A new burner design is presented in this work for highly stabilized partially premixed flames using gaseous fuel. The partially premixed flow is created in a concentric flow tube and the flames are stabilized by a relatively large diverging conical nozzle. The concentric flow conical nozzle burner (CFCN) creates highly stabilized flames at high Reynolds number, up to 60000. Three versions of the burner have been investigated and a maximum load of about 250 kW with 20 mm diameter nozzle has been achieved in partially premixed flame. Higher load is expected for larger burner size. The stability characteristics of the CFCN burner show that it is suitable for industrial applications. The burner turndown ratio is between 15 and 20. Fundamental research studies and modeling of the flames in CFCN are feasible because of the simple flow geometry of the burner. Therefore, four flames have been selected in the present work for detailed thermal reaction zone structure investigation and OH radical distribution using ...

A Concentric Flow Conical Nozzle Burner for Highly Stabilized Partially Premixed Flames

Turbulent partially premixed methane flames stabilized in a concentric flow conical nozzle burner have been investigated and presented in this work. The flames are classified in the thin reaction zones regime. The flames were investigated experimentally based on simultaneous measurements of the velocity field and OH-radical. A combined planar imaging velocimetry (PlV) and laser-induced predissociation fluorescence (LIPF) technique was applied. The mean, rms, and instantaneous structure of four flames are presented and discussed in this article. High stability of the investigated flames is partially due to the partial premixing of the jet and mainly to the flow divergence created by the conical nozzle. This creates a stabilization core with lower mean velocity at the center and lower rms of the velocity fluctuations at the flame brush. No significant recirculation could be observed within the stabilization core above the conical nozzle tip. The reaction zone structure in the present partially premixed flam...

A study of turbulent partially premixed flames based on simultaneous imaging of velocity field and oh radical

This is an experimental investigation of the flow structure and turbulence characteristics of a turbulent axisymmetric shear layer between two primary streams under the influence of three-dimensional stationary boundary conditions. These conditions result from skewing the primary streams relative to the trailing edge. Two configurations were investigated: both primary streams were parallel but skewed relative to the trailing edge (i.e. slanted trailing edge) and the primary streams were non-planar (i.e. had cross-shear). Although these flows are simplified models, their understanding should provide more insight into the mechanisms of real life three-dimensional shear flows than studies on classical two-dimensional shear flows have done to date. The investigated shear layers were generated at the interface between two coaxial jets with different axial velocities. Additionally, azimuthal velocity components were imposed by means of a swirl generator on the shear layer either in the same or the opposite direction. Results from various experimental measurements including 4-sensor hot-wire probes, hot-wire rakes and visualizations indicate an increase of the total turbulent kinetic energy, and of the growth rates compared to cases with no skewing. Further, the vortex rings resulting from the the Kelvin-Helmholtz instability were deformed by coherent structures having axis not parallel to the trailing edge. It is assumed that these structures are helical vortices competing with the vortex rings in a complex structural manner which lead to the observed increase of the turbulent quantities.

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Investigation of the three-dimensional shear layer between confined coaxial jets with swirl

Effect of operating and geometrical parameters of tangential entry type dual swirling flame burner on impingement heat transfer

Flame pulsation has a significant effect on combustion, and understanding its oscillatory behavior is important to the combustion community. An experiment was performed to analyze the pulsation characteristics of a swirl non-premixed flame under various parameters. The results showed that as fuel mass flow rate increased, the puffing frequency increased due to the decreased flame radiation fraction, and the puffing amplitude became smaller resulting in a more stable flame. With an increase in combustor pressure, the flickering frequency declined because of the increasing soot radiation, while the flickering amplitude uniformly increased, leading to more deteriorative flame stability. With an increment in mass flow rate of primary air, the puffing frequency decreased due to the enhanced mixing between fuel and primary air. Also, the puffing amplitude had an oscillating relationship with the mass flow rate of primary air. When the exit velocity of the injector was increased, the flickering frequency diminished nearly linearly because of the improving swirl intensity, and the flickering amplitude was approximately unaffected by injector exit velocity. Moreover, the measured puffing frequencies summarized over all cases varied within the range of 3–22 Hz, the predicted values from theoretical models based on non-swirl flame also fell within this range. The puffing frequency of swirl combustion was more sensitive to the variation in operating conditions than that of non-swirl combustion. Additionally, the obtained correlations indicated that the Strouhal number St was proportional to Fr−1.4 (the Froude number) and Re−2.9 (the Reynolds number), respectively.

An Experimental Investigation on Flame Pulsation for a Swirl Non-Premixed Combustion

Analysis of swirling recirculating reacting turbulent jets passing through diffusers

Investigation have been conducted to find out the region of high turbulent intensities in a swirling jet passing through a divergent passage. A hot wire anemometer is used to measure the turbulence intensity using a four position method. It has been concluded that the jet spreads with increasing diffuser angle and the region of high turbulent intensity also spreads. The high turbulence intensity region lies around the recirculation zone and it decays rapidly along the main flow direction.

http://publications.drdo.gov.in/ojs/index.php/dsj/article/download/6371/3430

V. M. Domkundwar

Papers

Analysis of swirling recirculating reacting turbulent jets passing through diffusers

Turbulence Measurements in Swirling Flows