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APEX: Measuring Emissions So That Future Aircraft Fly Cleaner
Photo of NASA's DC-8 aircraft in flight. NASA has been studying various types of emissions from commercial aircraft to develop ways to reduce emissions and protect the environment. In recent years, fine particle emissions from aircraft have been identified as possible contributors to global climate changes and to lowering local air quality.

Image right: NASA's DC-8 is a flying science laboratory. It was used this year in the successful APEX tests of particulate emissions from commercial aircraft.
Credit: NASA

These emissions are produced when a hydrocarbon fuel (such as modern jet fuel, which is primarily kerosene) does not burn completely. Incomplete combustion often occurs at the lower power settings used for aircraft descent, idling and taxiing. This produces fine carbon particles, or soot, as well as particles of nonvolatile organic compounds. In addition, engine erosion and small amounts of metal impurities in jet fuel can be emitted in engine exhaust. Another type of particle emission is formed when exhaust cools, converting volatile aerosols of sulfur compounds and organic compounds to small solid particles.

These types of emissions are not addressed by current international regulations, which focus on visible smoke; but the international community is concerned about the effects that these emissions may have and is identifying possible regulations. In addition, reducing all types of aircraft emissions is necessary for the U.S aircraft industry to remain competitive in the global market.

Recently, the NASA Glenn Research Center took part in the very successful Aircraft Particle Emissions Experiment (APEX). NASA's DC-8 was used with CFM-56 engines to improve our understanding of particle emissions from commercial aircraft engines. It was the first and most extensive set of data obtained about gaseous and particulate emissions from an in-service commercial engine. Many different instruments were used, and a tremendous amount of data was obtained.

APEX project manager Dr. Chowen Wey and team membersImage left: APEX Project Manager Dr. Chowen Wey of Glenn's Vehicle Systems Project Office (woman in the center with the light hat) discusses the day's test plans with APEX team members. The assembly and probe stand used to measure the emissions are shown in the far left of the photograph. Credit: NASA

NASA ran tests to investigate the effects of thrust and fuel type. The team used different engine operating settings to vary thrust, and three different fuels were used: a typical jet fuel, a fuel with high sulfur content, and a fuel with high aromatic compound content. In addition, the Environmental Protection Agency ran tests to simulate landing-takeoff cycles to study the emissions that would be created at an airport.

It was the first time that so many different groups had worked together to study so many different aspects of the emissions from commercial aircraft engines. The research team included members from the NASA Glenn Research Center, Cleveland; NASA Langley Research Center, Hampton, Va.; NASA Dryden Flight Research Center, Edwards, Calif.; General Electric Aircraft Engines, Evendale, Ohio; The Boeing Company, Seattle, Wash.; Southwest Research Institute, San Antonio, Texas; Arnold Engineering Development Center, Arnold AFB, Tenn.; University of Missouri, Rolla, Mo.; Aerodyne Research, Inc., Billerica, Mass.; EPA, Research Triangle Park, N.C.; Wright Patterson Air Force Base, Dayton, Ohio; University of California, Riverside, Calif.; and Process Metrics, Inc., San Ramon, Calif.

The researchers met this November to discuss the results and determine the next steps for this research.

NASA Glenn Research Center