Sensors and Instrumentation and Nondestructive Evaluation

Ion-mobility Spectrometry Based NOx Sensor

Figure 1: Laboratory prototype of the ion-mobility spectrometry based NOx sensor
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Real-time measurement of NO_x content in the exhaust gas can provide the needed control parameter for the diesel-engine combustion management system. Such a NO_x sensor must be sensitive (ppm), fast response (ms), robust, and low cost. Furthermore, the NO_x sensor must be able to function under the environment of the exhaust gas recirculation line or the after-treatment catalyst stream. To date, available NO_x 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 NO_x 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.

Figure 2: Typical IMS peaks detected for different NO₂ concentrations
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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 NO_x 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:

1. sensitivity better than 5%,
2. response time less than 200 ms,
3. long-term stability,
4. detecting both NO and NO₂, and
5. able to function under wide ranges of temperature (38°C to 760°C) and flow rate (0 to 4 m/sec).

Energy System Applications
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Last Modified: Thu, April 21, 2016 5:01 AM