System for cooling catalytically combusted exhaust gases of hydrocarbon-fueled internal combustion engines used in small power plants and power tools

Abstract

The invention relates to a system for cooling catalytically combusted exhaust gases of hydrocarbon-fueled internal combustion engines used in small power plants and power tools. An exhaust gas cooling system for cooling catalytically combusted exhaust gas in a small power plant is disclosed. The system includes a cooling air guide and a mixing chamber. The mixing chamber includes an intake end, an exhaust end, and at least one cooling inlet. A short length exhaust device including a catalytic converter is operably connected to the intake end of the mixing chamber and is operable to direct catalytically combusted exhaust through the intake end into the mixing chamber. A cooling air guide is operably connected to the at least one cooling inlet and is operable to direct cooling air through the at least one cooling inlet into the mixing chamber. The mixing chamber is operable to promote mixing of catalytically combusted exhaust gas and cooling air to reduce a peak temperature of the combined exhaust gas.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. patent application serial number 63 / 521,945 filed on June 20, 2023 and U.S. patent application serial number 63 / 524,098 filed on June 29, 2023, which are incorporated herein by reference in their entirety. Technical Field

[0003] The present disclosure relates to a system for reducing the peak temperature of catalytically burned exhaust gas emitted by a hydrocarbon fueled internal combustion engine having a short length exhaust system typically used in small power equipment and power tools. Such a system is expected to reduce the risk of fire, equipment damage, and injury to operators and personnel near the system. Background Art

[0004] Internal combustion engines utilize combustion, which is a chemical process that releases energy from a fuel and air mixture. An internal combustion engine converts the energy from the combustion of fuel and air into work at its core, and work is defined as force multiplied by distance. For example, in a typical spark-ignition internal combustion engine, fuel is mixed with air and forced into a cylinder, which is then compressed by a piston and ignited by a spark, which is combustion. The expansion of the combustion gases produced pushes the piston, which in turn rotates the crankshaft connected to the gear system in the powertrain. The powertrain then applies the power and torque generated by the engine to any application being used (e.g., wheels of a car, alternators of a generator, cutting blades of a lawn mower, etc.). There are two main byproducts of combustion, namely heat and exhaust. Both heat and exhaust must be carefully controlled to prevent engine failure, harm to the operator, and damage to the surrounding environment and personnel.

[0005] As mentioned, an internal combustion engine burns a mixture of fuel and air. The fuel used in an internal combustion engine is typically a hydrocarbon fuel composed exclusively of hydrogen atoms and carbon atoms. Air is primarily composed of nitrogen (about 78%) and oxygen (about 21%). During the combustion of the fuel-air mixture, a chemical reaction occurs in which the hydrocarbon reacts with the oxygen to produce carbon dioxide, water, and heat. Specifically, the carbon in the hydrocarbon fuel combines with the oxygen in the air to produce carbon dioxide (CO 2 ), the hydrogen in the hydrocarbon fuel combines with oxygen in the air to produce water vapor (H 2 O). Most of the nitrogen (N 2 ) through the internal combustion engine. Therefore, in a complete combustion, the only emission is nitrogen (N 2 ), carbon dioxide (CO 2 ) and water vapor (H 2 O).

[0006] Unfortunately, however, combustion in an internal combustion engine is never complete and produces a number of lesser amounts of harmful byproducts. The most common harmful byproducts are carbon monoxide (CO), hydrocarbons or volatile organic compounds (VOCs, mainly evaporated, unburned fuel); and nitrogen oxides (NO and NO 2 , collectively referred to as NOx). These harmful byproducts pose serious health and environmental risks. Therefore, since about the 1980s, government agencies (such as the EPA in the United States) have legislated that larger internal combustion engines used in most new cars, trucks, and boats include catalytic converters to eliminate or reduce the amount of harmful byproducts produced by the combustion process.

[0007] Catalytic converters use catalytic events (i.e., chemical reactions) to burn off harmful byproducts of combustion exhaust at very high temperatures. Catalytic converters typically include two types of catalysts: reduction catalysts and oxidation catalysts. These converters consist of a ceramic structure coated with a metal catalyst, which typically contains platinum, rhodium, and / or palladium. Reduction catalysts use platinum and rhodium to help reduce NOx emissions by separating molecules into nitrogen and oxygen. Nitrogen is trapped within the catalytic converter, while oxygen passes through it. Oxidation catalysts reduce unburned hydrocarbons and carbon monoxide by burning (i.e., oxidizing) them over platinum and palladium catalysts, thereby producing carbon dioxide.

[0008] The chemical reaction in the catalytic converter generates significant heat. In small internal combustion engine applications with short exhaust systems, this significant heat can be more difficult to manage. Due to the short flow length between the catalytic converter and the muffler outlet in such small engine applications, the catalytically burned exhaust gas temperature at the muffler outlet can reach 700-1200°F. A non-catalyzed exhaust system of the same length will have significantly lower muffler outlet temperatures, in the range of 400-600°F.

[0009] In contrast, for the larger-scale internal combustion engine applications used in various machines and vehicles (such as cars, trucks, or boats), there are various ways to cool the exhaust gas through catalytic combustion before it is released into the environment. For example, in many vehicles with large-length exhaust systems, the exhaust system design itself can help to cool the exhaust gas before it leaves the tail pipe. These exhaust systems are typically composed of pipes, mufflers, and resonators that guide the combustion exhaust gas from the internal combustion engine to the tail pipe. The length, diameter, and route of the exhaust pipe can help dissipate heat from the gas when the gas flows through the system and its different components, thereby allowing the exhaust gas through catalytic combustion to cool before it is released into the atmosphere.

[0010] Some vehicles also utilize exhaust gas recirculation (EGR) systems to control combustion temperatures. EGR involves redirecting a portion of the combustion exhaust gas back into the intake system of the internal combustion engine. This process reduces the oxygen concentration in the combustion chamber, lowering the peak combustion temperature and thus lowering the temperature of the combustion exhaust gas. EGR systems typically employ a heat exchanger to further cool the recirculated combustion exhaust gas before it is reintroduced into the engine.

[0011] Likewise, internal combustion engines used in marine applications on ships or boats have additional cooling options due to the ample availability of cooling water. For example, many water-cooled internal combustion engines used on boats have cooling water injected into the exhaust pipe, which greatly cools the exhaust and also significantly dampens engine noise.

[0012] Therefore, while catalytic converters are required in larger internal combustion engine applications that power cars, trucks, and boats, manufacturers have developed ways to cool the exiting catalytically burned exhaust gases before releasing them into the atmosphere, thereby reducing the risk of fire, component failure, and injury.

[0013] Unlike cars, trucks, and boats, which have been subject to stringent emission requirements set by the EPA (U.S. Environmental Protection Agency) for many years, regulations for small power equipment and power tools that utilize hydrocarbon fuel internal combustion engines have been much less restrictive until now. Such power equipment may include, but is not limited to, gasoline or gas generators (conventional generators and inverters), lawn mowers, leaf blowers, chain saws, and weed beaters. In the past, these smaller internal combustion engine applications used on small power equipment and power tools did not require the use of catalytic converters to reduce harmful byproducts, and therefore did not require exhaust thermal management systems to reduce the risk of fire and damage to the equipment itself, because non-catalytic combustion exhaust has a significantly lower temperature than exhaust that has passed through a catalytic converter.

[0014] Potential regulatory changes may require the use of catalytic converters on many smaller hydrocarbon fueled internal combustion engines, which presents new problems for manufacturers. Many of these smaller internal combustion engine applications used in small power equipment and power tools are tightly packaged and have short length exhaust systems that do not have the same heat dissipation characteristics as the larger exhaust systems used in many vehicles as described above. Therefore, the use of catalytic converters (which produce catalytically burned exhaust gas that exits at higher temperatures) poses significant safety issues to both the power tool and the operator of the power equipment, creating a risk of failure of the equipment itself, and a risk of fire to anything or anyone in the immediate vicinity of the equipment.

[0015] For example, certain equipment powered by internal combustion engines that are stationary when in use (e.g., portable generators (conventional portable generators and inverters), air compressors, or pumps) are often located near buildings or residences. In addition, the fact that the equipment is stationary when in use provides an additional complication because there is no constant moving air to help dissipate the combustion exhaust. Therefore, not only is there an increased risk of the equipment itself melting or catching fire, but there is also a risk of fire for anything near the equipment that is subject to the catalyzed combustion exhaust. Similarly, tools powered by internal combustion engines (e.g., chain saws, blowers, weed beaters) and movable equipment (e.g., lawn mowers, snow blowers, etc.) are also at an increased risk once the combustion exhaust is catalyzed. While these devices are often in motion and therefore have some passive airflow to dissipate the combustion exhaust, there is an increased risk of burns or injuries to the operator because these devices and tools are held or operated in close proximity to people.

[0016] The present disclosure provides various systems to cool catalytically combusted exhaust gases in short length exhaust systems used in small power equipment and power tools to significantly reduce the temperature of these exhaust gases before they are released into the atmosphere. The systems described in the present disclosure significantly reduce the risk of fire, equipment failure, or injury to operators and personnel in close proximity to the equipment. Summary of the invention

[0017] According to an embodiment, an exhaust cooling system for cooling catalytically burned exhaust gas in a small power plant includes: a cooling air guide; and a mixing chamber, the mixing chamber including an intake end, an exhaust end, and at least one cooling inlet, wherein: a short-length exhaust device including a catalytic converter is operably connected to the intake end of the mixing chamber, and is operable to guide the catalytically burned exhaust gas through the intake end and into the mixing chamber; the cooling air guide is operably connected to at least one cooling inlet, and is operable to guide cooling air through at least one cooling inlet and into the mixing chamber; and the mixing chamber is operable to promote mixing of the catalytically burned exhaust gas and cooling air to reduce the peak temperature of the combined exhaust gas. The short length exhaust device may further include a muffler outlet pipe; the mixing chamber may further include a vortex mixer; and the cooling air guide may further include an air guide panel, wherein: the vortex mixer may include a vortex vane assembly positioned around a cylindrical sleeve, wherein the vortex vane assembly may be operable to introduce cooling air and catalytic combustion exhaust gas into the mixing chamber to promote mixing of catalytic combustion exhaust gas with cooling air, the cylindrical sleeve may be operably connected to the muffler outlet pipe, and the air guide panel may include at least one radial rib, wherein the at least one radial rib may be operable to guide cooling air into at least one cooling inlet. The air guide panel may include an orifice sized to accommodate the mixing chamber. At least one cooling inlet may include a plurality of cooling inlets, and at least one radial rib may include a plurality of radial ribs. The mixing chamber may further include a diffuser, which is operable to diffuse the combined exhaust gas before the combined exhaust gas leaves the exhaust end of the mixing chamber. The diffuser may include a conical diffuser. The diffuser may include a vane diffuser. The diffuser may include a perforated tube diffuser. The mixing chamber may further include a venturi section, and at least one cooling inlet may include at least one venturi inlet, wherein the venturi section may include a reduced diameter section, and at least one venturi inlet is arranged in the reduced diameter section; and the venturi section may be operable to promote mixing of the catalytic combustion exhaust gas with the cooling air. The mixing chamber may further include a vortex mixer, the vortex mixer including a plurality of vortex blades positioned around the venturi section, wherein the plurality of vortex blades may be operable to introduce cooling air and the catalytic combustion exhaust gas into the mixing chamber. The mixing chamber may further include a coaxial mixer, wherein: at least one cooling inlet may include an external cooling air duct, the internal muffler outlet pipe may be at least partially positioned within the external cooling air duct, and the coaxial mixer may be operable to coaxially mix the catalytic combustion exhaust gas with the cooling air to promote mixing of the catalytic combustion exhaust gas with the cooling air.The mixing chamber may further include a tangential vortex mixer, and the at least one cooling inlet may further include at least one tangential inlet duct; wherein: the tangential inlet duct may be operable to tangentially direct cooling air into the mixing chamber to introduce cooling air and catalytic combustion exhaust into the mixing chamber, thereby promoting mixing of the catalytic combustion exhaust and the cooling air.

[0018] According to an embodiment, a small power device includes: an internal combustion engine; a short-length exhaust device, the short-length exhaust device including a catalytic converter operably connected to the internal combustion engine, the short-length exhaust device being operable to receive combustion exhaust from the internal combustion engine; an exhaust cooling system, the exhaust cooling system being operably connected to the short-length exhaust device, the exhaust cooling system being operable to receive catalytically burned exhaust from the short-length exhaust device; wherein the exhaust cooling system includes: a cooling air guide; and a mixing chamber, the mixing chamber including an intake end, an exhaust end, and at least one cooling inlet, wherein: the short-length exhaust device is operably connected to the intake end of the mixing chamber; the cooling air guide is operably connected to at least one cooling inlet and is operable to guide cooling air through at least one cooling inlet and into the mixing chamber; and the mixing chamber is operable to promote mixing of the catalytically burned exhaust and the cooling air to reduce the peak temperature of the combined exhaust. The short-length exhaust device may further include a muffler outlet pipe; the mixing chamber may further include a vortex mixer; and the cooling air guide may further include an air guide panel, wherein: the vortex mixer may include a vortex vane assembly positioned around a cylindrical sleeve, wherein the vortex vane assembly may be operable to introduce cooling air and catalytic combustion exhaust gas into the mixing chamber to form a vortex to promote mixing of the catalytic combustion exhaust gas and the cooling air, the cylindrical sleeve may be operably connected to the muffler outlet pipe, and the air guide panel may include at least one radial rib, wherein the at least one radial rib may be operable to guide the cooling air into at least one cooling inlet. The mixing chamber may further include a venturi section, and the at least one cooling inlet may include at least one venturi inlet, wherein the venturi section may include a reduced diameter section, and the at least one venturi inlet is arranged in the reduced diameter section; and the venturi section may be operable to promote mixing of the catalytic combustion exhaust gas and the cooling air. The mixing chamber may further include a vortex mixer including a plurality of vortex blades positioned around the venturi section, wherein the plurality of vortex blades may be operable to introduce cooling air and catalytic combustion exhaust gas into the mixing chamber. The mixing chamber may further include a coaxial mixer, wherein: at least one cooling inlet may include an external cooling air duct, the internal muffler outlet pipe may be at least partially positioned within the external cooling air duct, and the coaxial mixer may be operable to coaxially mix the catalytic combustion exhaust gas with the cooling air to promote mixing of the catalytic combustion exhaust gas with the cooling air. The mixing chamber may further include a tangential vortex mixer, and at least one cooling inlet may further include at least one tangential inlet duct; wherein: the tangential inlet duct may be operable to tangentially direct cooling air into the mixing chamber to introduce cooling air and catalytic combustion exhaust gas into the mixing chamber, thereby promoting mixing of the catalytic combustion exhaust gas with the cooling air.The small power plant may further include a powered fan operable to force a flow of cooling air into the cooling air guide.

[0019] According to an embodiment, a method for cooling catalytically burned exhaust gas in a small power plant including a short-length exhaust device includes: providing an exhaust cooling system, the exhaust cooling system including a cooling air guide and a mixing chamber; guiding the catalytically burned exhaust gas into the mixing chamber; guiding the cooling air into the mixing chamber via the cooling air guide; and mixing the catalytically burned exhaust gas with the cooling air in the mixing chamber to reduce the peak temperature of the combined exhaust gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The following is a brief description of the drawings related to the present disclosure, which will be discussed in more detail in the detailed description section below:

[0021] Figure 1 A perspective cutaway view of a portable generator including an exhaust cooling system for cooling catalytically combusted exhaust gas is illustrated.

[0022] Figure 2 A perspective cutaway view of a cooling assembly for a portable generator including a mixing chamber and an air directing panel is illustrated, and a flow diagram is depicted showing the path of a mixture of engine cooling air, catalytically combusted exhaust gas, and combined exhaust gas.

[0023] Figure 3 A partially cut-away top plan view of a cooling assembly for a portable generator including a mixing chamber and an air directing panel is illustrated, and a flow diagram showing the path of a mixture of engine cooling air, catalytically combusted exhaust gas, and combined exhaust gas is depicted.

[0024] Figure 4 A detailed perspective view of a cooling assembly for a portable generator including a mixing chamber and a vortex mixer is illustrated.

[0025] Figure 5 A partially cut-away perspective view is illustrated showing a cooling assembly including a mixing chamber, a vortex mixer, and a portion of an air directing panel.

[0026] Figure 6 A front perspective view of a cooling assembly for a portable generator is illustrated, the cooling assembly including a mixing chamber, a vortex mixer, and an air directing panel.

[0027] Figure 7 A rear perspective view thereof is shown.

[0028] Figure 8 The figure shows a top plan view thereof.

[0029] Fig. 9 Illustrated is a front elevation view of an alternative configuration of an exhaust cooling assembly including a plurality of bypass holes that allow some of the engine exhaust to escape such that only a portion of the engine cooling air is directed into the vortex mixer.

[0030] Fig.10 A rear perspective view thereof is shown.

[0031] Fig.11 A front perspective view of a vortex mixer is shown.

[0032] Fig.12 A rear perspective view thereof is shown.

[0033] Fig.13 The diagram shows its front elevation view.

[0034] Fig.14 The figure shows a top plan view thereof.

[0035] Fig.15 A partially cut-away perspective view of an alternative configuration of a mixing chamber is illustrated, the mixing chamber including a muffler outlet having a venturi section and an aspiration port for drawing cooling air into the exhaust flow.

[0036] Fig.16 yes Fig.15 A flow diagram for the illustrated configuration shows the paths of the mixture of engine cooling air, catalytically combusted exhaust gas, and combined exhaust gas.

[0037] Fig.17 A partially cut-away perspective view of an alternative configuration of a mixing chamber is illustrated, the mixing chamber including a muffler outlet having a venturi section and an extraction port for drawing cooling air into the exhaust flow, and further including a vortex mixer.

[0038] Fig.18 yes Fig.17 A flow diagram for the illustrated configuration shows the paths of the mixture of engine cooling air, catalytically combusted exhaust gas, and combined exhaust gas.

[0039] Fig.19 A detailed perspective view of an alternative configuration of a mixing chamber and swirl mixer is illustrated, the configuration including a concentric air gap between the muffler outlet pipe and the swirl vane assembly.

[0040] Fig. 20 Picture shows Fig.19 A partially cutaway perspective view of the configuration shown.

[0041] Fig.21A front elevation view of an alternative configuration of a mixing chamber and swirl mixer is illustrated, the configuration including an air gap between a muffler outlet pipe and a plurality of swirl vanes of a swirl vane assembly directly attached to the mixing chamber.

[0042] Fig. 22 Picture shows Fig.21 A partially cutaway perspective view of the configuration shown.

[0043] Fig.23 Illustrated is a front elevation view of an alternative configuration of a concentric flow mixing chamber omitting the swirl vane assembly.

[0044] Fig.24 Picture shows Fig.23 A partially cutaway perspective view of the configuration shown.

[0045] Fig.25 A perspective view of an exemplary coaxial mixer is illustrated.

[0046] Fig.26 A perspective view of an alternative configuration of an exhaust cooling system for use with an internal combustion engine powering small power equipment and power tools is illustrated, the exhaust cooling system including a coaxial mixer and a mixing chamber.

[0047] Fig. 27 A perspective view of an alternative configuration of an exhaust cooling system for use with an internal combustion engine powering small power equipment and power tools is illustrated, the exhaust cooling system including a coaxial mixer and a venturi section.

[0048] Fig.28 is a detailed cross-sectional view of an alternative mixing chamber including a tangential inlet duct.

[0049] Fig.29 is along Fig.28 A cross-sectional view taken along line 29-29 in FIG.

[0050] Fig.30 An exemplary damper for use with an exhaust cooling system used with an internal combustion engine that powers small power equipment and power tools is illustrated, which damper may be used to adjust the volume of air directed into and out of a cooling assembly.

[0051] Fig.31 An alternative configuration of an exhaust cooling system for use with an internal combustion engine powering small power equipment and power tools is illustrated, the exhaust cooling system including an auxiliary electric fan for controlling the flow of cooling air directed into the system.

[0052] Fig.32 A perspective cutaway view of an alternative configuration including a diffuser is illustrated.

[0053] Fig.33 A detailed perspective view of the swirl vane assembly and diffuser is shown.

[0054] Fig.34 A perspective view of an exemplary conical diffuser attached to a coaxial mixer is illustrated.

[0055] Fig.35 A perspective view of an exemplary conical diffuser is illustrated.

[0056] Fig.36 A perspective view of an exemplary perforated tube diffuser attached to a coaxial mixer is illustrated.

[0057] Fig.37 Illustrated is a partial perspective view of an open frame generator including an exhaust cooling system including an air guide to direct engine cooling air into a closed muffler assembly for cooling catalyzed engine combustion exhaust gas.

[0058] Fig.38 Picture shows Fig.37 Another partial perspective view of the configuration shown.

[0059] Fig.39 is an exemplary open frame generator along Fig.38 A cross-sectional view taken along line 39-39 of FIG. 1 shows an exemplary open frame generator including an exhaust cooling system utilizing a mixing chamber and a vortex mixer, and depicts a flow diagram showing the flow of a mixture of engine cooling air, catalytically combusted exhaust, and combined exhaust.

[0060] Fig.40 An exemplary open frame generator including an exhaust cooling system utilizing a mixing chamber and a venturi section is illustrated, and a flow diagram showing the flow of a mixture of engine cooling air, catalytically combusted exhaust gas, and combined exhaust gas is depicted.

[0061] Fig.41 Illustrated is a perspective view of an alternative configuration of an exhaust cooling system for use with an internal combustion engine for powering small power equipment and power tools, the exhaust cooling system including a venturi section attached at the muffler outlet for drawing in ambient air for mixing with the catalytically combusted exhaust gas.

[0062] Fig.42 Another perspective view of an alternative configuration of an exhaust cooling system for use with an internal combustion engine for powering small power equipment and power tools is illustrated, the exhaust cooling system including a venturi section attached at the muffler outlet and depicting a flow diagram showing the flow of a mixture of cooling air, catalytically combusted exhaust gas, and combined exhaust gas.

[0063] Fig.43 A stereoscopic view of an alternative configuration of an exhaust cooling system for use with an internal combustion engine for powering small power equipment and power tools is illustrated, the exhaust cooling system including a tightly packed exhaust extension and a venturi section, and a flow diagram showing the flow of a mixture of cooling air, catalytically combusted exhaust gas through the tightly packed exhaust extension, and the combined exhaust gas.

[0064] Fig.44 A perspective view of an alternative configuration for a venturi section is shown.

[0065] Fig.45 Picture shows Fig.44 Front elevation view of the venturi section.

[0066] Fig.46 A front elevation view of an alternative configuration for a venturi section is illustrated.

[0067] Fig.47 A perspective view of an alternative configuration of an exhaust cooling system for use with an internal combustion engine powering small power equipment and power tools is illustrated, the exhaust cooling system being integrated into the muffler of the exhaust system and showing a partially recessed venturi section.

[0068] Fig.48 Picture shows Fig.47 A partial cross-sectional view of a system showing the internal chamber of the exhaust system, the catalytic converter and the exhaust cooling system, and depicting a flow diagram showing the flow of the mixture of engine cooling air, catalytically combusted exhaust gas, and combined exhaust gas.

[0069] Fig.49 Picture shows Fig.47 A partially cut-away side view of an alternative configuration of a system depicting different geometries of the cooling air inlet.

[0070] Fig.50 Picture shows Fig.47 0026] A partial cross-sectional side view of another alternative configuration of a system of FIG. 1 depicting a different geometry of the cooling air inlet.

[0071] Fig.51 A partially cutaway stereoscopic view of an alternative configuration of an exhaust cooling system for use with an internal combustion engine for powering small power equipment and power tools is illustrated, showing a mixing chamber integrated into the muffler enclosure of the exhaust system, and depicting a flow diagram showing the flow of catalytically combusted exhaust gas through a tightly packaged exhaust extension.

[0072] Fig.52A perspective view of an alternative configuration of an exhaust cooling system for use with an internal combustion engine for powering small power equipment and power tools is illustrated, the exhaust cooling system including a tightly packaged exhaust extension surrounding a muffler enclosure surrounding a Fig.51 The outer walls of the system are shown as translucent to illustrate the internal path of the tightly packed exhaust extension.

[0073] Fig.53 Picture shows Fig.52 Another perspective view of a system of FIG. 1 and depicting a flow diagram showing the flow of catalytic combustion exhaust gas through a tightly packed exhaust extension. The outer wall of the system is shown as semi-transparent to illustrate the internal path of the tightly packed exhaust extension.

[0074] Fig.54 A perspective view of an alternative configuration of an exhaust cooling system for use with an internal combustion engine that powers small power equipment and power tools is illustrated, the exhaust cooling system including a tightly packed exhaust extension surrounding a muffler enclosure, and depicting a flow diagram showing the flow of catalytic combustion exhaust gas through the tightly packed exhaust extension. The outer wall of the system is shown as semi-transparent to illustrate the internal path of the tightly packed exhaust extension.

[0075] Fig.55 A perspective view of an alternative configuration of an exhaust cooling system for use with an internal combustion engine for powering small power equipment and power tools is illustrated, showing an alternative configuration of an air directing panel. For clarity of illustration, the air directing panel is shown as being translucent.

[0076] Fig.56 is along Fig.55 The cross-sectional view taken along line 56 - 56 in FIG. 5 depicts a flow diagram showing the path of the mixture of engine cooling air, catalytically combusted exhaust gas, and combined exhaust gas.

[0077] Fig.57 A perspective view of an alternative configuration of an exhaust cooling system for use with an internal combustion engine powering small power equipment and power tools is illustrated, showing an alternative configuration of an air directing panel and including a venturi section. For clarity of illustration, the air directing panel is shown as translucent.

[0078] Fig.58 is along Fig.57 The cross-sectional view taken along line 58 - 58 in FIG. 5 depicts a flow diagram showing the path of the mixture of engine cooling air, catalytically combusted exhaust gas, cooling air, and combined exhaust gas.

[0079] Fig.59is a partial perspective view of an alternative configuration of an exhaust cooling system for use with an internal combustion engine for powering small power equipment and power tools, showing an auxiliary fan and cooling air guide integrated into an exemplary open frame generator.

[0080] Fig.60 yes Fig.59 A partially cut-away perspective view of a mixing chamber of , depicting a flow diagram showing the flow of catalytically combusted exhaust gas mixed with forced cooling air in the mixing chamber.

[0081] Fig.61 is a partially cutaway perspective view of an alternative configuration of an exhaust cooling system for use with an internal combustion engine for powering small power equipment and power tools, showing a failsafe device that allows exhaust gas to escape if the exhaust end of a mixing chamber becomes blocked.

[0082] Fig.62 is a block diagram of another configuration of an exhaust cooling system for use with an internal combustion engine that powers small power equipment and power tools, the exhaust cooling system including a heat exchanger.

[0083] Fig.63 is a flow chart illustrating example steps of a method for cooling catalytically combusted exhaust gas in a small power plant including a short length exhaust.

[0084] The foregoing summary and the following detailed description of certain features of the present application are better understood when read in conjunction with the accompanying drawings. For illustrative purposes, certain features are shown in the accompanying drawings. However, it should be understood that the present disclosure is not limited to the arrangements shown in the accompanying drawings. Although specific features of various embodiments may be shown in some drawings and not in other drawings, this is only for convenience. Any feature of any drawing may be referenced and / or claimed in conjunction with any feature of any other drawing.

[0085] Unless otherwise indicated, the drawings provided herein are intended to illustrate features of the embodiments of the present disclosure. These features are believed to be applicable to a wide variety of applications, including one or more embodiments of the present disclosure. Therefore, the drawings are not intended to include all conventional features known to those of ordinary skill in the art required for practicing the embodiments disclosed herein. DETAILED DESCRIPTION

[0086] The present disclosure provides an exemplary embodiment of a system and method for cooling the exhaust of a hydrocarbon fueled internal combustion engine having a short length exhaust system used in small power equipment and power tools. Specifically, the cooling system described herein provides a solution for cooling the catalytically burned exhaust gas produced by the chemical reaction occurring in the catalytic converter to remove harmful byproducts produced by the combustion. Basically, the system described in the present disclosure is a gas-gas mixer that combines the catalytically burned exhaust gas with cooling air to reduce the peak temperature of the combined exhaust gas. It should be understood that the term cooling air can include ambient air, engine cooling air, and / or forced cooling air.

[0087] Specifically, the system described herein utilizes the principle of adiabatic mixing: when two gases with initial temperatures come into contact with each other, the peak temperature of the combined gas will decrease, and the total temperature will begin to equalize. Eventually, the temperatures of the two gases reach thermodynamic equilibrium and are completely equalized, thereby establishing a final mixing temperature. The system discussed in the present disclosure seeks to effectively mix the catalytic combustion exhaust gas with cooling air (e.g., ambient air, engine cooling air, or forced cooling air) so that the temperature of the combined gas is as close to the final mixing temperature as possible (i.e., also with a significantly reduced peak temperature) before being released into the atmosphere. In a preferred application, the temperature of the combined exhaust gas leaving the device or tool will be similar to that of non-catalytic combustion exhaust gas: between 400°F and 600°F.

[0088] The accompanying drawings and the corresponding description below are exemplary configurations of the system on a closed frame portable generator 10. However, it should be understood that the present disclosure can be applied to any small power equipment or power tool powered by a hydrocarbon fuel internal combustion engine. The basic components of the exhaust cooling system 1 include a cooling assembly 40 attached to a short length exhaust device 24. The cooling assembly 40 includes a mixing chamber 60 and an air guide 50. The mixing chamber 60 generally includes an intake end 72, an exhaust end 73, and at least one cooling inlet. The air guide 50 guides cooling air (which may include ambient air, engine cooling air, or forced cooling air) through the cooling inlet into the mixing chamber 60, which mixes the cooling air with the catalytic combustion exhaust gas to promote adiabatic mixing of the two gases. It should be understood that the air guide 50 may include any number of air guide panels 51, channels, and / or ducts to guide cooling air into the mixing chamber 60. It should also be understood that the term air guide may mean that the mixing chamber 60 is exposed to the ambient atmosphere so that ambient air can be introduced into the mixing chamber 60.

[0089] Figure 1A small power tool powered by an internal combustion engine 11 is shown. A closed frame portable generator 10 is specifically shown. The generator uses hydrocarbon fuel (i.e., gasoline) stored in a fuel tank 25 to generate electricity by running the internal combustion engine 11 to rotate the alternator 16. As shown, the generator 10 includes an air inlet 14 and a filter (not shown) for drawing cooling air (and air used in the combustion process) into the heat shield and muffler enclosure 12 enclosure and the engine 11. A system for cooling catalytic combustion exhaust is also shown, which includes a heat shield and muffler enclosure 12, a muffler 19, and a cooling assembly 40, which will be discussed in more detail below. The cooling assembly 40 may further include an air guide panel 51 and a vortex mixer 70.

[0090] like Figure 1 and Figure 2 As shown, one configuration of the system includes a mixing chamber 60 including a vortex mixer 70, a plurality of radial air inlet ports 71, and a vortex vane assembly 80. As shown, the mixing chamber 60 includes a circular tube 74 positioned around the muffler outlet pipe 17. An air guide panel 51 positioned perpendicular to the axis of the vortex mixer 70 directs at least a portion of the engine cooling air entering the muffler enclosure 12 into the vortex mixer 70. The vortex in the airflow helps promote improved mixing of the catalytic combustion exhaust gas and the engine cooling air, thereby reducing the peak temperature of the combined exhaust gas.

[0091] Figure 2 and Figure 3 And the corresponding legend shows the flow paths of cooling air (dashed line), combustion exhaust (dotted line), catalytic combustion exhaust (dotted line), and a mixture of combined exhaust (solid line). Specifically, as shown in the illustrated example, the internal combustion engine 11 that powers a small device (in this case, a closed frame portable generator 10) is air-cooled, and a continuous flow of cooling air is required to pass through the cooling fins or hot areas of the engine 11 to prevent the engine 11 from overheating. Providing cooling air to the engine 11 can be achieved in two ways: passively and / or forcedly. Passive cooling can be achieved, for example, by exposing the engine 11 directly to the air or by sending an airflow into the engine 11. Forced cooling can be achieved, for example, by using an auxiliary fan or a fan 20 directly attached to the drive shaft 21 of the engine 11, which forces cooling air to pass over the engine 11.

[0092] The closed frame portable generator 10 shown in the illustrated embodiment utilizes a fan 20 attached directly to the drive shaft 21 of the engine 11, which pulls cooling air (dashed line) from the intake side 15 of the engine 11 through the air inlet 14 into the closed housing 22 of the generator 10. As shown, a portion of the cooling air is directed into the air intake 13 of the engine 11, while the remainder is forced over the engine 11 and the alternator 16. The engine cooling air that has been forced over the engine has a higher temperature (approximately 150-200°F under normal operation) than the ambient air or cooling air, having absorbed some of the heat from the engine 11 and the alternator 16.

[0093] As in Figures 3 to 5 As best seen in FIG. 1 , before exiting the close housing 22, the engine cooling air is directed into the heat shield and muffler enclosure 12, directed through the muffler 19, and into the vortex mixer 70 via the air guide 50, and specifically via the air guide panel 51. Specifically, as shown, the engine cooling air gas is directed through the swirl vane assembly 80, specifically through a plurality of swirl vanes 81, and into the mixing chamber 60 at the inlet end 72 of the mixing chamber 60 or through radial air inlet ports 71, which are arranged on the wall 75 of the mixing chamber 60, near the inlet end 72. The swirl vanes 81 are positioned slightly downstream of the inlet end 72 of the mixing chamber 60 and near the radial air inlet ports 71. Thus, the engine cooling air is forced to form a vortex as it enters the mixing chamber 60, and then exits at the exhaust end 73 of the mixing chamber 60.

[0094] Once the engine cooling air is forced into a vortex by the swirl vanes 81, it mixes with the catalytically burned exhaust gas (dash-dotted line) in the mixing chamber 60, creating a vortex of the combined exhaust gas (solid line) which is then released into the atmosphere at the exhaust end 73 of the mixing chamber 60. The mixing of the engine cooling air (having ambient temperature or approximately 150-200°F if it is forced across the engine) with the catalytically burned exhaust gas (approximately 700-1200°F) results in a significant reduction in the peak temperature of the combined exhaust gas (approximately 400-600°F, but may be higher or lower depending on operating conditions). Because these gases are forced into a vortex, the overall flow length of the combined exhaust gas before it is released into the atmosphere is extended. This increased flow length aids in adiabatic mixing because the contact between the two gases before leaving the system is extended. It should be noted that Figure 2 and Figure 3 The flow diagrams shown in depict exemplary embodiments and should not be considered limiting of the present disclosure.Alternative embodiments are discussed below.

[0095] Figures 4 to 5A detailed view of one embodiment of a mixing chamber 60 and a vortex mixer 70 attached to a portable generator 10 is shown. As shown, the vortex mixer 70 is positioned adjacent to the muffler 19 and surrounds the muffler outlet pipe 17. The housing 22 of the generator 10 (or other device) is designed to surround the mixing chamber 60 so that the risk of accidental contact with the mixing chamber 60 is reduced. The housing 22 additionally prevents accidental contact with the air guide panel 51 and the muffler 19. Figure 5 Picture shows Figure 4 , showing a vortex mixer 70 and a portion of an air guide panel 51 positioned between the muffler 19 and the housing 22. In an alternative embodiment, the vortex mixer 70 is integrated into the housing 22 of the device. Such an embodiment provides a cost-effective way to achieve a vortex of the combined exhaust gas without the need for additional components.

[0096] Figures 6 to 8 Detailed view of one embodiment of a cooling assembly 40 is shown, which includes a mixing chamber 60, a vortex mixer 70, and an air guide panel 51. Figure 7 In the illustrated embodiment, the air guide panel 51 includes six radial ribs 52 that direct engine cooling air to corresponding six radial air inlet ports 71 located near the intake end 72 of the mixing chamber 60. Likewise, six swirl vanes 81 force the engine cooling air into the mixing chamber 60 to form a swirl. It should be understood that the illustrated embodiment is representative and that more or fewer radial ribs 52, inlet ports 71, and swirl vanes 81 may be used.

[0097] Fig. 9 and Fig.10 An alternative configuration of the cooling assembly 40 is shown, including a plurality of bypass holes 55 in the muffler heat shield and enclosure 12. Specifically, as illustrated, the air guide panel 51 includes a plurality of bypass holes 55 that allow some of the engine cooling air to exit the muffler enclosure 12 before passing through the mixing chamber 60 and the vortex mixer 70 and mixing with the catalytic combustion exhaust gas. This configuration can be advantageous in controlling the flow volume of the engine cooling air into the vortex mixer 70 to ensure optimal adiabatic mixing of the gas in the vortex mixer 70.

[0098] Figures 11 to 14A detailed view of an embodiment of a mixing chamber 60 and a vortex mixer 70 including a swirl blade assembly 80 is shown. The vortex mixer 70 includes a circular hollow tube 74 and includes an intake end 72 and an exhaust end 73. Positioned near the intake end 72 are a plurality of radial air inlet ports 71 that feed engine cooling air into the mixing chamber 60. It should be understood that the size, shape, length, and diameter of the mixing chamber 60 can vary depending on the application. Therefore, the proportions depicted in the accompanying drawings should not be limiting, because the present disclosure contemplates a mixing chamber 60 of any size sufficient to generate a vortex of the combined exhaust gas to effectively reduce the peak temperature of the mixed gas. In addition, the present disclosure should not be limited to the specific shape and size of the radial air inlet port 71 depicted in the accompanying drawings. The shape and size of the radial air inlet port 71 can vary depending on the application and the required airflow. Finally, the present disclosure contemplates an alternative embodiment of the mixing chamber 60 that does not include any inlet port (not shown). In such an embodiment, all engine cooling air enters the mixing chamber 60 via the intake end 72 of the mixing chamber 60.

[0099] Figures 11 to 14 Also shown is a detailed view of one embodiment of a swirl vane assembly 80. In the illustrated embodiment, the swirl mixer 70 includes a plurality of swirl vanes 81 positioned around a cylindrical sleeve 82. The sleeve 82 encloses the muffler outlet pipe 17 (see FIG. Figure 4 and Figure 5 ). It should be understood that any shape or size of swirl vane 81 may be used that effectively forces the engine cooling air to swirl. The present disclosure also contemplates alternative arrangements of the swirl vane 81. For example, clockwise and counterclockwise swirl vanes 81 are contemplated. In addition, the present disclosure contemplates different ways of mounting the swirl vanes, as discussed in more detail below.

[0100] Figures 15 to 18 An alternative configuration of a system including a mixing chamber 60 is shown, which includes a venturi section 90 positioned downstream of the muffler outlet pipe 17. The venturi section 90 includes an inlet 91, an outlet 92, and one or more suction ports 93 positioned in a reduced diameter section 94. The venturi section 90 effectively draws in engine cooling gas exhaust via the principle of pressure differential. Specifically, the hourglass shape of the venturi section 90 creates a pressure drop in the flow of combustion exhaust. In other words, the combustion exhaust entering the venturi section 90 has a higher pressure than when it leaves. The pressure differential creates a vacuum at the suction port 93 located at the reduced diameter section 94, which draws engine cooling air into the suction port 93.

[0101] For example, Fig.16The venturi principle in operation is shown as applied to an exhaust cooling system 1 for a small power plant or power tool powered by an internal combustion engine 11 having a short length exhaust 24. Engine cooling air (dashed line) is directed into the muffler enclosure 12 and flows over and under the muffler 19. Catalytically combusted exhaust gas (dash-dotted line) passing through the venturi section 90 creates a vacuum and draws engine cooling air into the suction port 93 of the venturi section 90, whereupon the engine cooling air mixes with the catalytically combusted exhaust gas to reduce the peak temperature of the combined exhaust gas (solid line). Optionally, as Fig.17 and Fig.18 As shown, the mixing chamber 60 may include a venturi section 90 connected to the swirl mixer 70. The addition of the swirl mixer 70 and the resulting swirl may aid in the mixing of the engine cooling air and the catalytically combusted exhaust gas to more effectively reduce the peak temperature of the combined exhaust gas, as described in more detail above.

[0102] Fig.19 and Fig. 20 An alternative configuration of the vortex mixer 70 is depicted. In this configuration, the vortex vane assembly 80 includes an inner sleeve 83 having an inner diameter wider than the outer diameter of the muffler outlet pipe 17. As a result, there is a concentric air gap between the muffler outlet pipe 17 and the sleeve 83, thereby allowing some coaxial airflow in the engine cooling air to enter the mixing chamber 60. This coaxial airflow can help promote the mixing of the catalytic combustion exhaust gas with the engine cooling air. In addition, this configuration can be beneficial to isolate the vortex vane assembly 80 from absorbing heat from the muffler outlet pipe 17. It may be advantageous to prevent conductive heat soaking of the vortex vane assembly 80 to ensure that the engine cooling air is as low as possible before entering the mixing chamber 60. It should be understood that the present disclosure is not limited to the precise size of the gap depicted, and the gap may be wider or narrower depending on the application.

[0103] Fig.21 and Fig. 22 Another alternative configuration of the vortex mixer 70 is depicted. In this configuration, the swirl vane 81 is attached directly to the wall 75 of the mixing chamber 60. As illustrated, the swirl vane 81 does not extend all the way to the muffler outlet pipe 17, thereby allowing some concentric airflow and reducing heat soaking of the swirl vane 81. It should be understood that the swirl vane 81 can be located farther away from or closer to the muffler outlet pipe 17 depending on the application.

[0104] Fig.23 and Fig.24Another alternative configuration of the exhaust cooling system 1 is depicted which utilizes a radial feed path 100 of the engine cooling air. As shown, the system includes a mixing chamber 60 including a radial air inlet port 71 positioned near an intake end 72 of the mixing chamber 60. The muffler outlet pipe 17 is concentrically positioned within the mixing chamber 60. When the engine cooling air enters the mixing chamber 60 via the radial air inlet port 71, it is drawn into a radial path and mixed with the catalytically combusted exhaust gas before exiting at an exhaust end 73 of the mixing chamber and being released into the atmosphere.

[0105] Figure 25 to Figure 27 Another alternative configuration of the exhaust gas cooling system 1 is depicted, the exhaust gas cooling system comprising a mixing chamber 60 including a coaxial mixer 110. Fig.25 As shown, the coaxial mixer 110 includes an L-shaped tube 111 including a cooling air inlet 112, an exhaust end 113, and an opening 114 for a muffler outlet pipe 17. The muffler outlet pipe 17 is inserted into the opening 114 and is at least partially positioned within the coaxial mixer 110 so that the flow of cooling air (dashed line) and the flow of catalytic combustion exhaust gas (dotted line) are substantially coaxial at the exhaust end 113. The muffler outlet pipe 17 may include a portion 118 of reduced diameter, as shown, or have a consistent diameter. It should be understood that the present disclosure is not limited to the illustrated embodiments and may include any shape of coaxial mixer 110 that combines the cooling air flow with the catalytic combustion exhaust flow coaxially. It should be further understood that the muffler outlet pipe 17 does not necessarily need to be concentrically positioned within the opening 114 of the coaxial mixer 110 as shown in the illustrated embodiment. Further, cooling air may include, but is not limited to, ambient air, imported cooling air, forced cooling air, passive intake of cooling air, and / or engine cooling air. It should also be understood that the illustrated embodiment may be reversed (not shown). For example, catalytic combustion exhaust may be directed through outer tube 111, and cooling air may be directed through inner tube 117. Finally, it should be understood that the present disclosure contemplates alternative configurations of inlet shapes including, for example, multiple radial inlets or other coaxial shapes.

[0106] Fig.26 and Fig. 27 Describes the Fig.25 An exemplary manner of integrating the coaxial mixer 110 into the exhaust gas cooling system 1. For example, Fig.26As shown, the catalytic combustion exhaust gas (dotted line) is directed into the coaxial mixer 110 via the silencer outlet pipe 17 (inner pipe 117), and the cooling air (dashed line) is directed into the coaxial mixer 110 via the cooling air inlet 112 (outer pipe 111). In the extension pipe 115, the catalytic combustion exhaust gas is coaxially mixed with the cooling air, and the combined mixture of gases (solid line) leaves the coaxial mixer 110 at the exhaust outlet 116.

[0107] The present disclosure contemplates Fig.25 The coaxial mixer 110 configuration can be combined with any other configuration of the mixer described in the present disclosure. Fig. 27 As shown, the venturi section 90 may be integrated into the mixing chamber 60. In this configuration, the venturi section 90 draws in additional cooling air and mixes it with the catalytically combusted exhaust gas and cooling air mixture to further reduce the peak temperature of the mixed gas at the exhaust gas outlet 116.

[0108] Fig.28 and Fig.29 An alternative mixing chamber 60 is shown, comprising a vortex mixer 70 including a tangential inlet duct 120 . Fig.29 yes Fig.28 A cross section taken along line 29-29. The tangential intake duct 120 can be used to force the airflow to form a vortex without using the swirl vane 81. As shown, the engine cooling air flows into the mixing chamber 60 via the tangential intake duct 120 and is forced to form a vortex. The catalytic combustion exhaust gas mixes in the vortex, thereby generating a vortex of the combined exhaust gas. As described above, the mixing of the two gases in the vortex effectively reduces the peak temperature of the combined gas.

[0109] Fig.30 An exemplary damper 130 for use in an exhaust cooling system 1 according to one aspect of the present disclosure is shown, which can be used to adjust the volume of air directed into and out of the cooling assembly. Specifically, the damper includes a grille 131, a damper 132, and a motor 133 or actuator that actuates the damper 132. Such a damper 130 can be used in another part of an equipment cover or housing to control the flow of air into and out of the exhaust cooling system 1. For example, in one configuration, the damper 130 can be closed when the engine 11 is running to guide the cooling air flow through the cooling assembly 40, and open when the engine is shut down to help passive cooling and avoid heat soaking. The damper 132 can also be actuated using a mechanical connection (such as a control cable connected to a throttle / run / stop knob). Alternatively, the damper 132 can be actuated by a vacuum actuator, electrically actuated, or pneumatically actuated, or manually actuated.

[0110] Fig.31An alternative configuration of the exhaust cooling system 1 is shown, including an auxiliary electric fan 140, which is used to control the flow of cooling air directed into the exhaust cooling system 1. The auxiliary fan 140 can be arranged anywhere in the equipment housing 22, or on a duct that supplies cooling air to the exhaust cooling system 1. For example, as shown, the auxiliary fan 140 is arranged adjacent to the heat shield and the muffler enclosure 12. When the auxiliary fan 140 is powered, it provides additional cooling air to the system, which can help adiabatic mixing of catalytic combustion exhaust gas and cooling air. The illustrated embodiment, for example, utilizes both engine cooling air and forced cooling air from the auxiliary fan 140. Other configurations are also possible. For example, the engine cooling system 1 can be supplied only with cooling air forced into the system by the auxiliary fan 140, while the engine cooling air leaves the equipment from other locations. An additional benefit provided by using the auxiliary fan 140 is to run the fan 104 after the engine 11 has been shut down, thereby performing heat soak protection.

[0111] Fig.32 and Fig.33 An alternative configuration of an exhaust cooling system 1 is shown, the exhaust cooling system including a mixing chamber 60, which further includes a diffuser 150. As illustrated, the exhaust cooling system 1 can include a diffuser 150 and a plurality of additional swirl blades 151 optionally attached to a body 152. In the illustrated embodiment, the diffuser 150 is positioned within the wall 75 of the mixing chamber 60 and coaxial with the cylindrical sleeve 82 of the swirl blade assembly 80. As the swirl blade assembly 80 causes the resulting swirl of the combined exhaust, the combined exhaust diffuses over the body 152 of the diffuser 150 and through the swirl blades 151 due to the shape of the body 152 directing the combined exhaust toward the swirl blades 151. In this way, the diffuser 150 can help further reduce the velocity of the combined exhaust to help the combined exhaust continue to adiabatically mix and dissipate after being released into the atmosphere. The use of the diffuser 150 can be beneficial in preventing a concentrated flow of the combined exhaust from flowing a certain distance after it leaves the device. Instead, it is desirable that the combined exhaust gas dissipates as quickly as possible to avoid heating, burning, or ignition of adjacent objects. The present disclosure contemplates alternative arrangements of the swirl vanes 151 on the diffuser 150. For example, clockwise and counterclockwise swirl vanes 151 are contemplated. The present disclosure also contemplates alternative shapes of the body 152 of the diffuser 150, such as a cone, pyramid, or hemisphere.

[0112] Fig.34 and Fig.35An example of a diffuser configuration is shown that utilizes a conical diffuser 160 mounted at the exhaust end 113 of the coaxial mixer 110. The conical diffuser 160 includes a conical body 162 attached to a ring 161 by a rod 163. The use of a conical diffuser 160 in the coaxial mixer 110 can promote improved mixing and / or prevent the catalytic combustion exhaust gas flow from the muffler outlet pipe 17 from leaving the system in a direct path. As illustrated, when the flow of catalytic combustion exhaust gas (dotted double line) impinges on the conical diffuser 160, it spreads on the conical body 162 and is forced outward toward the ring 161 into the cooling air flow (dashed line). This diffusion can help mix the two gases and help reduce their peak temperatures. Fig.34 and Fig.35 The configuration may optionally be combined with a downstream extension pipe 115 (see Fig.26 ) combination to further promote mixing of the gases before they are released into the atmosphere.

[0113] Fig.36 Another example of a diffuser configuration is shown that utilizes a perforated tube diffuser 170 mounted on the muffler outlet pipe 17 (inner pipe 117) of the coaxial mixer 110. In some embodiments, the perforated tube diffuser 170 can be positioned within the extension pipe 115 (see, e.g., Fig.26 ). Likewise, the use of a perforated tube diffuser 170 in the coaxial mixer 110 can promote improved mixing and / or prevent the catalytic combustion exhaust flow from the muffler outlet pipe 17 from leaving the system in a direct path. As illustrated, when the flow of catalytic combustion exhaust (dash-dotted line) impinges on the end wall section 171 of the perforated tube diffuser 170, the flow is forced radially outward into the flow of cooling air (dashed line). In some embodiments, the two flows of catalytic combustion exhaust and cooling air are mixed in the extension tube 115 before being released into the atmosphere. The illustrated perforated tube diffuser 170 includes a flat end wall 171, but may also be constructed of alternative shapes such as a cone.

[0114] It should be understood that Figure 32 to Figure 36 The depicted diffuser configuration should not be limited to the illustrated embodiments. The present disclosure contemplates diffusers of any shape and size operable to diffuse the catalytic combustion exhaust stream, thereby forcing the catalytic combustion exhaust stream directly into a cooling air stream, which may include ambient air, imported cooling air, forced cooling air, passive intake of cooling air, and / or engine cooling air, or any combination thereof. It is further understood that the illustrated configuration may be reversed (not shown). For example, cooling air may be diffused into a stream of catalytic combustion exhaust.

[0115] Figures 37 to 43An alternative configuration of an exhaust cooling system 1 integrated into an open frame device (e.g., an open frame generator 30) is shown. All of the above systems can be applied to an open frame device. The main difference between an open frame device and a closed frame device is the introduction of air into the engine and the exhaust cooling system. As shown, air is drawn into the air intake 33, passes through the engine 31 and enters the muffler enclosure 32 via the air guide 34. Once the cooling air (engine cooling air or direct cooling air) has been introduced into the muffler enclosure 32, the function of the system is the same as described above. The exhaust cooling system 1 may include, for example, a mixing chamber 60, specifically a vortex mixer 70, a venturi section 90, or a combination thereof ( Fig.37 and Fig.38 (not shown) to reduce the peak temperature of the catalytically combusted exhaust gas.

[0116] Fig.39 and Fig.40 An exemplary flow diagram of an open frame generator is shown, including the flow paths of ambient air / cooling air (dashed line), combustion exhaust (dotted line), catalytic combustion exhaust (dotted line), and a mixture of combined exhaust (solid line). Specifically, Fig.39 A flow diagram of an exhaust gas cooling system 1 including a vortex mixer 70 for an open frame generator 30 is shown. Fig.40 A flow diagram of an exhaust cooling system 1 including a venturi section 90 for an open frame generator 30 is shown. As illustrated, ambient air (dashed line) is drawn into the engine 31 through the air intake 33, and a portion of the engine cooling air (dashed line) is directed into the muffler enclosure 32 through the air guide 34. Once within the muffler enclosure 32, the engine cooling air flows around the muffler 35 and mixes with the catalytically combusted exhaust gas (solid line) via the vortex mixer 70 or the venturi section 90.

[0117] Fig.41 and Fig.42 An alternative configuration of an exhaust cooling system 1 for use with an internal combustion engine for powering small power equipment and power tools is shown, the exhaust cooling system including a venturi section 90 configured to draw in ambient air rather than engine cooling air and mix it with the catalytically combusted exhaust gas. Fig.42 ), when the catalytically burned exhaust gas (dotted line) passes through the venturi section 90, a vacuum is created, which draws ambient air into the suction port 93 of the venturi section 90, whereupon the ambient air mixes with the catalytically burned exhaust gas to reduce the peak temperature of the combined exhaust gas (solid line). The benefit of this particular configuration is that the ambient air typically has a lower temperature than the engine cooling air.

[0118] Fig.41and Fig.42 The configuration shown in may also be combined with any other configuration discussed in the present application. For example, as discussed in more detail above, the venturi section 90 can be configured to simultaneously draw in engine cooling air and ambient air (e.g., via the use of a containment shell, an air guide panel, and / or an air duct (not shown)). Alternatively, the ambient cooling air configuration can utilize a forced flow of ambient (cooling) air. For example, a portion of the engine cooling fan flow can bypass and be directed into the venturi inlet 91 prior to engine cooling (not shown), or an auxiliary fan or blower can be used to force air to the venturi inlet 91.

[0119] Fig.43 1 shows an alternative configuration of an exhaust cooling system 1, the exhaust cooling system comprising a mixing chamber 60, the mixing chamber further comprising a tightly packed exhaust extension 180. Specifically, as Fig.43 As shown, the system includes an exhaust pipe extension 181 that is bent into a series of U-shaped bends 182 into a tightly packed configuration. The illustrated configuration includes three U-shaped bends 182 and two elbows 183 to significantly increase the overall exhaust length. The exhaust length is increased while maintaining tight packaging, which allows use in power equipment and power tools. It should be understood that the illustrated configuration of the tightly packed exhaust extension 180 is exemplary, and other lengths, shapes, and configurations are also possible. The present disclosure contemplates any length, shape, and configuration of a tightly packed exhaust extension 180 that is wired in a manner that maximizes flow length and minimizes packaging space for use with small power equipment and power tools.

[0120] For example, Fig.43 As shown, the increase in exhaust length allows heat to be dissipated as the catalytically combusted exhaust (dash-dotted line) travels through the tightly packed exhaust extension 180, thereby helping to significantly reduce the peak temperature of the catalytically combusted exhaust before it is released into the atmosphere. Fig.43 The catalytically combusted exhaust gas is shown cooling as it passes through the tubes 181 of the tightly packed exhaust extension 180. This configuration alone can help reduce the peak temperature of the catalytically combusted exhaust gas from over 1200°F to approximately 450°F.

[0121] like Fig.43As shown, the tightly packed exhaust extension 180 can be combined with any other alternative configuration discussed in the present disclosure. For example, the venturi section 90 can be attached to the end 184 of the tightly packed exhaust extension 180. As illustrated, when the catalytic combustion exhaust gas (dotted line) passes through the tightly packed exhaust extension 180, heat from the catalytic combustion exhaust gas is dissipated. When the catalytic combustion exhaust gas passes through the venturi section 90, a vacuum is created, which draws ambient air (dashed line) into the suction port 93 of the venturi section 90 and mixes with the catalytic combustion exhaust gas to further reduce the peak temperature of the combined exhaust gas (solid line).

[0122] The tightly packed exhaust extension 180 may also be implemented in a configuration where the engine cooling air is ducted to help further dissipate the heat (not shown). For example, some or all of the engine cooling air may be directed to flow through the tightly packed exhaust extension (not shown). Likewise, a forced flow of ambient (cooling) air may be used to further dissipate heat from the tightly packed exhaust extension 180. For example, a portion of the engine cooling fan flow may be bypassed and directed to the tightly packed exhaust extension 180 prior to the engine cooling (not shown), or an auxiliary fan or blower may be used to force air to the tightly packed exhaust extension 180.

[0123] Finally, although in Fig.43 Not shown, but one or more heat shields or enclosures may be used to provide a barrier between the tightly packed exhaust extension 180 and the environment to reduce the risk of operator contact burns.

[0124] Figures 44 to 46 Alternative configurations of venturi sections 90 are shown which may be incorporated into any of the systems described herein. The functions of these alternative venturi sections are similar to those described above with respect to Figures 15 to 18 As illustrated, the venturi section 90 includes a venturi inlet 91, a venturi outlet 92, and one or more suction ports 93, the one or more suction ports being located in the reduced diameter section 94. The venturi section 90 may also include one or more mounting brackets 95 operable to mount the venturi section 90 to, for example, the mixing chamber 60 or the muffler outlet pipe 17. Fig.45 and Fig.46 A plurality of fins 96 are shown arranged on the venturi section 90. The fins 96 may be formed by cutting a c-shaped or arcuate suction port 93 and pushing the cut portion inward. The fins 96 may assist in adiabatic mixing of the catalytically combusted exhaust gas with cooling air (whether engine cooling air, ambient air, or forced cooling air) by directing the combined exhaust gas into a coaxial flow or vortex.

[0125] Figures 47 to 50An alternative configuration of the exhaust cooling system 1 is shown, which is integrated into the muffler housing 191 of the exhaust system 190. Specifically, the air guide 50 and the mixing chamber 60 including the venturi section 90 are integrated and recessed into the muffler housing 191 of the exhaust system 190. This is to ensure that the entire system is tightly packaged and prevent the mixing chamber 60 from protruding significantly from the muffler housing 191. Further, since the suction port 93 is located on the inside of the muffler housing 191, the air guide 50 must be recessed into the muffler housing to ensure that the cooling air reaches the cooling inlet (suction port 93). The exhaust system 190 may also optionally include a spark arresting net 201, which is used to capture any sparks or other particles flowing through the exhaust system 190.

[0126] Fig.48 A cross-sectional view of an exhaust system 190 is illustrated, and a flow diagram is depicted, which shows the flow of a mixture of cooling air, combustion exhaust, and combined exhaust. The exhaust system 190 includes a plurality of chambers 192, which are separated by a partition wall 193 to force the engine exhaust to flow along a guide path, thereby extending the entire flow path. As illustrated, a jumper tube 194 including a perforated pipe end 195 connects the first chamber 192a and the third chamber 192c. Further, a perforated section 196 in the partition wall connects the second chamber 192b and the third chamber 192c. A catalyst (catalytic converter) 199 is also positioned in the muffler housing 191 and includes an inlet 200 in the second chamber 192b. The muffler outlet 198 is directly connected to the cooling assembly 40.

[0127] For example, Fig.48 As shown, the combustion exhaust (dotted line) enters the first chamber 192a through the muffler inlet 197. The combustion exhaust then enters the crossover tube 194 at the perforated tube end 195 in the first chamber 192a and flows through the opposite perforated tube end 195 into the third chamber 192c. At this point, the combustion exhaust flows through the perforated section 196 of the partition wall 193 that separates the second chamber 192b from the third chamber 192c, and enters the second chamber 192b. The combustion exhaust then enters the catalyst 199 via the inlet 200, undergoes a catalytic chemical reaction, and exits the muffler outlet 198 into the cooling assembly 40. Once in the cooling assembly 40, the cooling air (dashed line) is directed to the venturi section 90 and the air guide 50, is drawn into the suction port 93, and is mixed with the catalyzed combustion exhaust in the mixing chamber 60 to reduce the peak temperature of the combined exhaust (solid line). The increased flow path length within the muffler housing 191 may help to attenuate engine noise and allow heat to be dissipated as the combustion exhaust flows through the muffler housing 191. Fig.49 and Fig.50Alternative configurations of the mixing chamber 60 and the air guide 50 are shown.

[0128] Fig.51 A partially cutaway perspective view of an alternative configuration of the exhaust cooling system 1 is illustrated, showing that the mixing chamber 60 is integrated into the muffler housing 191 of the exhaust system 190. The exhaust system includes a first chamber 192a, a second chamber 192b, and a third chamber 192c connected by a perforated section 196 in a partition wall 193. A catalyst 199 is located in the first chamber 192a. As illustrated in the flow diagram, the combustion exhaust (dotted line) enters the exhaust system 190 via the muffler inlet 197 and flows into the catalyst 199, undergoing a catalytic chemical reaction. The catalytic combustion exhaust (dotted line) leaves the catalyst 199 via the perforated pipe end 195 and enters the second chamber 192b. The gas then enters the third chamber 192c through the perforated section 196, passes through the air guide 50 and enters the mixing chamber 60. Once in the mixing chamber 60, the catalytic combustion exhaust is coaxially mixed with the cooling air (dashed line).

[0129] Fig.52 and Fig.53 Shown around Fig.51 The optional close-packed exhaust extension 180 of the muffler housing 191 of the embodiment. It should be understood that Fig.52 and Fig.53 The tightly packed exhaust extension 180 of the embodiment may also be applied to other muffler housings. The tightly packed exhaust extension 180 includes a spiral wall 185 surrounded by an outer wall 186 (shown as translucent for clarity of illustration). In such an embodiment, the muffler housing 191 may include a double wall structure separated by an air gap (not shown) to help isolate the tightly packed exhaust extension 180. Fig.53 As shown in the flow diagram in FIG. 1 , the combined exhaust (solid line) or alternatively the catalytic combustion exhaust (not shown) flows out of the muffler outlet 198, is trapped by the outer wall 196, and is forced to follow the path of the spiral wall 185 until the exhaust flows out of the extension outlet 187 into the atmosphere. As described above with reference to Fig.43 As discussed, the increase in exhaust length allows heat to be dissipated as the combined exhaust (solid line) travels through the tightly packed exhaust extension 180, thus can help to significantly reduce the peak temperature of the catalytically combusted exhaust gas before it is released into the atmosphere. Given the high temperature of the catalytically combusted exhaust gas, high temperature materials (such as austenitic stainless steel) can be used to form the tightly packed exhaust extension 180.

[0130] Fig.54Another alternative configuration of the exhaust cooling system 1 is shown, which includes a tightly packed exhaust extension 180 surrounding a muffler housing 191. As illustrated, the tightly packed exhaust extension 180 includes an outer wall 186 (shown as translucent for clarity of illustration), and one or more flow walls located between the muffler housing 191 and the outer wall 186 to form a circuitous path. The catalytically combusted exhaust gas (dash-dotted line) exits the muffler outlet 198 into the tightly packed exhaust extension 180 and is forced by the flow wall 188 and the outer wall 186 to flow along a desired flow path to the extension outlet 187. Likewise, heat is dissipated as the catalytically combusted exhaust gas (dash-dotted line) travels through the tightly packed exhaust extension 180 in an increased exhaust length.

[0131] Fig.55 and Fig.56 Another alternative configuration of the exhaust gas cooling system 1 is shown, comprising an alternative air guide panel 50, which comprises an air guide panel 51, and the mixing chamber 60 comprises a coaxial mixer 110. Fig.56 As illustrated, engine cooling air (dashed line) is directed into the air directing panel 51 and into the extension tube 115 of the coaxial mixer 110. The catalytically combusted exhaust gas (dash-dotted line) flows out of the exhaust system 190 through the spark arrester mesh 201 and into the coaxial mixer 110 of the mixing chamber 60. The mixing of the catalytically combusted exhaust gas (dash-dotted line) with the engine cooling air (dashed line) or other cooling air (not shown) reduces the peak temperature of the combined exhaust gas (solid line).

[0132] Fig.57 and Fig.58 A variation of the aforementioned system including a window grille section 230 is shown. As illustrated, the mixing chamber 60 includes both the window grille section 230 and the coaxial mixer 110. The air guide 50 includes both an air guide panel 51 and an additional air guide channel 53 for guiding cooling air to the window grille section 230. Fig.58 As illustrated, engine cooling air (dashed line) is directed into the air directing panel 51 and into the extension duct 115 of the coaxial mixer 110. Catalytic combustion exhaust gas (dash-dotted line) flows out of the exhaust system 190 through the spark arrester mesh 201 and into the coaxial mixer 110 of the mixing chamber 60. Further, additional cooling air (dashed line) is drawn into the port 231 of the window grille section 230 and enters the extension duct 115 of the mixing chamber 60. The mixing of the catalytic combustion exhaust gas (dash-dotted line), the engine cooling air (dashed line), and the cooling air (dashed line) reduces the peak temperature of the combined exhaust gas (solid line).

[0133] Fig.59 and Fig.60Another alternative configuration of the exhaust cooling system 1 is shown, which includes an electric auxiliary fan 140 and a cooling air guide 50, which includes a duct 56 integrated into the exemplary open frame generator 30. Specifically, the duct 56 supplies cooling air to the channel 53, into the coaxial mixer 110 entering the mixing chamber 60. Fig.59 and Fig.60 As shown, the electric auxiliary fan 140 pressurizes the cooling air (dashed line), which flows through the tube 56 into the passage 53 and into the coaxial mixer 110 of the mixing chamber 60, where the pressurized air is combined with the catalytic combustion exhaust gas (dash-dotted line). The mixing of the catalytic combustion exhaust gas (dash-dotted line) and the forced cooling air (dashed line) reduces the peak temperature of the combined exhaust gas (solid line).

[0134] Fig.61 One configuration of an exhaust cooling system 1 including a venturi section 90 is shown, which may act as a fail-safe device that allows exhaust gas to be discharged if the outlet 92 of the venturi section 90 is blocked by a blockage 210. Fig.61 As shown, in the presence of obstruction 210, combined exhaust gas and / or catalytically combusted exhaust gas may exit through suction port 93. Other embodiments, such as Figures 47 to 50 and Figure 57 to Figure 58 The embodiment shown in FIG. 1 can also act as a failsafe device in the event that the outlet of the venturi section 90 is blocked. For example, in the presence of a blockage 210, the combined exhaust gas can exit through the suction port 93 of the venturi section 90 of the coaxial mixer 110 (see, for example, Fig.58 ). In the presence of the obstruction 210, this fault protection prevents the combustion exhaust gas from flowing back into the generator housing. It should be understood that Fig.57 and Fig.58 The grille section 230 shown in FIG. 1 similarly serves as a failsafe. It should be further understood that the failsafe principle of the blocked outlet flow path can also be applied to a forced air mixing scheme (not shown), but other components will be required, such as a check valve flap (not shown) in the cooling air flow path, which can prevent the combustion exhaust from flowing back into the cooling air source and can cause the engine to shut down. Finally, the present disclosure contemplates that an overpressure vent (not shown) can be included elsewhere in the cooling system 1, similar to a cabin pressure relief valve on the vehicle body.

[0135] Fig.62A block diagram of another configuration of the exhaust cooling system 1 including a heat exchanger 220 is shown. Common exhaust system heat exchangers (such as EGR coolers) use a gas-to-water heat exchanger that utilizes engine coolant, which is much more efficient in removing heat and air. Most small power equipment and power tools (including portable generators) powered by the internal combustion engine 11 are air cooled. Therefore, there is no existing liquid cooling system for the gas-to-water heat exchanger 220. However, larger power equipment (such as fixed generators or large portable generators) can include a liquid cooling system (not shown). For these applications, it will be potentially useful to combine a gas-to-liquid heat exchanger 220 to significantly reduce the peak temperature of the catalytically combusted exhaust gas.

[0136] like Fig.62 As shown, the combustion exhaust gas (dotted line) generated by the engine 11 enters the catalyst 199 and undergoes a catalytic chemical reaction. The catalytic combustion exhaust gas (double dotted line) then enters the heat exchanger 220, where the catalytic combustion exhaust gas and cooling air (dashed line) can be separated by a wall (not shown) and / or an air guide 50. The outer wall of the heat exchanger 220 can also include fins (not shown) to maximize the surface area, and is most effective when forced to supply cooling air (e.g., bypass cooling fan air, engine cooling air, dedicated electric blower, etc.) flowing through the heat exchanger 220. The catalytic combustion exhaust gas and / or cooling air can then flow through the internal passages (not shown) of the heat exchanger 221 and can leave as a combined exhaust gas (solid line) with a reduced peak temperature. These internal passages can be finned and / or can include a circuitous path to maximize the flow length and surface area. In view of the high temperature of the catalytic combustion exhaust gas, high temperature materials (such as austenitic stainless steel) can be used to form the internal passages. The heat exchanger 220 may also be combined with any of the above-described cooling systems 1 to further reduce the peak temperature of the catalytically combusted exhaust gas.

[0137] The present disclosure also contemplates a method for cooling catalytically burned exhaust gas in a small power plant including a short length exhaust device. The exemplary method steps begin at step 301. At step 302, the method includes providing an exhaust cooling system including a cooling air guide 50 and a mixing chamber 60. It should be understood that any of the above-described cooling systems 1 and / or cooling assemblies 40 can be incorporated into the method. At step 303, the method includes directing the catalytically burned exhaust gas into the mixing chamber 60. At step 304, the method includes directing cooling air into the mixing chamber 60 via the cooling air guide 50. At step 305, the method includes mixing the catalytically burned exhaust gas with the cooling air in the mixing chamber 60 to reduce the peak temperature of the combined exhaust gas. The exemplary method can stop at step 306. It should also be understood that the described method can be applied to any exhaust cooling system 1 used with an internal combustion engine that powers small power plants and power tools.

[0138] The present disclosure described at present is described in such complete, clear, concise, and accurate terms so that any technician in the field involved in the present disclosure can practice the present disclosure. It should be understood that the preferred aspects of the present disclosure are described above, and modifications can be made in the present disclosure without departing from the spirit of the scope of the present disclosure set forth in the appended claims. The scope of the present disclosure will be given the broadest interpretation to cover all such modifications and equivalent structures and functions. Therefore, the application is not intended to be limited to the specific aspects illustrated or described, but the application will include all aspects falling within the general disclosure.

Claims

1. An exhaust gas cooling system for cooling catalytic combustion exhaust gas in a small power plant, the system comprising: cooling air guide; as well as A mixing chamber, the mixing chamber comprising an air intake end, an exhaust end, and at least one cooling inlet, wherein: a short length exhaust device including a catalytic converter operably connected to an intake end of the mixing chamber and operable to direct catalytically combusted exhaust gas through the intake end and into the mixing chamber; The cooling air guide is operably connected to the at least one cooling inlet and is operable to direct cooling air through the at least one cooling inlet and into the mixing chamber; and The mixing chamber is operable to promote mixing of the catalytically combusted exhaust gas and cooling air to reduce a peak temperature of the combined exhaust gas.

2. The system of claim 1, wherein: The short length exhaust device further includes a muffler outlet pipe; The mixing chamber further comprises a vortex mixer; and The cooling air guide further comprises an air guide panel, wherein: The swirl mixer includes a swirl vane assembly positioned about a cylindrical sleeve, wherein the swirl vane assembly is operable to introduce the cooling air and the catalytically combusted exhaust gas into the mixing chamber to promote mixing of the catalytically combusted exhaust gas with the cooling air, The cylindrical sleeve is operably connected to the muffler outlet pipe, and The air guide panel comprises at least one radial rib, wherein the at least one radial rib is operable to guide cooling air into the at least one cooling inlet.

3. The system of claim 2, wherein: The air directing panel includes an aperture sized to accommodate the mixing chamber.

4. The system of claim 2, wherein: The at least one cooling inlet comprises a plurality of cooling inlets, and the at least one radial rib comprises a plurality of radial ribs.

5. The system of claim 2, wherein: The mixing chamber further includes a diffuser operable to diffuse the combined exhaust gas prior to exiting the exhaust end of the mixing chamber.

6. The system of claim 5, wherein: The diffuser includes a conical diffuser.

7. The system of claim 5, wherein: The diffuser comprises a vane diffuser.

8. The system of claim 5, wherein: The diffuser comprises a perforated tube diffuser.

9. The system of claim 1, wherein: The mixing chamber further comprises a venturi section, and the at least one cooling inlet comprises at least one venturi inlet, wherein The venturi section includes a reduced diameter section, and the at least one venturi inlet is disposed in the reduced diameter section; and The venturi section is operable to promote mixing of the catalytically combusted exhaust gas and the cooling air.

10. The system of claim 9, wherein: The mixing chamber further includes a swirl mixer including a plurality of swirl vanes positioned about the venturi section, wherein the plurality of swirl vanes are operable to introduce the cooling air and catalytically combusted exhaust gas into the mixing chamber.

11. The system of claim 1, wherein: The mixing chamber further comprises a coaxial mixer, wherein: The at least one cooling inlet comprises an external cooling air duct, an inner muffler outlet pipe being positioned at least partially within said outer cooling air duct, and The coaxial mixer is operable to coaxially mix the catalytically combusted exhaust gas with the cooling air so as to promote mixing of the catalytically combusted exhaust gas with the cooling air.

12. The system of claim 1, wherein: The mixing chamber further comprises a tangential vortex mixer, and the at least one cooling inlet further comprises at least one tangential inlet duct; wherein: The tangential inlet duct is operable to direct cooling air tangentially into the mixing chamber to introduce the cooling air and catalytically combusted exhaust gas into the mixing chamber to promote mixing of the catalytically combusted exhaust gas with the cooling air.

13. A small power device, comprising: Internal combustion engines, a short length exhaust device including a catalytic converter operably connected to the internal combustion engine, the short length exhaust device being operable to receive combustion exhaust gas from the internal combustion engine, an exhaust cooling system operatively connected to the short length exhaust, the exhaust cooling system operable to receive catalytically combusted exhaust gas from the short length exhaust; Wherein, the exhaust cooling system comprises: a cooling air guide; and A mixing chamber, the mixing chamber comprising an air intake end, an exhaust end, and at least one cooling inlet, wherein: The short length exhaust device is operatively connected to the intake end of the mixing chamber; The cooling air guide is operably connected to the at least one cooling inlet and is operable to direct cooling air through the at least one cooling inlet and into the mixing chamber; and The mixing chamber is operable to promote mixing of the catalytically combusted exhaust gas and cooling air to reduce a peak temperature of the combined exhaust gas.

14. The small power device according to claim 13, wherein: The short length exhaust device further includes a muffler outlet pipe; The mixing chamber further comprises a vortex mixer; and The cooling air guide further comprises an air guide panel, wherein: The vortex mixer includes a vortex blade assembly positioned around a cylindrical sleeve, wherein the vortex blade assembly is operable to introduce the cooling air and the catalytic combustion exhaust gas into the mixing chamber to form a vortex to promote mixing of the catalytic combustion exhaust gas and the cooling air. The cylindrical sleeve is operably connected to the muffler outlet pipe, and The air guide panel comprises at least one radial rib, wherein the at least one radial rib is operable to guide cooling air into the at least one cooling inlet.

15. The small power device according to claim 13, wherein: The mixing chamber further comprises a venturi section, and the at least one cooling inlet comprises at least one venturi inlet, wherein The venturi section includes a reduced diameter section, and the at least one venturi inlet is disposed in the reduced diameter section; and The venturi section is operable to promote mixing of the catalytically combusted exhaust gas and the cooling air.

16. The small power device according to claim 15, wherein: The mixing chamber further includes a swirl mixer including a plurality of swirl vanes positioned about the venturi section, wherein the plurality of swirl vanes are operable to introduce cooling air and catalytically combusted exhaust gas into the mixing chamber.

17. The small power device according to claim 13, wherein: The mixing chamber further comprises a coaxial mixer, wherein: The at least one cooling inlet comprises an external cooling air duct, an inner muffler outlet pipe being positioned at least partially within said outer cooling air duct, and The coaxial mixer is operable to coaxially mix the catalytically combusted exhaust gas with the cooling air so as to promote mixing of the catalytically combusted exhaust gas with the cooling air.

18. The small power device according to claim 13, wherein: The mixing chamber further comprises a tangential vortex mixer, and the at least one cooling inlet further comprises at least one tangential inlet duct; wherein: The tangential inlet duct is operable to direct cooling air tangentially into the mixing chamber to introduce the cooling air and catalytically combusted exhaust gas into the mixing chamber to promote mixing of the catalytically combusted exhaust gas with the cooling air.

19. The small powered device of claim 13, further comprising a powered fan operable to force a flow of cooling air into the cooling air guide.

20. A method for cooling catalytically combusted exhaust gas in a small power plant including a short length exhaust, the method comprising: providing an exhaust cooling system comprising a cooling air guide and a mixing chamber; directing the catalytically combusted exhaust gas into the mixing chamber; directing cooling air into the mixing chamber via the cooling air guide; The catalytically combusted exhaust gas is mixed with the cooling air in the mixing chamber to reduce a peak temperature of the combined exhaust gas.

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