Numerical Study On Combustion Characteristics Of Hydrogen-enrichment Low Swirl Combustor

Hydrogen is an important alternative fuel for gas turbine.However,high flame speed makes hydrogen combustion more susceptible to flashback,traditional lean premix combustion technology is not suitable for hydrogen flame.Low swirl combustion（LSC）technology is potential to burn hydrogen fuel in gas turbine because it could reduce flashback possibility and NO_x emission.This paper conducts a series of numerical studies on the influencing factors of flame flashback and NO_xemission for low swirl hydrogen-rich flame and provides some reference for the design of hydrogen low swirl combustor.In this paper,the numerical results were verified by experimental data,and the prediction abilities of five turbulence models on reacting flow field were compared.Then,the SST k-ωmodel and FGM model were used to compare various distributions of the non-reacting and reacting flows for open and confined low swirl injectors,including velocity,temperature and species.The basic characteristics of low-swirl hydrogen-rich combustion and the influence of combustor geometry on flame were analyzed.Finally,the effects of different hydrogen-rich fuels,geometry parameters and operating parameters on low-swirl combustion characteristics and NO emission were studied.The results of model validations show that k-ωmodels have better prediction on the flame lift-off height,the acceleration process of the reaction zone and the downstream flow field distribution compared than k-εmodels.The numerical results of the SST k-ωmodel are in the best agreement with the experimental values.Although the used NO_x models have underestimated NO_x emission,the variation trend of NO emissions is accurately predicted.The results of open and confined devices show that the combustor has a great influence on the central recirculation zone,but has no significant effect on the flow field characteristics in the core region.Flow acceleration exists in the reaction zone and is more obvious in the combustor.The encloser limits the expansion of the flow field,resulting in narrower flame front width and lower lift-off height,and promotes the formation of the outer recirculation zone,which makes the flame adhere to the outer shear layer and the nozzle rip.The study results for hydrogen-rich fuels show that the flame front gradually moves upstream with the increase of the equivalence ratio,and the NO emission gradually increases.Hydrogen has great effect on the flow field and the flame in the shear zone.With the increase of the proportion of H₂,the flame length in the shear zone decreases significantly.The NO emission decreases initially and increases afterwards,and the N₂O-intermediate mechanism becomes the main path of NO formation.Compared with H₂O and N₂,CO₂ has the best effect on reducing the temperature and NO emission.The study results for different structural parameters show that reducing the swirl number by reducing the blade angle or increasing the hole diameter of the perforated plate can raise the flame position and reduce the risk of flashback.Under the same geometric swirl number,the effect of increasing the aperture diameter is better,but two methods will lead to an increase in NO emissions.The convex perforated plate can effectively increase the velocity near the axis of the combustor.With the increase of the convex inclination,the flame shape changes from U-type to W-type,and the NO emission gradually decreases.Divergent inlet can suppress the generation of the outer recirculation zone and greatly change the shape of the flame.When the external recirculation zone disappears,the NO emission significantly decreases.The study results for gas turbine conditions show that the lift-off height of the flame decreases when the inlet temperature increases or the inlet velocity decreases.Pressure has no effect on the flame height.The NO emission increases when the inlet temperature or pressure increases and decreases when the inlet velocity decreases.