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Using a MISiC-FET sensor for detecting NH3 in SCR systems
Linköping University, Department of Physics, Chemistry and Biology, Applied Physics . Linköping University, The Institute of Technology.
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2005 (English)In: IEEE Sensors Journal, ISSN 1530-437X, E-ISSN 1558-1748, Vol. 5, no 5, 1099-1105 p.Article in journal (Refereed) Published
Abstract [en]

One way to decrease the emitted levels of NOx from diesel engines is to add NH3 in the form of urea to the exhausts after combustion. NH3 will react with NOx in the catalytic converter to form N2 and water, which is called selective catalytic reduction (SCR). The amount of NH3 added may be regulated through closed-loop control by using an NH3 sensor. The metal-insulator silicon-carbide field-effect transistor (MISiC-FET) sensor has previously been tested for this application and has been shown to be sensitive to NH3. Here, the sensors have been further studied in engine SCR systems. Tests on the cross sensitivity to N2O and NO2, and studies concerning the influence of water vapor have been performed in the laboratory. The difference between Ir and Pt films, with regard to catalytic activity, has also been investigated. The sensors were found to be sensitive to NH3 in diesel engine exhausts. The addition of urea was computer controlled, which made it possible to add NH3 in a stair-like fashion to the system and detect it with the MISiC-FET sensors. The presence of water vapor was shown to have the largest effect on the sensors at low levels and the NH3 response was slightly decreased by a background level of NO2.

Place, publisher, year, edition, pages
2005. Vol. 5, no 5, 1099-1105 p.
Keyword [en]
Ammonia, field-effect transistor (FET) sensor, iridium, platinum, selective catalytic reduction (SCR)
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-13408DOI: 10.1109/JSEN.2005.854489OAI: oai:DiVA.org:liu-13408DiVA: diva2:20680
Available from: 2005-11-10 Created: 2005-11-10 Last updated: 2017-12-13
In thesis
1. Development of high temperature SiC based field effect sensors for internal combustion engine exhaust gas monitoring
Open this publication in new window or tab >>Development of high temperature SiC based field effect sensors for internal combustion engine exhaust gas monitoring
2003 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

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 NOx emissions and particulates, in the case when diesel is utilized, and emissions at cold start from gasoline engines. One way of treating the high NOx levels is to introduce ammonia in the diesel exhausts and let it react with the NOx to form nitrogen gas and water, which is called SCR (Selective Catalytic Reduction). However, in order to make this system reduce NOx efficiently enough for meeting future legislations, closed loop control is required. To realize this type of system an NOx 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.

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.

Place, publisher, year, edition, pages
Institutionen för fysik, kemi och biologi, 2003. 74 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1051
Keyword
field effect sensor, gas detection, selective catalytic reduction, lambda, cold start, ammonia, silicon carbide, engine exhaust.
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-4673 (URN)91-7373-767-4 (ISBN)
Presentation
2003-11-05, Hörsal Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Note
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.Available from: 2005-11-10 Created: 2005-11-10 Last updated: 2014-01-09
2. Studies of MISiC-FET sensors for car exhaust gas monitoring
Open this publication in new window or tab >>Studies of MISiC-FET sensors for car exhaust gas monitoring
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The increasing size of the car fleet makes it important to find ways of lowering the amounts of pollutants from each individual diesel or gasoline engine to almost zero levels. The pollutants from these engines predominantly originate from emissions at cold start, in the case when gasoline is utilized, and high NOx emissions and particulates from diesel engines.

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.

One way of treating the high NOx levels from diesel engines is to introduce ammonia in the exhausts and let it react with the NOx in a special catalytic converter to form nitrogen gas and water, which is called SCR (selective catalytic reduction). However, in order to make this system reduce NOx efficiently enough for meeting future legislations, closed loop control is required. To realize this type of system an NOx or ammonia sensor is needed.

This thesis presents the efforts made to test the SiC-based field effect sensor device both as a cold start lambda sensor for gasoline engines and as an NH3 sensor for SCR systems in diesel engines.

The MISiC (metal insulator silicon carbide) lambda sensor has proven to be both sensitive and selective to lambda, and its properties have been studied in lambda stairs both in gasoline engine exhausts and in the laboratory. There is, however, a small cross-sensitivity to CO. The influence of metal gate restructuring on the linearity of the sensor has also been investigated. The metal tends to form islands by time, which decreases the catalytic activity and thereby gives the sensor, which is binary when fresh, a linear behavior. Successful attempts to prevent the restructuring through depositing a protective layer of insulator on top of the metal were made. The influence of increasing the catalytic activity in the measurement cell was also studied. It was concluded that the location of the binary switch point of MISiC lambda sensors could be moved towards the stoichiometric value if the consumption of gases in the measurement cell was increased.

The MISiC NH3 sensor for SCR systems has been shown to be highly sensitive to ammonia both in laboratory and diesel engine measurements. The influence of other diesel exhaust gas components, such as NOx, water or N2O has been found to be low. In order to make the ammonia sensor more long-term stable experiments on samples with different types of co-sputtered Pt or Ir/SiO2 gas-sensitive layers were performed. These samples turned out to be sensitive to NH3 even though they were dense and NH3 detection normally requires porous films.

The speed of response for both sensor types has been found to be fast enough for closed loop control in each application.

Place, publisher, year, edition, pages
Institutionen för fysik, kemi och biologi, 2005
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 931
Series
Keyword
field effect sensor, gas detection, selective catalytic reduction, lambda, cold start, ammonia, silicon carbide, engine exhaust
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-4674 (URN)91-85297-61-5 (ISBN)
Public defence
2005-04-22, Hörsal Planck, Fysikhuset, Campus Valla, Linköpings univeristet, Linköping, 10:15 (English)
Opponent
Supervisors
Note
On the day of the ublic defence of the doctoral thesis, the status of article IV was: accepted, article V was: submitted and article VII was: manuscript.Available from: 2005-11-10 Created: 2005-11-10 Last updated: 2014-01-09

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Wingbrant, HelenaLöfdahl, MikaelLloyd Spetz, Anita

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