
The hull 4 and the inner surface of the deck 5 are firmly supported by the partition wall 11. A propulsion device 12 mounted on the hull 3 for propelling the hull 3 is provided. This propulsion device 1
Reference numeral 2 denotes a two-cycle multi-cylinder (three-cylinder) internal combustion engine 13 installed in the front chamber 9.
In the width direction, and is located substantially at the center thereof. Further, a fuel tank 14 for storing fuel to be supplied to the internal combustion engine 13 is also provided in the front chamber 9. An intake system member 15 for introducing air introduced into the front chamber 9 from the outside of the hull 3 through a vent (not shown) into the interior of the internal combustion engine 13, and extends from the internal combustion engine 13. An exhaust system member 16 is provided for taking out the exhaust of the internal combustion engine 13 to the rear of the hull 3.
The exhaust system member 16 is composed of an exhaust manifold 18, a first exhaust pipe 19, a backflow prevention box 20, and a second exhaust pipe 21, which are connected to each other in this order. The exhaust manifold 18 is connected to each cylinder of the internal combustion engine 13, while the downstream end of the second exhaust pipe 21 opens toward the rear of the hull 3, and the backflow prevention box 20 and the second exhaust pipe 21 Is installed in the rear room 10. A water pipe 23 having a front end connected to a bottom plate at the rear of the hull 4 and opening downward of the hull 3 and a rear end opening rearward of the hull 3 is provided. The flowing water pipe 23 has a circular cross section, and the inside thereof forms a water passage 24 for communicating the lower part of the rear part of the hull 3 with the rear of the hull 3. A jet injection means 27 is provided which is driven by receiving power from the internal combustion engine 13. The jet injection means 27 has a propulsion shaft 28 that rotates by receiving power from the internal combustion engine 13. The propulsion shaft 28 extends in the front-rear direction, and its front end is interlocked with the crankshaft of the internal combustion engine 13. The rear end is located in the water passage 24, and an impeller 29 is attached to the rear end. A steering pipe 30 which is fitted to the rear end of the water pipe 23 and is supported at the rear of the hull 3 is provided. The steering pipe 30 is supported so that its rear part can be turned up and down and left and right. I have. On the other hand, a handle 31 is projected from an upper portion of the hull 3, and the steering pipe 30 is connected to the handle 31 in an interlocking manner. Behind the handle 31, a straddle-type seat 32 is provided on the upper surface of the hull 3.
The handle 31 can be gripped by a rider seated on the steering wheel 2. When the internal combustion engine 13 is driven, the power output by the internal combustion engine 13 is applied to the jet injection means 27.
Of the water 25 in the water passage 24 by the impeller 29 which is transmitted to the propulsion shaft 28 and rotates with the propulsion shaft 28.
Is accelerated rearward, so that water 25 below the hull 3 moves from the front end of the water passage 24 to the water passage 24.
While being sucked into the inside, it is jetted rearward from the rear end through this water passage 24, and by the reaction force of this injection,
The boat 1 is propelled forward. Further, if the steering wheel 31 is operated to rotate the steering pipe 30 so as to change the attitude, the direction of the injection is changed so that the boat 1 is steered in a desired direction. Has become. Referring to FIGS. 4 and 5, the internal combustion engine 13 includes:
A rubber elastic buffer 35 and a bracket 3 are mounted on the hull 3.
6 and a crankshaft 38 having an axis extending substantially horizontally in the front-rear direction is provided in the crankcase 37.
8 is supported by the crankcase 37 so as to be rotatable around its axis. A cylinder 40 is supported on the upper surface of the crankcase 37. The cylinder 40 has an aluminum alloy cylinder block 40a attached to the upper surface of the crankcase 37. The cylinder block 40a is formed with three holes 40b whose axes are substantially vertical and penetrates in the vertical direction, and these holes 40b are arranged side by side in the front-rear direction. A sleeve 40c made of cast iron is fitted into each of the holes 40b by shrink fitting, and the inside of each of the sleeves 40c is formed as a cylinder hole 40d.
The axes are substantially vertical and extend parallel to one another. The lower ends of these cylinder holes 40d are communicated with the inside of the crankcase 37. An aluminum alloy cylinder head 4 that integrally closes and opens the upper end opening of each of the cylinder holes 40d.
The cylinder head 40e is detachably fastened to the upper end surface of the cylinder block 40a by a fastener 40f. A gasket 40g is interposed between the upper end surface of the cylinder block 40a and the lower end surface of the cylinder head 40e, and the gasket 40g seals between the cylinder block 40a and the cylinder head 40e. The gasket 40g has three circular openings 40h corresponding to the cylinder holes 40d. A piston 41 is slidably fitted in each cylinder hole 40d of the cylinder 40 in the axial direction, and these pistons 41 and the crankshaft 38 are connected to each other by a connecting rod 42. The crankcase 37 has an intake port 44 for each cylinder, and each of the intake ports 44 is provided with a reed valve 45. On the other hand, the cylinder 40
The crankcase 3
A scavenging passage 47 communicating from the inside of the chamber 7 to the combustion chamber 46 is formed, and an exhaust port 48 communicating from the combustion chamber 46 to the exhaust manifold 18 is formed. Also,
A spark plug 49 whose discharge section faces the combustion chamber 46 is attached to a cylinder head 40e of the cylinder 40. An intake guide member 51 constituting a part of the intake system member 15 is attached to the crankcase 37 of the internal combustion engine 13. This intake guide member 51 is
The intake pipe 52 has one end attached to the crankcase 37 and a floatless vaporizer 53 attached to the other end of the intake pipe 52. The intake guide member 51 includes an intake passage 54 that communicates the outside of the internal combustion engine 13 into the crankcase 37 of the internal combustion engine 13.
have. An intake box 56 constituting a part of the intake system member 15 is supported on the upper end surface of the carburetor 53, and the internal space of the intake box 56 communicates the outside with the intake passage 54. On the other hand, the inner holes of the exhaust manifold 18, the first exhaust pipe 19, the backflow prevention box 20, and the second exhaust pipe 21 form an exhaust passage 55 for communicating the exhaust port 48 to the outside of the hull 3. . When the internal combustion engine 13 is driven and the piston 41 moves toward the top dead center, a negative pressure is generated in the crankcase 37, and external air 57 is released by the negative pressure into the intake box. 56 and the intake passage 54 of the intake guide member 51, and is sucked toward the inside of the crankcase 37. The intake passage of the carburetor 53 is connected to the air 57
When the fuel gas passes, fuel 58 is supplied to the air 57 from the carburetor 53, and an air-fuel mixture 59 is generated. The air-fuel mixture 59 is sucked into the crankcase 37 through the intake port 44 and the reed valve 45 by the negative pressure in the crankcase 37. Next, when the piston 41 moves toward the bottom dead center, the inside of the crankcase 37 is pressurized,
With this pressure, the air-fuel mixture 59 sucked into the crankcase 37 is pre-compressed and supplied to the combustion chamber 46 through the scavenging passage 47, where it is subjected to combustion. Thereafter, the piston 41 moves toward the bottom dead center again, and at this time, the gas generated by the combustion is exhausted as the exhaust 60, the exhaust manifold 18, the first exhaust pipe 19, the backflow prevention box 20, and The exhaust gas is discharged to the outside of the hull 3 through the exhaust passage 55 of the second exhaust pipe 21. Thereafter, the above operation is repeated to convert the energy by the combustion into power, and this power is transmitted to the jet injection means 27 as described above, and the boat 1 is propelled. 1 to 7, an internal combustion engine 13 of the propulsion device 12 and an exhaust gas 6 discharged from the internal combustion engine 13 are shown.
A cooling device 63 is provided for cooling each of the cooling water 0 and water 2 with water 2. The cooling device 63 will be described. A first cooling water jacket 64 is formed in the exhaust manifold 18. A second cooling water jacket 64 is formed in the cylinder block 40 a so as to communicate with the first cooling water jacket 64.
A cooling water jacket 65 is formed, and a third cooling water jacket 67 that communicates with the second cooling water jacket 65 through a water passage hole 66 formed in the gasket 40g.
Are formed on the cylinder head 40e. In FIGS. 1, 6, and 7, the first exhaust pipe 1
Reference numeral 9 denotes a metal exhaust pipe main body 69 extending from the exhaust manifold 18, and a rubber elastic exhaust pipe 70 for communicating the extension end of the exhaust pipe main body 69 with the backflow prevention box 20.
The elastic exhaust pipe 70 is formed by elastic deformation of the elastic exhaust pipe 70 and the extension end of the exhaust pipe main body 69 and the backflow prevention box 2.
Dimensional errors between zero and zero are absorbed,
Are communicated with each other. An intermediate portion in the longitudinal direction of the exhaust pipe main body 69 is composed of an inner cylinder 71 and an outer cylinder 72 fitted substantially coaxially with each other. A fourth cooling water jacket 73 is formed. A seal member 74 is provided between each downstream end of the inner cylinder 71 and the outer cylinder 72.
Are interposed and sealed. The downstream portion of the exhaust pipe main body 69 is a bent portion that is bent downward in an arc shape when viewed in the flow direction of the exhaust gas 60. Looking at the flow direction of the exhaust 60, the fourth
A pair of first water passages 76 are formed in the inner cylinder 71 to communicate the cooling water jacket 73 with the exhaust passage 55 in the downstream portion of the exhaust pipe main body 69. A pair of water injection ports 77, 77 ′, which are downstream ends of the first water passages 76 opening toward the exhaust passage 55, are formed on an end face 71 a at a downstream end of the inner cylinder 71, and are connected to the exhaust passage 55. Located at the top of. More specifically, of the pair of water injection ports 77, 77 ', one water injection port 77 is
5, that is, the one water injection port 77
Is a virtual perpendicular 75 passing through the center of the cross section of the exhaust passage 55.
Are arranged in the vicinity. The exhaust pipe main body 69 is located near the side of the internal combustion engine 13, and the other water injection port 77 ′ is disposed on the opposite side of the virtual perpendicular 75 from the internal combustion engine 13. . Each of the water injection ports 77 and 77 ′ opens in a direction along the exhaust gas 60 flowing through the exhaust passage 55, and is formed on the inner surface of the bent portion at the downstream portion of the exhaust pipe main body 69. The opening is open toward the arcuate concave surface 69b where the radius of curvature about the center of bending of the bent portion is substantially maximum. At the downstream end of the inner cylinder 71, a projection 78 is integrally provided to project in a direction along the exhaust gas 60 flowing through the exhaust passage 55, and the fourth cooling water jacket 73 is attached to the projection 78. A second water passage 79 communicating with the exhaust passage 55 in the downstream portion of the exhaust pipe main body 69 is formed. A water injection port 80, which is a downstream end of the second water passage 79 that opens toward the exhaust passage 55, is formed at a protruding end of the projection 78, and is located above the exhaust passage 55 and the virtual perpendicular. It is arranged on the internal combustion engine 13 side with reference to 75. The water injection port 80 of the second water passage 79 is located near the inner surface 69a of the exhaust pipe main body 69 of the first exhaust pipe 19, and the water injection port 80 has The inner surface 69a faces the inner surface 69a so as to be substantially perpendicular to the inner surface 69a. Further, a third water passage 81 which connects the fourth cooling water jacket 73 to the exhaust passage 55 in the elastic exhaust pipe 70 is formed in the exhaust pipe main body 69. On the other hand, a water supply pipe 82 made of a tube is provided for communicating the water passage 24 near the downstream side of the impeller 29 with the first cooling water jacket 64 of the exhaust manifold 18. As described above, when the boat 1 is propelled forward by driving the internal combustion engine 13, the water passage 24 near the downstream side of the impeller 29
Since the pressure of the water 2 is increased, a part of the water 2 is supplied to the first cooling water jacket 64 through the water supply pipe 82 at that pressure, and then the second cooling water jacket 65 is supplied therefrom.
And the third cooling water jacket 67 and the fourth cooling water jacket 73 are sequentially supplied to the internal combustion engine 13 and the first cooling water jacket 73.
The exhaust pipe 19 and the exhaust 60 are cooled. A part of the water 2 supplied to the fourth cooling water jacket 73 is discharged to the outside of the hull 3, and the other part is the first water passage 76, the second water passage 79, and the third water passage 81.
The water 2 is supplied to the exhaust gas 60 passing through the exhaust gas passage 55, whereby the water 2 is supplied to the exhaust gas 60 passing through the exhaust gas passage 55, whereby the exhaust gas 60 is cooled.
And the exhaust 60 are discharged outside the hull 3. In the above case, at the bent portion on the downstream side of the exhaust pipe main body 69, the exhaust air 60 is
Since it flows while contacting a larger amount, the arcuate concave surface 69
The portion b is likely to be heated by the exhaust gas 60 to have a high temperature. However, as described above, since the water injection ports 77 and 77 'are open toward the arcuate concave surface 69b, these water injection Water 2 injected from the mouth 77, 77 '
Accurately collides with the arcuate concave surface 69b to surely cool it. On the other hand, the water injection port 80 of the second water passage 79
Is located near the inner surface 69a of the exhaust pipe main body 69 and is substantially perpendicular to the inner surface 69a. Therefore, the water 2 injected from the water injection port 80 toward the exhaust passage 55 is The exhaust gas 60 passing through the exhaust passage 55 does not flow down to the downstream side of the exhaust passage 55 but collides with the inner surface 69a of the exhaust pipe main body 69 with almost the same momentum. Therefore, the water 2 injected from the water injection port 80 collides with the inner surface 69a and rebounds vigorously, scatters in all directions of the exhaust passage 55, and
Each portion of the exhaust 60 passing through 5 is supplied more uniformly.
For this reason, it is prevented that the cooling of the exhaust 60 is biased, and the cooling is sufficiently performed. Further, since the water injection port 80 is disposed on the side of the internal combustion engine 13 with respect to the virtual perpendicular 75, the water injection port 80 is heated by the internal combustion engine 13 and the temperature of the exhaust pipe body 69 tends to increase. The side portion on the internal combustion engine 13 side is more reliably cooled by the water 2 injected from the water injection port 80. As described above, since the water injection port 80 is open at the upper part of the exhaust passage 55 of the exhaust pipe main body 69, at least a part of the water 2 injected from the water injection port 80 The exhaust pipe main body 69 reaches the top of the inner surface 69a of the exhaust pipe main body 69 by vigor.
Allow to cool to the top of Therefore, each part in the cross section of the exhaust pipe main body 69 is more uniformly cooled. Each of the water injection ports 7 of the first water passage 76
7, 77 'may face the inner surface 69a of the exhaust pipe main body 69 in the same manner as the water injection port 80 of the second water passage 79. Further, one water injection port 77 of the first water passage 76 may be located on the virtual perpendicular 75. 5, 8 to 10, the structure of the gasket 40g will be described in detail. The gasket 40g is composed of an upper plate 85 and a lower plate 86 which are superimposed on each other, and
The plates 85 to 87 are made of stainless steel and fixed to each other. The upper and lower plates 85, 8
6 have the same thickness, the intermediate plate 87 is made thinner than this thickness, and the opening edge of the circular opening 40h of the intermediate plate 87 is folded back to form a double structure. It has a substantially flat shape. As described above, the gasket 40g has three circular openings 40h corresponding to the respective cylinder holes 40d of the three cylinders of the internal combustion engine 13. Seen in the radial direction of each of these circular ports 40h, the gasket 40g is
Each of the cylinders has an annular inner portion 89, an intermediate portion 90, and an outer portion 91 in a radially outward direction, and an inner bent portion 92 between the inner portion 89 and the intermediate portion 90. Between the intermediate portion 90 and the outer portion 91.
3 are interposed, and these 89 to 93 are integrated with each other. The thickness of the inner portion 89 (upper and lower plates 8)
Dimension between the outer surfaces of 5,86, the same below) is H _1,
85 and 86 above, the lower plate of the inner bent portion 92, the thickness dimension of H ₂ the intermediate portion 90 is bent, respectively so as to be larger than the H _1. The upper and lower plates 85 and 86 in the outer bent portion 93 are connected to the outer portion 9.
1 are each bent so that the thickness dimension H ₃ is larger than the above H ₂ . The inner portion 89 is provided on the sleeve 4
0c and the cylinder head 40e facing this.
The intermediate portion 90 and the inner bent portion 92 face the upper end surface of the cylinder block 40a radially outwardly adjacent to the upper end surface of the sleeve 40c. The outer portion 91 and the outer bent portion 9 are sandwiched between the lower end surface of the cylinder head 40e and the outer portion 91.
3 is sandwiched between the upper end face of the cylinder block 40a including the periphery of the fastener 40f and the lower end face of the cylinder head 40e facing the same. In the above case, the fastening force of the fastener 40f between the cylinder block 40a and the cylinder head 40e tends to be lower at the front and rear ends than at the midway in the front-rear direction between the two blocks 40a and 40e. Before and at the rear end, the sealing performance of the gasket 40g tends to decrease. Therefore, the radial width L ₁ of the inner bent portion 92 at the front and rear ends of the gasket 40 g is set to the radial width of the inner bent portion 92 at the middle part in the front-rear direction of the gasket 40 g. smaller than the dimension L _2, thereby, before the gasket 40 g, to increase the surface pressure of the inner bent portion 92 at the rear end portion, with, thereby preventing deterioration of sealing performance as described above. According to the present invention, an internal combustion engine is mounted on a hull floating on water, an exhaust pipe extending from the internal combustion engine is provided, and an exhaust hole from the internal combustion engine is provided through an inner hole of the exhaust pipe. The exhaust pipe is connected to each cylinder of the internal combustion engine.
Equipped with an exhaust pipe body extending from the connected exhaust manifold.
The middle part of the exhaust pipe body in the longitudinal direction is fitted to each other.
Of the inner and outer cylinders
Forming a cooling water jacket between them, this cooling water jacket
The water with an increased pressure is supplied to the exhaust pipe, and a water injection port that opens toward the exhaust passage is formed in the exhaust pipe. In the exhaust cooling structure of a marine vessel propulsion device , a sealing material is provided between each downstream end of the inner cylinder and the outer cylinder.
Through the exhaust passage at the downstream end of the inner cylinder.
A projection is integrally provided in the direction along the exhaust
First, the cooling water jacket is connected to the downstream portion of the exhaust pipe main body.
Forming a water passage communicating with an exhaust passage in the inside of the water passage;
With the downstream end of the water jet as the water jet
Formed at the protruding end of the exhaust pipe main body.
It is located near the inner surface of the downstream portion and faces this inner surface. For this reason, the water injected from the water injection port toward the exhaust passage is not swept away by the exhaust passing through the exhaust passage, but collides with the inner surface of the exhaust pipe main body with almost the same momentum. Becomes Therefore, the injected water collides with the inner surface and rebounds vigorously, scatters in all directions of the exhaust passage, and is more uniformly supplied to each part of the exhaust passing through the exhaust passage. For this reason, it is prevented that the cooling of the exhaust gas is biased, and the cooling is sufficiently performed. Further, as described above, when the water injected from the water injection port is scattered in all directions in the exhaust passage, the water injection port is simply made to face the inner surface near the inner surface of the exhaust pipe main body. In other words, since an additional member such as an injection nozzle for scattering water is not required, the above-described effect of sufficiently cooling the exhaust gas can be achieved with a simple configuration.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partially enlarged view of FIG. FIG. 2 is an overall side view of the boat. FIG. 3 is an overall plan view of the boat. FIG. 4 is a rear view of the boat propulsion device. FIG. 5 is a partially enlarged sectional view of FIG. 4; FIG. 6 is a partially enlarged sectional view of FIG. 2; FIG. 7 is a sectional view taken along line 7-7 in FIG. 1; FIG. 8 is a partially cutaway plan view of a gasket of a cylinder. FIG. 9 is a sectional view taken along line 9-9 of FIG. 8; FIG. 10 is a sectional view taken along line 10-10 of FIG. 8; [Description of Signs] 1 boat 2 water 3 hull 12 propulsion device 13 internal combustion engine 14 fuel tank 18 exhaust manifold 19 first exhaust pipe (exhaust pipe) 51 intake guide member 54 intake passage 55 exhaust passage 60 exhaust 63 cooling device 69 exhaust Pipe body 69a Inner surface 75 Virtual perpendicular 71 Inner cylinder 72 Outer cylinder 73 Fourth cooling water jacket (Cooling water jacket) 74 Seal material 78 Projection 79 Second water passage (Water passage) 80 Water injection port

Claims (1)

(57) [Claims 1] An internal combustion engine is mounted on a hull floating on water, an exhaust pipe extending from the internal combustion engine is provided, and an inner hole of the exhaust pipe is connected to the internal combustion engine. An exhaust passage for guiding exhaust gas, wherein the exhaust pipe is connected to each cylinder of the internal combustion engine.
An exhaust pipe body extending from the air manifold is provided.
The inside of the trachea body with the longitudinal middle part
It consists of a cylinder and an outer cylinder, and the cooling water is
A jacket is formed and pressure is applied to this cooling water jacket.
A water jet that supplies the obtained water, the water jet opening that opens toward the exhaust passage is formed in the exhaust pipe, and the water is jetted into the exhaust passage through the water jet. In the exhaust cooling structure of the propulsion device , a sealing material is provided between each downstream end of the inner cylinder and the outer cylinder,
At the downstream end of the inner cylinder, along the exhaust flowing through the exhaust passage
A projection is integrally provided in the direction of
Exhaust passage in the downstream part of the exhaust pipe body
Water passage that communicates with the
This water jet is used as a water jet at the protruding end of the projection.
An exhaust cooling structure for a boat propulsion device, wherein the water injection port is formed near the inner surface of a downstream portion of the exhaust pipe main body, and faces the inner surface.