Linda S. Ellis
High-Speed Aircraft Research Combustor Tests Exceed Goal
Cleveland, OH -- NASA-industry research experiments to reduce exhaust emissions to environmentally compatible levels for future
supersonic airliners have yielded results that substantially exceed program goals.
The tests, which used an engine fuel combustion chamber sector, representing about one-fifth of a full-scale design, beat NASA's goal of generating no more than 5 grams of oxides of nitrogen (NOx) per kilogram of fuel burned at supersonic flight speed.
Scientific studies suggest that a fleet of future supersonic airliners, equipped with these ultra-low NOx engine combustors, possibly would have relatively small effects on stratospheric ozone.
"Protecting Earth's stratospheric ozone layer is our highest priority," said Louis J. Williams, Director of the High-Speed Research Program at NASA Headquarters, Washington, D.C., "so developing the technology to assure environmental compatibility for future supersonic airliners is the most important goal of our program."
"The results of these initial ultra-low emissions combustor tests make us more confident that we'll achieve that goal," Williams added.
The combustor sector evaluated was a "Lean Premixed Prevaporized" concept designed by GE Aircraft Engines, Evendale, Ohio.
It mixes fuel and air upstream of the burning zone and allows enough time for the liquid fuel to vaporize completely before combustion.
The fuel-air mixture then enters the combustion system and ignites downstream of a flame stabilizer where the speed of the mixture flow is somewhat slower.
"The ultra-low levels of nitrogen oxide we've achieved in these tests are extremely encouraging. It shows that the ultra-low levels we
previously saw in the laboratory can transition to combustor hardware," said Richard W. Niedzwiecki, Chief of the Combustion Technology Branch, Propulsion Systems Division at NASA's Lewis Research Center, Cleveland.
NASA also is testing a "Rich Burn-Quick Quench-Lean Burn" concept developed by Pratt & Whitney Division of United Technologies, East
Hartford, Conn. This design uses two combustion stages to reduce NOx production.
First, excess fuel is put into a small amount of air. This "rich burn" environment causes chemical reactions that minimize NOx emissions. As the mix flows through the combustor, more air is added and combustion is completed in a final fuel-lean burning stage. Experimental work with this concept has been started.
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