US20110179779A1

US20110179779A1 - Emissions treatment in genset engines through air injection into the exhaust system of a genset

Info

Publication number: US20110179779A1
Application number: US12/695,458
Authority: US
Inventors: David T. Falkowski; Deborah A. Klinkert; Luke R. Staples; Jeffrey D. Peterson; Steven M. Swanson; Shimkiri S. Syiem; Michael J. Turbak; Aaron C. Johnson
Original assignee: Cummins Power Generation Inc
Current assignee: Cummins Power Generation Inc
Priority date: 2010-01-28
Filing date: 2010-01-28
Publication date: 2011-07-28

Abstract

An exhaust system that can improve emissions treatment by reducing certain emissions species. The exhaust system draws air into the exhaust system from an air source, when exhaust pressure decreases to a threshold so that air can enter the exhaust system. The exhaust system is in a genset engine. The air source is a pressurized air source, such as an existing fan of the genset engine. A portion of the air generated by the air source is pulled off so that it flows directly toward the exhaust system, using a one-way valve and conduit that fluidly connects the air source to the exhaust system.

Description

FIELD

The present disclosure generally relates to exhaust emissions treatment of internal combustion engines. More particularly, the present disclosure relates to reducing engine emissions of a genset engine by drawing air into its exhaust system, when a pressure differential between the exhaust pressure and the pressure from an available source of secondary air is at a threshold, which allows secondary air to enter the exhaust system.

BACKGROUND

Engines have been known to deliver air into the engine's exhaust system to reduce certain emission species. This has generally been known as secondary air injection because air is delivered to the exhaust system, which is downstream from the air intake and combustion chamber.
Secondary air injection has been known to be used with engines that have an aftertreatment system, oftentimes employing a catalyst, to thereby provide air into the exhaust system to reduce certain emissions species. Many systems have used natural aspiration of the exhaust system to draw air into the emissions stream. Other systems have used a one-way (e.g., reed) valve that allows only one-way flow from the inlet side (air source) of the one-way valve to the outlet side (i.e., exhaust side) of the one-way valve. Air can be drawn into the exhaust system when the pressure on the outlet side of the one-way valve is sufficiently lower than the inlet side of the one-way valve, such that the pressure differential is able to open the one-way valve. In such systems, flow rate is dependent on parameters of tubing used to fluidly connect the valve and the exhaust system. That is, flow rate has been known to be dependent on a function of the diameter of the tubing and length of the tubing between the valve and the exhaust system. On the one hand, the length and diameter of tubing that is needed in some applications to provide an acceptable amount of air flow is relatively large, which makes packaging the overall engine and system difficult and costly. On the other hand, if the length and diameter are too small, not enough air will be provided to meet the required emissions output.
Improvements may be made upon current designs to treat engine emissions by injecting additional air into the engine exhaust.

SUMMARY

An exhaust system and a method of treating engine emissions are generally described that can improve emissions treatment by reducing certain emissions species, for example in exhaust systems employing a catalyst. An exhaust system described herein draws air into the exhaust system from an air source, when a pressure differential between the exhaust pressure and the pressure from an available source of secondary air is at a threshold, which allows secondary air to enter the exhaust system. For example, when the threshold is reached, the exhaust system allows air to be injected or drawn from an air source into the exhaust system. In one particular implementation, the exhaust system is a system residing in a genset engine.
In one embodiment, the threshold is an exhaust pressure differential between the exhaust system and an air source and the threshold may be reached, for example, when the exhaust pressure is lower than the pressure of the air source. In some embodiments, the threshold is repeatedly reached based on exhaust pulses during an engine's operating cycle.
In one embodiment, the air source is a pressurized air source. As one example, the pressurized air source is a fan. In some embodiments, the pressurized air source is an existing air source of a genset engine, such as an existing fan of a genset engine.
In one embodiment, a genset incorporating the exhaust system herein operates as follows. External air is brought into the genset, such as with an existing cooling fan of the genset. When a cooling fan is used, a main air flow from the air source is customarily directed past the alternator and engine to cool them. A portion of the air from the air source is pulled off the main air flow and directed toward the exhaust system using a one-way valve and conduit that fluidly connects the air source to the exhaust system. Air flows into the exhaust system when a pressure differential between the exhaust pressure and the pressure from the cooling fan is at a threshold that opens the valve. If the pressure differential is not large enough, the valve stays closed and no air is injected into the exhaust system.
With the concepts described herein, one embodiment of a genset comprises an exhaust system that includes an exhaust manifold configured to fluidly connect to a genset engine and receive exhaust flow from the genset engine. The exhaust manifold is fluidly connected with a catalytic device configured to provide aftertreatment of the exhaust flow. The genset also include a source of air, which may be pressurized for example, and a one-way valve connected to the source of air. The one-way valve is configured to fluidly connect the source of air to the exhaust manifold. The one-way valve also is configured to deliver an amount of air from the source of air to the exhaust manifold, when a pressure differential between the exhaust pressure and the pressure from the source of air is at a threshold, which allows secondary air to enter the exhaust system. For example, when the threshold is reached, such as when the exhaust pressure decreases, the one-way valve allows air to be injected or drawn from the source of air into the exhaust system.
With the concepts described herein, one embodiment of a method of reducing emissions in a genset engine comprises receiving exhaust flow from a genset engine into an exhaust manifold, and decreasing exhaust pressure in the exhaust manifold. Air is injected from a pressurized source of air into the exhaust manifold, when the exhaust pressure decreases. The air is mixed with the exhaust flow, and the exhaust flow is treated with an aftertreatment device to thereby reduce engine emissions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a genset showing one embodiment of an exhaust system with an air injection apparatus.

FIG. 2 is a side view of one embodiment of a genset showing one embodiment of an exhaust system with an air injection apparatus.

FIG. 3 is a top view of the genset and exhaust system of FIG. 2.

FIG. 4 is a side view of the genset and exhaust system of FIG. 2 without the engine.

FIG. 5 is a top view of the genset and exhaust system of FIG. 4 without the engine.

FIG. 6 is a graph showing an example of exhaust pressure across an engine having a four-stroke cycle.

DETAILED DESCRIPTION

FIGS. 1-6 of the present disclosure generally relate to an exhaust system and a method of treating engine emissions, for example in exhaust systems employing a catalyst, which can improve emissions treatment by reducing certain emissions species. Some examples of emissions species that are reduced from the disclosure herein include hydrocarbon (HC) emissions reduced by using oxygen from a source of secondary air. At the same time, the catalyst may reduce carbon monoxide (CO) emissions by using the oxygen from the available secondary air. An exhaust system described herein draws air into the exhaust system from an air source, for example a pressurized air source, when a pressure differential between the exhaust pressure and the pressure from the air source is at a threshold which allows secondary air to enter the exhaust system. For example, when the threshold is reached, the exhaust system allows air to be injected or drawn from the air source into the exhaust system. In one particular implementation, the exhaust system is a system residing in a generator set (genset) engine.
Genset engines are well known and may be stand-alone devices that generate power to run electrical devices. A genset engine may be a back-up power source in the event of a loss of electrical grid power. In one embodiment, genset engines are provided in recreational vehicles to subsidize grid electricity or as the primary power source when grid electricity is not being used. In other embodiments, the genset engine may be provided as a secondary source of power for a home or business. In yet another embodiment, the genset engine may be the primary source of power where grid power is not readily available, such as remote locations or construction sites. It is to be realized that genset engines have many uses and are not limited to the uses in the above stated embodiments. While the exhaust system concepts herein are described as being particularly useful for a genset engine, it will be appreciated that the exhaust system may be used in any type of internal combustion engine where appropriate.
With reference to FIG. 1, a schematic of a genset 10 shows one embodiment of an exhaust system 16 incorporating an air injection apparatus. The genset 10 includes an engine that, in one embodiment, is an internal combustion engine fueled using the combustion of air and fuel. See fuel flow, air flow, and exhaust flow arrows. An air intake system 22 delivers the air/fuel mixture to the engine 12. In the embodiment shown, an air scroll with a cooling fan 14 delivers cooling air through the cooling fan 14 to cool an alternator 20 and the engine 12. See arrow to the cooling fan 14 and arrows from the cooling fan to the alternator 20 and engine 12. Usually, such a fan already exists in such gensets.
With reference to the exhaust system 16, an exhaust manifold 24 is fluidly connected with the engine 12 and is fluidly connected with an aftertreatment device 26. The exhaust manifold 24 delivers exhaust flow from the engine 12 to the aftertreatment device 26. In one embodiment, the aftertreatment device 26 is a muffler with a catalyst. Aftertreatment devices and exhaust manifolds are well known and are not further described. It will be appreciated that one of skill in the art could employ various aftertreatment devices as known in the art and modify one accordingly for use with the concepts herein or, in the alternative, design an aftertreatment device suitable for use with the concepts herein.
With reference to the air injection apparatus, a valve 18 is fluidly connected to a source of air which, when the valve 18 is opened, allows a flow of air to be delivered or drawn into the exhaust system 16. As shown, the valve 18 is fluidly connected to the exhaust manifold 24, where the exhaust manifold 24 would have an inlet (see arrow to the manifold 24) to allow entry of air when the valve 18 is opened. The valve 18 may be disposed at any portion of the exhaust manifold, from where the exhaust flows into the exhaust manifold up to the catalyst (e.g. aftertreatment device). As one example, the valve 18 is a one-way valve such as, but not limited to, a one-way (reed) valve structure. It will also be appreciated that the valve 18 may also be an electro-mechanical valve which can be controlled by an ECU (see e.g. dotted box 28 and arrow of FIG. 1). Reed valve structures, their construction and function, are well known and not further described.
As one preferred example, the source of air is a pressurized air source, such as but not limited to a fan. In some embodiments, the pressurized air source is an existing air source of a genset engine such as the fan 14 shown in FIG. 1. The existing air source can include but is not limited to, for example, an existing fan of a genset engine. As shown in the embodiment of FIG. 1, the existing system fan is the air scroll with cooling fan 14 used to provide a main flow of air for cooling the alternator 20 and engine 16.
In operation, the genset 10 incorporating the exhaust system 16 operates as follows. External air is brought into the air scroll with fan 14. The fan 14 directs the air as a main air flow to the alternator 20 and engine 12 to cool them. A portion of the air from the fan 14 is pulled off the main air flow and directed toward the exhaust system 16 using a one-way valve 18. In some embodiments, a conduit fluidly connects the air source (e.g. fan) and valve 18 to the exhaust system 16, such that generally no exhaust escapes past the valve 18, for example such that no exhaust from the exhaust manifold 24 flows past the valve 18 into the ambient (i.e., into the “clean” side of the valve 18).
With further reference to air flow into the exhaust system 16, one preferred approach to injecting air into the exhaust system 16 is to use a pressure differential between the exhaust pressure and the pressure from the cooling fan. When the exhaust pressure (e.g. at the inlet of the manifold 24) has decreased to a certain threshold such that the pressure on the inlet side of the valve is higher than on the outlet side of the valve, the valve 18 can open allowing air from the cooling fan to enter the exhaust system. If the pressure differential is not large enough, the valve stays closed and no air is injected into the exhaust system 16. Generally, whenever the pressure differential is large enough to overcome the valve's 18 resistance, then the valve will open to allow air to enter the exhaust system.
That is, in the exemplary configuration shown in FIG. 1, air is brought into the air scroll via the cooling fan 14. Most of the air is then directed past the alternator 20 and engine 12 to cool them. A portion of air from the fan 16 is drawn through the one-way valve to the exhaust system 16. Air flows into the exhaust system 16 when a differential of the pressure in the exhaust system 16 and the pressure from the cooling fan 14 is able to open the valve 18. If the pressure differential is not large enough, the valve 18 stays closed.
While FIG. 1 shows that the air source is the cooling fan 14, one of skill in the art will appreciate that the air source could be any other type of fan (e.g., electrical fan) or blower device already employed in the genset for delivering air flow, for example a centrifugal blower, engine cooling fan, turbocharger. Use of such an existing air source provides a non-parasitic aftertreatment system using genset components already part of the design. It also will be appreciated that a separate dedicated air source (e.g. separate fan) may be employed where appropriate and/or necessary to deliver air to the exhaust system.
With further reference to the pressure differential and threshold to open the valve 18, in one embodiment, the threshold is an exhaust pressure differential between the exhaust system and an air source and is reached, for example, when the exhaust pressure is lower than the pressure of the air source.
In some embodiments, the threshold is repeatedly reached based on exhaust pulses during an engine's operating cycle. Exhaust pulses in the exhaust manifold are a function of exhaust valve timing, exhaust manifold lengths/volumes, muffler/catalyst geometries, etc. For example, whenever a relatively abrupt change in pressure or mass flow occurs, an exhaust pulse can be created in the exhaust flow. Generally, more flow allows for emissions reduction. For example, the amount of air flow can be dependent on what level of emissions reduction is targeted and which emissions species is targeted. In the application of gensets, for example, a relatively small amount of air flow could have a significant effect on hydrocarbon (HC) emissions reduction, but perhaps additional flow is needed to have a relatively significant effect on carbon monoxide (CO) reduction. To get a larger reduction on CO emissions, a larger amount of flow may be needed.
For example in engines having a four-stroke cycle, the exhaust pressure on some engines can dip below the atmospheric pressure during a part of the four-stroke cycle. With reference to FIG. 6, a graph shows such an example of exhaust pressure across an engine having a four-stroke cycle. In FIG. 6, a one-way valve can be opened when the exhaust pressure has decreased within a certain range. In such circumstances, air from an air source (e.g. fan) can be injected through the valve and into the exhaust system (e.g. at the exhaust manifold). As shown in FIG. 6, depending on the crank angle during the cycle, the exhaust pressure will change. With reference to the term “exhaust back pressure”, the term is generally synonymous with the pressure in the exhaust. The term ‘back pressure’ is generally known as the pressure that pushes ‘back’ against the exhaust flow being pushed out past the exhaust valve by the piston. When the exhaust pressure has decreased within a certain range (see e.g. bracketed double arrow in FIG. 6), the valve opens in this pressure range due to the pressure at the exhaust-side of the valve being lower than the pressure on the other side of the valve (e.g. the side of the pressurized air source).
With reference to FIGS. 2-5, a genset 100 shows an example of an actual exhaust system incorporating an air injection apparatus along with some of the concepts described in the broader schematic of FIG. 1 above. FIGS. 4 and 5 show the genset of FIGS. 2 and 3, but without the engine, so that the air injection apparatus can be more easily viewed.
As shown in FIGS. 2-5, the genset 100 includes an exhaust system incorporating an air injection apparatus. The genset 100 includes an engine 102 that, in one embodiment, is an internal combustion engine fueled using the combustion of air and fuel. As with FIG. 1, the engine 102 can use an air intake system that delivers an air/fuel mixture to the engine 102. An air source shown by pressurized air housing 104 delivers cooling air to cool the engine 102. The air housing is an already existing component in gensets such as genset 100 to provide engine cooling.
With reference to the exhaust system, an exhaust manifold 108 is fluidly connected with the engine 102 and is fluidly connected with an aftertreatment device 106. The exhaust manifold 108 delivers exhaust flow from the engine 102 to the aftertreatment device 106. In one embodiment, the aftertreatment device 106 is a muffler with a catalyst. As described above, aftertreatment devices and exhaust manifolds are well known and are not further described. It will be appreciated that one of skill in the art could employ various aftertreatment devices as known in the art and modify one accordingly for use with the concepts herein or, in the alternative, design an aftertreatment device suitable for use with the concepts herein.
With reference to the air injection apparatus, a valve 112 is fluidly connected to the pressurized air housing 104. When the valve 112 is opened, a flow of air is allowed to be delivered to the exhaust manifold 108. As shown, the valve 112 is fluidly connected to the exhaust manifold 108, where the exhaust manifold 108 would have an inlet to allow entry of air when the valve 18 is opened. In one embodiment, the valve 112 is a one-way valve such as, but not limited to, a reed valve structure. As described above, reed valve structures, their construction and function, are well known and are not further described. While FIGS. 2-5 show a one-way valve, it will be appreciated that the one-way valve may not be a reed valve, which is generally mechanical in nature. In other examples, the one-way valve design could be accomplished using a solenoid (electrical) valve that is actuated by a controller.
In the event that an electrically driven valve is used (e.g. a solenoid), an electronic control unit ECU (see e.g. 28 in FIG. 1) would operatively control the valve. Generally, ECUs are provided in such engine systems and are known as the system computers. The ECU in such an embodiment would be configured to have a lookup table, determined through calibration work that one of skill in the art could accomplish. Based on the lookup table, the ECU would then decide when to open and close the valve, such as when the pressure differential is reached.
As described above, the valve 112 is fluidly connected to the exhaust manifold 108. In the embodiment shown in FIGS. 2-5, a conduit 114 is used to fluidly connect an outlet of the valve 112 to an inlet of the exhaust manifold 108. It will be appreciated that the conduit 114 can be designed and constructed as needed to allow for air to flow through the conduit to deliver air passing through the valve 112 to the exhaust manifold 108. For example, the conduit 114 is not limited to the specific configuration shown, as the turns of the conduit and as well as its diameter/length can be modified by one of skill in the art as needed or appropriate to achieve desired air flow results.
In operation, the exhaust system of the genset 100 operates as follows. External air is brought to the pressurized air housing 104. A fan of the pressurized air housing 104 directs air as a main air flow to the engine 102 to cool it. A portion of the air from the pressurized air housing 104 is pulled off the main air flow and directed toward the exhaust system using the one-way valve 112.
As described above, one preferred approach to injecting air into the exhaust system is to use a pressure differential between the exhaust pressure and the pressure from the pressurized air housing. For example, when the exhaust pressure (e.g. at the inlet of the manifold 108) has decreased to a certain threshold, the valve 112 can open allowing air from the fan to be injected into the exhaust system. If the pressure differential is not large enough, the valve stays closed and no air is injected into the exhaust system 16.
With the concepts described herein, a genset is provided with an exhaust system that includes an exhaust manifold configured to fluidly connect to a genset engine and receive exhaust flow from the genset engine. The exhaust manifold is fluidly connected with a catalytic device configured to provide aftertreatment of the exhaust flow. The genset also includes an air injection apparatus including a pressurized source of air and a one-way valve connected to the pressurized source of air. The one-way valve is configured to fluidly connect the pressurized source of air to the exhaust manifold. The one-way valve also is configured to deliver an amount of air from the pressurized source of air to the exhaust manifold, when an exhaust pressure in the exhaust system decreases. The exhaust system herein can be used in a method for reducing emissions in a genset engine. Such a method includes receiving exhaust flow from a genset engine into an exhaust manifold, and decreasing exhaust pressure in the exhaust manifold. Air is injected from a pressurized source of air into the exhaust manifold, for example, when the exhaust pressure decreases. The air is mixed with the exhaust flow, and the exhaust flow is then treated with an aftertreatment device to thereby reduce engine emissions.
The concepts herein can improve engine emissions by reducing certain emissions species. For example, emissions reductions have been observed by at least 20% in hydrocarbons and 8% in carbon monoxide by using the concepts herein to force or inject air into an exhaust system. Other improvements to the system (e.g., by increasing air flow) can cause further reductions in emissions. Further, the concepts herein can solve issues of having too long a length of tubing or too large a diameter of tubing (which increase costs and system packaging complexity) by using a pressurized source of air to force more air into the exhaust than if the air source is at ambient pressure (e.g. non-pressurized). The concepts described above are difficult to implement in some systems due to the lack of pressurized air that is available. For example, some liquid-cooled engines may not have a fan, and if a fan is available, it may be relatively far from the exhaust manifold, which could make the packaging of such a system more difficult. However, where appropriate, a separate dedicated fan may be employed in such systems, where no existing fan is available or if it is disposed relatively far from the exhaust manifold, in order to achieve the secondary air injection in accordance with the principles herein if emissions treatment is desired and/or needed.
The exhaust system herein is also different in that few applications use secondary air injection, which is mainly used with engines that operate rich of stoichiometric. Many applications operate at stoichiometric or lean of stoichiometric conditions and may also have a use and/or need for secondary air injection. For example, stoichiometric engines could still use secondary air injection. There may be less of a need for secondary air injection for engines that operate lean of stoichiometric, because they already have excess air in the exhaust by definition.
Also, packaging is often a limiting constraint in genset designs. Applicants have considered this in the concepts described herein. By using an existing air source, for example, emissions requirements are able to be met without increases in packaging profiles or, in some instances, with smaller packaging than current systems that use non-pressurized secondary air injection.
While the above is a complete description of the preferred embodiments of the invention, various alternatives, modifications, and equivalents may be used. Therefore, the above description should not be taken as limiting the scope of the invention which is defined by the appended claims.

Claims

1. A genset comprising:

an exhaust system including an exhaust manifold configured to fluidly connect to a genset engine and receivable of exhaust flow from the genset engine, the exhaust manifold is fluidly connected with a catalytic device configured to provide aftertreatment of the exhaust flow;

a pressurized source of air; and

a one-way valve connected to the pressurized source of air and configured to fluidly connect the pressurized source of air to the exhaust manifold,

wherein the one-way valve is configured to deliver an amount of air from the pressurized source of air to the exhaust manifold, when an exhaust pressure in the exhaust system decreases.

2. The genset of claim 1, wherein the pressurized source of air is a cooling fan.

3. The genset of claim 1, wherein the pressurized source of air is an existing fan configured to provide a main flow to other genset components, and provide a secondary air flow to the exhaust system.

4. The genset of claim 1, wherein the one-way valve is a reed valve configured to open when the exhaust pressure decreases to a threshold and configured to be closed when the exhaust pressure has not reached the threshold.

5. The genset of claim 1, wherein the one-way valve is configured to deliver a pulse of air to the exhaust manifold each time the exhaust pressure in the exhaust system is lower than the pressurized source of air.

6. The genset of claim 1, further comprising a conduit that fluidly connects the one-way valve to the exhaust manifold.

7. A method of reducing emissions in a genset engine comprising:

receiving exhaust flow from a genset engine into an exhaust manifold;

decreasing exhaust pressure in the exhaust manifold;

injecting air from a pressurized source of air into the exhaust manifold when the exhaust pressure decreases; and

mixing the air with the exhaust flow and treating the exhaust flow with an aftertreatment device to thereby reduce engine emissions.

8. The method of claim 7, wherein the step of injecting air comprises delivering a pulse of air for each instance the exhaust pressure decreases to a certain threshold.

9. The method of claim 8, wherein the pulse of air being delivered through a one-way valve configured to open when the exhaust pressure decreases to a threshold and configured to be closed when the exhaust pressure has not reached the threshold.