Patent Application
20230128285
The following is a tabulation of some prior art that presently appears relevant:
This invention relates to internal combustion engine exhaust systems for off-road vehicles (ORVs) such as motorcycles, three and four wheel all-terrain vehicles (ATVs), side by side or utility task vehicles (UTVs), two and four wheel drive off-road automobiles and trucks, any of which could have the disclosed invention applied to their exhaust systems, however; for the purposed of discussion, will be described specifically for motorcycles.
Currently in the U.S.A. it is required for all federal public lands, in addition to most state and locally owned lands used by the public, that internal combustion engines operated on said lands must possess a functional spark arresting device on the exhaust system to prevent emission of hot sparks in the form of particulate matter or debris such as carbon particles that may start fires. The arresting efficiency of these spark arrestors is tested by measuring the percent of carbon particles retained or destroyed by the spark arrestor under test conditions described by the United States Forest Service (USFS) and Society of Automotive Engineers (SAE), with a passing arresting efficiency of 80% or greater.
The two classifications of spark arrestors for small engines as described by the USFS include:
Spark arrestors are typically mounted downstream in the exhaust flow just prior to the exhaust exit and traditionally for motorcycles attached to the end of or internal to the silencer, which is the last component of the exhaust system and functions to attenuate the exhaust noise. Because the spark arrestor is placed inside of the silencer, the size is critical and preferred to be as small as possible so that more of the overall silencer volume may be utilized to perform its primary function of attenuating the exhaust noise. If a spark arrestor is too long and takes up too much of the allocated silencer volume, the resulting exhaust system can be too loud to meet maximum sound restrictions, specifically the 96 decibel maximum as defined by the USFS for off-highway vehicles.
The primary design challenge for a spark arrestor is to meet the 80% arresting efficiency requirement while imparting a minimal change to exhaust flow rate. This is a significant design challenge because the two factors of exhaust flow rate and spark arresting efficiency are fundamentally competing mechanisms such that as the spark arrestor design is modified to increase arresting efficiency there is classically a reduction of exhaust flow rate that accompanies this improvement. Specifically for screen type spark arrestors: the addition of a screen mesh to the exhaust flow path disrupts laminar flow which increases back pressure and creates a significant reduction in exhaust flow rate. Additionally, as the screen becomes clogged with particulate matter, back pressure is further increased as the available flow path area is reduced and the reduction in exhaust flow rate compounded until the screen is removed and cleaned. Compared to screen type spark arrestors, centrifugal type spark arrestors typically have less of an effect on exhaust flow rate and do not become clogged because the particulate matter is removed from and trapped outside of the flow path. The increased back pressure and associated flow rate reduction created by centrifugal type spark arrestors is a result of turbulent flow disorders caused by the addition of flow path directors such as fins and annular chambers which serve to accelerate flow, change flow direction, divert, and then trap the exhaust particulate matter. Typically as more flow path directors are added to the system, arresting efficiency goes up along with the number of turbulent flow disorders which causes an increase in back pressure and decrease in exhaust flow rate.
Specifically for motorcycle engines, the current state of the art screen and centrifugal spark arresting devices meeting the 80% arresting efficiency requirement produce roughly a 25-55% change in flow rate for a given back pressure. The 25-55% change in flow rate reduces the engines volumetric efficiency and hence performance. Historically this decrease in engine performance has been accepted as a necessary compromise to meet the 80% arresting efficiency requirement and acts as a deterrent to the use of a spark arrestor.
The disclosed spark arrestor design is the first that has been shown to reach the goal of no change in flow rate, while at the same time meeting the 80% arresting efficiency requirement. In addition, the disclosed design is compact enough to fit inside of existing original equipment manufacturer (OEM) off-highway vehicle exhaust system silencers without adding additional length to the silencer, and also meeting the goal of not increasing sound levels. This compact size characteristic increases marketable value for the design because an aftermarket spark arrestor slip-in for existing OEM silencers may be produced at a much lower cost compared to a completely new silencer system containing a centrifugal type spark arrestor.
Both U.S. Pat. No. 3,407,575 to Krizman (1968) and U.S. Pat. No. 3,009,539 to Papp (1961) disclose centrifugal type spark arrestors but make no claims as to capability of meeting any specific arresting efficiencies, flow rate goals, or size requirements. This prior art does not disclose the novel features of a centrifugal whirling means having an elliptically shaped apex section, compound curvature of fins on two planes, teardrop tail, nor interior shell novel features of both converging and diverging sections with a plurality of passages, or the radiused transition disclosed. It has been demonstrated that the application of these features results in a design which meets the 80% arresting efficiency goal with no change in flow rate. In addition, the compact size of this design has been fit into existing off-highway vehicle silencers and allows for more than sufficient silencing space to meet the 96 decibel requirement.
Papp discloses fin curvature but not compound curvature and curvature in one plane not two which is required to reduce turbulent flow and still provide significant directional velocity for particulate matter to be ejected from the exhaust flow stream. Furthermore, Papp discloses the location of these fins to be on the upstream conical component of the centrifugal whirling means as opposed to the disclosed spark arrestor identifying fin placement after the conical component.
Both Papp and Krizman disclose conical sections to the leading profile of the centrifugal whirling means with the conical sections having open bodies at the rear, this open body design produces significant turbulent flow post whirling means which reduces flow rate & decreases arresting efficiency. By adding a trailing cylinder and closed section tail cone with a teardrop shape the post turbine flow turbulence is significantly reduced so as not to affect flow rate. The bulb tail cone also serves to deflect impacting particulate matter from the exhaust flow stream increasing arresting efficiency.
A compact slip-in spark arrestor with novel features consisting of: a centrifugal whirling means having an elliptically shaped apex section, compound curvature of fins on two planes, teardrop tail, an interior shell of both converging and diverging sections with a plurality of passages, and the radiused transition disclosed. This novel spark arrestor design is compact enough such that it may be inserted into existing OEM exhaust system silencers without increasing sound output and exhibits performance attributes of a minimum of 80% spark arresting efficiency with no change in exhaust flow rate.
One embodiment of the disclosed spark arrestor is shown in
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.
The interior shell 125 is also in assembled relation to an outlet cap member 145 by use of tabs 200 visible in
Again referencing
Referring to
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
In function, as exhaust flow enters the spark arrestor shown in
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.
This application claims the benefit of provisional patent application Ser. No. 63/271,858, filed 2021 Oct. 26 by the present inventor.
| Number | Date | Country | |
|---|---|---|---|
| 63271858 | Oct 2021 | US |
