Jeffrey A. Manion
Donald R. Burgess, Jr.
Thomas C. Allison
Jeffrey W. Hudgens
Wing Tsang
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Jeffrey A. Manion |
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Strategies for Development of Simulation Models for Real Transportation Fuels Simulations that combine detailed Chemical Kinetic Modeling (CKM) with Computational Fluid Dynamics (CFD) are increasingly needed for the purposes of guiding development of real devices such as engines and turbines. We will address some of the barriers to the efficient translation of our underlying scientific understanding of combustion to technological development, with an emphasis on what is needed to further develop chemical kinetic models. Real transportation fuels such as gasoline, diesel, and aviation fuels are complex liquids containing hundreds or thousands of compounds. Chemical Kinetic Models containing all possible reactions of all compounds would be hopelessly large. Nonetheless there is a path forward. The general consensus of a recent workshop held at NIST is that this will involve the use of surrogate fuels. The idea is that, although the absolute numbers of compounds in Real Fuels are large, the number of chemical classes is very limited, and each chemical class can be adequately represented by a single or small number of model compounds. With this approach, various surrogate mixtures of these model compounds can be matched to and used to mimic the chemical and physical properties of the real mixtures. There are a number of obvious advantages to this approach: 1) researchers could conduct experiments on highly reproducible standards; 2) a greatly reduced reaction set would be required to develop detailed chemical kinetic models; 3) all fuels would make use of the same database of information (or a subset thereof). The surrogate fuels approach makes the chemical problem tractable. Nonetheless there remain areas where the existing databases are inadequate. The somewhat simplified picture of the combustion of a Real Fuel is a process involving 1) breakdown of large molecules into smaller fragments, 2) combustion of the small fragments, and 3) buildup of small fragments into PAH and soot. Reasonably complete databases exist for combustion of the small fuel fragments currently exist. More limited progress has been on PAH and soot, while the breakdown of large fuel molecules has only recently begun to be addressed at a detailed level. In general, the main scientific challenge in the treatment of the larger molecules characteristic of real fuels is the proper description of the isomerization reactions of the intermediate radicals. Combination of experimental and theoretical work should, however, close this knowledge gap. A final difficulty is one of infrastructure within the combustion community. Simulations of real combustion devices span length scales ranging from atoms and molecules up to engines and turbines. The required disciplines include kinetics, thermodynamics, computational chemistry, fluid dynamics, mechanical design, and a host of mathematical methods. The facile exchange of data across these scientific domains and multiple length scales is a large barrier to progress in the area of combustion processes. Some of the ways in which the infrastructure issue is beginning to be addressed will be touched on.
Physical and Chemical Properties Division, MS 8380 |