On The Relationship Between H2 Addition, Local Extinction And Hydrodynamic Instability In Non-Premixed Bluff-Body Stabilized Flames
K. Rajamanickam, F. Lefebvre, C. Gobin, G. Godard, C. Lacour, B. Lecordier, A. Cessou, D. Honore
CORIA-UMR 6614, CNRS, 76801 Saint Etienne Du Rouvray Cedex, France
In the race for decarbonization of the power sector, H2 is found to be a better candidate as it can be readily produced in large scales from renewables (e.g. wind and solar energy). Nevertheless, the difference in the thermophysical properties of H2 in comparison to the conventional fuels possesses additional operational challenges. For instance, although the high flame speed together with a wide flammability range offer improved flame stabilization, however, it intensifies the risk of flashback. Besides, the increased strain resistance due to H2 enrichment is expected to alter the flame shape significantly. Hence, it is apparent that the widespread implementation of H2 across various practical systems needs a thorough understanding of the various physical mechanisms. In this context, we examined the effect of hydrogen (H2) enrichment to methane (CH4) in a non-premixed bluff-body stabilized burner operating under typical central jet dominated flame mode. In the chosen mode of operation, globally, the flow field and flame feature three important successive spatial regions, namely, recirculation zone, neck zone and jet-like flame zone. In such configuration, the flame is exposed to a higher stretch rate in the neck zone and eventually undergoes local extinction. Such local extinction and subsequent re-ignition of broken flame branches have strong implications over the hydrodynamic instability of the coaxial annular air shear layer. It is well known that H2 addition increases the flame extinction strain rate and thus alters the local extinction phenomenon. To understand this phenomenon, we performed experiments at 10%, 20 %, 30% and 50 % hydrogen proportion in (H2-CH4) blend. High repetition rate (5 KHz) PIV and OH PLIF measurements are performed simultaneously to perceive the quantitative insights. The results obtained from POD and 1D wavelet transform indicated the suppression of vortex shedding at the annular air shear layer for H2 addition greater than 20 %, and thus quantified the beneficial effect of H2 addition in turbulent flame stabilization.