The flow field characteristics of confined flames have been investigated for propane nonpremixed flames in cylindrical furnaces. The effects of furnace inner diameter D 1 , air inlet velocity difference ∆U a , and global equivalence ratio φ on the flow field are related to NOx emission. The emission index of NOx, EINOx, decreases roughly with the increases of the above parameters. This decrease is observed as a consequence of flame stretch and dilution by the burned gas. The flame stretch is related to the velocity difference introduced by multiple inlets, and the dilution is attributable to the recirculation structure formed at the bottom of the furnace. The present investigation shows the mechanism of burner/chamber configuration inciting the flow field and indirectly controlling NOx emission.

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Confined flames are widely used in the industrial field. The flame characteristics can be strongly dominated by the combination of a burner and furnace geometries, which were not paid much attention before. In the present study, flow fields in confined flames are discussed in terms of the flame characteristics. The flow characteristics of confined flames have been investigated for propane nonpremixed flames in cylindrical furnaces. The effects of the inner diameter of the cylindrical furnace D1, the turbulence at the flame boundary, and the global equivalence ratio φ are examined in terms of the relation between the emission of NOx and the flow fields. The emission index of NOx, EINOx, decreases roughly with these parameters. The decrease in EINOx is thought to be related to the dilution of mixtures by the burned gas and the flame stretch. The dilution is attributable to vortices formed at the bottom of the furnace, and the flame stretch is attributable to the air velocity difference ΔUa created by two air nozzles. In the present study, it was found that the increases in D1, ΔUa, and φ enlarge and strengthen recirculation vortices to dilute the flame.

This study proposes an idea of NOx reduction and high efficiency combustion by combination of burner and furnace. This is basically attributed to the use of entrainment of burnt gases to flame in furnace. The entrainment of burnt gases leads the dilution of flame and the recovery of heat to be exhausted. The phenomena are strongly related to the geometry of burner and furnace. The temperature, concentration, and flow field characteristics were investigated for piloted propane non-premixed flames in the cylindrical furnaces in terms of NOx emission. The effects of the furnace inner diameter, D 1 , air inlet velocity difference, ∆U a , and global equivalence ratio,φ, on NOx emission were investigated.Moreover, two kinds of materials: Pyrex glass and stainless steel were used as the furnace wall to evaluate the radiation effect through the comparison of the flame characteristics. The emission index of NOx, EINOx, decreases roughly with the increase of above parameters. This decrease is observed to be a consequence of dilution by the burnt gases and flame stretch. The dilution is attributed to the recirculation structure, which is formed at the bottom of the furnace. The flame stretch is related to the velocity difference, which is introduced by multiple air inlets. The EINOx of confined non-premixed flame is scaled by the parameter D 1 U F ∆U a , which is proportional to Re,cDa -1 . Here, U F is the fuel velocity, Re,c is the furnace Reynolds number reflecting the turbulence in the furnace, and Da is the Damköhler number reflecting the flame stretch. The parameter D 1 U F ∆U a is related linearly to the volume flow rate entrained in to the flame. Thus, this study verified that the EINOx of confined non-premixed flame is dominated primarily from the entrainment of burnt gases by the recirculation vortex and secondarily by the turbulence at the flame boundary, which is generated by the air velocity difference. In addition, it is found that under present experimental conditions, the radiation effect on the EINOx is small and constant with respect to the parameters. Thus, this idea has a potential for practical applications.

The current research focuses on the aerodynamic design of a centrifugal compressor and the effect of tip tailoring on the aerodynamic impeller efficiency. To this extent a high-fidelity multi-point design optimization process has been developed and exploited on a high pressure ratio transonic impeller. By manipulating the shape of the impeller blades and endwalls and by including advanced geometrical features such as winglets on the impeller blades, the behavior of the impeller flow has been investigated. Here, the results of three-dimensional RANS simulations with the Spalart-Allmaras turbulence model on a structured multi-block mesh is used for the evaluation of the flow characteristics. In the context of radial machines, the results of the aerodynamic design optimization show an important improvement of the impeller isentropic efficiency compared to the reference impeller, with a significant contribution from the presence of the impeller tip winglets. Furthermore, the integration of the impeller winglet has encouraged this study to provide a detailed analysis on the impeller flow structures in order to have a better understanding of the effects of tip tailoring on impeller performance.