Selective Catalytic Reduction (SCR) is a technology hitherto predominantly used for trucks. Though it is considered effective, it is also expensive and not overly user friendly for passenger cars. The solution requires a small additional tank in the vehicle that contains an aqueous urea solution, typically referred to as AdBlue. This solution is injected into the exhaust pipe and reacts with the harmful NOx exhaust gases. As a result of the chemical reaction, the NOx is transformed into non-toxic nitrogen and water.
The technique requires accurate control of the urea solution injected, which in turn requires sensors. Continental has developed an urea sensor capable of measuring the concentration of the solution as well as the filling level in the tank and the temperature of the liquid. The data provided by the sensor are fed into the control unit that injects the correct amount of urea, depending on the operation parameters of the engine. In addition, the data are used for the on-board diagnosis of the exhaust aftertreatment. The sensor also monitors the filling level in the AdBlue tank to alert the driver as soon as a refill is needed.
The sensor makes use of piezo elements, an NTC thermometer and a proprietary ASIC from Continental that is already in used to determine the oil level in the engine. It operates with ultrasound signals to measure the urea percentage in the water as well as the filling level. Therefore, the sensor can used in the tank as well as in the dosing unit, facilitating the OEM’s logistics.
Against the background of future Euro 6c legislation that will put tighter limits to diesel exhausts, Continental expects increased demand for SCR systems and thus the sensors. A question if the Volkswagen diesel scandal had an effect on the SCR business remained unanswered.