Exhaust-gas purification apparatus and method for purifying exhaust gas

Abstract

A NOx catalyst is provided in an exhaust passage of an internal combustion engine for selectively purifying NOx in exhaust gas with a reducing agent. A charging unit charges the reducing agent at an upstream of the NOx catalyst. A pressurizing unit supplies the reducing agent to the charging unit. An obtaining unit detects or estimates catalyst temperature of the NOx catalyst or temperature information, which is correlated with the catalyst temperature. A particle size control unit changes reducing-agent pressure of reducing agent, which is pressurized by the pressurizing unit and supplied to the charging unit, to control an atomized particle size of the reducing agent, which is atomized from the charging unit and charged into exhaust gas, based on the catalyst temperature or the temperature information.

1 . An exhaust-gas purification apparatus for an exhaust-gas-purification system for an internal combustion engine, the system including a NOx catalyst, which is provided in an exhaust passage of the internal combustion engine for selectively purifying NOx in exhaust gas with a reducing agent, charging means, which is for charging the reducing agent into exhaust gas at an upstream of the NOx catalyst, and pressurizing means, which is for pressurizing the reducing agent and supplying the reducing agent to the charging means, the exhaust-gas purification apparatus comprising:
 obtaining means for detecting or estimating catalyst temperature of the NOx catalyst or temperature information, which is correlated with the catalyst temperature; and   particle size control means for changing reducing-agent pressure of reducing agent, which is pressurized by the pressurizing means and supplied to the charging means, to control an atomized particle size of the reducing agent, which is atomized from the charging means and charged into exhaust gas, based on the catalyst temperature or the temperature information.   
   
   
       2 . The exhaust-gas purification apparatus according to  claim 1 , wherein the particle size control means controls the pressurizing means to increase the reducing-agent pressure when the catalyst temperature is in a low-temperature range. 
   
   
       3 . The exhaust-gas purification apparatus according to  claim 2 ,
 wherein the particle size control means is configured to control a particle diameter of the reducing agent at a large size and a small size, and   the low-temperature range is less than a temperature threshold, at which a purification rate of the NOx catalyst is saturated when the particle size control means controls the particle diameter at the large size.   
   
   
       4 . The exhaust-gas purification apparatus according to  claim 1 , wherein the particle size control means is configured to decrease the atomized particle size in an start operation of the internal combustion engine and configured to increase the atomized particle size after elapsing a predetermined period subsequent to the start operation. 
   
   
       5 . The exhaust-gas purification apparatus according to  claim 4 , further comprising:
 heating means for heating the reducing agent charged by the charging means,   wherein the particle size control means is configured to control the heating means to heat the reducing agent to change the atomized particle size, in addition to pressurization of the reducing agent by the pressurizing means.   
   
   
       6 . The exhaust-gas purification apparatus according to  claim 1 , further comprising:
 means for detecting the reducing-agent pressure; and   means for manipulating at least one of a cycle, at which the charging means charges the reducing agent, and a charge time of urea water for each injection, based on the detected reducing-agent pressure.   
   
   
       7 . A method for purifying exhaust gas of an internal combustion engine, the method comprising:
 detecting or estimating catalyst temperature of a NOx catalyst, which is provided in an exhaust passage of the internal combustion engine for selectively purifying NOx in exhaust gas with a reducing agent, or temperature information, which is correlated with the catalyst temperature; and   manipulating reducing-agent pressure of reducing agent, which is charged into exhaust gas at an upstream of the NOx catalyst, to control an atomized particle size of the reducing agent based on the catalyst temperature or the temperature information.   
   
   
       8 . The method according to  claim 7 ,
 wherein the manipulating further includes:   increasing the reducing-agent pressure when the catalyst temperature is in a low-temperature range.   
   
   
       9 . The method according to  claim 8 ,
 wherein the manipulating further includes:   controlling a particle diameter of the reducing agent at a large size and a small size,   wherein the low-temperature range is less than a temperature threshold, at which a purification rate of the NOx catalyst is saturated when the particle diameter is controlled at the large size.   
   
   
       10 . The method according to  claim 7   wherein the manipulating further includes:   decreasing the atomized particle size in an start operation of the internal combustion engine; and   increasing the atomized particle size after elapsing a predetermined period subsequent to the start operation.   
   
   
       11 . The method according to  claim 10 , further comprising:
 heating the reducing agent to change the atomized particle size, in addition to pressurization of the reducing agent by the pressurizing means.   
   
   
       12 . The method according to  claim 7 , further comprising:
 detecting the reducing-agent pressure; and   manipulating at least one of a cycle, at which the charging means charges the reducing agent, and a charge time of urea water for each injection, based on the detected reducing-agent pressure.