Sensing Exhaust NO2 Emissions Using the Mixed Potential Principle 2014-01-1487

NO_x aftertreatment is an essential subsystem to enable diesel and lean gasoline engines to meet emissions regulations. A selective catalytic reduction (SCR) system, which uses urea to create ammonia (NH₃) for NO_x reduction, is one popular form of NO_x aftertreatment system. These urea based NO_x aftertreatment systems can benefit from closed-loop control when appropriate NH₃, NO_x, or NO₂ exhaust gas sensors are available. For example, knowing exhaust NO₂ emissions after a diesel oxidation catalyst can help the urea dosing strategy to maximize the efficiency of a urea SCR system. Such sensing capability, combined with ammonia sensing, can provide enhanced closed-loop control of the SCR system as well as information for on-board diagnosis.

This paper covers Delphi's progress in developing an exhaust NO₂ sensor. Sensor data from a synthetic gas bench and from engine testing is presented for four NO₂ sensors, along with investigations into the sensor's sensitivity to a variety of relevant factors such as oxygen concentration, humidity, and operating temperature. Data regarding the sensor's cross-sensitivity to NO and NH₃ are also presented, in both gas bench and engine conditions.