TITLE: System for Onboard Engine and Bleed Air Monitoring and Filtering
TECHNOLOGY AREA(S): Air
Platform, Human Systems
ACQUISITION PROGRAM: PMA-265
F/A-18 Hornet/Super Hornet
OBJECTIVE: Develop a
microelectromechanical system (MEMS) to detect and filter aircraft breathing
air contaminants in-flight.
DESCRIPTION: Knowledge gaps
exist about aeronautical health-compromising situations encountered by today’s
Navy airmen. Incidents have occurred in which Navy F/A-18 pilots experienced
symptoms such as shortness of breath, disorientation, confusion, and headache
with no clearly identified cause. The Navy seeks a system to improve cabin air
quality and remove bleed air contaminants encountered in the aircraft, which
could affect the health of pilots.
Aircraft such as the F/A-18 utilize engine bleed air filtered through an
onboard oxygen generating system to provide the oxygen supply for pilots. The
On-Board Oxygen Generating System (OBOGS) uses a molecular sieve to concentrate
oxygen in pressurized air from the turbine engine compressor on a schedule
associated with aircraft altitude in order to compensate for the decrease in
partial oxygen pressure and to protect the pilot against rapid decompression.
Investigations conducted by the Navy of in-flight, physiological incidents did
not identify volatile organic compound and organophosphate contaminants as a
root cause in any reported cases; however, a gap exists in the ability for real-time
monitoring and filtering of pre- and post-OBOGS-provided pilot air supply.
Development of a MEMS for use in flight will enable continuous assessment of
pilot air quality and will prove invaluable in the evaluation of OBOGS
efficiency and pilot health. Finally, real-time separation, detection and
filtering of volatile organic compounds, organophosphates, and other bleed air
contaminants in the pilot air supply would allow investigators to determine if
those specific contaminants contribute to pilot ill health incidents and, if
so, the source. That would enable engineers to eliminate or mitigate the
problem and ensure protection of the pilots and their full capability to
operate the aircraft.
Monitoring the OBOGS product air in-flight presents many technical challenges
not faced by ground-based air quality analysis. For example, the F/A-18
aircraft is extremely limited in terms of space and weight; any chip-scale
technology or MEMS sensor and filter packages must be minimal in terms of their
space footprint and weight. The MEMS sensor dimensions must be no greater than
height 2.6 inches, width 1.6 inches, depth 0.6 inches, and weigh less than one
pound. The MEMS sensor power must be no greater than one watt. The MEMS must
function in a high-oxygen, low-humidity environment that may experience rapid
altitude (pressure) changes as dictated by aircraft missions. Additionally, the
chip-scale gas sensors used in the MEMS would be for detection of volatile
organic compounds and organophosphates as well as broad screening of other
bleed air contaminants (i.e., complex mixtures of carbon monoxide (CO), carbon
dioxide (CO2), methanol (CH4O) and water (H2O)). The chip-scale gas sensors in
the MEMS should be able to monitor aerosol sizes ranging from 50 µm to 10 nm.
The chip-scale gas sensors MEMS must be able to detect volatile organic
compounds and organophosphates at thresholds below physiological relevance
levels at a sub-nano-gram detection at a sub-second response time. Design
considerations will also have to be made for a MEMS to be installed on an
F/A-18 aircraft. Such considerations include (1) performing non-obstructive
filtering in the pre- and post-OBOGS air stream, (2) not introducing potential
leaks in the pre- and post-OBOGS air supply, (3) minimizing electrical power
and acoustic noise generation, and (4) containing all required electronics and
algorithms necessary for signal processing, chemical identification and
quantitation, display, and data logging. Candidate MEMS should provide high
efficiency and long-lived (100 flight hours) filter or absorbent removal
capacity able to capture 99.7% of all particles larger than 25 nanometers (nm).
ISO 29463, high-efficiency filters and filter media for removing particles in
air, Parts 1, 2, 3, 4, and 5 will be used as the evaluation criteria.
Successful MEMS must sense and filter or absorb aerosols and vapors from
organic compounds and organophosphates in aircraft engine lubricants, Mobil Jet
Oil II, Castrol 5000 Jet Engine Oil, Exxon Turbo Oil 2380, Aeroshell Turbine
Oil 560, and BP Turbo Oil 274. The ability to post-process data to identify
contaminants not present in the pre-programmed library is desirable as well as
is the collection of samples onto media suitable for removal and analysis in a
laboratory setting for purposes of verification and unknown compound
General OBOGS operating conditions to consider are as follows: (1) Bleed air
flow into the OBOGS is approximately 1 pound-mass per minute with measurements
taken each minute of flight time; (2) OBOGS oxygen pressures supplied from the
OBOGS unit to the pilot’s breathing regulator ranges from 8 to 60 PSIG (pounds
per square inch gauge). Pressures downstream of the pilot’s breathing regulator
are approximately atmospheric pressure; (3) Oxygen flow from the OBOGS to the
pilot(s) ranges from 8 to 200 liters/minute at atmospheric pressure; (4)
Atmospheric pressure ranges from sea level to 50,000 ft.; and (5) The operating
temperature of the OBOGS for this application can range from -40 °F to +160 °F
(objective) and 0 °F to +160 °F (threshold).
PHASE I: Develop a concept
for chip-scale nanoengineered semiconducting material prototypes with the
capability to detect and filter volatile organic compounds, organophosphates,
and other aircraft breathing air contaminants. Test key modules of a MEMS to
detect volatile organic compounds, organophosphates, and other aircraft
breathing air contaminants in flight and then filter and remove these
contaminants and destructively adsorb organophosphate chemicals such as xylenyl
dicresyl phosphate and trixylenyl phosphate, simulate and analytically model
device behavior, develop interface and control electronics, and develop novel
techniques for aerosol sampling and filtering with minimal pressure drop.
Produce plans to develop a prototype(s) in Phase II.
PHASE II: Demonstrate
end-to-end implementation of the sampling, sensing, and electronics necessary
for real-time, air quality sensing and filtering in a form factor compatible
with in-flight F/A-18 testing developed in Phase I. The developed MEMS sensor
and filtering package will not be required to be self-powered, but should be
capable of sustaining operation in flight conditions on-board an F/A-18
aircraft (i.e., high-G, variable pressure, high-vibration environment) [Ref 9].
Interface, power, and form factor specifications will be provided. ISO 29463,
High-efficiency filters and filter media for removing particles in air, Parts
1, 2, 3, 4, and 5 will be used as the evaluation criteria.
Successful completion of Phase II will require: (1) ground test demonstrations
with experimental engine operating temperature range 200 °C to 600 °C ±2 °C for
real time measurement to quantify composition of critical constituents in
turbine engine exhaust products, including xylenyl dicresyl phosphate and
trixylenyl phosphate. A list of specific target compounds and chemical classes
will be provided; and (2) demonstration that this offered system prototype can
filter and remove the ultrafine (<0.5 µm) particulates and selectively
remove or absorb volatile organic compounds, organophosphates, and other
contaminants in pre or post OBOGS air stream. The technical approach will also
involve regeneration of filters using a low-energy process.
PHASE III DUAL USE
APPLICATIONS: Produce the components for incorporation in the F/A-18 aircraft
or into F/A-18 aircraft OBOGS.
The developed MEMS could supplement, extend, or improve on existing air quality
products to comply with regulatory requirements, or could make it possible for
non-regulated parties (e.g., nonprofit organizations, small businesses, members
of the public) to monitor and filter their air quality environments. Examples
include: indoor air quality (IAQ) monitoring and remediation, industrial
pollution containment and elimination, narcotics detection, cargo monitoring,
explosives detection, Heating Ventilation Air Conditioning (HVAC), cleanroom
air filters, automotive cabin air, and specialty gas-phase filtration.
1. Centers, P.W. “Potential
neurotoxin formation in thermally degraded synthetic ester turbine lubricants.”
Archives of Toxicology, 1992, 66(9), pp. 679-680. https://www.ncbi.nlm.nih.gov/pubmed/1482292
2. Liyasova, M., Li, B., et
al. “Exposure to tri-o-cresyl phosphate detected in jet airplane passengers.”
Toxicology and Applied Pharmacology, 2011, 256(3), pp. 337-347. https://www.ncbi.nlm.nih.gov/pubmed/21723309
3. Megson, D., Ortiz, X., et
al. “A comparison of fresh and used aircraft oil for the identification of
toxic substances linked to aerotoxic syndrome.” Chemosphere, 2016, 158, pp.
4. Michaelis, S.
“Contaminated aircraft cabin air.” Journal of Biological Physics and Chemistry,
2011, Vol. 11, pp. 132-145. http://www.itcoba.net/24MI11A.pdf
5. Neer, A., Andress, J.R.,
Haney, R.L., and Mathison, L.C. “Preliminary investigation into thermal
degradation behavior of mobil jet oil II.” 41st International Conference on
Environmental Systems, 2011, Portland, Oregon, pp. 17-21. DOI:
6. Overfelt, R.A., Jones, B.W.,
Loo, et al. “Sensors and prognostics to mitigate bleed air contamination
events.” Airliner Cabin Environmental Research, Report No.
7. Ramsden, J.J. “Jet engine
oil consumption as a surrogate for measuring chemical contamination in aircraft
cabin air.” Journal of Biological Physics and Chemistry, Vol. 13 (2013), pp.
8. Winder, C. and Balouet,
J.C. “The toxicity of commercial jet oils.” Environmental Research, 2002,
89(2), pp. 146-164. https://www.ncbi.nlm.nih.gov/pubmed/12123648
9. MIL-PRF-27210H. (2009)
“Performance Specification: Oxygen, Aviator’s Breathing, Liquid and Gas”. http://everyspec.com/MIL-PRF/MIL-PRF-010000-29999/MIL-PRF-27210H_32996/
Contamination; Gas Sensors; Oil; Microelectromechanical Systems; Air; Filters
Chandraika (John) Sugrim
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