Exhaust gas purification apparatus of engine and exhaust gas purification method of engine

Abstract

A control unit calculates an amount of produced ammonia from an amount of a dosed urea aqueous solution according to an engine operation state, and calculates a NOx purification ratio in the case of dosing the amount of the dosed urea aqueous solution according to the operation state to exhaust gas on an exhaust upstream side of an SCR catalyst. Moreover, the control unit estimates an amount of adsorbed ammonia to the SCR catalyst based on the produced ammonia amount and the NOx purification ratio. Then, the control unit subtracts the amount of the urea aqueous solution corresponding to the amount of the adsorbed ammonia from the amount of the dosed urea aqueous solution according to the operation state to correct the amount of the dosed urea aqueous solution, and controls the dosing of the urea aqueous solution based on the corrected amount of the dosed urea aqueous solution.

1 . An exhaust gas purification apparatus of an engine, comprising:
 a selective reduction catalyst disposed in an exhaust pipe of the engine to selectively reduce a nitrogen oxide by use of ammonia produced from an urea aqueous solution;   a dosing unit which doses the urea aqueous solution to exhaust gas on an exhaust upstream side of the selective reduction catalyst; and   a control unit having a built-in computer,   wherein the control unit calculates an amount of the produced ammonia from an amount of the dosed urea aqueous solution in accordance with an engine operation state,   calculates a purification ratio of the nitrogen oxide by the selective reduction catalyst on the basis of a first nitrogen oxide concentration in the exhaust gas discharged from the engine and a second nitrogen oxide concentration in the exhaust gas passed through the selective reduction catalyst,   performs calculation to estimate an amount of the ammonia to be adsorbed to the selective reduction catalyst on the basis of the amount of the produced ammonia and the purification ratio of the nitrogen oxide,   corrects the amount of the urea aqueous solution to be dosed in accordance with the engine operation state on the basis of the amount of the adsorbed ammonia, and   controls an operation of the dosing unit on the basis of the corrected amount of the urea aqueous solution to be dosed.   
     
     
         2 . The exhaust gas purification apparatus of the engine according to  claim 1 , wherein the control unit subtracts an amount of the adsorbed urea aqueous solution corresponding to the amount of the adsorbed ammonia from the amount of the urea aqueous solution to be dosed in accordance with the engine operation state, to correct the amount of the urea aqueous solution to be dosed in accordance with the engine operation state. 
     
     
         3 . The exhaust gas purification apparatus of the engine according to  claim 1 , wherein the control unit further corrects the amount of the adsorbed ammonia on the basis of an ammonia concentration in the exhaust gas passed through the selective reduction catalyst. 
     
     
         4 . The exhaust gas purification apparatus of the engine according to  claim 1 , wherein the amount of the urea aqueous solution to be dosed in accordance with the engine operation state is calculated from an exhaust temperature, a rotation speed and a load of the engine. 
     
     
         5 . An exhaust gas purification apparatus of an engine comprising:
 a selective reduction catalyst disposed in an exhaust pipe of the engine to selectively reduce a nitrogen oxide by use of ammonia produced from an urea aqueous solution;   a dosing unit which doses the urea aqueous solution to exhaust gas on an exhaust upstream side of the selective reduction catalyst; and   a control unit having a built-in computer,   wherein the control unit calculates a purification ratio of the nitrogen oxide by the selective reduction catalyst on the basis of a first nitrogen oxide concentration in the exhaust gas discharged from the engine and a second nitrogen oxide concentration in the exhaust gas passed through the selective reduction catalyst,   perform calculation to estimate an amount of the adsorbed urea aqueous solution corresponding to the ammonia to be adsorbed to the selective reduction catalyst on the basis of an amount of the urea aqueous solution to be dosed in accordance with an engine operation state and the purification ratio of the nitrogen oxide,   corrects the amount of the urea aqueous solution to be dosed in accordance with the engine operation state on the basis of the amount of the adsorbed urea aqueous solution, and   controls an operation of the dosing unit on the basis of the corrected amount of the urea aqueous solution to be dosed.   
     
     
         6 . The exhaust gas purification apparatus of the engine according to  claim 5 , wherein the control unit subtracts the amount of the adsorbed urea aqueous solution from the amount of the urea aqueous solution to be dosed in accordance with the engine operation state, to correct the amount of the urea aqueous solution to be dosed in accordance with the engine operation state. 
     
     
         7 . The exhaust gas purification apparatus of the engine according to  claim 5 , wherein the control unit further corrects the amount of the adsorbed urea aqueous solution on the basis of an ammonia concentration in the exhaust gas passed through the selective reduction catalyst. 
     
     
         8 . The exhaust gas purification apparatus of the engine according to  claim 5 , wherein the amount of the urea aqueous solution to be dosed in accordance with the engine operation state is calculated based on an exhaust temperature, a rotation speed and a load of the engine. 
     
     
         9 . An exhaust gas purification apparatus of an engine which corrects an amount of an urea aqueous solution to be dosed in accordance with an engine operation state on the basis of a purification ratio of a nitrogen oxide by a selective reduction catalyst, and doses the corrected amount of the urea aqueous solution to be dosed to exhaust gas on an exhaust upstream side of the selective reduction catalyst. 
     
     
         10 . An exhaust gas purification method of an engine, in which a control unit having a built-in computer corrects an amount of an urea aqueous solution to be dosed in accordance with an engine operation state on the basis of a purification ratio of a nitrogen oxide by a selective reduction catalyst, and doses the corrected amount of the urea aqueous solution to be dosed to exhaust gas on an exhaust upstream side of the selective reduction catalyst.