Response Characteristics of a Stable Mixed Potential Ammonia Sensor in Simulated Diesel Exhaust

Abstract

A mixed potential sensor using Au and Pt dense wire electrodes embedded between tape-casted layers of 8 mol% yttria stabilized zirconia (YSZ) was tested for application toward NH3, NO, NO2, C3H6 and C3H8. In single-gas testing, the sensor exhibited the highest response toward NH3, while still exhibiting reasonably high sensitivity toward other interferent gases. The sensor was tested in a high-flow reactor at the National Transportation Research Center (NTRC) in order to simulate exhaust gas constituents and flow rates produced by lean-burn vehicles powered by Compression-Ignition Direct-Injection (CIDI), diesel engines. The sensor was characterized at 525 and 625°C for NH3, CO, C3H6, C3H8, and NOx in a base gas composition of 10% O2, 5% H2O, and 5% CO2 flowing at 15 slpm. The sensor exhibited fast response time equal to the response time of the system's switching valve (T90<0.6s). Moreover, in simulations of overdosing a selective catalytic reduction (SCR) system, the sensor was able to selectively respond to 20ppm injections of NH3 slip despite the presence of the interferent gas species at combined concentrations ten times higher than that of the NH3. The laboratory sensor construct was transitioned to a pre-commercial, automotive stick sensor configuration that was demonstrated to retain the advantageous characteristics of the tape-cast device.