Aviation Research Tutorial Page 4c

Aviation Research

Tutorial

4.c. Environment

The second major environmental challenge is aircraft emissions. Aircraft engines emit nitrogen oxides. This negatively affects the local air quality. Nitrogen oxide produces smog and other pollutants. Like noise, aircraft engine emissions are already causing communities to limit airport use. For example, in Europe airports are adjusting landing fees to control these emissions. These fees ensure that airlines do not overexpose the air surrounding the airport to their toxic emissions through too many arrivals and departures in a short period of time.

Aircraft engine emissions affect atmospheric changes in the following 3 ways:

· From the engine's burning of fossil fuels, aircraft produce about 3% of all global carbon dioxide emissions per year. (The altitude chamber test at right is characterizing the chemical composition of exhaust from a full-scale turbofan engine.)

Nitrogen oxide emission at altitude · At high altitudes (25,000 - 50,000), other aircraft engine combustion products have more potent effects. Nitrogen oxides affect the production of ozone.

Contrail and cirrus formation · Also at high altitudes, the emissions of aerosols and particulate matter influence the radiative nature of the atmosphere which result in increased cirrus clouds and more persistent contrails.

Global nitrogen oxides NASA has established goals to reduce aircraft engine emissions of nitrogen oxides. In 10 years these emissions will be reduced by a factor of 3 and in 25 years by a factor of 5. So far NASA has achieved success in lowering emissions using advanced materials that are lighter, yet stronger than current materials used with engines. Because they can also withstand greater engine temperatures these new materials are capable of increased emissions filtration. NASA will continue its research to reduce noise and engine emissions to meet its goals.

NASA Research
The Zero CO₂ Research Project is focused on radically reducing polluting emissions from subsonic aircraft engines. Currently all subsonic commercial aircraft use hydrocarbon fuels as their energy source. These fuels result in the emission of large amounts of CO₂ and water vapor, and to a lesser degree oxides of nitrogen and unburned hydrocarbons. All of these emissions, with the possible exception of water vapor, are emerging as threats to the long-term health of the planet. Under the Zero CO₂ project, a recent feasibility study was performed on fuel cell powered light aircraft. Fuel cells offer higher energy efficiency with no harmful emissions when compared to existing piston and turbine engines. A fuel cell uses hydrogen and oxygen as the source of energy. Results from this initial analysis show that a fuel cell-powered aircraft could fly a demonstration flight with current state-of-the-art components. The all-electric aircraft was shown capable of a 140-mile flight carrying 270 lbs (pilot and payload). "The results are quite encouraging for the future of electric flight", said Bruce Bream, Zero CO₂ project manager. "Advanced fuel cell technologies currently under development will only increase both range and payload capability." NASA pioneered the practical development of fuel cells to provide electrical power for the Gemini and Apollo spacecraft. The design was further refined for use on the Space Shuttle.