Study Of Combustion Characteristics And Flame Stabilization Mechanism Of Hydrogen-containing Multiple Micro-mixing Jet Flames

The Micro-mixing Combustion(MMC)technology proposed for gas turbine combustor has become a hot research topic in recent years,which is a technology to achieve low NOx combustion by reducing the mixing scale of fuel and air flow to achieve enhanced outlet uniformity.The conventional natural gas lean premixed combustor mainly promotes fuel and air mixing through cyclonic structure and induces high temperature flue gas recirculation at the nozzle outlet with counter pressure gradient to achieve flame stabilization,while the fuel and air in the micro-mixing combustor are mostly mixed in the form of jet-in-crossflow or coaxial jet,and generally do not have air or fuel cyclonic structure,so the micro-mixing combustion has the advantages of flashback suppression and auto-ignition,especially for the high flame propagation speed.However,it is crucial for micro-mixing combustion with multiple jets to achieve stable combustion at high combustion intensities,and in this study,a research on the flame stabilization mechanism of micro-mixing combustion has been carried out,and the main work is as follows.(1)Based on the concept of MMC,a novel micro-mixing model burner that can achieve high-efficiency mixing(inhomogeneity ?1%)in short distance(L/D ratio ?1)was firstly designed and developed.The effects of hydrogen content and heat load on flame structure,flame stability and CO/NOx emission under atmospheric pressure conditions were investigated to obtain the flame and emission characteristics of MMC.The results of the atmospheric pressure experiments preliminarily verify the feasibility of stable and low-emission combustion in a wide range of hydrogen content,which has the potential to be applied in gas turbine combustion chambers.(2)The three-dimensional cold flow field of the micro-mixing model burner was investigated experimentally and numerically,and it was found that the burner is at a high turbulence intensity level inside each single nozzle,with the jet converging point shifted upstream compared to the multi-round jet.The turbulence intensity within the nozzle exit potential core was about 10%,while the turbulence intensity within the shear layer was up to 30%,and the average velocity distribution was in the shape of a top hat.The results of the mean velocity field and pulsating velocity field simulated by RANS were in general good agreement with the experimental results.(3)Based on the validation of the velocity field,the Flamelet Generated Manifolds(FGM)method was used to predict the structure of hydrogen-containing micro-mixing flames by introducing the triangular dissection interpolation method and taking into account the preferential diffusion effect of hydrogen-containing fuels to complete the autonomous generation of flamelets.The validity of the method for hydrogen-rich fuel flames was experimentally verified.(4)Based on two typical fuels,pure methane and hydrogen-rich methane,the turbulent flame velocity models under two kinds of micro-mixing flames were verified,and the flame stabilization mechanism of MMC was found to include three effects,which are the basic effect of premixed flame,the shear layer stretching effect,and the flue gas recirculation effect.Among them,the shear layer stretching effect dominates the flame stabilization of the hydrogen-rich MMC flame,while the flame stabilization of the pure methane premixed flame is achieved by the flue gas recirculation effect.