| 摘要 |
PURPOSE:To use aq. urea with the concn. variable as a reducing agent by successively measuring the urea concn. in aq. urea to be added to an exhaust gas, calculating the requisite amt. of aq. urea to be added based on the measured value and controlling the actual amt. of aq. urea to be added. CONSTITUTION:Aqueous urea is added to the exhaust gas from an internal-combustion engine 1 as a reducing agent and brought into contact with a catalyst to reduce the nitrogen oxides in the exhaust gas. In this case, the urea concn. in the aq. urea to be added is continuously and successively measured by a urea concn. meter 13. The requisite amt. of aq. urea equivalent to the requisite amt. of urea to be added is calculated by a computing element 9 based on the measured value. The opening degree of an aq. urea flow control valve 12 is corrected based on the calculated value, and the aq. urea equivalent to the requisite amt. of aq. urea to be added is added to an exhaust gas duct 2. Consequently, aq. urea with the concn. variable is used as a reducing agent without using a constant-concn. aq. urea prepared with a constant-concn. continuous dissolver, and the amt. of aq. urea to be added to the exhaust gas is accurately controlled. |
