Hydrocarbon retaining and purging system
Methods and systems are provided for operating an engine having a hydrocarbon retaining system and an emission control device coupled to an engine exhaust, the engine exhaust comprising a venturi. One example method comprises, during a storing condition, routing exhaust gas through the venturi without generating a venturi action, and then to the hydrocarbon retaining system, while bypassing the emission control device, to store hydrocarbons in the hydrocarbon retaining system, and during a purging condition, routing exhaust gas through the venturi while generating venturi action, then to the emission control device, and then to the hydrocarbon retaining system, to purge stored hydrocarbons, wherein a flow of purged hydrocarbons is drawn back to the venturi via venturi action.
1. A method for operating an engine having a hydrocarbon retaining system and an emission control device coupled to an engine exhaust, the engine exhaust comprising a venturi, the method comprising:
during a storing condition, routing exhaust gas through the venturi without generating a venturi action, and then to the hydrocarbon retaining system, while bypassing the emission control device, to store hydrocarbons in the hydrocarbon retaining system, the hydrocarbon retaining system including a first HC-trap and a second HC-trap with different pore sizes; and
during a purging condition, routing exhaust gas through the venturi while generating venturi action, then to the emission control device, and then to the hydrocarbon retaining system, to purge stored hydrocarbons, wherein a flow of purged hydrocarbons is drawn back to the venturi via venturi action.
2. The method of claim 1 wherein the venturi is positioned at a junction between an exhaust conduit and a bypass conduit of the engine exhaust, the hydrocarbon retaining system positioned in the bypass conduit.
3. The method of claim 2 wherein the venturi includes at least a first, second, and third opening, the first opening located at a broad inlet region of the venturi, the second opening located at a broad outlet region of the venturi, and the third opening located at a narrow region of the venturi.
4. The method of claim 3 wherein routing exhaust gas through the venturi without generating venturi action includes restricting flow through the second opening and flowing exhaust gas from the first opening to the third opening.
5. The method of claim 3 wherein routing exhaust gas through the venturi while generating venturi action includes enabling flow through the second opening and flowing exhaust gas from the second opening to the third opening.
6. The method of claim 3 wherein routing exhaust gas through the venturi without generating venturi action includes restricting flow through the third opening and flowing exhaust gas from the first opening to the second opening.
7. The method of claim 3 wherein routing exhaust gas through the venturi while generating venturi action includes un-restricting flow through the third opening and flowing exhaust gas from the first opening to the third opening via the second opening.
8. The method of claim 2 wherein the flow of purged hydrocarbons directed towards the venturi is adjusted with a valve.
9. The method of claim 1 wherein the flow of purged hydrocarbons is adjusted responsive to a hydrocarbon load of the hydrocarbon retaining system.
10. The method of claim 1 wherein the flow of purged hydrocarbons is adjusted responsive to an air-fuel ratio of the exhaust.
11. The method of claim 1 wherein the first and second HC-traps include zeolites of differing porosity.
12. A system for a vehicle including an engine having an exhaust, the system comprising:
a venturi coupled in the engine exhaust;
a hydrocarbon retaining system coupled to the engine exhaust with a first and second HC-trap having different pore sizes; and
a controller configured to,
route exhaust gas to the hydrocarbon retaining system through a first path in the venturi to store hydrocarbons in the hydrocarbon retaining system during a storing condition;
route exhaust gas to the hydrocarbon retaining system through a second path in the venturi to purge stored hydrocarbons during a purging condition, wherein a flow of purged hydrocarbons is directed back towards the venturi via a reduced pressure generated in the venturi by venturi action.
13. The system of claim 12 wherein the controller is further configured to, during the purging condition, adjust a combustion air-fuel ratio responsive to an operating condition of the hydrocarbon retaining system.
14. The system of claim 13 wherein the operating condition of the hydrocarbon retaining system includes a HC load of the hydrocarbon retaining system, and wherein adjusting a combustion air-fuel ratio responsive to an operating condition of the hydrocarbon retaining system includes, adjusting the combustion air-fuel ratio to be more lean when the HC load is higher and adjusting the combustion air-fuel ratio to be less lean when the HC load is lower.
15. An engine method, comprising:
routing engine exhaust gas through a venturi without generating a venturi action, and then to an HC-trap with mesopore and micropore zeolites, while bypassing a three-way catalyst, to store hydrocarbons in the HC-trap; and
routing exhaust gas through the venturi while generating venturi action, then to the three-way catalyst, and then to the HC-trap, purging stored hydrocarbons from the HC-trap and drawing them back to the venturi via venturi action.