Abstract
Countercurrent shear layer control has been introduced as a novel flame stabilization technique for axisymmetric propane-air premixed flames. The technique relies on the application of suction driven countercurrent flow around the periphery of a nozzle burner. In this study, the effect of countercurrent shear layer control on the flow and stability characteristics of premixed jet flames is experimentally investigated. For this purpose, a low speed jet flame facility is designed, validated and built from the ground up. A new optical measurement technique, Laser Speckle Displacement (LSD), is developed to map whole temperature fields and stereoscopic Particle Image Velocimetry (PIV) is applied to obtain the velocity and turbulence fields. Initially, blow-off experiments are carried out for varying suction velocity and equivalence ratio values to identify the stable flame regions. The results show that by increasing the suction velocity, an order of magnitude increase in premixed flame blow-off velocity can be obtained. To investigate the suction effect on the flow and flame characteristics of countercurrent stabilized premixed flames, PIV and LSD experiments are performed for six cases at the equivalence ratio of 1.0. For the comparison of reacting and non-reacting flow fields, isothermal jet experiments are carried out at the same conditions as well. The suction effect on the flow fields is examined in terms of mean temperature, velocity fields, shear layer development, turbulence characteristics, dilatation fields, vorticity fields, and integral length scales. It is seen that in countercurrent stabilized premixed flames, increased suction velocity results in increased mixing. Comparison of reacting and non-reacting turbulence characteristics reveals the laminarization effect of combustion in the shear layers. The integral length scales for both reacting and non-reacting flows are calculated in whole field and used for investigating the turbulent premixed flame regimes. It is found that the structure of investigated countercurrent stabilized premixed flame cases varies from wrinkled flamelets to thin reaction zones with increasing suction velocity.
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