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Development of a Robust and Reliable Ignition Assistance System for Multi-fuel Capable Engines

Description:

TECHNOLOGY AREA(S): Air Platform 

OBJECTIVE: To develop and demonstrate a highly robust and reliable ignition system for an aviation diesel engine capable of igniting low ignition quality jet fuels. 

DESCRIPTION: The Army has a critical need for an ignition source for Army Unmanned Aerial Vehicle (UAV) engines that can burn fuels with low ignition quality, characterized by the cetane number. Defense logistics agency’s (DLA) fuel analysis has shown a wide variation in fuel properties including samples with poor ignition behavior. Combustion instability derived from low ignition quality fuels can lead to increased maintenance, loss of aircraft and capability, and increased risk to the Warfighter. A robust system for ignition energy assistance is critical to enable operation of propulsion systems using a wider range of fuel, allowing Army propulsion systems to be more tolerant to low ignition quality fuels. This will enable semi-independent operation for future Warfighters with reduced logistics burden. The highest priorities for this SBIR are that the ignition system be robust, similar in size and shape to existing glow plug technology, easy to install, and capable of operating in a military environment using a variety of fuels. Historically, glow plugs have been used to assist ignition of diesel engines during cold start conditions by increasing the combustion chamber temperature before fuel injection. However, existing glow plugs are not designed for long duration ignition-assistance because of operating temperature limitations and energizing response times. The proposed ignition assistance system should have similar geometrical, and weight restrictions as a glow plug. It should be capable of enduring engine environments which are prone to vibrations, pressure cycles and thermal stresses. A new ignition system design employing novel materials should be considered that will ensure consistent engine ignition, regardless of operating conditions and fuel types. The primary challenge of this application is the development of materials suited for each component of the device that are capable of withstanding the harsh environment. Current existing materials have potential to handle the high temperatures or high strengths, but have not yet been evaluated for the desired application. Through research and investigation, an optimal combination of materials can be identified that meets the restrictions imposed in this ignition system. The part of the device inside the engine block, should use materials capable of withstanding combustion temperatures, with surface temperatures reaching higher than 1600°C. The primary body material should be resistant to temperatures higher than 800°C, with the material for the transition section between the part inside the engine and the body having a tolerance of higher than 1000°C. A fracture toughness of higher than 15 MPa m1/2 is desired since the system is expected to perform at high reliability for no less than 1000-hr under such conditions. The system should have a response time of less than 1 sec and the igniter should be powered by aviation standard 28 Volt DC power. The system should also be capable of adjusting its output energy to match the requirements of the input fuel. The unit should operate in the extreme environments found at altitude, where pressures may be as low as 30 kPa (absolute) and temperatures as low as -40°C. With these requirements met, a new ignition system could be incorporated into compression ignition engines, allowing for their operability with different fuels, while mitigating the risks of engine damage and flame blow-out. With this risk abated, Army UAV engines will perform more reliably, enabling highly sought capabilities. The new ignition system will support the Future Vertical Lift Cross Functional Team (FVL CFT) via the “Multi-fuel capable hybrid electric” task within the Future UAS project in the Advanced Unmanned Aircraft System Line of Effort (AUAS LOE). Commercialization of this technology can allow for higher combustion reliability when used in terrestrial engines, and a high degree of insensitivity to variations in fuel properties for aerial applications. 

PHASE I: Develop and design a new ignition assistance system concept that can meet the Army requirements of igniting low cetane number fuels (20-40) in extreme environmental conditions. The designed system shall be powered by 28 Volt DC. It shall operate at high surface combustion temperatures exceeding 1600°C, where output energy is controllable, and a fast response time of less than 1 sec from 400°C to 1600°C is attainable. It shall embody dimensional and operational characteristics that would enable its integration into compression ignition engines via a typical glow plug port for an existing system of comparable weight. Novel materials with suitable properties for the part inside the engine, main body, and transition section should be identified with measured fracture toughness (>15 MPa m1/2), and maximum allowable temperatures exceeding 1600°C, 800°C, and 1000°C, respectively. Additional operating requirements may be provided by the Army once contract award is made. The awardee shall provide a comparative analysis between the concept ignition assistance system and existing off-the-shelf technologies. CAD models should be supplied to the Army to determine interface compatibility with existing Army engines. The manufacturability of the proposed technology shall be assessed, identifying crucial fabrication process elements and projected production costs. The expected result is a thorough feasibility study, design, and proof of concept of an ignition assistant system. The success of Phase I will be judged based on the metrics of energy deposition level, response time, and fatigue analysis. 

PHASE II: Develop and demonstrate the technology and manufacturing methods of the assisted ignition system. Assess and quantify the capabilities of the ignition system in realistic diesel engine operating conditions with a variety of Army supplied aviation fuels. Implement new materials that meet the Army requirements for fracture toughness and maximum allowable temperatures as part of the ignition assistant system. Parameters for assessment include the Army requirements of less than 1 sec response time, ignitability of low cetane number fuels (20-40), operating on a 28 Volt DC power supply, weight restrictions of less than 0.5 lbs and ability to perform with high reliability for no less than 1000-hr within conditions of a compression ignition engine. In addition, system complexity and ease of installation will be assessed. Manufacturing assessment will evaluate the method, repeatability, materials and tolerance-holding capability. Deliverables include a formal report, test and analysis results and (10) prototype sensors and hardware. 

PHASE III: This technology, as envisioned, can be commercialized for terrestrial and aerial vehicles by increasing fuel insensitivity and therefore overall fuel efficiency, as well as providing a high degree of combustion reliability. A more direct impact will be on small manned and unmanned aircraft systems, which is a rapidly growing industry. A reliable ignition assistance system would allow for further development of multi-fuel capable aviation engine systems. This in-turn could facilitate the development of higher efficiency, reliable small UAV engines fueled with heavy fuels such as F-24, Jet A, diesel, and alternative, bio-derived heavy fuels. Success of the project would lead to more advanced and reliable propulsion systems for future commercial and DoD UAV systems. 

REFERENCES: 

1: Mueller, Charles J., and Mark P. Musculus. "Glow Plug Assisted Ignition and Combustion of Methanol in an Optical DI Diesel Engine." SAE Technical Paper Series, 2001, doi:10.4271/2001-01-2004.

KEYWORDS: Ignition Assistance System, Igniter, Multi-fuel Capable Engine, Unmanned Aerial System, Compression Ignition, Altitude, Aviation, Performance, Reliability, Unmanned Ground System 

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