Stringent U.S. Environmental Protection Agency (EPA) regulations for engine emissions dictate the need to reduce emissions from gas turbine engines currently used for military aircraft and for land- and marine-based generators.
The Air Force Research Laboratory is working with General Electric to develop an optimized trapped vortex (TV) design for use in advanced gas turbine engines. A 40 percent increase in operating range and a 57 percent reduction in lean blow out are expected. The environmental objective is to reduce nitrogen oxides (NOx), volatile organic compounds (VOC), carbon monoxide and particulate emissions to 60 percent of EPA’s regulatory levels proposed in 1996. The emissions reduction levels for aircraft and shipboard operations will be evaluated in high-pressure sector rig tests performed at the Air Force Research Laboratory.
Four TV sectors were designed and fabricated. The TV innovation departs from the conventional swirl-stabilized design used in gas turbine engines for the past 40 years. The three components in the overall TV design are (1) an integrated fuel injector/diffuser; (2) a TV combustor; and (3) a thermal management system. A pilot combustor consisting of cavities sized to trap a vortex provides stability. This allows operation at higher flow-through velocities and reduced pressure drop. The approach to reducing NOx emissions is to redistribute the airflow so that more air is participating in the combustion process. Computational fluid dynamics were applied to experimental sector rigs to investigate different TV configurations under realistically sized conditions.
The research team successfully demonstrated that a TV combustor could reduce emissions of both NOx and VOCs by about 50 to 60 percent for aircraft and ship turbines, respectively, compared to current technology systems. Over 250 hours of total hot test time was accumulated on the 12-inch sector. This included over 50 hours at pressures greater than 200 psi and inlet temperatures greater than 400°C. The tests showed NOx emissions to be as good as or better than current production, low-emission technology combustors. As an added bonus, operational characteristics improved dramatically. This project was completed in FY00 and has since successfully transitioned to the Integrated High Performance Turbine Engine Technology Program and the Environmental Security Technology Certification Program.
There will be a significant emissions reduction, which is related directly to the amount of fuel consumed by a gas turbine engine. VOC emissions at some Department of Defense bases could decrease by as much as 90 percent, and NOx could decrease by 20 to 40 percent if all military aircraft were to adopt this technology. The potential benefit would be even greater if also adopted by U.S. commercial aircraft, which account for about 88 percent of annual jet fuel consumption.