The Decomposition Pipe is a device for dosing DEF to exhaust air and mixing the dosed DEF therewith. Normally a DEF injector is installed on a decomposition pipe for providing atomized DEF, and a mixer is positioned downstream for creating a more uniformed flow. In our decomposition pipe, in addition to the injector and mixer, a mass-flow sensor, a pressure sensor, and a temperature sensor are further included. These sensors provide most information in DEF dosing control, thereby the SCR control system can be less dependent to engine control, since engine control information, such as engine speed, and fueling rate, are no longer required. This SCR control system is especially useful in applications of diesel engines with mechanical fuel systems, in which engine-out NOx level can also be estimated with the sensing information obtained from these sensors. In applications of electrically controlled engines, the sensing information can be further used for diagnosing engine system problems.
The Mass-flow Sensor in the decomposition pipe is realized with a Venturi structure in which pressure sensors and a temperature sensor are used for measuring a pressure drop and exhaust air density, through which exhaust mass flow rate is calculated. In addition to exhaust mass flow rate, air pressure upstream and downstream from the decomposition can also be obtained with the mass-flow sensor.