Exhaust gas purification system for a lean burn engine

An exhaust gas purification system for an engine equipped with a turbocharger and an exhaust pipe having a catalyst therein, the system comprising:

• an engine control unit;
• a reservoir for storing pressurized air received from the turbocharger;
• a valve in fluid communication with the reservoir and responsive to a valve control signal for delivering a quantity of pressurized air from the reservoir;
• a reductant injector in fluid communication with a reductant supply and responsive to an injection signal for atomizing and injecting a quantity of reductant;
• and
• a mixing chamber in fluid communication with the valve and connected to the reductant injector, the mixing chamber including an elongated conduit in fluid communication with the exhaust pipe for introducing a quantity of air and reductant mixture from the mixing chamber into the exhaust gas flow upstream of the catalyst;
• the engine control unit including logic adapted to output the valve control signal and reductant injection signal to achieve a desired level of catalyst efficiency.

In an exhaust gas purification system for an engine equipped with a turbocharger and an exhaust pipe having a catalyst therein, the system comprising a reservoir for storing pressurized air received from the turbocharger, a valve in fluid communication with the reservoir and responsive to a valve control signal, a reductant injector in fluid communication with a reductant supply and responsive to an injection signal, a mixing chamber in fluid communication with the valve and connected to the reductant injector, the mixing chamber in fluid communication with the exhaust pipe, a differential pressure transducer positioned between the mixing chamber and the exhaust pipe, and an upstream and downstream temperature sensor located upstream and downstream, respectively, of the catalyst, a method for increasing the efficiency of the catalyst comprising the steps of:

• determining a quantity of air to introduce into the mixing chamber from the reservoir;
• determining a quantity of reductant to be injected into the mixing chamber;
• outputting the valve control signal to activate the valve to deliver the desired quantity of pressurized air from the reservoir to the mixing chamber;
• and
• outputting the injection signal to activate the reductant injector to deliver the desired quantity of reductant to the mixing chamber,
• the quantity of air being such that the pressure within the mixing chamber is greater than pressure within the exhaust pipe upstream of the catalyst such that the air/reductant mixture is introduced into the exhaust pipe upstream of the catalyst to achieve a desired level of catalyst efficiency.