Experimental and kinetic modeling studies of flames of H 2, Co, and C1-C4 hydrocarbons

Developing reliable chemical kinetic models is a key ingredient in current and future efforts to develop science-based predictive tools, which will be used for the design of more efficient, less polluting, and flexible-fuel combustion systems. While a variety of combustion properties are needed for the comprehensive validation of detailed kinetic models, a minimum requirement for a model's validity is the prediction of fundamental mixture properties including the laminar flame speed that is a measure of the heat release rate, and thus the driving force of dilatation that leads to power production.;In this study, the combustion characteristics of hydrogen/carbon monoxide/C 1-C4 hydrocarbons were investigated both experimentally and numerically in laminar premixed and non-premixed flames. These characteristics included laminar flame speeds and extinction limits. Experimentally, flames were established in the counterflow configuration and flow velocity measurements were made using the particle image and laser Doppler velocimetry. Numerically, laminar flame speeds and extinction limits were simulated using quasi-one-dimensional codes, which integrated the conservation equations with detailed descriptions of molecular transport and chemical kinetics.;Although the hierarchical importance of hydrogen chemistry to the modeling of combustion kinetics has long been recognized, there exist notable discrepancies between experimental and computed fundamental combustion properties especially in flames. Hydrogen/air mixtures are flammable for a wide range of equivalence ratios, with reactivity that ranges quite notably from near-limit to near-stoichiometric conditions. Among others, the extent of reactivity is manifested by the laminar flame speed that could vary from several cm/s to few m/s under atmospheric conditions. Additionally, due to the very low molecular weight of hydrogen, its lean mixtures with nitrogen containing oxidizers are thermo-diffusionally unstable due to the sub-unity Lewis numbers. In the present investigation, accurate experimental data were determined for hydrogen/oxygen/nitrogen flames and compared against computed results. The novelty of this investigation is that reference flame speeds that are raw experimental data obtained in positively stretched flames were compared against computed results, which eliminates issues related to cellular flames and linear or non-linear extrapolations.;In addition, uncertainties still exist in modeling of important three-body recombination reactions, such as for example the H-terminating H + O 2 + M → HO2 + M. The collision efficiency of the water molecule is known to be large, and as a result its presence at conditions of high density can have a notable effect on various combustion phenomena. The influence of water vapor addition on the extinction of premixed and non-premixed H2/air flames was investigated experimentally and numerically in low temperature flames.;One of the critical elements towards accurate predictions of combusting flows is to characterize and minimize the uncertainties associated with predictions of fundamental flame properties. In this work, a large set of laminar flame speed data, systematically collected for C1-C4 hydrocarbons with well-defined uncertainties, were used to demonstrate how well-characterized laminar flame speed data can be utilized to explore and reduce the remaining uncertainties in a reaction model for small hydrocarbons. The USC Mech II kinetic model was used as a case study. The method of uncertainty minimization using polynomial chaos expansions (MUM-PCE) was employed to constrain the model uncertainty in laminar flame speed prediction. In addition, the types of hydrocarbon fuels with the greatest impact on model uncertainty reduction are identified along with the attendant accuracy that is needed in flame measurements to facilitate better reaction model development. Results demonstrate that a reaction model constrained only by laminar flame speeds of methane/air flames reduces notably the uncertainty in the predictions of the laminar flame speeds of C3 and C4 alkanes, because the key chemical pathways of all of these flames are similar to each other. However, the uncertainty in the model predictions for flames of unsaturated C3-C4 hydrocarbons remains significant without considering their laminar flames speeds in the constraining target data set, because the secondary rate controlling reaction steps are different from those in methane flames.