CA2179651A1

CA2179651A1 - Catalyst muffler system

Info

Publication number: CA2179651A1
Application number: CA002179651A
Authority: CA
Inventors: Michael S. Despain; Kevin F. Beaulieu; Kim Liechty
Original assignee: Individual
Current assignee: WCI Outdoor Products Inc
Priority date: 1994-11-18
Filing date: 1995-10-20
Publication date: 1996-05-30
Also published as: SE9602506L; EP0740739A1; AU4101496A; SE9602506D0; DE19581467T1; JPH09507898A; MX9602681A; US5521339A; SE510216C2; WO1996016258A1; JP3816953B2

Abstract

A muffler for coupling to an exhaust port of an internal combustion engine includes a housing, a first hollow body within the housing, a catalyzer within the first hollow body, and a second hollow body within the housing . The first hollow body has an inner surface defining a first chamber and an inlet adjacent the exhaust port to admit the exhaust gas into the first chamber. The exhaust gas is exothermally treated as it flows through the catalyst in the first chamber in a direction away from the engine and passes through an outlet of the first hollow body to a second chamber. The second chamber is formed by an inner surface of the second hollow body and an outer surface of the first hollow body. The treated exhaust gas flows through the second chamber in a direction toward the engine over the outer surface of the first hollow body and passes through an outlet of the second hollow body to a third chamber. The third chamber is formed by an outer surface of the second hollow body and an inner surface of the housing.
The outlet of the second hollow body is provided with louvers for directing the exhaust gas in a direction away from the engine in the third chamber. After expanding and mixing in the third chamber, the exhaust gas is expelled from the third chamber through an outlet of the housing adjacent the engine.

Description

2 ~ 7965 1 CATALY8T MUFFLER 8Y8TEM . -BACKGROUND OF TH~ INVENTIO~

3 The present invention relates to mufflers for internal

4 combustion engines and, more particularly, to a catalyst muffler system for an internal combustion engine used on 6 portable tools such as air blowers, f lexible line trimmers, 7 edgers, chain saws, and the like.

9 It is known to use a catalytic element or catalyzer in a muffler for a small two-cycle internal combustion engine 11 used on portable tools to reduce noxious components of 12 exhaust gas, such as hydrocarbons and carbon (1P. An 3 exothermal chemical conversion takes place in the catalyzer 14 where, for example, hydrocarbons are converted to carbon dioxide and water. The exhaust gas typically enters the 16 catalyzer with a temperature of approximately 600 degrees 17 centigrade (C). The conversion causes the temperature of 18 the exhaust gas to increase in the catalyzer to about 1000 19 degrees C.
Typically the catalyzer is relatively small because 21 the mufflers used on portable tools must be compact and 22 light weight. Because the catalyzer is small, and the 23 exhaust gas is typically energy rich for two-stroke 24 engines, a complete conversion of the noxious components of the exhaust gas is not obtained. This is particularly a 26 problem with regulations requiring increasingly low exhaust emission output levels. Additionally, the exhaust gas can 2 ignite if it reaches ambient air containing oxygen, through 3 the exhaust outlet or through a gap at the partition 4 interface of the muffler housing, at temperatures high enough for ignition. In hand-held portable tools, 6 operating personnel can be endangered by both high 7 temperature exhaust gas and ignition of exhauGt gas.
8 U.S. Patent No. 4,867,270, the disclosure of which is 9 herein expressly incorporated in its entirety, discloses a 10 muffler for a two-stroke engine having a catalyzer. The 11 catalyzer is located in a gas tight hollow body mounted in 12 a housing so as to be spaced on all sides from the housing 13 walls. The untreated exhaust gas passes over a portion of 14 the exterior surface of the hollow body to cool the hollow 15 body before entering the hollow body and passing through 16 the catalyzer. The hollow body has an outlet portion 17 tapered in the direction of f low to reduce self ignition of 18 the hot treated exhaust gas.
I9 U.S. Patent No. 4,890,690, the disclosure of which is 20 herein expressly incorporated in its entirety, discloses a 21 muffler for a two-stroke engine having a catalyzer. The 22 catalyzer and a partition wall establish two chambers in a 23 housing. The exhaust gas enters the first chamber and 24 passes through the catalyzer into the second chamber. The 25 treated exhaust gas leaves the housing through an outlet in 26 the second chamber. The partition wall is located 27 downstream of an interface of the housing so that the 8 treated exhaust gas cannot get back to the interface. The 2 ~ 79~5 1 partition wall includes a bypass hole so that-a portion of 2 the exhaust gas can bypass the catalyzer.
3 U.S. Patent ~o. 5,048,290, the disclosure of which is 4 herein expressly incorporated in its entirety, discloses a muffler for a two-stroke engine having a catalyzer. The 6 catalyzer is located in a tube spaced within a muffler 7 housing. An inner end of the tube facing the engine 8 exhaust port is closed by a convex perf orated plate so that g there i5 . les6 heat transmission to the engine. The outer end of the tube is closed by a lid with cooling plates.
11 The exhaust gas enters the housing and passes into the 12 catalyzer through the perforated plate. After passing 13 through the catalyzer, the exbaust gas is deflected by the 14 lid through an opening in the side of the tube to an outlet tube.
..
16 While these mufflers may reduce exhaust gas exit 17 temperature or muffler housing surface temperature, they 18 may have relatively high exhaust emission output levels.
19 Accordingly, there is a need for a compact and light weight 20 muffler for a two-stroke engine having a relatively low 21 exhaust emission output level and relatively low exhaust 22 gas exit temperature and muffler housing surface 23 temperature. Additionally, the muffler should provide good 24 noise reduction, maintain good engine performance, and be 25 reliable, inexpensive, and easy to manufacture.
26 SUMMI~RY OF T~IF INV~TIQN
27 The present invention provides a muffler for coupling to an exhaust port of an internal combustion~ engine that 2 solves the above-noted problems of the related art. The 3 muffler according to the invention includes a housing, a 4 first hollow body within the housing, and a catalyzer

5 within the first hollow body for exoth~rr-l ly treating

6 exhaust gas. The first hollow body has an inner surface

7 that f orms a f irst chamber and an outer 6urf ace that f orms

8 a 6econd chamber. An inlet is provided in the f irst hollow

9 body f or communicating the f irst chamber with the exhaust

10 port to admit the exhaust gas into the f irst chamber . The

11 first hollow body is also provided with an outlet for

12 passing gas from the f irst chamber to the second chamber .

13 The second chamber is provided with an outlet opposite the

14 outlet of the first hollow body such that treated exhaust

15 gas within the second chamber flows substantially across

16 the outer surface of the first hollow body in the second

17 chamber to reach the second chamber outlet.

18 BRT~ DESCRIPTION OF TH~ DRAWINGS

19 These and further features of the present invention will be apparent with reference to the following 21 description and drawings, wherein:
22 FIG. 1 is an elevational view, in cross-section, of a 23 power head of a portable tool with a two-cycle internal 24 combustion engine and a muffler according to the present invention;
26 FIG. 2. is a fragmentary plan view, partially in 27 cross-6ection, of the muffler;

FIG. 3 is a sectional view, taken along line 3-3 of 2 FIG . 2, of the muf f ler;
3 FIG. 4 i3 a sectional view, taken along line 4-4 of 4 FIG. 3, of an exhaust gas flow path through the muffler;
FIG. 5 is a sectional view, taken along line 5-5 of 6 FIG. 2, of the muffler;
7 FIG. 6 is a fragmentary eleYational view, partially in 8 cross-section, of an exhaust outlet of the muffler.
9 DETAILED D~GRTPTIO~ OF TR~ pR~EF~RR~n E~BOD~M~I~T
FIG. 1 illustrates a power head lO of a portable tool, 11 particularly a chain saw, including a muffler 11 according 12 to the present invention. The power head 12 is intended to 13 be representative of power heads f or portable tools in 14 general that are powered by internal combustion engines such as, for example, line trimmers, blowers, hedge 16 trimmers, edgers, lawn mowers, chain saws, and snow 17 throwers.
18 The power head 10 is powered by a two-cycle, single 19 cylinder, air cooled internal combustion engine 12. The engine 12 includes a cylinder 14 provided with a plurality 21 of externally disposed cooling fins 16. Preferably, the 22 cylinder 14 is made substantially of aluminum which is 23 lightweight and has a high thermal conductivity so that 24 heat from the interior of the cylinder 14 will be transferred to the cooling fins 16. In a conventional 26 manner a piston 18 reciprocates generally along an axis 20 27 within a bore 22 of the cylinder 14. The reciprocating 21 7965~
movement of the pi6ton 18 is translated into ~otation of a 2 crankshaft about the axis 20 by a rod 24 turning a crank 3 pin 26. The crankshaft is obscured by a counterweight 28 4 and the crank pin 26.
The top edge of the piston 18 controls the opening and 6 closing of a window 30 to an exhaust port 32. The exhaust 7 port 32 is directly coupled to an inlet 34 of the muffler 8 11. Exhaust gas from the bore 22 i8 discharged through the 9 exhaust port 32 and directed into the muffler 11 through the inlet 34. The muffler 11 is fastened directly to the 11 cylinder 14 using mounting bolts 36. Other types of 12 fasteners or retention methods such as springs may be 13 used.
14 As best seen in FIG. 4 the exhaust port 32 is lined with a steel sleeve 38 to form an air gap 40 circumscribing 16 the sleeve 38. The sleeve 38 and the air gap 40 have lower 17 coefficients of heating than the cylinder 14. The sleeve 18 38 and the air gap 40 thus act as insulators to slow the 19 rate of heat transference from the exhaust gas to the walls of the cylinder 14 . U. s . Patent Application Serial No.
21 08/072 164 the disclosure of which is expressly 2 2 incorporated herein in its entirety should be consulted 23 for more information on such sleeves.
24 A heat shield 42 is located between the muffler 11 and the cylinder 14 to reduce heat radiating from the muffler 26 11 to the cylinder 14. The heat shield 42 is preferably 27 made of aluminum for good heat dissipation. The heat 28 ~hield ~2 include~ an exhaust ope~ing which is aligned . ~ ?
during assembly with the exhaust port 32 and the muffler 2 inlet 34 to allow passage of the exhaust gas. The bolts 36 3 retaining the muffler 11 against the cylinder 14 extend 4 through openings in the heat shield 4 2 to retain the proper alignment. The surface of the heat shield 42 is preferably 6 generally e~ual to the muffler 11 so that it does not 7 obstruct the flow of cooling air past the cylinder 14 and 8 muf f ler 11.
9 The heat shield 42 is spaced apart from the cylinder 14 by an insulator or gasket 44 to introduce a layer of air 11 between the heat shield 42 and the cylinder 14 to slow 12 transmission of heat to the cylinder 14. The gasket 44 is 13 preferably made of steel or other materials providing some 14 degree of insulation. The gasket 44 includes an exhaust opening which is aligned during assembly with the exhaust . . _. .
16 port 32, the exhaust opening of the heat ~;hield, and the 17 muffler inlet 34 to allow passage of the exhaust gas. The 18 bolts 36 retaining the muffler 11 against the cylinder 14 19 extend through openings in the gasket 44 to retain the

20 proper alignment.

21 As seen in FIGS. 2-6, the muffler 11 includes a

22 housing 46, a catalyst tube assembly 48, a reflector 50, a

23 flame arrestor screen 52, and an exhaust outlet deflector

24 or louver 54. The muffler housing 46 is made of first and

25 second oppositely concave complementary shell members 56,

26 58. The shell members 56, 58 are formed by stamping a

27 rigid material such as sheet metal. The material must be

28 capable of withstanding extreme temperatures of the exhaust ~ - 21 7965~
gas generated by the engine.
2 As seen in FIG. 5, the first shell member 56 includes 3 a back wall 60, a side wall 62, and a flange 64. The 4 muffler inlet 34 is located in the back wall 60 such that it is in fluid communication with the exhaust port 32. The 6 back wall 60 also includes openings 66 for the mounting 7 bolts 36. The side wall 62 perpendicularly extends from 8 the periphery of the back wall 60. A muffler outlet 68 9 (FIG. 4) is located in the side wall 62 generally adjacent the back wall 60 at an upper portion of the first shell 11 member 56. The flange 64 outwardly extend6 from an outer 12 end of the side wall 62 opposite the back wall 60.
13 The second shell member 58 includes a front wall 70, a 14 side wall 72, and a flange 74. Three recesses 76 are formed in the front wall 70 and have openings 78 for the 16 mounting bolts 36. The side wall 72 perpendicularly 17 extends from the periphery of the front wall 70. The 18 flange 74 outwardly extends from an end of the side wall 72 19 opposite the front wall 70 and is crimped around the flange 64 of the first shell member 56 to attach the shell members 21 56, 58 in a gas tight manner and hold the muffler 11 22 together. The shell members 56, 58 could alternatively be 23 attached by other attaching means having a gas tight seal 24 such as, for example, welding or mechanical fasteners.
The housing 46 could alternatively have a double wall.
26 The double wall could comprise an inner wall and an outer 27 wall spaced from the inner wall to form an air gap. The 28 air gap could be filled with a high-temperature resistant ~1 21 79651 insulating material. The double walled housLng reduces the 2 skin temperature on the outside surface of the housing 46 3 by reducing the ability of the heat to transfer from the 4 inside of the housing 46.
As best seen in FIGS. 3-5, the catalyst tube assembly 6 48 is held within the housing 46 and includes a first 7 hollow body 80, a catalyzer 82, and a second hollow body 8 84. Each component of the catalyst tube assembly are g formed by stamping a rigid material such as sheet metal or other material that is capable of withstanding the extreme 11 temperatures of the exhaust gas. A central axis 85 of the 12 catalyst tube assembly 48 is coaxial with the exhaust port 13 32. ~he first hollow body 80 is tubularly-shaped having a 14 length sized to extend substantially from the back wall 60 of the first shell member 56 to the reflector 50. The 6 first hollow body 80 has a diameter sized to encircle the 17 muffler inlet 34. A plurality of outlets 86 are spaced 18 about the circumference of the first hollow body 80 19 adjacent an outer end of the first hollow body 80 close to the front wall 70 of the second shell member 58 and 21 opposite the inlet 34. As shown in FIG. 3, the illustrated 22 ~ r-~t includes seven circularly shaped outlets 86:
23 four equally spaced about the bottom of the first hollow 24 body 80; and three equally spaced about the top of the first hollow body 80.
26 As seen in FIGS. 3-5, the catalyzer 82 is located 27 within the first hollow body 80 at an inner end of the 28 ~lr:3t hollov body 80 ~dj ::ent the Inl~t 34 and opposlte th~

! 2 l 7965 1 outlets 86. The catalyzer 82 is generally sized to fill 2 the full cross-section of the first hollow body 80, but 3 preferably includes an axially extending opening 88 at the 4 central axis 85 of the cataly6t tube assembly 48.
Alternatively, a plurality of axially eXtending openings 6 could be provided.
7 The second hollow body 84 i5 tubularly-shaped having a 8 length generally equal to the length of the f irst hollow 9 body 80 and ~ulluul-ds the first hollow body 80. The second lo hollow body 84 has a diameter larger than the diameter of 11 the first hollow body 80. As best seen in FIG. 3, three 12 radially inwardly extending recesses 90 are formed in the 13 second hollow body 84. The recesses 90 are spaced on the 14 circumference of the second hollow body 84 and are sized 15 for accepting the mounting bolts 36. The recesses 90 and . . _ .
16 the diameter of the second hollow body 84 are sized such 17 that the first hollow body 80 is centered and held in 18 alignment with the central axis 85 of the catalyst tube 19 assembly 48. As best seen in FIG. 4, outlets 92 are spaced 20 about the circumference of the second hollow body 84 at the 21 inner end of the second hollow body 84 adjacent the muffler 22 inlet 34. The illustrated embodiment includes four of the 23 outlets 92 spaced around the circumference of the second 24 hollow body 84. Formed at each of the outlets 92 is a 25 deflector or louver 94 shaped for directing the exhaust gas 26 exiting the outlets 92 in a direction toward the outer end 27 of the second hollow body 84 opposite the muffler inlet 34.

28 The reflector 50 is generally planar, and has a shape ~ - ' 2 1 7~5 ~
~:ubstantially equal to the crol 6-E;ection Or the ~econd 2 shell member 58. The reflector 50 is formed by stamping a 3 rigid material such as sheet metal or other material that 4 is capable of withstanding the extreme temperatures of the exhaust gas. A generally perpendicularly extending lip 96 6 is provided at the periphery of the ref lector 50 . The 7 reflector 50 includes op~ninq~ 98 for the mounting bolts 8 36. As best seen in FIG. 4, arcuate first ridges 100 are 9 formed in the reflector 50 and extend from an outer surface of the reflector 50. The first ridges 100 are sized and 11 shaped to cooperate with the recesses 76 in the front wall 12 70 of the second shell member 58 to position the reflector 13 50 within the housing 46. The recesses 76 of the front 14 wall 70 of the second shell member 58 space the reflector 50 from the front wall 70 to reduce the temperature of the 16 front wall 70 by preventing the exhaust gas from directly 17 contacting the front wall. Arcuate second ridges 102 are 18 formed in the reflector 50 and extend from an inner surface 19 of the reflector 50. The second ridges 102 are sized and shaped to cooperate with the second hollow body 84 to 21 locate the catalyst tube assembly 48 centrally within the 22 housing 4 6 .
23 The flame arrestor screen 52 is generally tubularly-24 shaped having a length substantially equal to the second hollow body 84. The flame arrestor screen 52 has a 26 diameter slightly larger than a diameter formed by outer 27 surfaces of the louvers 94 of the second hollow body 84 so 28 that the flame arrestor screen 52 is coaxial with the first and second hollow bodies 80, 84. The flame arrestor screen 2 52 is preferably made of stainless steel mesh having 3 openings of . 020 inches or smaller.
4 The exhaust outlet louver 54 is attached to the housing 46 adjacent the exhaust outlet 68 in the first 6 shell member 56 of the housing 46. The louver 54 is shaped 7 for directing the exhaust gas exiting the exhaust outlet 68 8 in a direction away from the engine cylinder 14. As shown 9 in FIG. 6, an opening 104 is located in the exhaust outlet o louver 54 to admit ambient air into a low pressure zone in 11 the louver 54 created by the exiting exhaust gas. The 12 ambient air mixes with the exhaust gas to lower the 13 temperature of the exiting exhaust gas. The exhaust outlet 14 louver 54 or the exhaust outlet 68 is also provided with a spark arrestor screen. The spark arrestor 105 screen 52 is 16 preferably made of stainless steel mesh having openings of 17 . 020 inches or smaller.
18 The muffler 11 is assembled by placing the catalyst 19 tube assembly 48 in the first shell member 56 such that the inner end of the first hollow body 80 and the inner end of 21 the second hollow body 84 each abut the back wall 60 of the 22 first shell member 56. The flame arrestor screen 52 is 23 placed around the catalyst tube assembly 48 and against the 24 back wall 60 of the first shell member 56. The reflector 50 is positionea to abut and close the outer end of the 26 first hollow body 80 and the outer end of the second hollow 27 body 84. The outer end of the second hollow body 84 is 28 positio~ed within the ~ cond r dges 102 of the reflector 50 to position and orient the catalyst tube as6embly 48 2 relative to the reflector 50. The second shell member 58 3 is placed over the reflector 50 and positioned with the 4 recesses 76 within the first ridges 100 of the reflector 50 to position and orient the reflector 50 relative to the 6 housing 46. The flange 74 of the second shell member 58 is 7 crimped to the flange 64 of the first shell member 56. The 8 shell members 56, 58 thus clamp the catalyst tube assembly 9 48, the reflector 50, and the flame arrestor screen 52 in position.
ll As best seen in FIG. 4, the muffler 11 has first, 12 6econd, and third chambers 106, 108, 110. The first 13 chamber 106, which is cylindrically-shaped, is defined by 14 an inner surface of the first hollow body 80, the reflector 50, and the back wall 60 of the housing 46. The second 16 chamber 108, which is annularly shaped, is defined by an 17 outer surface 112 of the first hollow body 80, an inner 18 surface of the second hollow body 84, the reflector 50, and 19 the back wall 60 of the housing 46. The third chamber 110 i6 defined by an outer surface of the second hollow body 21 84, the reflector 50, and an inner surface of the housing 22 46.
23 As illustrated in FIG. 4, the exhaust gas flows 24 through the inlet 34, adjacent the exhaust port 32, and into the first chamber 106 at a temperature of about 600 26 degrees C. In the first chamber 106 the exhau6t gas enters 27 and flows through the catalyzer 82 in a direction away from 28 the engine cylinder 14. In the catalyzer 82 initial emission reduction occurs. After passing through the 2 catalyzer 82, the exhaust gas exits the first chamber 106 3 in a radial direction through the outlets 86, remote from 4 the inlet 34 and the exhaust port 32, and enter the second chamber 108. The exhaust gas exit6 the catalyzer 82 at a 6 very high temperature compared to its temperature upon 7 entering the catalyzer 82, typically from about 900 to 8 about 1000 degrees C. The reflector 50 closes off the 9 outer end of the first chamber 106 and prevents the hot 10 treated exhaust gas from contacting the front wall 70 of 11 the second shell member 56 to maintain a relatively low 12 surface temperature at the front of the muffler 11.
13 In the second chamber 108 the exhaust gas is directed 14 back toward the engine cylinder 14 such that it flows over the entire periphery of the outer surface 112 of the first 16 hollow body 80, which is very hot. The second chamber is a 17 relatively narrow annularly-shaped flow path for the 18 exhaust gas. An additional emission reduction occurs in 19 the second chamber 108 by a thermal reaction due to the high temperature o~ the outer surface 112 of the first 21 hollow body 80. The temperature required to continue 22 combustion in the second chamber 108 is at least about 750 23 degrees C. It can be further advantageous to provide a 24 catalytic coating on the outer surface 112 of the first hollow body 80 to obtain further emissiQn reduction in the 26 second chamber 108.
27 The exhaust gas exits the second chamber 108 through 28 the outlets 92 of the second hollow body 84, adjacent the 2 1 7q6~ 1 engine cylinder 14, and enters the third chamber llo. The 2 louvers 94 of the second hollow body 84 direct the exhaust 3 gas in a direction away from the engine cylinder 14. The 4 exhaust gas passes through the f lame arrestor screen 52 to 5 help insure that no f lames exit the muf f ler 11. Within the 6 third chamber 110 the exhaust gas is expanded and 7 thoroughly mixed. The exhaust gas exits the housing 46 by 8 pas6ing through the muf f ler outlet 68 into the exhaust 9 outlet louver 54. As the exhaust gas passes through the 10 orif ice in the exhaust outlet louver 54, ambient air is 11 drawn into the exhaust outlet louver 54 through the opening 12 104 and mixes with the exhaust gases to further cool the 13 exhaust gases. The exhaust gas exits the exhaust outlet 14 louver 54 and the spark arrestor screen 105 and is expelled 15 into the atmosphere in a direction away from the cooling . . _ 16 fins 16 of the engine cylinder 14.
17 Although a particular f -' ' i nt of the invention has 18 been described in detail, it will be understood that the 19 invention is not limited correspondingly in scope, but 20 includes all changes and modifications coming within the ~1 ~pirl ~nd term~ o~ the clai~ :ppended hereto.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:-

1. A muffler for coupling to an exhaust port of an internal combustion engine, said muffler comprising a housing;
a first hollow body within said housing having an inner surface partially defining a first chamber, an outer surface partially defining a second chamber, an inlet providing fluid communication between said first chamber and the exhaust port to admit exhaust gas from the internal combustion engine into said first chamber, and an outlet for communicating treated exhaust gas from said first chamber to said second chamber;
a catalyzer within said first chamber for exothermally treating said exhaust gas; and wherein said second chamber has an outlet opposite said outlet of said first hollow body such that treated exhaust gas flows substantially across said outer surface of said first hollow body in said second chamber.

2. The muffler according to claim 1, wherein said inlet to said first hollow body is located adjacent the exhaust port and said outlet from said first hollow body is located remote from the exhaust port such that the exhaust gas flows through said first chamber in a direction away from the exhaust port.

3. The muffler according to claim 1, further comprising a second hollow body within said housing having an inner surface partially defining said second chamber, an outer surface partially defining a third chamber, and an outlet communicating exhaust gas from said second chamber to said third chamber, said outlet of said second hollow body being located such that said treated exhaust gas flows substantially across said outer surface of said first hollow body.

4. The muffler according to claim 3, wherein said outlet of said second hollow body is provided with louvers adapted for directing the treated exhaust in a generally opposite direction of flow in said second chamber than in said first chamber.

5. The muffler according to claim 3, wherein said inlet of said first hollow body is located adjacent the exhaust port and said outlet of said first hollow body is located opposite said exhaust port such that said exhaust gas flows through said first chamber in a direction generally away from the exhaust port.

6. The muffler according to claim 4, wherein said outlet of said second hollow body is located at an end of said second hollow body adjacent the engine such that the treated exhaust gas flows through said second chamber in a direction generally toward the engine.

7. The muffler according to claim 6, wherein said outlet of said second hollow body is provided with louvers adapted for directing said treated exhaust gas in a direction generally away from the engine.

8. The muffler according to claim 3, further comprising a flame arrestor screen across said outlet of said second hollow body.

9. The muffler according to claim 3, wherein said first and second hollow bodies are tubularly-shaped and said muffler further comprises a reflector closing ends of said first and second hollow bodies opposite said engine.

10. The muffler according to claim 9, wherein at least a portion of said reflector is spaced from an inner surface of said housing.

11. The muffler according to claim 1, wherein said housing has an outlet with a louver for expelling said exhaust gas from said housing and directing said treated exhaust gas in a direction generally away from the engine.

12. The muffler according to claim 11, wherein said treated exhaust gas expelled from said housing creates a low pressure zone in said louver and said louver has an opening for admitting ambient air into said low pressure zone to mix said ambient air with said treated exhaust gas and cool said treated exhaust gas.

13. A muffler for coupling to an exhaust port of an internal combustion engine, the muffler comprising:
a housing having an inner surface;
a first hollow body within said housing and having an outer surface, an inner surface partially defining a first chamber, and an inlet for admitting exhaust gas into said first chamber;
a catalyzer within said first hollow body for exothermally treating said exhaust gas;
a second hollow body within said housing and having an inner surface and an outer surface, said inner surface of said second hollow body cooperating with said outer surface of said first hollow body to partially define a second chamber, said outer surface of said second hollow body cooperating with said inner surface of said housing to partially define a third chamber;
wherein said first hollow body has an outlet providing fluid, communication between said first chamber and said second chamber, said second hollow body has an outlet providing fluid communication between said second chamber and said third chamber, and said housing has an outlet for expelling exhaust gas from said third chamber.

14. The muffler according to claim 13, wherein said outlet of the second hollow body is located such that said treated exhaust gas flows substantially across said outer surface of said first hollow body in said second chamber.

15. The muffler according to claim 14, wherein said outlet of said second hollow body is provided with louvers adapted for directing said treated exhaust gas in a direction generally opposite a direction of treated exhaust gas flowing in said secondary chamber.

16. The muffler according to claim 13, wherein said inlet of said first hollow body is located adjacent the exhaust port and said outlet of said first hollow body is located remotely from the exhaust port and said inlet such that exhaust gas flows through said first chamber in a direction away from the exhaust port.

17. The muffler according to claim 16, wherein said outlet of said second hollow body is located at an end of said second hollow body adjacent the engine such that said treated exhaust gas flows through said second chamber in a direction toward the engine.

18. The muffler according to claim 17, wherein said outlet of said second hollow body is provided with louvers adapted for directing said treated exhaust gas in a direction generally away from the engine.

19. The muffler according to claim 13, further comprising a flame arrestor screen across said outlet of said second hollow body.

20. The muffler according to claim 13, wherein said first and second hollow bodies are generally tubularly-shaped and said muffler further comprises a reflector closing ends of said first and second hollow bodies opposite the engine.

21. The muffler according to claim 20, wherein said reflector plate is spaced from an inner surface of said housing.

22. The muffler according to claim 13, wherein said outlet of said housing has a louver for directing said treated exhaust gas in a direction away from the engine.

23. The muffler according to claim 22, wherein said treated exhaust gas exiting said outlet of the housing creates a low pressure zone in said louver and said louver has an opening for admitting ambient air into said low pressure zone to mix said ambient air with said treated exhaust gas and cool said treated exhaust gas.

24. A portable tool powered by an internal combustion engine, said portable tool comprising:
an internal combustion engine having a cylinder with an exhaust port for expelling exhaust gas from said cylinder after combustion;
a muffler comprising a housing, a first hollow body within said housing, and a catalyzer within said first hollow body for exothermally treating said exhaust gas, said first hollow body having an inner surface defining a first chamber, an outer surface defining a second chamber, an inlet providing fluid communication between said first chamber and said exhaust port to admit exhaust gas into said first chamber, and an outlet providing fluid communication between said first chamber and said second chamber to pass treated exhaust gas from said first chamber to said second chamber, said second chamber having an outlet opposite said outlet of said first hollow body such that treated exhaust gas flows substantially across said outer surface of said first hollow body in said second chamber; and fastening means for retaining said muffler against said cylinder.

25. The portable tool according to claim 24, said muffler further comprising a second hollow body within said housing having an inner surface cooperating with said outer surface of said first hollow body to define said second chamber, an outer surface cooperating with an inner surface of said housing to define a third chamber, and an outlet providing fluid communication between said second chamber and said third chamber, said outlet of said second hollow body being located such that said treated exhaust gas flows substantially across said outer surface of said hollow body .

26. The portable tool according to claim 25, wherein said first hollow body inlet of said muffler is located adjacent said exhaust port and said outlet of said first hollow body is located remote from said inlet and exhaust port such that said exhaust gas flows through said first chamber in a direction generally away from said exhaust port .

27 . The portable tool according to claim 26, wherein said second hollow body outlet of said muffler is located at an end of said second hollow body adjacent said engine such that treated exhaust gas flows through said second chamber in a direction generally toward said engine.

28. The portable tool according to claim 27, wherein said second hollow body outlet of said muffler is provided with louvers adapted for directing treated exhaust gas in a direction generally away from said engine.

29. The portable tool according to claim 25, said muffler further comprising a flame arrestor screen across the outlet of said second hollow body.

30. The portable tool according to claim 25, wherein said muffler housing has an outlet with a louver for expelling said exhaust gas from said housing and directing said treated exhaust gas in a direction generally away from said engine.

31. The portable tool according to claim 30, wherein said exhaust gas expelled from said housing creates a low pressure zone in said louver and said louver has an opening for admitting ambient air into said low pressure zone to mix said ambient air with said treated exhaust gas and cool said treated exhaust gas.