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Chemical Kinetic Pathway Effects in Turbulent Reacting Flows

Description:

TECHNOLOGY AREA(S): Weapons

OBJECTIVE: Develop a methodology to assess the effects of turbulence-flame interactions on chemical kinetic pathways up to extinction and blow-out, and employ this methodology to develop tractable reduced chemical mechanisms for routine, large scale gas turbine combustor simulations that accurately capture these effects.

DESCRIPTION: To assess kinetic effects, detailed chemical mechanisms for gas turbine fuel surrogates have been developed [1]. These mechanisms are required to support a range of simulation activities that include fundamental kinetics research for surrogate and alternative fuel blends, and computational evaluation of advanced turbine combustor designs. Regarding turbine combustor assessments, detailed surrogate chemical mechanisms are too large for routine application. For example, the JetSurf Version 2.0 mechanism [1] includes 348 chemical species and 2163 chemical reactions. This type of mechanism is appropriate for kinetics research in reduced dimensional computational models. However, for realistic turbine combustor assessments, this detailed mechanism is much too large for deployment within a multi- dimensional flowfield simulation, especially in the context of large-eddy simulation (LES) approaches that are commonly used. For multi-dimensional simulations, detailed chemical mechanisms are reduced to form mechanisms that are tractable for a computational application, while retaining the general behavior of the detailed mechanisms. One approach to this reduction procedure includes several steps which are: 1) Selection of the skeletal mechanism from the detailed mechanism. 2) Selection of chemical species that may be assumed to be in quasi-steady state. 3) Implementation of the quasi-steady state assumption for species and reduction of the mechanism. Step 1 of this procedure is typically accomplished through researcher insight into the fuel mixtures to be investigated and the anticipated applications. Step 2 is accomplished either through researcher insight or through reaction pathway analysis [2]. Step 3 may be accomplished through automated numerical procedures (e.g., Lu and Law [3]) to complete the generation of a reduced mechanism. The reduced mechanism is then measured for accuracy against the skeletal and detailed mechanisms for reduced order problems [4][5]. In all cases, these problems are for laminar flows that do not include the interaction of chemistry with microscale turbulence. For example, reduced mechanisms are measured for accuracy for predictions of ignition delay times in homogeneous mixtures, laminar flame properties (i.e., species distributions and flame speeds), and laminar counter flow flame properties (i.e., species distributions with strain and extinction limits). A fundamental question regarding such reduced mechanism development is “Are chemical kinetic pathways altered by the interaction of micro-scale turbulence with flame structure?” The answer to this question has profound implications for the development of accurate reduced chemical mechanisms, and this question has not been significantly addressed [6]. For many years experimental investigations have observed differences in species production for laminar and turbulent flames (e.g., super equilibrium OH production in turbulent jet flames [7]). Such differences suggest that the interaction of turbulence with the flame structure may fundamentally alter the chemical kinetic pathways, especially as flame extinction is approached. If this is indeed the case, reduced chemical mechanisms developed for application to turbulent flows cannot be created based solely on the prediction of laminar flame properties. It is of fundamental importance to the US Army to assess the effect of turbulent interactions with chemical kinetics pathway especially in the context of high performance propulsion systems that operate under extreme conditions near the blow- out limit. Computational support for the development and assessment of such systems could be substantially limited if the chemical mechanisms that are applied do not properly account for the effect of turbulence-flame interactions that alter the chemical kinetic pathways. As a result, the Army desires a methodology to assess the effect of turbulence on chemical kinetic pathways, and use this information to systematically create accurate chemical mechanisms for turbulent flame simulations. Relevant fuels or surrogate fuels of interest to the Army should be considered. Close collaboration with academia is strongly encouraged to develop or identify appropriate detailed kinetic models and in order to leverage on innovative reaction mechanism reduction procedures arising from fundamental combustion research.

PHASE I: The Phase I effort will focus on the development and demonstration of a methodology or procedure to assess the effects of turbulence-flame interactions on chemical kinetic pathways. A plan should then be formulated to use this methodology to develop a computationally-tractable chemical kinetic mechanisms for routine application within large scale gas turbine combustor simulations.

PHASE II: Implement the plan identified in Phase I to fully develop an integrated procedure to generate tractable reduced chemical mechanisms that account for turbulence-flame interactions on chemical kinetic pathways. Apply and validate this procedure to a range of kinetics problems characteristic of gas turbine combustor flows.

PHASE III DUAL USE APPLICATIONS: For military applications, this technology is directly applicable to all high speed missile systems. This topic has direct application in both the military and commercial supersonic and hypersonic arenas. The most likely customer and source of Government funding for Phase-III will be those service project offices responsible for the development of advanced supersonic and hypersonic missile systems such as the Navy/DARPA HyFly, Air Force X-51, and DARPA Facet programs. However, it is possible that as NASA continues its access to space projects, this technology will become very important.

REFERENCES:

    • H. Wang, E. Dames, B. Sirjean, D. A. Sheen, R. Tangko, A. Violi, J. Y. W. Lai, F. N. Egolfopoulos, D. F. Davidson, R. K. Hanson, C. T. Bowman, C. K. Law, W. Tsang, N. P. Cernansky, D. L. Miller, R. P. Lindstedt, A high-temperature chemical kinetic model of n-alkane (up to n-dodecane), cyclohexane, and methyl-, ethyl-, n-propyl and n-butyl-cyclohexane oxidation at high temperatures, JetSurF version 2.0, September 19, 2010 (http://melchior.usc.edu/JetSurF/JetSurF2.0)

 

    • Tomlin, A.S., Turanyi, T. and Pilling, M.J., “Mathematical tools for the construction, investigation and reduction of combustion mechanisms” in Comprehensive Chemical Kinetics, Elsevier, pp. 293-437, 1997.

 

    • Lu, T. and Law, C. K., “Systematic Approach To Obtain Analytic Solutions of Quasi Steady State Species in Reduced Mechanisms,” Journal of Physical Chemistry A, Vol. 110, No. 49, pp. 13202–13208, 2006.

 

    • Sung, C.J., Law, C.K, and Chen, J.-Y., "An Augmented Reduced Mechanism for Methane Oxidation with Comprehensive Global Parametric Validation", Twenty-Seventh Symposium (International) on Combustion, The Combustion Institute, Pittsburgh, PA, pp. 295-304 (1998).

 

    • Montgomery, C., Cannon, S., Mawid, M., and Sekar, B., "Reduced chemical kinetic mechanisms for JP-8 combustion", 40th AIAA Aerospace Sciences Meeting & Exhibit, 2002.

 

    • Editorial Comment, Combustion and Flame, Vol. 159, 2012, pp. 2531 – 2532.

 

  • . Seitzman, J.M., Ungut, A., Paul, P.H., and Hanson, R.K., “Imaging and Characterization of OH Structures in a Turbulent Nonpremixed Flame,” proceedings of the Twenty-Third Symposium (Int.) on Combustion, The Combustion Institute, 1990, pp. 636 – 644.

KEYWORDS: turbulence, turbulent combustion, reduced chemical mechanisms

  • TPOC-1: Kevin Kennedy
  • Phone: 256-876-7278
  • Email: kevin.d.kennedy14.civ@mail.mil
  • TPOC-2: Melissa McDaniel
  • Phone: 256-313-0114
  • Email: melissa.a.mcdaniel16.civ@mail.mil
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