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 lower local air quality.

These emissions are produced when a hydrocarbon fuel (such as jet-A, which is primarily kerosene) does not burn completely. Incomplete combustion–which often occurs at the lower power settings used for descent, idle and taxi–produces soot and 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.

While current international regulations, which focus on visible smoke, do not address these types of emissions, the international community is concerned about the environmental effects these emissions may have and is considering enacting regulations. Additionally, manufacturers that fail to reduce all types of aircraft emissions might not remain competitive in the global market.

Recently, the NASA Glenn Research Center in Cleveland took part in the Aircraft Particle Emissions Experiment (APEX). As part of these tests, researchers fitted NASA’s DC-8 with CFM56 engines to better understand the effects 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 wealth of data was obtained.

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: jet-A, a fuel with high sulfur content and a fuel with high aromatic compound content. In addition, the Environmental Protection Agency (EPA) 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 NASA Glenn; NASA Langley; NASA Dryden; General Electric Aircraft Engines; Boeing; Southwest Research Institute; Arnold Engineering Development Center; University of Missouri; Aerodyne Research; the EPA; Wright Patterson AFB; University of California; and Process Metrics.

According to NASA, the researchers met late last year to discuss the results and determine the next steps for this research project.