Sensors and Instrumentation and Nondestructive Evaluation
Ion-mobility Spectrometry Based NOx Sensor
Real-time measurement of NOx content in the exhaust gas can provide the needed control parameter for the diesel-engine combustion management system. Such a NOx sensor must be sensitive (ppm), fast response (ms), robust, and low cost. Furthermore, the NOx sensor must be able to function under the environment of the exhaust gas recirculation line or the after-treatment catalyst stream. To date, available NOx sensors are mostly solid-state electrochemical sensors such as Yttria-stabilized zirconia (YSZ) sensors. Poor accuracy, slow response (in minutes), cross sensitivity, and aging problems are the main shortcomings of the YSZ sensors. Argonne has recently developed a practical fast-response NOx sensor based on ion-mobility spectrometry (IMS) technique. The sensor uses a corona/spark-discharge ionization source replacing the conventional radioactive ion source. The sensor is expected to function in a hostile exhaust-line environment with long-term stability and at low cost.
This development project is a collaborative effort between Argonne and Cummins, Inc. under a CRADA agreement. Argonne will be responsible for sensor development, testing, and integration of control electronics. Cummins will establish a field test facility and conduct field evaluation of the sensor performance. The first year effort will focus on development and testing of a modified laboratory prototype that addresses the remaining technical barriers. Figure 1 shows the laboratory prototype. At present, the sensor measures negative NO2 ion intensity to estimate the total NOx concentration. Figure 2 shows the typical IMS peaks detected for different NO2 concentrations. To determine the go/no-go decision, the sensor must satisfy the following:
- sensitivity better than 5%,
- response time less than 200 ms,
- long-term stability,
- detecting both NO and NO2, and
- able to function under wide ranges of temperature (38°C to 760°C) and flow rate (0 to 4 m/sec).
Last Modified: Fri, February 15, 2013 5:13 PM