N141-021 TITLE: Improved Reliability Laser Based Ignition System

TECHNOLOGY AREAS: Sensors, Electronics

ACQUISITION PROGRAM: JSF-Prop

OBJECTIVE: Develop an innovative laser based ignition system to increase the reliability of igniters and excitation systems on aircraft gas turbine engines.

DESCRIPTION: Aircraft gas turbine engines normally operate at high altitude where conditions for an engine relight in the event of a flameout are far from ideal. The low temperatures encountered at high altitudes cause a decrease in fuel volatility, which makes it difficult to ignite the fuel charge. Ignition systems are usually of the spark igniter type where it is necessary to have a very high voltage to jump a wide igniter plug spark gap, and also, a high intensity spark. The high energy capacitor type ignition system is generally used for gas turbine engines since it provides both a high voltage and an exceptionally hot spark which covers a large area. Excellent chances of igniting the fuel/air mixture are assured at high altitudes. A typical system uses aircraft electrical power per MIL-STD-704 of 113 volts /400 hertz to generate high voltage pulses of 27 kilovolts at 4 joules of energy level for a period of 15 sparks/second. The igniter plug spark gap is sealed into the combustion chamber where running temperatures are high with fast transients and high pressures.

Igniters are a leading cause of removals on aircraft gas turbine engines. Top problems are cracked ceramic insulators, buildup of combustion contaminants at the plug tip, erosion of the plug tip, and fouling. Cracked ceramic insulators occur due to the combined environment effects of temperature, thermal transients, and moisture. Buildup of combustion contaminants at the plug tip results in tracking that diverts and shorts out the spark energy. Erosion of the plug tip is a natural effect of the plasma arc sparking process. Fouling is due to the accumulation of unburnt fuel or other airborne particles.

Prevalent ignition system designs also contain the failure modes within the exciter box. Components are hermetically sealed in the boxes. Seal malfunction requires replacement of the entire exciter. There can be breakdown or short circuits in the high tension circuitry. Breakdown damage to high tension igniter wires results in loss of abrasion and radio interference protection.

An innovative laser based design solution is sought to reduce or eliminate these failure modes in ignition systems. A successful solution will also have key characteristics comparable to typical ignition system designs on metrics of, response, power consumption, Electromagnetic Interference (EMI), package size, weight, cost, and electrical interface. Key environmental concerns that need to be taken into consideration are temperature, noise, humidity and vibration extremes. The laser based ignition system must be compatible with a current aerospace gas turbine engine control system.

Collaboration with an aircraft gas turbine manufacturer is strongly encouraged.

PHASE I: Determine technical feasibility and design a concept for an innovative laser based ignition system.

PHASE II: Develop, test using procedures defined by SAE AIR784C, and demonstrate a prototype ignition system and characterize the response, power consumption, and EMI.

PHASE III: Finalize testing and transition the technology to the appropriate platforms.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Ignition systems of this type are typically very similar to those used on commercial, business or general purpose turbine engine aircraft. Slightly modified derivatives of this technology could find use on most types of internal combustion engines. Therefore, improved ignition system technology can benefit multiple industries including power generation, marine, automotive, and other ground or air vehicle applications.

REFERENCES:
1. SAE International. (1995). Interrelation of Engine Design and Burner Configuration with Selection and Performance of Electrical Ignition Systems for Gas Turbine Engines (SAE Standard AIR784C). http://standards.sae.org/air784c/

2. Department of Defense (1977). Aircraft Electric Power Characteristics: Military Standard (MIL-STD-704C). Washington, DC. http://www.everyspec.com/MIL-STD/MIL-STD-0700-0799/MIL-STD-704C_21344/

3. Patent EP2458177A1 (2012). Advanced laser ignition systems for gas turbines including aircraft engines. www.google.com/patents/EP2458177A1?cl=en

4. Optical Society of America. (2011, April 20). Laser sparks revolution in internal combustion engines. http://phys.org/news/2011-04-laser-revolution-internal-combustion.html

5. Marshall, L. S. (Ed.). (2012). Laser Car Ignition Dream Sparks Multiple Approaches. http://www.photonics.com/Article.aspx?AID=51731

KEYWORDS: Laser, Ignition, Igniters, Gas Turbine Engines, Electronics, Sensor

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