Research On Ignition Characteristics And Flame Stability Of Syngas Fuels

Changes of compostions of syngas fuels have a great influence on basiccombustion properties, and this will take a great challenge on syngas utilization in gasturbine combustion. In the thesis, ignition characteristics and flame stability of syngasare studied in the model gas turbine combustor systematically. Premixed andnon-premixed burners are employed to investigate the syngas ignition behavior, and theignition control mechanisms of different fuels are discussed. Later, the dynamicresponse of premixed swirl flames are studied, and finally modes of combustioninstability are predicted using the linear perturbation method. The main contents are asfollows:Fundamental characteristics of syngas combustion are calculated, it shows that themaximum laminar flame speeds of syngas is in the rich condition, while that is near thestoichiometric for methane. Results of minimum ignition energy of spherical flames insteady state show that the minimum ignition energy is less in lean condition for thesame fuel, and it soared exponentially in the rich condition. So, it is much easier forignition in the lean condition.Experiments on premixed burner present that ignition time of syngas is shorter inlean condition compared with rich condition. Meanwhile, ignition model based on Daand flame kernel propagation speed is established, it is to analysis the effects ofcomposition and flow on ignition control mechanisms. Syngs with7%hydrogen andmethane are mainly controlled by stretch rate in the ignition process. When thehydrogen content is more than10%, high Da number of the fuel is controlled by stretchrate, and this effects changed when Da and kernel speeds decreases, finally the ignitionis controlled by heat loss of kernel.Ignition time of non-premixed flames are longer compared with premixed in thesame condition. Subsequent flames are classified, and it shows that combustioninstability occurs only near the hydrogen content of12%for non-premixed burners,while combustion instability exist on the whole range near lean ignition limits forpremixed burners.In order to study the response of premixed swirl flames, compressed airloudspeaker is installed in the upstream of the combustor. Reaction zone of methane is prolonged when equivalence ratio increases from0.75to0.85, and reaction zonebehaves like “V” pattern. For syngs fuels, when hydrogen increases from18%to24%,the flame becomes lifted in the same inlet perturbation condition, and reaction zone isasymmetry. The flame becomes much more sensitive, and response rate increases, gainof flame transfer function is higher. When hydrogen is increased to58%, two reactionzones emerge, and heat release perturbation is less, and flames become more stabilized.Using the linear perturbation method to model the combustor, it can predict thecombustion instability frequency and growth rate information. Combustion instabilityfrequency lies in70-100Hz for methane, and it is in450-1200Hz for syngas, it has agood match with the experiment results.