Exhaust gas treatment system for controlling hydrocarbon adsorption/desorption in hydrocarbon trap

An exhaust gas treatment system, comprising:

• an internal combustion engine comprising an exhaust gas outlet;
• a first three way catalyst downstream of the exhaust gas outlet, wherein the first three way catalyst receives an exhaust output from the exhaust gas outlet;
• a hydrocarbon trap downstream of the first three way catalyst, wherein the hydrocarbon trap receives an exhaust output from the first three way catalyst;
• an exhaust heating unit downstream of the hydrocarbon trap, wherein the exhaust heating unit receives an exhaust output from the hydrocarbon trap;
• and
• a second three way catalyst downstream of the exhaust heating unit, wherein the second three way catalyst receives an exhaust output from the heating unit,
• wherein an air injection port is configured to selectively deliver a stream of air upstream of the hydrocarbon trap and downstream of the first three way catalyst, and
• a control unit configured to deliver the stream of air upstream of the hydrocarbon trap after the hydrocarbon trap stops absorbing hydrocarbons, before the hydrocarbon trap begins to desorb the hydrocarbons, and while the hydrocarbon trap desorbs the hydrocarbons.