Premixed Hydrocarbon Stagnation Flames: Experiments and Simulations to Validate Combustion Chemical-Kinetic Models

Citation

Benezech, Laurent Jean-Michel (2008) Premixed Hydrocarbon Stagnation Flames: Experiments and Simulations to Validate Combustion Chemical-Kinetic Models. Engineer's thesis, California Institute of Technology. doi:10.7907/TVB9-4266. https://resolver.caltech.edu/CaltechETD:etd-05302008-113043

Abstract

A methodology based on the comparison of flame simulations relying on reacting flow models with experiment is applied to C₁–C₃ stagnation flames. The work reported targets the assessment and validation of the modeled reactions and reaction rates relevant to (C₁–C₃)-flame propagation in several detailed combustion kinetic models. A concensus does not, as yet, exist on the modeling of the reasonably well-understood oxidation of C₁–C₂ flames, and a better knowledge of C₃ hydrocarbon combustion chemistry is required before attempting to bridge the gap between the oxidation of C₁–C₂ hydrocarbons and the more complex chemistry of heavier hydrocarbons in a single kinetic model.

Simultaneous measurements of velocity and CH-radical profiles were performed in atmospheric propane(C₃H₈)- and propylene(C₃H₆)-air laminar premixed stagnation flames stabilized in a jet-wall configuration. These nearly-flat flames can be modeled by one-dimensional simulations, providing a means to validate kinetic models. Experimental data for these C₃ flames and similar experimental data for atmospheric methane(CH₄)-, ethane(C₂H₆)-, and ethylene(C₂H₄)-air flames are compared to numerical simulations performed with a one-dimensional hydrodynamic model, a multi-component transport formulation including thermal diffusion, and different detailed-chemistry models, in order to assess the adequacy of the models employed. A novel continuation technique between kinetic models was developed and applied successfully to obtain solutions with the less-robust models. The 2005/12 and 2005/10 releases of the San Diego mechanism are found to have the best overall performance in C₃H₈ and C₃H₆ flames, and in CH₄, C₂H₆, and C₂H₄ flames, respectively.

Flame position provides a good surrogate for flame speed in stagnation-flow stabilized flames. The logarithmic sensitivities of the simulated flame locations to variations in the kinetic rates are calculated via the "brute-force" method for fifteen representative flames covering the five fuels under study and the very lean, stoichiometric, and very rich burning regimes, in order to identify the most-important reactions for each flame investigated. The rates of reactions identified in this manner are compared between the different kinetic models. Several reaction-rate differences are thus identified that are likely responsible for the variance in flame-position (or flame-speed) predictions in C₁–C₂ flames.

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