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A method for operating a spark-ignition engine having a three-way catalyst and a particulate filter downstream thereof, comprising: oscillating an exhaust air-fuel ratio entering the particulate filter to generate air-fuel ratio oscillations downstream of the particulate filter, while increasing exh

A method for operating a spark-ignition engine having a three-way catalyst and a particulate filter downstream thereof, comprising: oscillating an exhaust air-fuel ratio entering the particulate filter to generate air-fuel ratio oscillations downstream of the particulate filter, while increasing exhaust temperature; when the downstream oscillations are sufficiently dissipated, enleaning the exhaust air-fuel ratio entering the particulate filter; and reducing the enleanment when an exhaust operating parameter is beyond a threshold amount.

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1. An engine system comprising: an engine configured to combust air and at least one of gasoline and alcohol;an exhaust system configured to receive exhaust from the engine, the exhaust system comprising: an emissions control device;a particulate filter positioned downstream from the emissions contr

1. An engine system comprising: an engine configured to combust air and at least one of gasoline and alcohol;an exhaust system configured to receive exhaust from the engine, the exhaust system comprising: an emissions control device;a particulate filter positioned downstream from the emissions control device;an oxygen sensor positioned downstream from the particulate filter; anda temperature sensor configured to provide a temperature of the particulate filter; anda controller configured to, during regeneration of the particulate filter, increase the temperature of the particulate filter, and in response to the temperature of the particulate filter provided from the temperature sensor being greater than a temperature threshold and a time that a lambda of the oxygen sensor is biased rich is greater than a time threshold, introduce secondary air to a location downstream from the emissions control device and upstream from the particulate filter. 2. The system of claim 1, further comprising: an air pump; andthe controller being configured to introduce secondary air by operating the air pump to pump the secondary air to the location downstream from the emissions control device and upstream from the particulate filter. 3. The system of claim 1, further comprising: a turbocharger including a turbine; andthe controller being configured to introduce secondary air by directing secondary air from an outlet of a compressor to the location downstream from the emissions control device and upstream from the particulate filter. 4. The system of claim 1, further comprising: an exhaust gas recirculation passage in fluid communication with an inlet of the particulate filter; andthe controller being configured to introduce secondary air by directing the secondary air from the exhaust gas recirculation passage to the location downstream from the emissions control device and upstream from the particulate filter. 5. The system of claim 4, wherein the exhaust gas recirculation passage is a high pressure exhaust gas recirculation passage in fluid communication with an outlet of a compression device and the inlet of the particulate filter; and the controller being configured to introduce secondary air by directing the secondary air from the outlet of the compression device through the high pressure exhaust gas recirculation passage to the location downstream from the emissions control device and upstream from the particulate filter. 6. The system of claim 4, wherein the exhaust gas recirculation passage is a low pressure exhaust gas recirculation passage in fluid communication with an air intake of the engine and the inlet of the particulate filter; and the controller being configured to introduce secondary air by directing the secondary air from the air intake through the low pressure exhaust gas recirculation passage to the location downstream from the emissions control device and upstream from the particulate filter. 7. The system of claim 6, wherein the secondary air is directed through the low pressure exhaust gas recirculation passage via positive intake manifold air pressure. 8. The system of claim 1, wherein the controller is configured to stop introduction of the secondary air in response to the temperature of the particulate filter as provided by the temperature sensor being greater than the temperature threshold and the lambda of the oxygen sensor being greater than a lambda threshold. 9. The system of claim 1, wherein the controller is configured to stop introduction of secondary air in response to at least one of a time since particulate filter regeneration start being greater than a time threshold, a particulate filter inlet pressure being greater than a pressure threshold, and a soot level being greater than a soot reduction threshold. 10. The system of claim 1, wherein the controller is configured to increase the temperature of the particulate filter by retarding spark timing of the engine. 11. The system of claim 1, wherein the controller is configured to increase the temperature of the particulate filter by ramping up the temperature of the particulate filter at a rate of between 1 and 10 degrees Celsius per second. 12. A method for performing regeneration of a particulate filter of a spark ignition engine having an exhaust system that includes the particulate filter, an emissions control device positioned upstream from the particulate filter, a temperature sensor configured to provide a temperature of the particulate filter, and a downstream oxygen sensor positioned downstream from the particulate filter, the method comprising: during regeneration of the particulate filter, increasing the temperature of the particulate filter; in response to the temperature of the particulate filter being greater than a temperature threshold and a time that a lambda of the downstream oxygen sensor is biased rich is greater than a time threshold, introducing secondary air to a location downstream from the emissions control device and upstream from the particulate filter; andin response to the temperature of the particulate filter being greater than the temperature threshold and the time that the lambda of the downstream oxygen sensor is biased rich is not greater than the time threshold, setting a particulate filter degradation condition. 13. The method of claim 12, further comprising: in response to a time that the lambda of the downstream oxygen sensor is biased lean after secondary air is introduced to an inlet of the particulate filter being not greater than a second time threshold, set a particulate filter degradation condition. 14. The method of claim 12, wherein the exhaust system includes an upstream oxygen sensor positioned upstream from the emissions control device, the method further comprising: during regeneration of the particulate filter, maintaining air-fuel at an inlet of the emissions control device with air-fuel oscillating between lean and rich stoichiometry based on closed loop feedback from the upstream oxygen sensor. 15. The method of claim 12, wherein introducing secondary air to an inlet of the particulate filter includes at least one of operating an air pump, and directing secondary air through an exhaust gas regeneration passage to the inlet of the particulate filter. 16. A method for operating a spark-ignition engine having a three-way catalyst and a particulate filter downstream thereof, comprising: oscillating an exhaust air-fuel ratio entering the particulate filter to generate air-fuel ratio oscillations downstream of the particulate filter, while increasing exhaust temperature;when the downstream oscillations are sufficiently dissipated,enleaning the exhaust air-fuel ratio entering the particulate filter; andreducing the enleanment when an operating parameter is beyond a threshold amount. 17. The method of claim 16, wherein the operating parameter is a temperature of the particulate filter that rises above a temperature threshold. 18. The method of claim 17, further comprising terminating enleanment when sufficient exhaust gas temperature loss has occurred. 19. The method of claim 16, wherein the operating parameter is a particulate filter inlet pressure that stabilizes and then decreases below a pressure threshold. 20. The method of claim 16, wherein the operating parameter is elapsed time that exceeds a time threshold. 21. The method of claim 16, wherein sufficient dissipation of the downstream oscillations include when a downstream air-fuel ratio no longer switches between lean and rich even though an upstream air-fuel ratio continues to switch between lean and rich, and the enleanment includes introducing fresh air in between the three-way catalyst and the particulate filter.