Compact slip-in spark arrestor

Abstract

A compact slip-in spark arrester having an interior shell (125) with a circular cross-section changing in diameter along its axial length which is axially aligned between an inlet cap member (115) and an outlet cap member (145). The tubular center section (130) of the interior shell (125) containing a centrifugal whirling means to remove any particulate matter from the exhaust flow by means of centrifugal force or deflection and trapping the particulate matter in an outer chamber (155) between the interior shell (125) and existing silencer shell (100).

Claims

1. A spark arrestor capable of fit interior to an existing silencer shell of an internal combustion engine exhaust system, comprising: An interior shell comprising a tubular center section located between an inlet cap member and an outlet cap member having passage diameters axial to and smaller in diameter compared to said tubular center section and said interior shell having a circular cross-section changing in diameter along the axial length between said inlet and outlet cap members with the largest of said diameter at said inlet cap member thereafter tapering down to the smallest of said diameter at said tubular center section before said diameter increases reaching a final diameter intermediate to said smallest and said largest and remaining constant thereby forming a second tubular section thereto having a plurality of passages cut into said second tubular section and said inlet cap member periphery fitting interior to said existing silencer shell and being rigidly mounted to said first shell thereby constraining exhaust flow into said spark arrestor to the passage diameter of said inlet and; an exterior shell containing a tubular conduit fixed in said passage diameter of said outlet cap member and communicating there between the atmosphere, said exterior shell forming a juncture with said tubular conduit at the atmosphere communicating end and also with said existing silencer shell and said outlet cap member thereby creating an enclosure about said tubular conduit, and also completing an outer chamber to said interior shell such that exhaust flow out of said spark arrestor and into the atmosphere is constrained to said tubular conduit; means axially disposed in said center section for reducing cross-sectional area thereof, for creating a whirling of said exhaust flow, and for deflecting any particulate matter out of said exhaust flow and through said plurality of passages into said outer chamber, said means including an apex section attached to a trailing cylinder oriented such that said cross-sectional area is gradually reduced with respect to said exhaust flow direction and thereby forming an annular passage where said exhaust flow is accelerated due to the reduced cross-sectional area, said means including a plurality of fins radially spaced in said annular passage and transversely oriented to said exhaust flow to impart said whirling thereby centrifugally accelerating said exhaust flow and any particulate matter suspend therein to the interior periphery of said interior shell wherein said particulate matter is removed from said exhaust flow as it passes through said plurality of passages and into said outer chamber.

2. A spark arrestor included as an original integral component of a silencer of an internal combustion engine exhaust system, comprising: An interior shell comprising a tubular center section located between an inlet cap member and an outlet cap member having passage diameters axial to and smaller in diameter compared to said tubular center section and said interior shell having a circular cross-section changing in diameter along the axial length between said inlet and outlet cap members with the largest of said diameter at said inlet cap member thereafter tapering down to the smallest of said diameter at said tubular center section before said diameter increases reaching a final diameter intermediate to said smallest and said largest and remaining constant thereby forming a second tubular section thereto having a plurality of passages cut into said second tubular section and said inlet cap member periphery fitting interior to said existing silencer shell and being rigidly mounted to said first shell thereby constraining exhaust flow into said spark arrestor to the passage diameter of said inlet and; an exterior shell containing a tubular conduit fixed in said passage diameter of said outlet cap member and communicating there between the atmosphere, said exterior shell forming a juncture with said tubular conduit at the atmosphere communicating end and also with said existing silencer shell and said outlet cap member thereby creating an enclosure about said tubular conduit, and also completing an outer chamber to said interior shell such that exhaust flow out of said spark arrestor and into the atmosphere is constrained to said tubular conduit; means axially disposed in said center section for reducing cross-sectional area thereof, for creating a whirling of said exhaust flow, and for deflecting any particulate matter out of said exhaust flow and through said plurality of passages into said outer chamber, said means including an apex section attached to a trailing cylinder oriented such that said cross-sectional area is gradually reduced with respect to said exhaust flow direction and thereby forming an annular passage where said exhaust flow is accelerated due to the reduced cross-sectional area, said means including a plurality of fins radially spaced in said annular passage and transversely oriented to said exhaust flow to impart said whirling thereby centrifugally accelerating said exhaust flow and any particulate matter suspend therein to the interior periphery of said interior shell wherein said particulate matter is removed from said exhaust flow as it passes through said plurality of passages and into said outer chamber.

3. A spark arrestor as defined in claim 1 and 2 wherein the length of said spark arrestor from said inlet cap member to said outlet cap member is less than 4 times the passage diameter of said inlet cap member.

4. A spark arrestor as defined in claim 1 and 2 wherein the profile of said apex section is elliptical.

5. A spark arrestor as defined in claim 1 and 2 wherein said means includes a teardrop tail attached axially to said trailing cylinder opposite of said apex section having a diameter equal thereto and thereafter progressively increasing before decreasing on approach to said outlet cap member thereby producing a deflecting surface transversely oriented to said exhaust flow whereby said particulate material from said exhaust flow impacting said deflecting surface is re-directed into said plurality of passages and said outer chamber outside of said exhaust flow.

6. A spark arrestor as defined in claims 1 and 2 wherein said tubular conduit is not consistent in cross-sectional area.

7. A spark arrestor as defined in claims 1 and 2 wherein the interior shape of said tubular conduit begins as circular at the point of exhaust flow entry thereafter changing to other than circular.

8. A spark arrestor as defined in claims 1 and 2 wherein said plurality of fins exhibit airfoil shaped surfaces with curvature including a first compound curvature in a plane parallel to the axis of said trailing cylinder, said first compound curvature having the characteristics of a curve made up of two or more circular arcs of successively shorter radii, joined tangentially without reversal of curvature thereby producing an airfoil mean camber line near parallel at said fins leading edge to said annular passage thereafter progressively diverging from alignment to said annular passage until reaching a maximum divergence at the rounded trailing edge of said airfoil shape.

9. A spark arrestor as defined in claims 1 and 2 wherein said plurality of fins exhibit airfoil shaped surfaces with curvature including a second compound curvature in a plane perpendicular to the axis of said trailing cylinder, said second compound curvature having the characteristics of a curve made up of two or more circular arcs of successively longer radii, with respect to proximity to the axis of said trailing cylinder, joined tangentially without reversal.

10. A spark arrestor as defined in claims 1 and 2 wherein a radiused transition exists between the outer periphery of said tubular conduit and said outlet cap member at or near said exhaust flow entrance to said tubular conduit.

11. A spark arrestor as defined in claims 1 and 2 wherein removal of said particulate matter from said exhaust flow of said internal combustion engine exhaust system is performed with a minimum of 80% efficiency.

12. A spark arrestor as defined in claims 1 and 2 wherein installation of said spark arrestor into said internal combustion engine exhaust system does not change the exhaust flow rate by more than about 0.5 cubic feet per minute at any operational back pressure compared to the exhaust flow rate prior to installation.

Description

DRAWINGS—FIGURES

[0016] FIG. 1 front vertical longitudinal sectional view of a spark arrestor constructed in accordance with the present invention as installed in an existing motorcycle silencer shell.

[0017] FIG. 2 isometric view of the interior shell.

[0018] FIG. 3 front view of the centrifugal whirling means.

[0019] FIG. 3A bottom view of the centrifugal whirling means.

[0020] FIG. 4 Flow comparison chart comparing current state of the art spark arrestors to the disclosed spark arrestor.

[0021]

TABLE-US-00002 Drawings-Reference Numerals 100 existing silencer shell 105 perforated tube 110 tubular conduit 115 inlet cap member 120 silencer packing 125 interior shell 130 tubular center section 135 second tubular section 140 plurality of passages 145 outlet cap member 150 radiused transition 155 outer chamber 160 exterior shell 165 apex section 170 trailing cylinder 175 plurality of fins 180 teardrop tail 185 small aperture 200 tabs 300 first compound curvature 305 second compound curvature

DETAILED DESCRIPTION—FIGS. 1, 2, 3, 3A

[0022] One embodiment of the disclosed spark arrestor is shown in FIG. 1 as it would be fit inside of an existing silencer shell 100 of a motorcycle exhaust system having an elliptical shape. The exhaust flow enters the spark arrestor at the bottom of FIG. 1 through a perforated tube 105 common to motorcycle silencers, and exits through a tubular conduit 110 to the atmosphere at the top of FIG. 1. The perforated tube 105 and entrance to the tubular conduit 110 are aligned axially. An inlet cap member 115 is positioned perpendicular to and in contact with the perforated tube 105 in addition to being in contact with the interior of the existing silencer shell 100 thereby producing a barrier between the silencer packing 120 used in motorcycle silencers, and the spark arrestor.

[0023] An interior shell 125 is aligned axially to the perforated tube 105 and exhibits a circular cross-section the diameter of which changes along its axial length. The diameter of the interior shell 125 is at a maximum where it is attached to the inlet cap member 115, this diameter may be truncated at the attachment to the inlet cap member 115 as required by geometrical constraints of the existing silencer shell 100. The diameter of the interior shell 125 subsequently tapers inward in a linear fashion to a radius transition into a tubular center section 130 having a diameter larger than that of the tubular conduit 110, thereafter the diameter continues to a second radius transition before increasing in a linear fashion and reaching a third radius transition into the second tubular section 135 of a diameter intermediate to the tubular center section 130 and maximum observed at the connection to the inlet cap member 115. A plurality of passages 140 are cut out of the second tubular section 135 and third radius transition. The subject embodiment presents 4 of such passages having equivalent shape, size, and equal symmetrical placement about the longitudinal axis of interior shell 125.

[0024] The interior shell 125 is also in assembled relation to an outlet cap member 145 by use of tabs 200 visible in FIG. 2. Again referring to FIG. 1, the outer periphery of the entrance to the tubular conduit 110 is joined to the outlet cap member 145 through a radiused transition 150 while an exterior shell 160 contains the tubular conduit 110 and completes an enclosure about it by forming a juncture with the tubular conduit 110 at the atmosphere communicating end and also with the existing silencer shell 100 and outlet cap member 145 creating an outer chamber 155 to the interior shell 125 such that exhaust flow into the atmosphere is constrained to the tubular conduit 110.

[0025] Again referencing FIG. 1, a centrifugal whirling means consisting of an apex section 165, a trailing cylinder 170, a plurality of fins 175, and a teardrop tail 180, is fixed in axial alignment with and interior to the interior shell 125 thereby forming an annular passage through which exhaust flow must pass. The apex section 165 is of a general conical shape having the apex oriented such that it is piercing oncoming exhaust flow and henceforth increasing in diameter to a maximum equal to the trailing cylinder 170 and attached thereto. The subject embodiment identifies six fins spaced evenly about the circumference of the trailing cylinder 170, and being contiguous to the interior shell 125 and trailing cylinder 170. Additionally a teardrop tail 180 is attached axially to the trailing cylinder 170 opposite of the apex section 165 having a diameter equal thereto and thereafter progressively increasing before decreasing on approach to the outlet cap member 145 and converging down to a small aperture 185.

[0026] Referring to FIG. 3 and FIG. 3A, the plurality of fins 175 of the present embodiment exhibit airfoil shaped surfaces with compound curvatures on two separate planes. In FIG. 3 a first compound curvature 300 is on a plane parallel to the interior shell 125 axis having the characteristics of a curve made up of two or more circular arcs of successively shorter radii, joined tangentially without reversal of curvature, producing an airfoil mean camber line near parallel at leading edge to the interior shell 125 axis thereafter progressively diverging from alignment until reaching a maximum divergence at the rounded trailing edge of said airfoil shape. As shown in FIG. 3A, a second compound curvature 305 in a plane perpendicular to the axis of the interior shell 125 is shown with the second compound curvature 305 having the characteristics of a curve made up of two or more circular arcs of successively longer radii, with respect to proximity to the axis of the trailing cylinder, joined tangentially without reversal.

Operation—FIGS. 1, 2, 3, 3A

[0027] Depending on the embodiment the disclosed spark arrestor may be installed interior to the existing silencer shell 100 of an internal combustion engine exhaust system as shown in FIG. 1, or constructed as an original integral internal component to a new silencer for an internal combustion engine exhaust system.

[0028] In function, as exhaust flow enters the spark arrestor shown in FIG. 1 through the perforated tube 105 and into the interior shell 125, the relatively large initial cross-sectional area therein compared to the perforated tube 105, serves to reduce the exhaust flow velocity and turbulence as the exhaust flow is re-directed into the annular passage created by the apex section 165 and tubular center section 130. As the exhaust flow enters the annular passage at the tubular center section 130 the cross-sectional area available for exhaust flow is reduced thereby increasing the exhaust flow velocity, also acting on the exhaust flow in this area are the plurality of fins 175 re-directing the flow into a whirling motion and imparting centrifugal force on the exhaust flow and particulate matter contained therein. The previously disclosed airfoil shape and compound curvature of the plurality of fins 175 are designed such that the typical turbulent flow region caused by the leading edge and body of straight flat fins of prior art is all but eliminated in this region, providing a reduction in back pressure compared to prior art. As the whirling exhaust flow exits the tubular center section 130, centrifugal force acts on particulate matter in the exhaust flow forcing it to the outside perimeter of the interior shell 125 where it passes through one of the plurality of passages 140 and is captured in the outer chamber 155. Additional particulate matter capture mechanisms include deflection of particulate matter off of the teardrop tail 180 or the radiused transition 150 of the outlet cap member 145 before entering one of the plurality of passages 140 and being removed from exhaust flow. The disclosed teardrop tail 180 also provides a tapering surface leading into the tubular conduit 110 that supports non-disrupted exhaust flow reducing back pressure and maintaining exhaust flow rate. The small aperture 185 in the teardrop tail 180 allows escape of pressure internal to the centrifugal whirling means if a brazing or welding construction method is used and also during normal operation as hot exhaust flow increases the internal temperature of the centrifugal whirling means. The curved nature of the tubular conduit 110 is common for motorcycle silencers for the purpose of exhaust flow noise attenuation and to prevent entrance of foreign matter when the exhaust flow is not present. The curvature may be adjusted depending on the spark arrestor mounting orientation for both of these purposes.

Example 1—FIG. 4

[0029] FIG. 4 summarizes flow testing performed on multiple aftermarket brands and models of new state of the art silencer systems that included integral centrifugal spark arrestors designed to replace the OEM silencer of 2017 KTM 250SX two-stroke motorcycles (KTM OEM part #554.05.079.000). Flow testing was also performed on the OEM non-spark arrested silencer (KTM OEM part #554.05.079.000) in addition to testing on the OEM silencer with 2 different screen type spark arrestors installed as well as the disclosed spark arrestor installed. The flow testing apparatus consisted of A LAMB brand blower used to generate airflow, a Pitot tube to capture dynamic pressure, and a port in the ducting for static pressure. Both pressures were measured using the same digital manometers and ducting diameter feeding the silencers was controlled in size to allow standard flow calculations using Bernoulli's equation. The flow rate range tested covers that which the subject engine would produce, 0-80 Cubic feet per minute (CFM), under normal operating conditions. All testing was performed under the same ambient conditions on the same day. As shown in FIG. 4 the disclosed spark arrestor installed into the OEM silencer produced the same flow rate for all given back pressure conditions compared to the OEM silencer without a spark arrestor. By comparison, all of the other spark arrestors tested produced moderate to severe reductions in flow rate at the subject back pressures compared to the OEM silencer without a spark arrestor.

Example 2—Table I

[0030] The arresting efficiency of the disclosed spark arrestor installed in an existing silencer shell (KTM OEM part #554.05.079.000) was tested by the USFS San Dimas laboratory and passed testing with an arresting efficiency of 80% or greater. Table I summarizes said test results.

TABLE-US-00003 TABLE I Flow rate Carbon size Back pressure Arresting Run (CFM) SAE J997 (psi) efficiency (%) 1 125 Large 0.99 87.21 2 125 Small 0.99 87.75 3 94 Large 0.78 82.38 4 94 Small 0.68 81.35 5 69 Large 0.28 89.91 6 69 Small 0.28 86.56 7 41 Large 0.5 84.35 8 41 Small 0.12 87.82 9 13 Large 0.01 N/A 10 13 Small 0.02 N/A