Method and systems are provided for operating an engine having a hydrocarbon retaining system coupled to an engine exhaust and an engine intake. During an engine cold start, routing exhaust gas to the hydrocarbon retaining system to store hydrocarbons in the hydrocarbon retaining system. Then, depen
Method and systems are provided for operating an engine having a hydrocarbon retaining system coupled to an engine exhaust and an engine intake. During an engine cold start, routing exhaust gas to the hydrocarbon retaining system to store hydrocarbons in the hydrocarbon retaining system. Then, depending on temperature, the hydrocarbons are purged with varying amounts of exhaust gas and fresh air in order to maintain proper temperature control.
대표청구항▼
1. An engine method, comprising: storing exhaust hydrocarbons by routing engine exhaust through a hydrocarbon trap assembly in a first direction through a first hydrocarbon trap and then a second hydrocarbon trap;storing fuel tank vapors in both a purging canister and the first and second hydrocarbo
1. An engine method, comprising: storing exhaust hydrocarbons by routing engine exhaust through a hydrocarbon trap assembly in a first direction through a first hydrocarbon trap and then a second hydrocarbon trap;storing fuel tank vapors in both a purging canister and the first and second hydrocarbon traps by routing the fuel tank vapors in the first direction; andpurging both the hydrocarbon traps and the canister to an engine intake with an adjustable mixture of exhaust gas and fresh air routed through the hydrocarbon traps opposite the first direction, wherein the first hydrocarbon trap has a larger porosity than the second hydrocarbon trap, and wherein the adjustable mixture has a composition that brings a temperature of the adjustable purging mixture entering the hydrocarbon traps below a threshold that is based on each of oxygen content of the exhaust gas, adsorbent used in the hydrocarbon traps and canister housing used in the hydrocarbon trap assembly. 2. The method of claim 1 wherein the second hydrocarbon trap is downstream of the first hydrocarbon trap in a direction of exhaust flow during storing operation, and wherein the first hydrocarbon trap is downstream of the second hydrocarbon trap in a direction of exhaust flow during purging operation. 3. A method comprising: storing exhaust hydrocarbons by routing engine exhaust through each of a first upstream trap and a second downstream trap of a hydrocarbon trap assembly in a first direction, the first trap having a larger porosity than the second trap;retaining fuel tank vapors in both a purging canister and the hydrocarbon trap assembly by routing the fuel tank vapors in the first direction; andpurging both the hydrocarbon trap assembly and the canister to an engine intake with a purging gas mixture having an adjustable composition of exhaust gas and fresh air adjusted responsive to temperature so as to bring the temperature of the purging gas mixture entering the hydrocarbon trap assembly below a threshold, the threshold based on a combination of adsorbent and canister housing used in the hydrocarbon trap assembly and further based on an oxygen content of the exhaust gas, the exhaust gas and fresh air mixed before entering the hydrocarbon trap assembly, the mixture routed in an opposite direction through the second trap followed by the first trap. 4. The method of claim 3 wherein the temperature is a temperature of exhaust gas downstream of the second trap. 5. The method of claim 4 wherein adjusting the composition of the purging gas mixture responsive to temperature includes, as the temperature increases beyond the threshold, increasing an amount of fresh air in the purging gas mixture. 6. A method for operating an engine having a hydrocarbon trap assembly coupled to an engine exhaust and an engine intake, comprising: during an engine cold start, routing exhaust gas and fuel tank vapors in a first direction through a first, upstream trap and then a second, downstream trap of the hydrocarbon trap assembly to store hydrocarbons, the first trap having a larger porosity than the second trap;during a first purging condition where the exhaust gas is at a first, lower temperature, purging stored hydrocarbons from the hydrocarbon trap assembly to the engine intake with at least exhaust gas routed through the second trap and then the first trap in a second direction opposite to the first direction; andduring a second purging condition where the exhaust gas is at a second, higher temperature, mixing the exhaust gas with an amount of fresh air to form a purging gas mixture that enters the hydrocarbon trap assembly, and purging the stored hydrocarbons from the hydrocarbon trap assembly to the engine intake with said purging gas mixture routed in the second direction. 7. The method of claim 6 wherein the amount of fresh air is adjusted based on the second temperature of the exhaust gas to bring a temperature of the purging gas mixture entering the hydrocarbon trap assembly below a threshold, and where an engine intake manifold vacuum draws in the purging gas mixture. 8. The method of claim 7 wherein the amount of fresh air is adjusted within a range. 9. The method of claim 7 wherein adjusting the amount of fresh air based on the second temperature of the exhaust gas includes, as the second temperature of the exhaust gas increases beyond a threshold, increasing the amount of fresh air in the purging gas mixture. 10. The method of claim 9 further comprising, adjusting the threshold responsive to a hydrocarbon load of the hydrocarbon retaining system. 11. The method of claim 9 further comprising, adjusting the threshold responsive to an air/fuel ratio of the exhaust gas. 12. The method of claim 11 wherein adjusting the threshold responsive to the air/fuel ratio of the exhaust gas includes, as an oxygen content of the exhaust gas increases, reducing the threshold. 13. The method of claim 6 wherein the first and second hydrocarbon traps include zeolite. 14. The method of claim 6, wherein the hydrocarbon trap assembly has a plastic housing. 15. The method of claim 6 further comprising, during the hydrocarbon storing, detecting degradation of the hydrocarbon trap assembly in response to a temperature of exhaust gas being below a predetermined threshold. 16. The method of claim 15 wherein the temperature of exhaust gas includes a temperature gradient of the exhaust gas.
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