Gas sensors that are low-power, light-weight, and rugged, while also
remaining low-cost, have considerable appeal to areas from automotive to
space flight. There are increasing demands for higher efficient
vehicles with lower emissions in order meet regulations that are meant
to mitigate or lessen the effects of climate change. An affordable, fast
response sensor that can measure transient carbon monoxide (CO) and
carbon dioxide (CO2) has broad application which can lead to more
efficient, fuel flexible engines and regulations of harmful emissions.
With compact, economical, low-power sensors that are able to continually
monitor gases that are characteristic of burning materials, a
distributed sensor array could be implemented on space vehicles that
would allow early detection of fires, gas leaks, or other critical
events. With careful selection of targeted gases, it may be possible to
identify the material that is burning or smoldering, better informing
the crew so that they may respond and prioritize high emergency events.
Further applications may include fuel/ hazardous gas leak detection on
space vehicles and atmospheric constituent sensor for portable life
support systems (PLSS) used by astronauts in extra vehicular activity
(EVA). Non-dispersive infrared NDIR gas sensors are attractive due to
their simplicity and low-cost; and by using light-emitting-diodes (LEDs)
in this approach, power efficient, lightweight, and stable gas sensors
can be developed to meet these needs.
This thesis discusses a sensor that was developed for simultaneous, time
resolved measurements of carbon monoxide (CO) and carbon dioxide (CO2).
This sensor utilizes low-cost and compact light emitting diodes (LEDs)
that emit in the 3-5μm wavelength range. Light emission of LEDs is
spectrally broader and more spatially divergent compared to that of
lasers, which presented many design challenges. Optical design studies
addressed some of the non-ideal characteristics of the LED emissions.
Measurements of CO and CO2 were conducted using their fundamental
absorption bands centered at 4.7μm and 4.3μm, respectively, while a
3.6μm reference LED was used to account for scattering losses (e.g., due
to soot, window deposits, etc.) common to the three measurement LEDs.
Instrument validation and calibration was performed using a laboratory
flow cell and bottled-gas mixtures. The sensor was able to detect CO2
and CO concentration changes as small as 30 ppm and 400 ppm,
respectively. Because of the many control and monitor species with
infra-red absorption features, which can be measured using the strategy
described, this work demonstrates proof of concept for a wider range of
fast (250Hz) and low cost sensors for gas measurement and process
monitoring.
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