Studies of rich and ultra-rich combustion for syngas production
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Syngas is a mixture of hydrogen (H2), carbon monoxide (CO) and other species including nitrogen (N2), water (H2O), methane (CH4) and higher hydrocarbons. Syngas is a highly desired product because it is very versatile. It can be used for combustion in turbines or engines, converted to H2 for use in fuel cells, turned into diesel or other high-molecular weight fuels by the Fischer-Tropsch process and used as a chemical feedstock. Syngas can be derived from hydrocarbons in the presence of oxidizer or water as in steam reforming. There are many demonstrated methods to produce syngas with or without water addition including catalytic methods, plasma reforming and combustion. The goal of this study is to add to the understanding of non-catalytic conversion of hydrocarbon fuels to syngas, and this was accomplished through two investigations: the first on fuel conversion potential and the second on the effect of preheat temperature. A primarily experimental investigation of the conversion of jet fuel and butanol to syngas was undertaken to understand the potential of these fuels for conversion. With these new data and previously-published experimental data, a comparison amongst a larger set of fuels for conversion was also conducted. Significant soot formation was observed in experiments with both fuels, but soot formation was so significant in the jet fuel experiments that it limited the range of experimental operating conditions. The comparison amongst fuels indicated that higher conversion rates are observed with smaller molecular weight fuels, generally. However, equilibrium calculations, which are often used to determine trends in fuel conversion, showed the opposite trend. In order to investigate preheat temperature, which is one important aspect of non-catalytic conversion, experiments were undertaken with burner-stabilized flames that are effectively 1-D and steady-state. An extensive set of model calculations were compared to the obtained experimental data and was used to investigate the effect of preheat temperatures that were beyond what was achievable experimentally. Throughout the range of operating conditions that were tested experimentally, the computational model was excellent in its predictions. Experiments where the reactants were preheated showed a significant expansion of the stable operating range of the burner (increasing the equivalence ratio at which the flame blew off). However, increasing preheat temperature beyond what is required for stabilization did not improve syngas yields.