<p>While the car fleet becomes increasingly larger it is important to lower the amounts of pollutants from each individual diesel or gasoline engine to almost zero levels. The pollutants from these engines predominantly originate from high NO<sub>x</sub> emissions and particulates, in the case when diesel is utilized, and emissions at cold start from gasoline engines. One way of treating the high NO<sub>x</sub> levels is to introduce ammonia in the diesel exhausts and let it react with the NO<sub>x</sub> to form nitrogen gas and water, which is called SCR (Selective Catalytic Reduction). However, in order to make this system reduce NO<sub>x</sub> efficiently enough for meeting future legislations, closed loop control is required. To realize this type of system an NO<sub>x</sub> or ammonia sensor is needed. The cold start emissions from gasoline vehicles are primarily due to a high light-off time for the catalytic converter. Another reason is the inability to quickly heat the sensor used for controlling the air-to-fuel ratio in the exhausts, also called the lambda value, which is required to be in a particular range for the catalytic converter to work properly. This problem may be solved utilizing another, more robust sensor for this purpose.</p><p>This thesis presents the efforts made to test the SiC-based field effect transistor (SiC-FET) sensor technology both as an ammonia sensor for SCR systems and as a cold start lambda sensor. The SiC-FET sensor has been shown to be highly sensitive to ammonia both in laboratory and engine measurements. As a lambda sensor it has proven to be both sensitive and selective, and its properties have been studied in lambda stairs both in engine exhausts and in the laboratory. The influence of metal gate restructuring on the linearity of the sensor has also been investigated. The speed of response for both sensor types has been found to be fast enough for closed loop control in each application.</p> / On the day of the public defence of the doctoral thesis, the status of article III was: in press. Report code: LiU-Tek-Lic-2003:50.
| Identifer | oai:union.ndltd.org:UPSALLA/oai:DiVA.org:liu-4673 |
| Date | January 2003 |
| Creators | Wingbrant, Helena |
| Publisher | Linköping University, Linköping University, Applied Physics, Institutionen för fysik, kemi och biologi |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Licentiate thesis, comprehensive summary, text |
| Relation | Linköping Studies in Science and Technology. Thesis, 0280-7971 ; 1051 |
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