Method and system for reducing pollutant emissions of a power system

[0019]FIG. 1 provides a pictorial representation of an exemplary machine 5 having multiple systems and components that may cooperate to accomplish a task. Machine 5 may include a system for reducing pollutant emissions. Machine 5 may embody a fixed or mobile machine that performs some type of operation associated with an industry such as mining, construction, farming, transportation, or any other industry known in the art. For example, machine 5 may be an earth moving machine such as an excavator, a dozer, a loader, a backhoe, a motor grader, a dump truck, or any other earth moving machine. Additionally, machine 5 may include on-highway vehicles such as tractors, passenger cars, heavy and light trucks, and other similar vehicles. Machine 5 may include a first power source 18, a second power source 46, auxiliary devices 48, and an input member 16 connecting a transmission assembly 10 to power source 18 via a torque converter 19. Machine 5 may also include a frame 14 and an output member 20 connecting the transmission assembly 10 to one or more traction devices 22 operatively connected to frame 14. Power source 18 may be operatively connected to frame 14 and may further be fluidly connected to an exhaust system 17, which may in turn be fluidly connected to an SCR system catalyst 23. Second power source 46 may be designed to provide power to auxiliary devices 48.

[0020]FIG. 2 schematically illustrates a power system capable of implementing the disclosed systems and methods for reducing pollutant emissions of a power system. In an exemplary pollutant emission reduction system, first power source 18 and second power source 46 may be present. First power source 18 may include an internal combustion engine, e.g., a diesel engine, a gasoline engine, a gaseous fuel-powered engine, and the like, or any other lean-burn engine apparent to one skilled in the art. Alternatively, first power source 18 may be another source of power, such as a furnace, gas-turbine, or another suitable source of power for a powered system (e.g., a factory or power plant) designed to operate with an excess of oxygen. First power source 18 may include, for example, an intake manifold 26, intake passages 24, exhaust ports 29, an exhaust manifold 28, combustion chambers 30, additive supply devices 32, and fuel sources 38. First power source 18 may further include a fuel pump 34, fuel storage 36, additive pump 40, additive controller 52, and additive storage 42, among other things.

[0021] Combustion chambers 30 may be configured to receive and combust materials including fuel and air. Additionally, each combustion chamber 30 may be configured to receive at least one additive material including, for example, an ethanol additive and/or a hydrous ethanol additive. Hydrous ethanol will be understood to mean any combination of ethanol and water in any proportion appropriate for addition to a combustion chamber. The term ethanol additive, as referred to throughout this specification, will be understood to mean any substance or mixture containing ethanol in amounts greater than 15 percent by volume, including fuel-grade ethanol, denatured ethanol, and hydrous ethanol. For example, an ethanol additive may include between 30 percent ethanol by volume and 80 percent ethanol by volume. In one embodiment, the ethanol additive is a hydrous ethanol and includes approximately 40 percent ethanol by volume and 60 percent water by volume. A hydrous ethanol additive may be similar to vodka or other distilled spirits, or the hydrous ethanol additive may be denatured. Hydrous denatured ethanol may be less expensive than pure ethanol and may be substantially more stable for easier storage and transport. One of ordinary skill in the art will recognize that the ethanol additive compositions described herein are exemplary only, and numerous variations of ethanol additives may be used without departing from the scope of the disclosed systems and methods.

[0022] Combustion chambers 30 may be configured for compression ignition (CI), spark ignition (SI), homogeneous charge compression ignition (HCCI), or any other type of combustion ignition. For example, a diesel engine may initiate combustion as a piston (not shown) within combustion chamber 30 nears top-dead-center and critical temperature and pressure are reached.

[0023] Combustion chambers 30 may be configured to receive a supply of fuel from fuel sources 38. Fuel sources 38 may include injectors or atomizers configured to inject fuel directly into combustion chambers 30. Alternatively, fuel sources 38 may be configured to supply fuel to intake manifold 26 or intake passages 24. Fuel sources 38 may be configured to supply fuel at a specific time (timed injection) or, alternatively, may be configured to introduce fuel continuously or at random intervals. Configuration of fuel sources 38 may depend upon the combustion configuration of combustion chambers 30 (e.g., CI, SI, or HCCI).

[0024] Fuel sources 38 may be operatively connected to fuel pump 34. Fuel pump 34 may be configured to deliver fuel from fuel storage 36 to fuel sources 38. Fuel pump 34 may include an injection pump of the rotary or distributor variety, or any other suitable pump, and may be driven indirectly by gears or chains from the crankshaft or by other methods (e.g., electrically). One of skill in the art will recognize that many types of pumps may function adequately and fall within the scope of the current disclosure.

[0025] The fuel supplied to combustion chambers 30 may include, for example, diesel fuel, gasoline, alcohols, propane, methane, or any other suitable fuel. The fuel may be supplied to fuel sources 38 under pressure, and/or fuel sources 38 may, themselves, be configured to further increase the pressure or velocity of the fuel. Fuel storage 36 may be configured to store fuel, among other things, and may include a tank or other similar container. Fuel may be supplied at timed intervals (e.g., based on first power source 18 rotational position), randomly, and/or continuously. Control of the fuel source 38 may be regulated by methods known by those of ordinary skill in the art and appropriate for the type of power source in operation.

[0026] Intake manifold 26 may be configured to draw air from atmosphere or from an air source (e.g., a turbocharger) and provide the air to combustion chambers 30 via intake passages 24. For example, intake manifold 26 may be fluidly connected to a forced induction system such as the outlet of a turbocharger or supercharger. Intake manifold 26 may further be fluidly connected to at least one intake passage 24, which in turn may be fluidly connected to a combustion chamber 30. In one embodiment consistent with the disclosure, intake manifold 26 may also be fluidly connected to an additive supply device 32 configured to supply an ethanol additive to intake manifold 26. It is important to note that while additive supply devices 32 are depicted in FIG. 2 as being fluidly connected to intake passages 24, additive supply devices 32 may be located at any suitable location for providing the ethanol additive to combustion chambers 30. For example, additive supply devices 32 may also be located at intake manifold 26, combustion chambers 30, a turbocharger outlet (not shown), or any other suitable location such that an ethanol additive may by provided to combustion chambers 30. Additive supply devices 32 may include an injector or atomizer similar to that depicted by additive supply device 32 and may be installed in intake manifold 26 to cause an ethanol additive to be introduced and mixed with other substances contained therein. Fuel or other additive substances (e.g., performance boosting substances including propane) may also be supplied to intake manifold 26.

[0027] Intake passages 24 may be configured to carry substances including, air, fuel, an ethanol additive, other substances, or any combination thereof, to combustion chambers 30. Intake passages 24 may contain additive supply devices 32 configured to supply an ethanol additive to combustion chambers 30. Intake passages 24 may further include devices to facilitate mixing of materials entering combustion chambers 30. Such devices may be configured to impart rotation to the flow of materials within intake passages 24. Intake passages 24 may be opened to combustion chambers 30 via intake valve assemblies (not shown) which may open and close, as desired, to facilitate flow of materials (e.g., air and/or ethanol additive) into combustion chambers 30.

[0028] Additive supply devices 32 may be fluidly connected to additive pump 40 or other apparatus designed to pressurize or impart motion to fluid or gas. Additive pump 40 may be an injection pump of the rotary or distributor variety, among others, and may be driven indirectly by gears or chains from the crankshaft or by other methods (e.g., electrically). One of skill in the art will recognize that many types of pumps may function adequately and fall within the scope of the current disclosure. Additive pump 40 may further be communicatively connected to additive controller 52. Additive pump may be configured to draw an ethanol additive from additive storage 42 and supply the ethanol additive to additive supply devices 32, a secondary additive supply device 44, and/or second power source 46 based on a determination by additive controller 52. Additive pump 40 may be configured to supply ethanol additive to additive supply devices 32 under pressure, or alternatively, additive supply devices 32 may be configured to increase the pressure or velocity of the ethanol additive. Supply of an ethanol additive may occur at timed intervals, continuously, or randomly and may be based on additional determinations made by additive controller 52. Additive storage 42 may be configured to store an ethanol additive, among other things, and may include a tank or other similar container.

[0029] Additive controller 52 may be a mechanical or an electrical based controller configured to control the flow of ethanol additive from additive pump 40. For example, additive controller 52 may send electric signals causing valves on additive pump 40 to open and close thereby directing flow of ethanol additive to additive supply devices 32, second power source 46, secondary additive supply device 44, or any other suitable location. Flow control may be based on factors including power requirements, emissions requirements, fuel availability, and other parameters. Control of the ethanol additive supply may also be regulated based on sensors present in exhaust system 17 and engine timing, among other things. For example, where a sensor present in the exhaust-gas stream indicates the presence of unacceptable levels of unburned ethanol, the ethanol additive supply rate to secondary additive supply device 44 may be modified by additive controller 52 accordingly. One of ordinary skill in the art will recognize that other methods for providing and controlling the flow of ethanol additive may be available and fall within the scope of this disclosure.

[0030] Combustion within combustion chambers 30 may result in combustion of at least a portion of the fuel and at least a portion of the ethanol present in the ethanol additive. Heat and/or power may be derived from the combustion of both the fuel and the ethanol. For example, ethanol from the ethanol additive may be combusted in amounts up to 95 percent and may produce up to 50 percent of available brake horsepower. Further, water from the hydrous ethanol additive may assist in reducing flame temperature in combustion chamber 30, and may therefore assist in reducing NOx produced during the combustion. One of skill in the art will recognize that such effects may vary based on ethanol and water concentrations in the ethanol additive.

[0031] As a result of combustion, an exhaust-gas stream including NOx, unburned ethanol, water, and hydrocarbons (e.g., unburned fuel), among other things, may be generated. The unburned ethanol may include gas phase ethanol and may be substantially mixed with the exhaust-gas stream via the combustion process within combustion chamber 30. Gas-phase ethanol may be present in the exhaust-gas stream in amounts between about 10 ppm by volume and about 10000 ppm by volume of the exhaust-gas stream. One of ordinary skill in the art will recognize that higher or lower concentrations of ethanol may be present in the exhaust-gas stream based on numerous conditions (e.g., temperature, water content, ethanol additive input, etc.).

[0032] Exhaust ports 29 may be fluidly connected to combustion chambers 30 and configured to receive the exhaust-gas stream generated as a result of combustion of the fuel and at least a portion of an ethanol additive within combustion chambers 30. The fluid connection from combustion chambers 30 to exhaust ports 29 may be opened and closed using exhaust valve assemblies (not shown) to allow flow of an exhaust-gas stream from combustion chambers 30 into exhaust ports 29. The exhaust valve assemblies may also be configured to allow such flow to occur at timed intervals. Further, exhaust ports 29 may be fluidly connected to a secondary additive supply device 44 configured to provide additional ethanol additive to the exhaust-gas stream. It is important to note that although secondary additive supply device 44 is depicted in FIG. 2 as being fluidly connected to exhaust system 17, secondary additive supply device 44 may be located at any suitable location for providing the ethanol additive to the exhaust-gas stream. For example, secondary additive supply device 44 may also be located at exhaust manifold 28, exhaust ports 29, or any other suitable location for providing an ethanol additive to the exhaust gas stream.

[0033] Exhaust manifold 28 may be fluidly linked to at least one exhaust port 29 and may collect and receive an exhaust-gas stream from the at least one exhaust port 29. Exhaust manifold 28 may operate to link several exhaust ports 29 together and receive the cumulative exhaust from exhaust ports 29. Exhaust manifold 28 may further include devices for supplying other substances (e.g., urea, ethanol, etc.) for mixture in the exhaust-gas stream, or, alternatively, no such additional devices may be present. For example, exhaust manifold 28 may be fluidly connected to secondary additive supply device 44, which may be configured to supply ethanol additive to exhaust manifold 28. Exhaust manifold 28 may include sensors (not shown) for detecting levels of exhaust gas pollutants as well as levels of remaining ethanol and/or other substances within the exhaust-gas stream. Where the sensors indicate low levels of unburned ethanol, additional ethanol additive may be provided to exhaust manifold 28, or other suitable location, by secondary additive supply device 44. Exhaust manifold 28 may further include fluid connections to allow for recirculation of some exhaust gas and/or coupling of exhaust gas to the turbine of a turbocharger (not shown).

[0034] Exhaust manifold 28 may be fluidly connected to exhaust system 17, which may be configured to receive the exhaust-gas stream from exhaust manifold 28. Exhaust system 17 may include pipes, tubes, clamps, etc., and may direct the flow of the exhaust-gas stream in various directions. Exhaust system 17 may also be fluidly connected to secondary additive supply device 44 and configured to receive additional ethanol additive for combination with the exhaust-gas stream. Exhaust system 17 may also include sensors, mixing devices, and fluid connections to recirculation devices and turbocharger turbines (not shown), among other things.

[0035] SCR system catalyst 23 may be disposed in exhaust system 17 downstream of exhaust manifold 28. Exhaust system 17 may direct flow of the exhaust-gas stream such that the exhaust-gas stream is received by SCR system catalyst 23 and caused to contact the SCR system catalyst.

[0036] SCR system catalyst 23 may be made from a variety of materials. SCR system catalyst 23 may include a catalyst support material and a metal promoter dispersed within the catalyst support material. The catalyst support material may include at least one of alumina, zeolite, aluminophosphates, hexyluminates, aluminosilicates, zirconates, titanosilicates, and titanates. In one embodiment, the catalyst support material may include at least one of alumina and zeolite, and the metal promoter may include silver (Ag). Combinations of these materials may be used, and the catalyst material may be chosen based on the type of fuel used, the ethanol additive used, the air to fuel-vapor ratio desired, and/or for conformity with environmental standards. One of ordinary skill in the art will recognize that numerous other catalyst compositions may be used without departing from the scope of this disclosure. Further, multiple SCR system catalysts may also be included in exhaust system 17.

[0037] The lean-NOx catalytic reaction is a complex process including many steps. One of the reaction mechanisms, however, that may proceed in the presence of SCR system catalyst 23 can be summarized by the following reaction equations:

NO+O2→NOx  (1)

HC+O2→oxygenated HC  (2)

NOx+oxygenated HC+O2→N2+CO2+H2O  (3)

[0038] SCR system catalyst 23 may catalyze the reduction of NOx to N2 gas, as shown in equation (3). Further, as shown in equation (2), a hydrocarbon reducing agent may be converted to an activated, oxygenated hydrocarbon that may interact with the NOx compounds to form organo-nitrogen containing compounds. These materials may possibly decompose to isocyanate (NCO) or cyamide groups and eventually yield nitrogen gas (N2) through the series of reactions as summarized above. As noted, the unburned ethanol may be well mixed within the exhaust-gas stream as a result of the combustion process in combustion chamber 30. This well-mixed, unburned ethanol, and any additional ethanol additive, may further react in the presence of other hydrocarbons (e.g., unburned fuel) in order to aid in the production of oxygenated hydrocarbons, as represented by equation (2).

[0039] Second power source 46 may be configured to supply power to one or more components of machine 5 or to any other suitable device. Second power source 46 may include fuel cells, fuel processors, heat exchangers, catalysts, combustion engines, and other devices known to those skilled in the art. Fuel cell, as used herein, means any fuel consuming electrochemical energy conversion device. For example, a fuel cell may include a proton exchange membrane fuel cell and/or a solid-oxide fuel cell. In one embodiment, second power source 46 may include a fuel cell or a stacked arrangement of fuel cells. Such fuel cells may be configured to react a fuel (e.g., hydrogen) with an oxidizer (e.g., air) to generate electrical energy and water.

[0040] A fuel processor may be fluidly connected with a fuel cell or fuel cell stack within second power source 46 and configured to provide a fuel to the fuel cell. Fuel processor, as used herein, means any device capable of converting one or more substances into a fuel for consumption within a fuel cell. For example, a fuel processor may include a steam reformer configured to convert a hydrous ethanol additive into various components including hydrogen, water, and CO2. A steam reformer may include steam generators, catalysts, and other items known to those of skill in the art. Hydrous ethanol may be provided to the fuel processor via a fluid connection to additive supply pump 40 based on a control message sent by additive controller 52. For example, auxiliary devices 48 may request power, causing additive controller 52 to determine whether first power source 18, second power source 46, or a combination thereof are available for power production (e.g., available and not overloaded). Upon making such a determination, additive controller 52 may cause valves within additive pump 40 to open and/or close thereby directing flow of ethanol additive to first power source 18, second power source 46, and/or secondary additive supply device 44. In another example, a power request may indicate that auxiliary devices 48 are requesting power and first power source 18 is not available to supply auxiliary devices 48 with power (e.g., not running, disabled, or overloaded). Additive controller 52 may cause valves within additive pump 40 to open and/or close thereby directing flow of ethanol additive to second power source 46.

[0041] Processing of an ethanol additive may occur in the presence of steam and a catalyst within a fuel processor similar to the following equations:

C2H5OH+H20 CH4+CO2+2H2 (4)

CH4+H20 CO+3H2 (5)

CO+H20 CO2+H2 (6)

[0042] The ethanol additive may react in the presence of steam and one or more catalysts to form methane, carbon dioxide and hydrogen gas as shown in equation 4. The methane generated by the process may then further react in the presence of steam and one or more catalysts to produce carbon monoxide and additional hydrogen gas as shown in equation 5. The carbon monoxide may then react in the presence of additional steam and one or more catalysts to form additional carbon dioxide and hydrogen gas as shown in equation 6. The presented equations are meant to be exemplary only and other reactions may also proceed without departing from the scope of this disclosure.

[0043] In one embodiment, steam for use in a steam reformer may be generated utilizing waste heat obtained during the operation of first power source 18. For example, a heat exchanger (not shown) may be fluidly connected to a coolant line from first power source 18. The heat exchanger may then extract heat from the coolant and use such heat to produce steam or preheat water for use in steam production. Additionally, waste heat generated at second power source 46 may also be utilized to produce steam or preheat water for use in steam production. Waste heat from second power source 46 may be used alone or in combination with other heat sources such as, heat derived from first power source 18.

[0044] Hydrogen (H2) produced by a fuel processor may be provided to a fuel cell or fuel cell stack within second power source 46, or, alternatively, the hydrogen may be stored in a hydrogen storage container (not shown) for later use. A fuel cell within second power source 46 may be configured to provide electrical energy based on a process of reacting hydrogen and oxygen to form water which may be illustrated by the following equations:

H2→2H++2e− (7)

½O2+2H++2e−→H2O  (8)

[0045] Reactive hydrogen gas may be stripped of electrons as shown in equation 7. Products of the reaction in equation 7 may then react in the presence of oxygen to form water and electricity (e.g., free electrons) as shown in equation 8. The electricity generated from the reaction may then be provided to other devices utilizing such power (e.g., auxiliary devices 48), or may be used for other suitable purposes.

[0046] Auxiliary devices 48 may be provided with power from second power source 46. Auxiliary devices 48 may include, motors, lights, pumps, compressors, resistance heaters, and any other device utilizing electrical or mechanical energy. For example, an electric motor may be powered by second power source 46 and may in turn be operatively connected to transmission assembly 10 or traction devices 22. Electrical power provided by second power source 46 may thereby cause motion of machine 5. In another example, hydraulic pressure for use with a hydraulic crane may be provided by a hydraulic pump powered by auxiliary power supply 46. Any number of other configurations and devices may be utilized without departing from the scope of this disclosure.

INDUSTRIAL APPLICABILITY

[0047] The disclosed systems and methods may be applicable to any powered system that includes a power source that produces an exhaust-gas stream, such as an engine. The disclosed systems and methods may allow for reduction efficiencies of NOx from an exhaust-gas stream of greater than 90 percent, and reduction of overall pollutants by up to 100 percent when operating with an alternative power source exclusively. Operation of the disclosed systems and methods will now be explained.

[0048] Operation of combustion chambers 30 may be dependant on the ratio of air to fuel-vapor that is supplied during operation. When determining the air to fuel-vapor ratio, primary fuel as well as other combustible materials in combustion chamber 30 (e.g., ethanol additive, propane, etc.) may be included as fuel-vapor. The air to fuel-vapor ratio is often expressed as a lambda value, which is derived from the stoichiometric air to fuel-vapor ratio. The stoichiometric air to fuel-vapor ratio is the chemically correct ratio for combustion to take place. A stoichiometric air to fuel-vapor ratio may be considered to be equivalent to a lambda value of 1.0.

[0049] Combustion chambers may operate at non-stoichiometric air to fuel-vapor ratios. A combustion chamber with a lower air to fuel-vapor ratio has a lambda less than 1.0 and is said to be rich. A combustion chamber with a higher air to fuel-vapor ratio has a lambda greater than 1.0 and is said to be lean.

[0050] Lambda may affect combustion chamber NOx emissions and fuel efficiency. A lean-operating combustion chamber may have improved fuel efficiency compared to a combustion chamber operating under stoichiometric or rich conditions. However, lean operation may increase temperature and, therefore, increase NOx production, making elimination of NOx in the exhaust gas difficult.

[0051] SCR systems can provide a method for decreasing exhaust-gas NOx emissions through the use of additives such as ethanol. In an exemplary embodiment of the present disclosure, NOx and unburned ethanol generated by lean combustion (lambda greater than 1.0) in combustion chambers 30 may be converted into acetaldehyde, nitrogen, water, and other substances in the presence of an SCR system catalyst 23.

[0052]FIG. 3 is a flowchart depicting one exemplary method for operation of the disclosed systems and methods. In one embodiment, a request for power is received by additive controller 52 (step 300). Based on a determination of the request for power and the operational states of first power source 18 and second power source 46, additive controller 52 may cause a supply of an ethanol additive to be directed to first power source 18 (step 305: primary power) and/or second power source 46 (step 305: auxiliary power). Where additive controller 52 determines that power should be provided by first power source 18, additive controller 52 may cause ethanol additive to be provided to additive supply devices 32 which may provide an ethanol additive to combustion chambers 30 (step 310). Once the ethanol additive has been supplied to combustion chambers 30, along with a suitable amount of air, fuel may be supplied to combustion chambers 30 (step 315). Following the supply of fuel, combustion of the materials within combustion chambers 30 may be initiated (step 320). A fluid connection between exhaust manifold 28 and exhaust system 17 may then allow an exhaust-gas stream formed as a result of combustion, to be received by exhaust system 17. Exhaust system 17 may be configured to direct the exhaust-gas stream to be received by SCR system catalyst 23 via a fluid connection (step 325). The exhaust-gas stream may then flow through SCR system catalyst 23, thus contacting SCR system catalyst 23 based on the design and flow pattern of SCR system catalyst 23. SCR system catalyst 23 may facilitate reactions resulting in the reduction/conversion of NOx from the exhaust-gas stream (step 330). The products of such conversion may include nitrogen, water, and acetaldehyde, among other things. The resulting reduction efficiencies of SCR system catalyst 23 for NOx may, therefore, be increased to greater than 90 percent. In other words, NOx within an exhaust-gas stream may be reduced by greater than 90 percent and may meet federal regulations for year 2010 NOx emissions.

[0053] Where additive controller 52 determines that power should be provided by second power source 46, additive controller 52 may cause ethanol additive to be provided to second power source 46 (step 335). The ethanol additive may then be processed by a fuel processor to produce hydrogen gas among other things (step 340). Hydrogen gas produced during the processing may then be provided to the fuel cell for use as fuel (step 345). Power generated by the fuel cell may then be provided to auxiliary devices 48 or another requesting device (step 350). Utilizing second power source 46 in this way can eliminate harmful emissions with the only byproduct being water.

[0054] Several advantages may be associated with the disclosed systems and method for reducing pollutant emissions of a power system. For example, ethanol additives containing water (i.e., hydrous ethanol), whether denatured or not, may be substantially less reactive than pure fuel-grade ethanol. Further, pure fuel-grade ethanol may act as a desiccant drawing in water from the surrounding atmosphere, whereas hydrous ethanol additives may be stored at equilibrium. Therefore, requirements for storage and transportation of a hydrous ethanol additive may be substantially lower than for storage and transportation of pure fuel-grade ethanol. Use of hydrous ethanol additives may lead to significant cost savings over pure fuel-grade ethanol and other benefits such as, cooler combustion chamber temperatures and/or reduced combustion chamber production of NOx.

[0055] Moreover, by providing a system for supplying an ethanol additive to an intake port, intake manifold, or combustion chamber, using equipment distinct from the fuel supply system, systems designed for ethanol specific applications may be used. Ethanol may be corrosive to rubber and some metal parts and can damage parts designed for use with petroleum based products, for example, pumps, injectors, etc. By using parts designed specifically designed for ethanol (e.g., plastics), this damage can be reduced or eliminated.

[0056] Additionally, injection of an ethanol additive into an intake port prior to combustion may allow for greater mixing of any remaining ethanol within an exhaust-gas stream. Increased mixing may occur as the result of many mechanisms related to the combustion process (e.g., turbulence, compression, etc.). Complete mixing of ethanol within the exhaust-gas stream may be beneficial to increasing the reduction efficiency of an SCR system catalyst. Therefore, combining an SCR system catalyst with intake port injection of ethanol may result in substantial increased efficiency of the reaction between NOx and ethanol contained in the exhaust-gas stream, as the stream contacts the SCR system catalyst. Moreover, allowing a portion of the ethanol to be combusted in combustion chambers 30 may further result in benefits to brake specific fuel consumption, while also leaving an amount of unburned ethanol in the exhaust-gas stream. The amount of ethanol remaining in the exhaust-gas stream may be sufficient to facilitate catalytic reduction reactions and may improve the efficiency of an SCR system catalyst. But, the amount of unburned ethanol in the exhaust-gas stream may remain small enough to substantially prevent emission of reactive ethanol species into the air post catalyst.

[0057] Provisioning a portion of ethanol additive for use in an alternative fuel source may further provide the benefit of power generation with a substantial reduction in petroleum based fuel use and little or no pollutant emissions. By determining which power source is better suited to provide power for a particular request, power needs may be met while also minimizing overall pollutant output.

[0058] It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed system and methods for reducing pollutant emissions of a power system. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed systems and methods for reducing pollutant emissions of a power system. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.