TECHNOLOGY AREA(S): Chem Bio_defense, Sensors, Electronics, Battlespace
OBJECTIVE: Develop physically accurate and computationally efficient combustion chemistry modules, physics and pathway-centric kinetics models; validate and improve the models and quantum-chemistry computations; quantify and reduce the module's uncertainty.
DESCRIPTION: Combustion chemistry governs the changes from high-energy-state fuel/oxidizer molecules to low-energy-state product molecules during the energy conversion process in Air Force propulsion systems. Physically accurate and computationally efficient combustion chemistry models is a critical part of physics-based modeling and simulation (M/S) tools for developing future generations of Air Force propulsion systems such as solid/liquid rockets, aviation jet engines, and hypersonic scramjets. A major challenge facing advanced model development is the prediction of combustion dynamics phenomena, such as flame blow-out, combustion instabilities and/or ignition issues, wherein the chemical time-scales may be comparable to or shorter than fluid dynamics and acoustics time-scales [1,2]. Under such circumstances, the development of accurate and efficient chemical kinetics mechanisms are of critical importance. The current state-of-the-practice for combustion kinetics models used in large scale computations such as large eddy simulations (LES) remain mostly inadequate. The vast majority of the codes and simulations utilize simplified global kinetics models that are anchored on global quantities (such as flame speed) at limited conditions. Such models are inherently incapable of capturing the rich dynamics present in non-premixed and partially premixed turbulent flames. At the other end of the spectrum are highly detailed combustion reaction models. For Air Force relevant heavy hydrocarbon fuels, these detailed models involve thousands of species and hundreds of thousands of reaction steps with even larger numbers of underdetermined model parameters. Not only are these intractable for reacting-LES calculations, the vast majority of such detailed mechanisms remain significantly un-validated for Air Force relevant conditions. To meet the challenges in both physics model representation and computation efficiency in combustion chemistry modeling, AFOSR and other agencies have been funding research in this area for many years. Recently, a promising new direction has been developed based on tracking a limited number of key/dominant reaction pathways using quantum chemistry consideration/computation and state-of-art experimental methods and diagnostics techniques. For real hydrocarbon fuels, it resulted in splitting the combustion chemical process into mainly experimental anchored pyrolysis phase followed by an oxidative phase only involving lower molecular-weight pyrolysis products, modeled by both experiments and quantum chemistry computations [3,4,5]. This topic focuses on the transition of the state-of-art, physics based, path-centric combustion chemistry models for Air Force relevant hydrocarbon fuels, leading to the development of accurate, robust and efficient computational modules with quantified and acceptable uncertainty. Proposals should consider all of the following areas in an integrated fashion: (1) Selecting state-of-art combustion chemistry models for Air-Force relevant hydrocarbon fuels and modularizing these models to be portable to and usable for available CFD codes; (2) Quantifying physical accuracy, computational efficiency, and prediction uncertainty of the developed modules using state-of-art evaluation approaches based on a set of logically defined unit-physics and canonical engineering test problems; (3) Defining the accuracy, efficiency and uncertainty targets acceptable for simulating relevant Air Force propulsion systems and identifying model gaps; (4) Defining needed experiments and quantum chemistry computations to close these gaps; and (5) Executing the previously defined experimental and quantum chemistry computations and improving the underlying combustion chemistry model to achieve the desired levels of accuracy, efficiency and uncertainty.
PHASE I: Phase I efforts are comprised of the above items (1)-(4), leading to a road map for a model/module improvement path using experiments and quantum chemistry computations to achieve the targeted physical accuracy, computational efficiency and prediction uncertainty acceptable for Air Force propulsion systems.
PHASE II: Phase II efforts focus on the above item (5), i.e., executing the required improvements using experiments and quantum chemistry computations to achieve the targeted physical accuracy, computational efficiency and predication uncertainty acceptable for modeling/simulating Air Force propulsion systems.
PHASE III: Demonstration of newly developed and validated kinetics model to canonical problems relevant to Air Force propulsion systems, in particular, involving non-stationary and off-design operation.
1. Sardeshmukh, S., Anderson, W., Harvazinski, M., Sankaran, V., Study of Combustion Instability with Detailed Chemical Kinetics, AIAA Paper, 2015 SciTech Meeting, Kissimmee, FL, Jan 2015.
2. Sardeshmukh, S., Huang, C., Anderson, W., Harvazinski, M. and Sankaran, V., Impact of Detailed Chemical Kinetics on the Predictions of Bluff-body Stabilized Flames, AIAA Paper, 2016 SciTech Meeting, San Diego, CA, Jan 2016.
3. Yang Gao, Ruiqin Shan, Sgouria Lyra, Cong Li, Hai Wang, Jacqueline H.Chen, Tianfeng Lu, On lumped-reduced reaction model for combustion of liquid fuels, Combustion and Flame 163 (2016) 437-446.
4. Sayak Banerjee, Rei Tangko, David A. Sheen, Hai Wang, C. Tom Bowman, An experimental and kinetic modeling study of n-dodecane pyrolysis and oxidation, Combustion and Flame (2015) 1-19.
5. Klippenstein, S. J., Pande, V. S., Truhlar, D. G. "Chemical kinetics and mechanisms of complex systems: A perspective on recent theoretical advances.Ã‚¬ Journal of the American Chemical Society, 136, 528-546 (2016).
KEYWORDS: Combustion Kinetics, Hydrocarbon Fuels, Pyrolysis And Oxidation, Aerospace Propulsion Systems