Nitrogen oxide sensor

Nitrogen oxide sensor

A nitrogen oxide sensor or NOx sensor is typically a high temperature device built to detect nitrogen oxides in combustion environments such as an automobile or truck tailpipe or a smokestack.

Contents

Availability

Continental Automotive Systems/NGK are in production of a NOx sensor for automotive and truck applications. Several automobile and related companies such as 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), NO2 (nitrogen dioxide) and N2O (nitrous oxide aka laughing gas). In a gasoline engine NO is the most common form of NOx being around 93% while NO2 is around 5% and the rest is N2O. There are other forms of NOx such as N2O4 (the dimer of NO2), which only exists at lower temperatures, and N2O5, for example. However, owing to much higher combustion temperatures due to high cylinder compression and turbo or supercharging, diesel engines produce much higher engine-out NOx emissions than do spark-ignition gasoline engines, but the nonexistent NOx after-treatment causes diesel engines to emit significantly more NOx at the tailpipe compared to a typical gasoline engine with a 3-way catalyst. In addition, the diesel oxidation catalyst significantly increases the fraction of NO2 in "NOx" by oxidizing over 50% of NO using the excess oxygen in the diesel exhaust gases.

Motivating factors

The drive to develop a NOx sensor comes from environmental factors. NOx gases can cause various problems such as smog and acid rain. 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 CO2 (carbon dioxide) and hydrocarbons). Companies have realized that one way of minimizing NOx emissions is to first detect them and then employ some sort of feedback loop in the combustion process, minimizing NOx production by, for example, combustion optimization or 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 (O2-) 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 NO2 20-200 ppm in a range of 1-10% O2. 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 electrodes 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 includes the packaging and electronics. The development of a very good NOx sensor is highly desirable and has the potential to serve a large market. Thus there is a large push to produce a robust sensor that works reliably and accurately over a wide temperature range. It is currently one of the most sought after combustion gas sensors. Degradation by CO2 and SO2 gases, however, remains a major problem of NOx sensors.

See also

External links

Prabir Dutta Research group at Ohio State University, USA, that develops combustion sensors, including NOx. A Research Summary and


Wikimedia Foundation. 2010.

Игры ⚽ Нужно сделать НИР?

Look at other dictionaries:

  • Nitrogen oxide — Contents 1 NOx 2 Derivatives 3 See also 4 References …   Wikipedia

  • Nitrous oxide engine — This page discusses the use of nitrous oxide in a racing context. For other uses, see Nitrous oxide. Dragster in near lane is purging nitrous oxide Nitrous oxide (N2O) is a chemical compound used as an oxidizing agent to increase an internal… …   Wikipedia

  • Glossary of fuel cell terms — The Glossary of fuel cell terms lists the definitions of many terms used within the fuel cell industry. The terms in this glossary may be used by fuel cell industry associations, in education material and fuel cell codes and standards to name but …   Wikipedia

  • List of sensors — * Accelerometer * Touch sensor * Active pixel sensor * Air flow meter * Alarm sensor * Bedwetting alarm * Bhangmeter * Biochip * Biosensor * Breathalyzer * Capacitance probe * Carbon paste electrode * Carbon monoxide detector * Catadioptric… …   Wikipedia

  • Chimney — For other uses, see Chimney (disambiguation). Smokestack redirects here. For the 1963 avant garde jazz album, see Smokestack (album). The world s tallest chimney, of GRES 2 in Ekibastuz, Kazakhstan. A chimney is a structure for venting hot flue… …   Wikipedia

  • Exhaust system — Exhaust manifold (chrome plated) on a car engine …   Wikipedia

  • Catalytic converter — A catalytic converter (colloquially, cat or catcon ) is a device used to reduce the toxicity of emissions from an internal combustion engine. First widely introduced on series production automobiles in the US market for the 1975 model year to… …   Wikipedia

  • Airbag — An airbag is part of a vehicle s safety restraint system, a flexible envelope designed for rapid inflation in an automobile collision, to prevent vehicle occupants from striking hard interior objects such as steering wheels. It is considered a… …   Wikipedia

  • Titanium dioxide — Chembox new Name = Titanium dioxide ImageFile = Titanium(IV) oxide.jpg ImageSize = 200px ImageName = Titanium(IV) oxide ImageFile1 = Rutile unit cell 3D balls.png ImageSize1 = 200px ImageName1 = The unit cell of rutile IUPACName = Titanium… …   Wikipedia

  • Carbon monoxide — chembox Name = Carbon monoxide ImageFileL1 = Carbon monoxide 2D.svg ImageSizeL1 = 100px ImageNameL1 = Structure of the carbon monoxide molecule ImageFileR1 = Carbon monoxide 3D vdW.png ImageSizeR1 = 120px ImageNameR1 = Space filling model of the… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”