Apparatus and method for regenerating NOx catalyst for diesel engine

Apparatus comprising:

• a diesel engine;
• an exhaust pipe connected to said diesel engine for passage of exhaust gas from said diesel engine through said exhaust pipe;
• a NOX catalyst device, positioned in said exhaust pipe, said NOX catalyst device containing a NOX catalyst which has a performance for reducing NOX in exhaust gas passing through said exhaust pipe, which performance is lowered by said NOX catalyst absorbing SOx from said exhaust gas;
• a reductant fuel adding nozzle, associated with said exhaust pipe for adding a reductant fuel into said exhaust pipe at a location upstream of said NOX catalyst;
• a flow rate control valve, for controlling a feed rate of the reductant fuel to said reductant fuel adding nozzle;
• a NOX catalyst temperature sensor, disposed in said exhaust pipe for providing a temperature signal representative of a temperature of said NOX catalyst;
• a hydrocarbon concentration sensor disposed at a downstream side of said NOX catalyst to provide a hydrocarbon concentration signal representing a hydrocarbon concentration in the exhaust gas at the downstream side of said NOX catalyst;
• and
• a regeneration control unit;
• wherein, when said temperature signal indicates that the temperature of said NOX catalyst is higher than a predetermined value and said hydrocarbon concentration signal indicates that the hydrocarbon concentration at the downstream side of said NOX catalyst is greater than a predetermined amount, said regeneration control unit determines that said NOX catalyst is deteriorating and outputs an instruction to said flow rate control valve to supply a quantity of reductant fuel which is larger than a predetermined quantity which is suitable for a current operational condition of said diesel engine, to thereby regenerate said NOX catalyst.

A method for regenerating a NOX catalyst in a NOX catalyst device for a diesel engine, which device contains a NOX catalyst which has a performance for reducing NOX in exhaust gas passing through an exhaust pipe of said diesel engine when a reductant fuel is added to said exhaust pipe upstream of said NOX catalyst, which performance is lowered by said NOX catalyst absorbing SOx from said exhaust gas, said method comprising the steps of:

• determining if a temperature of said NOX catalyst is higher than a predetermined temperature value;
• determining if a hydrocarbon concentration in exhaust gas downstream of said NOX catalyst is greater than a predetermined concentration value;
• and
• when said temperature of said NOX catalyst is higher than said predetermined temperature value and said hydrocarbon concentration is greater than said predetermined concentration value, determining that the NOX catalyst is deteriorating, and regenerating the NOX catalyst, which has been determined to be deteriorating by adding a quantity of the reductant fuel which is larger than a predetermined quantity which is suitable for a current operational condition of said diesel engine.