An aqueous urea dosing system has a first tube through which the urea solution is conveyed to a small mixing chamber. Compressed air is continuously conveyed through an annular space between the outer surface of the first tube and the inner surface of a second tube which has a distal end that extends beyond a distal end of the first tube. The mixing chamber is positioned between the respective distal ends of the first and second tubes. The urea solution is discharged into the small mixing chamber, and subsequently immediately into an exhaust gas, in a series of discreet pulses, the width and period of which are controlled by a pulse-width-modulated flow control valve spaced from the exhaust gas.
Lee G. Dodge;Paul H. Kunkel