Patent ID: 8069649

Claim:
An exhaust emission purifying apparatus for engine comprising: a reducing agent tank that stores a liquid reducing agent or its precursor; a reduction catalytic converter that reductively purifies nitrogen oxides in exhaust emission by using the liquid reducing agent or its precursor in the reducing agent tank; a level measuring device that measures a level of the liquid reducing agent or its precursor in the reducing agent tank; a concentration measuring device that measure a concentration of the liquid reducing agent or its precursor based on temperature rise characteristics of a heating element obtained by operating the heating element disposed in the reducing agent tank for a predetermined time; and a control unit incorporating therein a computer, wherein the control unit executes: a different type discriminating process of discriminating that the liquid reducing agent or its precursor is any different type of aqueous solution which does not function as a reducing agent when the concentration measured by the concentration measuring device is lower than a predetermined threshold; an adequacy judging process of judging, based on a temperature of the heating element and a temperature change rate thereof, and also, the concentration measured by the concentration measuring device, whether or not the different type discrimination is adequate, when it is discriminated in the different type discriminating process that the liquid reducing agent or its precursor is the different type of aqueous solution; a first counting process of counting up the number of different type discriminating times based on a predetermined counted value when it is judged in the adequacy judging process that the different type discrimination is adequate; a first different type discrimination determining process of determining the different type discrimination, when the number of different type discriminating times counted in the first counting process is equal to or larger than the first predetermined number of times; and a first setting process of dynamically setting at least one of the predetermined counted value and the first predetermined number of times based on the level measured by the level measuring device.