Microsensors for Automotive Emissions Applications
Monitoring vehicle emissions is critical to efficient vehicle operation and imperative for environmental protection. Measuring gaseous compounds, such as carbon monoxide, carbon dioxide, hydrocarbons, and nitrogen oxides, in the hot, hostile environments in automotive exhaust systems is nearly impossible for current commercial sensors. Such sensors can be expensive and have limited versatility and sensitivity. In addition, they may not be portable, requiring sample collection and transportation. Novel, rugged cermet (ceramic-metallic) microsensors are being developed at Argonne that have the potential to overcome many of these limitations.
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| Later generation single, array, and high-temperature array prototype microsensors |
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| Commercially made voltammetric microsensors and stereolithography (SLA) enclosure |
An Integrated Technology
Argonne's microsensor program integrates materials, measurement, and computation technologies to develop devices that can serve as the core for electronic noses. The program has developed a suite of solid-state sensors tailored to (1) detect, discriminate, and quantify individual gases and (2) identify and classify families of gases that contain similar voltammetric response features. Advanced chemometrics algorithms process the voltammetry signatures. These algorithms are compact enough to execute on inexpensive microcontroller chips.
The low-power sensors operate in near real time and function over a wide range of ambient temperatures and humidity levels. The voltammetric devices have been developed for specific sponsor needs, but the technology is flexible and can characterize a growing number of chemicals.
Voltammetric Microsensor-Detectable Gases and Vapors
| oxygen (>100 ppm) |
carbon monoxide
(>10 ppm) |
carbon dioxide (>0.25%) |
nitric oxide (>1 ppm) |
| methane (>0.1%) |
propane (>1 ppm) |
chlorine (>10 ppm) |
m-xylene (<900 ppm) |
| butane (>1000 ppm) |
xylene (>5 ppm) |
toluene (>10 ppm) |
acetone (>2500 ppm) |
| ethanol (>10 ppm) |
methanol (>10 ppm) |
isopropanol (<33 ppm) |
dichloroethane (vapor test) |
| methylene chloride (>100 ppm) |
hydrogen sulfide (>10 ppm) |
ammonia (<100 ppm) |
chloroethylethylsulfide (<100 ppm)* |
| acrolein (<1 ppm) |
1,3-butadiene
(24 ppm) |
formaldehyde (>10 ppm) |
di-isopentylsulfide(<100 ppm)* |
| acetaldehyde (<1 ppm) |
benzene (>1 ppm) |
cyanogen chloride (<10 mg/m3)* |
hydrogen cyanide*
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The numbers in parentheses represent the lowest concentration tested, not the lowest detection limit. Most gases can be detected from their lower limit to saturation.
* Diesel emissions testing. |
Transportation Applications
The voltammetric microsensors have been used for detecting specific components of diesel exhaust, including the U.S. Environmental Protection Agency Urban Air Toxics benzene, acetaldehyde, acrolein, and 1,3-butadiene in exhaust. Other constituents analyzed include ammonia, carbon monoxide, carbon dioxide, and oxygen. Various hydrocarbons also react uniquely over a different range of applied potentials and can easily be distinguished from each other and other compounds.
Voltammograms of various concentrations of benzene in diesel exhaust. Six runs of each concentration are represented. Standard deviations are also plotted to show that concentrations are statistically distinct. |
Argonne's cermet sensors are unique in that they are able to detect ranges of gases from low parts per million levels to percent levels. The chemometrics algorithms translate these voltammograms directly into concentration values with engineering units for recording and control systems.
Argonne's transportation research facilities allow in-house testing of diesel engines under controlled conditions. The microsensor program works with these facilities to conduct sensor evaluation tests.
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Voltammetric response to ammonia showing quantity information. |
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| Voltammetric response to various hydrocarbons demonstrating multi-gas response capability. |
Argonne has developed patents and collaborations with both industry and military sponsors for diesel emissions monitoring. General Atomics Corporation and the U.S. Navy have both funded the technology for emissions detection.
August 17, 2004
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