Scalar Measurements in Bluff Body Stabilized Flames Using Cars Diagnostics

Abstract

Measurements of mean and rms temperature fluctuations were performed in confined turbulent premixed methane-air flames, stabilized on a conical flameholder. A CARS system was used for these measurements. These tests employed flameholders of different blockage ratios (13% and 25%), and mixtures with different equivalence ratios (0.56, 0.65, 0.8, and 0.9) and approach turbulence intensity (2%, 17%, and 22%). It was found that the recirculation zone closely resembles a perfectly well-stirred reactor. Blockage ratio, equivalence ratio, or approach turbulence intensity did not alter the scalar field. The turbulent flame structure enveloping the recirculation zone comprises: (i) an ignition/thin flame region in the vicinity of the flameholder base, (ii) a reacting shear layer region of large-scale coherent structures, and (iii) a thick flame region where entrainment is the dominant mechanism. Finally, analysis suggests that the scalar gradient-diffusion relationship is valid and areas of non-gradient diffusion, if any, are probably small.

A scaling law for the recirculation zone length behind a bluff body in reacting flows

“…A small velocity of U air = 0.2 m s −1 is specified at the boundary in line with the combustor exit, as shown in figure 1, in order to mimic the ambient air entrainment. Langella et al (2016a) showed that the velocity close to the bluff body base could be affected by the heat losses from the recirculation zone to the bluff body base and this loss was reported to be approximately 5-8 % by Pan et al (1991b). The previous study by Langella et al (2016a) demonstrated that the computed recirculation zone length agreed well with measurements, although this heat loss was excluded in the LES.…”

“…(2016 a ) showed that the velocity close to the bluff body base could be affected by the heat losses from the recirculation zone to the bluff body base and this loss was reported to be approximately – by Pan et al. (1991 b ). The previous study by Langella et al.…”

“…Figure 1( a ) illustrates the schematic of the bluff body burner investigated here, which was studied experimentally by Pan et al. (1991 a , b , 1992), Nandula et al. (1996) and Nandula (2003).…”

“…The influences of TI and on the recirculation zone length behind a bluff body have not been investigated thoroughly, although some trends have been reported by Pan et al. (1991 a , b , 1992). It was suggested that the influences of combustion on the recirculation zone may come through the pressure dilatation influencing the turbulent kinetic energy.…”

Rayleigh/Raman/LIF measurements in a turbulent lean premixed combustor

“…The residence times at this point are small, The shear layer growth is caused by the entertainment process, where isolated pockets gas sampling probes. The NO/NO, measurements were performed with a chemilumiof hot products (from the recirculation zone) and cold reactant gases (from the premixed fuel-air stream) are entrained into the shear layer (Pan et al, 1991b (Mellor, 1994). Optical and gas sampling probe measurements of the exhaust pollutants (NO and CO) at x/d = 6 are shown in Fig.…”