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 �m 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 identification.

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 �m) 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.

REFERENCES:

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. 116-123. https://www.ncbi.nlm.nih.gov/pubmed/27258902

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: 10.2514/6.2011-5110.

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. RITE-ACER-CoE-2012-05.� http://bleedfree.eu/wp-content/uploads/2015/10/bleedairreport.pdf

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. 114-118. http://www.oprus2001.co.uk/11RA13L.pdf

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//

KEYWORDS: Chemical Contamination; Gas Sensors; Oil; Microelectromechanical Systems; Air; Filters