A provision of assemblies and methods for treating an exhaust gas from an internal combustion engine. The treatment method comprises at least two catalyst stages. The exhaust gas is directed to a first stage catalyst. After the first stage catalyst, the exhaust is passed to an inter-catalyst stage c
A provision of assemblies and methods for treating an exhaust gas from an internal combustion engine. The treatment method comprises at least two catalyst stages. The exhaust gas is directed to a first stage catalyst. After the first stage catalyst, the exhaust is passed to an inter-catalyst stage comprising an exhaust cooling process and an oxygen enrichment process. Next, the exhaust is passed to a second stage catalyst for reducing carbon monoxide, ammonia and hydrocarbon concentration in the exhaust gas, before exiting via an outlet.
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1. A method for treating an exhaust gas discharged from a rich-burn, spark ignited engine, the method comprising the steps of: (a) controlling combustion of air-fuel mixture to produce an exhaust gas that is substantially free of oxygen;(b) passing the exhaust gas from the engine to a first stage ca
1. A method for treating an exhaust gas discharged from a rich-burn, spark ignited engine, the method comprising the steps of: (a) controlling combustion of air-fuel mixture to produce an exhaust gas that is substantially free of oxygen;(b) passing the exhaust gas from the engine to a first stage catalyst for substantially reducing nitrogen oxide (NOx) and carbon monoxide concentration in the exhaust gas;(c) passing the exhaust gas resulting from step (b) to an inter-catalyst stage having (i) an oxygen enrichment process wherein oxygen containing gas is discontinuously injected at an injection point into the exhaust gas, and(ii) an exhaust cooling process wherein the exhaust gas is cooled to a predetermined temperature for inhibiting the generation of NOx in the second stage catalyst; andd) passing the exhaust gas resulting from step (c) to a second stage catalyst for substantially reducing carbon monoxide concentration in the exhaust gas and reducing ammonia concentration in the exhaust gas depending on temperature of exhaust passing through the second stage catalyst, before exiting via an outlet,whereby the concentration of NOx, carbon monoxide, and hydrocarbons in the treated exhaust gas that exits the second stage catalyst is substantially reduced. 2. The method of claim 1, wherein the oxygen content of the exhaust gas downstream of the injection point is intermittently less than 0.24% and not greater than about 1.35% as a result of discontinuous injection of oxygen containing gas. 3. The method of claim 1, wherein an engine control device receives signals from two or more oxygen sensors wherein one oxygen sensor is placed upstream of the first stage catalyst and a second oxygen sensor is placed downstream of the inter-catalyst stage. 4. The method of claim 1, wherein the exhaust cooling process cools the exhaust to a temperature range of 380 to 650 degrees Fahrenheit. 5. The method of claim 1, wherein the generation of NOx by the oxidation of ammonia in the second stage catalyst is substantially limited when second stage exhaust gas temperature is less than 480 degrees Fahrenheit. 6. The method of claim 2, wherein intermittently discontinuing the injection of oxygen containing gas lowers the oxidation state of noble metals, which comprise the second stage catalyst. 7. The method of claim 1, wherein the engine air-fuel ratio is dithered thereby reducing the amount of ammonia exiting the first stage catalyst. 8. The method of claim 7, wherein the concentration of ammonia in the treated exhaust that exits the second stage catalyst is less than 2.0 ppm corrected to 15% oxygen based on time-average data taken over an extended period. 9. The method of claim 2, wherein the injection of oxygen containing gas is briefly ceased at a frequency of every 0.4 to 40 seconds. 10. The method of claim 2, wherein the injection of oxygen containing gas is briefly ceased at a frequency of every 40 seconds to 15 minutes. 11. The method of claim 1, wherein the concentration of NOx in the treated exhaust that exits the second stage catalyst is less than 3.7 ppm corrected to 15% oxygen based on time-average data taken over an extended period. 12. The method of claim 1, wherein the concentration of carbon monoxide in the treated exhaust that exits the second stage catalyst is less than 8.3 ppm corrected to 15% oxygen based on time-average data taken over an extended period. 13. The method of claim 1, wherein the concentration of carbon monoxide in the treated exhaust that exits the second stage catalyst is less than 6.7 ppm corrected to 15% oxygen based on time-average data taken over an extended period. 14. The method of claim 1, wherein the concentration of carbon monoxide in the treated gas that exits the second stage catalyst is less than 5.0 ppm corrected to 15% oxygen based on time-average data taken over an extended period. 15. The method of claim 1, wherein the concentration of carbon monoxide in the treated exhaust exiting the first stage catalyst is less than 625 ppm corrected to 15% oxygen based on time-average data taken over an extended period. 16. The method of claim 2, wherein the exhaust cooling process cools the exhaust to a temperature range of 380 to 500 degrees Fahrenheit. 17. The method of claim 1, wherein the concentration of ammonia in treated exhaust that exits the second stage catalyst is less than 3.0 ppm corrected to 15% oxygen based on time-average data taken over an extended period. 18. The method of claim 1, wherein the oxygen enrichment process comprises injection of oxygen containing gas through a plurality of injection ports. 19. The method of claim 1, wherein the concentration of a precursor for particulate matter is reduced in the exhaust gas exiting the second stage catalyst. 20. The method of claim 1, wherein the air to fuel ratio of the engine is controlled by a system utilizing a venturi mixer and an electronically controlled valve. 21. An apparatus for treating an exhaust gas discharged from a rich-bum, spark ignited internal combustion engine, comprising: a first stage catalyst adapted to receive the exhaust gas from the engine and to substantially reduce NOx and carbon monoxide content in the exhaust gas;an inter-catalyst stage configured to discontinuously enrich the exhaust gas with oxygen and cool the exhaust to a predetermined temperature prior to catalytic conversion;a second stage catalyst adapted to receive the exhaust gas from the inter-catalyst stage and to substantially reduce carbon monoxide content in the exhaust gas; andan outlet for allowing the treated exhaust to exit the apparatus,whereby the concentration of NOx, carbon monoxide, and hydrocarbons in the treated exhaust gas that exits the second stage catalyst is substantially reduced. 22. The apparatus of claim 21, wherein an engine control device receives signals from two or more oxygen sensors wherein one oxygen sensor is placed upstream of the first stage catalyst and a second oxygen sensor is placed after the first stage catalyst and upstream of the second stage catalyst. 23. A method for limiting the generation of NOx on a second stage catalyst receiving an exhaust gas from a combustion device, the method comprising: (i) controlling combustion of air-fuel mixture to produce an exhaust gas that is substantially free of oxygen;(ii) providing a least one exhaust cooling stage where the exhaust gas is cooled to a predetermined temperature and at least one air injection stage where the exhaust gas is discontinuously enriched with oxygen before being passed to the second of at least two catalyst stages,whereby the generation of NOx in the exhaust gas that passes over the second stage catalyst is substantially limited based on an average of measurements taken over an extended time period. 24. The method of claim 23, wherein an engine control device receives signals from two or more oxygen sensors wherein one oxygen sensor is placed upstream of the first stage catalyst and a second oxygen sensor is placed after the first stage catalyst and upstream of the second stage catalyst.
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이 특허에 인용된 특허 (6)
Gehret, Joseph B.; Panora, Robert A.; Roser, Ranson, Assembly and method for reducing nitrogen oxides, carbon monoxide and hydrocarbons in exhausts of internal combustion engines.
Burk Patrick Lee ; Hochmuth John Karl ; Dettling Joseph Charles ; Heck Ronald Marshall ; Steger John Joseph ; Tauster Samuel Jack, Method and apparatus for treating an engine exhaust gas stream.
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