NOx sensor 2310059 212708682 2008-05-15T22:24:32Z Rjwilmsi 203434 Typo/date fixing using [[Project:AutoWikiBrowser|AWB]] {{orphan|date=December 2007}} A '''NOx sensor''' is typically a high temperature device built to detect [[nitrogen oxide]]s in combustion environments such as an [[automobile]] or truck [[tailpipe]] or a [[smokestack]]. ==Availability== [[Siemens]] VDO / NGK are in production of a NOx sensor for automotive and truck applications. Several automobile and related companies such as [[Delphi (auto parts)|Delphi]], [[Ford]], [[Chrysler]], and [[Toyota]] have also put extensive research into development of NOx sensors. Many academic and government labs are pushing to develop the sensors as well. The term NOx actually represents several forms of nitrogen oxides such as NO ([[nitric oxide]]), NO<sub>2</sub> ([[nitrogen dioxide]]) and N<sub>2</sub>O ([[nitrous oxide]] aka laughing gas). In a [[gasoline]] engine NO is the most common form of NOx being around 93% while NO<sub>2</sub> is around 5% and the rest is N<sub>2</sub>O. There are other forms of NOx such as N<sub>2</sub>O<sub>4</sub> (the [[dimer]] of NO<sub>2</sub>) but it only exists at lower temperatures and N<sub>2</sub>O<sub>5</sub> for example. Owing to higher combustion temperatures, [[diesel engine]]s produce even greater quantities of NOx than do spark-ignition gasoline engines. ==Motivating factors== The drive to develop a NOx sensor is pushed by environmental factors. The NOx gases can cause various problems such as [[smog]] and [[acid rain]]. So many governments around the world have passed laws to limit their emissions (along with other combustion gases such as [[SOx]] (oxides of [[sulfur]]) , CO ([[carbon monoxide]]) and CO<sub>2</sub> ([[carbon dioxide]], [[CO2 sensor]]) and [[hydrocarbon]]s) Companies have realized that a way to minimize NOx is to first detect them and then employ some sort of feedback loop in the combustion process to minimize emissions by means such as combustion optimization or by the regeneration of NOx traps. ==Difficulties== ===Harsh environment=== Due to the high temperature of the combustion environment only certain types of material can operate ''[[in situ]]''. The majority of NOx sensors developed have been made out of [[ceramic]] type metal oxides with the most common being [[yttria]] stabilized [[zirconia]] (YSZ), which is currently used in the decades old [[oxygen sensor]]. The YSZ is compacted into a dense ceramic and actually conducts oxygen ions (O<sup>2-</sup>) at the high temperatures of a tailpipe such at 400 °C and above. To get a signal from the sensor a pair of high temperature electrodes such as noble metals ([[platinum]], [[gold]], or [[palladium]]) or other metal oxides are placed onto the surface and an electrical signal such as the change in voltage or current is measured as a function of NOx concentration. ===High sensitivity and durability required=== The levels of NO are around 100-2000 ppm ([[parts per million]]) and NO<sub>2</sub> 20-200 ppm in a range of 1-10% O<sub>2</sub>. The sensor has to be very sensitive to pick up these levels. The main problems that have limited the development of a successful NOx sensor (which are typical of many sensors) are: Selectivity, Sensitivity, Stability, Reproducibility, Response time, Limit of Detection and Cost. In addition due to the harsh environment of combustion the high gas flow rate can cool the sensor which alters the signal or it can delaminate the eletrodes over time and [[soot]] particles can degrade the materials. ==Conclusion== The NOx sensing element mentioned above is only a part of the whole device, which also include the packaging and electronics. The development of a very good NOx sensor is very highly desirable and has the potential to serve a large market thus there is a large push to make one work. It is often the most sought combustion gas sensor.CO2 and SO2 gas is also a main problem of Nox sensor. ==See also== *[[List of sensors]] ==Links== Prabir Dutta Research group at Ohio State University, USA, that develops combustion sensors, including NOx. A [http://www.chemistry.ohio-state.edu/~dutta/index_files/Sensors.html Research Summary] and [http://www.chemistry.ohio-state.edu/~dutta/index_files/SensorsReview.pdf Review Article]. [[Category:Engine sensors]] [[fr:Capteur NOx]]