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Embodiments for controlling fuel vapors are disclosed. In one example, a method comprises during a purge of a fuel vapor canister, adjusting a heater of the fuel vapor canister based on a rate of a purge flow exiting the fuel vapor canister and a concentration of hydrocarbons released from the fuel

Embodiments for controlling fuel vapors are disclosed. In one example, a method comprises during a purge of a fuel vapor canister, adjusting a heater of the fuel vapor canister based on a rate of a purge flow exiting the fuel vapor canister and a concentration of hydrocarbons released from the fuel vapor canister. In this way, a fuel vapor canister purge efficiency may be increased.

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1. A method comprising: responsive to a fuel vapor load on a fuel vapor canister exceeding a threshold load, initiating a purge of the fuel vapor canister; andduring the purge of the fuel vapor canister, adjusting a heater of the fuel vapor canister based on a rate of a purge flow exiting the fuel v

1. A method comprising: responsive to a fuel vapor load on a fuel vapor canister exceeding a threshold load, initiating a purge of the fuel vapor canister; andduring the purge of the fuel vapor canister, adjusting a heater of the fuel vapor canister based on a rate of a purge flow exiting the fuel vapor canister and a concentration of hydrocarbons in the purge flow, including: delaying activation of the heater until the concentration of hydrocarbons in the purge flow increases to a first threshold level; andactivating the heater responsive to onset of an endothermic reaction in the fuel vapor canister as detected by the concentration of hydrocarbons increasing to the first threshold level. 2. The method of claim 1, wherein the first threshold level includes a peak concentration of hydrocarbons, and wherein the first threshold level is different from the threshold load. 3. The method of claim 1, wherein adjusting the heater comprises deactivating the heater when the concentration of hydrocarbons in the purge flow reaches a second threshold level. 4. The method of claim 3, wherein the first threshold level is higher than the second threshold level, and further comprising, continuing to purge fuel vapor after the heater is deactivated. 5. The method of claim 3, further comprising determining the concentration of hydrocarbons in the purge flow based on output from an oxygen sensor coupled between the fuel vapor canister and an engine. 6. The method of claim 3, further comprising determining the concentration of hydrocarbons in the purge flow based on one or more of a temperature of the purge flow and a temperature of the fuel vapor canister. 7. The method of claim 1, wherein initiating the purge comprises initiating the purge by opening a canister purge valve to draw fresh air through the fuel vapor canister and route the hydrocarbons to an engine for combustion, the hydrocarbons desorbed by the fresh air. 8. The method of claim 1, wherein the heater is a first heater, and further comprising adjusting a second heater based on the rate of the purge flow exiting the fuel vapor canister and the concentration of hydrocarbons in the purge flow, wherein the first heater is positioned near a vent port coupling the fuel vapor canister to atmosphere, wherein the second heater is positioned near a purge port coupling the fuel vapor canister to an engine, and wherein adjusting the first heater and the second heater comprises activating the first heater prior to activating the second heater. 9. The method of claim 1, further comprising initiating the purge responsive to a temperature of the fuel vapor canister at a vent port of the fuel vapor canister increasing to a peak temperature and then subsequently decreasing in temperature. 10. The method of claim 1, wherein adjusting the heater based on the rate of purge flow comprises adjusting the heater to maintain the fuel vapor canister at a desired temperature based on the purge flow rate. 11. A vehicle system, comprising: an engine configured to receive fuel from a fuel tank for combustion;a fuel vapor canister configured to trap hydrocarbons in fuel vapor from the fuel tank;a purge line coupling the fuel vapor canister to the engine, the purge line including a canister purge valve and a sensor;a heater positioned in the fuel vapor canister; anda controller storing instructions for: opening the canister purge valve to initiate a purge of hydrocarbons from the fuel vapor canister to the engine;after the purge is initiated, purging the hydrocarbons with the heater deactivated until a concentration of hydrocarbons in the purge line has increased to a peak concentration of hydrocarbons; andactivating the heater once output from the sensor indicates the concentration of hydrocarbons in the purge line has increased to the peak concentration of hydrocarbons. 12. The system of claim 11, wherein the controller stores further instructions for initiating the purge responsive to a temperature of the fuel vapor canister at a vent port of the fuel vapor canister increasing to a peak temperature and then subsequently decreasing in temperature. 13. The system of claim 12, wherein the temperature of the fuel vapor canister at the vent port is determined based on output from a temperature sensor positioned in a vent line fluidly coupled to the vent port, the vent port coupling the fuel vapor canister to atmosphere, and wherein the controller stores further instructions for deactivating the heater once output from the sensor indicates the concentration of hydrocarbons in the purge line has reached a lower threshold level. 14. The system of claim 13, wherein the sensor is one or more of a hydrocarbon sensor or a temperature sensor, and wherein the controller stores further instructions for continuing to purge hydrocarbons from the fuel vapor canister to the engine after the deactivation of the heater. 15. A method, comprising: responsive to a load on a fuel vapor canister exceeding a threshold load, opening a canister purge valve to purge stored hydrocarbons from the fuel vapor canister to an engine without activating a heater; andafter the purge is initiated, activating the heater of the fuel vapor canister once a concentration of hydrocarbons in a purge flow increases to an upper threshold level. 16. The method of claim 15, wherein opening the canister purge valve further comprises purging the stored hydrocarbons while maintaining the heater in a deactivated state until the concentration of hydrocarbons in the purge flow increases to the upper threshold level, and further comprising, once the heater is activated, adjusting the heater to maintain a temperature of the fuel vapor canister at a designated temperature, the designated temperature based on one or more of a purge flow rate, the concentration of hydrocarbons, and a hydrocarbon load of the fuel vapor canister. 17. The method of claim 16, further comprising deactivating the heater once the concentration of hydrocarbons in the purge flow reaches a lower threshold level while continuing to purge the stored hydrocarbons. 18. The method of claim 15, further comprising, when the load on the fuel vapor canister does not exceed the threshold load, maintaining the canister purge valve closed and routing fuel vapors from a fuel tank to the fuel vapor canister. 19. The method of claim 15, wherein the heater is a first heater, and further comprising activating a second heater once the concentration of hydrocarbons in the purge flow reaches the upper threshold level.