N24A-T016 TITLE: Plasma Assisted Combustion for Enhanced Performance and Operability in Naval Air Vehicles and Weapons

OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Hypersonics; Sustainment

OBJECTIVE: Develop, demonstrate, and validate a novel Plasma Assisted Combustion (PAC) device that can be integrated into future naval air platforms and weapons propulsion systems.

DESCRIPTION: The Office of Naval Research seeks development and demonstration of an innovative PAC system to improve the performance, efficiency, and operability of gas turbine engines in naval aircraft. The primary goal of this STTR topic is to identify and explore advanced combustion technologies that will enable significant improvements in performance, fuel efficiency, operational capabilities, and integration with various fuel types, while maintaining or enhancing reliability, maintainability, and safety. The target application for this technology is gas turbine primary combustors, augmentors, rotating detonation combustors, and inter-turbine burners. A brief description of these devices is provided below:

1. Primary Combustor: The primary combustor is where most of the combustion in a gas turbine occurs. Fuel is injected and ignited at high temperatures and pressures and the products drive the turbine stages of the engine.

2. Augmentor: The augmentor, or afterburner, is used to significantly increase the thrust of military aircraft at the expense of fuel efficiency. Fuel is injected in the exhaust stream and ignited to accelerate the exhaust gas existing the engine. These types of combustors take up a significant amount of volume and weight on military aircraft.

3. Rotating Detonation Combustors (RDCs): RDCs use a continuous detonation wave to burn a fuel-air mixture. The rotating detonation wave enables shorter combustion lengths and the device could theoretically produce a pressure rise, which is beneficial to the engine cycle. These type of devices are often difficult to operate and control.

4. Inter-Turbine Burners (ITBs): In an ITB, fuel is added and combusted between stages of a multi-stage turbine to raise the enthalpy of the flowfield in a compact space. While not as efficient as a primary combustor, the ITB is useful for scenarios where additional thrust is needed (similar to the Augmentor). ITBs are challenging to design because of the aerodynamic and pressure changes caused by turbine stage rotation.

Targeted and controllable combustion in naval aviation gas turbine engines is desirable since they provide thrust over a wide operational envelope for critical mission phases such as takeoff, supersonic cruise, and combat while being weight and volume constrained. Combustor length is typically constrained by the combined resonance time required to atomize, vaporize, mix, heat, and react liquid fuels with oxygen molecules at high flow rates, without blowing the flame out of the desired burn location.

A plasma assisted combustor uses plasma discharges to initiate and stabilize combustion, leading to more efficient fuel burning and improved combustion performance. This innovative technology can potentially lower the ignition temperature while enabling faster and more stable combustion. Additionally, electrically driven and controlled plasma may be used to actively control combustion properties. These improvements could yield significant benefits for naval aircraft including increased operational range, reduced fuel consumption, enhanced mission capabilities, and better component reliability. Specific goals for this effort include:

1. Increased combustion efficiency: Achieve a significant improvement in combustion efficiency relative to traditional combustor designs.

2. Decreased burning length: Decreasing the combustion resonance time will enable shorter combustor designs, which reduce the size and weight of the engine.

3. Improved operational flexibility: Develop a PAC system that can adapt to various operating conditions and fuel types.

4. Acceptable reliability and maintainability: Develop a PAC system that maintains or improves upon the reliability and maintainability of conventional systems, with a focus on minimizing downtime and maintenance costs.

5. Scalable and ready for integration: Design a PAC system that can be readily integrated into future naval aircraft, with the ability to scale the technology for different engine sizes and configurations.

Please note that the Office of Naval Research is specifically interested in liquid Jet fuel PAC solutions for this STTR topic, not gaseous. Although gaseous fuels may be used to minimize risk, they should not be the emphasis of this work.

PHASE I: Conduct a comprehensive feasibility study and develop a conceptual design for the proposed PAC system. Thoroughly explore existing and emerging plasma assisted combustion technologies Assess their applicability to naval aircraft. The research and development efforts in Phase 1 should focus on the following key areas:

1. Literature review and technology assessment: Perform a thorough review of the current state of the art in plasma assisted combustion, including research publications, patents, and ongoing research projects in both academia and industry. Identify and assess the most promising plasma generation methods, plasma-fuel interaction processes, and combustion enhancement techniques that have potential for integration into naval aircraft gas turbine engines

2. Analysis of critical technical challenges: Identify the critical technical challenges associated with developing a PAC system for naval aviation gas turbine engines. These challenges may include, but are not limited to, plasma generation methods, plasma-fuel interaction, combustion stability, integration with engine components and systems, and the ability to adapt to various operating conditions and fuel types. Propose innovative solutions to address these challenges, and evaluate the feasibility of these solutions in the context of the overall PAC system design.

3. Conceptual design: Develop a conceptual design for the liquid Jet fuel PAC system, incorporating the lessons learned from the literature review and technology assessment. The design should clearly illustrate the key components and subsystems of the PAC system, their function and operational requirements. Preliminary engine integration requirements and scaling constraints should also be identified.

4. Preliminary benefits and cost assessment: Quantify the performance benefit and cost impact of using a PAC over existing combustor technology in a Navy-like engine. Among others, the analysis should consider factors such as combustion resonance time, combustion efficiency, operability envelope, fuel consumption, reliability, and maintainability. Please note that performers will need to use their own tools and cycle models to conduct these types of studies.

5. Risk assessment and mitigation: Identify potential risks associated with the development testing, and implementation of the PAC system, including technical, operational, and programmatic risks. Develop a risk mitigation plan that outlines the strategies and measures that will be employed to address these risks throughout the course of the project.

6. Development plan and schedule: Develop a detailed plan and schedule for the subsequent phases of the project, including Phase II (Prototype Development and Preliminary Testing) and Phase III (Full-Scale Testing and Validation). This plan should outline the specific tasks and milestones that will be completed in each phase, the resources and expertise that will be required, and the anticipated timeline for completion.

7. Program cost analysis: Conduct a preliminary cost analysis for the development and testing of the PAC system, including estimates for research and development, prototyping, and testing costs.

8. Close collaboration with original engine manufacturers is highly encouraged starting in Phase I.

Upon completion of Phase I, the resulting feasibility study and conceptual design will serve as the foundation for the subsequent phases of the project, providing a clear roadmap for the development and testing of the PAC system in naval aircraft gas turbine engines.

PHASE II: Develop a prototype PAC system based on the conceptual design from Phase I and conduct preliminary testing to assess its performance, efficiency, and adaptability to various operating conditions and fuel types. Perform design refinement, testing, and optimization, with the goal of addressing the critical technical challenges identified in Phase I and demonstrating the potential operational improvements and benefits of the PAC system. The research and development efforts in Phase II should focus on the following key areas:

1. Detailed design and component selection: Develop a detailed design for the liquid jet fuel PAC system, including the selection of appropriate materials, components, and subsystems that meet the requirements for each test. This design process should involve a thorough evaluation of various plasma generation techniques, plasma-fuel interaction strategies, and combustion enhancement approaches, with the goal of selecting the most promising and feasible options for a Navy PAC system.

2. Prototype fabrication: Fabricate a prototype PAC system based on the detailed design, using advanced manufacturing techniques and materials, as required. Performers are expected to collaborate with engine manufacturers, materials suppliers, and other relevant stakeholders to ensure relevance and facilitate technology transition.

3. Preliminary bench-scale testing: Conduct preliminary bench-scale testing of the prototype PAC system using liquid jet fuels to assess its performance, efficiency, and adaptability to various operating conditions and fuel types.

4. Data analysis and design optimization: Analyze the data collected during the preliminary bench-scale testing to identify any areas of the prototype’s design that required refinement or optimization. This analysis should involve a thorough evaluation of the PAC system’s performance, efficiency, and adaptability, as well as its overall impact on engine operation, maintenance, and safety. Based on this analysis, refine and optimize the design of the PAC system to address any identified issues and maximize its potential benefits for naval aircraft gas turbine engines.

5. Updated risk assessment and mitigation: Revisit the risk assessment and mitigation plan developed in Phase I, and update it based on the results of the prototype development and preliminary testing. This update should include any new risk mitigation strategies and measures that have been employed during the course of Phase II.

6. Phase III planning: Develop a detailed plan for Phase III (Full-Scale Testing and Validation), outlining the specific tasks, milestones, and resources that will be required to conduct full-scale testing of the optimized PAC system, validate its performance and efficiency improvements, and develop a plan for integrating the system into future naval aircraft gas turbine engines.

Upon completion of Phase II, the resulting optimized prototype PAC system will serve as the basis for the subsequent Phase III, demonstrating the potential benefits and feasibility of implementing this advanced combustion technology in naval aircraft gas turbine engines.

PHASE III DUAL USE APPLICATIONS: Conduct full-scale testing of the optimized PAC system in a relevant engine environment, validating its performance, efficiency, and operability improvements. The research and development efforts in Phase III should focus on the following key areas:

1. Full-scale testing: Conduct full-scale testing of the optimized liquid jet fuel PAC system in a representative engine environment, evaluating its performance under different operating conditions and using various fuel types.

2. Performance validation: Validate the performance, efficiency, and operational improvements achieved by the PAC system through rigorous data analysis. Compare the results with traditional combustor designs to better quantify the benefits and drawbacks of the new technology. Evaluate the PAC system’s capability to meet the predefined goals and requirements established during Phase I and Phase II.

Upon completion of Phase III, the resulting validated PAC system will be ready for detailed engine integration studies and manufacturing readiness level maturation. Ideally, this effort will result in significant combustion performance and operability improvements over the state of the art.

Improvements in combustion efficiency, fuel consumption, and operational flexibility make it an attractive solution for commercial aviation. In commercial aviation, fuel efficiency is a critical concern for airlines. Implementing PAC technology in aircraft engines could significantly reduce fuel consumption and emissions, leading to substantial cost savings for airlines and reduced environmental impact. Furthermore, enhanced combustion efficiency and operability could enable the use of alternative and sustainable fuels, supporting the aviation industry’s ongoing effort to transition towards more environmentally friendly energy sources. PAC could also improve ground based power generation.

REFERENCES:

1. Starikovskaia, S. M. "Plasma-assisted ignition and combustion: nanosecond discharges and development of kinetic mechanisms." Journal of Physics D: Applied Physics, 47(35), 353001. https://iopscience.iop.org/article/10.1088/0022-3727/47/35/353001/meta
2. Li, M.; Wang, Z.; Xu, R.; Zhang, X.; Chen, Z. and Wang, Q. "Advances in plasma-assisted ignition and combustion for combustors of aerospace engines." Aerospace Science and Technology, 117, 106952, 2021. https://www.sciencedirect.com/science/article/pii/S1270963821004624
3. Sun, W. and Ju, Y. "Nonequilibrium plasma-assisted combustion: a review of recent progress." J. Plasma Fusion Res, 89(4), 2013, pp. 208-219. http://www.jspf.or.jp/Journal/PDF_JSPF/jspf2013_04/jspf2013_04-208.pdf
4. Starikovskiy, A. and Aleksandrov, N. "Plasma-assisted ignition and combustion." Progress in Energy and Combustion Science, 39(1), 2013, pp. 61-110. https://www.sciencedirect.com/science/article/pii/S0360128512000354
5. Ju, Y. and Sun, W. "Plasma assisted combustion: Dynamics and chemistry." Progress in Energy and Combustion Science, 48, 2015, pp. 21-83. https://www.sciencedirect.com/science/article/pii/S0360128514000781
6. Ju, Y. and Sun, W. "Plasma assisted combustion: Progress, challenges, and opportunities." Combustion and Flame, 162(3), 2015, pp. 529-532. https://www.sciencedirect.com/science/article/pii/S0010218015000280

KEYWORDS: Plasma Assisted Combustor (PAC), Gas Turbine Engines, Combustor, Combustion Efficiency, Fuel Consumption, Plasma, Rotating Detonation, inter turbine burning

---