Description: Electric propulsion represents an attractive path for reducing overall emissions. For larger commercial aircrafts operating in the mega-watt range, power turboelectric and hybrid electric aircraft propulsion will continue to rely on gas turbine engines/generators to provide part of the thrust, charging batteries and driving generators. As a result, reduction of emissions such as oxides of nitrogen (NOx) remains a key concern. The innovation proposed is a software toolkit supporting high-fidelity yet computationally-tractable predictions of NOx emissions and other pollutants in gas-turbine engines/generators within the context of unsteady Computational Fluid Dynamics (CFD) simulations. A well-known difficulty limiting the accurate prediction of NOx levels in turbulent flames is related to the fact that NOx production can evolve through several different chemical pathways characterized by drastically different time scales. In this regard, a fast-running turbulent combustion approach called Multi-TimeScale Flamelet/Progress Variable (MTS-FPV) is being developed to address NOx emissions in a computationally-tractable manner and by capturing the relevant characteristic chemical time scales. The MTS-FPV formulation will be matured and extended to model two-phase droplet vaporization and then subsequently packaged as a software toolkit. Furthermore, this software toolkit will be interfaced with NASA’s OpenNCC CFD code. As a result, at the conclusion of the SBIR program, NASA will have available in-house (i) the enhanced emission prediction capabilities of OpenNCC as well as (ii) a methodology for leveraging these capabilities in system-level trade analyses of hybrid electric aircraft propulsion concepts.

Benefits: This product addresses NASA Aeronautics Research Mission Directorate (ARMD) core needs for enabling safe and reliable operation of next-generation (e.g., N+3 generation and beyond) ultra low-emission power turboelectric and hybrid electric aircraft propulsion, where gas turbine engines will continue to play a critical role. With increasingly stringent environmental regulations, reduction of emissions, including NOx, remains a key concern, in particular for larger aircrafts operating in the mega-watt range. In hybrid electric propulsion concepts such as STAR-ABL, emission requirements are also coupled with the need for the optimal budgeting of the power requirements for propulsion and power generation. This product also addresses core needs of NASA's vision for next-generation aircraft systems with hybrid integrated wing/body systems that feature significant improvements in engine performance, emissions and noise reduction. Since low-emission combustor designs tend to operate at fuel lean conditions near the flame lean blow-out limit, a detailed understanding of flame dynamics and unsteady combustion effects is required to develop fuel-efficient, low-emission, stable combustor designs. Advanced CFD design tools can provide fundamental physical insight that is difficult or cost-prohibitive to obtain experimentally. Given the inherent modularity of the MTS-FPV approach, interfacing with the OpenNCC will provide NASA with a powerful design support tool.

The commercial market for this product includes the broad aerospace, power-generation and defense industry. The primary driver for the commercial market for this product is represented by commercial aircraft gas turbine engines. The proposed software toolkit directly addresses the resulting increased demand for high-fidelity design tools that accurately characterize emissions and unsteady combustion effects and will benefit commercial gas turbine OEMs (both commercial and military) by providing them with a powerful and tractable supplement to minimize the need for experimental testing. Other applications encompass power-generation turbines and internal combustion, HCCI and diesel engines, e.g., using engine recirculation (EGR) devices to mitigate harmful NOx production. DoD applications include the design of gas-turbine engines, scramjets, pulse-detonation-engines (PDEs), augmentors, UAVs propulsion systems and rocket engines. Of particular relevance is the Army single fuel policy mandate to use jet fuel in ground vehicle diesel engines to simplify the supply chain logistics in the battle space and to strengthen domestic energy security. Also noteworthy is the DoD growing interest in fuel blends with alternative or renewable fuels, e.g., synthetic paraffinic kerosene or camelina-derived bio-fuel, as an acceptable form of "drop-in" fuels.