|Acquisition Program: ||Joint Strike Fighter|
| ||RESTRICTION ON PERFORMANCE BY FOREIGN CITIZENS (i.e., those holding non-U.S. Passports): This topic is “ITAR Restricted”. The information and materials provided pursuant to or resulting from this topic are restricted under the International Traffic in Arms Regulations (ITAR), 22 CFR Parts 120 - 130, which control the export of defense-related material and services, including the export of sensitive technical data. Foreign Citizens may perform work under an award resulting from this topic only if they hold the “Permanent Resident Card”, or are designated as “Protected Individuals” as defined by 8 U.S.C. 1324b(a)(3). If a proposal for this topic contains participation by a foreign citizen who is not in one of the above two categories, the proposal will be rejected.|| Objective: ||Identify, test, and verify uniquely shaped flame holding concept(s) that reduce the fuel-air ratio at lean blowout for high-altitude, low-Mach-number flight conditions.
|| Description: ||Gas turbine augmentors employ bluff body flame holders to anchor and stabilize the flame. Legacy augmentors have utilized spray bars/spray rings and v-gutter flame holders. To avoid potential auto ignition due to high-inlet air temperatures, modern augmentors employ close-coupled fuel injector/flame holder designs.
There are difficult challenges in static stability, especially in the upper left hand corner of the flight envelope where the aircraft is traveling at low Mach numbers and at high-altitude. This results in conditions in the augmentor that are less favorable for robust ignition and flame holding. In this portion of the flight envelope the pressure in the afterburner is very low and the air entering the afterburner is vitiated with low oxygen content, both of which challenge robust combustion. Further, low pressure and vitiation reduces the required fuel flow, resulting in poor fuel preparation to the flame holder prior to combustion.
Novel flame holding concepts are desired for the improvement of static stability. Concepts should not be limited to flame holding architecture, but also should consider fuel delivery and fuel mixing into an integrated concept. Concepts should take advantage of the existing augmentor architectures in legacy and pipeline augmentor systems. Design modifications should only minimally affect the overall augmentor design, thus allowing for retrofits into legacy and advanced engines. Novel concepts should enhance stability without sacrificing durability or performance from the baseline.
|| ||PHASE I: Determine the feasibility of the proposed flame holding concept through both numerical analysis and reacting bench scale experiments. Perform accurate numerical simulations to assess which design configurations best improve lean blowout. Fabricate and test the best designs in a single flame holder rig to demonstrate improved lean blowout characteristics. Phase I tests may be performed at ambient pressure and temperature inlet conditions.
|| ||PHASE II: Optimize Phase I design using validated numerical simulation to further develop the prototype flame holding concept. The improved design should be demonstrated in a single flame holder rig at the same flow conditions as used in Phase I. Perform follow-on testing at realistic augmentor operating conditions. Two rounds of testing should be proposed to ensure the best designs are demonstrated. Close interaction with an engine original equipment manufacturer (OEM) is desired.
|| ||PHASE III: Finalize the flame holding concept design and testing in compliance with OEM specifications. Fabricate engine-quality hardware and perform testing in an engine augmentor. Transition the flame holding technology to a military gas turbine engine.
|| ||PRIVATE SECTOR COMMERCIAL POTENTIAL: This technology could be used by any engine manufacturers working with after-burners.
|| References: ||1. Acoustic Characterization of a Piloted, Premixed Flame Under Near Blowout Conditions, S. Nair, T.M. Muruganandam, R. Hughes, L. Wu, J. Seitzman, and T. Lieuwen, AIAA Paper 2002-4011, AIAA/ASME/SAE/ASEE Joint Propulsion Conference, July 7-10, 2002, Indianapolis, IN, 2002.
2. Flame Stabilization of Bluff Bodies at Low and Intermediate Reynolds Numbers, Edward E. Zukowski, PhD Dissertation, California Institute of Technology, January, 1954.
3. Correlation of Blowout Limits of Cavity, Strut, and Bluff-Body-Stabilized Non-Premixed Flames in High-Speed Airflows, James F. Driscoll and Chadwick C. Rasmussen, Joint Meeting of the U.S. Sections of the Combustion Institute, March, 2005.
4. Advanced Demonstration of Fuel Injector/Flame holder for High Speed Ramburners, S. Alan Spring, Clifford E. Smith, and Andy D. Leonard, Air Force Report WL-TR-95-2068 (Approved for Public Release, Distribution Is Unlimited), May, 1995.
|Keywords: ||Flame Holder; Augmentor; Afterburner; Stability; Lean Blowout; Combustion|