Global burning velocities of methane-air-steam mixtures are measured on prismatic laminar Bunsen flames and lifted turbulent V-flames for various preheating temperatures, equivalence ratios and steam mixture fractions at atmospheric pressure. Experiments are conducted on a new rectangular slot-burner. Experimental burning velocities are compared to computed flame speeds of one dimensional adiabatic premixed flames using detailed mechanisms (Konnov 0.5 and GRI Mech 3.0). Mean profiles of radicals OH * are also extracted from these flames and compared to simulation results.

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In the current study, the influence of pressure and steam on the emission formation in a premixed natural gas flame is investigated at pressures between 1.5 bar and 9 bar. A premixed, swirl-stabilized combustor is developed that provides a stable flame up to very high steam contents. Combustion tests are conducted at different pressure levels for equivalence ratios from lean blowout to near-stoichiometric conditions and steam-to-air mass ratios from 0% to 25%. A reactor network is developed to model the combustion process. The simulation results match the measured NOx and CO concentrations very well for all operating conditions. The reactor network is used for a detailed investigation of the influence of steam and pressure on the NOx formation pathways. In the experiments, adding 20% steam reduces NOx and CO emissions to below 10 ppm at all tested pressures up to near-stoichiometric conditions. Pressure scaling laws are derived: CO changes with a pressure exponent of approximately −0.5 that is not noticeably affected by the steam. For the NOx emissions, the exponent increases with equivalence ratio from 0.1 to 0.65 at dry conditions. At a steam-to-air mass ratio of 20%, the NOx pressure exponent is reduced to −0.1 to +0.25. The numerical analysis reveals that steam has a strong effect on the combustion chemistry. The reduction in NOx emissions is mainly caused by lower concentrations of atomic oxygen at steam-diluted conditions, constraining the thermal pathway.

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C h ris tia n O liv e r P a s c h e r e it1In flu en ce of Pressure and S team D ilu tio n on NOx and CO Em issions in a P rem ixed N atu ral Gas F lam eIn the current study, the influence o f pressure and steam on the emission formation in a premixed natural gas flame is investigated at pressures between 1.5 bar and 9 bar. A pre mixed, swirl-stabilized combustor is developed that provides a stable flame up to very high steam contents. Combustion tests are conducted at different pressure levels fo r equivalence ratios from lean blowout to near-stoichiometric conditions and steam-to-air mass ratios from 0% to 25%. A reactor network is developed to model the combustion process. The simulation results match the measured NOx and CO concentrations very well fo r all operating conditions. The reactor network is used fo r a detailed investigation o f the influence o f steam and pressure on the NOx formation pathways. In the experi ments, adding 20% steam reduces NOx and CO emissions to below 10 ppm at all tested pressures up to near-stoichiometric conditions. Pressure scaling laws are derived: CO changes with a pressure exponent o f approximately -0.5 that is not noticeably affected by the steam. For the NOx emissions, the exponent increases with equivalence ratio from 0.1 to 0.65 at dry conditions. At a steam-to-air mass ratio o f 20%, the NOx pressure expo nent is reduced to -0.1 to +0.25. The numerical analysis reveals that steam has a strong effect on the combustion chemistry. The reduction in NOx emissions is mainly caused by lower concentrations o f atomic oxygen at steam-diluted conditions, constraining the ther mal pathway. plants [1,2] but with lower installation costs and emission levels [3]. In contrast to the complex combined-cycle plants, ultra wet gas turbines have a substantially smaller footprint. Depending on the cycle configuration, short start-up times and excellent load control capabilities can be achieved. Furthermore, the high steam content allows for low-NOx, near-stoichiometric combustor oper ation and, thus, enables postcombustion CO2 capture at low cost, since the concentration of CO2 reaches the highest possible value for air breathing gas turbines after condensation of the steam. It was recently shown for a lean premixed and for a rich-quenchlean combustor, that steam dilution significantly reduces NOx

The influence of humidity and fuel composition on thermoacoustic flame characteristics is investigated. This is an important aspect in the development of combustion chambers for humidified gas turbines. Thermoacoustic issues are in the focus of the current investigation. These pressure pulsations result from the interaction of combustor acoustics with an unsteady heat release of the flame and have a negative influence on the combustion process and can even damage components of the engine. A key point concerning combustion dynamics is the role of convective time lags which are determined by the temporal delay between the appearance of a perturbation and the response of the flame. Experiments are conducted with different fuel mixtures containing natural gas, hydrogen, and nitrogen, each with steam contents in the air mass flow of up to 40%. The multi-microphone method and OH* chemiluminescence measurements with a photomultiplier and an intensified CCD camera are used to determine the flame transfer function and flame dynamics. It is observed that the characteristics of the flame response are related to the flame shape and position rather than to the fuel composition or the steam content. Using a Strouhal-number normalization based on the bulk velocity of the annular jet and the distance between fuel injection and the flame, a good agreement between the phases of the flame transfer functions of all flames attached to the burner outlet is found.

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