Emissions control system for increasing selective catalytic reduction efficiency

An emissions control system for a compression ignition engine capable of producing an exhaust gas stream to be treated by a reduction agent which is mixed with the exhaust gas stream to convert the exhaust gas stream prior to being directed into an SCR catalyst capable of reducing NOx emissions in the exhaust gas stream, the system comprising:

• a sensor for determining the temperature of the exhaust gas stream prior to being mixed with the reduction agent;
• an exhaust gas recirculation valve associated with the compression ignition engine for directing the exhaust gas stream back into the compression ignition engine;
• a bypass valve associated with the exhaust gas stream and positioned prior to an input of the SCR catalyst, the bypass valve being operated to selectively provide the exhaust gas stream to the input of the SCR catalyst and to bypass the SCR catalyst
• an electronic control unit connected to the temperature sensor, the exhaust gas recirculation valve, and the bypass valve for determining whether the temperature of the exhaust gas stream is at a predetermined temperature and if so for controlling operation of the exhaust gas recirculation valve to allow a portion of the exhaust gas stream to be directed to the bypass valve and for controlling operation of the bypass valve to either direct the exhaust gas stream which reaches the bypass valve selectively and alternatively into the SCR catalyst and to bypass the SCR catalyst;
• and
• wherein the electronic control unit is capable of determining whether the temperature of the exhaust gas stream is below the predetermined temperature and if so for controlling operation of the valve to direct all of the exhaust gas stream to bypass the SCR catalyst.

An emissions control system for a compression ignition engine capable of producing an exhaust gas stream to be treated by a reduction agent which is mixed with the exhaust gas stream to convert the exhaust gas stream prior to being directed into an SCR catalyst capable of reducing NOx emissions in the exhaust gas stream, the system comprising:

• a sensor for determining the temperature of the exhaust gas stream prior to being mixed with the reduction agent;
• an exhaust gas recirculation valve associated with the compression ignition engine for directing the exhaust gas stream back into the compression ignition engine;
• a bypass valve associated with the exhaust gas stream and positioned prior to an input of the SCR catalyst, the bypass valve being operated to selectively provide the exhaust gas stream to the input of the SCR catalyst and to bypass the SCR catalyst
• an electronic control unit connected to the temperature sensor, the exhaust gas recirculation valve, and the bypass valve for determining whether the temperature of the exhaust gas stream is at a predetermined temperature and if so for controlling operation of the exhaust gas recirculation valve to allow a portion of the exhaust gas stream to be directed to the bypass valve and for controlling operation of the bypass valve to either direct the exhaust gas stream which reaches the bypass valve selectively and alternatively into the SCR catalyst and to bypass the SCR catalyst;
• and
• wherein the electronic control unit is capable of determining whether the temperature of the exhaust gas stream is above the predetermined temperature to control operation of the exhaust gas recirculation valve to allow all of the exhaust gas stream to be directed to the bypass valve and to control operation of the bypass valve to allow the exhaust gas stream to be directed into the SCR catalyst.