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Show INTRODUCTION A reliable chemical kinetics mechanism for natural gas combustion and N O emissions is a critical requirement for the successful use of computer modeling tools in guiding design improvements to gas fired equipment. Even when one is limited to shorter, reduced mechanisms by the complexities of fluid dynamics simulations, the detailed mechanism provides the basis from which the reduced mechanisms are directly or indirectly derived. The detailed mechanism must meet three criteria: • It must be consistent with the large body of current experimental knowledge and theoretical understanding of the elementary reaction steps involved. • It should also be capable of successfully predicting the array of experimental results on basic flame properties, data such as flame speeds, ignition delays, and species profiles. Error bars on basic rate expressions typically allow a significant range of model results for these flame properties. Thus w e have developed and applied a systematic optimization technique to adjust key rate parameters within their assigned, evaluated error bars in order to achieve the best simultaneous fit to the target database of flame properties. • The resulting optimized mechanism should be easy to use. The GRI-Mech Calculator has been created and installed on the World Wide W e b to serve as an on-line user-friendly modeling tool designed to simulate natural gas combustion chemistry scenarios using combinations of well-mixed and plug flow reactors. The focus of these mechanism development efforts is the high temperature oxidation of natural gas, particularly methane, and the chemistry of N O formation and reburn. This has produced the oxidation mechanism GRI-Mech 1.2,[1] and with the addition of nitrogen chemistry the N O mechanism, version 2.11.[2] The current mechanism, documentation on rate constants and targets, and comparisons of some validation experiments with modeling results are available via a link from the GRI/Net home page at http://www.gri.org. or directly on the GRI-Mech W e b site http://www.me.berkeley.edu/gri mecn/. Mechanism development and optimization is an inherently iterative process, fed by new results from kinetics measurements, additional or refined target experiments, and needs for extending the range of applicability. After a description of the optimization process, w e will show how this is being applied to the development of version 3.0 of GRI-Mech. The new mechanism uses updated kinetics and target values, n o w includes propane as a species representing trace amounts of higher hydrocarbons present in natural gas, and adds new targets focusing on formaldehyde oxidation and the C H intermediate involved in prompt N O formation and reburn chemistry. A final section will describe the improved version of the GRI-Mech Calculator. This on-line user-friendly modeling tool, designed to simulate natural gas combustion chemistry scenarios using the GRI-Mech mechanism, enables natural gas researchers and applications engineers to carry out interactive combustion chemistry modeling using their own W e b browsers. It provides exhaust concentrations, temperatures, and pressures computed from user-selected input conditions and reaction times for well-stirred or plug flow reactors under user-selected constraints. Temperature profiles m a y be calculated through solution of the energy balance equation or m a y be provided by the user. Graphical and numerical outputs are available for archiving at the user's site. A newly added feature in version 3.0 will allow the user to simulate a process as a specified network of reactors. 2 |
