N151-016 TITLE: Direct Replacement Ignition Upgrade for Present and Future Combustors and Augmentors

TECHNOLOGY AREAS: Air Platform, Ground/Sea Vehicles

ACQUISITION PROGRAM: JSF-Prop

OBJECTIVE: Develop an advanced ignition system as a direct "drop-in" replacement for in-service and/or next-generation combustor and afterburner systems.

DESCRIPTION: Widely varying operating conditions (e.g., temperature, pressure, fuel/air mixture) as well as emerging alternative fuels, present challenges to ignition of aviation combustion systems used by the DoD. In the augmentor, for example, these conditions can be exacerbated by the presence of vitiated reactants from the combustor section that have lower oxygen content and higher concentrations of carbon dioxide, oxides of nitrogen and water vapor. In addition, if a flameout occurs at high altitude, the temperature and pressure in the combustor and/or augmentor are low, which makes ignition more difficult. The appropriate amount of energy required by the igniter to start the reaction process over a wide range of engine operating conditions varies significantly due to these competing physical processes. Finally, the chemical composition of kerosene-based (e.g., JP-5, JP-8, Jet A, Jet A-1) and alternative fuels have widely varying thermo-physical properties and therefore different ignition characteristics.

As a result, many combustion systems have operating envelopes at least partially defined by the ignition limit, i.e., the boundary condition at which the ignition system is unable to provide sustained combustion. Near the limits of the operating envelope (i.e., low temperature, lean fuel/air mixtures, high altitude, and low pressure) a reduction in ignition system or other subsystem performance may lead to slow light or no-light conditions. Increased operating margins provided by the ignition system would compensate for minor subsystem deficiencies, thus reducing unscheduled maintenance that would increase maintenance intervals. This would lead to increased fleet readiness levels, reduced overall maintenance costs, and would potentially increase capabilities available to the Warfighter. Ideally, such a system would be capable of being developed as a direct replacement on existing engines with minimal modification to the current control system, mounting location, electrical buss, or the existing igniter port.

Previous testing has shown that simply increasing energy output from fielded ignition concepts yields only small performance benefits with severe durability penalties. The increased performance demands from 5th-generation and 6th-generation engines may heighten the need for increased energy at the combustor and augmentor, thus creating further durability challenges as the environment pushes material limits.

Current modeling technology uses simple empirical correlations of lean blowout (LBO) to determine ignition likelihood. Empirical models by King (1957), DeZubay (1950), Ozowa (1970), and Kiel et al. (2011) assume a global extinction parameter based on global conditions. These models imply a relationship between blowout physics and ignition physics that may be unfounded. While much recent work continues to focus on finding solutions through improving ignition models, recent empirical work has shown promise through the investigation of new approaches that address parameters to increase ignition effectiveness. Recent work at Georgia Tech (B.Sforzo. et.al. 2013 and B.Sforzo et.al. 2011) has shown that ignition energy location relative to the cross section of the flow field may be a key factor in ignition effectiveness. By projecting energy beyond what is presently possible with present ignition systems, an ignition solution providing enhanced capabilities without durability penalties may be achievable.

An ignition technology which provides an increase in performance/durability, which in turn provides some combination of improved light-off/relight capability that can be implemented as a direct replacement upgrade without modification to the engine, control system, or other subsystems is sought. This ignition system should meet current DoD performance-based specifications (JSSG-2007B).

Describe how the proposed ignition system could be an enabling technology allowing further development of 5th-generation and 6th generation engines. This ignition system should also have the ability to dynamically adapt the ignition energy content and location as needed by the engine via direct control of an advanced full authority digital engine control (FADEC) in order to further simultaneously improve the flight envelope while increasing durability/reducing maintenance.

Close collaboration with an Original Equipment Manufacturer (OEM) of gas turbine engines and aircraft ignition systems is highly encouraged to ensure successful transition of improved ignition technology following a successful Phase II effort.

PHASE I: Design and develop a retrofit or direct replacement of the proposed system concept for naval aviation applications. Detail required test facilities and measurement techniques for system validation. Demonstrate feasibility of ignition capability enhancement of the proposed approach in an appropriate environment.

PHASE II: Develop and validate an improved ignition system prototype including igniters, leads, and exciter over the representative range of operating conditions found in legacy, 5th-generation, and 6th-generation combustor and augmentor system for naval aviation applications. Develop a transition plan.

PHASE III: Complete development and transition to DoD and commercial gas turbine engine ignition system manufacturer and/or their vendors, including validation and certification testing.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: The technology has the true potential for dual-use applications by improving ignition systems in legacy, 5th-generation, and 6th-generation military combustor and augmentor systems as well as civil gas turbine engines. It also has the potential for stationary combustion systems used for power generation, furnaces, and boilers.

REFERENCES:
1. Ozawa, R. I. (1970). Survey of Basic Data on Flame Stabilization and Propagation for High Speed Combustion Systems. U.S. Air Force AFAPL-TR-70-81. <http://www.easyfilecatcher.net/easydownload/62c8b33ch32i0/ao473728.pdf.html>

2. King, C.R. (1957). A Semi-empirical Correlation of Afterburner Combustion Efficiency and Lean-Blowout Fuel-Air-Ratio Data with Several Afterburner-Inlet Variables and Afterburner Length. National Advisory Committee for Aeronautics. NACA RM E57F26

3. DeZubay, E. A. (1950). Characteristics of Disk-Controlled Flame. Aero Digest. 61, 1, 54-56, 102-104.

4. Adelman, H. G. (1981). A Time Dependent Theory of Spark Ignition. The Proceedings of the Combustion Institute. 1333-1342.

5. Drake M. C., Fansler, T. D., & Lippert A. M. (2005). Stratified-charge combustion: modeling and imaging of a spray-guided direct-injection spark-ignition engine. Proceedings of the Combustion Institute. 30, 2683-2691.

6. Dahms R., Fansler, T. D., Drake, M. C., Kuo, T. W., Lippert, A. M., & Peters, N. (2009). Modeling ignition phenomena in spray-guided spark-ignited engines. Proceedings of the Combustion Institute. 32, 2743-2750.

7. Sforzo,B., Kim, J., Seitzman, J.M., & Jagoda, J. (2011). Spark Kernel Energy and Evolution Measurements for Turbulent Non-Premixed Ignition Systems. Augmentor Design Systems Conference. Ponte Verda Beach, FL, March 16-18.

8. Sforzo, B., Kim, J., Lambert, A., Jagoda, J., Menon, S., & Seitzman, J. (2013). High Energy Spark Kernel Evolution: Measurement and Modeling. Proceedings of the 8th US National Combustion Meeting. May 19-22, 2013.

9. Department of Defense Joint Specification Service Guide (JSSG). (2007). Engines, Aircraft, Turbine. JSSG-2007B.

10. Wu, H, & Ihme, M. (2014). Effects of flow-field and mixture inhomogeneities on the ignition dynamics in continuous flow reactors. Combustion and Flame. 161, 9, 2317-2326. <http://www.sciencedirect.com/science/article/pii/S0010218014000662>

KEYWORDS: Combustion; Ignition; direct replacement; plasma; chemical kinetics; augmentor

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